Patent Publication Number: US-10764906-B2

Title: Silent period method and apparatus for dynamic spectrum management

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/287,381, filed Nov. 2, 2011, and issued as U.S. Pat. No. 9,839,045 on Dec. 5, 2017, which claims the benefit of U.S. provisional application No.61/410,528, filed Nov. 5, 2010, the contents of which are hereby incorporated by reference herein. 
    
    
     FIELD OF INVENTION 
     This application is related to wireless communications. 
     BACKGROUND 
     Local Wireless Network systems such as Institute of Electrical and Electronics Engineers (IEEE) 802.11 may operate in a predefined spectrum, such as, for example, a contiguous spectrum channel. In addition, the spectrum allowed for cellular licensed devices and devices operating in unlicensed bands such as industrial, scientific and medical (ISM), may not change over time. 
     In the United States, 408 MHz of spectrum from 54 MHz to 806 MHz may be allocated for television (TV). A portion of that spectrum may be redeveloped for commercial operations through auctions and for public safety applications. The remaining portion of the spectrum may remain dedicated for over-the-air TV operations. However, throughout the United States, portions of that spectrum resource may remain unused. The amount and exact frequency of unused spectrum may vary from location to location. These unused portions of spectrum may be referred to as TV White Space (TVWS). Because there are fewer TV stations located outside top metropolitan areas, most of the unoccupied TVWS spectrum is available in low population density or rural areas that tend to be underserved with other broadband options such as Digital Subscriber Line (DSL) or cable. 
     Each available TV channel may provide 6 MHz of spectrum capacity that may be used for broadband connectivity. TVWS may have large coverage areas due to long range propagation of signals at these frequencies. For example, a wireless local area network (WLAN) access point (AP) location operating in TVWS may provide coverage for an area of a few square miles. In contrast, wireless equipment such as IEEE 802.11b/gin may have an average coverage area of 150 square feet. 
     Aggregating multiple channels and using a primary channel was introduced in IEEE 802.11n and 802.11ac. 802.11n and 802.11ac to deal with continuous channels. When operating in TVWS, multiple continuous channels may not be available, and aggregation on non-continuous channels may be required. The concept of silent measurement periods was introduced in IEEE 802.11 for detection of radar in the 5 GHz bands. A silent period may be used in physical layer/medium access control layer (PHY/MAC) devices operating in TVWS. In both cases, these were based on sensing silent period information on the beacon. However, they do not address sensing silent period information over aggregated channels. 
     The sse of silent periods may lead to a loss of throughput and an increase of delay/jitter. When a set of stations are silenced for measurements, the outgoing traffic may be buffered during the silent period, resulting in an increase of buffer space requirements. In addition, the loss of throughput and introduction of delay/jitter could adversely affect certain applications which are being run on the network. 
     SUMMARY 
     Described herein is a silent period method and apparatus for dynamic spectrum management. The methods include configuration and coordination of silent periods across an aggregated channel in a wireless communication system. A silent period management entity (SPME) dynamically determines silent period schedules for channels based on system and device information and assigns a silent period duration and periodicity corresponding for each silent period. The SPME may reconfigure the silent period schedule based on at least one of system delay, system throughput, channel quality or channel management events. A silent period interpretation entity (SPIE) receives and implements the silent period schedule. The silent periods for the channels may be synchronized, independent, or set-synchronized. Interfaces for communicating between the SPME, SPIE, a channel management function, a medium access control (MAC) quality of service (QoS) entity, a sensing/capabilities database, a MAC layer management entity (MLME) and a wireless receive/transmit unit (WTRU) MLME are described herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         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. 2  is a diagram of an example four-channel silent period schedule; 
         FIG. 3  is a diagram of another example four-channel silent period schedule; 
         FIG. 4  is a diagram of example silent period configurations; 
         FIGS. 5A and 5B  are diagrams of two example silent period configurations; 
         FIG. 6  is a block diagram of an example silent period management architecture; 
         FIGS. 7A and 7B  are flow diagrams of an example system initialization and silent period initiation method; 
         FIG. 8  is a flow diagram of an example channel reconfiguration method; 
         FIGS. 9A and 9B  are flow diagrams of an example asynchronous silent period configuration method; 
         FIG. 10  is a flow diagram of an example quality of service (QoS) requirements change method; 
         FIG. 11  is a flow diagram of an example method for using messages at a DSM client or a station; 
         FIG. 12  is a diagram of example default silent period lengths and periodicities; 
         FIG. 13  is a diagram of an example silent period configuration; 
         FIG. 14  is a diagram of another example silent period configuration; 
         FIG. 15  is a diagram of another example silent period configuration; 
         FIG. 16  is a diagram of another example silent period configuration; 
         FIG. 17  is a flow diagram for an example probing approach for primary user (PU) detection; 
         FIG. 18  is a flow diagram for an example probing approach for secondary user (SU) detection; 
         FIG. 19  is a diagram of an example message format; 
         FIGS. 20A, 20B and 20C  are examples of silent period intervals relative to beacon intervals; 
         FIG. 21  is a diagram of an example placement of silent periods with traffic indication map (TIM) and delivery traffic indication message (DTIM) times; 
         FIG. 22  is a diagram of an example station transmission pattern; 
         FIG. 23  is a diagram of an example channel independent silent period; 
         FIG. 24  is a diagram of another example channel independent silent period; and 
         FIG. 25  is an example call flow for asynchronous silent period. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Described herein are example communication systems that may be applicable and may be used with the description herein below. Other communication systems may also be used. 
       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 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. 
       FIG. 1C  is a system diagram of the RAN  104  and the core network  106  according to an embodiment. As noted above, the RAN  104  may employ an E-UTRA radio technology to communicate with the WTRUs  102   a ,  102   b ,  102   c  over the air interface  116 . The RAN  104  may also be in communication with the core network  106 . 
     The RAN  104  may include eNode-Bs  140   a ,  140   b ,  140   c , though it will be appreciated that the RAN  104  may include any number of eNode-Bs while remaining consistent with an embodiment. The eNode-Bs  140   a ,  140   b ,  140   c  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 eNode-Bs  140   a ,  140   b ,  140   c  may implement MIMO technology. Thus, the eNode-B  140   a , for example, may use multiple antennas to transmit wireless signals to, and receive wireless signals from, the WTRU  102   a.    
     Each of the eNode-Bs  140   a ,  140   b ,  140   c  may be associated with a particular cell (not shown) and may be configured to handle radio resource management decisions, handover decisions, scheduling of users in the uplink and/or downlink, and the like. As shown in  FIG. 1C , the eNode-Bs  140   a ,  140   b ,  140   c  may communicate with one another over an X2 interface. 
     The core network  106  shown in  FIG. 1C  may include a mobility management gateway (MME)  142 , a serving gateway  144 , and a packet data network (PDN) gateway  146 . 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 MME  142  may be connected to each of the eNode-Bs  142   a ,  142   b ,  142   c  in the RAN  104  via an S1 interface and may serve as a control node. For example, the MME  142  may be responsible for authenticating users of the WTRUs  102   a ,  102   b ,  102   c , bearer activation/deactivation, selecting a particular serving gateway during an initial attach of the WTRUs  102   a ,  102   b ,  102   c , and the like. The MME  142  may also provide a control plane function for switching between the RAN  104  and other RANs (not shown) that employ other radio technologies, such as GSM or WCDMA. 
     The serving gateway  144  may be connected to each of the eNode Bs  140   a ,  140   b ,  140   c  in the RAN  104  via the S1 interface. The serving gateway  144  may generally route and forward user data packets to/from the WTRUs  102   a ,  102   b ,  102   c . The serving gateway  144  may also perform other functions, such as anchoring user planes during inter-eNode B handovers, triggering paging when downlink data is available for the WTRUs  102   a ,  102   b ,  102   c , managing and storing contexts of the WTRUs  102   a ,  102   b ,  102   c , and the like. 
     The serving gateway  144  may also be connected to the PDN gateway  146 , which 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. An access router (AR)  150  of a wireless local area network (WLAN)  155  may be in communication with the Internet  110 . The AR  150  may facilitate communications between APs  160   a ,  160   b , and  160   c . The APs  160   a ,  160   b , and  160   c  may be in communication with STAs  170   a ,  170   b , and  170   c.    
     The core network  106  may facilitate communications with other networks. For example, the core network  106  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. For example, the core network  106  may include, or may communicate with, an IP gateway (e.g., an IP multimedia subsystem (IMS) server) that serves as an interface between the core network  106  and the PSTN  108 . In addition, the core network  106  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. 
     The description herein may use the following terms and may have the following definitions in addition to or that may supplement those used in the art. A DSM system may refer to the system comprising one (or more) DSM engines controlling and assisting various local networks and direct links. A DSM client may refer to a device that has a communication link to the DSM engine and may be part of a local network or a direct link. A DSM engine may be an entity responsible for spectrum management as well as coordination and management of local networks and direct links. A DSM link may refer to a communication link between DSM engine and DSM client, providing control plane and user plane functionality. A direct link may refer to a link between two dynamic spectrum management (DSM) clients. Operating channel(s) may be channel(s) chosen for the DSM communication links. An attachment may refer to the process by which a DSM client discovers the DSM operating channel, synchronizes to this channel, associates with the AP and informs the DSM engine of its presence and its capabilities. Discovery Process may refer to a process by which a DSM client finds the operating channel of the DSM engine, (scans to find the control channel and synchronizes to the DSM). 
     The descriptions herein may refer to television white space (TVWS) as an example of an opportunistic bandwidth or opportunistic frequency band. The same description may apply for operation in any opportunistic frequency bands where devices may operate opportunistically when certain defined priority users (primary users) are not operating. In addition, a database of priority users or primary users for an opportunistic band may be maintained in a database. For operation in TVWS, this database may be referred to as the TVWS database. However, operation with a similar database may be possible in any opportunistic band. Other non-limiting examples of opportunistic bands, opportunistic bandwidth or opportunistic frequency band may include unlicensed bands, leased bands or sublicensed bands. 
     An enabling station may refer to a station that has the authority to control when and how a dependent station may operate. An enabling station communicates an enabling signal, to its dependants, over the air. The enabling station may correspond to a Master (or Mode II) device in Federal Communications Commission (FCC) nomenclature. In the above context, “registered” may mean that the station has provided the necessary information to TVWS database, (e.g. FCC Id, location, manufacturer information, and the like). 
     Geo-location capability may refer to the capability of a TVWS device to determine its geographic coordinates within the level of accuracy, such as 50 meters, as a non-limiting example. 
     Industrial, Scientific and Medical (ISM) bands may refer to frequency bands open to unlicensed operation, governed by Part 15 Subpart B FCC rules in the US. For example, 902-928 MHz Region 2 only, 2.400-2.500 GHz, 5.725-5.875 GHz. 
     A Mode I device may be a personal/portable TVWS device that does not use an internal geolocation capability and access to a TV bands database to obtain a list of available channels. A Mode I device may obtain a list of available channels on which it may operate from either a fixed TVWS device or a Mode II device. A Mode I device may not initiate a network of fixed and/or personal/portable TVWS devices nor may it provide a list of available channels to another Mode I device for operation by such device. A Mode II device may be a personal/portable TVWS device that uses an internal geo-location capability and access to a TVWS database, either through a direct connection to the Internet or through an indirect connection to the Internet by way of fixed TWWS device or another Mode II TVWS device, to obtain a list of available channels. A Mode II device may select a channel itself and initiate and operate as part of a network of TVWS devices, transmitting to and receiving from one or more fixed TVWS devices or personal/portable TVWS devices. A Mode II device may provide its list of available channels to a Mode I device for operation on by the Mode I device. A sensing only device may refer to a personal/portable TVWS device that uses spectrum sensing to determine a list of available channels. Sensing only devices may transmit on any available channels in the frequency bands 512-608 MHz (TV channels 21-36) and 614-698 MHz (TV channels 38-51), for example. 
     TVWS bands may refer to TV channels, (in the VHF (54˜72, 76˜88, 174˜216 MHz) and UHF (470˜698 Mhz) bands), where regulatory authorities permit operation by unlicensed devices. Personal/portable devices which include Mode I, Mode II and sensing only devices, may transmit on available channels in the frequency bands 512-608 MHz (TV channels 21-36) and 614-698 MHz (TV channels 38-51). A primary user (PU) may refer to the incumbent user of a TVWS channel. 
     A method and apparatus may be used for configuring silent periods across aggregated channels in a managed WLAN system. The use of silent periods may be necessary for devices that perform sensing in order to utilize unlicensed spectrum in the TVWS bands without adversely affecting the primary users of these bands. Silent periods may also be used to determine the amount of interference on a TVWS band that may be caused by other secondary users outside of the managed system that may be utilizing the same channel. However, silent periods may result in a reduction of the throughput over the channel. Moreover, a silent period may result in a delay in traffic that may affect some time sensitive applications such as voice-over-Internet Protocol (VoIP). 
     Another issue that may exist with configuring silent periods in the context of multiple channels is how to ensure that out-of-band interference does not affect sensing performed by hardware (HW) that is co-located or in close proximity of the AP or stations that may be involved in transmission of the managed system. In a system that uses channel aggregation, silencing all channels simultaneously during each silent period may be performed to reduce interference. However, this strategy may result in significant throughput losses and may not be necessary depending on the type of channel that needs to be sensed, the location radio frequency (RF) properties of the sensing HW, and the managed communication devices. 
     Efficient configuration of these silent periods may be needed in a system using aggregated channels in order to maintain the throughput gains achieved by using aggregation. Silent periods may be configured on each of the individual physical (PHY) channels that may be used by the medium access control (MAC) aggregation scheme. The configuration of these silent periods may depend on multiple factors such as sensing requirements, knowledge of which primary users each of the channels are reserved for, and location and type of sensing radio HW. 
     Once silent periods have been efficiently configured, they may need to be coordinated across all nodes controlled by a central entity coordinating the sensing and silent period configuration. This coordination may require robust communication of the silent period to avoid having stations miss the silent period and result in degraded sensing results. Since a carrier sense multiple access (CSMA) system may incur some message loss, a method and apparatus may be used for ensuring that stations that miss a silent period indication do not adversely affect sensing performance. 
     Described herein are methods and apparatus for silent period configuration and coordination. The embodiments described herein may use both periodic and asynchronous silent periods. In order to schedule periodic silent periods over a set of aggregated channels, while maintaining channel throughput despite the presence of silent time, the silent periods may be scheduled in a non-synchronized fashion when possible. This may ensure that there is at least one channel to maintain the channel traffic on the aggregated channel link. 
     The description herein may use a certain number of channels for illustration purposes only. The examples and embodiments are not limited to, for example 4 channels, and may be applicable to N channels. Although TVWS may be used for illustration purposes, the methods are further applicable to any form of opportunistic spectrum where sensing through silent periods may be required. 
     The silent period is applicable to sensing for detection of primary users and sensing for measurement of other secondary systems for coexistence purposes. 
