Patent Publication Number: US-2020304179-A1

Title: METHOD AND SYSTEM FOR MILLIMETER WAVE HOTSPOT (mmH) BACKHAUL AND PHYSICAL (PHY) LAYER TRANSMISSIONS

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 16/140,119, filed Sep. 24, 2018, which is a continuation of U.S. application Ser. No. 15/029,837, filed Apr. 15, 2016, which is the U.S. National Stage, under 35 U.S.C. § 371, of International Application No. PCT/US2014/060973 filed Oct. 16, 2014, which claims the benefit of U.S. Provisional Application No. 61/891,738 filed Oct. 16, 2013, the contents of which are hereby incorporated by reference herein. 
    
    
     BACKGROUND 
     It is well known that the capacity demand in cellular networks has been growing exponentially for many years and is expected to continue this way for at least the next decade. While advances in spectral efficiency will continue, the gains that we can expect from these advances are limited. Densification of cellular networks will continue to be the leading source of capacity gains until the use of higher frequencies becomes feasible for access link. Small-cells are currently being used to increase the density of networks and address these capacity problems. This increase in cell density, however, requires a corresponding increase in backhaul cap abilities. 
     Rolling out fiber to all of these new nodes is cost prohibitive. The Millimeter Wave Hotspot (mmH) project proposes the use of highly directional millimeter (mm) wave links between these small-cell nodes as a way to address this concern. Small cells are expected to be rolled out first in dense urban environments of varying landscapes. 
     SUMMARY 
     A method and apparatus are disclosed for communication in a Millimeter Wave Hotspot (mmH) backhaul system which uses mesh nodes. A mmH mesh node may receive a control signal which includes a total number of available control slots. The mesh node may determine the number of iterations of a resource scheduling mechanism that can be made during the time period of all available control slots, signaled by the control signal, based on the number of neighbor nodes for the mesh node. Further, the mesh node may receive control slot information from neighbor nodes, wherein the control slot information includes information about traffic queues and priorities. The mesh node may then perform resource scheduling using the resource scheduling mechanism based on the currently received control slot information and control slot information received in previous iterations of resource scheduling. In an example, the control signal may be received from a mesh controller. 
     The resource scheduling mechanism may include a resource assignment algorithm. Further, the resource requests and temporary schedules for all priorities may be received in each iteration. Also, the number of control slot may vary based on the neighboring nodes. In an example, the control slot information may include only information concerning a current priority level and lower priority levels. In a further example, the mesh node may schedule higher priority traffic in initial scheduling iterations and lower priority traffic in later scheduling iterations. 
     The mesh node may also receive one or more signals regarding an initial preamble length. The mesh node may adjust a preamble based on a time between a last packet transmission and a current packet transmission to a neighboring node. The mesh mode may then send transmissions using the adjusted preamble to at least one neighboring node. In an example, the signals regarding an initial preamble length may be received from a central node. In a further example, the preamble length may be based on the content of the transmission. Also, the mesh node may further adjust the preamble based on estimated channel conditions for at least one neighboring node. If the mesh node receives an acknowledgement, the mesh node may send further transmissions using the adjusted preamble. If the mesh node fails to receive an acknowledgement, the mesh node may send further transmissions using a preamble longer than the adjusted preamble. 
     An mmH node may transmit a plurality of beacons during a beacon transmission interval. Each of the beacons may be transmitted in a different transmit antenna direction and separated by a beacon switch interframe spacing (BSIFS). The node may receive a plurality of beacon responses, each separated by a long interframe spacing (LIFS). The node may then transmit a beacon acknowledgment message in response to at least one of the beacon responses. The beacon acknowledgment message may be separated from the last beacon response by an LIFS. 
     In an additional embodiment, an mmH node may receive a control slot assignment for communication with a neighbor node and an indication of an initial direction for communication. The node may transmit a request to the neighbor node during the assigned control slot for a data slot for a subsequent transmission to the neighbor node and may receive a response from the neighbor node that includes a data slot for the subsequent transmission. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more detailed understanding may be had from the following description, given by way of example in conjunction with the accompanying drawings wherein: 
         FIG. 1A  is a system diagram of an example communications system in which one or more disclosed embodiments may be implemented; 
         FIG. 1B  is a system diagram of an example wireless transmit/receive unit (WTRU) that may be used within the communications system illustrated in  FIG. 1A ; 
         FIG. 1C  is a system diagram of an example radio access network and an example core network that may be used within the communications system illustrated in  FIG. 1A ; 
         FIG. 1D  is a system diagram of an example of a small-cell backhaul in an end-to-end mobile network infrastructure; 
         FIG. 2  is a diagram of an example superframe structure; 
         FIG. 3  is a diagram of an example Beacon Period; 
         FIG. 4  is a diagram of an example beacon transmission interval (BTI) slot (BTI_S); 
         FIG. 5  is a diagram of an example beacon response interval (BRI) slot (BRI_S); 
         FIG. 6  is a diagram of an example beacon response acknowledgement (BRA) slot (BRA_S); 
         FIG. 7  is a diagram of an example BTI preamble; 
         FIG. 8  is a diagram of an example BRI preamble; 
         FIG. 9  is a diagram of an example BRA preamble; 
         FIG. 10  is a diagram of an example process for coding and modulation for beacon messages; 
         FIG. 11  is a diagram of an example scheduling interval (SI); 
         FIG. 12  is a diagram of an example control period structure; 
         FIG. 13  is a diagram of an example control slot structure; 
         FIG. 14  is a diagram of an example preamble for control messages  1  and  2 ; 
         FIG. 15  is a diagram of an example preamble for control message  3 ; 
         FIG. 16  is a diagram of example control slot messages; 
         FIG. 17  is a diagram of an example high level message processing block diagram; 
         FIG. 18A  is a diagram of an example of encoding for control messages using Min ZeroPad; 
         FIG. 18B  is a diagram of an example of decoding for control messages using Min ZeroPad; 
         FIG. 19A  is a diagram of an example encoding for control messages using Min CodeRate; 
         FIG. 19B  is a diagram of an example decoding for control messages using Min CodeRate; 
         FIG. 20  is a diagram of an example long control message scrambler; 
         FIG. 21  is a diagram of an example iterative resource scheduling mechanism; 
         FIG. 22  is a diagram of an example process flow for performing resource scheduling using the resource scheduling mechanism; 
         FIG. 23  is a diagram of an example control slot assignment with a different number of control slots for different neighbors; 
         FIG. 24  is a diagram of an example of iterative scheduling with insufficient control slots; 
         FIG. 25  is a diagram of an example Control Slot Reassignment procedure; 
         FIG. 26  is a diagram of an example node mesh topology with variable control period sizes; 
         FIG. 27  is a diagram of an example of Data Period Structure; 
         FIG. 28  is a diagram of an example Data Preamble; 
         FIG. 29  is a diagram of example data slot scenarios for N cs  equal to 5 and no beam refinement; 
         FIG. 30A  is a diagram of example encoder bit handling for low MCS; 
         FIG. 30B  is a diagram of example decoder bit handling for low MCS; 
         FIG. 31  is diagram of an example Packet Delivery Time Probability with HARQ/ARQ; 
         FIG. 32A  is a diagram of an example of a variable-length preamble; 
         FIG. 32B  is a diagram of another example of a variable-length preamble; 
         FIG. 33  is a diagram of an example distribution of peak correlations to the IEEE 802.11ad Golay codes. 
         FIG. 34  is a diagram of an example result from a simulation; 
         FIG. 35  is a diagram of an example result from a simulation; 
         FIG. 36  is a diagram of another example result from a simulation; 
         FIG. 37  is a diagram of an example result from yet another simulation; 
         FIG. 38  is a diagram of an example of another result from another simulation; 
         FIG. 39  is a diagram of an example result from yet another simulation; 
         FIG. 40  is a diagram of another example result from an additional simulation; 
         FIG. 41  is a diagram of an example comparison of the results of simulations; and 
         FIG. 42  is a diagram of an example comparison of multiple simulations. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1A  is a diagram of an example communications system  100  in which one or more disclosed embodiments may be implemented. The communications system  100  may be a multiple access system that provides content, such as voice, data, video, messaging, broadcast, etc., to multiple wireless users. The communications system  100  may enable multiple wireless users to access such content through the sharing of system resources, including wireless bandwidth. For example, the communications systems  100  may employ one or more channel access methods, such as code division multiple access (CDMA), time division multiple access (TDMA), frequency division multiple access (FDMA), orthogonal FDMA (OFDMA), single-carrier FDMA (SC-FDMA), and the like. 
     As shown in  FIG. 1A , the communications system  100  may include wireless transmit/receive units (WTRUs)  102   a ,  102   b ,  102   c ,  102   d , a radio access network (RAN)  104 , a core network  106 , a public switched telephone network (PSTN)  108 , the Internet  110 , and other networks  112 , though it will be appreciated that the disclosed embodiments contemplate any number of WTRUs, base stations, networks, and/or network elements. Each of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may be any type of device configured to operate and/or communicate in a wireless environment. By way of example, the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may be configured to transmit and/or receive wireless signals and may include user equipment (UE), a mobile station, a fixed or mobile subscriber unit, a pager, a cellular telephone, a personal digital assistant (PDA), a smartphone, a laptop, a netbook, a personal computer, a wireless sensor, consumer electronics, and the like. 
     The communications systems  100  may also include a base station  114   a  and a base station  114   b . Each of the base stations  114   a ,  114   b  may be any type of device configured to wirelessly interface with at least one of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  to facilitate access to one or more communication networks, such as the core network  106 , the Internet  110 , and/or the other networks  112 . By way of example, the base stations  114   a ,  114   b  may be a base transceiver station (BTS), a Node-B, an eNode B, a Home Node B, a Home eNode B, a site controller, an access point (AP), a wireless router, and the like. While the base stations  114   a ,  114   b  are each depicted as a single element, it will be appreciated that the base stations  114   a ,  114   b  may include any number of interconnected base stations and/or network elements. 
     The base station  114   a  may be part of the RAN  104 , which may also include other base stations and/or network elements (not shown), such as a base station controller (BSC), a radio network controller (RNC), relay nodes, etc. The base station  114   a  and/or the base station  114   b  may be configured to transmit and/or receive wireless signals within a particular geographic region, which may be referred to as a cell (not shown). The cell may further be divided into cell sectors. For example, the cell associated with the base station  114   a  may be divided into three sectors. Thus, in one embodiment, the base station  114   a  may include three transceivers, i.e., one for each sector of the cell. In another embodiment, the base station  114   a  may employ multiple-input multiple-output (MIMO) technology and, therefore, may utilize multiple transceivers for each sector of the cell. 
     The base stations  114   a ,  114   b  may communicate with one or more of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  over an air interface  116 , which may be any suitable wireless communication link (e.g., radio frequency (RF), microwave, infrared (IR), ultraviolet (UV), visible light, etc.). The air interface  116  may be established using any suitable radio access technology (RAT). 
     More specifically, as noted above, the communications system  100  may be a multiple access system and may employ one or more channel access schemes, such as CDMA, TDMA, FDMA, OFDMA, SC-FDMA, and the like. For example, the base station  114   a  in the RAN  104  and the WTRUs  102   a ,  102   b ,  102   c  may implement a radio technology such as Universal Mobile Telecommunications System (UMTS) Terrestrial Radio Access (UTRA), which may establish the air interface  116  using wideband CDMA (WCDMA). WCDMA may include communication protocols such as High-Speed Packet Access (HSPA) and/or Evolved HSPA (HSPA+). HSPA may include High-Speed Downlink Packet Access (HSDPA) and/or High-Speed Uplink Packet Access (HSUPA). 
     In another embodiment, the base station  114   a  and the WTRUs  102   a ,  102   b ,  102   c  may implement a radio technology such as Evolved UMTS Terrestrial Radio Access (E-UTRA), which may establish the air interface  116  using Long Term Evolution (LTE) and/or LTE-Advanced (LTE-A). 
     In other embodiments, the base station  114   a  and the WTRUs  102   a ,  102   b ,  102   c  may implement radio technologies such as IEEE 802.16 (i.e., Worldwide Interoperability for Microwave Access (WiMAX)), CDMA2000, CDMA2000 1×, CDMA2000 EV-DO, Interim Standard 2000 (IS-2000), Interim Standard 95 (IS-95), Interim Standard 856 (IS-856), Global System for Mobile communications (GSM), Enhanced Data rates for GSM Evolution (EDGE), GSM EDGE (GERAN), and the like. 
     The base station  114   b  in  FIG. 1A  may be a wireless router, Home Node B, Home eNode B, or access point, for example, and may utilize any suitable RAT for facilitating wireless connectivity in a localized area, such as a place of business, a home, a vehicle, a campus, and the like. In one embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may implement a radio technology such as IEEE 802.11 to establish a wireless local area network (WLAN). In another embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may implement a radio technology such as IEEE 802.15 to establish a wireless personal area network (WPAN). In yet another embodiment, the base station  114   b  and the WTRUs  102   c ,  102   d  may utilize a cellular-based RAT (e.g., WCDMA, CDMA2000, GSM, LTE, LTE-A, etc.) to establish a picocell or femtocell. As shown in  FIG. 1A , the base station  114   b  may have a direct connection to the Internet  110 . Thus, the base station  114   b  may not be required to access the Internet  110  via the core network  106 . 
     The RAN  104  may be in communication with the core network  106 , which may be any type of network configured to provide voice, data, applications, and/or voice over internet protocol (VoIP) services to one or more of the WTRUs  102   a ,  102   b ,  102   c ,  102   d . For example, the core network  106  may provide call control, billing services, mobile location-based services, pre-paid calling, Internet connectivity, video distribution, etc., and/or perform high-level security functions, such as user authentication. Although not shown in  FIG. 1A , it will be appreciated that the RAN  104  and/or the core network  106  may be in direct or indirect communication with other RANs that employ the same RAT as the RAN  104  or a different RAT. For example, in addition to being connected to the RAN  104 , which may be utilizing an E-UTRA radio technology, the core network  106  may also be in communication with another RAN (not shown) employing a GSM radio technology. 
     The core network  106  may also serve as a gateway for the WTRUs  102   a ,  102   b ,  102   c ,  102   d  to access the PSTN  108 , the Internet  110 , and/or other networks  112 . The PSTN  108  may include circuit-switched telephone networks that provide plain old telephone service (POTS). The Internet  110  may include a global system of interconnected computer networks and devices that use common communication protocols, such as the transmission control protocol (TCP), user datagram protocol (UDP) and the internet protocol (IP) in the TCP/IP internet protocol suite. The networks  112  may include wired or wireless communications networks owned and/or operated by other service providers. For example, the networks  112  may include another core network connected to one or more RANs, which may employ the same RAT as the RAN  104  or a different RAT. 
     Some or all of the WTRUs  102   a ,  102   b ,  102   c ,  102   d  in the communications system  100  may include multi-mode capabilities, i.e., the WTRUs  102   a ,  102   b ,  102   c ,  102   d  may include multiple transceivers for communicating with different wireless networks over different wireless links. For example, the WTRU  102   c  shown in  FIG. 1A  may be configured to communicate with the base station  114   a , which may employ a cellular-based radio technology, and with the base station  114   b , which may employ an IEEE 802 radio technology. 
       FIG. 1B  is a system diagram of an example WTRU  102 . As shown in  FIG. 1B , the WTRU  102  may include a processor  118 , a transceiver  120 , a transmit/receive element  122 , a speaker/microphone  124 , a keypad  126 , a display/touchpad  128 , non-removable memory  130 , removable memory  132 , a power source  134 , a global positioning system (GPS) chipset  136 , and other peripherals  138 . It will be appreciated that the WTRU  102  may include any sub-combination of the foregoing elements while remaining consistent with an embodiment. 
     The processor  118  may be a general purpose processor, a special purpose processor, a conventional processor, a digital signal processor (DSP), a plurality of microprocessors, one or more microprocessors in association with a DSP core, a controller, a microcontroller, Application Specific Integrated Circuits (ASICs), Field Programmable Gate Array (FPGAs) circuits, any other type of integrated circuit (IC), a state machine, and the like. The processor  118  may perform signal coding, data processing, power control, input/output processing, and/or any other functionality that enables the WTRU  102  to operate in a wireless environment. The processor  118  may be coupled to the transceiver  120 , which may be coupled to the transmit/receive element  122 . While  FIG. 1B  depicts the processor  118  and the transceiver  120  as separate components, it will be appreciated that the processor  118  and the transceiver  120  may be integrated together in an electronic package or chip. 
     The transmit/receive element  122  may be configured to transmit signals to, or receive signals from, a base station (e.g., the base station  114   a ) over the air interface  116 . For example, in one embodiment, the transmit/receive element  122  may be an antenna configured to transmit and/or receive RF signals. In another embodiment, the transmit/receive element  122  may be an emitter/detector configured to transmit and/or receive IR, UV, or visible light signals, for example. In yet another embodiment, the transmit/receive element  122  may be configured to transmit and receive both RF and light signals. It will be appreciated that the transmit/receive element  122  may be configured to transmit and/or receive any combination of wireless signals. 
     In addition, although the transmit/receive element  122  is depicted in  FIG. 1B  as a single element, the WTRU  102  may include any number of transmit/receive elements  122 . More specifically, the WTRU  102  may employ MIMO technology. Thus, in one embodiment, the WTRU  102  may include two or more transmit/receive elements  122  (e.g., multiple antennas) for transmitting and receiving wireless signals over the air interface  116 . 
     The transceiver  120  may be configured to modulate the signals that are to be transmitted by the transmit/receive element  122  and to demodulate the signals that are received by the transmit/receive element  122 . As noted above, the WTRU  102  may have multi-mode capabilities. Thus, the transceiver  120  may include multiple transceivers for enabling the WTRU  102  to communicate via multiple RATs, such as UTRA and IEEE 802.11, for example. 
     The processor  118  of the WTRU  102  may be coupled to, and may receive user input data from, the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128  (e.g., a liquid crystal display (LCD) display unit or organic light-emitting diode (OLED) display unit). The processor  118  may also output user data to the speaker/microphone  124 , the keypad  126 , and/or the display/touchpad  128 . In addition, the processor  118  may access information from, and store data in, any type of suitable memory, such as the non-removable memory  130  and/or the removable memory  132 . The non-removable memory  130  may include random-access memory (RAM), read-only memory (ROM), a hard disk, or any other type of memory storage device. The removable memory  132  may include a subscriber identity module (SIM) card, a memory stick, a secure digital (SD) memory card, and the like. In other embodiments, the processor  118  may access information from, and store data in, memory that is not physically located on the WTRU  102 , such as on a server or a home computer (not shown). 
     The processor  118  may receive power from the power source  134 , and may be configured to distribute and/or control the power to the other components in the WTRU  102 . The power source  134  may be any suitable device for powering the WTRU  102 . For example, the power source  134  may include one or more dry cell batteries (e.g., nickel-cadmium (NiCd), nickel-zinc (NiZn), nickel metal hydride (NiMH), lithium-ion (Li-ion), etc.), solar cells, fuel cells, and the like. 
     The processor  118  may also be coupled to the GPS chipset  136 , which may be configured to provide location information (e.g., longitude and latitude) regarding the current location of the WTRU  102 . In addition to, or in lieu of, the information from the GPS chipset  136 , the WTRU  102  may receive location information over the air interface  116  from a base station (e.g., base stations  114   a ,  114   b ) and/or determine its location based on the timing of the signals being received from two or more nearby base stations. It will be appreciated that the WTRU  102  may acquire location information by way of any suitable location-determination method while remaining consistent with an embodiment. 
     The processor  118  may further be coupled to other peripherals  138 , which may include one or more software and/or hardware modules that provide additional features, functionality and/or wired or wireless connectivity. For example, the peripherals  138  may include an accelerometer, an e-compass, a satellite transceiver, a digital camera (for photographs or video), a universal serial bus (USB) port, a vibration device, a television transceiver, a hands free headset, a Bluetooth® module, a frequency modulated (FM) radio unit, a digital music player, a media player, a video game player module, an Internet browser, and the like. 
     As shown in  FIG. 1C , the RAN  104  may include base stations  140   a ,  140   b ,  140   c , and an ASN gateway  142 , though it will be appreciated that the RAN  104  may include any number of base stations and ASN gateways while remaining consistent with an embodiment. The base stations  140   a ,  140   b ,  140   c  may each be associated with a particular cell (not shown) in the RAN  104  and may each include one or more transceivers for communicating with the WTRUs  102   a ,  102   b ,  102   c  over the air interface  116 . In one embodiment, the base stations  140   a ,  140   b ,  140   c  may implement MIMO technology. Thus, the base station  140   a , for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU  102   a . The base stations  140   a ,  140   b ,  140   c  may also provide mobility management functions, such as handoff triggering, tunnel establishment, radio resource management, traffic classification, quality of service (QoS) policy enforcement, and the like. The ASN gateway  142  may serve as a traffic aggregation point and may be responsible for paging, caching of subscriber profiles, routing to the core network  106 , and the like. 
     The air interface  116  between the WTRUs  102   a ,  102   b ,  102   c  and the RAN  104  may be defined as an R1 reference point that implements the IEEE 802.16 specification. In addition, each of the WTRUs  102   a ,  102   b ,  102   c  may establish a logical interface (not shown) with the core network  106 . The logical interface between the WTRUs  102   a ,  102   b ,  102   c  and the core network  106  may be defined as an R2 reference point, which may be used for authentication, authorization, IP host configuration management, and/or mobility management. 
     The communication link between each of the base stations  140   a ,  140   b ,  140   c  may be defined as an R8 reference point that includes protocols for facilitating WTRU handovers and the transfer of data between base stations. The communication link between the base stations  140   a ,  140   b ,  140   c  and the ASN gateway  215  may be defined as an R6 reference point. The R6 reference point may include protocols for facilitating mobility management based on mobility events associated with each of the WTRUs  102   a ,  102   b ,  100   c.    
     As shown in  FIG. 1C , the RAN  104  may be connected to the core network  106 . The communication link between the RAN  104  and the core network  106  may defined as an R3 reference point that includes protocols for facilitating data transfer and mobility management capabilities, for example. The core network  106  may include a mobile IP home agent (MIP-HA)  144 , an authentication, authorization, accounting (AAA) server  146 , and a gateway  148 . While each of the foregoing elements are depicted as part of the core network  106 , it will be appreciated that any one of these elements may be owned and/or operated by an entity other than the core network operator. 
     The MIP-HA may be responsible for IP address management, and may enable the WTRUs  102   a ,  102   b ,  102   c  to roam between different ASNs and/or different core networks. The MIP-HA  144  may provide the WTRUs  102   a ,  102   b ,  102   c  with access to packet-switched networks, such as the Internet  110 , to facilitate communications between the WTRUs  102   a ,  102   b ,  102   c  and IP-enabled devices. The AAA server  146  may be responsible for user authentication and for supporting user services. The gateway  148  may facilitate interworking with other networks. For example, the gateway  148  may provide the WTRUs  102   a ,  102   b ,  102   c  with access to circuit-switched networks, such as the PSTN  108 , to facilitate communications between the WTRUs  102   a ,  102   b ,  102   c  and traditional land-line communications devices. In addition, the gateway  148  may provide the WTRUs  102   a ,  102   b ,  102   c  with access to the networks  112 , which may include other wired or wireless networks that are owned and/or operated by other service providers. 
     Although not shown in  FIG. 1C , it will be appreciated that the RAN  104  may be connected to other ASNs and the core network  106  may be connected to other core networks. The communication link between the RAN  104  the other ASNs may be defined as an R4 reference point, which may include protocols for coordinating the mobility of the WTRUs  102   a ,  102   b ,  102   c  between the RAN  104  and the other ASNs. The communication link between the core network  106  and the other core networks may be defined as an R5 reference, which may include protocols for facilitating interworking between home core networks and visited core networks. 
     Other networks  112  may further be connected to an IEEE 802.11 based wireless local area network (WLAN)  160 . The WLAN  160  shown here may be designed to implement the modified features of the present application. The WLAN  160  may include an access router  165 . The access router may contain gateway functionality. The access router  165  may be in communication with a plurality of access points (APs)  170   a ,  170   b . The APs  170   a ,  170   b  may be configured to perform the methods described below. The communication between access router  165  and APs  170   a ,  170   b  may be via wired Ethernet (IEEE 802.3 standards), or any type of wireless communication protocol. AP  170   a  is in wireless communication over an air interface with WTRU  102   d . WTRU  102  may be an IEEE 802.11 STA, and may also be configured to perform the methods described herein. 
       FIG. 1D  is a diagram of an example of a small-cell backhaul in an end-to-end mobile network infrastructure. A set of small-cell nodes  152   a ,  152   b ,  152   c ,  152   d , and  152   e  and aggregation points  154   a  and  154   b  interconnected via directional millimeter wave (mmW) wireless links may comprise a “directional-mesh” network and provide backhaul connectivity. For example, the WTRU  102  may connect via the radio interface  150  to the small-cell backhaul  153  via small-cell  152   a  and aggregation point  154   a . In this example, the aggregation point  154   a  provides the WTRU  102  access via the RAN backhaul  155  to a RAN connectivity site  156   a . The WTRU  102  therefore then has access to the core network nodes  158  via the core transport  157  and to internet service provider (ISP)  180  via the service LAN  159 . The WTRU also has access to external networks  181  including but not limited to local content  182 , the Internet  183 , and application server  184 . It should be noted that for purposes of example, the number of small-cell nodes  152  is five; however, any number of nodes  152  may be included in the set of small-cell nodes. 
     Aggregation point  154   a  may include a mesh gateway node. A mesh controller  190  may be responsible for the overall mesh network formation and management. The mesh-controller  190  may be placed deep within the mobile operator&#39;s core network as it may responsible for only delay insensitive functions. In an embodiment, the data-plane traffic (user data) may not flow through the mesh-controller. The interface to the mesh-controller  190  may be only a control interface used for delay tolerant mesh configuration and management purposes. The data plane traffic may go through the serving gateway (SGW) interface of the core network nodes  158 . 
     The aggregation point  154   a , including the mesh gateway, may connect via the RAN backhaul  155  to a RAN connectivity site  156   a . The aggregation point  154   a , including the mesh gateway, therefore then has access to the core network nodes  158  via the core transport  157 , the mesh controller  190  and to ISP  180  via the service LAN  159 . The core network nodes  158  may also connect to another RAN connectivity site  156   b . The aggregation point  154   a , including the mesh gateway, also may connect to external networks  181  including but not limited to local content  182 , the Internet  183 , and application server  184 . 
     As used herein, control region may refer to a control period and these terms may be used interchangeably. Further, as used herein, scheduling iteration may refer to an scheduling interval (SI) and these terms may be used interchangeably. 
     Densification of cellular networks may help meet a growing demand for increased capacity, but may also require an increase in backhaul capabilities. The Millimeter Wave Hotspot (mmH) project may use highly directional millimeter (mm) wave (mmW) links between these small-cell nodes to meet backhaul requirements. Unlike other mmW and microwave peer to peer (P2P) systems, the mmH backhaul may comprise a flexible mesh network employing electrically steerable mmW antennas. The electrically steerable antennas may enable low cost, flexible, self-configuring backhaul networks. The wide bandwidths in the mmW spectrum may enable very high data rates. The high directionality of the antennas may imply low interference but also may present challenges to mesh network operation. The proposed mmH system can utilize elements of the current IEEE 802.11ad standard as a baseline for the system design. However, various enhancements and modifications may be preferred beyond what is specified in the standard and several example physical layer (PHY) modifications and other modifications are disclosed herein. 
     Example PHY modifications are disclosed herein and include the following. Modified modulation and coding sets (MCSs) may enable longer range communications at the minimum required data rate (referred to as a low MCS). A regular periodic superframe structure may enable cellular-like contention free access, long range discovery, and topology formation. Modified beacon and beacon response messages may enable long range discovery with high gain directional antennas on both ends of a link. An SI frame may consist of control slots for exchanges of control messages on a per link basis to negotiate scheduling of data, and data slots (following the control slots) for the scheduled data transmission. 
     Example signaling to support fast hybrid automatic repeat request (HARQ) is described herein. It may be difficult to achieve the low latency and high throughput requirements over a multi-hop network. To help achieve this, fast re-transmissions with re-transmission combining are introduced. Modified preambles, coding and modulation schemes, and Golay codes are also supported. In many cases, the preambles may be shortened due to the stability of backhaul links and the way in which the links are maintained in the backhaul mesh system. 
     Modified coding and modulation schemes are introduced to support the modified control and beacon messages (as well as the modified low MCS). Long low-density parity-check codes (LDPCs) may be applicable to backhaul and known to have better performance. In examples, these are disclosed herein for data packets. 
     The preambles used in the mmW backhaul system may be constructed of Golay sequences similar to IEEE 802.11ad, but may be modified to enable a node to screen out (or fast detect) IEEE 802.11ad transmissions. Furthermore, the system may be configured to use a different set of Golay codes to further mitigate interference between IEEE 802.11ad networks as well as other from other nodes in own or other mm backhaul networks 
     Since highly directional antennas may be used on a limited set of links, the backhaul system may be predominantly noise limited. Therefore, power control may be mainly geared towards limiting the received power to not go much beyond that require by the largest MCS. Initial power control may be conducted during discovery. Because there may be less opportunity for scheduling around interference in control slots, control slot power control may be based on the reliability of the control messages. 
     The examples disclosed herein capture a PHY design for mmW mesh networks intended to provide small-cell backhaul for dense deployments. The PHY design may be based on the IEEE 802.11 Directional Multi-Gigabit amendment, IEEE 802.11ad. Examples are described that may introduce modifications to the existing specifications to better enable the envisioned directional mesh networks that are likely to be acceptable to the IEEE 802.11 community, but still not impose severe limitation on the overall directional mesh network performance. 
     The examples disclosed herein provide a preliminary PHY specification that may be capable of supporting the range and data rate requirements of the mmW backhaul system. It also provides a preliminary PHY specification that may be capable of supporting fully scheduled directional mesh networks. 
     The IEEE 802.11ad standard is used as a baseline for the newly proposed mmH backhaul system design. The required enhancements described herein may be summarized as follows. 
     A modified beacon period structure may include various enhancements to enable longer discovery and communication range, support mesh formation, and better support contention free access. A modified SI and control period design may be used to maintain mesh links and negotiate data field transmission-reception schedules. A shortened preamble design is in some cases allowable due to the inherent stability of the backhaul links and because each mesh link is maintained by frequent control message exchanges. A modified low MCS design may meet the requirement for longer communication range. In an example, the 802.11ad MCS1 data rate may be higher than is required in many cases. Longer codewords generally may have better performance and be also feasible in backhaul where there are generally larger amounts of data available per packet. A data header for a data packet may require changes but may be of similar size and performance of the 802.11ad SC header. Regarding HARQ and end-to-end latency, the multi-hop mesh network may need to have high reliability and low latency above the media access control (MAC) layer. Greater reliability may be provided through retransmissions, but the latency requirements may leave little latency budget. Retransmission combining may help ensure few re-transmissions are needed. 
     Modified complementary Golay codes for the backhaul (BH) may minimize interference with the 802.11ad codes already in use in un-coordinated 802.11ad networks and help mitigate interference between nodes of same or other BH network. Finally, due to the inherent low interference likely in the mmW BH, links may be typically noise limited (or error vector magnitude (EVM) limited). Furthermore, transmission and reception directions may be limited to those of a small set of semi-static links. Power control can be mostly limited to cases of receiver max power limits or cases of specific link-link interference, but may still require enhancement to 802.11ad. 
     The various transmission periods mentioned above may be logically ordered into a superframe. One of the major differences of the modified superframe compared to the unmodified 802.11ad superframe may be the scheduled transmission architecture adopted for the mmH project. 
       FIG. 2  is a diagram of an example superframe structure. In an example, the superframe structure  210 , including a Beacon Interval  220 , may be split into two major components: a Beacon Period  230 , which may be used for new node discovery, mesh formation, and other purposes, and an SI  270  which may be used to negotiate the scheduling of data slot resources between connected nodes, and for data packet transactions. 
     As shown, each SI  240 ,  250  may be further split into a Control Period  242 ,  252  and a Data Period,  244 ,  254 . There may be multiple SIs  240 ,  250  per superframe. Exemplary values for the various superframe timing parameters are listed in Table 1. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Superframe Timing Parameters  
               
