Patent Publication Number: US-10321451-B2

Title: Systems and methods for downlink frequency domain multiplexing transmissions

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 15/203,655, entitled “SYSTEMS AND METHODS FOR DOWNLINK FREQUENCY DOMAIN MULTIPLEXING TRANSMISSIONS” and filed on Jul. 6, 2016, which is a divisional of U.S. patent application Ser. No. 14/266,751, entitled “SYSTEMS AND METHODS FOR DOWNLINK FREQUENCY DOMAIN MULTIPLEXING TRANSMISSIONS” and filed on Apr. 30, 2014, which claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Application No. 61/819,109, entitled “SYSTEMS AND METHODS FOR DOWNLINK FREQUENCY DOMAIN MULTIPLEXING TRANSMISSIONS” and filed on May 3, 2013, each of which applications is hereby incorporated by reference in its entirety. 
    
    
     BACKGROUND 
     Field 
     The present application relates generally to wireless communications, and more specifically to systems, methods, and devices for downlink frequency domain multiplexing in wireless networks. 
     Background 
     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 is desired. 
     SUMMARY 
     The systems, methods, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention 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 invention provide advantages that include improved communications between access points and stations in a wireless network. 
     One aspect of this disclosure provides a method for receiving data. The method comprises receiving a first message. The first message may be transmitted over a first frequency channel and a second frequency channel. The first message may comprise an allocation of a first station to the first frequency channel and a second station to the second frequency channel. The first message may comprise a physical layer preamble comprising a first modulation and coding scheme (MCS) value associated with the first station and a second MCS value associated with the second station. The method further comprises receiving, after transmission of the first message, a second message over the second frequency channel. 
     Another aspect of this disclosure provides an apparatus for receiving data. The apparatus comprises means for processing a first message. The first message may be transmitted over a first frequency channel and a second frequency channel. The first message may comprise an allocation of a first station to the first frequency channel and a second station to the second frequency channel. The first message may comprise a physical layer preamble comprising a first modulation and coding scheme (MCS) value associated with the first station and a second MCS value associated with the second station. The apparatus further comprises means for receiving, after transmission of the first message, a second message over the second frequency channel. 
     Another aspect of this disclosure provides a non-transitory computer-readable medium comprising code that, when executed, causes an apparatus to process a first message. The first message may be transmitted over a first frequency channel and a second frequency channel. The first message may comprise an allocation of a first station to the first frequency channel and a second station to the second frequency channel. The first message may comprise a physical layer preamble comprising a first modulation and coding scheme (MCS) value associated with the first station and a second MCS value associated with the second station. The medium further comprises code that, when executed, causes an apparatus to receive, after transmission of the first message, a second message over the second frequency channel. 
     Another aspect of this disclosure provides an apparatus for receiving data. The apparatus comprises a processor configured to process a first message. The first message may be transmitted over a first frequency channel and a second frequency channel. The first message may comprise an allocation of a first station to the first frequency channel and a second station to the second frequency channel. The first message may comprise a physical layer preamble comprising a first modulation and coding scheme (MCS) value associated with the first station and a second MCS value associated with the second station. The apparatus further comprises a receiver configured to receive, after transmission of the first message, a second message over the second frequency channel. 
     Another aspect of this disclosure provides a method for receiving data. The method comprises receiving a first packet from an access point. A second packet may be transmitted by the access point to a first station over a primary frequency channel. The first station may only be configured to communicate over the primary frequency channel. The first packet may be transmitted over a secondary frequency channel and a ternary frequency channel. The first packet may comprise a physical layer preamble. The physical layer preamble may comprise an allocation of a second station to the secondary frequency channel and a third station to the ternary frequency channel. The physical layer preamble may comprise a first modulation and coding scheme (MCS) value associated with the second station and a second MCS value associated with the third station. The method further comprises receiving, after transmission of the first packet, a third packet over the secondary frequency channel. 