       FIG. 2  shows an example case with four channels and a channel acting as primary channel. Channel 1 may be the primary channel  205  during the majority of the time due to the quality of this channel as compared to channels 2, 3 and 4. Channel 2 may become the primary channel  210  during silent time periods  215  allocated to channel 1.  FIG. 3  shows another example where the choice of a primary channel  305  may be independent of the quality of the four channels. The role of the primary channel may change in a round-robin fashion based on a silent period schedule  310 , and may result in a scheme where the number of primary channel switches may be minimized. 
     Other examples for primary channel selection during the silent periods, such as random selection, may also be possible. Although  FIGS. 2 and 3  show the same silent period interval or periodicity across the four channels, a system may manage channels that have different sensing requirements, and therefore a different amount of silent time in each channel. In this case, silent periods may be scheduled in a channel-independent fashion. The scheduling decisions, including the choice of the alternate primary channel to be used and the use of channel independent silent periods, may be made by a logical entity, such as a Silent Period Management Entity. 
     A channel independent silent period may allow skewing of silent periods on different channels so that there may be at least one channel in the aggregated channel set that may be used by the DSM system at any given time rather than making all channels unusable at the same time. This may benefit transmission scenarios where the application is sensitive to a delay and also may avoid the scenario where the DSM engine may not be able to send control messages for a fixed period of time. 
     The channel independent silent period may allow tailoring of the silent period duration on each channel based on the channel type. For example, if one channel has a larger silent period duty cycle requirement than all the other channels, the other channels may not need to be disadvantaged by this as they may maintain their own channel duty cycle requirements, if possible. 
     The potential for scheduling silent periods in a channel-independent fashion, either on all channels or a subset of channels, may depend on whether the out-of-band interference for channels being utilized by the managed system will cause degradation in performance in the sensing of channels when the silent period is scheduled on those channels. Since this may depend on a number of factors, such as type of sensing HW, out-of-channel and out-of-band filtering characteristics of the devices in the managed system, type of sensing to be performed, and maximum transmit power of the stations utilizing the channels in the managed systems, this information may be made available to the Silent Period Management Entity to determine the schedule. Rather than using a fixed schedule to reduce out-of-band interference, the Silent Period Management Entity may dynamically change the schedule to create one or more channel-independent silent periods over the maximum number of channels. 
     In addition to the use of non-synchronized and channel-independent silent periods, throughput and delay optimizations may be achieved by modifying the silent period schedule for periodic silent periods based on real-time monitoring of the channel quality. This method may be used in a single channel example as well as in aggregated channels. This method is described herein the context of an aggregated channel system, however, the same method may be applied to a system that uses a single channel (non-aggregated) scheme. 
     Selection of a silent period duration and periodicity may be driven by requirements on the amount of time needed to perform accurate sensing. This sensing may provide detection of primary users, or it may obtain some metric of the channel quality that may be used to dynamically select the best channels available from the TVWS. 
     In general, a required silent period duty cycle may be associated with each channel and this duty cycle may be derived from the silent period requirements of each channel. A duty cycle requirement may be specified by giving the amount of silent time, x, per duty cycle interval, y, and may be referred to as an x/y requirement specification. For a given duty cycle specification, there may be multiple ways to satisfy these requirements by changing the duration and periodicity of the silent period on a specific channel. 
       FIG. 4  shows an example duty cycle requirement  400  of 2 ms/100 ms on a specific channel. The 2 ms of silent time duration  405  may be allocated in a single silent period over the 100 ms duty cycle interval  410 . In example duty cycle requirement  450 , 4 silent periods of 500 μs  455  may be distributed over a duty cycle interval  460 , resulting in a periodicity of 50 ms for the silent periods. A tradeoff between throughput and delay/jitter of the resulting traffic may be expected based on selection of either of the two schedules over the other. Stations may interrupt transmission at a specific time. This action may reduce the throughput, not only due to the lack of transmission during the silent period itself, but also in the stations preparing for a silent period. A silent period in a CSMA system may be scheduled at a fixed time. Some bandwidth loss may be incurred, both prior to and following the silent period. This bandwidth loss may be due to abstaining from transmission of a packet if the acknowledgement (ACK) is not received prior to the start of a silent period, or for re-accessing the medium using CSMA following the silent period. 
     For fixed duty cycle requirements, when silent periods are chosen with a longer duration and longer periodicity, (for example duty cycle requirement  400  in  FIG. 4 ), traffic delay/jitter may be sacrificed for better throughput, since the number of silent periods may be reduced over a fixed interval. When shorter silent periods are chosen and distributed over the same interval, the traffic delay/jitter caused by the silent period may be reduced. The throughput compared to duty cycle requirement  400  in  FIG. 4 , however, may be reduced as a result of increased channel usage reduction from switching into and out of a silent period. As a result, depending on the specific quality of service (QoS) requirement at a specific time, a different silent period configuration may be desirable over another. 
     A method and apparatus may be used to dynamically tailor the silent period configuration for a given duty cycle requirement to ensure that the QoS on the channels that are utilized may be satisfied in the best case. As a result, for traffic requiring low latency/jitter, silent periods that are in line with duty cycle requirement  450  may be used. In the case where the QoS requirements may dictate the need for maximum throughput, silent periods that are in line with example 1 may be used. The silent period configuration may therefore be changed dynamically with time based on changing one or more QoS requirements of the traffic utilizing each of the channels. The QoS may also be involved in the scheduling of silent period duration in asynchronous silent periods by dictating the maximum silent period duration of an asynchronous silent period. 
     The method and apparatus may be used to coordinate the silent periods with another station through the transmission of silent period information in a beacon. As an aggregated beacon may be employed, the silent period information may be transmitted in the aggregated beacon in order to improve robustness and avoid the scenario where a station may miss the notification of a silent period due to momentary fading. In addition, since the beacon may be missed by one or more stations due to multipath issues, collisions, and hidden node problems, a beacon dependant transmission may be implemented into the system to avoid these issues. This may require all stations that do not properly receive the beacon during a specific beacon interval to abstain from transmitting until the next beacon is received. Since the silent periods start times may be relative to the beacon times, knowledge of the exact timing of a silent period start time by each station may be dependent on the reception of the beacon that immediately precedes it. A station that does not receive the beacon may be forced to be silent during the beacon interval until the next beacon is received. This may guarantee that all stations will be silent during the silent period scheduled by the central entity. 
     The method and apparatus may also be used for providing efficient silent period configuration over an aggregated channel system for the DSM system. The method and apparatus may, however, be applied to a system with any architecture by assigning the logical entities described herein to different locations. 
     A number of assumptions may be made to illustrate the algorithm and messaging involved in the method and apparatus described herein. These assumptions should not limit the use of the method and apparatus in a system that may not use these same assumptions. The assumptions may include: 1) the use of up to 4 channels in the aggregation scheme, (in order to illustrate the scheduling examples); 2) limitation to two potential primary users—wireless microphone and digital television (DTV); and 3) a transmit radio for all devices in the DSM system that covers the TVWS using two separate wideband digital radio boards where one board may cover the lower band of the TVWS and another board may cover the upper band of the TVWS. Each board may have strong out-of-band interference rejection, however, out-of-channel interference rejection may only meet the requirements of a TVWS transmitter. 
     The silent period schedule may be tied to QoS. As stated hereinabove, there may be a tradeoff between delay and throughput that relates silent period scheduling to QoS. Periodic spectrum sensing may be convenient for practical implementation. In periodic spectrum sensing, in every time interval Tp, defined as the sensing period periodicity, a spectrum sensing algorithm may run to full completion to make a decision on the presence or absence of a primary spectrum user. A sensing duty cycle may be the ratio of the total time spent on spectrum sensing to the time interval Tp. For energy detection based spectrum sensing algorithms, there may be a minimum number of samples needed for a performance target. Since each sample corresponds to a sampling interval, the resulting total sensing time may be fixed. 
     The value of Tp may be determined by the spectrum access policies and the DSM system design, and may be fixed in practical implementations. The spectrum access policies may impose a requirement on the response time for the DSM system, and this requirement may dictate how often spectrum sensing is performed. For example, it may be required that a DSM system respond to a wireless microphone in less than 2 seconds. The response time may include the time for both spectrum sensing and the evacuation of the DSM system from the channel being used by the wireless microphone. In the DSM system design, if a fixed amount of time for the system evacuation is allocated, then the time budget left for spectrum sensing, i.e., Tp, may also be fixed. 
     The sensing time may be segregated into multiple time intervals while keeping the same sensing duty cycle. Each contiguous time interval for sensing may be termed a sensing duration and may be denoted as Td. Such segregation of the sensing time may offer a way to configure the sensing period.  FIGS. 5A and 5B  illustrate example relationships between Tp  500  and Td  505 , and sensing period configuration, where Tp=T′p ( 510 ) and Td=2*T′d ( 515 ). In  FIG. 5A , the sensing duty cycle=Td/Tp, and in  FIG. 5B , the sensing duty cycle=2*T′d/T′p=Td/Tp. 
     Td may be configured based on the sensing duty cycle and a fixed value for Tp. The number of Td&#39;s within a Tp may be configured in a similar fashion. Such configurations may give rise to a tradeoff between delay and throughput. Assuming uniform packet arrivals and negligible packet lengths, the average packet delay may be proportional to Td. Thus, as Td decreases, the average packet delay may decrease. On the other hand, as Td decreases, when the effects of packet lengths are considered, the fraction of time that may be useful for data transmission decreases. This decrease may be due to a contiguous time interval available for data transmission, shown as an un-shaded time interval in  FIG. 5A , that may not be able to fit multiple frames or transmission opportunities (TXOPs), and the time wasted as such may account for a larger portion as Td decreases. In addition, as Td decreases, the number of Td&#39;s within a Tp may increase. Since there may be a new round of contention after every sensing operation of duration Td, there may be more contention, which may further reduce the throughput. 
     There may be a lower bound on the possible values for Td, and it may be denoted as Td_min. The lower bound may occur in some applications when the sensing algorithm needs a minimum number of contiguous samples in order to accomplish the sensing task, for example, the duration of a pilot sequence used by the sensing algorithm. 
     In general, a silent period management entity (SPME) may be the main controller of silent periods that are used within the DSM system. This entity may be a medium access control (MAC) layer management entity that may be added to IEEE 802.11-based systems to manage the scheduling of silent periods, whether or not that system employs channel aggregation. 
       FIG. 6  shows example DSM system architecture  600  including an access point (AP) architecture  605  and a station (STA) architecture  610 . In particular,  FIG. 6  shows example architecture and basic interfaces between the SPMEs and MAC layer components in the AP  605  and STA  610 . Silent periods may be managed by each AP. For a DSM system that contains multiple APs, the SPME for each AP may contain an additional interface for coordination of silent periods across the multiple APs. 
     The AP  605  may include a SPME  615  connected to a sensing/capability database  620 , a sensing toolbox  625 , a channel management function (CMF)  630 , a MAC QoS entity  635  and a silent period interpretation entity (SPIE)  640 . The SPIE  640  may be connected to a MAC buffering and control entity  645 , which in turn may be connected to a MAC layer/sublayer management entity (MLME)  650 . The STA  610  may include a SPIE  655  which may be connected to a MAC buffering and control entity  660  and a MLME  665 . The MAC buffering and control entity  660  may be connected to the MLME  665 . The AP  605  and STA  610  may be connected through MLME  650  and MLME  665 . 
     The main components in the DSM system  600  are described herein. Each of the entities except for the sensing toolbox/processor  625  and the CMF  630 , may be MAC-layer management functions. They may therefore be integrated into a more complete MLME that contains silent period management functionality. In the architecture shown in  FIG. 6 , these entities may be separate from the MLME  650  to illustrate how silent period management may be added to an existing IEEE 802.11-based MLME. 
     The SPME  615  may be the main entity at the AP  305  that determines the length and scheduling of the silent periods on each channel in a dynamic fashion. It may handle both periodic and asynchronous silent periods. The roles of this entity may be: 1) select between channel independent and channel synchronized silent periods based on interference information from the capabilities database  620  and the maximum power transmitted by each station; 2) assign a silent period duration and periodicity for silent periods on each channel based on QoS information and duty cycle requirements; 3) jointly manage the scheduling of silent periods across the four aggregated channels in an intelligent fashion; and 4) notify the SPIE  640  of a change in the silent period schedule. 
     The SPIE  640  may ensure that the STA  610  adheres to the rules and timings required based on the silent period messages that are received at the STA  610  and interpreted by the STA  610  MLME  665 . The SPIE  640  may receive at the AP  605  the silent period schedule derived by the SPME  615  and may implement the schedule at the MAC layer  635 . The SPIE  640  tasks may include instructing the MAC buffering and control entity  645  how to buffer, reorder, and packetize frames in order to respect upcoming silent periods defined in the schedule. At the STA  610 , the SPIE  655  may receive the information from the beacon as interpreted by the MLME  665 . The SPIE  655  may instruct the MAC buffering and control entity  660  in the same way in order to implement the silent period from the station&#39;s perspective. 
     The sensing toolbox/processor  625  may coordinate the sensing of the utilized channels for determining the presence of interference or primary users (as applicable). It may control the sensing HW for any dedicated sensing boards, or sensing HW that may be located at the DSM clients. 
     The MAC QoS  635  may provide QoS services to the system  600  at the MAC layer. Its role, relative to silent periods, may be to provide inputs on the maximum allowable silent period duration, (for asynchronous silent periods), and to dynamically maintain the best efficiency for the silent periods in terms of the traffic type and QoS instructed by the higher layers. 
     The MAC buffering and control entity  645  and  660  may provide transmit buffering services, such as reordering, frame size adjustment based on channel properties and the like for the aggregated channel MAC. 
     The MLME  650  and  665  may be a standard MAC layer management entity as in IEEE 802.11-based systems, and may include enhancements for the support of silent periods as described herein. Some enhancements may involve the ability to interact with a MAC layer interpretation entity (not shown) and a MAC buffering and control entity, such as  645  and  660 . 
     The CMF  630  may be the main channel selection and channel management entity in a DSM engine. 
     The sensing/capability database  620  may be the main repository for device capabilities. For the purposes of silent period, the information of interest in database  620  may be the sensing capabilities of the radio frequency sensing board (RFSB) and the out-of-band and out-of-channel interference properties of the AP and devices in the DSM system. This information may be entered into the sensing/capability database  620  during the attach procedure. It is then used by the SPME  615  to schedule channel-independent silent periods where possible. 
     Described herein are the different messages that may be exchanged across each interface in the architecture of  FIG. 6 , as well as the contents of these messages. The S1 interface may be used to indicate the channels currently used for aggregation by the AP  605  in the DSM system  600  and any properties of these channels required by the SPME  615  for determining the silent period schedule. It may also be used to communicate the silent period duty cycle requirements to the SPME  615 . Table 1 shows some examples of S1 interface messages. 
     