            
           
           
               
               
               
            
               
                   
                 Parameter 
                 Value 
               
               
                   
                   
               
               
                   
                 F C : SC chip rate 
                 1760 MHz 
               
               
                   
                 T C : SC chip time 
                 0.57 ns = 1/Fc 
               
               
                   
                 T BP : Beacon Period duration 
                 0.5 ms = 880000 * T C   
               
               
                   
                 T SI : Scheduling Interval duration 
                 0.5 ms = 880000 * T C   
               
               
                   
                 N SI : Max. Number of Scheduling  
                 Configurable [1 . . . 999] 
               
               
                   
                 Intervals per Beacon Interval 
                   
               
               
                   
                 T BI : Beacon Interval duration  
                 (T BP  + N SI  * T SI ) =  
               
               
                   
                 (Superframe Duration) 
                 [1.0 ms . . . 0.5 s] 
               
               
                   
                   
               
            
           
         
       
     
     The Beacon Period  230  may be composed of a beacon followed by possible message exchanges in response to beacon reception. A further Beacon Period  260  may follow Beacon Period  230 . The Beacon Period  230  may be used for long range node discovery, node configuration, node admission, and mesh formation. Since the system may intend to make use of very high antenna gains for long range communications and not place a bound on the maximum gain, the discovery procedure may make use of high gain antennas at both the transmitter and the receiver. This may require a modified search algorithm compared to IEEE 802.11ad which does not simultaneously use high gain antennas at transmission (Tx) and reception (Rx). 
       FIG. 3  is a diagram of an example Beacon Period. As shown in the transmissions  300 , the Beacon Period  310  may be split into three major components: a Beacon Transmission Interval (BTI)  320 , a Beacon Response Interval (BRI)  330 , and a Beacon Response Acknowledgement (BRA)  340 . Each BTI may be split into multiple BTI slots  323 ,  325 ,  329  which may each be separated by the Beacon Switch Inter-Frame Spacing (BSIFS)  324 ,  326  to facilitate antenna beam direction switching between beacon transmissions. The space may be kept short (˜500 nSec) since such switching should be achievable. In an example, digital control interfaces and network architectures may need to be created to enable this fast switching, e.g., phase shift values for all phase shifters in the phased array antenna (PAA) could be preloaded in look-up tables (LUTs) and triggered by a fast event trigger. Further, a BTI slot (BTI_S)  322  may contain a BTI slot data (BTI_SD)  323  and a BSIFS  324 . 
     Attached nodes may transmit the beacon message over multiple transmit antenna directions, one direction per BTI_S. The sweep over directions may not be completed in one BTI, but may require multiple BTI&#39;s. The antenna gain may not be the maximum gain possible with the used antenna. If the size of the antenna is large compared to that required to discover at the maximum distance, the antenna beam may be widened so that the total sweep time to cover the full sweep range is reduced compared to the maximum gain beam. The search pattern may be determined to cover the full search range with no more than Ksearch dB (e.g., 3 dB for Tx and Rx antennas) loss due to Tx and Rx antenna pointing error with a minimal number of beams. New nodes may listen for beacon message in one particular receive antenna direction for each Beacon Interval. 
     The BRI  330  may be similarly split into slots  334 ,  336 ,  339  and separated by a Long Inter-Frame Spacing (LIFS)  333 ,  335 ,  337  to account for a range of propagation delays for the new node response. The node wishing to join the network may respond to only the node that provided the best signal strength over its listening period and may use the Tx beam that is its best estimate of the best beam to use based on the Rx beams it used to listen for the BTI. Further, a BRI slot (BRI_S)  332  may contain an LIFS slot  333  and a BRI slot data (BRI_SD)  334 . 
     The attached node may sweep its ‘listening’ Rx beam directions in the same order that was used when transmitting in the BTI during the BRI. The new node may have the option to transmit in one or multiple slots for the response message. For the one slot example, the new node may transmit the response in only the slot that corresponds to the attached node&#39;s transmit direction that resulted in the best received beacon. The one slot example may be used when the new node estimates that any miss calibration between the Tx and Rx beam directions (at its own PAA and an attached node&#39;s PAA) or asymmetry between Tx and Rx beam capabilities would not affect the choice of the best beam of the attached node to respond on. 
     For the multiple slot example, the new node may transmit the response in multiple slots. This mode may be used when the choice of the best beam to respond on is uncertain (e.g., received signal strength indicators (RSSIs) from multiple directions are within a certain tolerance). In this case, the node may respond on up to three BRI_Ss. For example, the node may respond on BRI_S  332  and two other BRI_Ss. 
     A final BSIFS  349  at the end of the Beacon Period allows the mesh node to re-orient its beam for the next message transmission. Attached nodes may transmit any beacon acknowledge messages with the best beam estimated from any BRI responses received. The attached node may not transmit a BRA if no BRI messages are correctly decoded. If BRI messages from one or more new nodes are correctly decoded, the attached node may respond for a BRA in the next BRA opportunity to one of the new nodes. If BRIs from multiple new nodes are detected, the beacons may be modified to indicate to new nodes that the expected BRA timing is changed. New nodes may listen for a beacon acknowledge message in the same receive antenna direction used to identify the best beacon. 
       FIG. 3  shows how the various Beacon Intervals may be further split into Beacon Slots, as described above. Further, a BRA slot (BRA_S)  342  may contain an LIFS slot  343  and a BRA slot data (BRA_SD)  344 . The Beacon Intervals may be split into varying number of Beacon slots. In an example, the number of BTI and BRI slots may determine the maximum number of sectors that may be swept through in one Beacon Period. 
       FIG. 4  is a diagram of an example BTI_S. In an example, the BTI_S  410  may be split into a BTI preamble section  420 , a BTI data section  430 , and finally end with a BSIFS section  440 . In a further example, the BTI_SD (not shown) may contain the BTI preamble section  420  and the BTI data section  430 . 
       FIG. 5  is a diagram of an example BRI_S. The BRI_S  510  may be similar to the Beacon Transmission slots except that they may lead with the interframe spacing section, LIFS  515 . For example, the BRI_S may contain an LIFS  515 , a BRI Preamble  520  and BRI Data  530 . In a further example, the BRI_SD (not shown) may contain the BRI Preamble  520  and BRI Data  530 . 
       FIG. 6  is a diagram of an example BRA_S. The BRA_Ss slots may be similar to the BTIs except that they lead with the beacon long interframe spacing section (BLIFS)  615 . As an example, the BRA_S may contain a BLIFS  615 , a BRA Preamble  620  and a BRA Data  630 . In a further example, the BRA_SD (not shown) may contain the BRA Preamble  620  and BRA Data  630 . Lastly, the Beacon Period may end with a final interframe spacing, a BSIFS  640  separating the Beacon Period from the SI. Exemplary values for the timing parameters related to  FIGS. 3, 4, 5 and 6  are shown in Table 2. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Beacon Period Timing Parameters 
               
            
           
           
               
               
            
               
                 Parameter 
                 Value 
               
               
                   
               
               
                 N BTI _S = N BRI _S: Number of Beacon  
                 22 
               
               
                 Transmission and Beacon Response  
                   
               
               
                 slots in a Beacon Period 
                   
               
               
                 T BTI _P: Duration of Beacon  
                 7552 * T C   
               
               
                 Transmission Preamble 
                   
               
               
                 T BTI _D: Duration of Beacon  
                 7168 * T C   
               
               
                 Transmission Data 
                   
               
               
                 T BTI _S: Duration of Beacon  
                 15744 * T C  = T BTI _P + T BTI _D +  
               
               
                 Transmission Slot 
                 BSIFS 
               
               
                 T BRI _P: Duration of Beacon Response  
                 3328 * T C   
               
               
                 Preamble 
                   
               
               
                 T BRI _D: Duration of Beacon Response  
                 7168 * T C   
               
               
                 Data 
                   
               
               
                 T BRI _S: Duration of Beacon Response  
                 23120 * T C  = LIFS + T BRI _P +  
               
               
                 Slot 
                 T BRI _D 
               
               
                 T BRA _P: Duration of Beacon Response 
                 3328 * T C   
               
               
                 Acknowledgement Preamble 
                   
               
               
                 T BRA _D: Duration of Beacon Response 
                 7936 * T C   
               
               
                 Acknowledgement Data 
                   
               
               
                 T BRA _S: Duration of Beacon Response 
                 26016 * T C  = BLIFS + T BRA _P +  
               
               
                 Acknowledgement Slot 
                 T BRA _D + BSFIS 
               
               
                 T BTI : Duration of Beacon  
                 (N BTI _S * T BTI _S − BSIFS) =  
               
               
                 Transmission Interval 
                 345344 * T C   
               
               
                 T BRI : Duration of Beacon Response  
                 (N BRI _S * T BRI _S) = 508640 * T C   
               
