Patent Publication Number: US-2015063327-A1

Title: High efficiency wireless (hew) access point (ap) coordination protocol

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application claims benefit of U.S. Provisional Patent Application Ser. No. 61/870,711, filed Aug. 27, 2013, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     I. Field of the Invention 
     The present application relates generally to wireless communications and, more specifically, to systems, methods, and devices for high efficiency wireless (HEW) access point (AP) coordination protocol. 
     II. Description of Related Art 
     In many telecommunication systems, communications networks are used to exchange messages among several interacting spatially-separated devices. Networks may be classified according to geographic scope, which could be, for example, a metropolitan area, a local area, or a personal area. Such networks would be designated respectively as a wide area network (WAN), metropolitan area network (MAN), local area network (LAN), wireless local area network (WLAN), or personal area network (PAN). Networks also differ according to the switching/routing technique used to interconnect the various network nodes and devices (e.g., circuit switching vs. packet switching), the type of physical media employed for transmission (e.g., wired vs. wireless), and the set of communication protocols used (e.g., Internet protocol suite, SONET (Synchronous Optical Networking), Ethernet, etc.). 
     Wireless networks are often preferred when the network elements are mobile and thus have dynamic connectivity needs, or if the network architecture is formed in an ad hoc, rather than fixed, topology. Wireless networks employ intangible physical media in an unguided propagation mode using electromagnetic waves in the radio, microwave, infra-red, optical, etc. frequency bands. Wireless networks advantageously facilitate user mobility and rapid field deployment when compared to fixed wired networks. 
     However, multiple wireless networks may exist in the same building, in nearby buildings, and/or in the same outdoor area. The prevalence of multiple wireless networks may cause interference, reduced throughput (e.g., because each wireless network is operating in the same area and/or spectrum), and/or prevent certain devices from communicating. Thus, improved systems, methods, and devices for communicating when wireless networks are densely populated are desired. 
     SUMMARY 
     The systems, methods, and devices of the disclosure each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this disclosure as expressed by the claims which follow, some features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled “Detailed Description” one will understand how the features of this disclosure provide advantages that include improved communications between access points and stations in a wireless network. 
     Techniques and apparatus are provided herein for high efficiency wireless (HEW) access point (AP) coordination protocol. 
     One aspect of this disclosure provides a method for coordinating access to a shared medium by an apparatus. The method generally includes synchronizing with one or more peer apparatuses based on synchronization messages detected during a listening time, outputting, for transmission, scheduling information to the one or more peer apparatuses, the scheduling information indicating one or more time periods during which coordinated access to the shared medium is desired, and outputting, for transmission, at least some of the scheduling information to devices served by the apparatus. 
     One aspect of this disclosure provides a method for coordinating access to a shared medium by an access point (AP). The method generally includes receiving, from another AP, a message to reserve a listening time for the other AP to listen to one or more synchronization messages, taking action to ensure stations served by the AP do not interfere with synchronization messages during the listening time, receiving, from the other AP, scheduling information indicating one or more reservation periods during which coordinated access to the shared medium is desired, and taking action to provide coordinated access during the one or more reservation periods. 
     One aspect of this disclosure provides an apparatus for wireless communications. The apparatus typically includes means for synchronizing with one or more peer apparatuses based on synchronization messages detected during a listening time, means for outputting, for transmission, scheduling information to the one or more peer apparatuses, the scheduling information indicating one or more time periods during which coordinated access to the shared medium is desired, and means for outputting, for transmission, at least some of the scheduling information to devices served by the apparatus. 
     One aspect of this disclosure provides an apparatus for wireless communications. The apparatus typically includes a processing system configured to synchronize with one or more peer apparatuses based on synchronization messages detected during a listening time and a transmitter configured to transmit scheduling information to the one or more peer apparatuses, the scheduling information indicating one or more time periods during which coordinated access to the shared medium is desired, and transmit at least some of the scheduling information to devices served by the apparatus. 
     One aspect of the present disclosure provides a computer program product for wireless communications. The computer program product generally includes a computer readable medium having instructions stored thereon for synchronizing with one or more peer apparatuses based on synchronization messages detected during a listening time, outputting, for transmission, scheduling information to the one or more peer apparatuses, the scheduling information indicating one or more time periods during which coordinated access to the shared medium is desired, and outputting, for transmission, at least some of the scheduling information to devices served by the apparatus. 
     One aspect of the present disclosure provides an access point (AP). The AP typically includes at least one antenna, a processing system configured to synchronize with one or more peer apparatuses based on synchronization messages detected during a listening time, and a transmitter configured to transmit, via the at least one antenna, scheduling information to the one or more peer apparatuses, the scheduling information indicating one or more time periods during which coordinated access to the shared medium is desired, and transmit, via the at least one antenna, at least some of the scheduling information to devices served by the apparatus. 
     Numerous other aspects are provided including methods, apparatus, systems, computer program products, and processing systems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above-recited features of the present disclosure can be understood in detail, a more particular description, briefly summarized above, may be had by reference to aspects, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only certain typical aspects of this disclosure and are therefore not to be considered limiting of its scope, for the description may admit to other equally effective aspects. 
         FIG. 1  shows an example wireless communication system in which aspects of the present disclosure may be employed. 
         FIG. 2A  shows an example wireless communication system in which multiple wireless communication networks are present. 
         FIG. 2B  shows another example wireless communication system in which multiple wireless communication networks are present. 
         FIG. 3  shows exemplary frequency multiplexing techniques that may be employed within the wireless communication systems of  FIGS. 1 and 2B . 
         FIG. 4  shows an example functional block diagram of an exemplary wireless device that may be employed within the wireless communication systems of  FIGS. 1 ,  2 B, and  3 . 
         FIG. 5  shows an example wireless communication system in which aspects of the present disclosure may be employed. 
         FIG. 5A  is a representation of an example management frame that may be employed within the wireless communication systems disclosed herein. 
         FIG. 5B  is a representation of an example action frame that may be employed within the wireless communication systems disclosed herein. 
         FIG. 5C  is a representation of an example generic advertisement service (GAS) frame that may be employed within the wireless communication systems disclosed herein. 
         FIG. 5D  is a representation of an example HTC control field that includes a reserve bit that may be employed within the wireless communication systems disclosed herein. 
         FIG. 6  is a representation of an example modified restricted access window (RAW) parameter set (RPS) information element defined by 802.11ah that may be employed within the wireless communication systems disclosed herein. 
         FIG. 7  is a representation of an example modified advertisement frame action field and of a transmission opportunity (TXOP) reservation field format defined by 802.11aa that may be employed within the wireless communication systems disclosed herein. 
         FIG. 8  is an exemplary wireless communication system employing time coordination that may be employed within the wireless communication systems disclosed herein. 
         FIG. 9  is an exemplary wireless communication system employing frequency coordination that may be employed within the wireless communication systems disclosed herein. 
         FIG. 10  illustrates cumulative distribution functions (CDFs) for downlink throughput in a regularly spaced network that may be employed within the wireless communication systems disclosed herein. 
         FIG. 11  illustrates an example frame field format for RAW that may be employed within the wireless communication systems disclosed herein. 
         FIG. 12  illustrates UL and DL schedule at the start of the power save multi-poll (PSMP) phase that may be employed within the wireless communication systems disclosed herein. 
         FIG. 13  illustrates example operations for coordinating access to a shared medium by an access point (AP) that may be performed within the wireless communication systems disclosed herein. 
         FIG. 13A  illustrates example means capable of performing the operations shown in  FIG. 13 , in accordance with certain aspects of the present disclosure. 
         FIG. 14  illustrates example operations for coordinating access to a shared medium by an AP that may be performed within the wireless communication systems disclosed herein. 
         FIG. 14A  illustrates example means capable of performing the operations shown in  FIG. 14 , in accordance with certain aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Various aspects of the novel systems, apparatuses, and methods are described more fully hereinafter with reference to the accompanying drawings. This disclosure may, however, be embodied in many different forms and should not be construed as limited to any specific structure or function presented throughout this disclosure. Rather, these aspects are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Based on the teachings herein one skilled in the art should appreciate that the scope of the disclosure is intended to cover any aspect of the novel systems, apparatuses, and methods disclosed herein, whether implemented independently of, or combined with, any other aspect of the disclosure. For example, an apparatus may be implemented or a method may be practiced using any number of the aspects set forth herein. In addition, the scope of the disclosure is intended to cover such an apparatus or method which is practiced using other structure, functionality, or structure and functionality in addition to or other than the various aspects of the invention set forth herein. It should be understood that any aspect disclosed herein may be embodied by one or more elements of a claim. 
     Although particular aspects are described herein, many variations and permutations of these aspects fall within the scope of the disclosure. Although some benefits and advantages of the preferred aspects are mentioned, the scope of the disclosure is not intended to be limited to particular benefits, uses, or objectives. Rather, aspects of the disclosure are intended to be broadly applicable to different wireless technologies, system configurations, networks, and transmission protocols, some of which are illustrated by way of example in the figures and in the following description of the preferred aspects. The detailed description and drawings are merely illustrative of the disclosure rather than limiting, the scope of the disclosure being defined by the appended claims and equivalents thereof. 
     Popular wireless network technologies may include various types of wireless local area networks (WLANs). A WLAN may be used to interconnect nearby devices together, employing widely used networking protocols. The various aspects described herein may apply to any communication standard, such as a wireless protocol. 
     In some aspects, wireless signals may be transmitted according to a high-efficiency 802.11 protocol using orthogonal frequency-division multiplexing (OFDM), direct-sequence spread spectrum (DSSS) communications, a combination of OFDM and DSSS communications, or other schemes. Implementations of the high-efficiency 802.11 protocol may be used for Internet access, sensors, metering, smart grid networks, or other wireless applications. Advantageously, aspects of certain devices implementing the high-efficiency 802.11 protocol using the techniques disclosed herein may include allowing for increased peer-to-peer services (e.g., Miracast, WiFi Direct Services, Social WiFi, etc.) in the same area, supporting increased per-user minimum throughput requirements, supporting more users, providing improved outdoor coverage and robustness, and/or consuming less power than devices implementing other wireless protocols. 
     In some implementations, a WLAN includes various devices which are the components that access the wireless network. For example, there may be two types of devices: access points (“APs”) and clients (also referred to as stations, or “STAs”). In general, an AP may serve as a hub or base station for the WLAN and an STA serves as a user of the WLAN. For example, an STA may be a laptop computer, a personal digital assistant (PDA), a mobile phone, etc. In an example, an STA connects to an AP via a WiFi (e.g., IEEE 802.11 protocol) compliant wireless link to obtain general connectivity to the Internet or to other wide area networks. In some implementations an STA may also be used as an AP. 
     An access point (“AP”) may also comprise, be implemented as, or known as a NodeB, Radio Network Controller (“RNC”), eNodeB, Base Station Controller (“BSC”), Base Transceiver Station (“BTS”), Base Station (“BS”), Transceiver Function (“TF”), Radio Router, Radio Transceiver, or some other terminology. 
     A station “STA” may also comprise, be implemented as, or known as an access terminal (“AT”), a subscriber station, a subscriber unit, a mobile station, a remote station, a remote terminal, a user terminal, a user agent, a user device, user equipment, or some other terminology. In some implementations an access terminal may comprise a cellular telephone, a cordless telephone, a Session Initiation Protocol (“SIP”) phone, a wireless local loop (“WLL”) station, a personal digital assistant (“PDA”), a handheld device having wireless connection capability, or some other suitable processing device connected to a wireless modem. Accordingly, one or more aspects taught herein may be incorporated into a phone (e.g., a cellular phone or smartphone), a computer (e.g., a laptop), a portable communication device, a headset, a portable computing device (e.g., a personal data assistant), an entertainment device (e.g., a music or video device, or a satellite radio), a gaming device or system, a global positioning system device, or any other suitable device that is configured to communicate via a wireless medium. 