       
         
           
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
             
            
               
                 Message 
                   
                   
               
               
                 Name 
                 Originator 
                 Description 
               
               
                   
               
               
                 CHANNEL_CONFIG 
                 CMF 
                 Sent by the CMF to 
               
               
                   
                   
                 indicate the channels to be used by 
               
               
                   
                   
                 the AP for communication with the 
               
               
                   
                   
                 associated stations/clients. A 
               
               
                   
                   
                 CHANNEL_CONFIG may also be 
               
               
                   
                   
                 used to reconfigure or remove a 
               
               
                   
                   
                 channel from the channels to be 
               
               
                   
                   
                 aggregated 
               
               
                 CHANNEL_CONFIG_CONF 
                 Silent 
                 Confirms a 
               
               
                   
                 Period 
                 CHANNEL_CONFIG message 
               
               
                   
                 Management 
               
               
                   
                 Entity 
               
               
                 SET_SILENT_PERIOD_REQUIREMENTS 
                 CMF 
                 Sets the required duty 
               
               
                   
                   
                 cycle for periodic silent periods 
               
               
                   
                   
                 when determining the presence of 
               
               
                   
                   
                 DTV, or wireless microphone, as 
               
               
                   
                   
                 well as the current duty cycle 
               
               
                   
                   
                 needs for sensing for channel 
               
               
                   
                   
                 quality determination. These 
               
               
                   
                   
                 requirements may be dependent 
               
               
                   
                   
                 on the sensing hardware 
               
               
                   
                   
                 capabilities available to the 
               
               
                   
                   
                 sensing processor, such as the 
               
               
                   
                   
                 number of devices performing 
               
               
                   
                   
                 sensing, the processing power of 
               
               
                   
                   
                 each device, etc. This information 
               
               
                   
                   
                 may be obtained from the sensing 
               
               
                   
                   
                 processor through message 
               
               
                   
                   
                 communication, or may be 
               
               
                   
                   
                 managed by the CMF. 
               
               
                 SET_SILENT_PERIOD_REQUIREMENTS_CONF 
                 Silent 
                 Confirms the 
               
               
                   
                 Period 
                 SET_SILENT_PERIOD_REQUIREMENTS_CONF 
               
               
                   
                 Management 
                   
               
               
                   
                 Entity 
               
               
                   
               
            
           
           
               
               
               
            
               
                   
                 Message 
                   
               
               
                   
                 Name 
                 Message Contents 
               
               
                   
                   
               
               
                   
                 CHANNEL_CONFIG 
                 numChannel - 
               
               
                   
                   
                 Number of channels 
               
               
                   
                   
                 freqs - List of channels 
               
               
                   
                   
                 and their associated frequency 
               
               
                   
                   
                 range 
               
               
                   
                   
                 EIRP - List of 
               
               
                   
                   
                 maximum EIRP that can be 
               
               
                   
                   
                 used on each channel 
               
               
                   
                   
                 dbInformation - 
               
               
                   
                   
                 Enumeration type indicating 
               
               
                   
                   
                 the information obtained about 
               
               
                   
                   
                 this channel from the TVWS 
               
               
                   
                   
                 database (a channel may be 
               
               
                   
                   
                 free, reserved for DTV, reserved 
               
               
                   
                   
                 for wireless microphone, or 
               
               
                   
                   
                 reserved for both) 
               
               
                   
                 CHANNEL_CONFIG_CONF 
                 statusCode - Success 
               
               
                   
                   
                 or reason code for failure 
               
               
                   
                 SET_SILENT_PERIOD_REQUIREMENTS 
                 dtvDetectionCycle - 
               
               
                   
                   
                 Required duty cycle needed for 
               
               
                   
                   
                 accurate DTV detection within 
               
               
                   
                   
                 timing requirements (in duty 
               
               
                   
                   
                 cycle of x ms per 100 ms, or x ms 
               
               
                   
                   
                 per interval of 100 ms). 
               
               
                   
                   
                 wmDetectionCycle - 
               
               
                   
                   
                 Required duty cycle needed for 
               
               
                   
                   
                 accurate wireless microphone 
               
               
                   
                   
                 detection within timing 
               
               
                   
                   
                 requirements (in duty cycle of x 
               
               
                   
                   
                 ms per 100 ms, or x ms per 
               
               
                   
                   
                 interval of 100 ms). 
               
               
                   
                   
                 channelQualDutyCycle - 
               
               
                   
                   
                 Required duty cycle needed for 
               
               
                   
                   
                 channel quality measurements 
               
               
                   
                   
                 (in duty cycle of x ms per 
               
               
                   
                   
                 100 ms, or x ms per interval of 
               
               
                   
                   
                 100 ms). 
               
               
                   
                 SET_SILENT_PERIOD_REQUIREMENTS_CONF 
                 statusCode - Success 
               
               
                   
                   
                 or a reason code explaining the 
               
               
                   
                   
                 failure. 
               
               
                   
                   
               
            
           
         
       
     
     The S2 interface may be the interface used to communicate the need for asynchronous silent periods, (as determined by the sensing processor  625 ) to the SPME  615 . Table 2 shows some examples of S2 interface messages. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 2 
               
               
                   
               
               
                 Message 
                   
                   
                   
               
               
                 Name 
                 Originator 
                 Description 
                 Message Contents 
               
               
                   
               
             
            
               
                 ASYNCHRONOUS_SILENT_PERIOD_REQ 
                 Sensing 
                 Message from the 
                 channelIDs - List of 
               
               
                   
                 Processor 
                 Sensing Processor to 
                 channel(s) on which 
               
               
                   
                   
                 the Silent Period 
                 sensing needs to be 
               
               
                   
                   
                 Management Entity to 
                 performed 
               
               
                   
                   
                 request an 
                 requestedDuration - 
               
               
                   
                   
                 asynchronous silent 
                 Silent period length 
               
               
                   
                   
                 period. 
                 requested by the 
               
               
                   
                   
                   
                 sensing processor 
               
               
                 ASYNCHRONOUS_SILENT_PERIOD_CONF 
                 Silent Period 
                 Message confirming 
                 numDistinctSilentPeriod - 
               
               
                   
                 Management 
                 the silent period 
                 The number of 
               
               
                   
                 Entity 
                 request and indicating 
                 distinct silent periods 
               
               
                   
                   
                 the number of distinct 
                 into which 
               
               
                   
                   
                 asynchronous silent 
                 requestedDuration 
               
               
                   
                   
                 periods into which the 
                 has been split (a 
               
               
                   
                   
                 requestedDuration has 
                 value of 0 indicates a 
               
               
                   
                   
                 been divided. The 
                 failure to schedule an 
               
               
                   
                   
                 actual silent period 
                 asynchronous silent 
               
               
                   
                   
                 may start with the 
                 period) 
               
               
                   
                   
                 SILENT_PERIOD_START_MESSAGE 
                 duration - Duration 
               
               
                   
                   
                 sent 
                 of each distinct silent 
               
               
                   
                   
                 on the S8 interface 
                 period. 
               