     Another aspect of this disclosure provides an apparatus for receiving data. The apparatus comprises means for processing a first packet received from an access point. A second packet may be transmitted by the access point to a first station over a primary frequency channel. The first station may only be configured to communicate over the primary frequency channel. The first packet may be transmitted over a secondary frequency channel and a ternary frequency channel. The first packet may comprise a physical layer preamble. The physical layer preamble may comprise an allocation of a second station to the secondary frequency channel and a third station to the ternary frequency channel. The physical layer preamble may comprise a first modulation and coding scheme (MCS) value associated with the second station and a second MCS value associated with the third station. The apparatus further comprises means for receiving, after transmission of the first packet, a third packet over the secondary frequency channel. 
     Another aspect of this disclosure provides a non-transitory computer-readable medium comprising code that, when executed, causes an apparatus to receive a first packet from an access point. A second packet may be transmitted by the access point to a first station over a primary frequency channel. The first station may only be configured to communicate over the primary frequency channel. The first packet may be transmitted over a secondary frequency channel and a ternary frequency channel. The first packet may comprise a physical layer preamble. The physical layer preamble may comprise an allocation of a second station to the secondary frequency channel and a third station to the ternary frequency channel. The physical layer preamble may comprise a first modulation and coding scheme (MCS) value associated with the second station and a second MCS value associated with the third station. The medium further comprises code that, when executed, causes an apparatus to receive, after transmission of the first packet, a third packet over the secondary frequency channel. 
     Another aspect of this disclosure provides an apparatus for receiving data. The apparatus comprises a processor configured to process a first packet. A second packet may be transmitted by the access point to a first station over a primary frequency channel. The first station may only be configured to communicate over the primary frequency channel. The first packet may be transmitted over a secondary frequency channel and a ternary frequency channel. The first packet may comprise a physical layer preamble. The physical layer preamble may comprise an allocation of a second station to the secondary frequency channel and a third station to the ternary frequency channel. The physical layer preamble may comprise a first modulation and coding scheme (MCS) value associated with the second station and a second MCS value associated with the third station. The apparatus further comprises a receiver configured to receive, after transmission of the first packet, a third packet over the secondary frequency channel. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary wireless communication system in which aspects of the present disclosure may be employed. 
         FIG. 2A  shows a wireless communication system in which multiple wireless communication networks are present. 
         FIG. 2B  shows another wireless communication system in which multiple wireless communication networks are present. 
         FIG. 3  shows frequency multiplexing techniques that may be employed within the wireless communication systems of  FIGS. 1 and 2B . 
         FIG. 4  shows a functional block diagram of an exemplary wireless device that may be employed within the wireless communication systems of  FIGS. 1, 2B, and 3 . 
         FIG. 5A  shows a wireless communication system in which aspects of the present disclosure may be employed. 
         FIGS. 5B-C  show a timing diagram in which aspects of the present disclosure may be employed. 
         FIGS. 5D-E  show another timing diagram in which aspects of the present disclosure may be employed. 
         FIGS. 5F-G  show another timing diagram in which aspects of the present disclosure may be employed. 
         FIGS. 6A-B  show another timing diagram in which aspects of the present disclosure may be employed. 
         FIGS. 6C-D  show another timing diagram in which aspects of the present disclosure may be employed. 
         FIG. 7  shows another timing diagram in which aspects of the present disclosure may be employed. 
         FIGS. 8A-C  show another timing diagram in which aspects of the present disclosure may be employed. 
         FIGS. 9A-E  shows another timing diagram in which aspects of the present disclosure may be employed. 
         FIG. 10  is a flowchart of a process for high-efficiency wireless frequency division multiplexing. 
         FIG. 11  is a flowchart of a process for transmitting data. 
         FIG. 12  is another flowchart of a process for transmitting data. 
         FIG. 13  is another flowchart of a process for transmitting data. 
         FIG. 14  is another flowchart of a process for transmitting data. 
         FIG. 15  is another flowchart of a process for transmitting data. 
         FIG. 16  is another flowchart of a process for transmitting data. 
     
    
    
     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 invention. 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 invention 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. 