     As discussed above, certain of the devices described herein may implement a high-efficiency 802.11 standard, for example. Such devices, whether used as an STA or AP or other device, may be used for smart metering or in a smart grid network. Such devices may provide sensor applications or be used in home automation. The devices may instead or in addition be used in a healthcare context, for example for personal healthcare. They may also be used for surveillance, to enable extended-range Internet connectivity (e.g. for use with hotspots), or to implement machine-to-machine communications. 
     Example Wireless Communications System 
       FIG. 1  shows an exemplary wireless communication system  100  in which aspects of the present disclosure may be employed. The wireless communication system  100  may operate pursuant to a wireless standard, for example a high-efficiency 802.11 standard. The wireless communication system  100  may include an access point (AP)  104 , which communicates with stations (STAs)  106 . 
     A variety of processes and methods may be used for transmissions in the wireless communication system  100  between the AP  104  and the STAs  106 . For example, signals may be sent and received between the AP  104  and the STAs  106  in accordance with orthogonal frequency division multiplexing (OFDM)/OFDM access (OFDMA) techniques. If this is the case, the wireless communication system  100  may be referred to as an OFDM/OFDMA system. Alternatively, signals may be sent and received between the AP  104  and the STAs  106  in accordance with code division multiple access (CDMA) techniques. If this is the case, the wireless communication system  100  may be referred to as a CDMA system. 
     A communication link that facilitates transmission from the AP  104  to one or more of the STAs  106  may be referred to as a downlink (DL)  108 , and a communication link that facilitates transmission from one or more of the STAs  106  to the AP  104  may be referred to as an uplink (UL)  110 . Alternatively, a downlink  108  may be referred to as a forward link or a forward channel, and an uplink  110  may be referred to as a reverse link or a reverse channel. 
     The AP  104  may act as a base station and provide wireless communication coverage in a basic service area (BSA)  102 . The AP  104  along with the STAs  106  associated with the AP  104  and that use the AP  104  for communication may be referred to as a basic service set (BSS). It should be noted that the wireless communication system  100  may not have a central AP  104 , but rather may function as a peer-to-peer network between the STAs  106 . Accordingly, the functions of the AP  104  described herein may alternatively be performed by one or more of the STAs  106 . 
     In some aspects, a STA  106  may be required to associate with the AP  104  in order to send communications to and/or receive communications from the AP  104 . In one aspect, information for associating is included in a broadcast by the AP  104 . To receive such a broadcast, the STA  106  may, for example, perform a broad coverage search over a coverage region. A search may also be performed by the STA  106  by sweeping a coverage region in a lighthouse fashion, for example. After receiving the information for associating, the STA  106  may transmit a reference signal, such as an association probe or request, to the AP  104 . In some aspects, the AP  104  may use backhaul services, for example, to communicate with a larger network, such as the Internet or a public switched telephone network (PSTN). 
     In an embodiment, the AP  104  includes an AP high-efficiency wireless component (HEWC)  154 . The AP HEWC  154  may perform some or all of the operations described herein to enable communications between the AP  104  and the STAs  106  using the high-efficiency 802.11 protocol. The functionality of the AP HEWC  154  is described in greater detail below with respect to  FIGS. 2B ,  3 ,  4 , and  5 . 
     Alternatively or in addition, the STAs  106  may include a STA HEWC  156 . The STA HEWC  156  may perform some or all of the operations described herein to enable communications between the STAs  106  and the AP  104  using the high-frequency 802.11 protocol. The functionality of the STA HEWC  156  is described in greater detail below with respect to  FIGS. 2B ,  3 ,  4 , and  5 . 
     In some circumstances, a BSA may be located near other BSAs. For example,  FIG. 2A  shows a wireless communication system  200  in which multiple wireless communication networks are present. As illustrated in  FIG. 2A , BSAs  202 A,  202 B, and  202 C may be physically located near each other. Despite the close proximity of the BSAs  202 A-C, the APs  204 A-C and/or STAs  206 A-H may each communicate using the same spectrum. Thus, if a device in the BSA  202 C (e.g., the AP  204 C) is transmitting data, devices outside the BSA  202 C (e.g., APs  204 A-B or STAs  206 A-F) may sense the communication on the medium. 
     Generally, wireless networks that use a regular 802.11 protocol (e.g., 802.11a, 802.11b, 802.11g, 802.11n, etc.) operate under a carrier sense multiple access (CSMA) mechanism for medium access. According to CSMA, devices sense the medium and only transmit when the medium is sensed to be idle. Thus, if the APs  204 A-C and/or STAs  206 A-H are operating according to the CSMA mechanism and a device in the BSA  202 C (e.g., the AP  204 C) is transmitting data, then the APs  204 A-B and/or STAs  206 A-F outside of the BSA  202 C may not transmit over the medium even though they are part of a different BSA. 
       FIG. 2A  illustrates such a situation. As illustrated in  FIG. 2A , AP  204 C is transmitting over the medium. The transmission is sensed by STA  206 G, which is in the same BSA  202 C as the AP  204 C, and by STA  206 A, which is in a different BSA than the AP  204 C. While the transmission may be addressed to the STA  206 G and/or only STAs in the BSA  202 C, STA  206 A nonetheless may not be able to transmit or receive communications (e.g., to or from the AP  204 A) until the AP  204 C (and any other device) is no longer transmitting on the medium. Although not shown, the same may apply to STAs  206 D-F in the BSA  202 B and/or STAs  206 B-C in the BSA  202 A as well (e.g., if the transmission by the AP  204 C is stronger such that the other STAs can sense the transmission on the medium). 
     The use of the CSMA mechanism then creates inefficiencies because some APs or STAs outside of a BSA may be able to transmit data without interfering with a transmission made by an AP or STA in the BSA. As the number of active wireless devices continues to grow, the inefficiencies may begin to significantly affect network latency and throughput. For example, significant network latency issues may appear in apartment buildings, in which each apartment unit may include an access point and associated stations. In fact, each apartment unit may include multiple access points, as a resident may own a wireless router, a video game console with wireless media center capabilities, a television with wireless media center capabilities, a cell phone that can act like a personal hot-spot, and/or the like. Correcting the inefficiencies of the CSMA mechanism may then be vital to avoid latency and throughput issues and overall user dissatisfaction. 
     Such latency and throughput issues may not even be confined to residential areas. For example, multiple access points may be located in airports, subway stations, and/or other densely-populated public spaces. Currently, WiFi access may be offered in these public spaces, but for a fee. If the inefficiencies created by the CSMA mechanism are not corrected, then operators of the wireless networks may lose customers as the fees and lower quality of service begin to outweigh any benefits. 
     Accordingly, the high-efficiency 802.11 protocol described herein may allow for devices to operate under a modified mechanism that minimizes these inefficiencies and increases network throughput. Such a mechanism is described below with respect to  FIGS. 2B ,  3 , and  4 . Additional aspects of the high-efficiency 802.11 protocol are described below with respect to  FIGS. 5-9 . 
       FIG. 2B  shows a wireless communication system  250  in which multiple wireless communication networks are present. Unlike the wireless communication system  200  of  FIG. 2A , the wireless communication system  250  may operate pursuant to the high-efficiency 802.11 standard discussed herein. The wireless communication system  250  may include an AP  254 A, an AP  254 B, and an AP  254 C. The AP  254 A may communicate with STAs  256 A-C, the AP  254 B may communicate with STAs  256 D-F, and the AP  254 C may communicate with STAs  256 G-H. 
     A variety of processes and methods may be used for transmissions in the wireless communication system  250  between the APs  254 A-C and the STAs  256 A-H. For example, signals may be sent and received between the APs  254 A-C and the STAs  256 A-H in accordance with OFDM/OFDMA techniques or CDMA techniques. 
     The AP  254 A may act as a base station and provide wireless communication coverage in a BSA  252 A. The AP  254 B may act as a base station and provide wireless communication coverage in a BSA  252 B. The AP  254 C may act as a base station and provide wireless communication coverage in a BSA  252 C. It should be noted that each BSA  252 A,  252 B, and/or  252 C may not have a central AP  254 A,  254 B, or  254 C, but rather may allow for peer-to-peer communications between one or more of the STAs  256 A-H. Accordingly, the functions of the AP  254 A-C described herein may alternatively be performed by one or more of the STAs  256 A-H. 
     In an embodiment, the APs  254 A-C and/or STAs  256 A-H include a high-efficiency wireless component. As described herein, the high-efficiency wireless component may enable communications between the APs and STAs using the high-efficiency 802.11 protocol. In particular, the high-efficiency wireless component may enable the APs  254 A-C and/or STAs  256 A-H to use a modified mechanism that minimizes the inefficiencies of the CSMA mechanism (e.g., enables concurrent communications over the medium in situations in which interference would not occur). The high-efficiency wireless component is described in greater detail below with respect to  FIG. 4 . 
     As illustrated in  FIG. 2B , the BSAs  252 A-C are physically located near each other. When, for example, AP  254 A and STA  256 B are communicating with each other, the communication may be sensed by other devices in BSAs  252 B-C. However, the communication may only interfere with certain devices, such as STA  256 F and/or STA  256 G. Under CSMA, AP  254 B would not be allowed to communicate with STA  256 E even though such communication would not interfere with the communication between AP  254 A and STA  256 B. Thus, the high-efficiency 802.11 protocol operates under a modified mechanism that differentiates between devices that can communicate concurrently and devices that cannot communicate concurrently. Such classification of devices may be performed by the high-efficiency wireless component in the APs  254 A-C and/or the STAs  256 A-H. 
     In an embodiment, the determination of whether a device can communicate concurrently with other devices is based on a location of the device. For example, a STA that is located near an edge of the BSA may be in a state or condition such that the STA cannot communicate concurrently with other devices. As illustrated in  FIG. 2B , STAs  206 A,  206 F, and  206 G may be devices that are in a state or condition in which they cannot communicate concurrently with other devices. Likewise, a STA that is located near the center of the BSA may be in a station or condition such that the STA can communicate concurrently with other devices. As illustrated in  FIG. 2 , STAs  206 B,  206 C,  206 D,  206 E, and  206 H may be devices that are in a state or condition in which they can communicate concurrently with other devices. Note that the classification of devices is not permanent. Devices may transition between being in a state or condition such that they can communicate concurrently and being in a state or condition such that they cannot communicate concurrently (e.g., devices may change states or conditions when in motion, when associating with a new AP, when disassociating, etc.). 
     Furthermore, devices may be configured to behave differently based on whether they are ones that are or are not in a state or condition to communicate concurrently with other devices. For example, devices that are in a state or condition such that they can communicate concurrently may communicate within the same spectrum. However, devices that are in a state or condition such that they cannot communicate concurrently may employ certain techniques, such as spatial multiplexing or frequency domain multiplexing, in order to communicate over the medium. The controlling of the behavior of the devices may be performed by the high-efficiency wireless component in the APs  254 A-C and/or the STAs  256 A-H. 
     In an embodiment, devices that are in a state or condition such that they cannot communicate concurrently use spatial multiplexing techniques to communicate over the medium. For example, power and/or other information may be embedded within the preamble of a packet transmitted by another device. A device in a state or condition such that the device cannot communicate concurrently may analyze the preamble when the packet is sensed on the medium and decide whether or not to transmit based on a set of rules. 