               
                   
               
            
           
         
       
     
     The S3 interface may be used to communicate the silent period schedule and dynamic changes in the schedule to the SPIE  640  that may implement this schedule in the MAC layer. Due to the assumption of a dual-band radio for all devices, the contents of the messages may be specific to this assumption. For a system with general radio assumptions, the message contents may change. Table 3 shows some examples of S3 interface messages. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 3 
               
               
                   
               
               
                 Message Name 
                 Originator 
                 Description 
                 Message Contents 
               
               
                   
               
             
            
               
                 PERIODIC_SCHEDULE_CONFIGURE 
                 Silent Period 
                 Schedule of periodic 
                 group1SilentRange - 
               
               
                   
                 Management 
                 silent periods to be 
                 Range of frequencies that 
               
               
                   
                 Entity 
                 implemented on the four 
                 can be sensed for group 1 
               
               
                   
                   
                 channels as decided by 
                 (to be passed to the 
               
               
                   
                   
                 the Silent Period 
                 sensing processor) 
               
               
                   
                   
                 Management Entity. 
                 group2SilentRange - 
               
               
                   
                   
                 This message may be 
                 Range of frequencies that 
               
               
                   
                   
                 sent each time a new 
                 can be sensed for group 2 
               
               
                   
                   
                 silent period 
                 (to be passed to the 
               
               
                   
                   
                 configuration is 
                 sensing processor) 
               
               
                   
                   
                 determined by the Silent 
                 group1Duration - 
               
               
                   
                   
                 Period Management 
                 Duration of silent period 
               
               
                   
                   
                 Entity. 
                 for channels in group1. 
               
               
                   
                   
                   
                 This may be a list of 
               
               
                   
                   
                   
                 durations, in the case 
               
               
                   
                   
                   
                 where multiple silent 
               
               
                   
                   
                   
                 periods may be required 
               
               
                   
                   
                   
                 on each channel (see 
               
               
                   
                   
                   
                 scheduling examples) 
               
               
                   
                   
                   
                 group1Periodicity - 
               
               
                   
                   
                   
                 Periodicity of silent period 
               
               
                   
                   
                   
                 for channels in group 1. 
               
               
                   
                   
                   
                 This may be a list of 
               
               
                   
                   
                   
                 periodicities, in the case 
               
               
                   
                   
                   
                 where multiple silent 
               
               
                   
                   
                   
                 periods may be required 
               
               
                   
                   
                   
                 on each channel (see 
               
               
                   
                   
                   
                 scheduling examples). 
               
               
                   
                   
                   
                 group2Duration - 
               
               
                   
                   
                   
                 Duration of silent period 
               
               
                   
                   
                   
                 in for channels in group 2 
               
               
                   
                   
                   
                 (empty if no channels in 
               
               
                   
                   
                   
                 group2). This may be a list 
               
               
                   
                   
                   
                 of durations, in the case 
               
               
                   
                   
                   
                 where multiple silent 
               
               
                   
                   
                   
                 periods may be required 
               
               
                   
                   
                   
                 on each channel (see 
               
               
                   
                   
                   
                 scheduling examples). 
               
               
                   
                   
                   
                 group2Periodicity - 
               
               
                   
                   
                   
                 Periodicity of silent period 
               
               
                   
                   
                   
                 for channels in group 2 
               
               
                   
                   
                   
                 (empty if no channels in 
               
               
                   
                   
                   
                 group 2). This may be a 
               
               
                   
                   
                   
                 list of periodicities, in the 
               
               
                   
                   
                   
                 case where multiple silent 
               
               
                   
                   
                   
                 periods may be required 
               
               
                   
                   
                   
                 on each channel (see 
               
               
                   
                   
                   
                 scheduling examples). 
               
               
                 ASYNCHRONOUS_SILENT_PERIOD_IND 
                   
                 This message indicates 
                 appliedGroups - Channel 
               
               
                   
                   
                 the immediate need to 
                 groups to which the 
               
               
                   
                   
                 configure an 
                 asynchronous silent period 
               
               
                   
                   
                 asynchronous silent 
                 applies 
               
               
                   
                   
                 period on one or more 
                 duration - Duration 
               
               
                   
                   
                 group. The Silent 
                 of each asynchronous 
               
               
                   
                   
                 Period Interpretation 
                 silent period in ms 
               
               
                   
                   
                 entity of the AP may 
                 numAsync - Number 
               
               
                   
                   
                 automatically suspend 
                 of asynchronous silent 
               
               
                   
                   
                 transmitting 
                 periods to send in a 
               
               
                   
                   
                 information concerning 
                 row on the 
               
               
                   
                   
                 the periodic silent period 
                 appliedGroups 
               
               
                   
                   
                 for this channel until 
                 timeSeparation - 
               
               
                   
                   
                 the asynchronous silent 
                 Separation in time 
               
               
                   
                   
                 period has been 
                 between 
               
               
                   
                   
                 completed. At that time, 
                 asynchronous silent 
               
               
                   
                   
                 the Silent Period 
                 periods 
               
               
                   
                   
                 Interpretation Entity 
               
               
                   
                   
                 may resume the regular 
               
               
                   
                   
                 periodic silent period 
               
               
                   
                   
                 from where they left off. 
               
               
                   
               
            
           
         
       
     
     The S4 interface may be used to limit the silent period durations based on the measured and targeted QoS. It may focus predominantly on limiting the length of the silent periods to ensure the end-to-end delay is limited over each channel. At system initialization, the default silent period duration may be configured while maintaining the required duty cycle. For example, the duty cycle may be satisfied with a single silent period. As clients join, the QoS may request the SPME  615  to decrease the duration, (increase the periodicity), of the silent periods. Table 4 shows some examples of S4 interface messages. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 4 
               
               
                   
               
               
                   
                   
                   
                 Message 
               
               
                 Message Name 
                 Originator 
                 Description 
                 Contents 
               
               
                   
               
             
            
               
                 DELAY_CHANGE_REQ 
                 MAC Layer 
                 Request message by the 
                 modifyType - 
               
               
                   
                 QoS 
                 MAC layer QoS block to 
                 Increase or 
               
               
                   
                   
                 reduce or increase the block 
                 decrease 
               
               
                   
                   
                 delay experienced by a 
                 channelList - 
               
               
                   
                   
                 specific channel(s) as a 
                 List of channel 
               
               
                   
                   
                 result of a silent period. For 
                 where delay may 
               
               
                   
                   
                 this design, each message 
                 be increased. 
               
               
                   
                   
                 may request an increase or 
               
               
                   
                   
                 decrease in the length of the 
               
               
                   
                   
                 silent periods by 50%. The 
               
               
                   
                   
                 result of the attempt may be 
               
               
                   
                   
                 communicated in the 
               
               
                   
                   
                 DELAY_CHANGE_RESP 
               
               
                 DELAY_CHANGE_RESP 
                 Silent Period 
                 Response to the 
                 statusCode - 
               
               
                   
                 Management 
                 DELAY_CHANGE_REQ 
                 Success or a 
               
               
                   
                 Entity 
                 indicating whether a change 
                 reason code 
               
               
                   
                   
                 in silent period 
                 explaining the 
               
               
                   
                   
                 configuration request could 
                 failure. 
               
               
                   
                   
                 be satisfied. 
               
               
                 SILENT_AMOUNT_CHANGE_REQ 
                 MAC Layer 
                 Request to change the 
                 modifyType - 
               
               
                   
                 QoS 
                 amount of silent time for a 
                 Increase or 
               
               
                   
                   
                 channel of type “Free”. This 
                 decrease 
               
               
                   
                   
                 message may not be applied 
                 channelList - 
               
               
                   
                   
                 to any channels where 
                 List of channel 
               
               
                   
                   
                 sensing for primary users is 
                 where delay may 
               
               
                   
                   
                 being performed, since these 
                 be increased. 
               
               
                   
                   
                 channels may keep the 
               
               
                   
                   
                 silent period duty cycle 
               
               
                   
                   
                 fixed. 
               
               
                 SILENT_AMOUNT_CHANGE_RESP 
                 Silent Period 
                 Response to the 
                 statusCode - 
               
               
                   
                 Management 
                 SILENT_AMOUNT_CHANGE_REQ 
                 Success or a 
               
               
                   
                 Entity 
                 indicating whether 
                 reason code 
               
               
                   
                   
                 a change in silent period 
                 explaining the 
               
               
                   
                   
                 configuration requested may 
                 failure. 
               
               
                   
                   
                 be satisfied. 
               
               
                 MAX_ALLOWABLE_ASYNC_DELAY_REQ 
                 Silent Period 
                 Sent by the Silent Period 
                 channelList - 
               
               
                   
                 Management 
                 Management Entity to 
                 List of channels 
               
               
                   
                 Entity 
                 obtain the maximum 
                 that require the 
               
               
                   
                   
                 allowable silent period 
                 silent period. 
               
               
                   
                   
                 duration for an 
               
               
                   
                   
                 asynchronous silent period 
               
               
                   
                   
                 requested by the sensing 
               
               
                   
                   
                 processor. 
               
               
                 MAX_ALLOWABLE_ASYNC_DELAY_RES 
                 MAC Layer 
                 Response to the 
                 maxDelayVal - 
               
               
                   
                 QoS 
                 MAX_ALLOWABLE_ASYNC_DELAY 
                 Maximum delay 
               
               
                   
                   
                   
                 in ms. 
               
               
                   
                   
                   
                 minSeparation - 
               
               
                   
                   
                   
                 Minimum 
               
               
                   
                   
                   
                 separation time 
               
               
                   
                   
                   
                 between 
               
               
                   
                   
                   
                 asynchronous 
               
               
                   
                   
                   
                 silent periods if 
               
               
                   
                   
                   
                 the requested 
               
               
                   
                   
                   
                 silent period is 
               
               
                   
                   
                   
                 split into 
               
               
                   
                   
                   
                 multiple pieces. 
               
               
                   
               
            
           
         
       
     
     The S5 interface may communicate the presence of a silent period and the required action to be taken by the Buffering and Control Entity in order to ensure data transmission on each of the aggregated channels may be maintained efficiently despite the presence of silent periods. This interface may exist both at the AP  605  and the STA  610  and is identical in each case. Table 5 shows some examples of S5 interface messages. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 5 
               
               
                   
               
               
                   
                   
                   
                 Message 
               
               
                 Message Name 
                 Originator 
                 Description 
                 Contents 
               
               
                   
               
             
            
               
                 SILENT_PERIOD_ARRIVAL 
                 Silent Period 
                 Notifies the 
                 duration - 
               
               
                   
                 Interpretation 
                 Buffering and 
                 Duration of the 
               
               
                   
                 Entity 
                 Control Entity 
                 upcoming silent 
               
               
                   
                   
                 of an upcoming 
                 period 
               
               
                   
                   
                 silent period 
                 timeExpected - 
               
               
                   
                   
                 that may 
                 Expected time 
               
               
                   
                   
                 require 
                 when the silent 
               
               
                   
                   
                 reordering 
                 period will occur 
               
               
                   
                   
                 and/or 
                 (this may be an 
               
               
                   
                   
                 modification of 
                 approximation 
               
               
                   
                   
                 frame 
                 since the MLME 
               
               
                   
                   
                 fragmentation 
                 may maintain 
               
               
                   
                   
                 to ensure 
                 the exact timing). 
               