               
                 Interval 
                   
               
               
                 T BRA : Duration of Beacon Response 
                 (T BRA _S + BSIFS) = 26016 * T C   
               
               
                 Acknowledgement Interval 
                   
               
               
                 BSIFS: Beam Switch Inter-Frame  
                 1024 * T C   
               
               
                 Spacing 
                   
               
               
                 LIFS: Long Inter-Frame Spacing 
                 12624 * T C   
               
               
                 BLIFS: Long Inter-Frame Spacing 
                 13728 * T C   
               
               
                 T BP : Beacon Period duration 
                 0.5 ms = 880000 * T C   
               
               
                   
               
            
           
         
       
     
     The beacon transmissions in the BTI may be the only messages in the system that may be received without the benefit of some timing information. In this way, the modified short training field (STF) requirements may be similar to that of unmodified 802.11ad. A Start of Packet (SoP) may be detected without benefit of a schedule. Furthermore, there may be no historical reception of packets on which some initial automatic gain control (AGC) or carrier frequency offset (CFO) estimation could be done. However, the IEEE 802.11ad Control PHY (C-PHY) preamble may not be reused since it may allow the new node attempting to join a mesh BH system to waste time receiving IEEE 802.11ad beacons. 
       FIG. 7  is a diagram of an example BTI preamble. The preamble shown in  700  may use both the Ga  752 ,  754  and Gb  751 ,  753  sequences in the STF. The last pair is inverted to mark the end of beacon STF and still use -Ga as the prefix of the channel estimation (CE) field (CEF)  760 . The Ga and Gb Golay sequences may also be replaced with other modified Golay sequences with low cross correlations to other Golays used in IEEE 802.11ad as described below. These sequences may also be longer (e.g., 256 bits rather than 128 bits). The specific sequence to use is indicated in the BRA. By modifying the BTI preamble  710  as below, use of the IEEE 802.11ad Golay sequences for Ga and Gb (and other sequences) may remain possible, but selection of modified sequences may be preferable. 
       FIG. 8  is a diagram of an example BRI preamble. The BRI preamble  800  may use both the Ga  852 ,  854  and Gb  851 ,  853  sequences, and may contain a CEF  860 . Unlike the beacon transmission messages, the beacon response messages may be received after some timing information has been gained in the BTI. This may allow for a relatively shortened STF period as shown in  800 . The BRI preamble duration  810  may have the same duration as one of the 802.11ad preambles, but again may have different structure to permit distinction in the case that 802.11ad sequences are re-used. 
       FIG. 9  is a diagram of an example BRA preamble. The BRA preamble  900  may use both the Ga  952 ,  954 , and Gb  951 ,  953  sequences, and may contain a CEF  960 . The beacon acknowledge message may use the same preamble as the beacon response messages since it may also have some prior timing information when it is received. In an example, the BTI preamble duration  910  may be the same as the BRA preamble duration  810 . 
     Each beacon period may consist of three beacon message types exchanged between an attached node (A) and new node (B). The BTI message may be transmitted from the attached nodes to the new nodes, (A→B). Elements of the BTI message are described in Table 3. The BRI message may be transmitted from the new nodes to the attached nodes, (B→A). It may use the same Golay sequence set that was received in BTI. Elements of the BRI message are described Table 4. The BRA message may be transmitted from the attached nodes to the new nodes, (A→B). Exemplary elements of the BRA message are described Table 5. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 BTI Message 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Size 
                   
               
               
                 Order 
                 Field 
                 [Bits] 
                 Description 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 Network  
                 16 
                 Full or partial network ID including operator  
               
               
                   
                 ID 
                   
                 ID. New node may use this in PLMN  
               
               
                   
                   
                   
                 selection and filtering 
               
               
                 2 
                 Node ID 
                 12 
                 ID of beacon transmitting node within the  
               
               
                   
                   
                   
                 network. 
               
               
                 3 
                 Sector ID 
                 8 
                 ID of the beam being transmitted. Unique  
               
               
                   
                   
                   
                 within the BTI, but non-unique between BTIs 
               
               
                 4 
                 Max  
                 8 
                 Total number of sectors (or beams) that the  
               
               
                   
                 Sectors 
                   
                 beacon transmitting node may transmit to  
               
               
                   
                   
                   
                 provide coverage over the sweep range 
               
               
                 5 
                 Timestamp 
                 8 
                 Full or partial time information of the  
               
               
                   
                   
                   
                 transmitted message to approx. 64 chip  
               
               
                   
                   
                   
                 resolution. May be used to measure air  
               
               
                   
                   
                   
                 propagation time between message  
               
               
                   
                   
                   
                 exchanging nodes 
               
               
                 6 
                 Beacon 
                 3 
                 Indicates the next available BRI during which 
               
               
                   
                 Response 
                   
                 mesh node will listen for new node&#39;s Beacon 
               
               
                   
                 Offset 
                   
                 response. The BRI immediately following the 
               
               
                   
                   
                   
                 current BTI may not be available for new node 
               
               
                   
                   
                   
                 response reception because it may have been 
               
               
                   
                   
                   
                 previously reserved for an association  
               
               
                   
                   
                   
                 procedure with another new node, interference  
               
               
                   
                   
                   
                 measurement, etc. 
               
               
                 7 
                 BRI use  
                 3 
                 Indicates the purpose for subsequent BRI. Valid 
               
               
                   
                 code 
                   
                 codes may include: available for new node  
               
               
                   
                   
                   
                 beacon response (default), interference  
               
               
                   
                   
                   
                 measurement, other new node association, etc. 
               
               
                 8 
                 Tx Power 
                 12 
                 Beacon Tx power, EIRP. Max EIRP 
               
               
                   
                 Info 
                   
                   
               
               
                 9 
                 Control  
                 2 
                 Number of control slots per control period  
               
               
                   
                 slots 
                   
                 {5,6,7,8} May alternatively go in the BRA 
               
               
                 10 
                 Reserve 
                 16 
                 Reserved for future use 
               
               
                 11 
                 FCS 
                 24 
                 Frame Check CRC sequence 
               
               
                   
                 Total 
                 112 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 4 
               
             
            
               
                   
               
               
                 BRI Message  
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Size 
                   
               
               
                 Order 
                 Field 
                 [Bits] 
                 Description 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 New node  
                 48 
                 MAC address of the responding node. 
               
               
                   
                 ID 
                   
                 Network may check its database for node 
               
               
                   
                   
                   
                 capabilities and if node may be admitted. 
               
               
                 2 
                 Additional 
                 8 
                 Configured capabilities not learnable from 
               
               
                   
                 capability  
                   
                 MAC address 
               
               
                   
                 class info 
                   
                   
               
               
                 3 
                 Mesh node  
                 12 
                 Beacon transmitting node&#39;s ID is echoed back 
               
               
                   
                 ID echo 
                   
                 to ensure that the pair are mutually ID&#39;d. 
               
               
                 4 
                 Timestamp  
                 8 
                 Beacon transmitting node&#39;s Timestamp is 
               
               
                   
                 echo 
                   
                 echoed back so that air propagation time may 
               
               
                   
                   
                   
                 be computed. 
               
               
                 5 
                 Gateway 
                 1 
                 This may prevent a gateway node from 
               
               
                   
                 Indication 
                   
                 directly connecting to another gateway node. 
               
               
                 6 
                 RSSI 
                 4 
                 Power of received beacon 
               
               
                 7 
                 Delta Rx  
                 2 
                 Difference between Rx gain and Max Rx gain 
               
               
                   
                 gain 
                   
                   
               
               
                 8 
                 Reserve 
                 13 
                 Reserved for future use 
               
               
                 9 
                 FCS 
                 16 
                 Frame Check CRC sequence 
               
               
                   
                 Total 
                 112 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 5 
               
             
            
               
                   
               
               
                 BRA Message 
               
            
           
           
               
               
               
               
            
               
                   
                   
                 Size 
                   
               
               
                 Order 
                 Field 
                 [Bits] 
                 Description 
               
               
                   
               
            
           
           
               
               
               
               
            
               
                 1 
                 Node ID 
                 12 
                 Responding node is given its node ID  
               
               
                   
                   
                   
                 for this network. A node ID of 0 is  
               
               
                   
                   
                   
                 not accepted into network. If node is  
               
               
                   
                   
                   
                 accepted, the following bits are  
               
               
                   
                   
                   
                 interpreted as: 
               
               
                 2 
                 Rx node ID  
                 24 
                 MAC address of receiving node  
               
               
                   
                 echo (Hash) 
                   
                 echoed back to ensure mutual node ID 
               
               
                   
                   
                   
                 Hash of 48 bit address to 24 bits. 
               
               
                   
                   
                   
                 Hash function is TBD. 
               
               
                 3 
                 Time Adjust 
                 8 
                 Offset to apply when transmitting to  
               
               
                   
                   
                   
                 this network node 
               
               
                 4 
                 Schedule 
                 8 
                 Indicator of control slots the new node  
               
               
                   
                   
                   
                 should initially listen to in linking to  
               
               
                   
                   
                   
                 this network node 
               
               
                 5 
                 Channel 
                 2 
                 Used to indicate a channel to use for  
               
               
                   
                   
                   
                 initial schedule message exchange. 
               
               
                 6 
                 Power adjust  
                 4 
                 Power adjust for subsequent control  
               
               
                   
                 for control  
                   
                 message transmission relative to BRI 
               
               
                   
                 messages 
                   
                   
               
               
                 7 
                 Configuration 
                 12 
                 System information and new node 
               
               
                   
                 message 
                   
                 configuration data (e.g., Channel  
               
               
                   
                   
                   
                 Quality Indicator (CQI) table  
               
               
                   
                   
                   
                 definition) 
               
               
                 8 
                 Initial control 
                 3 
                 Indicates to new node what control  
               
               
                   
                 slot 
                   
                 slot to initially use on this link 
               
               
                 9 
                 Reserve 
                 15 
                 Reserved for future use 
               
               
                 10 
                 Golay Sequence 
                 4 
                 Specifies a set of Golay sequences to  
               
               
                   
                 Indicator 
                   
                 use for Ga and Gb sequences. The  
               
               
                   
                   
                   
                 Golay Sequence Indicator may  
               
               
                   
                   
                   
                 indicate what set the new node  
               
               
                   
                   
                   
                 should use for its subsequent  
               
               
                   
                   
                   
                 transmissions on this link. 
               
               
                 11 
                 FCS 
                 24 
                 Frame Check CRC sequence 
               
               
                   
                 Total 
                 112 
                   
               
               
                   
               
            
           
         
       
     
     Coding and modulation of the BTI, BRI, and BRA (collectively called the beacon messages) may be similar to C-PHY in 802.11ad, potentially making it easier for a node to monitor/discover 802.11ad and mmW backhaul simultaneously. The Beacon MCS (MCSB) may not need the same level of protection. 
     The beacon messages may be used during the discovery process before beam refinement has taken place. Therefore, the full gain of the Tx and Rx antennas may not be assumed when estimating the discovery range. The discovery range should be commensurate with the low MCS communications range and an antenna configuration to support that range. An example desired range for the low MCS may be 350 m. The discovery range may be at least this range when the same antenna configuration is used. 
     The required Rx power to reliably receive the beacon may be determined as well (for instance, −70 dBm). However, there may be some differences in the link budget assumptions. First, there may be an additional loss of about ˜6 dB to be added due to beam misalignment. Second, there is no strong need to discover in heavy rain (25 mm/hr), which gives a 3.5 dB benefit. The net result may be a loss of about 2.5 dB relative to the Low MCS. Since there is about an 8 dB difference in performance between the low MCS and MCS0 in 802.11ad, there may be an ˜5.5 dB margin if MCS0 is used for the beacon messages. The MCS0 data rate is however comparatively low (˜27.5 Mbps), and it may be beneficial to use some of that margin to reduce the beacon message duration. This may be accomplished by modifying the IEEE 802.11ad MCS0. Possible methods may include reducing the spreading factor from 32× to 16×, adding a parallel spreading code with 32× spreading, and using quadrature phase-shift keying (QPSK) modulation with 32× spreading. 
     While each method has it benefits and drawbacks, in an example, the QPSK based method may be selected so that the effective symbol length of 32Tc may be maintained, more than 3 dB signal to noise ratio (SNR) may be expected to be required and Peak-to-Average Power Ratio (PAPR) may not be degraded much. Parallel spreading may also be attractive. From work on the use of Golay sequences for the use in DS CDMA, it is known that good sets of spreading codes based on complementary Golay sequences exist. A set of 32, 32-chip sequences may be found with very good mutual correlation properties. The set may be selected to also have good correlation properties relative the IEEE 802.11ad Golay codes. 
     Other possible modifications include a reduction in payload compared to the MCS0 1st LDPC codeword. This may provide some additional margin to either extend the range slightly beyond the new low MCS range or permit wider beams to be used in the discovery process. 
       FIG. 10  is a diagram of an example process for coding and modulation for beacon messages. At the beginning of an example process  1000 , the beacon message  1010  may be scrambled  1015  starting with the 5th bit, where the scrambler may be initialized with {x1, x2, x3, x4, 1, 1, 1}. The result is a sequence b  1020 . The scrambled beacon message  1020  may be split into two equal length sequences b 1   1022  and b 2   1024  of length L. Each sequence b 1   1022  and b 2   1024  may be padded with zeroes  1032  and zeroes  1034  to a length of 504 total bits. The padded sequences may be coded with the rate 3/4 LDPC code to produce the code words C m =(b m   1 , . . . , b m   L , 0, . . . , 0, p m   1 , . . . , p m   168 ), m={1, 2}, which may include parity (P) bits  1044 . The codewords may then have the zeros removed c 1 =(b 1   1 , . . . , b 1   L , p 1   1 , . . . , p 1   168 ), c 2 =(b 2   1 , . . . , b 2   L , p 2   1 , . . . , p 2   168 ). The two codewords c 1  and c 2  may be concatenated to create the sequence c 3 =(c 1 , c 2 ). The new sequence, c 3 , may be grouped into 2-bit symbols to create c 4   (k) =(c 3   (2k-1), c   3   (2k) ). The sequence c 4   (k)  may then be converted into a complex data stream according to the mapping function 
     
       
         
           
             { 
             
               
                 
                   c 
                   4 
                 
                  
                 
                   ( 
                   k 
                   ) 
                 
               
                
               
                 → 
                 
                   
                       
                   
                    
                   f 
                    
                   
                       
                   
                 
               
                
               
                 s 
                  
                 
                   ( 
                   k 
                   ) 
                 
               
             
             } 
           
         
       
     
     given by the following: 
     
       
         
           
             
               
                 00 
                 
                     
                 
                 ′ 
                   
                 
                     
                 
                 ′ 
               
               → 
               
                 e 
                 
                   j 
                    
                   
                     π 
                     4 
                   
                 
               
             
             , 
             
               
                 01 
                 
                     
                 
                 ′ 
                   
                 
                     
                 
                 ′ 
               
               → 
               
                 e 
                 
                   j 
                    
                   
                     
                       3 
                        
                       π 
                     
                     4 
                   
                 
               
             
             , 
             
               
                 11 
                   
                 ′ 
                   
                 
                     
                 
                 ′ 
               
               → 
               
                 e 
                 
                   
                     - 
                     j 
                   
                    
                   
                     
                       3 
                        
                       π 
                     
                     4 
                   
                 
               
             
             , 
             
               
                 and 
                  
                 
                     
                 
                  
                 
                   10 
                     
                   ′ 
                     
                   
                       
                   
                   ′ 
                 
               
               → 
               
                 
                   e 
                   
                     
                       - 
                       j 
                     
                      
                     
                       π 
                       4 
                     
                   
                 
                 . 
               
             
           
         
       
     
     The pi/4 differential QPSK modulated signal, d(k),  1050  may then be created as: d(k)=s(k)*d(k−1). In an example, d(0) may be defined to be e j0  so that the first symbol d(1)=s(1). The sequence may be spread  1060  using the designated length 32 spreading codes to create: 
     
       
         
           
             
               
                 
                   
                     r 
                      
                     
                       ( 
                       k 
                       ) 
                     
                   
                   = 
                   
                     
                       
                         G 
                         a 
                       
                        
                       
                         ( 
                         
                           
                             ( 
                             
                               k 
                               - 
                               1 
                             
                             ) 
                           
                            
                           mod 
                            
                           
                               
                           
                            
                           32 
                         
                         ) 
                       
                     
                      
                     
                         
                     
                      
                     
                       
                         d 
                          
                         
                           ( 
                           
                             ⌊ 
                             
                               
                                 ( 
                                 
                                   k 
                                   - 
                                   1 
                                 
                                 ) 
                               
                               
                                 3 
                                  
                                 2 
                               
                             
                             ⌋ 
                           
                           ) 
                         
                       
                       . 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     As stated above, one of the major differences in the mmH architecture compared to the IEEE 802.11ad baseline is the use of a regularly scheduled structure for multiple access as opposed to the contention based and contention free access methods specified for IEEE 802.11ad. Therefore, a modified scheduling period and data transfer period may be required. This is referred to as a SI and may contain both a Control Period and a Data Period. 
       FIG. 11  is a diagram of an example SI. The Control Period  1120  may be used to negotiate the scheduling of data slot resources between the various connected nodes. During each SI  1110  and for all nodes, a three message exchange may occur between the node and all of its neighbors. The exchange may include buffer status reports, grant requests, grants, channel quality information, Acknowledged (ACK)/Not Acknowledged (NACK) information and other information to assist in scheduling. Since failure to correctly decode control messages may result in no data slot grant/allocation on a particular link as well as loss of link maintenance data, these messages may be provided with extra coding protection relative to regular data transmissions. 
     The Control Period  1120  may be split into multiple Control Slots,  1121 ,  1122  through  1129 . The Data Period  1130  may be similarly split into multiple Data Slots,  1131  through  1139  that may be allocated to the nodes based on the negotiating procedure defined in the Control period  1120 . Various exemplary timing parameters related to the SI are shown in Table 6. 
     
       
         
           
               
             
               
                 TABLE 6 
               
             
            
               
                   
               
               
                 Scheduling Interval Timing Parameters 
               
            
           
           
               
               
            
               
                 Parameter 
                 Value 
               
               
                   
               
               
                 N CS : Number of Control Slots per 
                 5 default (configurable to 6, 7, 8) 
               
               
                 Control Period 
                   
               
               
                 N DS : Number of data slots per Data 
                 32 
               
               
                 Period 
                   
               
               
                 T CP : Duration of Control Period 
                 Default 109952*T C   
               
               
                 T DP : Duration of Data Period 
                 Default 770048*T C   
               
               
                 T SI : Duration of Scheduling Interval 
                 880000*T C  = T CP  + T DP  = 0.5 ms 
               
               
                   
               
            
           
         
       
     
       FIG. 12  is a diagram of an example control period structure. In an example each Control Period  1210  may be split into multiple Control Slots, such that each node  1 ,  2  . . . N in the network may be assigned at least one Control Slot,  1221 ,  1222  . . .  1229  respectively, for each of its connected neighbors. The Control Slots may be further split into three sections to accommodate a three message exchange sequence. An example of a message exchange sequence is shown in  FIG. 16 . 
       FIG. 13  is a diagram of an example control slot structure. In an example, each message may include a preamble section for synchronization  1321 ,  1331 ,  1341 , a data section  1322 ,  1332 ,  1342 , and an interframe spacing section  1324 ,  1334 ,  1344  used to avoid interference due to propagation delays. In an example, a data section  1322  may be a control message. Finally, the figure also shows that the interframe spacing section in the last Control Slot  1345  may be slightly longer than the others which may result in the difference between Duration of Control Slot  1315  and Duration of Last Control Slot  1310 . Exemplary timing parameters for the default configuration of Number of Control Slots (NCS=5) are shown in Table 7. 
     