       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 AP  104 , which communicates with 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 OFDM/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, 5A -G,  6 A-D,  7 ,  8 A-C,  9 A-E, and  10 - 23 . 
     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 5A . 
     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. 5A-23 . 
       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. For example, an AP  254 A-C can assign a STA  256 A-H a particular classification (e.g., the AP  254 A-C can assign a STA  256 A-H a particular classification based on the bandwidth capabilities of the STA  256 A-H). As another example, a STA  256 A-H can choose a classification and notify the appropriate AP  254 A-C. As another example, a STA  256 A-H can submit, to the appropriate AP  254 A-C, a request for a particular classification. 
     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 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. 
     In various embodiments, performance (e.g., RF) characteristics that affect the classification of a STA as being near the center of the BSA or near the edge of the BSA can include one or more of: a signal-to-interference-plus-noise ratio (SINR), an RF geometry, a received signal strength indicator (RSSI), a modulation and coding scheme (MCS) value, an interference level, a signal level, a transmission capability, and/or the like. In various embodiments, one or more physical and RF characteristics can be compared to one or more threshold levels. The comparisons can be weighted and/or combined. In various embodiments, devices can be determined to be in a condition such that they can or cannot communicate concurrently based on the solitary, weighted, and/or combined physical and RF characteristics and associated thresholds. 
     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 segments  308 ,  310 ,  312 , and  314  (e.g., channels), as illustrated in  FIG. 3 . A channel may be any portion of the spectrum where IEEE 802.11 operation is allowed. Generally, a channel has a bandwidth of 20 MHz in legacy operations, but the channels or segments as described herein may be of any bandwidth, such as 5 MHz, 10 MHz, 20 MHz, etc. The channels or segments as described herein may also include a subset of non-adjacent tones within the bandwidth of a BSS. Furthermore, the channels or segments illustrated herein are depicted as being part of a contiguous chunk of spectrum (e.g., each channel or segment covers consecutive and neighboring frequency ranges); however, the channels or segments as described herein may be part of a contiguous or non-contiguous chunk of spectrum. The channels or segments can also be subsets of other channels or segments within the spectrum. 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 . The APs  304 A-D may communicate with each other (e.g., by transmitting and/or receiving coordination messages) to determine which APs and STAs communicate over which segments  308 ,  310 ,  312 , and  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, that include the high-efficiency wireless component can communicate concurrently with other APs and STAs without interference (e.g., concurrently by chance or concurrently based on a time scheduled by an AP or STA). 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, 2B, 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. 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. 
     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. 
     As described above, network throughput and latency may be a major concern in wireless networks when the CSMA mechanism is used. For example, wireless devices associated with one wireless network may be located in close proximity to other wireless devices associated with other wireless networks. Wireless devices of one network may sense a transmission by another wireless device of another network, and thus refrain from transmitting over the medium, even when no interference would occur. Accordingly, a modified mechanism can be used in a high-efficiency 802.11 protocol to alleviate some of these issues. 
     In the modified mechanism, wireless devices may be classified according to a state or condition of the wireless device. For example, a wireless device may be in a state or condition in which the wireless device can communicate concurrently with other wireless devices (e.g., because the wireless device is located away from an edge of the BSA and thereby would not cause interference). As another example, a wireless device may be in a state or condition in which the wireless device cannot communicate concurrently with other wireless devices (e.g., because the wireless device is located near an edge of the BSA and thereby would cause interference). 
     In order to improve network throughput and reduce latency, some techniques may be employed to allow wireless devices to communicate concurrently even if they are near an edge of the BSA or otherwise cannot communicate concurrently under current protocols. One such technique is frequency domain multiplexing, which is described above with respect to  FIG. 3 . In particular, protocols may be developed and implemented to allow APs to transmit messages to STAs (e.g., DL communications) using frequency domain multiplexing techniques. As described below, an AP may transmit messages to a STA using a frequency channel determined based on how the STA is classified. 