     In another embodiment, devices that are in a state or condition such that they cannot communicate concurrently use frequency domain multiplexing techniques to communicate over the medium.  FIG. 3  shows frequency multiplexing techniques that may be employed within the wireless communication systems  100  of  FIG. 1 and 250  of  FIG. 2B . As illustrated in  FIG. 3 , an AP  304 A,  304 B,  304 C, and  304 D may be present within a wireless communication system  300 . Each of the APs  304 A,  304 B,  304 C, and  304 D may be associated with a different BSA and include the high-efficiency wireless component described herein. 
     As an example, the bandwidth of the communication medium may be 80 MHz. Under the regular 802.11 protocol, each of the APs  304 A,  304 B,  304 C, and  304 D and the STAs associated with each respective AP attempt to communicate using the entire bandwidth, which can reduce throughput. However, under the high-efficiency 802.11 protocol using frequency domain multiplexing, the bandwidth may be divided into four 20 MHz segments  308 ,  310 ,  312 , and  314  (e.g., channels), as illustrated in  FIG. 3 . The AP  304 A may be associated with segment  308 , the AP  304 B may be associated with segment  310 , the AP  304 C may be associated with segment  312 , and the AP  304 D may be associated with segment  314 . 
     In an embodiment, when the APs  304 A-D and the STAs that are in a state or condition such that the STAs can communicate concurrently with other devices (e.g., STAs near the center of the BSA) are communicating with each other, then each AP  304 A-D and each of these STAs may communicate using a portion of or the entire 80 MHz medium. However, when the APs  304 A-D and the STAs that are in a state or condition such that the STAs cannot communicate concurrently with other devices (e.g., STAs near the edge of the BSA) are communicating with each other, then AP  304 A and its STAs communicate using 20 MHz segment  308 , AP  304 B and its STAs communicate using 20 MHz segment  310 , AP  304 C and its STAs communicate using 20 MHz segment  312 , and AP  304 D and its STAs communicate using 20 MHz segment  314 . Because the segments  308 ,  310 ,  312 , and  314  are different portions of the communication medium, a first transmission using a first segment would not interference with a second transmission using a second segment. 
     Thus, APs and/or STAs, even those that are in a state or condition such that they cannot communicate concurrently with other devices when following 11ac or older protocols, if they include the high-efficiency wireless component, they can communicate concurrently with other APs and STAs without interference. Accordingly, the throughput of the wireless communication system  300  may be increased. In the case of apartment buildings or densely-populated public spaces, APs and/or STAs that use the high-efficiency wireless component may experience reduced latency and increased network throughput even as the number of active wireless devices increases, thereby improving user experience. 
       FIG. 4  shows an exemplary functional block diagram of a wireless device  402  that may be employed within the wireless communication systems  100 ,  250 , and/or  300  of  FIGS. 1 ,  2 B, and  3 . The wireless device  402  is an example of a device that may be configured to implement the various methods described herein. For example, the wireless device  402  may comprise the AP  104 , one of the STAs  106 , one of the APs  254 , one of the STAs  256 , and/or one of the APs  304 . 
     The wireless device  402  may include a processor  404  which controls operation of the wireless device  402 . The processor  404  may also be referred to as a central processing unit (CPU). Memory  406 , which may include both read-only memory (ROM) and random access memory (RAM), may provide instructions and data to the processor  404 . A portion of the memory  406  may also include non-volatile random access memory (NVRAM). The processor  404  typically performs logical and arithmetic operations based on program instructions stored within the memory  406 . The instructions in the memory  406  may be executable to implement the methods described herein. 
     The processor  404  may comprise or be a component of a processing system implemented with one or more processors. The one or more processors may be implemented with any combination of general-purpose microprocessors, microcontrollers, digital signal processors (DSPs), field programmable gate array (FPGAs), programmable logic devices (PLDs), controllers, state machines, gated logic, discrete hardware components, dedicated hardware finite state machines, or any other suitable entities that can perform calculations or other manipulations of information. 
     The processing system may also include machine-readable media for storing software. Software shall be construed broadly to mean any type of instructions, whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise. Instructions may include code (e.g., in source code format, binary code format, executable code format, or any other suitable format of code). The instructions, when executed by the one or more processors, cause the processing system to perform the various functions described herein. 
     The wireless device  402  may also include a housing  408  that may include a transmitter  410  and/or a receiver  412  to allow transmission and reception of data between the wireless device  402  and a remote location. The transmitter  410  and receiver  412  may be combined into a transceiver  414 . An antenna  416  may be attached to the housing  408  and electrically coupled to the transceiver  414 . The wireless device  402  may also include (not shown) multiple transmitters, multiple receivers, multiple transceivers, and/or multiple antennas. 
     The wireless device  402  may also include a signal detector  418  that may be used in an effort to detect and quantify the level of signals received by the transceiver  414 . The signal detector  418  may detect such signals as total energy, energy per subcarrier per symbol, power spectral density and other signals. The wireless device  402  may also include a digital signal processor (DSP)  420  for use in processing signals. The DSP  420  may be configured to generate a packet for transmission. In some aspects, the packet may comprise a physical layer data unit (PPDU). 
     The wireless device  402  may further comprise a user interface  422  in some aspects. The user interface  422  may comprise a keypad, a microphone, a speaker, and/or a display. The user interface  422  may include any element or component that conveys information to a user of the wireless device  402  and/or receives input from the user. 
     The wireless devices  402  may further comprise a high-efficiency wireless component  424  in some aspects. The high-efficiency wireless component  424  may include a classifier unit  428  and a transmit control unit  430 . As described herein, the high-efficiency wireless component  424  may enable APs and/or STAs to use a modified mechanism that minimizes the inefficiencies of the CSMA mechanism (e.g., enables concurrent communications over the medium in situations in which interference would not occur). 
     The modified mechanism may be implemented by the classifier unit  428  and the transmit control unit  430 . In an embodiment, the classifier unit  428  determines which devices are in a state or condition such that they can communicate concurrently with other devices and which devices are in a state or condition such that they cannot communicate concurrently with other devices without additional orthogonalization in time, frequency, or space. In an embodiment, the transmit control unit  430  controls the behavior of devices. For example, the transmit control unit  430  may allow certain devices to transmit concurrently on the same medium and allow other devices to transmit using a spatial multiplexing or frequency domain multiplexing technique. The transmit control unit  430  may control the behavior of devices based on the determinations made by the classifier unit  428 . 
     The various components of the wireless device  402  may be coupled together by a bus system  426 . The bus system  426  may include a data bus, for example, as well as a power bus, a control signal bus, and a status signal bus in addition to the data bus. Those of skill in the art will appreciate the components of the wireless device  402  may be coupled together or accept or provide inputs to each other using some other mechanism. 
     Although a number of separate components are illustrated in  FIG. 4 , those of skill in the art will recognize that one or more of the components may be combined or commonly implemented. For example, the processor  404  may be used to implement not only the functionality described above with respect to the processor  404 , but also to implement the functionality described above with respect to the signal detector  418  and/or the DSP  420 . Further, each of the components illustrated in  FIG. 4  may be implemented using a plurality of separate elements. 
     In some implementations, resources and operational modes of APs/STAs in networks with dense deployments of multiple BSSs are coordinated to reduce interference. In some aspects, one or more dimensions including time, frequency, space, and power are coordinated between APs/STAs. In some aspects, coordination messages are sent between APs/STAs. In some aspects, specific enhancements to 802.11ah scheduling and 802.11aa coordination protocol are employed. 
     Coordination can be achieved as explicit communication across APs/STAs of different BSSs. For example, via messages exchanged over the air or messages exchanged over a separate communication mean (e.g., cable backhaul connection). Messages can be exchanged directly between APs, between APs via STAs, directly between STAs, or between STAs via AP. 
     Coordination can be achieved as implicit communications/measurements based on observation of the traffic on the medium. For example, packets may be enhanced to carry partial information that can help the coordination 
     Coordination final decisions can be made by a central informed controller, at each AP, with a distributed heuristic, or at each STA, based on exchanged info. 
       FIG. 5  shows examples of coordinated transmissions that may be employed within the wireless communication systems  100  of  FIG. 1 and 250  of  FIG. 2B .  FIG. 5  illustrates three access points  504 A-C. Each access point  504 A-C manages a corresponding BSS  502 A-C. Each access point  504 A-C is in communication with a plurality of stations  506 . For example, access point  504 A is in communication with stations  506 A-C, while access point  504 C is in communication with stations  506 G-H. 
     In some aspects, the physical location of a station relative to other stations, its associated access point, and/or other access points may make the station more or less subject to interference. For example, because stations  506 D-E are positioned relatively close to their access point  504 B and relatively far from other BSS&#39;s  502 A and  502 C, and access points and stations communicating within those BSS&#39;s, stations  506 D-E may be less susceptible to interference when either of those BSS&#39;s communicate. Similarly, STA  506 H may be less susceptible to interference from transmissions generated by either BSS  502 A or  502 B. Because these devices may not be susceptible to interference, some of the devices may communicate concurrently with other devices, even if a traditional carrier sense media access mechanism would prevent such concurrent transmission. For example, STA  506 H may communicate with access point  504 C concurrently with access point  504 B communicating with stations  506 D or  506 E. 
     Other stations may be more susceptible to interference, for example, stations positioned relatively further from their access points and/or relatively closer to wireless devices of other BSSs may be more susceptible to interference. 
     The wireless device  402  may comprise an AP  104 , a STA  106 , an AP  254 , a STA  256 , and/or an AP  304 , and may be used to transmit and/or receive communications. That is, either AP  104 , STA  106 , AP  254 , STA  256 , or AP  304  may serve as transmitter or receiver devices. Certain aspects contemplate signal detector  418  being used by software running on memory  406  and processor  404  to detect the presence of a transmitter or receiver. 
     In a dense BSS scenario as illustrated in  FIG. 5 , significant throughput gains can be achieved if BSSs coordinate their access to the airwaves or medium in one or more of time, frequency, space, and power. In some implementations, APs  504 A,  504 B, and  504 C coordinate the use of resources and operational modes of the shared medium to reduce the likelihood that wireless devices  402  are subject to interference. A wireless device  402  can be subject to interference by either causing interference with another wireless device  402  or experiencing interference caused by another wireless device  402 . 
     In other implementations, one of the APs  504 A,  504 B, and  504 C receives instructions from another one of the APs  504 A,  504 B, and  504 C to modify its use or one of the wireless devices  402  associated with the receiving AP use of the airwaves or medium to reduce the likelihood that a wireless device  402  is subject to interference. In certain embodiments, the APs  504 A,  504 B, and  504 C exchange information to coordinate their use of the shared medium. In other embodiments the AP  504 A,  504 B, and  504 C receives an instruction from another AP  504 A,  504 B, and  504 C on how it should use the shared medium. 
     For example, the APs  504 A,  504 B, and  504 C can coordinate access to the shared medium even when the APs are associated with different BSS  502 A,  502 B, and  502 C. The APs  504 A,  504 B, and  504 C can determine whether one or more wireless devices  402  is subject to interference with another wireless device in the wireless network. The APs  504 A,  504 B, and  504 C identify the one or more wireless devices  402  that are subject to interference via identifying information such as a MAC address. The APs  504 A,  504 B, and  504 C then receive information from each other on the nature of the interference and/or the shared medium. The APs  504 A,  504 B, and  504 C then modify the use of the shared medium by one or more of the wireless devices  402  to reduce the likelihood that the wireless device is subject to interference. In some implementations, this modification includes transmission of one or more messages  508 A,  508 B, and  508 C between APs as illustrated in  FIG. 5 . 