               
                   
                   
                 buffers remain 
                 When a value of 
               
               
                   
                   
                 equal length. 
                 0 is sent, this 
               
               
                   
                   
                 This message 
                 means that the 
               
               
                   
                   
                 may be the 
                 silent period has 
               
               
                   
                   
                 same for the 
                 already begun. 
               
               
                   
                   
                 S5 interface on 
                 channelsAffected - 
               
               
                   
                   
                 the AP and the 
                 The list of PHY 
               
               
                   
                   
                 station. In the 
                 channels that 
               
               
                   
                   
                 case of an 
                 may be silenced. 
               
               
                   
                   
                 asynchronous 
               
               
                   
                   
                 silent period, 
               
               
                   
                   
                 the message 
               
               
                   
                   
                 may be sent 
               
               
                   
                   
                 with little or 
               
               
                   
                   
                 no advanced 
               
               
                   
                   
                 notice 
               
               
                   
                   
                 (depending on 
               
               
                   
                   
                 whether we are 
               
               
                   
                   
                 on the AP or 
               
               
                   
                   
                 station side 
               
               
                   
                   
                 respectively). 
               
               
                   
               
            
           
         
       
     
     The S6 interface may be used by the SPME  615  to obtain information about the sensing capabilities and transmit/receive (TX/RX) radio capabilities of the AP  605  and STAs  610  in the DSM system  600 . Using this information, the SPME  615  may determine which radio bands may be sensed simultaneously while normal data transmission is occurring on other bands. Table 6 shows some examples of S6 interface messages. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 6 
               
               
                   
               
               
                   
                   
                   
                 Message 
               
               
                 Message Name 
                 Originator 
                 Description 
                 Contents 
               
               
                   
               
             
            
               
                 GET_SENSING_RADIO_CAPABILITIES 
                 Silent Period 
                 Sent to request information 
                 None 
               
               
                   
                 Management Entity 
                 about the sensing radio 
               
               
                   
                   
                 capabilities and restrictions 
               
               
                   
                   
                 that may affect the silent 
               
               
                   
                   
                 period configurations 
               
               
                 SENSING_RADIO_GETCAPABILITIES 
                 Sensing/Capability 
                 Response to the 
                 group1Dependency 
               
               
                   
                 Database 
                 GET_SENSING_RADIO_CAPABILITIES 
                 Range - 
               
               
                   
                   
                 message 
                 Range of 
               
               
                   
                   
                   
                 channels in 
               
               
                   
                   
                   
                 the first 
               
               
                   
                   
                   
                 dependency 
               
               
                   
                   
                   
                 group 
               
               
                   
                   
                   
                 group2Dependency 
               
               
                   
                   
                   
                 Range - 
               
               
                   
                   
                   
                 Range of 
               
               
                   
                   
                   
                 channels in 
               
               
                   
                   
                   
                 the second 
               
               
                   
                   
                   
                 dependency 
               
               
                   
                   
                   
                 group. 
               
               
                   
               
            
           
         
       
     
     The S7 interface may include MLME service access point (SAP) primitives to implement the silent periods through beacon and control messages. At the AP  605 , the SPIE  640  may indicate to the MLME  650  the timing of the silent periods, (periodic and asynchronous), so that this timing may be incorporated appropriately in the beacon and control messages sent to the stations. At the station, the MLME  650  may interpret the beacon and control frames and send all silent period scheduling information to the SPIE  640 . Table 7 shows some examples of S7 interface messages. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 7 
               
               
                   
               
               
                   
                   
                   
                 Message 
               
               
                 Message Name 
                 Originator 
                 Description 
                 Contents 
               
               
                   
               
             
            
               
                 MLME_SILENT_SCHEDULE_CONFIGURE 
                 Silent Period 
                 This primitive 
                 channelGroup1 - 
               
               
                   
                 Interpretation 
                 may set up 
                 List of 
               
               
                   
                 Entity 
                 beacon 
                 channels 
               
               
                   
                   
                 information for 
                 associated with 
               
               
                   
                   
                 periodic silent 
                 the first 
               
               
                   
                   
                 periods in each of 
                 synchronous 
               
               
                   
                   
                 the channels. 
                 silent period. 
               
               
                   
                   
                   
                 This group may 
               
               
                   
                   
                   
                 be decided by 
               
               
                   
                   
                   
                 the Silent 
               
               
                   
                   
                   
                 Period 
               
               
                   
                   
                   
                 Management 
               
               
                   
                   
                   
                 Entity based on 
               
               
                   
                   
                   
                 several inputs 
               
               
                   
                   
                   
                 (see call flows) 
               
               
                   
                   
                   
                 channelGroup2 - 
               
               
                   
                   
                   
                 List of 
               
               
                   
                   
                   
                 channels (up to 
               
               
                   
                   
                   
                 3) associated 
               
               
                   
                   
                   
                 with the second 
               
               
                   
                   
                   
                 synchronous 
               
               
                   
                   
                   
                 silent period. 
               
               
                   
                   
                   
                 This group may 
               
               
                   
                   
                   
                 be empty. 
               
               
                 MLME_SILENT_PERIOD_START 
                 MLME 
                 Sent by the 
                 None 
               
               
                   
                   
                 MLME to 
               
               
                   
                   
                 indicate the exact 
               
               
                   
                   
                 starting time of a 
               
               
                   
                   
                 silent period. 
               
               
                 MLME_START_ASYNC_PERIOD 
                 Silent Period 
                 MAC layer 
                 duration - 
               
               
                   
                 Interpretation 
                 primitive that 
                 Required 
               
               
                   
                 Entity 
                 requests the 
                 duration of the 
               
               
                   
                   
                 MLME to start 
                 silent period 
               
               
                   
                   
                 an asynchronous 
                 moreFlag - 
               
               
                   
                   
                 silent period and 
                 Whether more 
               
               
                   
                   
                 consequently 
                 asynchronous 
               
               
                   
                   
                 suspend any 
                 silent periods 
               
               
                   
                   
                 synchronous 
                 are expected or 
               
               
                   
                   
                 silent periods 
                 if periodic silent 
               
               
                   
                   
                 that may be 
                 periods may be 
               
               
                   
                   
                 occurring on the 
                 rescheduled 
               
               
                   
                   
                 same frequency. 
                 following this 
               
               
                   
                   
                   
                 asynchronous 
               
               
                   
                   
                   
                 silent period. 
               
               
                   
                   
                   
                 phyChannels— 
               
               
                   
                   
                   
                 C List of PHY 
               
               
                   
                   
                   
                 channels on 
               
               
                   
                   
                   
                 which the 
               
               
                   
                   
                   
                 asynchronous 
               
               
                   
                   
                   
                 silent period 
               
               
                   
                   
                   
                 applies. 
               
               
                 MLME_QUIET_INFORMATION 
                 MLME 
                 This message 
                 The quiet 
               
               
                   
                   
                 may be used at 
                 information 
               
               
                   
                   
                 the station only. 
                 element on each 
               
               
                   
                   
                 It may send the 
                 of the channels 
               
               
                   
                   
                 quiet information 
                 may be received 
               
               
                   
                   
                 received in the 
                 (see section 
               
               
                   
                   
                 beacon to the 
                 TBD for 
               
               
                   
                   
                 Silent Period 
                 details). 
               
               
                   
                   
                 Interpretation 
               
               
                   
                   
                 Entity for 
               
               
                   
                   
                 management of 
               
               
                   
                   
                 the timing of the 
               
               
                   
                   
                 silent periods. 
               
               
                   
               
            
           
         
       
     
     The S8 interface may carry the timing information about the silent periods, (exact start time, duration, and bands), so that the sensing processor  625  may know when a sensing operation for a specific channel or set of channels should be started. Knowledge of this exact timing information may be ensured by a message from the MLME  650  to the SPIE  640  across the S7 interface. Table 8 shows some examples of S8 interface messages. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 8 
               
               
                   
               
               
                   
                   
                   
                 Message 
               
               
                 Message Name 
                 Originator 
                 Description 
                 Contents 
               
               
                   
               
             
            
               
                 SILENT_PERIOD_INFORMATION 
                 Silent Period 
                 Indicates to the 
                 freqRanges - 
               
               
                   
                 Interpretation Entity 
                 Sensing Processor 
                 Range of 
               
               
                   
                   
                 the properties of an 
                 frequencies 
               
               
                   
                   
                 upcoming silent 
                 (delimited 
               
               
                   
                   
                 period message. 
                 by start and 
               
               
                   
                   
                 This message may 
                 end 
               
               
                   
                   
                 be sent some time 
                 frequencies). 
               
               
                   
                   
                 prior to the 
                 duration - 
               
               
                   
                   
                 occurrence of the 
                 silent 
               
               
                   
                   
                 silent period to allow 
                 period 
               
               
                   
                   
                 confirmation. 
                 duration 
               
               
                   
                   
                   
                 applicable 
               
               
                   
                   
                   
                 to 
               
               
                   
                   
                   
                 freqRange 
               
               
                   
                   
                   
                 (each silent 
               
               
                   
                   
                   
                 period start 
               
               
                   
                   
                   
                 message 
               
               
                   
                   
                   
                 may be 
               
               
                   
                   
                   
                 associated 
               
               
                   
                   
                   
                 with a 
               
               
                   
                   
                   
                 single 
               
               
                   
                   
                   
                 duration 
               
               
                   
                   
                   
                 time) 
               
               
                 SILENT_PERIOD_INFORMATION_CONFIRM 
                 Sensing Processor 
                 Confirms the receipt 
                 statusCode - 
               
               
                   
                   
                 of the silent period 
                 Success or 
               
               
                   
                   
                 information 
                 a reason 
               
               
                   
                   
                 message. 
                 code 
               
               
                   
                   
                   
                 explaining 
               
               
                   
                   
                   
                 the failure. 
               
               
                 SILENT_PERIOD_START_MESSAGE 
                 Silent Period 
                 Indicates the exact 
                 None 
               
               
                   
                 Interpretation Entity 
                 starting time of the 
               
               
                   
                   
                 silent period 
               
               
                   
               
            
           
         
       
     