       FIG. 5A  shows a wireless communication system  500  in which aspects of the present disclosure may be employed. As illustrated in  FIG. 5A , the wireless communication system  500  includes a BSA  502 . The BSA  502  may include an AP  504  and STAs  506 A-E. In an embodiment, the AP  504  and the STAs  506 A-D each include the high-efficiency wireless component discussed above. However, the STA  506 E does not include the high-efficiency wireless component. Thus, STAs  506 A-D are referred to as high-efficiency STAs, whereas STA  506 E is referred to as a legacy STA (e.g., because it is compatible with regular IEEE 802.11 protocols, such as IEEE 802.11n, IEEE 802.11ac, etc.). 
     As described above, the AP  504  may classify the high-efficiency STAs and the legacy STAs as being or not being in a state or condition in which the respective STA can communicate concurrently with other wireless devices. The AP  504  may make such a classification based on the respective bandwidth capabilities of the STA. 
     The AP  504  may transmit data to STA  506 A via DL communication  510 , to STA  506 B via DL communication  512 , to STA  506 C via DL communication  514 , to STA  506 D via DL communication  516 , and to STA  506 E via DL communication  518 . As illustrated in  FIG. 5A , STAs  506 A-C may be located closer to the AP  504  than STAs  506 D-E. The DL communications  510 ,  512 ,  514 ,  516 , and  518  may be made by the AP  504  according to the downlink frequency domain multiplexing (DL FDM) protocol described herein. 
     A DL FDM protocol may include three data exchange stages: (1) data transmission; (2) protection; and (3) acknowledgment. The protection stage may precede the data transmission stage and the acknowledgment stage may follow the data transmission stage. In the protection stage, techniques may be employed to prevent interference. In the data transmission stage, data for one or more STAs may be transmitted to the respective STAs. In the acknowledgment stage, the AP may confirm that the respective STAs received the appropriate data. Each of these stages may occur concurrently on different channels according to the frequency domain multiplexing principles discussed herein. In addition, the DL FDM protocol may include rules related to the timing of the start of transmissions by the AP  504 . 
     Data Transmission Stage 
     In an embodiment, several data transmission options are available during the data transmission stage. In particular, several options are available for allocating STAs on different channels such that the STAs can communicate concurrently. These options may also allow for both legacy STAs and high-efficiency STAs to communicate concurrently. Thus, the techniques described herein to improve network throughput and reduce latency may be implemented in devices that are compatible with high-efficiency STAs and that are backwards compatible with existing legacy STAs. For example, an existing PHY layer of the regular IEEE 802.11 protocol (e.g., the 802.11n, 802.11ac, etc. PHY layer) may be coupled with a new media access control (MAC) mechanism to allocate STAs on different channels. As another example, a new PHY layer preamble may be created for the high-efficiency 802.11 protocol to allocate STAs on different channels. As another example, the existing PHY layer of the regular IEEE 802.11 protocol and the new PHY layer preamble may be used to allocate STAs on different channels. 
       FIGS. 5B-C  show a timing diagram in which aspects of the present disclosure may be employed. In particular,  FIGS. 5B-C  show a timing diagram that may be used in accordance with the existing PHY layer of the regular IEEE 802.11 protocol and the new MAC mechanism. As illustrated in  FIGS. 5B-C , four channels are present: channel  520 , channel  522 , channel  524 , and channel  526 . As used herein, channel  526  is referred to as a primary channel and channels  520 ,  522 , and  524  are referred to as secondary channels. A primary channel is a default channel used by STAs operating on the regular IEEE 802.11 protocol. Legacy STAs may receive or transmit data using the secondary channels, but the transmission to or from the legacy STAs must include the primary channel (e.g., packets for a legacy STA always include the primary channel). A high-efficiency STA, on the other hand, may receive or transmit data using the primary channel or may receive or transmit data only using the secondary channels (e.g., as long as the transmission to or from the high-efficiency STA includes at least one channel known by the high-efficiency STA). The channels  520 ,  522 ,  524 , and  526  may be contiguous (e.g., each channel  520 ,  522 ,  524 , and  526  covers consecutive 20 MHz frequency ranges, such as from 1000 MHz to 1080 MHz) or non-contiguous (e.g., there are gaps in frequency between one or more of the channels  520 ,  522 ,  524 , and/or  526 ). 