       
         
           
               
             
               
                 TABLE 7 
               
             
            
               
                   
               
               
                 Default Control Period Timing Parameters 
               
            
           
           
               
               
               
            
               
                   
                 Parameter 
                 Value 
               
               
                   
                   
               
               
                   
                 N CS : Number of Control Slots per 
                 5 
               
               
                   
                 Control Period 
                   
               
               
                   
                 T CP1 : Duration of Control Message 1 
                 2304*T C   
               
               
                   
                 Preamble 
                   
               
               
                   
                 T CM1 : Duration of Control Message 1 
                 1088*T C   
               
               
                   
                 T CP2 : Duration of Control Message 2 
                 2304*T C   
               
               
                   
                 Preamble 
                   
               
               
                   
                 T CM2 : Duration of Control Message 2 
                 1600*T C   
               
               
                   
                 T CP3 : Duration of Control Message 3 
                  640*T C   
               
               
                   
                 Preamble 
                   
               
               
                   
                 T CM3 : Duration of Control Message 3 
                 1088*T C   
               
               
                   
                 CIFS: Control Message Inter-frame 
                 4322*T C   
               
               
                   
                 Spacing 
                   
               
               
                   
                 CDIFS: Control Data Inter-frame 
                 4324*T C   
               
               
                   
                 Spacing 
                   
               
               
                   
                 T CS : Duration of Control Slots (1: N CS  − 1) 
                 21990*T C   
               
               
                   
                 T CS _L: Duration of Last Control Slot 
                 21992*T C   
               
               
                   
                 T CP : Duration of Control Period (See 
                 109952*T C  = T CS  *  
               
               
                   
                 also Table 6) 
                 (N CS  − 1) + T CS _L 
               
               
                   
                   
               
            
           
         
       
     
     As explained above, three separate messages may be defined in the control period of the SI. The messages may be prepended with a preamble that consists of both an STF and a CEF. One difference from the unmodified 802.11ad packet structure is that there may be no distinction between the header and the data region. The number of SC-PHY data blocks assigned to the control messages may be Ncb(n), where n={1,2,3} to indicate the control message number. Ncb(n) may be system parameters that are either fixed or are carried in the beacon or beacon ACK messages. The major difference, however, has to do with the preamble size, which may be shortened compared to the unmodified 802.11ad preamble size. 
     In the case of the first two messages the STF may be shortened. Specifically, control message  1  may have a shortened STF. Further, control message  2  may have a shortened STF. 
       FIG. 14  is a diagram of an example preamble for control messages  1  and  2 . The STF may be shortened for control messages  1  and  2 , shown as message  1400 , for several reasons. In an example, control messages  1  and  2  may be shortened because the SoP detection may not be necessary since the beginning of the message packet, for example, Ga  1   1421 , may be scheduled. However, some initial timing information may still be required. The packet may start in parallel to the AGC (i.e., AGC does not need to be triggered by SoP since the schedule can trigger it). 
     In a second example, control messages  1  and  2  may be shortened and the AGC may not need to start from the beginning. Each link may be used in each backhaul frame (every 0.5 mSec), and backhaul links may be pretty stable, so one AGC cycle may be sufficient. In a further example, there may be a wait for the gain to settle in Ga  2   1422 . If the AGC keeps a per-link memory, the initial gain may not need to change much. 
     In a third example, control messages  1  and  2  may be shortened and clocks may have less time to drift, so per-link CFO/sampling frequency offset (SFO) estimates may be maintained in much the same way as the AGC keeps track of per-link gains. The exact length for CFO/SFO may vary, but may use six Ga sequences, for example Ga  3   1423  though Ga  8   1428  (2 less than Blu Wireless Technology (BWT)) The six Ga sequences may be used in examples and simulations disclosed herein. In a further example, the message may contain the fine packet timing and End of Short training Field (EoSTF) of -Ga  9   1429  which may be followed by the CE field  1430 . 
       FIG. 15  is a diagram of an example preamble for control message  3 . 
     The example depicts a preamble for control message  3   1500 , where the STF may be even further reduced and the CEF may be totally eliminated. This additional shortening may be allowable since message  1  was received a short time ago and the channel estimate, timing, and CFO are still good. However, some fine timing, CFO, and time offset/phase correction may still be needed due to Tx/Rx switching, for example Ga  1   1521  through Ga  4   1524 , hence the inclusion of 5 Ga sequences for the preamble which may further include the fine packet timing and EoSTF -Ga  5   1525 . 
     Each node in the mesh network may be assigned at least one control slot for each of its connected neighbors. Each such link defined between a pair of neighbors may also be assigned an initial direction for control message exchanges, for example, node A transmits to node B first. 
       FIG. 16  is a diagram of example control slot messages. The example control slot messages  1600  may be transmitted in sequence. At a high level the control slot messages may be as follows. 
     For control message  1  (A→B), Node A may request grant of data slots to use for a transmission to Node B. Node A may acknowledge the reception of data from Node B in the previous SI. The example control message  1  shown in  FIG. 16  may be spread over two data blocks  1614  and  1616  based on Table 15, and may be configurable as described in Table 15. The data blocks  1614  and  1616  may be surrounded by Guard Intervals (GIs). 
     For control message  2  (B→A) Node B may request grant of data slots to use for a transmission to Node A. Node B may acknowledge the reception of data from Node A in the previous SI. Node B may grant resources to Node A based on the request from message  1 . The example control message  2  shown in  FIG. 16  may be spread over three data blocks  1624 ,  1626  and  1628  based on Table 15, and may be configurable as described in Table 15. The data blocks  1624 ,  1626  and  1628  may be surrounded by GIs. 
     For control message  3  (A→B), Node A may grant resources to Node B based on the request from message  2 . The example control message  3  shown in  FIG. 16  may be spread over two data blocks  1634  and  1636  based on Table 15, and may be configured as described in Table 15. The data blocks  1634  and  1636  may be surrounded by GIs. 
     The exemplary detailed message contents and the corresponding bitmaps are shown in Table 8, Table 9, and Table 10 for both high compression and minimal compression options. Compression may refer to use of a compact notation that may limit the range of values that a signal may indicate. If, for example, an error is detected in a message that carries grant request information (e.g., message  1  and message  2  carry Buffer Status Reports (BSRs), etc.) then a grant in the following message may not be made and an indication of the frame check sequence (FCS) error may be included in the responding messages. An error in decoding message  1  or  2  may be signaled by sending all 1&#39;s in the Grant field (an invalid Grant field) in message  2  or  3 , respectively. 
     
       
         
           
               
             
               
                 TABLE 8 
               
             
            
               
                   
               
               
                 Control Slot Message 1 (A → B) 
               
            
           
           
               
               
               
            
               
                   
                 Minimal 
                   
               
               
                   
                 Com- 
                   
               
               
                   
                 pression 
                   
               
               
                 Field 
                 Size [Bits] 
                 Description 
               
               
                   
               
               
                 BSR 
                 13 
                 This is a resource request from A to B. It may be 
               
               
                   
                 (Using  
                 signaled as a combination of requested data slots  
               
               
                   
                 a LUT 
                 and MCS/CQI where the last known good CQI  
               
               
                   
                 for 3 QoS  
                 indicates the approx. number of bits per data  
               
               
                   
                 queues 
                 slot (a default value may be used if there is no  
               
               
                   
                 0-32) 
                 last known good CQI). Resources may not be  
               
               
                   
                   
                 requested for data that is expected to be trans-  
               
               
                   
                   
                 mitted in semi-statically scheduled resources. 
               
               
                   
                   
                 Note: For High Compression mode the available  
               
               
                   
                   
                 slot length may also be added. 
               
               
                 MCS/ 
                  4 
                 Estimate of the channel quality from Node B to  
               
               
                 CQI 
                   
                 Node A, and may be signaled in terms of a  
               
               
                   
                   
                 requested MCS level. 
               
               
                   
                   
                 Note: MCS levels &gt; 12 may be reserved for  
               
               
                   
                   
                 indication of special purpose messages. 
               
               
                 Tx 
                 32 
                 Indication of available data slots for Node A to 
               
               
                 Bitmap 
                   
                 transmit to Node B. Each bit may refer to a  
               
               
                   
                   
                 data slot. 
               
               
                   
                   
                 Note: For High Compression mode this  
               
               
                   
                   
                 information is conveyed in the BSR. 
               
               
                 ACK 
                 2 or 9 
                 Node A may acknowledge successful reception  
               
               
                   
                   
                 of data packets from B in the previous  
               
               
                   
                   
                 scheduling interval. 
               
               
                   
                   
                 Option 1 (default): [2 bits] 
               
               
                   
                   
                 1-bit acknowledge for entire MAC Protocol 
               
               
                   
                   
                 Data Unit (MPDU) 
               
               
                   
                   
                 1-bit acknowledge for persistent traffic PHY 
               
               
                   
                   
                 Protocol Data Unit (PPDU) 
               
               
                   
                   
                 Option 2: [9 bits] 
               
               
                   
                   
                 8-bit acknowledgement. 
               
               
                   
                   
                 1-bit per PPDU, given maximum of 8 
               
               
                   
                   
                 MPDUs per PPDU. 
               
               
                   
                   
                 1-bit acknowledge for persistent traffic PHY 
               
               
                   
                   
                 Protocol Data Unit (PPDU) 
               
               
                 FCS 
                 12 
                 Frame Check CRC sequence 
               
               
                 Total 
                 63 or 70 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 9 
               
             
            
               
                   
               
               
                 Control Slot Message 2 (B → A) 
               
            
           
           
               
               
               
            
               
                   
                 Minimal 
                   
               
               
                   
                 Compression 
                   
               
               
                 Field 
                 Size [Bits] 
                 Description 
               
               
                   
               
               
                 BSR 
                 13 
                 This is a resource request from B to A. It may be 
               
               
                   
                 (Using a LUT  
                 signaled as a combination of requested data slots 
               
               
                   
                 for 3 QoS  
                 and MCS/CQI. 
               
               
                   
                 queues 0-32) 
                 Note: For High Compression mode the available 
               
               
                   
                   
                 slot length is also added. 
               
               
                 Tx 
                 32 
                 Indication of available data slots for Node B to 
               
               
                 Bitmap 
                   
                 transmit to Node A. Each bit refers to a data slot. 
               
               
                   
                   
                 Note: For High Compression mode this 
               
               
                   
                   
                 information may be conveyed in the BSR. 
               
               
                 ACK 
                 2 or 9 
                 Node B may acknowledge successful reception of 
               
               
                   
                   
                 data packets from A in the previous scheduling 
               
               
                   
                   
                 interval. 
               
               
                   
                   
                 Option 1: [2 bits] 
               
               
                   
                   
                 1-bit acknowledge for entire MAC Protocol 
               
               
                   
                   
                 Data Unit (MPDU) 
               
               
                   
                   
                 1-bit acknowledge for persistent traffic 
               
               
                   
                   
                 PHY Protocol Data Unit (PPDU) 
               
               
                   
                   
                 Option 2: [9 bits] 
               
               
                   
                   
                 8-bit acknowledgement. 
               
               
                   
                   
                 1-bit per PPDU, given maximum of 
               
               
                   
                   
                 8 MPDUs per PPDU 
               
               
                   
                   
                 1-bit acknowledge for persistent traffic 
               
               
                   
                   
                 PHY Protocol Data Unit (PPDU) 
               
               
                 Grant 
                 32 
                 Node B may grant data transmission slots to Node 
               
               
                   
                   
                 A based on its request and constraints due to 
               
               
                   
                   
                 previous allocations to other nodes. 
               
               
                   
                   
                 Minimal Compression Mode 
               
               
                   
                   
                 Grant bitmap 
               
               
                   
                   
                 High Compression Mode 
               
               
                   
                   
                 Grant Start + Grant Length 
               
               
                 MCS/ 
                  4 
                 Estimate of the channel quality from Node A to 
               
               
                 CQI 
                   
                 Node B and may be signaled in terms of a 
               
               
                   
                   
                 requested MCS level. 
               
               
                   
                   
                 Note: MCS levels &gt; 12 may be reserved for 
               
               
                   
                   
                 indication of special purpose messages. 
               
               
                 FCS 
                 12 
                 Frame Check CRC sequence 
               
               
                 Total 
                 100 or 107 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 10 
               
             
            
               
                   
               
               
                 Control Slot Message 3 (A → B) 
               
            
           
           
               
               
               
            
               
                   
                 Minimal 
                   
               
               
                   
                 Compression 
                   
               
               
                 Field 
                 Size [Bits] 
                 Description 
               
               
                   
               
               
                 Grant 
                 32 
                 Node A may grant data transmission slots to  
               
               
                   
                   
                 Node B based on its request and constraints  
               
               
                   
                   
                 due to previous allocations to other nodes. 
               
               
                   
                   
                 Minimal Compression Mode 
               
               
                   
                   
                 Grant bitmap 
               
               
                   
                   
                 High Compression Mode 
               
               
                   
                   
                 Grant Start + Grant Length 
               
               
                 FCS 
                 12 
                 Frame Check CRC sequence 
               
               
                 Total 
                 44 
               
               
                   
               
            
           
         
       
     
     A Control Period does not exist in the current IEEE 802.11ad standard. Therefore, a modified coding method may be required for the messages shown above. In an example, the coding method correlates well with the 802.11ad baseline and at the same time meet the requirements of the modified control messages. For example, given the varying sizes for the three control messages along with the relatively high level of protection required, the coding method may support a varying number of payload bits and code rates. The coding method also supports message repetition over a certain number of data blocks as well as message splitting across data blocks, which provides additional examples for payload protection other than relying only on code rate choice. Exemplary parameters that relate to the various coding options are shown in Table 11. 
     
       
         
           
               
             
               
                 TABLE 11 
               
             
            
               
                   
               
               
                 Coding Parameters 
               
            
           
           
               
               
               
            
               
                 Parameter 
                 Value 
                 Description 
               
               
                   
               
               
                 Nmp 
                 1-322 
                 Number of message 
               
               
                   
                   
                 payload bits 
               
               
                 Nrep 
                 1-inf 
                 Number of additional 
               
               
                   
                   
                 data blocks used when 
               
               
                   
                   
                 using message repetition. 
               
               
                 Nmf 
                 1-322 
                 Number of message 
               
               
                   
                   
                 fragments used when 
               
               
                   
                   
                 using message splitting. 
               
               
                 Nmfp 
                 1-322 
                 Number of message 
               
               
                   
                   
                 fragment payload bits in a 
               
               
                   
                   
                 particular message 
               
               
                   
                   
                 fragment. 
               
               
                 R 
                 [½, ⅝, ¾, 13/16] 
                 LDPC mother code rate. 
               
               
                 PuncMode 
                 {MinZeroPad,  
                 For a given Nmfp and 
               
               
                   
                 MinCodeRate} 
                 choice of R, the PuncMode 
               
               
                   
                   
                 is given. 
               
               
                   
                   
                 Note: This allows proper 
               
               
                   
                   
                 rate matching to bring 
               
               
                   
                   
                 the 672 bits from the 
               
               
                   
                   
                 LDPC encoder into the 
               
               
                   
                   
                 448 bits available per 
               
               
                   
                   
                 data block. 
               
               
                 Nmf p_max 
                 Default is 110, but can go 
                 Maximum number of 
               
               
                   
                 as much as 322 
                 message fragment 
               
               
                   
                   
                 payload bits. 
               
               
                   
               
            
           
         
       
     
     Both message splitting and message repetition may be used to offer more protection as mentioned above, however message splitting may be further required when {Nmp&gt;Nmfp_max}. For example, if {Nmp&gt;Nmfp_max}, the message may be split into Nmf message fragments, where 
     
       
         
           
             
               
                 
                   
                     
                       N 
                        
                       m 
                        
                       f 
                     
                     = 
                     
                       ⌈ 
                       
                         
                           N 
                            
                           m 
                            
                           p 
                         
                         Mmfp_max 
                       
                       ⌉ 
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
     
     and each message fragment of Nmfp bits may be coded separately, where 
     
       
         
           
             
               
                 
                   
                     
                       Nmfp 
                        
                       
                         ( 
                         x 
                         ) 
                       
                     
                     = 
                     
                       
                         ⌊ 
                         
                           
                             N 
                              
                             m 
                              
                             p 
                           
                           
                             N 
                              
                             m 
                              
                             f 
                           
                         
                         ⌋ 
                       
                       + 
                       α 
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     3 
                     ) 
                   
                 
               
             
             
               
                 
                   α 
                   = 
                   
                     { 
                     
                       
                         
                           
                             
                               1 
                               , 
                             
                           
                           
                             
                               
                                 x 
                                 = 
                                 
                                   1 
                                    
                                   
                                     
                                       : 
                                     
                                      
                                     
                                         
                                     
                                     [ 
                                     
                                       
                                         ( 
                                         
                                           Nmp 
                                           Nmf 
                                         
                                         ) 
                                       
                                       - 
                                       
                                         ( 
                                         
                                           ⌊ 
                                           
                                             Nmp 
                                             Nmf 
                                           
                                           ⌋ 
                                         
                                         ) 
                                       
                                     
                                     ] 
                                   
                                    
                                   Nmf 
                                 
                               
                               , 
                             
                           
                         
                         
                           
                             
                               0 
                               , 
                             
                           
                           
                             
                               x 
                               = 
                               Nmf 
                             
                           
                         
                       
                        
                       
                         
 
                       
                        
                       and 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     4 
                     ) 
                   
                 
               
             
             
               
                 
                   x 
                   = 
                   
                     1 
                      
                     
                       : 
                     
                      
                     
                         
                     
                      
                     
                       Nmf 
                       . 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     5 
                     ) 
                   
                 
               
             
           
         
       
     
     For the case of {Nmp≤Nmfp_max}, Nmf=1. 
     Repetition, as stated, may be configured independently based on the desire to add protection for the payload bits. For Nrep&gt;0, the additional data blocks may be constructed by creating another version of the codeword with different puncturing and inverting data blocks with odd repetition numbers, and concatenating them. In this sense, the rate matching block may produce two versions of the rate matched codeword that the repetition block may alternate between. 
     Finally, for a given number of message fragment payload bits (Nmfp), different choices of R may be available with a corresponding puncturing mode. Representative options for each message fragment are given in Table 12. 
     
       
         
           
               
             
               
                 TABLE 12 
               
             
            
               
                   
               
               
                 LDPC Code Rate and Puncture Mode Option per Message 
               
               
                 Fragment Size 
               
            
           
           
               
               
               
            
               
                   
                   
                 LDPC Code Rate [R] 
               
            
           
           
               
               
               
               
               
               
            
               
                 min(Nmfp) 
                 max(Nmfp) 
                 ½ 
                 ⅝ 
                 ¾ 
                  13/16 
               
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 1 
                 56 
                 MinZeroPad 
                 MinZeroPad 
                 NA 
                 NA 
               
               
                 57 
                 98 
                 MinCodeRate 
                 MinZeroPad 
                 MinZeroPad 
                 NA 
               
               
                 99 
                 112 
                 MinCodeRate 
                 MinCodeRate 
                 MinZeroPad 
                 MinZeroPad 
               
               
                 113 
                 140 
                 NA 
                 MinCodeRate 
                 MinZeroPad 
                 MinZeroPad 
               
               
                 141 
                 161 
                 NA 
                 MinCodeRate 
                 MinCodeRate 
                 MinZeroPad 
               
               
                 162 
                 280 
                 NA 
                 MinCodeRate 
                 MinCodeRate 
                 MinCodeRate 
               
               
                 281 
                 322 
                 NA 
                 NA 
                 MinCodeRate 
                 MinCodeRate 
               
               
                   
               
            
           
         
       
     
     As shown in Table 12, certain exemplary combinations of message fragment size and code rate may be supported by a given puncture mode. The main properties of each of the puncturing modes may be as follows. 
     For the Min ZeroPad, each 448-bit code block may be split into two 224-bit parts. The systematic bits may be repeated twice, once in each half of the 448-bit code block. Some of the parity bits may be repeated depending on the number of systematic bits being used. The number of parity bits repeated may be as many as all and as little as none. In order to obtain greater diversity in the repeated parity bits assuming that Nrep&gt;0, a puncture offset parameter, PO, may be defined such that a different combination of parity bits may be repeated for each repeated code block. 
     For the Min CodeRate, the 448-bit code blocks may not be split as in the Min ZeroPad method. The parity bits may not be repeated. Some of the systematic bits may be repeated depending on the number of parity bits being used. The number of systematic bits repeated may be as many as all and as little as none. In order to obtain greater diversity in the repeated systematic bits assuming that Nrep&gt;0, even numbered data blocks may repeat the systematic bits starting at the beginning of the message and odd numbered data blocks may repeat the systematic bits starting at the end of the message. 
     Although exemplary minimum and maximum message fragment sizes may be extracted from Table 12, a more direct mapping of the representative size range for each puncturing mode is shown in Table 13. 
     