     The S9 interface may be used to communicate the silent periods from the AP  605  to each of the STAs  610 . This interface may be implemented through information in the beacon and control messages. 
     The following call flow examples describe the main messages and their uses in the different scenarios where the silent period management may occur.  FIGS. 7A and 7B  are flow diagrams of an example system initialization and silent period initiation method  700 . A DSM system may include interaction between a sensing processor  702 , a CMF  704 , a SPME  706 , a SPIE  708 , a MLME  710 , a MAC buffering and control entity  712  and a sensing/capabilities database  714 . 
     When the DSM system boots up ( 720 ), the SPME  706  may receive the silent period requirements for each type of primary user interference ( 722 ) and send a confirmation ( 724 ). This information may guide the SPME  706  in creating the silent period schedule. When the CMF  704  selects the channels to be used by the system ( 726 ), it may send a CHANNEL_CONFIG message across the S1 interface to the SPME  706  ( 728 ), which in turn may send a confirmation ( 730 ). This message may also include additional information about the type of sensing that may be performed based on the dbInformation parameter within the message ( 732 ). If the channel is free, based on the TVWS database, this channel may be used as a channel used in a Mode I and a Mode II operation. If the channel is considered occupied, then it may be used by a sensing only mode device and primary user detection may be required. If additional information is present from the TVWS database, (whether the primary user is known to be sensing only or DTV), that may be reflected in this parameter. 
     The SPME  706  may generate a schedule based on the default settings related to QoS ( 734 ) and may send this schedule to the SPIE  708  ( 736 ). This schedule may then be sent to the MLME  710  through an MLME primitive ( 738 ) so that the MLME  710  may begin to include this information within the beacon ( 740 ). 
     At some time delta prior to the arrival of a silent period ( 742 ), the SPIE  708 , which may be maintaining the latest schedule, may notify the MAC buffering and control entity  712  so that it may adjust its frame buffering rules for the arrival of a silent period ( 744 ). Information about the upcoming silent period may be sent to the sensing processor  702  ( 746 ), which in turn may send a confirmation ( 748 ). 
     The MLME  710  may determine the start of the silent period based on knowledge of the beacon timing for silent periods starting immediately following the beacon, or based on the target transceiver unit (TU) of the silent period for silent periods occurring within the beacon interval ( 750 ). When the silent period time arrives, the MLME  710  may disable the channels affected by the silent period within the Enhanced Distributed Channel Access (EDCA) algorithm ( 752 ) and may send a message to the SPIE  708  ( 754 ) that may be forwarded to the sensing processor  702  for synchronizing the sensing operation ( 756 ). Depending on the implementation, advanced notice may be sent in order to account for messaging latencies with the sensing processor  702 . After the silent period ends, the MLME  710  may re-enable the channels affected by the silent period within the EDCA algorithm ( 758 ). This may be done for each silent period. 
       FIG. 8  is a flow diagram of an example channel reconfiguration  800  performed by a CMF  804  in a DSM system. The DSM system may include interaction between a sensing processor  802 , a CMF  804 , a SPME  806 , a SPIE  808 , a MAC QoS  810 , a MLME  812  and a MAC buffer and control entity  814 . 
     The CMF  804  may decide to change the active channels for various reasons during operation of the DSM system ( 820 ). The change in channels may involve a change in the active channels used by the aggregation, or a decrease in the channels followed by an eventual increase when a new available channel is found. In each case, the CMF  804  may send a CHANNEL_CONFIG message with a new set of active channels to the SPME  806  ( 822 ), which in turn may send a confirmation ( 824 ). The SPME  806  may be responsible for re-computing a new silent period schedule for the periodic silent periods ( 826 ). When the new silent period schedule has been sent to the SPIE  808  ( 828 ), the SPIE  808  may decide the best new time to have the new schedule take effect ( 830 ). This may result in the delay of the MLME_SCHEDULE_CONFIGURE primitive until an upcoming silent period occurs ( 832 ). The delay may occur if that silent period is less than the delta from the reconfiguration time, or if sensing information may be obtained from the upcoming silent period, such as, for example, alternate channel sensing information. After the delay lapses, the SPIE  808  may send the MLME_SCHEDULE_CONFIGURE primitive to the MLME  812  ( 834 ), which in turn may modify the information sent in the beacon according to the new schedule ( 836 ). 
       FIGS. 9A and 9B  are flow diagrams of an example asynchronous silent period configuration method  900 . The DSM system may include interaction between a sensing processor  902 , a CMF  904 , a SPME  906 , a SPIE  908 , a MAC QoS  910 , a MLME  912  and a MAC buffer and control entity  914 . 
     During communication between the CMF  904  and the sensing processor  902  for channel selection/evaluation ( 922  and  924 ), the sensing processor  902  may decide that an asynchronous silent period is required ( 926 ). An asynchronous silent period may be required where a channel is evacuated due to a primary user or strong interference, and an alternate channel is not yet available. In order to speed up the selection of a new channel for the system, the sensing processor  902  may request an asynchronous silent period to perform sensing on alternate channels ( 928 ). The SPME  906  may check this request with the MAC QoS entity  910  ( 930 ) to determine the maximum allowable silent period that is acceptable for a given channel ( 932 ). Based on the maximum allowable delay and, optionally, the minimum time between two asynchronous silent periods having that delay sent by the MAC QoS entity  910  ( 934 ), the SPME  906  may split the requested silent period from the sensing processor  902  into multiple asynchronous silent periods ( 936 ). This information may be sent to the sensing processor  902  ( 938 ) as well as the SPIE  906  ( 940 ). 
     The SPIE  908  may cancel any ongoing periodic silent periods for the affected channels within the maintained schedule ( 942 ) and begin a procedure for starting a silent period with the MAC buffer and control entity  914  ( 944 ) and MLME  912  ( 946 ). The MLME  912  may disable the periodic silent period on any affected channels as requested by the SPIE  908  at the receipt of the first MLME_START_ASYNC_PERIOD primitive ( 948 ). The MLME  912  may disable the channels affected by the silent period within the Enhanced Distributed Channel Access (EDCA) algorithm ( 950 ) and may send a message to the SPIE  908  ( 952 ) that may be forwarded to the sensing processor  902  for synchronizing the sensing operation ( 954 ). Depending on the implementation, advanced notice may be sent in order to account for messaging latencies with the sensing processor  902 . After the silent period ends, the MLME  910  may re-enable the channels affected by the silent period within the EDCA algorithm ( 956 ). The MLME  912  may also re-enable periodic silent periods on these channels after the last asynchronous silent period is received ( 958 ). The MLME may keep track of when the control frame has been sent by the physical (PHY) entity and may trigger the MLME_SILENT_PERIOD_START primitive to the SPIE  908  accordingly. 
       FIG. 10  is a flow diagram of an example QoS requirement change method  1000 . The DSM system may include interaction between a sensing processor  1002 , a CMF  1004 , a SPME  1006 , a SPIE  1008 , a MAC QoS  1010 , a MLME  1012  and a MAC buffer and control entity  1014 . 
     The MAC QoS entity  1010  may determine based on delay or throughput characteristics on certain channels that the configuration of the silent period may need to be changed ( 1020 ). In general, for a given duty cycle requirement, when the duty cycle requirement is satisfied using longer silent periods, the overall throughput may be greater but the application delay may also increase. On the other hand, when more and shorter silent periods are used, the application delay may be smaller but the overhead at the MAC layer or entity, (due to traffic pausing and restarting), may cause degradation to the overall throughput. The silent period duration may be managed in such a way as to optimize the QoS based on measurements made at the MAC QoS entity  1010 . The MAC QoS entity  1001  may indicate to the SPME  1006  when it requests an increase or decrease in the delay ( 1022 ). The SPME  1006  may create a new schedule for the periodic silent periods based on this request ( 1024 ), if possible and may send a DELAY_CHANGE_RESP message to the MAC QoS entity  1010 . The SPIE  1008  may receive the new schedule ( 1028 ) and may then determine the best time for implementing the new schedule ( 1030 ). The SPIE  1008  may wait for a silent period to pass ( 1032 ) and may then send a MLME_SCHEDULE_CONFIGURE message to the MLME  1012  ( 1034 ), which in turn may modify the information being sent in the beacon in accordance with the new schedule ( 1036 ). 
       FIG. 11  is a flow diagram  1100  of an example for using messages at DSM clients and/or stations. The call flow example in  FIG. 11  illustrates the messages used in the case of both periodic and asynchronous silent periods. The entities at a DSM client may include a SP IE  1105 , a MLME  1110 , and a MAC buffering and control entity  1115 . These entities may communicate using a reduced set of messages that may be defined over each interface. DSM clients may be aware of the presence of a silent period based on the arrival of beacon and control messages in the form of management frames received by the station MLME  1110  ( 1120 ). The MLME  1120  may send the silent period information to the SPIE  1105  ( 1125 ), which in turn may send a SILENT_PERIOD_ARRIVAL message to the MAC buffer and control entity  1115  ( 1135 ) when a silent period is about to start ( 1130 ). The SPIE  1105  may receive a MLME_SILENT_PERIOD_START message ( 1135 ) when the silent period starts ( 1140 ) and may update timing based on exact beacon arrival ( 1145 ). 
     With regard to asynchronous silent periods, DSM clients may be aware of the presence of a silent period based on the arrival of an asynchronous silent period control message in the form of management frames received by the station MLME  1110  ( 1150 ). The SPIE  1105  may receive a MLME_SILENT_PERIOD_START message ( 1155 ), cancel pending synchronous silent periods associated with this channel for this beacon interval ( 1160 ) and may send a SILENT_PERIOD_ARRIVAL message to the MAC buffering and control entity  1115  ( 1165 ). 
     As described herein, the SPME schedules silent periods. Based on the call flows described herein, a scheduling algorithm such as the creation of a schedule based on all available information, may be performed at the SPME at several instances in time. This algorithm may first process the information that is obtained from the capabilities database to generate the rules that it may use to define the schedule. These rules may remain fixed, unless they depend on the arrival of a new device with sensing capability or transmission (TX) band properties that may change the out-of-band interference assumptions. 
     Given this set of scheduling rules, the SPME may create a schedule for the silent periods for each of the channels each time the following events occur: 1) the CMF may change the channels utilized by the system and the current silent period schedule may be changed to avoid interference from transmitting stations affecting the sensing results; 2) the duty cycle requirements from the sensing toolbox may have been changed due to the arrival of a new device with sensing capability, (or the departure of a sensing device; and 3) the current QoS requirements of the utilized channels may have changed and the current silent period schedule may not give the best QoS performance for the new requirements. 
     Silent periods may be scheduled using the required duty cycle for each type of channel. When a required duty cycle is specified, the SPME may ensure that the amount of sensing time specified by the duty cycle may be allocated in terms of silent time. In order to simplify the silent period scheduling, duty cycles indicated in the SET_SILENT_PERIOD_REQUIREMENTS message may be given in terms of time per 100 ms or time per multiple of 100 ms. For example, 5 ms/100 ms, 1 ms/100 ms and 10 ms/300 ms are valid duty cycles. 
     In order to link a duty cycle with each of the channels, a particular channel may be associated with a channel type. This channel type may be sent to the SPME with each CHANNEL_CONFIG message. An example of each of the channel types that may be associated with a TVWS channel is shown in Table 9. Some arbitrary duty cycle requirements are shown to indicate how these requirements may be attached to each channel by the sensing processor, (through the SET_SILENT_PERIOD_REQUIREMENT). 
     
       
         
           
               
               
               
             
               
                 TABLE 9 
               
               
                   
               
               
                   
                 Channel Type 
                   
               
               
                   
                 (from the 
               
               
                   
                 dbInformation 
               
               
                 Channel Type ID 
                 parameter) 
                 Duty Cycle Requirement 
               
               
                   
               
             
            
               
                 Channel Type 1 
                 Reserved for 
                 2 ms/100 ms 
               
               
                   
                 Wireless 
               
               
                   
                 Microphone 
               
               
                 Channel Type 2 
                 Reserved for DTV 
                 2 ms/100 ms 
               
               
                 Channel Type 3 
                 Reserved for DTV 
                 4 ms/100 ms 
               
               
                   
                 and Wireless 
               
               
                   
                 Microphone 
               
               
                 Channel Type 4 
                 Free 
                 No requirement 
               
               
                   
                   
                 (default is 1 ms/1000 ms) 
               
               
                   
               
            
           
         
       
     