     In other embodiments, the AP  504 A,  504 B, and  504 C receives an instruction from another AP  504 A,  504 B, and  504 C on how it should use the shared medium. For example, the AP  504 A,  504 B, and  504 C can receive information associated with the first or second BSSs. The information can include an identification of one or more wireless devices that are subject to interference. The receiving AP  504 A,  504 B, and  504 C then modifies, based on the received information, the use of the shared medium to reduce the likelihood that the one or more wireless devices are subject to interference. The modification can be to resources including, but not limited to, time, frequency, and space. The modification can be to operation modes including, but not limited to, transmission parameters and access modes. 
     Time 
     In some implementations where the modification or coordination relates to time, orthogonal activity periods are scheduled across APs  504 A,  504 B, and  504 C. In some implementations, scheduling of orthogonal activity periods across APs  504 A,  504 B, and  504 C is only for transmission to a certain subset of wireless devices  402  or users. Other users can be served at any time. An exemplary subset is “edge users” or wireless devices  402  that may suffer interference from neighboring APs  504 A,  504 B, and  504 C. In some implementations, DL/UL transmissions are aligned across APs  504 A,  504 B, and  504 C. Additional implementations are described below. 
     Frequency 
     In some implementations where the modification or coordination relates to frequency, orthogonal channels are scheduled for transmission use across BSS  502 A,  502 B, and  502 C. For example, a primary channel location is scheduled across APs  504 A,  504 B, and  504 C. In some implementations, orthogonal channels are scheduled across APs  504 A,  504 B, and  504 C for only a subset of wireless devices  402  or STAs. Other wireless devices  402  or STAs can be served on any channel. In some implementations, channels used for DL/UL transmissions are aligned across APs  504 A,  504 B, and  504 C. Additional implementations are described below. 
     Space 
     In some implementations where the modification or coordination relates to spatial domains, orthogonal “beams” are scheduled across BSS  502 A,  502 B, and  502 C. In some implementations, beams are aligned across APs  504 A,  504 B, and  504 C. Additional implementations are described below. 
     Power 
     In some implementations where the modification or coordination relates to power, coordination is achieved by selecting transmission power for DL and UL transmissions across APs  504 A,  504 B, and  504 C. Additional implementations are described below. 
     Coordination of Resources 
     Coordination across APs  504 A,  504 B, and  504 C can be achieved as explicit communications across APs  504 A,  504 B, and  504 C/STAs  506 A-H of different BSS  502 A,  502 B, and  502 C and/or implicit communications/measurements based on observation of the traffic on the medium. For example, explicit messages (e.g., messages  508 A-C) can be sent over the air or over a separate communication means such as a cable backhaul. In some implementations, messages are exchanged directly between APs  504 A,  504 B, and  504 C, between APs  504 A,  504 B, and  504 C via STAs  506 A-H, directly between STAs  506 A-H, and/or between STAs  506 A-H via APs  504 A,  504 B, and  504 C. In some implementations which use implicit communications, packets are enhanced to carry partial information that can help the coordination. In some implementations, coordination of final decisions are made by a central informed controller, with a distributed heuristic at each AP, and/or based on exchanged information at each STA. 
     In some implementations of the coordination protocol, APs  504 A,  504 B, and  504 C/STAs  506 A-H exchange information on resources including time/frequency/space/power. In some implementations, APs  504 A,  504 B, and  504 C/STAs  506 A-H exchange information on operation modes including transmission parameters and access modes. The exchanged information can include positive or negative requests. For example, a positive request can be for the sender AP  504 A,  504 B, and  504 C to use a requested resources/operation modes. A negative request can be for the receiving AP  504 A,  504 B, and  504 C to not use the indicated resources/operation modes. 
     Time 
     In some implementations where time is coordinated across APs  504 A,  504 B, and  504 C, messages exchanged across APs  504 A,  504 B, and  504 C/STAs  506 A-H include positive/negative requests for one or more of start time, duration, periodicity of access time to which the positive/negative request is referred to, and/or types of allowed access. For example, types of access can include enhanced distributed channel access (EDCA)/backoff/schedule parameters such as an arbitration inter frame spacing (AIFS), contention window min or max (CWmin, CWmax), TXOP limit, and CCA thresholds. In some implementations, the type of access is traffic QoS such as admission control (AC), max amount of transmission time and/or bytes allowed. 
     In some implementations, the coordination protocol includes a mechanism that allows APs  504 A,  504 B, and  504 C/STAs  506 A-H to reach an agreement on time usage so that transmissions of neighboring APs  504 A,  504 B, and  504 C/STAs  506 A-H are disjoint in time and/or transmissions to/from a certain set of STAs  506 A-H. For example, STAs  506  that are indicated as interfering in the messaging are allocated non overlapping RAWs/TWTs across neighboring APs  504 A,  504 B, and  504 C. In certain implementations, the interfering wireless device may be an APs  504 A,  504 B, and  504 C. For example, STAs  506 A-H that are ‘likely to be interfered’ or have a weak link or have limitations on the BW such as edge STA  506 A,  506 F,  506 G are allocated disjoint time resources. In some implementations UL transmissions (from STAs only) are allowed or DL transmission (from AP) are allowed, or both in an overlapping restricted access window (RAW) timing and/or target wakeup time (TWT) timing. In some implementations, it is preferred that transmissions to/from STAs with same or similar access modes (QoS/EDCA parameters) happen at the same time while transmissions to/from STAs with different access modes (QoS/EDCA parameters) happen at different times. 
     STAs/APs Coordination 
     In some implementations, APs  504 A,  504 B, and  504 C/STAs  506 A-H exchange requests/responses for use of resources and operation modes by specific STAs  506 A-H/APs  504 A,  504 B, and  504 C. Messages exchanged across APs  504 A,  504 B, and  504 C/STAs  506 A-H can include positive/negative requests for one or more specific STAs  506 A-H/APs  504 A,  504 B, and  504 C. For example, the specific STAs  506 A-H/APs  504 A,  504 B, and  504 C can be a number/group of STAs that belong to the AP sending the message. The sending AP would like to be active in terms of address, location, and/or a transmission characteristic such as power, rate, and interference condition. 
     In some implementations, the specific STAs  506 A-H/APs  504 A,  504 B, and  504 C is a group of STAs that include STAs belonging to the neighboring AP that will receive the message. The specific STAs  506  may be identified in terms of address, location, and/or transmission characteristic such as power, rate, and interference condition. In some implementations, the information identifies STAs  506  that interfere with the sending AP operation, or with operation of STAs associated with the sending AP. 
     In some implementations, the specific STAs  506 A-H/APs  504 A,  504 B, and  504 C is a group of STAs that indicate operation capability of STAs such as type of protocols supported (802.11a/n/ac/b), TX/RX parameters supported, and/or type of operation/traffic supported. 
     In some implementations, the coordination protocol includes a mechanism that allows APs  504 A,  504 B, and  504 C/STAs  506 A-H to reach an agreement on which STAs are allowed access to prevent interfering STAs from using the same resource and/or to schedule the same resources for STAs that have similar transmission characteristics. For example, in some implementations, edge STAs  506 A,  506 F, and  506 G are scheduled at the same time while center STAs  506 B-E, H are scheduled at the same time. In some implementations, only STAs with compatible operation modes are sharing resources. 
     Frequency 
     In some implementations, APs  504 A,  504 B, and  504 C/STAs  506 A-H exchange requests/responses for use of resources and operation modes in certain frequency bands/channels. Messages exchanged across APs  504 A,  504 B, and  504 C/STAs  506 A-H can include positive/negative requests for one or more of a primary channel, channel(s) used for transmission, allowed transmission BW, allowed mode of transmission such as direction UL/DL and PHY mode, allowed STAs  506 A-H/APs  504 A,  504 B, and  504 C for transmission in each channel such as inner/outer STAs and interfering STAs that are allowed/not allowed to transmit. 
     In certain implementations, the coordination protocol includes a mechanism that allows APs  504 A,  504 B, and  504 C/STAs  506 A-H to reach an agreement on which STAs are allowed to access such that disjoint primary channels are allocated to interfering APs  504 A,  504 B, and  504 C/STAs  506 A-H. Allowed transmission BW can be optimized for reuse by, for example, limiting transmission BW such that independent resources are available for APs  504 A,  504 B, and  504 C. In some implementations, different channels/BW are used for STAs in different locations/transmit conditions. For example, center STAs  506 B-E, H can be allowed to use all the BW while edge STAs  506 A,  506 F, and  506 G use a channel that is different from the channel used by edge STAs  506 A,  506 F, and  506 G in neighboring APs  504 A,  504 B, and  504 C. 
     Spatial Coordination 
     In some implementations, APs  504 A,  504 B, and  504 C/STAs may exchange requests/responses for use of resources and operation modes in certain spatial domains. Messages exchanged across APs  504 A,  504 B, and  504 C/STAs  506 A-H can include positive/negative requests for one or more of a location of the STA/APs  504 A,  504 B, and  504 C that can use the shared medium including direction UL/DL. In some implementations, the requests relate to identification of the spatial domain such as absolute/relative geographical description/positioning or interfering relations between STAs/APs  504 A,  504 B, and  504 C. In other implementations, the requests include an indication of whether beam forming is allowed or which spatial sectors or spatial beams are to be used. In some implementations, interfering relations between STAs/APs  504 A,  504 B, and  504 C can be based on strength of interference and/or exact channel representation. 
     In some implementations, the communication protocol includes a mechanism that allows APs  504 A,  504 B, and  504 C/STAs to reach an agreement such that non interfering spatial domains are used across BSS  502 A,  502 B, and  502 C by, for example, employing orthogonal sectors, beams, and STAs locations. In some implementations, simultaneous transmissions are TX/RX filtered based on channel state information received by all involved STAs so that cross interference is minimized. 
     Transmission of Coordination Messages 
     In some implementations, coordination messages are sent by APs  504 A,  504 B, and  504 C/STAs  506 A-H on a common control channel. The common control channel can be a commonly identified frequency channel that is common among the operating BWs of the neighboring APs  504 A,  504 B, and  504 C/STAs  506 A-H. For example, the channel may be one of the 20 Mhz channels out of the 80/160/320 data operation band or in a band that is disjoint from the data operation band such as when data is exchanged in 2.4 GHz and control is exchanged in 900 MHz. An advantage of using 900 MHz is the transmission has a greater range than 2.4 GHz to reach distant APs  504 A,  504 B, and  504 C. In some implementations, the common control channel is statically identified by the standard specifications. For example, a default 20 MHz channel for each allowed operating 20/40/80/160 BSS  502 A,  502 B, AND  502 C operating channel is used in some implementations. In some implementations, channels are agreed across neighboring APs  504 A,  504 B, and  504 C via a distributed election protocol. In some implementations, the coordination messages are sent at a common time agreed across neighboring APs  504 A,  504 B, and  504 C/STAs  506 A-H. 
     In some implementations, coordination messages are sent by APs  504 A,  504 B, and  504 C and relayed by STAs  506 A-H to reach neighboring APs  504 A,  504 B, and  504 C. For example, the coordination messages can be carried by STA-STA or STA-AP communications across STAs  506 A-H/APs  504 A,  504 B, and  504 C that are not associated with each other. In some implementations, Generic Advertisement Service (GAS) frames or other frames are exchanged without an association in place to send coordination messages. In other implementations, coordination messages are carried by STA-STA or STA-AP communications across STAs/APs  504 A,  504 B, and  504 C associated with each other using, for example, a new form of STA-STA or STA-AP association across BSS  502 A,  502 B, and  502 C. 