     In an embodiment, the primary channel (and potentially additional secondary channels, as in legacy IEEE 802.11n operation, legacy IEEE 802.11ac operation, etc.) is used for communications from the AP  504  to legacy STAs (e.g., STA  506 E) and the secondary channels are used for communications from the AP  504  to the high-efficiency STAs (e.g., STAs  506 A-D). 
     The AP  504  may transmit a MAC message that associates STAs  506 A-E with channels, thereby indicating which channel the AP  504  plans to use to communicate with a respective STA  506 A-E. In some embodiments, the AP  504  defaults to communicating with the STA  506 E on the primary channel since the STA  506 E is a legacy STA. Thus, the AP  504  may not transmit the MAC message to the STA  506 E. Rather, the AP  504  may transmit the MAC message only to the high-efficiency STAs. In other embodiments, the AP  504  transmits the MAC message to each STA  506 A-E. The MAC message may be a management frame transmitted by the AP  504  to the STAs  506 A-E. The management frame may indicate the allocated channel(s) for one or more of the STAs  506 A-E. The MAC message is described in greater detail below with respect to  FIG. 7 . 
     As illustrated in  FIGS. 5B-C , the MAC message allocates STA  506 E to channel  526 , STA  506 A to channel  524 , STA  506 B to channel  522 , and STA  506 C to channel  520 . Transmissions from the AP  504  to the respective STAs  506 A-C and  506 E may begin at the same time (e.g., see  FIG. 5B ) or begin at different times (e.g., see  FIG. 5C ). If the transmissions from the AP  504  begin at different times, OFDM symbols transmitted to different STAs  506 A-E may still be aligned to help receiver processing. Likewise, the transmissions from the AP  504  may end at the same time (not shown) or end at different times (e.g., see  FIGS. 5B-C ). 
     The STAs  506 A-E may receive the MAC message and/or the actual data transmission using special filtering capabilities and/or an oversampled FFT. The legacy STA  506 E and/or any other legacy STAs in the BSA  502  may include a low modulation and coding scheme (MCS) value (e.g., four or five) in order to minimize potential channel interference from adjacent channels. 
     Accordingly, use of the existing PHY layer and the new MAC mechanism allows the AP  504  to multiplex transmissions to legacy STAs and high-efficiency STAs concurrently or nearly concurrently. 
       FIGS. 5D-E  show another timing diagram in which aspects of the present disclosure may be employed. In particular,  FIGS. 5D-E  show a timing diagram that may be used in accordance with the new PHY layer preamble. Since a new PHY layer preamble is defined,  FIGS. 5D-E  may apply only to high-efficiency STAs. 
     In an embodiment, the new PHY layer preamble includes an MCS associated with each STA  506 A-D, a duration of time that the AP  504  will transmit to each respective STA  506 A-D, a number of bytes that the AP  504  will transmit to each respective STA  506 A-D, an identification of a channel associated with each respective STA  506 A-D and the channel&#39;s bandwidth, a duration of time that legacy STAs should defer transmissions over the primary channel, additional indications on transmission modes (e.g., coding mode, pilot location mode, etc.) that will be used by the AP  504  when transmitting messages to each respective STA  506 A-D, and/or any other physical layer transmission parameter. If the new PHY layer preamble does not include any of the above-mentioned information, such information may be included in a MAC message transmitted previously to the STA  506 A-D. 
     The channel bandwidth may be the same or different for each STA  506 A-D. For example, as illustrated in  FIG. 5D , STAs  506 A-D are assigned a separate channel  520 ,  522 ,  524 , or  526 , where each channel has the same bandwidth. As another example, as illustrated in  FIG. 5E , STAs  506 A and  506 C are assigned a separate channel  522  or  526 , where each channel has the same bandwidth and where the bandwidth is double the bandwidth as in  FIG. 5D . As another example, not shown, STA  506 A and  506 C are assigned a separate channel  522  or  526 , where the bandwidth of channel  522  is different than the bandwidth of channel  526  (e.g., the bandwidth of channel  522  is double the bandwidth of channel  526 ). 