     By default, the SPME may allocate the duty cycle requirement in a single portion of silent time, as shown in  FIG. 12 . Based on the hypothetical values in Table 9, a silent period  1200  of duration 2 ms may occur with a period  1205  of 100 ms for a channel reserved for a wireless microphone, for example. Other silent periods  1210 ,  1215  and  1220  may depend on type of channel reservation or free channel status. 
     Silent periods allocated by the SPME over the four aggregated channels may be either channel synchronous or channel independent. When channel synchronous silent periods are used, all four channels may exhibit a silent period simultaneously. This means that the duration and periodicity of the silent periods on all channels may be the same. When channel independent silent periods are used, there may be one or more channels that may be performing data transmission, while one or more other channels may be performing a silent period. 
     In channel synchronous silent periods, the silent periods of all channels may match the worst case duty cycle of the four channels. The change in silent period configuration that may be commanded by the MAC QoS entity may apply to all of the four channels. For example, if the MAC QoS entity requests a decrease in delay, and the worst case duty cycle required is that of wireless microphone, the silent periods may change from 2 ms every 100 ms to 1 ms every 50 ms, for example, and this may occur on every channel. A minimum silent period duration may be adhered to for each channel type. This minimum may be dependent on the sensing hardware, and may be provided in the SET_SILENT_PERIOD_REQUIREMENTS message. Channels that do not have a duty cycle requirement, for example a channel of type “Free” as defined hereinabove, may have silent periods cancelled as determined by the MAC QoS entity. 
     An example implementation for the SPME may be based on some hypothetical assumptions to illustrate application of the methods described hereinabove. A wideband digital radio may be assumed for both device and AP transceiver (TRX) operations as well as for sensing operations. It may be assumed that the radio that performs the sensing is a different radio than the AP TRX radio, and may or may not be collocated with the AP. The digital radio may include two separate radio boards: a low-band board that may transmit over the 512-608 MHz frequency range and a high-band board that may transmit over the 614-698 MHz frequency range. Analog filtering may be applied only on a band basis, for example low band or high band. As a result, transmission on any TVWS channel in the low-band may create interference over the entire low band, and this interference may be limited only to the out-of-band transmission requirements of adjacent TVWS channels that may be ensured by digital filtering. This interference may create problems with sensing of wireless microphone and DTV signals, where the requirement is to detect signals below the noise floor, even when this sensing may be performed by a separate radio. As a result, sensing for wireless microphone and DTV signals may require a silent period that is “band-wide” such that the silencing is of the entire low-band or high-band and may depend on the location of the channel on which sensing is being performed. 
     The requirement of band-wide silencing may depend on the following factors. If wireless microphone or DTV sensing must be performed on a particular channel, transmission on other channels that are in the same band, (low-band or high-band), may need to be silenced as well. The decision on the necessity of silencing the other channels may depend on the second factor. In the case of sensing a channel of type “Free”, where only channel quality may be required, this may be performed without the need for silencing other channels within the same band. The expected interference caused by a separate sensing radio may be below the sensitivity of a WiFi terminal (˜−85 dbm). If the sensing radio being used is far enough from all of the devices transmitting, the interference created by the devices that are transmitting in the vicinity may be below the detection level of wireless microphone and DTV. In this case, independent silent periods may be used. 
     The information needed to distinguish the scenario based on the above two factors may reside in the capabilities database that is read by the SPME. It may be assumed that the SPME has made this decision and the silent period configuration is chosen accordingly. 
     The following scenarios illustrate the potential silent period schedules maintained and controlled by the SPME. The durations and periodicity values used in the illustrations serve only as examples to show how the schedule is derived based on the channel type, the allocation of channels to each radio band, and dynamic requests from the MAC QoS entity. The rules used by the SPME in each scenario are listed in Table 10. 
     
       
         
           
               
               
             
               
                 TABLE 10 
               
               
                   
               
               
                 Rule 
                 Description 
               
               
                   
               
             
            
               
                 Duty Cycle 
                 For all channel types except “Free”, the 
               
               
                   
                 minimum duty cycle requirement may be 
               
               
                   
                 maintained. For a channel of type “Free”, 
               
               
                   
                 the duty cycle may be changed with 
               
               
                   
                 commands coming from the QoS Entity. 
               
               
                 Silent Period Distribution 
                 The distribution of all silent period may be 
               
               
                   
                 such that all silent periods (independent or 
               
               
                   
                 synchronous) may be evenly distributed 
               
               
                   
                 over a cycle so that the Sensing Processor 
               
               
                   
                 will have a maximum amount of post- 
               
               
                   
                 processing time available to it. 
               
               
                 Dependence of Silent Periods 
                 When silent periods on different channels 
               
               
                   
                 need to be channel synchronous due to 
               
               
                   
                 interference considerations, all dependant 
               
               
                   
                 channels may inherit the silent period 
               
               
                   
                 duration and timing of the channel with 
               
               
                   
                 the worst case duty cycle requirements. 
               
               
                   
                 All channel types may inherit the silent 
               
               
                   
                 period timing of Channel Type 1. Channel 
               
               
                   
                 Type 4 may inherit the silent period timing 
               
               
                   
                 of both Channel Type 2 and Channel Type 
               
               
                   
                 3 as well. When a change in the silent 
               
               
                   
                 period configuration is requested by the 
               
               
                   
                 MAC Layer QoS, that same configuration 
               
               
                   
                 change may be applied all channels that 
               
               
                   
                 have channel synchronous silent periods. 
               
               
                 Behavior during 
                 When a DELAY_CHANGE_REQ of type 
               
               
                 DELAY_CHANGE_REQ. 
                 decrease is received, the silent period(s) for 
               
               
                   
                 a particular channel and its dependant 
               
               
                   
                 channels may be split into two equal 
               
               
                   
                 portions and redistributed to maintain the 
               
               
                   
                 Silent Period Distribution Rule. When a 
               
               
                   
                 DELAY_CHANGE_REQ of type increase is 
               
               
                   
                 received, silent periods for the channel 
               
               
                   
                 may be merged in pairs to return to the 
               
               
                   
                 configuration for that channel that existed 
               
               
                   
                 prior to previous decrease requests. 
               
               
                 Behavior during 
                 This message may have an effect only on 
               
               
                 SILENT_AMOUNT_CHANGE_REQ 
                 Channel Type 4. When a 
               
               
                   
                 SILENT_AMOUNT_CHANGE_REQ is 
               
               
                   
                 received, each silent period duration may 
               
               
                   
                 be either doubled (increase) or halved 
               
               
                   
                 (decrease). A decrease request made when 
               
               
                   
                 the silent period is the minimum required 
               
               
                   
                 value may cancel the silent periods. An 
               
               
                   
                 increase request made on a channel where 
               
               
                   
                 the silent periods have been cancelled may 
               
               
                   
                 introduce a silent period of the minimum 
               
               
                   
                 required with a periodicity of 1000 ms. 
               
               
                   
               
            
           
         
       
     