     In some implementations, the coordination messages used to exchange information are sent in new frames defined by the IEEE standard such as management frames  520  (see  FIG. 5A ), action frames  524  (see  FIG. 5B ), and/or GAS frames  526  (see  FIG. 5C ). The new frames can include HEW parameters  522  that can be exchanged across APs  504 A,  504 B, and  504 C. In some implementations, only certain of the existing indications of the new frames are employed. In some implementations additional indications, such as the HEW parameters  522 , are added to the existing indications already defined by the new frames. 
     In some implementations, the coordination messages are embedded in existing frames by using reserved bits. For example, reserved bits  528  can be used to override the HTC control field  530  in HT or VHT format as is illustrated in  FIG. 5D . In some implementations, parameters related to usage of resources are implicitly derived by measuring activity on the resource of interest. 
     Time Coordination 
     In some implementations where time is coordinated between APs  504 A,  504 B, and  504 C, existing communication protocols are used. For example, 802.11ah defines protocols (alternative to hybrid coordination function (HCF) Controlled Channel Access (HCCA)) for time schedule within BSS  502 A,  502 B, and  502 C with no coordination using restricted access window (RAW) and target wake time (TWT). RAW is an interval of time advertised by the AP in a beacon which is reserved for access to only a certain group of STAs. In a modification, the group is empty which prevents all STAs from transmitting at a certain time. TWT is an agreement between AP and an STA for a time when the STA is to be awake and engage in communication with the AP. In a modification, the STAs cannot transmit outside the agreed time. 
     In certain embodiments, the coordination protocol allows the exchange of RAW and TWT parameters across APs  504 A,  504 B, and  504 C so that RAW/TWT parameter settings can be coordinated across APs  504 A,  504 B, and  504 C. For example, the set of parameters that define a RAW are listed in the RPS Information element defined by 802.11ah. 
       FIG. 6  is a representation of a modified restricted access window (RAW) parameter set (RPS) information element defined by 802.11ah that includes HEW parameters  602  than can be exchanged across APs  504 A,  504 B, and  504 C. In some implementations, only certain of the existing indications defined by 802.11ah are employed. In some implementations additional indications, such as HEW parameters  602 , are added to the existing indications already defined by 802.11ah. Within the coordination protocol, APs  504 A,  504 B, and  504 C can exchange one or more of the above indications including the HEW parameters  602  per each potential RAW or TWT or equivalent reservation protocol. The provided parameters may refer to a (positive) request for the sender AP  504 A,  504 B, and  504 C to use the requested resources/operation modes or a (negative) request for the receiving AP  504 A,  504 B, and  504 C not to use the indicated time/operation. 
     In some implementations, one or more of the above indications is included in the same or similar message as the Transmit Opportunity (TXOP) Advertisement frame used in 802.11aa. 802.11aa defines a protocol for AP  504 A,  504 B, and  504 C to AP  504 A,  504 B, and  504 C coordination where APs  504 A,  504 B, and  504 C can decode each other&#39;s beacons. Protocol messaging is included in the beacon or exchanged though action frames. Messaging can be encrypted with a key known by APs  504 A,  504 B, and  504 C. In some implementations, the messages include time synchronization (TSF) and/or requests for the use of an interval of time for medium access (TXOP) that is always available to the AP. The coordination protocol allows agreement on the TXOP allocation across APs  504 A,  504 B, and  504 C. Under 802.11aa, APs  504 A,  504 B, and  504 C exchange information to manage their STAs medium access by using a medium access procedure such as HCF Controlled Channel Access (HCCA). Under HCCA STAs are not allowed to access the medium unless they are polled by the AP  504 A,  504 B, and  504 C. In this way the AP  504 A,  504 B, and  504 C is in full control of medium usage. However, 802.11aa is limited in that it only uses AP-AP direct communications, only allows for time allocation of TXOP, and only refers to the use of HCCA as medium access techniques. 
     In some implementations, APs  504 A,  504 B, and  504 C use action frames defined by 802.11aa to share request/responses about TXOP allocation. 
       FIG. 7  is a representation of a modified advertisement action frame action field and of a TXOP reservation field format defined by 802.11aa that includes HEW parameters  702 . In some implementation, additional information, such as HEW parameters  702 , is transported via the protocol defined by 802.11aa by means of modified or new frame formats. In some implementations, additional protocol rules are also defined as set forth above. 
     In some implementations, certain STAs from different BSS are allowed to transmit at the same time even in cases where the current WiFi CSMA procedure would not allow transmission. For example, “cell center” STAs  802  in  FIG. 8  are allowed to transmit at the same time. Certain STAs from the different BSSs are prevented from transmitting at the same time even in cases where the current WiFi CSMA procedure would allow transmission. For example, “cell edge” STAs  804  in  FIG. 8  are prevented from transmitting even if allowed by the current WiFi CSMA procedure. 
     Referring to  FIGS. 5 and 8 , in some implementations, coordination requires identification of the STAs/APs that interfere with each other such as cell center STAs  506 B-E,  506 H,  802  and cell edge STAs  506 A,  506 F,  506 G,  804 , communication across APs/STAs of different BSSs to agree on the time schedule, and/or the use of a scheduling protocol that determines the schedule. 
     In some implementations, interfered STAs such as cell center STAs  506 B-E,  506 H,  802  and cell edge STAs  506 A,  506 F,  506 G,  804  are reported by STAs to the AP. The interfered STA can be identified by its MAC address or a Partial AID (PAID) address. In some implementation, STAs report interfered STAs belonging to neighboring BSSs. In some implementations where the MAC address is not available because, for example, the address is sent at a high rate, a Partial AID may be used. However, a Partial AID may not be unique to the STA. To increases the uniqueness of the Partial AID, the neighboring APs  504 A,  504 B, and  504 C can use disjoint PAID spaces. Access points may exchange signaling to coordinate the selection of disjoint Partial AID spaces. In some implementations, the reporting STA includes additional interference information such as signal strength and frequency of interference. In some implementations, 802.11k messaging or similar is used. 
     In some implementations, STAs request to be considered in one of at least two classes such as interfered or non-interfered. The request can be based on the level of interference experienced from BSS AP/STA packets even without precise identification of the interference source. 
     In some implementations, interfered STAs such as cell center STAs  506 B-E,  506 H,  802  and cell edge STAs  506 A,  506 F,  506 G,  804  are classified by the AP based on throughput/Packet error rate or by messages sent by STAs over the air and collected by the AP. In some implementations, the messages are sent in management frames with contention or at scheduled times. 
     Referring back to  FIG. 5 , a time schedule can be agreed across APs  504 A,  504 B, and  504 C/STAs of different BSS  502 A,  502 B, and  502 C. In some implementations, a modified 802.11aa framework is used. For example, the messages being sent across APs  504 A,  504 B, and  504 C may include requested interval of time, a list of STAs that should be silenced during the requested time or that should adopt certain medium access procedure (may include AP), and/or the specific settings for the access procedure, such as QoS/enhanced distributed channel access (EDCA) parameters that should be used during that time, allowed Access Category, clear channel assessment parameters (CCA and energy detection threshold), maximum transmission duration, maximum amount of traffic that can be delivered, allowed power of transmission and other transmit operation modes parameters. 
     In some implementations where time coordination across APs  504 A,  504 B, and  504 C is based on received information, the protocol schedules reserved time or adapts the behavior of the interfering STA. For example, if reserved time is granted based on communication across APs  504 A,  504 B, and  504 C, the requesting AP/STAs uses the reserved time for transmission to the AP/STAs that would otherwise have experienced interference. During this time the requesting AP/STAs may access the medium with favorable access procedures. Favorable access procedures include the use of a less sensitive clear channel assessment or no clear channel assessment at all, the use of EDCA parameter settings that result in higher priority access to the medium, the use of a longer transmission, higher maximum amount of traffic delivered, higher power of transmission, and/or other favorable transmit operation modes. During this time the requesting AP/STAs may also not defer medium access upon detection of packets on the medium, as it would be requested by 802.11 medium access procedures. AP/STAs may instead drop certain detected packets and ignore them, considering the medium available for transmission. The certain packets may be identified by a Partial AID, a MAC address, and/or an explicit indication embedded in the PHY preamble. 
     In some implementations, interfering STAs are forbidden from accessing during the reserved time or their access is subject to less favorable procedures. Less favorable access procedures include the use of a more sensitive clear channel assessment, the use of EDCA parameter settings that result in lower priority access to the medium, the use of shorter transmission, lower maximum amount of traffic delivered, lower power of transmission and/or other less favorable transmit operation modes. During this time interfering AP/STAs may also defer medium access upon detection of certain packets on the medium. The certain packets may be all the detected packets or may be identified by a Partial AID, a MAC address (e/g referred to an interfered STA), and/or an explicit indication embedded in the PHY preamble indicating that deferral must happen. 
     In some implementations, if the behavior of the interfering STA is adapted to protect interfered STAs without strict time boundaries, the interfering STAs must use a more sensitive deferral to frames sent by/to interfered STAs. For frames sent by/to other STAs deferral may be weaker. In some implementations, frames sent by/to interfered STAs can be identified via Partial AID in the PHY header, a MAC address, and/or specific bits in the PHY preamble. Sensitive deferral may refer to CCA levels, EDCA parameters, duration of transmissions, and/or use of RTS/CTS. In some implementation, interfered STAs are allowed to use techniques that favor their access by indicating with one bit in the PHY header that their transmission is protected, using favorable EDCA parameters, and/or using RTS/CTS. 
     Frequency Coordination 
       FIG. 9  is an exemplary wireless communication system employing frequency coordination. In some implementations, cell center STAs  904  use the whole bandwidth (BW). Cell edge STAs  902  can only be served with BW 1  while cell edge STAs  906  can only be served with BW 2 . Of course other arrangements are within the scope of the disclosure that reduces the likelihood of interference. 
     In some implementations, coordination requires identification of the STAs/APs that interfere with each other such as cell edge STAs  902 ,  906 . In some implementations, coordination requires communication across APs/STAs of different BSS to agree on the channels schedule. In some implementations, coordination requires the use of a scheduling protocol that determines the channel schedule. 
     In some implementations, interfered STAs such as ‘cell center’ STAs and ‘cell edge’ STAs are reported by STAs to the AP. The interfered STA can be identified by its MAC address or a Partial AID address. In some implementation, the STA reports interfered STAs belonging to neighboring BSS and includes a channel indication. In some implementations where the MAC address is not available because, for example, the address is sent at high rate, a Partial AID may be used. However, a Partial AID may not be unique to the STA. To increases the uniqueness of the Partial AID, the neighboring APs can use disjoint PAID spaces. In some implementations, the reporting STA includes additional interference information such as signal strength and frequency of interference. In some implementations, 802.11k messaging or similar is used. 
     In some implementations, STAs request to be considered in one of at least two classes such as interfered or non-interfered. The request can be based on the level of interference experienced from BSS AP/STA packets even without precise identification of the interference source. 
     In some implementations, interfered STAs such as ‘cell center’ STAs and ‘cell edge’ STAs are classified by the AP based on throughput/Packet error rate/channel or by messages sent by STAs over the air and collected by the AP. In some implementations, the messages are sent in management frames with contention or at scheduled times. 
     Referring to  FIG. 5 , a frequency schedule can be agreed across APs  504 A,  504 B, and  504 C/STAs of different BSS  502 A,  502 B, and  502 C. In some implementations, a modified 802.11aa framework is used. For example, the messages being sent across APs  504 A,  504 B, and  504 C may include a requested frequency channel, a list of STAs that should be silenced on the requested channel or that should adopt certain medium access procedure (may include AP), and/or the specific settings for the access procedure, such as QoS/enhanced distributed channel access (EDCA) parameters that should be used on the requested channel, allowed Access Category, clear channel assessment parameters (CCA and energy detection threshold), maximum transmission duration, maximum amount of traffic that can be delivered, allowed power of transmission and other transmit operation modes parameters. 