       
         
           
               
             
               
                 TABLE 13 
               
             
            
               
                   
               
               
                 Minimum and Maximum Message Fragment Sizes 
               
            
           
           
               
               
               
            
               
                   
                 MinZeroPad 
                 MinCodeRate 
               
            
           
           
               
               
               
               
               
            
               
                 LDPC Code 
                 Min message 
                 Max message 
                 Min message 
                 Max message 
               
               
                 Rate 
                 size 
                 size 
                 size 
                 size 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 ½ 
                 0 
                 56 
                 56 
                 112 
               
               
                 ⅝ 
                 0 
                 98 
                 98 
                 196 
               
               
                 ¾ 
                 56 
                 140 
                 140 
                 280 
               
               
                  13/16 
                 98 
                 161 
                 161 
                 322 
               
               
                   
               
            
           
         
       
     
       FIG. 17  is a diagram of an example high level message processing block diagram. In the example, the message is first fragmented  1710 . Then the Nmfp may be processed  1720  to create the LDPC codeword. The code rate and puncture mode may also be determined in  1730 . Based upon the determined code rate and puncture mode, the LDPC processed message fragments may be rate matched  1740 . The output of which may be processed through a repetition step  1750 . This may result in the data blocks to be transmitted. 
       FIG. 18A  is a diagram of an example of encoding for control messages using Min ZeroPad. Coding may be done on a per message fragment basis. The message fragments  1810  may first be encoded into the PHY bits of one single carrier (SC) block with N GI  symbols. The number of PHY bits in a SC block N CBPB  may depend on the modulation type, and exemplary values are shown in Table 14. The number of SC blocks used for the entire transmission may be 1+N rep (n) for message n. The bits may be scrambled and encoded as follows. 
     The input message bits including the FCS bits (b 1 , b 2 , . . . , b N     mfp   ), where N mfp  is the payload of the message fragment being processed, may be scrambled as described below and illustrated in  FIG. 20  with the initialization vector (IV) given, starting from the first bit, to create d 1s =(q 1 , q 2 , . . . , q N     mfp   ). The LDPC codeword c=(q 1 , q 2 , . . . , q N     mfp   , 0 1 , 0 2 , . . . , 0 Z , p 1 , p 2 , p N     p   ) may be created by concatenating Z zeroes  1820  to the N mfp  bits of d 1s  and then generating the parity bits  1830  p 1 , p 2 , p N     p    such that Hc T =0, where H is the parity check matrix for the rate R LDPC code specified in IEEE 802.11ad. Note that Z=672R−N mfp  and N p =672(1−R). Parity bits  1831 ,  1832 ,  1835 ,  1836  and  1837  may also be used. 
     In an example, a code rate 1/2 may be used for two repetitions (Rep=2) for K 1 =1-56. In a further example, code rate 1/2 may also be used for one repetition (Rep=1) for K 1 =56-122, but a higher rate may also be used per Table 13 and the table in  FIG. 18A . In an example, information bits K 1  may all be repeated. Further parity bits may be preferentially punctured by placing the Puncture Offset (PO) to the right of the center of each codeword (CW). In  FIG. 18A , P 11   1831  may be a subset of P 21   1836  and P 22   1837  may be a subset of P 12   1832 . As a result, P 11   1831  and P 22   1837  may be repeated bits. Although not illustrated in  FIG. 18A  and  FIG. 18B , below, data scrambling, repetition scrambling and fragment concatenation may apply to the encoding. 
     The Information Bits  1815  may be preserved whereas the zeroes  1825  may be removed. Bits N mfp +1 through 672R and the parity bits P 0 -PL through P 0 - 1  of the codeword c may be removed to create the sequence cs 1 =(q 1 , q 2 , . . . , q N     mfp   , p 1 , p 2  . . . p P0-PL-1 , p P0 , . . . p N     p   ) and then XORed with a pseudo-random noise (PN) sequence that is generated from the linear feedback shift register (LFSR) used for data scrambling defined in IEEE 802.11ad. The LFSR may be initialized to the all ones vector. Bits N mfp +1 through 672R and the parity bits P 0  through P 0 +PL−1 of the codeword c may be removed to create the sequence cs 2 =(q 1 , q 2 , . . . , q N     mfp   , p 1 , p 2 , . . . , p Po−1 , p P0+PL , p P0+PL+1 , . . . , p N     p   ). Note that 
     
       
         
           
             L 
             = 
             
               
                 N 
                 mfp 
               
               + 
               
                 672 
                  
                 
                   ( 
                   
                     1 
                     - 
                     R 
                   
                   ) 
                 
               
               - 
               
                 
                   
                     N 
                     CBPB 
                   
                   2 
                 
                  
                 
                     
                 
                  
                 and 
               
             
           
         
       
       
         
           
             
               
                  
                 
                   
                     P 
                      
                     
                         
                     
                      
                     0 
                   
                   - 
                   
                     
                       N 
                       P 
                     
                     2 
                   
                 
                  
               
               + 
               PL 
             
             &lt; 
             
               
                 N 
                 P 
               
               2 
             
           
         
       
     
     may be satisfied. 
     The sequences cs 1  and cs 2  may be concatenated to form the sequence (cs 1 , cs 2 ). The resulting N CBPB  bits may then be mapped as π/2-BPSK as described in IEEE 802.11ad. The N GI  guard symbols may then be prepended to the resulting N CBPB  bits as described in IEEE 802.11ad. The results of the encoding may then be modulated and transmitted through the channel. 
       FIG. 18B  is a diagram of an example of decoding for control messages using Min ZeroPad. In an example, the process is effectively the reserve of the encoding process. Demodulation of the transmission results in a sequence which may contain a number of copies of information bits and punctured parity bit which corresponds to the number of repetitions performed in the encoding process. In an example, two information messages  1862  and  1864  may be included in the result of the transmission. At the receiver, the logarithm likelihood ratios (LLRs) per bit may be available. The punctured parity  1870  may then be recombined. The combination may then be decoded with the LDPC decoder  1880  and the parity may be further removed. The zeroes may then be further removed leaving only the information bits  1890 . The information bits  1890  may then be sent to the cyclic redundancy check (CRC). 
     
       
         
           
               
             
               
                 TABLE 14 
               
             
            
               
                   
               
               
                 Values of N CBPB   
               
            
           
           
               
               
               
            
               
                   
                 Modulation Type 
                 N CBPB   
               
               
                   
                   
               
            
           
           
               
               
               
            
               
                   
                 π/2 − BPSK 
                 448 
               
               
                   
                 π/2 − QPSK 
                 896 
               
               
                   
                 π/2 − 16QAM 
                 1792 
               
               
                   
                   
               
            
           
         
       
     
     Control message coding and modulation for the MinCoderate puncturing method is disclosed herein. Coding may be done on a per message fragment basis. The message fragments may first be encoded into the PHY bits of one SC block with N GI  symbols. The number of PHY bits in a SC block N CBPB  may depend on the modulation type, and exemplary values are shown in Table 14. The number of SC blocks used for the entire transmission may be 1+N rep (n) for message n. 
       FIG. 19A  is a diagram of an example encoding for control messages using Min CodeRate. The example shows how Min CodeRate may scramble and encode message bits. The input message  1910  bits may include the FCS bits (b 1 , b 2 , . . . , b N     mfp   ), where N mfp  is the payload of the message fragment being processed, and may be scrambled with the IV, as described below and illustrated in  FIG. 20 . The scrambling may start from the first bit, to create d 1s =(q 1 , q 2 , . . . , q N     mfp   ). 
     The LDPC codeword c=(q 1 , q 2 , . . . , q N     mfp   , 0 1 , 0 2 , . . . , 0 Z , p 1 , p 2 , p N     p   ) may be created by concatenating Z zeroes  1920  to the N mfp  bits of d 1s  and then generating the parity bits p 1 , p 2 , p N     p      1930  such that Hc T =0, where H is the parity check matrix for the rate R LDPC code specified in IEEE 802.11ad. Note that Z=672R−N mfp  and N p =672(1−R). 
     Bits N mfp +1 through 672R (the zero bits) may be removed to obtain c 1 =(q 1 , q 2 , . . . , q N     mfp   , p 1 , p 2 , . . . , p N     p   ). For mod 2 (N rep )=0, as described below and illustrated in  FIG. 20  with the IV given, the method may remove and scramble the first N sysRep  bits of the sequence c 1 . These bits may be appended to the beginning of c 1  to create the sequence c 2 =(q s   1 , q s   2 , . . . , q s   N     sysRep   , q 1 , q 2 , . . . , q N     mfp   , p 1 , p 2 , . . . , p N     p   ). Otherwise, as described below and illustrated in  FIG. 20  with the IV given, the method may remove and scramble the last N sysRep  bits of the sequence c 1 . These bits may be appended to the beginning of c 1  to create the sequence  1940  c 2 =(q s   N     mfp     −N     sysRep     +1 , q s   N     mfp     −N     sysRep   , . . . , q s   N     mfp   , q 1 , q 2 , . . . , q N     mfp   , p 1 , p 2 , . . . , p N     p   ). For example 
     
       
         
           
             
               
                 N 
                 sysRep 
               
               = 
               
                 
                   Z 
                   - 
                   
                     ( 
                     
                       672 
                       - 
                       
                         N 
                         CBPB 
                       
                     
                     ) 
                   
                 
                 = 
                 
                   
                     672 
                      
                     
                         
                     
                      
                     R 
                   
                   - 
                   
                     
                       N 
                       CBPB 
                     
                     2 
                   
                   - 
                   
                     N 
                     mfp 
                   
                 
               
             
             , 
             
               
 
             
              
             
               e 
               . 
               g 
               . 
             
             , 
             
               
                 { 
                 
                   
                     
                       For 
                        
                       
                           
                       
                        
                       R 
                     
                     = 
                     
                       1 
                       2 
                     
                   
                   , 
                   
                     
                       N 
                       sysRep 
                     
                     = 
                     
                       112 
                       - 
                       
                         N 
                         mfp 
                       
                     
                   
                 
                 } 
               
               . 
             
           
         
       
     
     The resulting N CBPB  bits may be multiplied with −1 mod 2 (N rep ) where N rep =0, 1, . . . N rep (n), and then mapped as π/2−BPSK as described in IEEE 802.11ad. The N GI  guard symbols may then be prepended to the resulting N CBPB  bits as described IEEE 802.11ad. The resulting sequence may then be appended after the sequence created for the first data block. After modulation, the resulting sequence may then be transmitted through the channel. 
     In an example, a code rate 1/2 may be used for two repetitions (Rep=2) for K 1 =1-56. In a further example, code rate 1/2 may also be used for one repetition (Rep=1) for K 1 =56-122, but other code rates are also possible. Further, in an example, the K 2  bits may be copied from the left. 
       FIG. 19B  is a diagram of an example decoding for control messages using Min CodeRate. The process for decoding is effectively the reverse of encoding. After demodulation, the sequence may include the scrambled information  1951 , the information bits that were not scrambled  1952  and the parity bits  1953 . The encoding process may then be further reversed resulting in information bits  1954 . The sequence may then be decoded by the LDPC decoder  1980  and the zeroes may be removed resulting in information bits  1990 . The information bits may then be further descrambled resulting in  1995 . These bits may then be sent to the CRC and concatenated with any other message fragments. 
     The Coding and Modulation procedures described above may support a variety of message lengths. In addition, the coding procedure for each message length may be further modified to support varying performance requirements. As such, given the exemplary message lengths detailed in Tables 8-10, simulations may be used to determine the particular coding and modulation parameters to be used. 
     The control messages may require high protection relative to regular data transmissions. With this, in an example, a set of coding parameters may give performance at least as good as the header performance shown in  FIG. 42 . Table 15 lists representative initial tentative coding options based on example simulations performed. There are multiple viable options may be chosen and the specific option to be used may be signaled in the beacon period. 
     
       
         
           
               
             
               
                 TABLE 15 
               
             
            
               
                   
               
               
                 Control Message Coding Parameters 
               
            
           
           
               
               
               
               
               
               
            
               
                   
                   
                   
                 Number of 
                   
                   
               
               
                 Message 
                 Compression 
                 Puncture 
                 Message 
                 Block 
                 Code 
               
               
                 Number 
                 Mode 
                 Mode 
                 Fragments 
                 Repetition 
                 Rate 
               
               
                   
               
               
                 1 
                 Minimal 
                 MinZeroPad 
                 2 
                 None 
                 ⅝ 
               
               
                 2 
                 Minimal 
                 MinZeroPad 
                 3 
                 None 
                 ½ 
               
               
                 3 
                 Minimal 
                 MinZeroPad 
                 2 
                 None 
                 ½ 
               
               
                   
               
            
           
         
       
     
     The control message scrambler may have a larger period than the normal header/data scrambler. The larger length may provide a larger IV so that every message in a backhaul superframe may have a distinct IV. For example there may be 1000 frames/superframe, 5 control slots per frame, 3 messages per control slot for a total of 15,000 control message per superframe or 14 bits. Furthermore, offsets into the scrambler may be desired that will not cause the scrambler to repeat its sequence. The offsets may provide distinct sequences based on the node or link identifications (IDs). In this way, two conditions may be satisfied. In one example condition, the scrambling sequences may be well mixed over the superframe. In another example condition, a node that is out of sync with the network (e.g., using the wrong control slot) may have a low probability of falsely thinking it received a grant to transmit without explicitly sending node IDs in the messages. 
     To accommodate a large number of local link identifiers, an additional 10 bits of LFSR may be added. In some circumstances there may not be 2-tap feedback solutions to the 24-bit m-sequence generator, a 25-bit LFSR may be defined with 2-taps (there may be two different 2-tap, 25-bit LFSRs with maximal length sequences). One such example is provided by the primitive polynomial: S(x)=x 25 +x 22 +1, and is illustrated in  FIG. 20 . 
       FIG. 20  is a diagram of an example long control message scrambler. The control message scrambler  2000  may include twenty-two delay units, such as delay units  2010  through  2090 . The control message scrambler initialization  2000  may be determined by the following: 
         IV= 1+mod 2     25     −1 ( IV   seed +LOC rx_id   +m+ 3 s+N   s   b ),  Equation (6)
 