       FIG. 13  is a diagram of an example scenario where there may be fully independent silent periods. This scenario may occur in the situation where either the sensing radio is far enough that the interference caused by the transmitters do not impede wireless microphone or DTV detection, or in the situation where all channels are of type “Free”. In this case, the SPME may maintain a separate schedule on each of the four channels. Requests by the MAC QoS entity to increase or decrease the delay on any particular channel or channels may affect the schedule only on that channel or channels and not on the other channel. In particular, the Channel 2 delay may be decreased from 1 ms to 0.5 ms. 
     The example illustrated in  FIG. 13  assumes silent periods  1300  with duration of 1 ms with periodicity of 1000 ms, (the default scenario for channels of type “Free”). A similar scheduling may occur for different values of silent period duration and periodicity. Because of the use of independent silent periods, a primary channel switch may occur during the silent period for Channel 1 so that Channel 2 may be temporarily used as the primary channel during this time. As shown, when independent silent periods are used, the skew of the silent periods over the different channels may be such that the silent periods are evenly distributed over the 1000 ms period. 
       FIG. 14  is a diagram of an example scenario where there may be two independent channel sets. This scenario may occur in the situation where the “far sensor” assumption does not apply. Two independent channel sets may be required if two channels are allocated in the low-band and two channels are allocated in the high-band. In addition, at least one of the two channels in the low-band range may require sensing of wireless microphone or DTV, and similarly with at least one of the channels in the high-band range. Although one or more channels may be of type “Free” and therefore require only quality measurements for that channel, that channel may inherit the silent period duration and periodicity of the channel requiring sensing of wireless microphone or DTV, as described in the Rule on Channel Dependence. The specific example in the scenario in  FIG. 14  shows two dependent channels matched to the Channel Type 1 duty cycle requirements, (i.e., Channels 1 and 2 having a silent period  1400  of 4 ms. over a period  1410  of 100 ms), and two dependent channels matched on the Channel Type 2 duty cycle requirements, (i.e., Channels 3 and 4 having a silent period  1415  of 2 ms). In this example, a temporary primary channel change may occur during the shaded region in the Channel Type 1 channels to the Channel Type 2 channels. 
     The scenario of two independent channel sets may also occur when one channel is allocated in the high band and three channels are allocated in the low-band, or vice-versa. For this case to fall in this scenario, at least one of the channels in the band where the three channels have been allocated may require sensing of wireless microphone or DTV, thus requiring these three channels to be independent. The behavior of the SPME may be similar to the example shown in  FIG. 15 , where three of the four channels may exhibit channel synchronous silent periods. 
       FIG. 15  is a diagram of an example scenario where there may be three independent channel sets. This scenario may require the “far sensor” assumption to not apply. This scenario may occur when two channels of Channel Type 4 are allocated in the same radio band, (i.e., channels 1 and 2 having a silent period  1500  and period  1510 ), while two other channels (one of which is not type 4) are allocated in the other radio band, (i.e., channels 3 and 4 having a silent period  1515  and period  1520 ). The two channels in the first band may form two channels that have independent silent periods. The two channels in the second band may form a dependent channel set, but may be independent from each of the channels in the first set. 
       FIG. 16  is a diagram of an example scenario where there may be fully channel synchronous silent periods  1600 .  1605 ,  1610  and  1615 . In this scenario, all four channels may require dependent silent periods. This scenario may occur in the case where the “far sensor” assumption does not apply, and all four channels may be allocated in the same radio band. In this case, the silent period duration and periodicity for all four channels may match the duration and periodicity of the channel with the highest silent period requirements. In this scenario, a switch of the primary channel may not be possible. As a result, the entire aggregated channel may be busy for the duration of the silent period time. 
     The MAC QoS entity may be designed for optimizing silent periods. The requirements for adapting the silent periods for PU detection and SU detection, (or channel quality), may be different. SU detection may occur for channels that are free of PUs, and it may provide information on the quality of the channel where sensing is being performed. For PU detection, for practical purposes, the silent period duty cycle may be fixed. However, there may not be such a restriction for SU detection. 
     Described herein are example signal exchanges between a MAC QoS entity and a SPME for PU detection. To support dynamic silent period configuration, the S4 interface may be used as described hereinabove. There may be a number of approaches that may be used, and each approach may differ in the way that it uses the DELAY_CHANGE_REQ message. 
     A first approach may use a one-time specification. In this approach, the QoS module may determine the desired value for Td for achieving desired delay and throughput performance, and send the desired value in the DELAY_CHANGE_REQ, (one-time value), message. However, the relationship between Td and the delay and throughput performance may be affected by the protocol behavior and the traffic condition, and may be difficult to be accurately captured. Therefore, this first approach may be more difficult to implement. However, it may allow for a more accurate specification of the required silent period schedule and reduce the messaging overhead. 
       FIG. 17  is an example call flow  1700  of a signal exchange between a MAC QoS entity  1705  and a SPME  1710  for PU detection. The call flow may be applicable to a second approach where probing may be used with a change in an absolute amount. The MAC QoS entity  1705  may determine the desired value for Td for achieving desired delay and throughput performance ( 1720 ) and may then send a DELAY_CHANGE_REQ, (i.e., an increase or decrease), to the SPME  1710  ( 1725 ). The SPME  1710  may increase/decrease the silent duration by a certain amount of time, for example, n ms. For example, Td←Td−n or Td←Td+n. The SPME  1710  may send a DELAY_CHANGE_RESP message to confirm whether the requested increase or decrease has occurred ( 1730 ). The MAC QoS entity  1705  and SPME  1710  may repeat these messages ( 1735 ) until the desired delay and throughput values are obtained ( 1740 ). 
     The example call  1700  may also be applicable for a third approach that may use probing and a change in a relative amount. The MAC QoS entity  1705  may determine the desired value for Td for achieving desired delay and throughput performance ( 1720 ) and may then send a DELAY_CHANGE_REQ, (i.e., an increase or decrease), to the SPME  1710  ( 1725 ). The SPME  1710  may decrease/increase the silent duration by a certain fraction, for example, Td←Td(1−v) or Td←Td(1+v), where v may be the fraction of decrease/increase. The SPME  1710  may send a DELAY_CHANGE_RESP message to confirm whether the requested increase or decrease has occurred ( 1730 ). The MAC QoS entity  1705  and SPME  1710  may repeat these messages ( 1735 ) until the desired delay and throughput values are obtained ( 1740 ). When Td is changed, the number of Td&#39;s within a Tp may be changed to keep the sensing duty cycle the same. 
     Described herein are example signal exchanges between a MAC QoS entity and a SPME for SU detection. In contrast to the PU detection example, there may be no restriction on the silent periods for SU detection. There may be a number of approaches, and each approach may differ in the way that it uses the SILENT_AMOUNT_CHANGE_REQ message. 
     A first approach may use a one-time specification. In this approach, the MAC QoS entity may determine the desired value for the silent period for achieving the desired delay and throughput performance, and may send the desired value in the SILENT_AMOUNT_CHANGE-REQ (value) message. The greater the silent period, (denoted as Ts), the better the sensing performance, and on the other hand, the less the time for the traffic delivery. This may degrade the network performance. However, if the silent period is too short, the sensing performance may be poor, making the DSM system unable to find good channels to operate on and hence may result in poor network performance. Accordingly, a proper value may be selected for the silent period. However, similar to the case of PU detection, there may be a problem with the first approach, because the relationship between silent period and the network performance may be affected by the protocol behavior and the traffic condition, and it may be difficult to be accurately captured. 
       FIG. 18  is an example call flow  1800  of a signal exchange between a MAC QoS entity  1805  and a SPME  1810  for SU detection. The call flow may be applicable to a second approach where probing may be used with a change in an absolute amount. The MAC QoS module  1805  may monitor network performance and determine the desired value for Ts for achieving desired delay and throughput performance ( 1820 ) and may send a SILENT_AMOUNT_CHANGE_REQ, (i.e., an increase or decrease), to the SPME  1810  ( 1825 ). The SPME  1810  may increase/decrease the silent period by a certain amount of time, for example, n ms. For example, Ts←Ts−n or Ts←Ts+n. The SPME  1810  may send a SILENT_AMOUNT_CHANGE_RESP message to confirm whether the requested increase or decrease has occurred ( 1830 ). The MAC QoS entity  1805  and SPME  1810  may repeat these messages ( 1835 ) until the desired delay and throughput values are obtained ( 1840 ). 
     The example call  1800  may also be applicable for a third approach that may use probing and a change in a relative amount. The MAC QoS module  1805  may monitor network performance and determine the desired value for Ts for achieving desired delay and throughput performance ( 1820 ) and may send a SILENT_AMOUNT_CHANGE_REQ, (i.e., an increase or decrease), to the SPME  1810  ( 1825 ). The SPME  1810  may increase/decrease the silent period by a certain fraction, for example, Ts←Ts(1+v)/Ts←Ts(1−v), where v may be the fraction of the increase/decrease. The SPME  1810  may send a SILENT_AMOUNT_CHANGE_RESP message to confirm whether the requested increase or decrease has occurred ( 1830 ). The MAC QoS entity  1805  and SPME  1810  may repeat these messages ( 1835 ) until the desired delay and throughput values are obtained ( 1840 ). 
     The MLME may be modified to support silent period coordination. Periodic silent periods may be coordinated across the DSM system by transmitting the silent period information within the beacon. The IEEE 802.11 beacon may contain a ‘quiet element’ field that defines an interval of time during which no transmission should occur in the current channel. This ‘quiet element’ may be added to the aggregated beacon and used to coordinate the silent periods. The quiet element may be modified to account for the factors described herein below. 
     To support the silent period scheduling, the aggregated beacon may send quiet elements on each of the channels to be aggregated. These quiet elements may represent the silent period duration and timing associated with all channels. This may ensure the maximum robustness for the system, so that if the beacon on one of the four channels is missed, the station may still be aware of the silent period for all channels based on the silent period information received on other channels. 
       FIG. 19  is a diagram of an example quiet element format  1900  for the aggregated channels. The quiet element may have an element ID field  1905  of 1 octet, a Length field  1910  of 1 octet, a Quiet Count field  1915  of 1 octet, a Quiet Period field  1920  of 1 octet, a Quiet Duration  1925  field of 2 octets, a Quiet offset field  1930  of 2 octets, a Ch ID 1 field  1935  of 1 octet . . . a CH ID N field of 1 octet. 
     A single quiet element  1900  may describe the silent period for more than one channel for the case of channel-synchronous silent periods. In addition, a single channel may require multiple quiet elements to describe the silent periods on it, as shown in the scheduling examples. For a channel with no silent periods defined for it, the quiet duration field  1925  may be set to 0, or a quiet element  1900  may not be sent on that channel. This may allow sending of a quiet element  1900  with the Quiet Count field  1930  of 0, which may not be allowed in IEEE 802.11, but may be necessary to ensure stations that first hear the beacon will not transmit if the current beacon interval contains a silent period. 
     In addition to this, the Quiet Offset field  1930  may be redefined to support silent period intervals, (time between silent periods), of less than 100 ms. A Quiet Offset field  1930  having a value of 0 may represent a silent period that occurs at most once every beacon period, (assuming a Quiet Period field  1920  having a value of 1). Therefore, setting the Quiet Offset field  1930  to a value of 0 may result in silent period intervals that are multiples of the beacon period, assuming 100 ms. When the Quiet Offset field  1930  has a value set to a non-zero value, this value may represent the length of time, (in time units (TUs)), between silent periods that may occur within the same beacon interval, as opposed to the offset from the start of the target beacon transmission time (TBTT) as in IEEE 802.11. 
     The quiet element  1900  may be modified to keep backward compatibility with the IEEE 802.11 quiet element. The length field  1910  may be used to indicate the number of channel identities (ID)s  1935  that may be attached to the end of the quiet element  1900 . Each channel ID  1935  may represent one of the channels that may have the periodic silent period described by this quiet element  1900 . In addition, the changes described herein below may be made to the interpretation of each field. The Quiet Count field  1915  may take on a value of zero to indicate that the silent period or periods may be within the current beacon interval. When at least one silent period may occur within each beacon interval, the Quiet Count field  1915  may have a value of zero. The Quiet Period field  1920  may continue to indicate the value of the number of beacon intervals between quiet periods. In addition, when the Quiet Period field  1920  may have a value of 0, the periodicity for this silent period may be smaller than one beacon interval, for example, there may be more than one silent period in the beacon interval. When the Quiet Period field  1920  may have a value of 1 or larger, the Quiet Offset field  1930  may have the same interpretation as in IEEE 802.11. When the Quiet Period field  1920  may have a value of 0, the Quiet Offset field  1930  may represent the interval between the silent periods occurring within the beacon interval. 
     Due to the advanced notice provided by the Quiet Count field  1915 , the MAC entity buffering scheme may prepare itself for the occurrence of a scheduled silent period. Since a given silent period schedule sent on a beacon may supersede all previously scheduled silent periods, silent period configuration may be changed at each beacon interval. 
     An alternative format to the quiet element  1900  may maintain the same fields as in IEEE 802.11 and split each field (quiet count, quiet period, and the like) into four subfields, where each subfield may represent one of the four channels. 
     An additional rule that may be followed by stations to ensure robust sensing during the silent time may be for stations to abstain from transmitting over any beacon interval when the station did not receive the beacon on any of the four channels. Since the silent period may be defined relative to the beacon, (either immediately following the beacon, or a specified number of TUs following a beacon), exact knowledge of the silent period time(s) in a beacon interval may require correct reception of the beacon for that interval. Since the silent period information for all channels may be transmitted on the aggregated beacon of each channel, the probability of a station having to abstain from transmission during a beacon interval may be low and the loss of efficiency may be low. 
     For the case where the number of aggregated channels is low and a high probability of missing a beacon is expected, the station may be allowed to transmit in the beacon interval where the beacon is missed and then rely on the silent period information from the previously received beacons. A safe padding may be added to the expected silent period time to account for the potential of the beacon having been delayed due to retransmissions and CSMA contention delay. This safe padding may be reduced to a reasonable amount by having the beacon referenced to the end of the TBTT. 
       FIGS. 20A, 20B and 20C  are examples of silent period intervals  2000  relative to beacon intervals  2005 . The examples use the Quiet Offset field to configure a silent period having different ranges of silent intervals relative to the beacon interval. In  FIG. 20A , the silent period interval is greater than the beacon interval. In  FIG. 20B , the silent period interval may be equal to the beacon interval. In  FIG. 20C , the silent period interval may be less than the beacon interval. 
     To simplify the insertion of the silent period within the regular IEEE 802.11 operation, the following rules may be used by the MLME. These rules may be independent of the channel in the aggregation scheme. 
     The timing of a first silent period  2100  of a beacon interval  2105  with respect to broadcast and poll messages is shown in  FIG. 21 . If a silent period  2100  is scheduled immediately following the beacon  2110 , it may occur between the beacon transmission and the traffic indication map (TIM) or delivery traffic indication message (DTIM) interval  2115  where the AP may transmit buffered broadcast/multicast frames, or the station may poll for buffered unicast frames. This means that stations may wakeup to send the poll message in response to the TIM in the beacon after the end of the scheduled silent period. This rule may ensure that the silent period occurs at a specific period in time, (due to the lack of any contention for frames or acknowledgements (ACKs)), and that the TIM/DTIM interval may remain at a fixed time instant, (since the silent period is a fixed number of TUs). Since all stations may be quiet during the beacon, the system may know that the silent period may start once the beacon has been transmitted by the AP. This knowledge may be used to ensure synchronization with the sensing processor/toolbox. 
       FIG. 22  is a diagram of an example station transmission pattern  2200  at the arrival of an intra-beacon silent period  2205 . For silent periods that occur between TBTTs, for example, when the Quiet Offset field is non-zero, an AP or a station may ensure that its frame transmission may complete at least a short interframe space (SIFS)  2210  before the scheduled start of the silent period. This may ensure that the start of the silent period coincides with a situation where no transmission is currently on the air. The start of a sensing operation may be synchronized with the scheduled start of a silent period. 
       FIG. 23  is a diagram of an example channel independent silent period that may affect non-primary channels. The MLME may allow silent periods  2300  on a subset of channels while maintaining the primary channel operation on the remaining channels. In order to do so, unacknowledged frames due to the silent period may be retransmitted on the available channels. 
       FIG. 24  is a diagram of an example channel independent silent period  2400  that may affect a primary channel. In this example, a primary channel switch mechanism  2410  may be required. This mechanism may be implemented by a switch message  2410  sent along with the beacon, as shown in  FIG. 24 . Other methods of performing the primary channel switch, such as a scheduled switch configured at each known switch time using a separate management message, may also be possible. 
     Asynchronous Silent Periods may be coordinated with stations using a special control channel message containing one or more quiet elements. The control channel message may transmit the quiet elements associated with each channel on all channels, for example, the message may be repeated on each of the channels. In the case of an asynchronous silent period, only the duration field may be used. The other elements may be “don&#39;t care” values. In addition to sending the asynchronous silent period message on all channels, the following procedure may be used to further improve robustness of the asynchronous silent period to the possibility of stations not receiving the control message. 
       FIG. 25  shows an example call flow  2500  for asynchronous silent periods between an AP  2505 , STAs  2510 , and a sensing processor  2515 . The AP may  2505  may broadcast the asynchronous silent period control message to all STAs  2510  stations ( 2520 ). Following transmission of the message, the AP  2505  may listen to the medium for distributed coordination function (DCF) interframe space (DIFS) ( 2525 ). If the medium is quiet for that time, the AP  2505  may trigger the sensing processor  2515  to initiate the sensing operation with the remaining time specified ( 2530 ). If a channel access was sensed on the medium by a device belonging to the DSM system, the AP may repeat the first two steps ( 2535 ) prior to sending the silent period start indication to the sensing processor  2515 . The first two steps may be repeated multiple times up to a predetermined maximum number of times. If the medium is still busy after that point, the AP  2505  may cancel scheduling of the asynchronous silent period and rely on periodic silent periods to satisfy the request from the sensing processor  2515 . 
     Although features and elements are described above in particular combinations, one of ordinary skill in the art may appreciate that each feature or element may 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.