     In some implementations where frequency coordination across APs  504 A,  504 B, and  504 C is based on received information, the protocol schedules a reserved channel or adapts the behavior of the interfering STA. For example, if a reserved channel is granted based on communication across APs  504 A,  504 B, and  504 C, the requesting AP/STAs uses the reserved channel for transmission to the AP/STAs that would otherwise have experienced interference. Interfering STAs are forbidden from accessing the reserved channel or their access is subject to transmission parameter limitations. For example, on the reserved channel the requesting AP/STAs may access the medium with favorable access procedures. Favorable access procedures include the use of a less sensitive clear channel assessment or no clear channel assessment at all, the use of EDCA parameter settings that result in higher priority access to the medium, the use of a longer transmission, higher maximum amount of traffic delivered, higher power of transmission, and/or other favorable transmit operation modes. On the reserved channel the requesting AP/STAs may also not defer medium access upon detection of packets on the medium, as it would be requested by 802.11 medium access procedures. AP/STAs may instead drop certain detected packets and ignore them, considering the medium available for transmission. The certain packets may be identified by a Partial AID, a MAC address, and/or an explicit indication embedded in the PHY preamble. 
     In some implementations, interfering STAs are forbidden from accessing the reserved channel or their access is subject to less favorable procedures. Less favorable access procedures include the use of a more sensitive clear channel assessment, the use of EDCA parameter settings that result in lower priority access to the medium, the use of shorter transmission, lower maximum amount of traffic delivered, lower power of transmission and/or other less favorable transmit operation modes. On the reserved channel interfering AP/STAs may also defer medium access upon detection of certain packets on the medium. The certain packets may be all the detected packets or may be identified by a Partial AID, a MAC address (e/g referred to an interfered STA), and/or an explicit indication embedded in the PHY preamble indicating that deferral must happen. 
     If the behavior of the interfering STA is adapted to protect interfered STAs without strict channel boundaries, the interfering STAs uses a lower transmission BW and/or a more sensitive deferral to frames sent by/to interfered STAs. For frames sent by/to other STAs the deferral may be weaker. In some implementations, frames sent by/to interfered STAs can be identified via Partial AID in the PHY header, a MAC address, and/or specific bits in the PHY preamble. Sensitive deferral may refer to CCA levels, EDCA parameters, duration of transmissions, and/or use of RTS/CTS. In some implementation, interfered STAs are allowed to use techniques that favor their access by indicating with one bit in the PHY header that their transmission is protected, using favorable EDCA parameters, and/or using RTS/CTS. Please note that although described separately, coordination in time and frequency may happen simultaneously. 
     Example High Efficiency Wireless (HEW) Access Point (AP) Coordination Protocol 
     Techniques and apparatus are provided herein for protocols that may allow access points (APs) to coordinate periods of time where interference can be controlled to desired levels. For example, the APs may coordinate resource usage and operation modes of APs and stations (STAs). This may useful in networks with dense deployments of multiple basic service sets (BSSs). The protocol provided herein may identify specific messaging, scheduling, and coordination. The techniques provided herein may provide enhancements, for example, to the 802.11ah scheduling and 802.11aa coordination protocols described above. 
     In an example implementation, using the techniques provided herein may allow APs to coordinate what frequencies the APs transmit on. According to certain aspects, the “time periods” for coordination may extend for many multiples of the beacon periods. 
     In a dense BSS scenario (e.g., similar to the dense BSS scenario illustrated in  FIG. 5 ), potentially significant throughput gains may be achieved if BSSs can coordinate their transmissions for certain periods of time. During these times the BSSs can coordinate the type of traffic they send (e.g., downlink/uplink), which part of the frequency band they use, and what kind of access parameters they use. 
       FIG. 10  is a graph  1000  illustrating cumulative distribution functions (CDFs)  1002 ,  1004 ,  1006  for downlink throughput in a regularly spaced network, in accordance with certain aspects of the present disclosure. As shown in  FIG. 10 , one curve may correspond to the CDF  1304  for reuse equal to 1, where all APs send without any coordination in time or frequency. The top thirty percent (30%) of users may get very good throughput (tput), but the bottom fifty percent (50%) of users may be in outage. A second curve may correspond to the CDF  1306  for reuse equal to ⅓, where APs coordinate in frequency, but not time. The bottom fifty percent (50%) of users may no longer be in outage, but the top thirty percent (30%) may not achieve high throughput. A third curve may correspond to the CDF  1302  for a HEW scheme with 1⅓ reuse, where the APs coordinate in both frequency and time. The bottom fifty percent (50%) may no longer be in outage and the top thirty percent (30%) may still have high throughput. In aspects, the time and frequency coordination may be performed by the APs as shown in  FIGS. 8 and 9 , for example. APs can use time slots (e.g., time periods) with a lower reuse factor to send to interference sensitive users. User on the cell edge get served on BW 1  or BW 2  during even time slots, while users closer to the AP can be served with the entire bandwidth during odd time slots. 
     Uplink transmissions may interfere with the downlink transmissions of neighboring overlapping BSSs (OBSSs). Hence, certain time periods (e.g., slots) may be allocated for downlink only. This may avoid interference with uplink transmissions during those times. Alternatively, certain time periods may be set aside for uplink traffic only, so that the uplink traffic does not interfere with downlink traffic during these times. In aspects, certain time periods may be uplink and downlink. In aspects, certain time periods may have different reuse factors. 
     According to certain aspects, certain time periods may be allocated where the AP requests that certain nodes in OBSSs do not transmit. This may allow nodes that are sensitive to interference to transmit is an environment with less interference. Conversely, the AP could request that only certain nodes from OBSSs transmit during a reserved time. 
     It may be desirable to have time periods where neighboring BSSs are transmitting on orthogonal frequency bands (i.e., orthogonalized) in order to reduce interference. This may be achieved in a variety of ways. In one example, a maximum bandwidth (BW) may be specified for a particular time period, and the BSSs may randomly choose a channel of this maximum BW. In another example, a maximum BW may be specified for a particular time period, and the BSSs may select a channel for transmission by starting with their primary channel and increasing the channel until the channel reaches the maximum BW specified. The BSSs may also prenegotiate which channel to use when asked to transmit on a channel of a particular size. Alternatively, a “no interference” frequency may be specified for a particular time period, in which case the BSSs may be free to send on any frequency but the one specified. The time periods where neighboring BSSs send on different frequency bands may or may not include additional restrictions on the type of traffic. For example, the time periods may be restricted to downlink only, uplink only, or uplink and downlink periods. These time periods may also have additional specifications regarding the way devices are to access the medium during that time. For example, they may be restricted to use baseline carrier sensing multiple access (CSMA) with different values of CWmin or to use a special set of enhanced distributed channel access (EDCA) parameters, etc. 
     It may also be beneficial to have time periods with modified deferral rules. The deferral rules could be such that participating nodes do not need to defer to nodes that have a BSSID different from their own BSSID. Alternatively, participating nodes would not need to defer to nodes that have specific BSSIDs. These specific BSSIDs could be communicated to the other APs in the coordinating messages. The specific BSSIDs would also be communicated to the participating STAs. APs could use these time periods to allow service for users that are less sensitive to interference. 
     According to certain aspects, it is also possible to always allow a certain set of nodes in a BSS to forgo the normal deferral rules. For example, STAs that are far from neighboring BSSs may be allowed to forgo deferring to nodes that use a BSSID different from their own. Or, the BSSs may be allowed to forgo deferring to nodes that have a specific BSSID. 
     Some of these reserved time periods may also be such that APs and STAs allowed to use these time periods are granted favorable access to the medium. For example they could have less sensitive clear channel assessment levels, less stringent deferral rules, the use of more favorable EDCA parameters allowing faster access to the medium, the use of higher power, and or other favorable transmission options. This could help users of the new protocol not be adversely affected by legacy users. 
     Techniques and apparatus are provided herein for allowing APs to coordinate periods of time where interference may be controlled to various levels. According to certain aspects, coordination may include time synchronization, intra-AP scheduling, and the enforcement of the scheduling within the AP. In aspects, the coordination may be performed with over the air (OTA) messaging. Time synchronization and intra-AP scheduling may be performed with backhaul connection messaging. 
     Time synchronization may be performed in order to maintain synchronization in time between APs. According to certain aspects, time synchronization may be performed in a manner similar to social wifi (e.g., using certain methods from social wifi). For example, all nodes in a coordinating set may listen to a single (e.g., periodic) message (e.g., from a single master node) to update their clocks. According to certain aspects, a node, which may be within the coordinating set, may be selected as the “master” node. The other nodes in the set may update their clocks based on the clock of the master node. The designated master of the coordinating set may send out the synchronizing message (e.g., any message with timing information about when the message was sent). For instance, the master of the coordinating set may send out beacons at a particular interval. Other APs in the coordinating set may listen to the master&#39;s beacon and adjust their clocks based on the timing information in the beacon. According to certain aspects, the message sent by the master may not be a beacon, instead, any message having timing information about when the message was sent (e.g., according to the Master&#39;s clock) may be used. Other devices (i.e., “agents”), whether they be APs or STAs, may be used to relay the master&#39;s timing message. Therefore, multiple coordinating sets can be synchronized in time. The timing messages of nodes may all happen in a particular time window or each node may send its timing messages at an unrelated time from the other nodes. 
     According to certain aspects, methods (e.g., similar to 802.11aa methods) may be used for timing synchronization. For example, all nodes in a coordinating set may listen to timing messages from all their members (e.g., there may not be any master node). Each node may update its timer so that it does not lose synch with any member. Alternatively, each node may update its timer so that it stays in synch with as many members as possible. For certain systems (e.g., 802.11aa systems), it may be assumed that APs can hear the beacons of other APs they want to coordinate with. According to certain aspects, the nodes may update their timers based on a node that is furthest away in time. According to certain aspects, the nodes may update their timers to stay in synch with as many other nodes as possible. For each OBSS APs, an AP may listen to the beacon and may calculate 
     
       
      
       T 
       offset 
       =TT−TR,  
      
     
     where T offset  is the timing offset value, TT is the value in the Timestamp field in the received Beacon frame, and TR is the Beacon frame reception time measured using the AP&#39;s TSF timer. The AP may also store T offset  which may be used for converting OBSS AP&#39;s time to AP&#39;s time. The AP may also perform drift adjustment. For each OBSS AP, the AP may calculate 
         T   ClockDrift   =T   offset,1   −T   offset,0 , 
     where T ClockDrift  is the clock drift amount represented as twos complement, in microseconds, T offset,1  is the T offset  obtained from the previous beacon reception, and T offset,0  is the T offset  obtained from the current beacon reception. 
     According to certain aspects, if max_OBSS(T ClockDrift )&gt;0, the AP may suspend its TSF timer for the duration of the largest T ClockDrift . 
     According to certain aspects, coordinating sets may each have a Master which sends out periodic timing information (e.g., a beacon or other similar message). Nodes may belong to multiple coordinating sets. These nodes may listen to the timing messages of each master. The nodes may set their clocks so that they can stay in synch with as many masters as possible 
     It may be desirable to ensure that the APs can hear the messages that carry timing information so that the APs may remain in sync. For example, an AP may listen for synchronization messages during a quiet period for its STAs. According to certain aspects, the AP may send various messages in order to specify (i.e., reserve) the quiet period. Certain systems (e.g., 802.11aa systems) assume that the APs are in control of all transmissions and, hence, there may not be any uplink traffic in the BSS to interfere with a beacon reception from another AP in the coordinating set. Social wifi assumes that all nodes are listening for the timing messages. However, this may not be the case in a HEW system. In HEW, uplink transmissions may interfere with timing messages from other APs. If the AP misses beacons (e.g., due to interference from the UL transmissions), the AP may lose time synchronization with the other nodes it is coordinating with. 