     As illustrated in  FIGS. 5D-E , a PHY layer preamble  528  is transmitted by the AP  504  over channels  520 ,  522 ,  524 , and  526 . In some embodiments, the PHY layer preamble  528  includes information for all the STAs  506 A-D on each channel. This may allow a STA  506 A-D to listen on any of the channels and receive the channel allocation information. In other embodiments, the PHY layer preamble  528  includes information for different STAs  506 A-D in different channels. Here, a STA  506 A-D may be informed a priori of the channel the STA  506 A-D should be listening to via an additional MAC message. Each of the STAs  506 A-D may listen for messages on a separate channel. In this way, each of the STAs  506 A-D may receive the PHY layer preamble  528 . After receiving the PHY layer preamble  528 , the STAs  506 A-D may receive the DL communication  510 ,  512 ,  514 , or  516 . The STAs  506 A-D may use the information provided in the PHY layer preamble  528  to properly receive the DL communication from the AP  504  and/or to properly transmit UL communication to the AP  504 . Accordingly, the AP  504  may be able to transmit data over multiple channels to multiple STAs  506 A-D using the new PHY layer preamble  528 . Note that the transmissions may be of the same or different duration on each channel. 
       FIGS. 5F-G  show another timing diagram in which aspects of the present disclosure may be employed. In particular,  FIGS. 5D-E  show a timing diagram that may be used in accordance with the existing PHY layer in the regular IEEE 802.11 protocol and the new PHY layer preamble. 
     As described above with respect to  FIGS. 5B-C , the primary channel (e.g., channel  526 ) and/or one or more of the secondary channels (e.g., channels  520 ,  522 , and/or  524 ) may be used for transmissions to legacy STAs (e.g., STA  506 E) and the secondary channels may be used for transmissions to high-efficiency STAs (e.g., STAs  506 A-D). Since the new PHY layer preamble  528  is compatible with the high-efficiency STAs, the PHY layer preamble  528  may be transmitted over the secondary channels such that only the high-efficiency STAs receive the PHY layer preamble  528 , as illustrated in  FIGS. 5F-G . 
     In an embodiment, as described above, each of the channel bandwidths may be the same size or a different size. In an embodiment, the channels  520 ,  522 ,  524 , and/or  526  may or may not be contiguous. In some embodiments, the primary channel is always used and associated with at least one STA  506 A-E. In other embodiments, the primary channel is not used or associated with any of the STAs  506 A-E. 
     Accordingly, use of the existing PHY layer and the new PHY layer preamble  528  allows the AP  504  to multiplex transmissions to legacy STAs and high-efficiency STAs concurrently or nearly concurrently. The new MAC mechanism may not be necessary in order to properly instruct STAs  506 A-E to listen for messages on the appropriate channels; however, the new MAC mechanism may be used in connection with the existing PHY layer and the new PHY layer preamble  528 . 
     In an embodiment, a (legacy) transmission on the primary channel may include or may be preceded by a MAC message, where the MAC message includes an indication of the presence of additional high-efficiency transmissions in one or more of the secondary channels. This may allow high-efficiency STAs to listen to the primary channel only and be notified of the presence of additional packets on the secondary channels that may be addressed to one or more of the high-efficiency STAs. High-efficiency STAs may then switch to the second channel and detect the preamble, where the preamble contains additional information for decoding the transmission. 
     Timing of Start Transmission 
     In an embodiment, the timing of the start of a transmission may be based on rules based on a random backoff counter and a point coordination function inter frame space (PIFS) and/or a schedule set by the AP  504  and/or STAs  506 A-E. 