     where IV seed  is an optional 5-bit parameter signaled in the beacon response ACK message and is a function of the beacon transmitter ID. LOC rx_id  may be a globally non-unique, but locally unique ID given to the new node used to distinguish nodes of the local mesh. With scrambling based on LOC rx_id , the ID may not need to be explicitly transmitted (message not decodable if different LOC rx_id  used). m is the Message Number-1 {0,1,2}. s is the Control Slot Number-1, b is the SI (SI Number-1) {0, 1, . . . 999}, and N s  is Number of Control Slots. 
     A backhaul network requires support of service-level agreements (SLAs). In packet backhaul networks, these SLAs determine if the guaranteed throughput and latency requirements are met. This may be achieved by utilizing committed information rate (CIR) and excess information rate (EIR) terminology. 
     CIR is the average guaranteed capacity to be given to a data flow under normal conditions. Under operating conditions, the capacity should not fall below the CIR. EIR is the upper bound allowed above CIR rate. In order to provide differentiated services in the backhaul network, multiple classes of service or QoS are supported in the small-cell backhaul network. 
     In order to maximize the amount of higher priority traffic for directional mesh backhaul networks, scheduling support may be required to enable iterative scheduling to achieve this in a purely distributed manner. As a result, the directional mesh backhaul may be capable of handling bursty traffic while respecting the corresponding QoS/class of service. 
     In one embodiment, the total number of control slots (N) in the Control Period may be determined a-priori, may be common to all the mesh nodes in the network and may remain constant for a specific configuration of the network. For a mesh node in the network with K neighbors, there are at most M=floor(N/K) complete iterations of control slots, where each neighbor is allotted one control slot per iteration. This allows each node to exchange scheduling information with its neighbors more than once per SI. Each of these control slots may involve a three-way message exchange between the nodes. The three-way message exchange was discussed above. 
     As the number of control slots may be common for all mesh nodes in the network, there may be instances where the number of neighbors may be lower than the number of available control slots. The network may also configure more control slots than the highest number of possible neighbors allowed for each mesh node to enable more than one exchange of control slot information in order to achieve better differentiated class of service and allocation of CIR data over EIR. This allows for the possibility of iterative scheduling. Iterative scheduling enables priority-based resource reservation to be performed dynamically in each SI. If traffic priorities are known, then higher priority traffic may be scheduled in the initial scheduling iterations while lower priority data may be scheduled in later scheduling iterations. If traffic classification based on CIR and EIR labelling is available, then CIR traffic may be scheduled in initial scheduling iterations followed by EIR traffic scheduling. 
     The multiple scheduling iterations may be used for prioritized resource reservation in several different ways. In one embodiment, resource requests and schedules associated with one or few priority levels may be exchanged in a particular scheduling iteration. Here, resources may be allotted for high priority traffic first and then any remaining resources may be allotted to lower priority traffic. This may ensure that all the nodes have exchanged required information about higher priority traffic with their neighbors and may allow for this traffic to be scheduled before allowing lower priority traffic, thereby avoiding reversal of traffic class/QoS prioritization. 
     In another example, mesh nodes may send their resource requests and temporary schedules for all priorities in each scheduling iteration. Then, the receiver may determine the schedule for the current priority level based on the received resource requests and previously scheduled resources for higher priority traffic. Fairness among different priority levels may be ensured by exchanging more information about different priority traffic in each scheduling iteration. 
     In another example, where information about current priority level and lower priorities may be exchanged, the control signaling overhead may be reduced. Further, the scheduling information exchanged may be in the form of bitmaps to reduce the message sizes, but this may eliminate the priority information of previously scheduled traffic. Consequently, a trade-off is possible between control message overhead and traffic prioritization efficiency. 
       FIG. 21  is diagram of an example of an iterative resource scheduling mechanism. The resource scheduling mechanism  2100  may apply to control slots, for example control slots in a control region  2110  or control period. A data region  2120  may follow the control region  2110 . Here, the control region  2110  has sufficient control slots for M iterations  2111 ,  2112  and  2119  of the scheduling algorithm. Each iteration  2111 ,  2112  and  2119  may include a sufficient number of bi-directional control slots for each mesh node to exchange scheduling information with each of its neighbors. The exchange of scheduling information with each neighbor may occur in a three message sequence, including message  1   2131 , message  2   2132  and message  3   2133 . In an example, the neighbors may exchange control slot information in this way. The number of control slots for iterative scheduling may vary from neighbor to neighbor. In an example, during consecutive periods,  2130 ,  2140 ,  2150 , in algorithm iteration  1   2111 , each node may communicate with a different one of its neighbor nodes. For instance, in the period  2130 , node G  2139  may exchange information with neighbor node A  2134 , Node B  2135  may communicate with neighbor Node E  2138  and Node C  2136  may communicate with neighbor Node D  2137 . All neighbors may not be allotted a control slot in each scheduling iteration. The number of iterations for a particular neighbor may depend on the number of active traffic priority levels associated with it or the number of active neighbor nodes. In an exemplary embodiment, signals, such as a control signal, are received by a mesh node from a mesh controller. Further, in an exemplary embodiment, the resource scheduling mechanism may include a resource scheduling algorithm. 
       FIG. 22  is a diagram of an example process flow for performing resource scheduling using the resource scheduling mechanism. In an example, the process  2200  may begin when a mesh node receives a control signal which may include the number of available control slots  2110 . The control signal may be received from a mesh controller. The number of available control slots may be determined by the network. The node may then determine  2220  the number of iterations of a resource scheduling mechanism that can be made during the time period of the total number of available control slots. The node may maximize the number of possible iterations based on local topology. In an example, the node may determine the number of iterations based on the number of available neighbor nodes for the mesh node. The node may then receive  2230  control slot information from neighbor nodes. This information may include information about one or more of traffic queues, priorities and channel conditions. The node may then perform resource scheduling  2240  using the resource scheduling mechanism. The resource scheduling may be based on current control slot information, as well as control slot information received in prior resource scheduling iterations. In a further example, the resource scheduling may also be based on current traffic information and historic traffic loads. 
       FIG. 23  is a diagram of an example control slot assignment with a different number of control slots for different neighbors. It shows an example where a mesh node may allocate a different number of scheduling iterations to different neighbors due to a varying neighbor count for one of the neighbors. Here, Node  2   2320  may not be accommodated in the second iteration by Node  1   2310  because there are no common control slots between the two nodes that are unallocated slots, such as  2332 . Further node  1   2310  may not communicate with node  2   2320  using its last unallocated slot as node  2  has allocated node  7  for that slot. The number of scheduling iterations and control slot allocations may be changed between nodes by a control slot reassignment procedure described below. 
     In an example, if there are insufficient slots in the control period for a complete iteration of the resource scheduling mechanism or scheduling algorithm, then slots may be assigned to a sub-set of the neighbors. As a result, resource scheduling may include maintaining relative fairness. 
       FIG. 24  is a diagram of an example of iterative scheduling with insufficient control slots. In this example, the number of control slots may not be an exact multiple of the number of neighbors that a mesh node has. Here, the last two control slots are distributed among the three neighbors and this distribution may be rotated in successive scheduling iterations to maintain relative fairness. The scheduling iterations may include SIs, such as SIs  2410 ,  2420  and  2490 . The control slot assignment may be pre-determined and communicated to all the affected nodes but may be changed occasionally due to topology or traffic pattern changes. 
     Mesh nodes may use the Control Slot Reassignment procedure to re-arrange control slots allotted to their neighbors. This may be required when new nodes join the network, when there is node or link failure and when the number of priority levels used by the scheduling algorithm needs to be changed. This may be accomplished by exchanging a series of messages between the affected nodes. 
     The procedure may start with the requesting node sending a Control Slot Reassignment Request message to the affected neighbors. The neighbors may then respond with Control Slot Reassignment Response message, which includes information about their available control slots. The requesting node may send a Control Slot Reassignment Confirm message to the neighbors with the new control slot assignments. The neighbors may respond with a Control Slot Reassignment Confirm message to confirm receipt of the new assignment. 
       FIG. 25  is a diagram of an example Control Slot Reassignment procedure. In the example, Node  1   2510  has Nodes  2   2520  and Node  3   2530  as neighbors, and may send Control Slot Reassignment Requests  2551  and  2552  to them, respectively, to initiate the procedure. Nodes  2   2520  and  3   2530  may respond with their available control slots in Control Slot Reassignment Response frames  2556  and  2557  respectively. In this example, Node  1   2510  may send a New Slot Allocation  2559  to Node  3   2530 , included in Control Slot Reassignment Confirm message, that may require Node  3   2530  to further re-assign slots with its other neighbor, Node  4   2540 . Consequently, Node  3   2530  may send Control Slot Reassignment Request  2561  to Node  4   2540  and complete the Slot Reassignment communications with Node  4   2540  (Control Slot Reassignment Response  2566 , Control Slot Reassignment Confirm  2569  and Control Slot Reassignment Confirm Result Code  2571 ), before responding to Node  1   2510  with Control Slot Reassignment Confirm message  2573 . Then, Node  1  may send Control Slot Reassignment Confirm message  2581  to Node  2   2520 , including New Slot Allocation  2581 , and receive a Control Slot Reassignment Confirm message  2583  with the ResultCode that indicates the status of the reassignment. 
     The Control Slot Reassignment procedure may also be utilized to revoke one or more control slots allocated to a neighboring node if the mesh node identifies that it needs to allocate these control slots to one or more of its other neighbors or newly formed neighbors. In a further example, the Control Slot Reassignment procedure may be coordinated by a mesh controller, such as a Central Mesh Controller, by sending appropriate messages to affected mesh nodes. This message may include time instance at which the new configuration will take into effect. 
     Small-cells are expected to be rolled out first in dense urban and urban environments. Given the varying landscape of dense urban and urban environments, the small-cell mesh backhaul connectivity for each mesh node may vary significantly from one part of the network to the other. Configuring the entire mesh network with constant amount of control slots may incur large overhead in parts of the network where connectivity is low. On the other hand, if fewer control slots are used throughout the network, this may artificially limit the number of links a mesh node can form even though there are good quality links that can be formed in certain parts of the network. To avoid this and to enable appropriate scaling of control period based on local mesh connectivity for each mesh node, variable control periods may be used. 
     Different parts of the mesh network may use different number of control slots, and consequently variable Control Period sizes. A Domain may be defined as a contiguous collection of mesh nodes that share the same Control Period size. At the boundary between different Domains may lie mesh nodes that use different Control Period sizes to communicate with different neighbors. Such mesh nodes may belong to more than one Domain as they need to communicate with mesh nodes that belong to two or more domains. 
     A mesh network may start off with a default number of control slots that may be either pre-configured in the mesh nodes and read during start-up, or optionally communicated by the mesh controller, if one exists. The default or initial Control Period size may be changed later either in a distributed manner or via central messaging. To change the Control Period size in a distributed manner, the requesting node may send a Control Period Reconfiguration Request message to all or a subset of its neighbors. The size change may be confirmed when the neighbors respond with a Control Period Reconfiguration Confirm message. In the centralized approach, the mesh controller may send Control Period Reconfiguration Request message to all or some mesh nodes to change the Control Period size, by adding or removing control slots. The boundary nodes may use different number of control slots with neighbors belonging to different Domains. 
       FIG. 26  is a diagram of an example node mesh topology with variable control period sizes. In an example, Node  1   2611  and Node  2   2612  may belong to Domain  1   2610 , while Node  4   2624  and Node  5   2625  may belong to Domain  2   2620 . Node  3   2632  may belong to both Domain  1   2610  and Domain  2   2620 . Nodes belonging to Domain  1   2610  may use 6 control slots  2613 , while those belonging to Domain  2   2620  may use 8 slots  2634 . Node  3   2633  may use the first 6 control slots while communicating with nodes belonging to Domain  1   2610  and may use all 8 control slots for communicating with nodes belonging to Domain  2   2620 . Node  3   2633  may use the time required for control slots  6  and  7  for data transmissions within Domain  1   2610 , if they do not cause interference to Control Period transmissions in Domain  2   2620 . Alternatively, all Control Period transmissions may employ a low MCS for additional protection against interference. Node  3   2633  allots control slots to neighbors belonging to Domain  1   2610  (for example Node  2   2612 ) in the first 6 control slots. For neighbors belonging to Domain  2   2620  (for example Node  4   2624  and Node  5   2625 ), all 8 control slots may be used. Here two scheduling slot allocation options are shown. In another embodiment, the extra control slots may be left vacant in Domain  2   2620 . 
     The iterative scheduling defined above may be used in conjunction with variable control period sizes to get the additional benefit of differentiated service level scheduling. For instance, the extra slots may be used for scheduling Domain  2   2620  neighbors (for example Node  4   2624  and Node  5   2625 ), which may execute more iterations of the scheduling algorithm. This situation may arise if Node  3   2633  needs allocations for only two priority levels for Domain  1   2610  neighbors (hence two iterations of scheduling) and three priority levels for Domain  2   2620  neighbors. Another reason could be that some of the nodes in Domain  2   2620  may have more number of neighbors than those in Domain  1   2610 , hence requiring more number of control slots. The nodes may be reconfigure the control slot assignment using Control Slot Reassignment procedure  2500  either after or before changing the Control Period size, depending on whether the Control Period size is increased or decreased, respectively. 
     In a further example, the domains could also be structured to limit the impact of interference of control slots in one domain towards another. In an example case, adjacent domains may have different control period sizes and the data transfer in the domain with smaller control period size may impact the domain with relatively larger control period size. In order to achieve optimal allocation of domain and to manage the impact of interference on control period, the centralized mesh controller may trigger interference measurements at each of the mesh nodes and to determine the interference zone of each mesh node. These interference measurements may be configured so as to determine the impact of interference of each link between a pair of mesh nodes on neighboring links within a conservative distance range and can be further refined based on received measurement reports by the mesh controller. Based on the received interference measurement report from each of the mesh nodes, the mesh controller may determine the domains and what the control period size of each of the domains. 
     As shown in  FIG. 11  each SI may contain both a Control Period and a Data Period. The Data Period may be further split into N ds  Data Slots, where one or more Data Slots are assigned for a particular packet transmission from a node. As will be explained below, these Data Slots may be structured differently based on the size of the packet being delivered. As shown in  FIG. 27 , the Data Period may contain the following components: a preamble, described below, a header, and a payload. Certain fields in the header may require changes with respect to the unmodified IEEE 802.11ad SC packet. Examples of these changes are detailed in Table 17 below. The payload may include LDPC coded data (possibly longer LDCP codewords, with respect to the unmodified IEEE 802.11ad SC packet). Table 16 shows exemplary related timing parameters for the default case of Ncs=5. 
     
       
         
           
               
             
               
                 TABLE 16 
               
             
            
               
                   
               
               
                 Default Data Period Timing Parameters 
               
            
           
           
               
               
            
               
                 Parameter 
                 Value 
               
               
                   
               
               
                 N DBM : Maximum Number of Data  
                 47 
               
               
                 Blocks in a Data Slot (Refer to FIG. 23) 
                   
               
               
                 T DPR : Duration of Data Preamble 
                 2048*T C   
               
               
                 T DH : Duration of Data Header 
                 1024*T C   
               
               
                 IDS: Inter-Frame Data Spacing 
                 3520*T C   
               
               
                 T DS : Duration of Data Slot 
                 N DBM *512*T C  = 24064*T C   
               
               
                 T DP : Duration of Data Period 
                 N DS *T DS  = 770048*T C   
               
               
                   
               
            
           
         
       
     
     The Data Preambles may be substantially shortened compared to the IEEE 802.11ad Data Preambles based on the scheduled access architecture. 
       FIG. 27  is a diagram of an example of Data Period Structure. In the example period  2700 , the header data  2717  may be spread across two data blocks. The first slot  2710  may contain a preamble  2715 , a header  2717  and a payload  2719 . Subsequent slots, for example slot  2   2720 , may contain data blocks. The final slot N  2730  may contain a data block, a GI, and inter-frame data spacing (IDS). Exemplary header fields are specified in Table 17. The coding and modulation may be identical to the IEEE 802.11ad header coding and modulation. 
       FIG. 28  is a diagram of an example Data Preamble. The example shows the shortened preamble  2800 , which contains only 7 Ga sequences used for AGC, CFO/SFO, and EoSTF. In an example, the preamble includes Ga  1   2810 , Ga  2   2820 , Ga 3   2830 , Ga  4   2840 , and -Ga  7   2850 , followed by CE block  2860 , GA  5   2870  and GA  6   2880 . There may also be an additional 9 Ga sequences that are intended to be used for channel estimation. 
     
       
         
           
               
             
               
                 TABLE 17 
               
             
            
               
                   
               
               
                 Data Header Contents 
               
            
           
           
               
               
               
            
               
                 Field 
                 Size [Bits] 
                 Description 
               
               
                   
               
            
           
           
               
               
               
            
               
                 MCS 
                 5 
                 Index into the currently used MCS table 
               
               
                   
                   
                 Identifies encoding scheme used to 
               
               
                   
                   
                 encode the message body. 
               
               
                   
                   
                 There may be multiple MCS tables 
               
               
                   
                   
                 for nodes with different 
               
               
                   
                   
                 capabilities. 
               
               
                   
                   
                 This may be signaled when a 
               
               
                   
                   
                 node performs initial 
               
               
                   
                   
                 association. 
               
               
                 Length 
                 18 
                   
               
               
                 Additional  
                 1 
                 Indicates if the current PPDU is 
               
               
                 PPDU 
                   
                 immediately followed by another PPDU 
               
               
                   
                   
                 without a Preamble or Inter-frame 
               
               
                   
                   
                 spacing. 
               
               
                   
                   
                 Set to ‘1’ in the first and 
               
               
                   
                   
                 subsequent PPDUs (if any) that are 
               
               
                   
                   
                 aggregated. 
               
               
                   
                   
                 Set to ‘0’ in the last PPDU. 
               
               
                   
                   
                 As an example, the first 
               
               
                   
                   
                 PPDU may correspond to 
               
               
                   
                   
                 persistent traffic, while the 
               
               
                   
                   
                 second PPDU may contain 
               
               
                   
                   
                 bursty traffic packets. 
               
               
                   
                   
                 The current design requires 
               
               
                   
                   
                 a maximum of 2 PPDUs per 
               
               
                   
                   
                 SI, however this value may 
               
               
                   
                   
                 be increased as an 
               
               
                   
                   
                 alternative implementation 
               
               
                   
                   
                 option. 
               
               
                 Re-transmission 
                 2 or 4 
                 Indicates whether the current PPDU is a 
               
               
                 Indicator 
                   
                 new transmission or a HARQ re- 
               
               
                   
                   
                 transmission. 
               
               
                   
                   
                 Multiple bits may be needed to signal if 
               
               
                   
                   
                 the current transmission corresponds to 
               
               
                   
                   
                 persistent or bursty traffic, at a 
               
               
                   
                   
                 minimum. 
               
               
                 FEC Indicator 
                 1 or 2 
                 Indicates if the long, short, or possibly 
               
               
                   
                   
                 other specific size LDPC code is used 
               
               
                 Power Control 
                 2 
                   
               
               
                 Reserved 
                 18 or 15 
                   
               
               
                 Beam training  
                 5 
                 Used to initiate and control beam training 
               
               
                 info 
                   
                 Length: 3 bits (Number of TRN-T/R 
               
               
                   
                   
                 subfields appended or requested) 
               
               
                   
                   
                 Beam Tracking Request: 1 bit (1: beam 
               
               
                   
                   
                 tracking requested, 0: no beam tracking 
               
               
                   
                   
                 requested) 
               
               
                   
                   
                 Packet Type: 1 bit (0: indicates either 
               
               
                   
                   
                 packet that has TRN-R subfields 
               
               
                   
                   
                 appended, or that sender is requesting 
               
               
                   
                   
                 TRN-R subfields be appended in a future 
               
               
                   
                   
                 response, 1: packet has TRN-T subfields 
               
               
                   
                   
                 appended.) 
               
               
                 RSSI 
                 4 
                 RSSI of last control message from this 
               
               
                   
                   
                 link 
               
               
                 Header Check 
                 8 
                 A short CRC sequence may be added to 
               
               
                 Sequence (HCS) 
                   
                 check for decoding errors. 
               
               
                 Total 
                 64 
               
               
                   
               
            
           
         
       
     
     A data packet may span multiple Data Slots. In addition each packet may be preceded by a preamble and a header and may end with a GI and IDS. These observations may lead to four possible configurations for a Data Slot in the default configuration of N cs =5 and when no beam training is performed. 
       FIG. 29  is a diagram of an example of Various Data Slot Scenarios for N cs  equal to 5 and no beam refinement. In this example four possible scenarios scenario  2910 , scenario  2920 , scenario  2930  and scenario  2940  are depicted. In the example first scenario  2910 , a data slot for the start of packet that spans only one slot (i.e., the data slot is the first and last slot of packet) may start with a preamble of length T DPR , as required for each AGC, Timing Synchronization, and Channel Estimation. The Preamble  2912  may be followed by a Header  2914  of length T DH , which may provide required parameters, shown in Table 17, in order for the node to be able to properly decode the data packet that follows. The Header may be followed by 34 Data Blocks  2915 , each of which may contain 448 coded bits followed by a 64 bit GI  2916 . The GI  2916  may be used to update the CFO and other related timing parameters. After the GI  2916 , the 34 Data Blocks  2915  may be followed by an IDS  2918 . 
     In the second example scenario  2920 , a data slot for the start of a packet that spans multiple slots may start with the same Preamble field  2922  and Header field  2924  as described above. The header field  2924  may be followed by 41 Data Blocks  2925 . Since the packet may continue into the next Data Slot, there may be no final GI or IDS required. 
     In the third example scenario  2930 , a data slot for the continuation of a packet that spans additional slots (i.e., a slot that is neither the first or last slot of the packet) contains only 47 Data Blocks  2935 , since the preamble and header were sent on the previous Data Slot. In addition, since the packet may continue into the next Data Slot, there no final GI or IDS may be required. 
     In the fourth example scenario  2940 , a data slot for the continuation of a packet that ends in the current slot may start with only Data Blocks  2945  as above, however, since the data packet ends in this slot, a GI  2946  and IDS  2948  may both be required. There may be 40 Data Blocks  2945  transmitted in this type of Data Slot. 
     When beam training is included in a packet, up to ceil{K*(4992/512)} data blocks may be lost to beam testing where K is the number of beams. For example when the number of control slots N cs  is greater than 5, then ceil{(22000/512)*(Ncs−5)}=ceil{(42.96875)*(Ncs−5)} data blocks may be uniformly removed from the data region, reducing each slot by 1-2 data blocks per slot per added control slot. 
     The following section considers a modified Low MCS Design at, for example, 160 Mbps. The minimum required MAC-level data rate for the BH may be targeted at 100 Mbps at a range of 350 meters. This may translate to a PHY-level data rate of 160 Mbps using a 62.5% MAC efficiency rate. The current 802.11ad MCS for single carrier (SC) provides PHY data rates in the range of 385 Mbps to 4602 Mbps. These data rates are above the required minimum for BH, however providing these rates may limit the range to less than the desired maximum range of 350 meters. Another potential MCS already specified in IEEE 802.11ad is the CTRL-PHY MCS, which is more robust that any of the SC MCSs. Unfortunately, this MCS option provides a PHY data rate of only 27.5 Mbps, which is well below the target BH data rate. 
     Table 18 lists the various exemplary parameters used throughout the below description. 
     
       
         
           
               
             
               
                 TABLE 18 
               
             
            
               
                   
               
               
                 Low MCS Design Parameters 
               
            
           
           
               
               
            
               
                 Parameter 
                 Description 
               
               
                   
               
               
                 Length 
                 Length of PSDU in octets 
               
               
                 R sc   raw   
                 Raw SC-PHY Data Rate 
               
               
                 R T   
                 Target bit rate for Low MCS [160 Mbps] 
               
               
                 ρ 
                 Repetition factor with respect to N ρ   
               
               
                 R 
                 LDPC Code Rate [½, ⅝, ¾, 13/16] 
               
               
                 R e   
                 Effective Code Rate 
               
               
                 L CW   
                 Base LDPC codeword length [672] 
               
               
                 N CWLM   
                 LDPC codeword length multiplier 
               
               
                 L FCW   
                 Full LDPC codeword length [N CWLM L CW ] 
               
               
                 L IW   
                 Length of Information word 
               
               
                 F C   
                 Chip Rate in MHz [1760] 
               
               
                 L DB   
                 Length of Data Block [512] 
               
               
                 L GI   
                 Length of Guard Interval [64, 0] 
               
               
                 N ρ   
                 Number of Information bits per codeword 
               
               
                 N DATA _PAD 
                 Number of zero pad bits appended to the end of  
               
               
                   
                 the original PSDU 
               
               
                 N CW   
                 Number of codewords in one PSDU 
               
               
                 N BLKS   
                 Number of Data Blocks 
               
               
                 N CBPB   
                 Number of coded bits per Data Block [L DB  − L GI ] 
               
               
                 N BLK _PAD 
                 Number of zero pad bits appended to the last Data Block 
               
               
                   
               
            
           
         
       
     
     In order to determine the number of information bits required per data block to provide a target bit rate, RT, of 160 Mbps, the raw SC-PHY data rate may first be determined. Assuming Binary Phase Shift Keying (BPSK) modulation the raw SC-PHY bit rate may be found to be 1540 Mbps through the following equation: 
     
       
         
           
             
               
                 
                   
                     R 
                     
                       s 
                        
                       c 
                     
                     raw 
                   
                   = 
                   
                     
                       ( 
                       
                         
                           
                             L 
                             
                               D 
                                
                               B 
                             
                           
                           - 
                           
                             L 
                             GI 
                           
                         
                         
                           L 
                           
                             D 
                              
                             B 
                           
                         
                       
                       ) 
                     
                      
                     
                       F 
                       c 
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     7 
                     ) 
                   
                 
               
             
           
         
       
     
     The SC-PHY information data rate, however, may need to take into account the fraction of information bits coming from the LDPC encoder, which may be defined as: 
     
       
         
           
             
               
                 
                   
                     R 
                     e 
                   
                   = 
                   
                     
                       L 
                       IW 
                     
                     
                       L 
                       
                         C 
                          
                         W 
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     8 
                     ) 
                   
                 
               
             
           
         
       
     
     Using the two equations above the length of the information word per base LDPC codeword length required, L IW , to support the target PHY-level data rate, R T  may be determined as: 
     
       
         
           
             
               
                 
                   
                     
                       L 
                       IW 
                     
                     = 
                     
                       
                         ⌈ 
                         
                           
                             
                               R 
                               T 
                             
                              
                             
                               L 
                               
                                 C 
                                  
                                 W 
                               
                             
                              
                             
                               L 
                               
                                 D 
                                  
                                 B 
                               
                             
                           
                           
                             
                               F 
                               c 
                             
                              
                             
                               ( 
                               
                                 
                                   L 
                                   DB 
                                 
                                 - 
                                 
                                   L 
                                   GI 
                                 
                               
                               ) 
                             
                           
                         