     According to certain aspects, the AP may send a broadcast message reserving the time it will listen (listening time) to timing messages from other APs. According to certain aspects, this message may include the start times and durations that the AP wants to reserve so it can listen to timing messages. According to certain aspects, the message may be sent directly after the beacon. 
     According to certain aspects, the AP may send a quiet element to silence STAs in its BSS. The quiet element may define an interval during which no transmission should occur in the current channel. A quiet element may (e.g., as defined by the 802.11 standard) include the following fields: element ID, length, quiet count, quiet period, quiet duration, and quiet offset. In the case where multiple interference free periods (i.e., quiet periods) are desired, the AP may send multiple quiet elements to reserve the multiple periods. Alternatively, the quiet element itself may be modified to reserve multiple non-consecutive quiet periods. For example, a field for the number of quiet periods may be added to the quiet element as well as additional fields for quiet count, quiet period, quiet duration, and quiet offset. The multiplicity of the fields may be determined by the number of quiet periods desired. 
     According to certain aspects, the AP may wake sleeping users only after the reserved times have passed. The AP may wake users with target wake times (TWT). In this way, the AP may ensure that STAs do not send during the reserved periods. According to certain aspects, the AP may use a modified RAW frame or modified power save multi-poll (PSMP) message to reserve the period for listening without interference.  FIG. 11  illustrates an example frame  1100  field format for RAW, in accordance with certain aspects of the present disclosure. According to certain aspects, the AP may include a group ID in the RAW frame to which no STAs belong so that the STAs sleep during the reserved times. If there are multiple time periods that the AP wants to reserve per beacon frame, then the AP may send a RAW frame before each of the multiple time periods. Alternatively, the AP may modify the RAW frame to have multiple reserved periods. For example, the AP may add additional RAW start time &amp; RAW duration fields and a “number of reservations” field. As yet another alternative, the AP may send multiple consecutive RAW frames to reserve multiple periods for listening (e.g., 1 for each reservation needed). 
     According to certain aspects, the AP may send a single PSMP frame to schedule multiple STAs, for example, instead of sending direct quality of service (QoS)(+) contention free (CF)-Poll (e.g., as used in hybrid coordinated function (HCF) controlled channel access (HCCA)). This may reduce power consumption by providing an UL and DL schedule at the start of the PSMP phase so that each STA may only turn on its receiver if there is a downlink transmission time (DTT) scheduled for the STA and each STA may transmit only if it has an assigned uplink transmission time (UTT). There may be no need to perform clear channel assessment (CCA). The frame format of an example PSMP message  1200  is shown in  FIG. 12 . The AP may assign PSMP DTTs or UTTs to a STA ID corresponding to non-existent STAs, or other reserved STA ID, in order to make sure the medium is interference free. It can then listen to the timing messages from the other members of the coordinating set without interference from inside the BSS. If non-contiguous time reservations are desired, the PSMP message can be modified so that DTTs may be non-contiguous. 
     Intra-AP Scheduling 
     For intra-AP scheduling, scheduling information may be communicated across APs. One example of scheduling information to be communicated may be time allocation of reservation slot which may include: start time, where the start time is measured from (e.g., from the end of the sender&#39;s beacon time), duration of reservation, and periodicity of reservation time—if applicable. For example, the AP may specify that the reserved period will occur once during each of the next “x” beacon periods, where “x” could be 1-128. Alternatively, the AP may specify that the reserved period occurs during each beacon period until specified otherwise. 
     In addition to the timing of the reserved slot, another example of scheduling information that may be communicated across APs may include the type of coordinated access allowed per reservation may also be communicated across APs. According to certain aspects, the AP may reserve the listening time only for uplink, only for downlink, or for both uplink and downlink. According to certain aspects, the AP may reserve the listening period for silence from other members of the coordinated set. According to certain aspects, the AP may communicate bandwidth information for the reservation (e.g., when time coordination is paired with frequency coordination). For example, the AP may specify a particular bandwidth to reserve (i.e., for neighboring APs not to use during the reserved time) or a maximum bandwidth for its neighbors to use during the reserved time. According to certain aspects, the AP may specify which EDCA/backoff/schedule parameters (e.g., arbitrary interframe space (AIFS), CWmin, CWmax, TXOP limit, CCA thresholds) the neighboring APs may use during the reserve time. According to certain aspects, the AP may specify access classes during the reserved listening time. For example, the AP may specify a traffic quality of service (QoS) (e.g., ACs, max amount of transmit time/bytes allowed). 
     According to certain aspects, only master nodes can send out scheduling information (e.g., send a reservation). According to certain aspects, there may be only one master node per coordination set. Alternatively, there may be more than one master node per coordination set, but not all nodes in the coordination set are master nodes. In another alternative, all nodes in the coordination set may send out schedule information. According to certain aspects, non-scheduling nodes (i.e., nodes that do not send out scheduling information) may send input to the master node before the master node sends the schedule. 
     According to certain aspects, nodes sending out the schedule (i.e., scheduling nodes) may make the schedule based on their own needs. In this case, the scheduling node(s) do not solicit input from other nodes in the coordination sets and do not request/require responses to the scheduling messages. According to certain aspects, nodes sending out the schedule may make the schedule based on input received from other nodes in the coordination set prior to sending the schedule, but may not request/require responses from the other nodes before sending the scheduling message. 
     According to certain aspects, nodes sending out the schedule may request/require responses from members of the coordination set. According to certain aspects, a node sending a schedule sends the scheduling to, and gets a response to the message from, each member in the coordinating set. According to certain aspects, only nodes that contest the schedule send a response. According to certain aspects, a node sending a schedule may or may not get responses from other members of the coordinating set. According to certain aspects, a node sending the scheduling message may send a single scheduling message to all the members of the coordinating set and may set aside a time period after the message to receive responses from other members of the coordinating set. According to certain aspects, the responses may be scheduled. According to certain aspects, the response schedule may be contained in the original schedule message (e.g., the response schedule may be prenegotiated). Responders may contend for the medium (e.g., using standard 802.11 contention methods). According to certain aspects, responders may send simultaneously on different parts of the bandwidth using OFDMA. According to certain aspects, responders may send simultaneously using different spreading sequences. According to certain aspects, the scheduling node may keep sending until it receives a response. 
     According to certain aspects, scheduling information may be sent out at predetermined (e.g., prior to transmission of the scheduling information) times—for example, directly following the beacon period or within a predetermined recurring time slot where APs can contend to send scheduling messages. Alternatively, the scheduling messages may be sent during the same period as the timing coordination messages. This may allow the nodes in the coordinating set have already cleared the medium of interference so they can listen. If the scheduling messages are being sent out at predetermined times that are different from the timing messages, then the APs may reserve the medium for these times just as they reserved the medium for the timing messages. Alternatively, scheduling information may be sent out at times not predetermined (e.g., whenever the AP wants to send the message and has access to the medium). 
     According to certain aspects, any combinations of the various aspects and options described above for which nodes may send scheduling information, whether and how the scheduling is negotiable, and when the scheduling information is sent may be used. 
     As described above, the scheduling node may receive input from non scheduling nodes prior to scheduling. According to certain aspects, the input may specify whether extra protection is needed for that node, how much data a node has to be protected (e.g., how much data in each QoS class to be protected), what kind of protection is needed (e.g., downlink only, lower frequency reuse, complete silence from interferers, etc.), or if the current schedule provides too much or too little protected times. 
     According to certain aspects, non scheduling nodes in a coordination set may provide response to the scheduling messages sent from the scheduling nodes. The responses may include an ACK or NACK to the proposed reservation time. If the response includes a NACK, the response may also include the reason for the NACK (e.g., conflicts with another reserved time or too many reserved times). The response may also include an alternative reservation (e.g., alternative time for reservation, alternative duration for reservation, or alternative type of reservation). 
     According to certain aspects, for 802.11aa standard protocols setup, all nodes in the coordinating set may send scheduling requests. These requests may be called transmission opportunity (TxOP) advertisements. TxOP advertisements may request silence from the other nodes in the coordination set (e.g., overlapping BSSs) during the TxOP. All nodes in the coordinating set may respond to these scheduling requests. Responses may include alternate schedule suggestions. A TxOP advertisement frame may includes category, public action, dialog token, number of reported TxOP reservation, and number of pending TxOP reservations, active reservations, and TxOP reservations. The TxOP reservation field may include duration, service interval (SI), and start time. The duration subfield may specify the duration of the TxOP in units of 32 ns. The SI subfield may contain an 8-bit unsigned integer that specifies the SI of the reservation in units of milliseconds. The Start Time subfield is the offset from the next target beacon transmission time (TBTT) to the start of the first SP and may indicate the anticipated start time, expressed in microseconds, of the first TxOP after the TBTT. The response to TxOP advertisement frame may include category, public action, dialog token, status code, schedule conflict, alternative schedule, and avoidance request. 
     According to certain aspects, a modified TXOP frame may used by HEW APs to schedule coordination among other nodes in the coordination set. For HEW, “shared reservations” may be desirable. Additional fields may be added to the TxOP reservation frame to enumerate the type of reservation requested. For example, the fields may specify type of traffic allowed (e.g., UL, DL, or UL and DL), bandwidth info (e.g., reserved bandwidth or maximum bandwidth to use), and/or type of medium access (e.g., normal EDCA, no backoff, or only certain QoS Classes). According to certain aspects, the reservation may be longer than a normal TxOP since the reservation could be for more than a single user&#39;s data. According to certain aspects, periodicity information may be added (e.g., whether or not the reservation happens repeatedly with some periodicity). 
     According to certain aspects, a HEW TxOP reservation frame may include an octet for duration, an octet for SI, four octets for start frame, two bits specifying UL, DL, or UL+DL, three bits specifying type of medium access (e.g., bandwidth information), and two bits periodicity information. 
     According to certain aspects, the messages described above for coordination may be exchanged between APs via non-OTA methods such as backhaul communications. For example, the medium access control (MAC) message may be sent through a (wireline) “layer 2” network, such as Ethernet or similar. A bridging operation for the address translation/switching/routing may be used where messages are routed through the L2 network until the destination AP. 
     According to certain aspects, the MAC message may be sent encapsulated through a higher layer protocol. For example, LLC preamble may be set to an Ethertype value corresponding to a Layer 3 or above protocol dedicated to the transport of the coordination messages. 
     According to certain aspects, the protocol may be delegated to higher layer protocols. For example, the coordination message may not be in the form of a MAC message, instead, the MAC management entity may communicate with higher layers for the generation of messages at the higher layer protocol. 
     According to certain aspects, a mechanism may be in place for an AP to discover the address of a neighboring AP which is the destination of the coordination messages. For example, the AP may discover the neighboring AP address through existing OTA signaling (e.g., beacons, sniffing of frames sent by APs/STAs), through an explicit OTA discovery protocol (e.g., social WiFi or WiFi-D), programmed at deployment or set by the user though an application. 
     Inter-AP Scheduling 
     For inter-AP scheduling, once an AP knows the reservation times, the AP may indicate that information to its STAs. If the AP is using HCCA, it may already be in full control of the medium. If the AP is not using HCCA, there are various methods reserving the medium. According to certain aspects, information may be added to the RAW frame. The information may include whether the reservation is for DL, UL, or DL+UL, which bandwidth the reservation is for, the type of channel access (e.g., standard access or modified deferral rules), and which EDCA parameters to use. 