       FIGS. 6A-B  show another timing diagram in which aspects of the present disclosure may be employed. As described above, the primary channel (e.g., channel  526 ) and/or one or more of the secondary channels (e.g., channels  520 ,  522 , and/or  524 ) may be used for transmissions to legacy STAs and the secondary channels may be used for transmissions to high-efficiency STAs. The channels  520 ,  522 ,  524 , and/or  526  may or may not be contiguous. In an embodiment, a random backoff counter may be associated with the primary channel, as defined by the enhanced distributed channel access (EDCA) procedure of IEEE 802.11. When the random backoff counter expires, the AP  504  may begin preparing the DL communication  518  for transmission to the STA  506 E. If channel  520  has been idle since a time period  602  before the time that the random backoff counter expired, then the AP  504  may transmit the PHY layer preamble  528  and/or the DL communication  514  to the STA  506 C at the same or nearly same time as the transmission to the STA  506 E. Likewise, if channel  522  has been idle since the time period  602  before the time that the random backoff counter expired, then the AP  504  may transmit the PHY layer preamble  528  and/or the DL communication  512  to the STA  506 B at the same or nearly same time as the transmission to the STA  506 E. Furthermore, if channel  524  has been idle since the time period  602  before the time that the random backoff counter expired, then the AP  504  may transmit the PHY layer preamble  528  and/or the DL communication  510  to the STA  506 A at the same or nearly same time as the transmission to the STA  506 E. 
     Thus, once the random backoff counter expires, at least one transmission is made over the primary channel. Concurrently, transmissions may be made over one or more of the secondary channels if the secondary channel is idle. In an embodiment, the time period  602  may be based on a PIFS time. The PIFS time may be chosen by the AP  504  and/or STAs  506 A-E. 
       FIGS. 6C-D  show another timing diagram in which aspects of the present disclosure may be employed. As described above, the primary channel (e.g., channel  526 ) may be reserved for legacy STAs and the secondary channels (e.g., channels  520 ,  522 , and  524 ) may be reserved for high-efficiency STAs. The channels  520 ,  522 ,  524 , and/or  526  may or may not be contiguous. In an embodiment, a random backoff counter may be associated with the primary channel and a one or more random backoff counters may be associated with one or more of the secondary channels. For example, a separate random backoff counter may be associated with each of the secondary channels. 
     In an embodiment, when a random backoff counter associated with the primary channel or one of the secondary channels expires, the AP  504  begins preparing to transmit (e.g., the PHY layer preamble  528  or the DL communications  510 ,  512 ,  514 , or  518 ) on the channel associated with the expired random backoff counter. For example, if the random backoff counter associated with channel  524  expires first, the AP  504  may begin preparing to transmit the PHY  528  and/or the DL communication  510  to STA  506 A. If any of the channels associated with unexpired random backoff counters have been idle since the time period  602  before the time that the first random backoff counter expired, then the AP  504  may transmit the PHY layer preamble  528  and/or the appropriate DL communication to the STAs  506 A-E associated with the idle channel(s). The PHY layer preamble  528  and/or the appropriate DL communication may be transmitted at the same or nearly same time as the transmission to the STA  506 A-E associated with the random backoff counter that expired first. 
     In another embodiment, access to the channel may be based only on the expiration of the random backoff counter on the primary channel. The secondary channels may be used only if the random backoff counter on the corresponding secondary channel already expired. Note that in this case, the expiration of the random backoff counter on the secondary channel may not trigger a transmission. Rather, expiration of the random backoff counter on the secondary channel may allow trigger a transmission once the random backoff counter on the primary channel also expires. In this way, stricter fairness in accessing the secondary channels may be achieved. 
     Thus, once one random backoff counter expires, at least one transmission is made over the channel associated with the expired random backoff counter. Concurrently, transmissions may be made over one or more of other channels if any of those channels is idle. 