                         ⌉ 
                       
                       = 
                       
                         
                           ⌈ 
                           
                             
                               1 
                                
                               6 
                                
                               0 
                               * 
                               6 
                                
                               7 
                                
                               2 
                               * 
                               5 
                                
                               1 
                                
                               2 
                             
                             
                               1 
                                
                               7 
                                
                               6 
                                
                               0 
                                
                               
                                 ( 
                                 
                                   
                                     5 
                                      
                                     1 
                                      
                                     2 
                                   
                                   - 
                                   
                                     6 
                                      
                                     4 
                                   
                                 
                                 ) 
                               
                             
                           
                           ⌉ 
                         
                         = 
                         
                           7 
                            
                           0 
                         
                       
                     
                   
                    
                   
                       
                   
                    
                   bits 
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     9 
                     ) 
                   
                 
               
             
           
         
       
     
     With this in mind a modified MCS, referred to as “low MCS” is described herein. This modified MCS may integrate seamlessly with the existing SC-PHY MCSs. An LDPC code rate of 1/2 may allow for 
     
       
         
           
             
               L 
               CW 
             
             2 
           
         
       
     
     information bits per base LDPC codeword. Given that the length of the information bits, L IW , required for the modified low MCS may be lower than 
     
       
         
           
             
               
                 L 
                 CW 
               
               2 
             
             , 
           
         
       
     
     along with the desire to integrate this modified MCS with the existing SC-PHY MCSs, an extension of the code word shortening and repetition used in the IEEE 802.11ad standard may be used. The next section describes the modifications to the SC-PHY coding procedure required to support the modified low MCS. The coding procedure uses the existing MCSs and may use LPDC code word size of L FCW =N CWLM L CW , which is transparent to the coding procedure. The reason for making the LDPC codeword size larger is explained below. 
     First, the total number of information bits per codeword may be calculated. If low MCS is used, this implies ρ&gt;2 and is calculated as: 
                       N   ρ     =     ⌈         R     B      T            L     F      C      W            L     D      B             F   C          (       L     D      B       -     L   GI       )         ⌉       ,           Equation                   (   10   )                 ρ   =           L     F      C      W          R       N   ρ       .             Equation                   (   11   )                 Otherwise, 
     
       
         
           
             
               
                 
                   
                     N 
                     ρ 
                   
                   = 
                   
                     ⌈ 
                     
                       
                         
                           L 
                           
                             F 
                              
                             C 
                              
                             W 
                           
                         
                          
                         R 
                       
                       ρ 
                     
                     ⌉ 
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     12 
                     ) 
                   
                 
               
             
           
         
       
     
     Next, the number of data pad bits NDATA_PAD may be calculated using the number of LDPC codewords N CW : 
     
       
         
           
             
               
                 
                   
                     
                       N 
                       
                         C 
                          
                         W 
                       
                     
                     = 
                     
                       ⌈ 
                       
                         
                           8 
                            
                           
                               
                           
                            
                           Length 
                         
                         
                           N 
                           ρ 
                         
                       
                       ⌉ 
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     13 
                     ) 
                   
                 
               
             
             
               
                 
                   
                     N 
                     
                       D 
                        
                       ATA_PAD 
                     
                   
                   = 
                   
                     
                       
                         N 
                         
                           C 
                            
                           W 
                         
                       
                        
                       
                         N 
                         ρ 
                       
                     
                     - 
                     
                       8 
                        
                       
                           
                       
                        
                       
                         Length 
                         . 
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     14 
                     ) 
                   
                 
               
             
           
         
       
     
     N CW     min    may be defined for BRP packets in IEEE 802.11ad. The scrambled PHY service data unit (PSDU) may be concatenated with N DATA_PAD  zeros. They may be scrambled using the continuation of the scrambler sequence that scrambled the PSDU input bits. The procedure for converting the scrambled PSDU data to LDPC codewords may depend on the repetition factor. 
     If ρ=1 (an 802.11ad MCS), the output stream of the scrambler may be broken into blocks of N ρ  bits such that the mth data word is (b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) ), m≤N CW . To each data word, n−k=L FCW −N ρ  parity bits may be added to create the codeword c (m) =(b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) , p 1   (m) , p 2   (m) , . . . , p n−k   (m) ) such that Hc (m)     T   =0. 
     If ρ=2, which implies R=½ only with MCS1 as per IEEE 802.11ad, the data bits in each codeword (b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) ) may be concatenated with N ρ  zeros to produce a sequence in length of 2N ρ , (b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) , 0 1 , . . . , 0 N     ρ   ). The LDPC codeword c (m) =(b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) , 0 1 , . . . , 0 N     ρ   , p 1   (m) , p 2   (m) , . . . , p 2N     ρ     (m) ) may be created by generating the parity bits p 1   (m) , p 2   (m) , . . . , p 2N     ρ     (m)  such that Hc (m)     T   =0, where H is the parity matrix for rate 1/2 LDPC coding specified in IEEE. Bits N ρ +1 through 2N ρ  of the codeword c may be replaced with bits from the sequence b 1   (m) , b 2   (m) , . . . , b N     ρ     (m)  XORed by a PN sequence that is generated from the LFSR used for data scrambling as defined in IEEE. The LFSR may be initialized to the all ones vector and reinitialized to the same vector after every codeword. 
       FIG. 30A  is diagram of an example encoder for bit handling for low MCS. If ρ&gt;2 this may indicate a low MCS condition. In this case, the output stream of the scrambler may be broken into blocks  3010  of N ρ  bits such that the mth data word is (b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) ), m≤N CW . For example a R value of R=½ may be used, but there may a range of applicable values. Each data word may be concatenated with N z =(L FCW R−N ρ ) zeros  3020  to produce the following: (b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) , 0 1   (m) , 0 2   (m) , . . . , 0 N     z     (m) ). The LDPC codewords c (m) =(b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) , 0 1   (m) , 0 2   (m) , . . . , 0 N     z     (m) , p 1   (m) , p 2   (m) , . . . , p L     FCW       (1−R)     (m) ) may be created by generating the parity bits  3030  (p 1   (m) , p 2   (m) , . . . , p L     FCW       (1−R)     (m) ) such that Hc T =0, where H is the parity matrix for rate R LDPC coding specified in IEEE 802.11ad. Bits  3042  N ρ +1 through 2N ρ  of codeword c may be replaced with bits from the sequence (b 1   (m) , b 2   (m) , . . . , b N     ρ     (m) ) XORed by a PN sequence that is generated from the LFSR used for data scrambling as defined in IEEE 802.11ad. The LFSR may be initialized to the all ones vector and reinitialized to the same all ones vector after every codeword. Parity bits  3044  2N ρ +1 through L FCW R of codeword c may be replaced with bits from the sequence (p PR   (m) , p PR+1   (m) , . . . , p L     FCW       (1−R)     (m) ) XOR&#39;ed by a PN sequence that is generated from the LFSR used for scrambling, as defined in IEEE 802.11ad, where PR=[(L FCW (1−R))−(L FCW R−2N ρ +1)]. The LFSR may be initialized to the all ones vector and reinitialized to the same vector after every codeword. 
     The codewords may then be concatenated  3052  one after the other to create the coded bits stream c=(c 1 , c 2 , . . . , c L     FCW     N     CW   ). The number of symbol blocks, N BLKS , and the number of symbol block padding bits, N BLK_PAD , may be calculated as follows: 
     
       
         
           
             
               
                 
                   
                     
                       N 
                       
                         B 
                          
                         L 
                          
                         K 
                          
                         S 
                       
                     
                     = 
                     
                       ⌈ 
                       
                         
                           
                             N 
                             
                               C 
                                
                               W 
                             
                           
                            
                           
                             L 
                             
                               F 
                                
                               C 
                                
                               W 
                             
                           
                         
                         
                           N 
                           
                             C 
                              
                             B 
                              
                             P 
                              
                             B 
                           
                         
                       
                       ⌉ 
                     
                   
                   , 
                   and 
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     15 
                     ) 
                   
                 
               
             
             
               
                 
                   
                     
                       N 
                       BLK_PAD 
                     
                     = 
                     
                       
                         
                           N 
                           
                             B 
                              
                             L 
                              
                             K 
                              
                             S 
                           
                         
                          
                         
                           N 
                           
                             C 
                              
                             B 
                              
                             P 
                              
                             B 
                           
                         
                       
                       - 
                       
                         
                           N 
                           
                             C 
                              
                             W 
                           
                         
                          
                         
                           L 
                           
                             F 
                              
                             C 
                              
                             W 
                           
                         
                       
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     16 
                     ) 
                   
                 
               
             
           
         
       
     
     where N CBPB  is number of coded bits per data block. N CBPB  may be taken from IEEE 802.11ad. 
     The value for N BLKS  may be at most equal to the granted N BLKS , i.e., the number of data blocks contained the grant for the packet being coded as described above. The coded bit stream may be concatenated with N BLK_PAD  zeros  3054 . They may be scrambled with a continuation of the scrambler sequence that scrambled the PSDU data, and modulated  3056  as per IEEE 802.11. The bit streams may then be transmitted through a channel. 
       FIG. 30B  is diagram of an example decoder for bit handling for low MCS. The decoding process is effectively the reverse of the encoding process described above. After demodulation, the demodulated sequence may contain Information LLRs (for example,  3061  and  3062 ) and Parity LLRs (for example,  3064 ,  3066  and  3068 ). The Information LLRs may then be descrambled, resulting in  3085 . The resulting information bits  3085  may then be combined with Zeroes  3090  and the parity bits. This combination may then be send to the LDPC decoder per codeword. 
     Longer LDPC codewords are now considered. As mentioned above, the backhaul use case generally has more data available per packet than a typical IEEE 802.11ad use case. The performance generally improves as codeword length increases. For these reasons, in examples longer LDPC codewords may be supported for these backhaul use cases. 
     In a first example, LDPC codeword length and rate options may be broadcast in beacon message  1  (no negotiation, system wide). In a second option, LDPC codeword length and rate options may be negotiated in discovery message exchange (a.k.a. beacon message exchange). Node capabilities may be determined from its unique ID in the BRI. The network/existing node may decide on the LDPC length based on capabilities of new and existing node and other things, and may include instructions in the beacon ACK. This may be done on a per link basis. LDPC word size may be indicated on a per data packet basis, either in the control message exchange or in the data packet header. In a proposed example, supported Forward error correction (FEC) methods may be included in the capabilities LUT. The attached nodes/network may determine the FEC capabilities from the signaled unique ID of the new node (learn from BRI). All connected nodes may then know the capacities of their neighbors. The FEC method (e.g., LDPC codeword length) may be signaled in the data header per packet. 
     Considering HARQ and end-to-end latency, the mesh backhaul network may be required to support very low latency packet delivery over at least 5 hops through the mesh. The latency budget may require packets to be delivered within 5 ms with high probability when there are no queuing delays. The system may be designed such that failed packets may be retransmitted in the SI following the SI where the failure occurred. For example, if each SI is 0.5 mSec, the system may permit up to a total of 5 retransmissions of the packet in route to the destination node. 
     HARQ may be used as a means to ensure this can be achieved without resorting to setting very low target packet error rates (PERs) on each link which could limit the ultimate achievable throughput. Such retransmission may be identical copies to support chase combining or may use multiple redundancy versions. 
     In chase combining, either soft bits or soft symbols may be buffered for retransmission combining. When a first transmission fails, the re-transmission may be combined (soft bit-wise or symbol-wise addition, possibly weighted for varying SNR between transmissions). In the Additive White Gaussian Noise (AWGN) channel and a given target first transmission PER, the retransmission may enjoy nearly 3 dB of SNR improvement for the purpose of estimating the PER on the retransmission. For example the LDPC codes may cause the 3 dB improvement results to be better PER than simple automatic repeat request (ARQ) retransmission. An example improvement in end-to-end packet delivery for line of sight (LOS) channels with minimal fading is estimated in  FIG. 31  with and without HARQ. 
     The following section gives examples of simulation descriptions. In one example AWGN, the retransmit probability is nearly 3 dB better than the 1st transmit probability for Chase combining, however 2.5 dB will be assumed to allow some margin for practical scenarios. If it is assumed that channels vary slowly compared to the retransmit rate, which is typical for the BH case, then a conservative estimate for the SNR variation for the retransmission should be limited to ˜+/−1.5 dB. The overall SNR improvement for the retransmission may then be calculated to be about 1.9 dB. 
     Each link may use link adaptation techniques to achieve a target PER. For HARQ, the PER of a retransmission may then be computed by interpolating a PER curve from the target PER point to the PER that results with 1.5 dB better SNR. In other words, the retransmit PER may be estimated from the rate 1/2 LDPC curves by increasing the effective SNR by 1.5 dB relative to the SNR required to obtain the target 1st transmission PER in the legend. 
     For ARQ, the statistical behavior for each transmission and retransmission may be considered to be independent and identically distributed (iid). With these assumptions ARQ lends itself to analytical analysis similar to a Bernoulli trial as follows. Given the iid characteristics as mentioned above, the probability of a packet being successfully delivered to the final destination node in exactly N SI  SIs using N H  hops and having failed N F  times along the way, may be written as follows: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           P 
                           ~ 
                         
                         S 
                         
                           E 
                            
                           2 
                            
                           E 
                         
                       
                        
                       
                         ( 
                         
                           
                             N 
                             SI 
                           
                           , 
                           
                             N 
                             H 
                           
                           , 
                           
                             N 
                             F 
                           
                         
                         ) 
                       
                     
                     = 
                     
                       
                         
                           ( 
                           
                             P 
                             S 
                           
                           ) 
                         
                         
                           N 
                           H 
                         
                       
                        
                       
                         
                           ( 
                           
                             1 
                             - 
                             
                               P 
                               S 
                             
                           
                           ) 
                         
                         
                           
                             N 
                             SI 
                           
                           - 
                           
                             N 
                             H 
                           
                         
                       
                        
                       
                         ( 
                         
                           ( 
                           
                             
                               
                                 
                                   N 
                                   H 
                                 
                               
                             
                             
                               
                                 
                                   N 
                                   F 
                                 
                               
                             
                           
                           ) 
                         
                         ) 
                       
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     17 
                     ) 
                   
                 
               
             
           
         
       
     
     where {tilde over (P)} s   E2E (N SI , N H , N F ) is the probability of a successful end-to-end packet delivery in exactly N SI  SIs, using N H  hops and having N F  failures along the way; N SI  is the number of SIs used for the end-to-end transmission; N H  is the number of Hops used for the end-to-end transmission; N F  is the number of single-hop failures for the end-to-end transmission, each requiring a retransmission; P s  is the probability of a successful single-hop transmission; and 
     
       
         
           
               
             
               ( 
               
                 ( 
                 
                   
                     
                       n 
                     
                   
                   
                     
                       k 
                     
                   
                 
                 ) 
               
               ) 
             
           
         
       
     
     is the multiset coefficient, which represents the number of ways that the N F  failures could have occurred over the N H  hops, which is equal to: 
     
       
         
           
             
               
                 
                   ( 
                   
                     n 
                     + 
                     k 
                     - 
                     1 
                   
                   ) 
                 
                 ! 
               
               
                 k 
                  
                 
                   ! 
                   
                     
                       ( 
                       
                         n 
                         - 
                         1 
                       
                       ) 
                     
                     ! 
                   
                 
               
             
             . 
           
         
       
     
     Furthermore, the probability of a packet being successfully delivered to the final destination node within N SI  SIs using N H  hops and having failed N F  times along the way may be found by summing the above probabilities for all successes. The summation starts from N H , which is the minimum number of SIs required to deliver the packet to the destination node, and ends at the maximum number of SIs chosen, N SI   max : 
         P   S   E2E ( N   SI   max   ,N   H   ,N   F )=Σ i=N     H     N     SI       max     {tilde over (P)}   s   E2E ( i,N   H   ,N   F ).  (18)
 
     Finally, the probability of the packet not being delivered by the N SI   max  SI may be written as: 
     
       
         
           
             
               
                 
                   
                     
                       P 
                       F 
                       
                         E 
                          
                         
                             
                         
                          
                         2 
                          
                         E 
                       
                     
                      
                     
                       ( 
                       
                         
                           N 
                           SI 
                           max 
                         
                         , 
                         
                           N 
                           H 
                         
                         , 
                         
                           N 
                           F 
                         
                       
                       ) 
                     
                   
                   = 
                   
                     
                       [ 
                       
                         1 
                         - 
                         
                           
                             P 
                             S 
                             
                               E 
                                
                               
                                   
                               
                                
                               2 
                                
                               E 
                             
                           
                            
                           
                             ( 
                             
                               
                                 N 
                                 SI 
                                 max 
                               
                               , 
                               
                                 N 
                                 H 
                               
                               , 
                               
                                 N 
                                 F 
                               
                             
                             ) 
                           
                         
                       
                       ] 
                     
                     = 
                     
                         
                       
                         
                           [ 
                           
                             1 
                             - 
                             
                               
                                 ∑ 
                                 
                                   i 
                                   = 
                                   
                                     N 
                                     H 
                                   
                                 
                                 
                                   N 
                                   SI 
                                   max 
                                 
                               
                                
                               
                                 
                                   
                                     ( 
                                     
                                       P 
                                       s 
                                     
                                     ) 
                                   
                                   
                                     N 
                                     H 
                                   
                                 
                                  
                                 
                                   
                                     ( 
                                     
                                       1 
                                       - 
                                       
                                         P 
                                         S 
                                       
                                     
                                     ) 
                                   
                                   
                                     i 
                                     - 
                                     
                                       N 
                                       H 
                                     
                                   
                                 
                                  
                                 
                                   ( 
                                   
                                     ( 
                                     
                                       
                                         
                                           
                                             N 
                                             H 
                                           
                                         
                                       
                                       
                                         
                                           
                                             N 
                                             F 
                                           
                                         
                                       
                                     
                                     ) 
                                   
                                   ) 
                                 
                               
                             
                           
                           ] 
                         
                         . 
                       