     According to certain aspects, information may be added to the PSMP frame. The information may include which bandwidth to use, what kind of channel access to use during reservation, and what access parameters to use during reservation (e.g., which EDCA parameters). The information may be for the whole PSMP reservation, on a STA by STA basis (e.g., PSMP has a reservation per STA), or based on UL/DL intervals. According to certain aspects, a management negotiation may be performed where the AP and its STAs agree on whether the STAs are allowed to transmit on the medium when not polled by a PSMP request. According to certain aspects, the AP and STAs may agree on a time when the PSMP is expected 
     According to certain aspects, a management negotiation may be performed where AP and STA agree on whether the STA is allowed to transmit on the medium when not explicitly given permission to send. Explicit permission to send can be granted via a RAW, TWT, PSMP, reverse direction grant (RDG), or any other message sent by the AP which allows certain user to transmit during a given amount of time. 
     According to certain aspects, the RAW or PSMP frame may not be modified to indicate the reservation to the STAs. Instead, the AP may use the frames in a manner to indicate the information. 
     According to certain aspects, minimizing primary channel interference may help with throughput. However, the closest APs may not coordinate because coordination is done over the beacons—or other such message—on the primary channel. According to certain aspects, the AP may transmit duplicate beacons on the whole bandwidth. For dense networks, beacon range may not be of importance. According to certain aspects, APs may choose their closest APs to coordinate with regardless of primary channel, as long as operating bandwidth is the same. APs may detect and decode beacons on multiple channels—possibly simultaneously. According to certain aspects, a common coordination channel may be used. Alternatively, beacons may be sent only on the primary channel, but messages for coordination may be sent on all the channels. As another alternative, nodes may transmit coordinating messages only on their primary channels, but they may listen for coordinating messages on all their channels. 
       FIG. 13  illustrates example operations  1300  for coordinating access to a shared medium, in accordance with certain aspects of the present disclosure. The operations  1300  may be performed, for example, by an AP (e.g., AP  504 ). The operations  1300  may begin, at  1302 , by synchronizing with one or more peer apparatuses based on synchronization messages detected during a listening time. According to certain aspects, the one or more peer apparatus may be in a coordinating set (e.g., a BSS) or in multiple coordinating sets. The AP and other peer apparatus may synchronize to a single time. For example, the AP may select a master, and the AP and the peer apparatus may synchronize to the master&#39;s time (e.g., clock). 
     According to certain aspects, the AP may transmit a message (e.g., to the one or more peer apparatuses) to reserve the listening time for listening to the synchronization messages. According to certain aspects, the message may be a quiet element, a RAW frame, or a PSMP message. According to certain aspects, the RAW frame may indicate a groupID to which no devices belong. Alternatively, the RAW frame may indicate multiple non-consecutive times to reserve for listening. According to certain aspects, the transmission time of the PSMP message may be used to indicate listening times to reserve. According to certain aspects, the PSMP message may indicate a device ID corresponding to a non-existent device. According to certain aspects, the PSMP message may indicate multiple non-consecutive times to reserve for listening to the synchronization messages. 
     At  1304 , the AP may output, for transmission, scheduling information to the one or more peer apparatuses, the scheduling information indicating one or more time periods during which coordinated access to the shared medium is desired. According to certain aspects, the scheduling information may include a start time or a duration of the one or more time periods during which coordinated access to the shared medium is desired (e.g., in one or more additional fields included in the RAW frame or PSMP message). According to certain aspects, the scheduling information may include an indication of a type of coordinated access allowed for the one or more time periods (e.g., uplink access, downlink access, or both uplink and downlink access). According to certain aspects, the scheduling information may include information related to a bandwidth allowed during the one or more time periods (e.g., a particular bandwidth to use or a maximum bandwidth to be used). According to certain aspects, the scheduling information may include information relating to one or more types of deferral rules. For example, a modified deferral rule that allows the one or more peer apparatuses and the devices served by the apparatus to ignore packets from other peer apparatuses and devices that have certain BSS IDs. According to certain aspects, the scheduling information may include information relating to achieving favorable access to the shared medium. 
     At  1306 , the AP may output, for transmission, at least some of the scheduling information to devices served by the apparatus. According to certain aspects, at least some of the scheduling information may identify a subset of the devices that should transmit during a scheduled time. According to certain aspects, the AP may transmit the scheduling information to the one or more peer apparatuses independently of input from the one or more peer apparatuses. According to certain aspects, the AP may solicit input from the one or more peer apparatuses prior to transmitting the scheduling information to the one or more peer apparatuses. According to certain aspects, the AP may wait to receive responses from the one or more peer apparatuses prior to transmitting the scheduling information to the one or more peer apparatuses. According to certain aspects, the AP may require responses from the one or more peer apparatus. According to certain aspects, the AP may generate the scheduling information based, at least in part, on the responses. 
     According to certain aspects, the AP may transmit the scheduling information to the one or more peer apparatuses following a beacon period. Alternatively, the AP may transmit the scheduling information to the one or more peer apparatuses within a predetermined recurring time period. According to certain aspects, the AP may contend to send scheduling messages within the predetermined recurring time period. According to certain aspects, the AP may transmit the scheduling information to the one or more peer apparatuses if the apparatus has access to the shared medium. According to certain aspects, the AP may transmit the scheduling information OTA. Alternatively, the AP may transmit the scheduling information via a backhaul connection. 
     According to certain aspects, the AP may transmit the scheduling information to the devices served by the apparatus using RAW frame or PSMP message. According to certain aspects, the RAW frame or PSMP message may indicate the one or more time periods are for downlink access, uplink access, or both; a bandwidth to use during the one or more time periods, a type of channel access to use during the one or more time periods; what deferral rules to use, or what EDCA parameters to use during the one or more time periods. According to certain aspects, the AP may transmit the scheduling information to the devices served by the apparatus using a PSMP message. 
     According to certain aspects, the AP may transmit the scheduling information to the one or more peer apparatuses on-primary channels. According to certain aspects, the AP may transmit duplicated scheduling information on non-primary channels. According to certain aspects, the AP may receive synchronization messages on primary channels and/or on non-primary channels. According to certain aspects, the scheduling information may identify the one or more peer apparatuses in OBSSs that should not transmit during a scheduled time. 
       FIG. 14  illustrates example operations  1400  for coordinating access to a shared medium, in accordance with certain aspects of the present disclosure. The operations  1400  may be performed, for example, by an AP (e.g., AP  504 ). The operations  1400  may begin, at  1402 , by receiving, from another AP, a message to reserve a listening time for the other AP to listen to one or more synchronization messages. 
     At  1404 , the AP may take action to ensure stations served by the AP do not interfere with synchronization messages during the listening time. At  1406 , the AP may receive, from the other AP, scheduling information indicating one or more reservation periods during which coordinated access to the shared medium is desired. At  1408 , the UE may take to provide coordinated access during the one or more reservation periods. 
     The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application specific integrated circuit (ASIC), or processor. Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering. For example, operations  1300  and operations  1400  illustrated in  FIG. 13  and  FIG. 14 , respectively, correspond to means  1300 A and means  1400 A illustrated in  FIG. 13A  and  FIG. 14A , respectively. 
     For example, means for transmitting may comprise a transmitter (e.g., the transmitter  410 ) and/or an antenna(s)  416  of the wireless device  402  illustrated in  FIG. 4 . Means for receiving may comprise a receiver (e.g., the receiver  412 ) and/or an antenna(s)  416  of the wireless device  402  illustrated in  FIG. 4 . Means for processing, means for generating, means for waiting, means for synchronizing, means for selecting, and means for contending may comprise a processing system, which may include one or more processors, such as the processor  404  illustrated in  FIG. 4 . 
     In some cases, an interface for outputting a frame may be an actual transmitter (e.g., physical RF front end) or may be an interface for receiving a frame (e.g., from a processor) and outputting that frame (e.g., to a physical RF front end) for transmission. 
     As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database or another data structure), ascertaining and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory) and the like. Also, “determining” may include resolving, selecting, choosing, establishing and the like. Further, a “channel width” as used herein may encompass or may also be referred to as a bandwidth in certain aspects. 
     As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c. 
     The various operations of methods described above may be performed by any suitable means capable of performing the operations, such as various hardware and/or software component(s), circuits, and/or module(s). Generally, any operations illustrated in the Figures may be performed by corresponding functional means capable of performing the operations. 
     The various illustrative logical blocks, modules and circuits described in connection with the present disclosure may be implemented or performed with a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field programmable gate array signal (FPGA) or other programmable logic device (PLD), discrete gate or transistor logic, discrete hardware components or any combination thereof designed to perform the functions described herein. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any commercially available processor, controller, microcontroller or state machine. A processor may also be implemented as a combination of computing devices, e.g., a combination of a DSP and a microprocessor, a plurality of microprocessors, one or more microprocessors in conjunction with a DSP core, or any other such configuration. 
     In one or more aspects, the functions described may be implemented in hardware, software, firmware, or any combination thereof. If implemented in software, the functions may be stored on or transmitted over as one or more instructions or code on a computer-readable medium. Computer-readable media includes both computer storage media and communication media including any medium that facilitates transfer of a computer program from one place to another. A storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. Also, any connection is properly termed a computer-readable medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of medium. Disk and disc, as used herein, includes compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray® disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Thus, in some aspects, computer readable medium may comprise non-transitory computer readable medium (e.g., tangible media). In addition, in some aspects computer readable medium may comprise transitory computer readable medium (e.g., a signal). Combinations of the above should also be included within the scope of computer-readable media. 
     Thus, certain aspects may comprise a computer program product for performing the operations presented herein. For example, such a computer program product may comprise a computer readable medium having instructions stored (and/or encoded) thereon, the instructions being executable by one or more processors to perform the operations described herein. For certain aspects, the computer program product may include packaging material. For example, the instructions may be executed by a processor or processing, such as processor  404 , and stored in a memory, such as memory  404 , illustrated in  FIG. 4 . For example, the computer-readable medium may have computer executable instructions stored thereon for synchronizing with one or more peer apparatuses based on synchronization messages detected during a listening time, instructions for transmitting scheduling information to the one or more peer apparatuses, the scheduling information indicating one or more time periods during which coordinated access to the shared medium is desired, and instructions for transmitting at least some of the scheduling information to devices served by the apparatus. 
     The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims. 
     Software or instructions may also be transmitted over a transmission medium. For example, if the software is transmitted from a website, server, or other remote source using a coaxial cable, fiber optic cable, twisted pair, digital subscriber line (DSL), or wireless technologies such as infrared, radio, and microwave, then the coaxial cable, fiber optic cable, twisted pair, DSL, or wireless technologies such as infrared, radio, and microwave are included in the definition of transmission medium. 
     Further, it should be appreciated that modules and/or other appropriate means for performing the methods and techniques described herein can be downloaded and/or otherwise obtained by a user terminal and/or base station as applicable. For example, such a device can be coupled to a server to facilitate the transfer of means for performing the methods described herein. Alternatively, various methods described herein can be provided via storage means (e.g., RAM, ROM, a physical storage medium such as a compact disc (CD) or floppy disk, etc.), such that a user terminal and/or base station can obtain the various methods upon coupling or providing the storage means to the device. Moreover, any other suitable technique for providing the methods and techniques described herein to a device can be utilized. 
     It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims. 
     While the foregoing is directed to aspects of the present disclosure, other and further aspects of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.