                     
                   
                 
               
               
                 
                   Equation 
                    
                   
                       
                   
                    
                   
                     ( 
                     19 
                     ) 
                   
                 
               
             
           
         
       
     
     A closed form expression for the probability of a successful end-to-end packet delivery in the HARQ case has not yet been identified and so simulations may be required. To get below 10 −7  probability of a packet not being received before 10 transmission time intervals (TTIs) in a 5 hop route, ARQ may require a PER target ˜2%, but with HARQ a PER target greater than 20% may be supported. The scenario may be further extended to include errors in both link adaptation and accounts explicitly for channel quality variations between 1st and 2nd transmission. 
     The use of multiple redundancy versions may further improve HARQ performance, but for the backhaul, these gains may be expected to be smaller than for access links. In an example, multiple redundancy versions may be used. 
       FIG. 31  is diagram of an example Packet Delivery Time Probability with HARQ/ARQ. The graph  3100  depicts the probability of a packet not delivered in N TTIs for different PER and 5 hops. 
     Variable-length preambles for Control Period messages are relevant for backhaul networks due to the static nature of the nodes, and due to relatively high periodicity of message exchange between the nodes. These two conditions imply that the channel between the mmW backhaul nodes remains fairly static between successive message exchanges, and a shorter preamble would suffice for the AGC settling, channel estimation, and other related purposes. Although this variable-length preamble idea is described here in the context of backhaul mesh nodes, it may be applied whenever the change in channel conditions between the transmitting and receiving nodes is less than a particular threshold. This procedure may allow node pairs to determine the best preamble size, based on local channel conditions. In addition it may reduce the control overhead due to the preamble significantly, which is a direct overhead for each PHY layer frame transmission. 
     Determining the optimal preamble size so as not to impact performance of AGC (channel estimation etc.), and at the same time reducing the preamble size taking into account the static nature of the backhaul links may significantly improve the overall good-put of the system. Further, taking into account when the last data transmission has occurred may further improve the overall good-put of the system. 
       FIG. 32A  is a diagram of an example of a variable-length preamble. In an example variable-length preamble, the node may have a-priori knowledge of preamble lengths. In this example, when the requirements of the time difference between successive packet transmissions of the same pair of nodes are satisfied, the transmitter may implicitly switch to a shorter length preamble  3220  for the second and subsequent packet N, as long as the duration between successive transmissions is less than some predefined value. In an example a first packet may contain Preamble  1   3210  and Information  3219  and a subsequent packet may contain Preamble  2   3220  and Information  3225 . Further, later packets may follow, through a packet which may contain Preamble N  3230  and Information  3235 . In an example, the transmitter may switch to a shorter preamble for Preamble  2   3220  and Preamble N  3230 , if the duration is less than the predefined value. This predefined value may be signaled as part of initial configuration or can be loaded from memory. The transmitter may choose the appropriate preamble length based on the duration since the last successful transmission to the same receiving node. In a further example, signals regarding the initial preamble length may be received from a central node. In a further example, the preamble length may be based on the content of the transmission. Therefore, there may be multiple possible preamble lengths and the transmitter may choose the appropriate one depending on one or more of several factors. 
     The receiver may also determine the preamble size in the next transmission from the same node in a similar manner. In an example, the packet is correctly received by the receiver, but an acknowledgement sent in response is not received at the first node. The first node may use a longer preamble (if a short preamble timer has elapsed) in the next transmission because the first node failed to receive the acknowledgement. Nevertheless, the second node may still expect a short preamble. In this circumstance, the second node may simply ignore the remaining part of the preamble. If the acknowledgement is received at the first node, then the first node may continue to use the shorter preamble. In a further example, the transmitter may also know the appropriate preamble length based upon the estimated channel conditions, and adjust the preamble length accordingly. In a further example, the transmitter may adjust the preamble length based on local channel conditions. 
       FIG. 32B  is a diagram of another example of a variable-length preamble. In this second example, the explicit signaling of the preamble length may be at the start of the preamble itself. Accordingly, the preamble may have two parts the first part of the preamble  3242  may indicate the length of the second part  3244 . Information  3245  may follow the second part of the preamble  3244 . The transmitter may use one out of N possible sequences for the first part of the preamble. The different sequences correspond to N different lengths for the second part of the preamble. The receiver may then determine the preamble length by cross-correlating the first part of the preamble against all N possible sequences. Explicit signaling of the preamble length may make it possible for the transmitter to adapt the preamble length according to local channel conditions. In a further example, the transmitter may also adapt the preamble length to estimated channel conditions. It may also be desirable for the codes used to determine the preamble length to have good auto correlation properties (low non-zero lag peaks) and low cross correlation peaks between members of the possible sequences. 
     In the third example, the requested preamble length may be signaled by a mesh node to its peer neighboring node. This signaling may either in absolute terms or relative to the preamble length used for the previous transmission from the peer node. This field may be included in the Physical layer (PHY) or Physical Layer Convergence Protocol (PLCP) Header. For example, one example may reserve two bits in the PHY/PLCP Header to indicate requested change in preamble size. Here 00 may represent no change, 01 may represent request for longer preamble and 10 may represent request for shorter preamble size. Accordingly, Node  1  may set the value of this field to 10 to request Node  2  to reduce the preamble length in its next transmission to Node  1 , if time limitations are satisfied. 
     Conversely, if Node  1  fails to correctly decode the previous transmission from Node  2  due to insufficient preamble size, resulting in incorrect channel estimation or failure of AGC to settle, it may request longer preamble in the next transmission from Node  2  by sending a Null-Data frame with the Preamble Length field in the PHY/PLCP Header set to 01. This may provide a closed-loop mechanism for the nodes to adjust the preamble size according local channel conditions. If the duration between successive data transmissions to the same receiving node is larger than a particular limit, then the transmitting node may default to a larger preamble size, irrespective of the request from the receiving node in the previous transmission. In another variation, the requesting node may include the requested preamble length in absolute terms, but this may need a larger field in the Header depending on the number of active preamble sizes. 
     In example disclosed herein, modified complementary Golay codes are used. The Golay sequences and complementary pairs used in the preamble of the backhaul system may be similar to the ones used in IEEE 802.11ad and may be composed of 128-chip long sequences. Further the code may have a recursive construction. However, the system may support the use of multiple such Golay building blocks and the exact codes used may be selected to have good properties relative to IEEE 802.11ad and to each other. The Golay sequences used in the backhaul system may be designed to have low correlation at any lag to the Ga and Gb sequences of 802.11ad, good auto correlation properties (low non-zero lag peaks), and low cross correlation peaks between members of the possible Golay sequences. 
     During discovery, each node may be given an index that points to one or more sets of Golay sequences (e.g., a Ga and Gb Golay complementary pair (GCP) of 128 chips). The index may be node or link specific. There are 8-16 different sets of GCPs available for use. During discovery, the new node may be told which Golay index to use to determine which sequences it will use to transmit. 
     There are 2 M M! Golay codes (with GCPs) that can be generated from recursive or direct construction For M=7, that is just over half a million and within reach of exhaustive search for codes with low correlation to the IEEE 802.11ad 128 chip codes. 
       FIG. 33  is a diagram of an example distribution of peak correlations to the 802.11ad Golay codes. Distribution  3300  shows a peak value distribution of a set of all of the Golay codes of length 128 that can be constructed from the Direct construction method. A set of codes with low cross correlations between IEEE 802.11ad Ga and Gb may be chosen in a further example. Of these codes,  1140  have a peak cross correlation of less than 28 (the minimum correlation values in 24, but the set is small). 
     From this set, a smaller set of Ga sequences may be found that have low non-zero lag auto correlation peaks so that they may make for good sequences for packet detection without use of the complementary pair. For example, a set of codes is desired such that each of the codes has a maximum peak no more than 5 greater than the sequence with the minimum maximum peak. This may reduce the set to about 190 sequences. While this set is drastically reduced from the original half million, finding a good set of codes, for example 8-16 codes, with good cross correlation properties may not be required as a random search produces reasonably low cross correlation sets. The delays and weights for an exemplary set of 8 GCPs with peak cross correlation of 28 or less is shown in Table 19 and Table 20. Another set of 16 GCPs with peak cross correlation of 34 or less is shown in Table 21 and Table 22. Better search methods may be used to further refine this set but may not be required as the initial selection of Golay codes only show that ‘good enough’ codes may indeed be found. 
     After the initial setting of the Golay index, the node may be reconfigured to use a different Golay index via higher layer signaling. The selection of codes is meant to minimize the effects of large cross corrections that could impact packet detection and timing estimates as well as channel estimation due to interfering sequences from IEEE 802.11ad networks, from other nodes within the backhaul network, or from nodes in other backhaul. 
     
       
         
           
               
             
               
                 TABLE 19 
               
             
            
               
                   
               
               
                 Example Set of Delays for the Generation of 8 
               
               
                 GCP with Mutual Xcorr &lt;= 28 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 D1 
                 D2 
                 D3 
                 D4 
                 D5 
                 D6 
                 D7 
                 D8 
               
               
                   
               
               
                  1 
                  1 
                  4 
                  4 
                  1 
                 16 
                  1 
                  1 
               
               
                 64 
                 64 
                 64 
                 64 
                  4 
                  8 
                  2 
                  8 
               
               
                  8 
                  8 
                  1 
                  1 
                 16 
                  4 
                 16 
                 16 
               
               
                  2 
                  2 
                  2 
                  2 
                 64 
                 64 
                  8 
                  4 
               
               
                 16 
                 16 
                  8 
                  8 
                  2 
                 32 
                 64 
                  2 
               
               
                  4 
                  4 
                 32 
                 32 
                 32 
                  1 
                 32 
                 64 
               
               
                 32 
                 32 
                 16 
                 16 
                  8 
                  2 
                  4 
                 32 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 20 
               
             
            
               
                   
               
               
                 Example Set of Weights for the Generation of 8 
               
               
                 GCP with Mutual Xcorr &lt;= 28 
               
            
           
           
               
               
               
               
               
               
               
               
            
               
                 W1 
                 W2 
                 W3 
                 W4 
                 W5 
                 W6 
                 W7 
                 W8 
               
               
                   
               
               
                  1 
                  1 
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
                  1 
               
               
                  1 
                  1 
                 −1 
                 −1 
                 −1 
                  1 
                  1 
                 −1 
               
               
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                  1 
                  1 
                 −1 
               
               
                 −1 
                 −1 
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                 −1 
               
               
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                 −1 
                  1 
                 −1 
               
               
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                  1 
                  1 
                  1 
               
               
                  1 
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
                 −1 
                  1 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 21 
               
             
            
               
                   
               
               
                 Example Set of Delays for the Generation of 16 GCP with Mutual Xcorr &lt;= 34 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D 
                 D1 
                 D1 
                 D1 
                 D1 
                 D1 
                 D1 
                 D1 
               
               
                   
               
               
                  1 
                  2 
                  3 
                  4 
                  5 
                  6 
                  7 
                  8 
                  9 
                  0 
                  1 
                  2 
                  3 
                  4 
                  5 
                  6 
               
               
                  1 
                  1 
                 16 
                  2 
                 16 
                  1 
                  1 
                  1 
                  1 
                  4 
                  1 
                  1 
                  1 
                  1 
                 16 
                 16 
               
               
                  2 
                 64 
                  8 
                 64 
                  8 
                 64 
                  2 
                 64 
                 16 
                 64 
                  4 
                 64 
                  8 
                 16 
                  8 
                  8 
               
               
                 64 
                  8 
                  1 
                  1 
                  1 
                  2 
                  4 
                 16 
                  4 
                  1 
                 16 
                  8 
                 16 
                  2 
                  1 
                  4 
               
               
                  8 
                  2 
                 64 
                 32 
                 64 
                 32 
                 64 
                  2 
                 64 
                  2 
                 64 
                  2 
                  4 
                 32 
                 64 
                 64 
               
               
                 16 
                 16 
                 32 
                 16 
                 32 
                 16 
                 32 
                  8 
                  2 
                  8 
                  2 
                 16 
                  2 
                  4 
                 32 
                 32 
               
               
                  4 
                  4 
                  4 
                  8 
                  4 
                  8 
                  8 
                 32 
                  8 
                 32 
                 32 
                  4 
                 64 
                  8 
                  4 
                  1 
               
               
                 32 
                 32 
                  2 
                  4 
                  2 
                  4 
                 16 
                  4 
                 32 
                 16 
                  8 
                 32 
                 32 
                 64 
                  2 
                  2 
               
               
                   
               
            
           
         
       
     
     
       
         
           
               
             
               
                 TABLE 22 
               
             
            
               
                   
               
               
                 Example Set of Weights for the Generation of 16 GCP with Mutual Xcorr &lt;= 34 
               
            
           
           
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
               
            
               
                 W1 
                 W2 
                 W3 
                 W4 
                 W5 
                 W6 
                 W7 
                 W8 
                 W9 
                 W10 
                 W11 
                 W12 
                 W13 
                 W14 
                 W15 
                 W16 
               
               
                   
               
               
                  1 
                 −1 
                 −1 
                  1 
                 −1 
                  1 
                  1 
                 −1 
                 −1 
                 −1 
                  1 
                  1 
                  1 
                 −1 
                 −1 
                 −1 
               
               
                  1 
                  1 
                 −1 
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                 −1 
                  1 
               
               
                  1 
                  1 
                 −1 
                  1 
                  1 
                 −1 
                 −1 
                  1 
                  1 
                 −1 
                  1 
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
               
               
                 −1 
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
                 −1 
                 −1 
                 −1 
                 −1 
                 −1 
               
               
                 −1 
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
                  1 
                 −1 
                  1 
                  1 
                 −1 
                  1 
               
               
                 −1 
                 −1 
                  1 
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                  1 
                 −1 
                  1 
                  1 
                  1 
                 −1 
                  1 
                  1 
               
               
                 −1 
                  1 
                 −1 
                 −1 
                  1 
                  1 
                 −1 
                 −1 
                 −1 
                 −1 
                  1 
                  1 
                  1 
                  1 
                  1 
                  1 
               
               
                   
               
            
           
         
       
     
     The 64 chip code used in the GI period may be derived from the Golay code indicator as well. A similar procedure may be used to find appropriate sets of Ga-64 can be used. Power control procedures may also be updated in a further example. 
     During the creation of each of the 224 bit-codewords, parity bits may be punctured from the center of the LDPC parity bit field plus some offset. PO max  represents the maximum offset, or PO, relative to the center of the parity bit field of the LDPC codeword that can be supported. In order to gain insight into how the particular choice of PO affects the performance a number of simulations were configured where PO was swept over a given range. For reference a simulation was also run where PO was kept constant. The configurations of the various example simulations were as shown in Table 23. 
     
       
         
           
               
             
               
                 TABLE 23 
               
             
            
               
                   
               
               
                 PO Sweep Test Configurations 
               
            
           
           
               
               
               
               
            
               
                 Simulation 
                   
                   
                   
               
               
                 Number 
                 Code Rate [R] 
                 Message Size [Bits] 
                 PO values 
               
               
                   
               
               
                 0 
                 ½ 
                 46 
                 PO max   
               
               
                 1 
                 ½ 
                 46 
                 {−PO max :PO max } 
               
               
                 2 
                 ⅝ 
                 46 
                 {−PO max :PO max } 
               
               
                 3 
                 ¾ 
                 64 
                 {−PO max :PO max } 
               
               
                   
               
               
                 Note: 
               
               
                 Simulation 3 is the same as the SC-PHY header used on 802.11ad 
               
            
           
         
       
     
       FIG. 34  is a diagram of an example result from a simulation. Result  3400  may show results with a shortened code and repetition, a rate of 0.5 LDPC, 46 msgBits and 5000 Num blocks. Result  3400  may further show a reference example of multiple runs of the same PO. Result  3400  may also show there may be less of a variation in performance of simulation 0 compared to simulations 1, 2 and 3. This observation validates the conclusions that will be drawn from simulations 1, 2 and 3. 
       FIG. 35  is a diagram of an example result from another simulation. Result  3500  may show results with a shortened code and repetition, a sweep of POs, a rate of 0.5 LDPC, 46 msgBits and 5000 Num blocks. Result  3500  shows the performance spread of simulation 1 may be about ½ dB at 1% block error rate (BLER). Result  3500  may also show R of ½, a message size of 46 and PO=−PO max: −10. 
       FIG. 36  is a diagram of another example result from another simulation. Result  3600  of simulation 1 highlights that −PO max  is the best choice in the typical sense. Result  3600  may show BER at −4 dB, −3 dB SNR versus PO and message bit=46 rate=0.5. Result  3600  may also show BLER plotted versus PO at two different SNRs. 
       FIG. 37  is a diagram of an example result yet another simulation. Result  3700  may show results with a shortened code and repetition, a sweep of POs, a rate of 0.625 LDPC, 46 msgBits and 5000 Num blocks. Result  3700  of simulation 2 shows a similar performance spread as in simulation 1. Result  3700  may also show R of ⅝, a message size of 46 and PO=−PO max: −10. 
       FIG. 38  is a diagram of an example of another result from another simulation. Result  3800  of simulation 2 shows that −PO max  may be the best choice in the typical sense. Result  3800  may show BER at −4 dB, −3 dB SNR versus PO and message bit=46 rate=0.625. Result  3800  may also show BLER plotted versus PO at two different SNRs. 
       FIG. 39  is a diagram of an example result from yet another simulation. Result  3900  may show results with a shortened code and repetition, a sweep of POs, a rate of 0.75 LDPC, 64 msgBits and 10,000 Num blocks. Result  3900  of simulation 3 shows a similar performance spread as in simulation 1. Result  3900  may also show R of ¾, a message size of 64 and PO=−PO max: −10. 
       FIG. 40  is a diagram of another example result from an additional simulation. Result  4000  of simulation 3 may also show that −PO max  is the best choice in the typical sense. Result  4000  may also show BER at −4 dB, −3 dB SNR versus PO and message bit=64 rate=0.75. Result  4000  may also show BLER plotted versus PO at two different SNRs. Note that this simulation may be configured similar to the SC-PHY header in IEEE 802.11ad. More importantly, IEEE 802.11ad uses −PO max  which is actually the worst PO that could be selected according to the simulation. 
       FIG. 41  is a diagram of an example comparison of the results of simulations. Result  4100  compares simulation 2 with simulation 3. Result  4100  may show results with a shortened code and repetition, a sweep of LDPC coderates, 64 msgBits, 10,000 Num blocks and an efficiency rate per each method for 2 CWs of 0.2857. Further, result  4100  may show the modified method performs better because it can utilize the lower code rate. Further, the modified method may be flexible enough to take a large range of word sizes. 
     The IEEE 802.11ad method uses the 3/4 rate code, possibly to minimize zero padding. This strategy, however, may increase the overall code rates and thus may lead to lower performance depending on the message payload. The best choice of R is not clear for the general case and therefore the R is left as a system parameter so that best performance can be obtained for any payload size. 
     In examples, the low MCS was integrated with the existing MCSs in the BWT link level (LL) test bench (TB). Simulations were run to verify the performance. In order to use the existing SC-PHY header (or small modification of it), the performance of the modified low MCS, although expected to be better than MCS1, may still leave ˜2 dB margin with respect to the header performance. With this in mind three separate example performance simulations were run: SC-PHY header (the 802.11ad version is used, but we note the modified version will have performance at least as good as the 802.11ad version), MCS1, and Low MCS. 
     The simulation parameters were as follows: lx data sampling, AWGN channel, ideal SoP/EoSTF, no radio impairments, realistic CHEST and data detection, and PSDU length. While these simulations are idealistic, the relative performance of the different transmissions should not be overly distorted by these assumptions. 
       FIG. 42  is a diagram of an example comparison of multiple simulations. The following may be observed in result  4200 : Low MCS performs at about 2 dB better than MCS1 at 1% PER (this was expected due the lower effective coding rate), and the header performance may still be better than low MCS by ˜4 dB at 1% PER. This may meet the ˜2 dB margin, which may allow for the original SC-PHY header to be used unchanged. Result  4200  may also show one times sampling, an ideal SoP/EoSTF, realistic CHEST and no radio impairments. 
     The IEEE 802.11ad standard lists the receiver sensitivity for all SC-PHY MCSs. The receiver sensitivity for the modified low MCS may be calculated using the same performance criteria and degradation assumptions. The performance criterion is stated as “The PER shall be less than 1% for a PSDU length of 4096 octets using the input level defined at the antenna port.” The simulation specification also assumes a 5 dB example loss and a 10 dB noise factor. However, using the MCS1, the criteria may be compared to the performance obtained with the simulation parameters specified as above. The specified receiver sensitivity, S_p, for MCS1 is started at −68 dBm. Next, using a 1.76 GHz BW, the thermal noise power is calculated as 
         N   p =10 log( KTB )=−81.5 dBm.  Equation (20)
 
     Therefore the required SNR at the antenna port to be supported is: 
       SNR AP   =S   p   −N   p =−68+81.5=13.5 dB.  Equation (21)
 
     Next, assuming 15 dB of degradation, as specified above, the SNR at which the 1% PER requirement refers to is −1.5 dB: 
       SNR R =SNR AP −SNR D =−1.5 dB.  Equation (22)
 
     Result  4200  shows the 1% PER is at about −1.5 dB for MCS1 matching the specification. It may be assumed the operating environment used in the simulations is accurate. As shown in Result  4200 , the modified low MCS may perform ˜2 dB better so that the SNR R  at 1% PER is about −3.5 dB and 
       SNR AP =SNR R +SNR D =11.5 dB.  Equation (23)
 
     The receive sensitivity for the modified low MCS may now be calculated as: 
         S   P =SNR AP   +N   p =11.5−81.5=−70 dBm.  Equation (24)
 
     To achieve an example range of 350 m with the modified low MCS, a received power of −70 dBm at the antenna port (after any array gain and antenna losses) is required. There are multiple antenna configurations that may be used to achieve this. For the purposes of this example, the following assumptions are made: the same number of antenna elements are used for Tx and Rx; the elements are printed patch antennas with gain of 5.5 dBi; Equivalent Isotropically Radiated Power (EIRP) limited Federal Communications Commission (FFC) limit of 40 dBm; total Tx power is less than 10 dBm (European Union (EU) and other regional limits); molecular oxygen absorption is equal to 13 dB/km; rainfall losses is equal to 10 dB/Km (25 mm/Hr); and 3 dB a loss in Rx antenna (e.g., feed network). 
     With these assumptions, the low MCS link may be closed at 350 m with 100 Tx and Rx antenna elements, total Tx power equal to 10 dBm, EIRP equal to 35.5 dBm, Half Power Beamwidth (HPBW) equal to 11.5 deg (for square 10×10 arrangement). While these arrays are seemingly large, the following observations may be made. The 10 dBm Tx power limit is only for 60 GHz and outside of the US. The FCC permits higher power, and the EIPR limit is higher outside of the US and outside of 60 GHz. Techniques to scale antenna to thousands of elements may be feasible with mass production techniques. Most links may not need to support 350 m; 150 m is more typical. 
     Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a radio frequency transceiver for use in a WTRU, UE, terminal, base station, RNC, or any host computer.