     In another embodiment, the AP  504  may designate one of the secondary channels as a high-efficiency primary channel. For example, channel  524  may be designated as the high-efficiency primary channel. The high-efficiency primary channel may be associated with a random backoff counter (e.g., like the primary channel). When the random backoff counter associated with the high-efficiency primary channel expires, the AP  504  may transmit on the high-efficiency primary channel. In some embodiments, the AP  504  may transmit concurrently on the other secondary channels if the other secondary channels have been idle since a time period based on the PIFS timing before the time that the random backoff counter expired. In other embodiments, the AP  504  may transmit concurrently on the other secondary channels if the other secondary channels have been idle since a time period based on an arbitration inter frame spacing (AIFS) timing before the time that the random backoff counter expired. In still other embodiments, the AP  504  may transmit concurrently on the other secondary channels if the other secondary channels have been idle since a time period based on the AIFS timing before the time that the random backoff counter expired, where at least a portion of the random backoff counter associated with the respective secondary channel has expired. For example, the AP  504  may transmit concurrently on channel  520  if channel  520  has been idle since a time period based on the AIFS timing before the time that the random backoff counter associated with channel  524  expired and if the random backoff counter associated with channel  520  has expired. 
     In any of the modes described above, the backoff procedure in different channels may follow different countdown parameters. For example, each backoff procedure may depend on an access category of the traffic that is going to be delivered on the channel. The backoff procedures in each channel may follow the EDCA procedure defined in IEEE 802.11. 
     Detection of Packets by STAs 
     A high-efficiency STA may be able to determine that an incoming transmission comprises a high-efficiency component (OFDMA) and may include information intended for the high-efficiency STA. As described above, legacy STAs may listen for packets from the AP  504  on the primary channel (also referred to as the legacy primary channel). In an embodiment, high-efficiency STAs are assigned to a channel (e.g., a secondary channel) to listen for packets from the AP  504 . In another embodiment, high-efficiency STAs detect packets on each channel used by the AP  504  (e.g., each channel used in the BSS). In still another embodiment, the AP  504  defines one or more high-efficiency primary channels. In an embodiment, each high-efficiency STA may detect packets on the legacy primary channel and on the high-efficiency primary channels. In another embodiment, each high-efficiency STA may detect packets on one or more of the high-efficiency primary channels. In another embodiment, each high-efficiency STA may detect packets on the legacy primary channel only. In any of the above embodiments, detection of an incoming high-efficiency transmission may be based on reception of a message. For example, detection of an incoming high-efficiency transmission may be based on reception of a PPDU with the new PHY layer preamble  528  (e.g., high-efficiency PHY layer preamble) that includes information about the high-efficiency transmission on the current channel and/or other channels. As another example, detection of an incoming high-efficiency transmission may be based on reception of a MAC message (e.g., sent either in a legacy or high-efficiency PPDU) that may advertise a high-efficiency transmission starting at a determined time after the MAC message and/or corresponding parameters, as described herein. As another example, detection of an incoming high-efficiency transmission may be based on reception of a legacy PHY layer preamble that also identifies the presence of a high-efficiency transmission on secondary channels via signaling in the STF field, the LTF field, and/or the SIG field that does not compromise the legacy nature of the preamble. 
     In other embodiments, scheduling mechanisms are used to define a time that the STAs should expect packets from the AP  504 . For example, one scheduling mechanism may be based on a target wakeup time (TWT) timing, which is defined in the IEEE 802.11ah protocol. The TWT timing may be a time during which a STA is scheduled to be awake. As another example, another scheduling mechanism may be based on a restricted access window (RAW) timing, which is defined in the IEEE 802.11ah protocol. The RAW timing may be an interval of time during which access to a medium is restricted to a group of STAs. The AP  504  may further include in management messages used to set up the scheduled time (e.g., an RPS information element for RAW, TWT setup messages for TWT, etc.) an indication of the channel allocation for the benefit of the STAs. In another embodiment, the allocation indicated by the AP  504  in such a message may be in response to a message transmitted by a STA to the AP  504  requesting the use of a specific channel or simply the allocation of a channel. The message may be included in a management frame. 
     The transmissions from the AP  504  may start at the time scheduled according to the TWT timing or the RAW timing. In an embodiment, the random backoff counter, the PIFS timing, and/or the AIFS timing may be used as described herein to determine whether the channel has been idle for an appropriate amount of time. A benefit of scheduling a transmission time based on the TWT timing or the RAW timing may be that the AP  504  then knows when the STAs  506 A-E will be awake. In another embodiment, the AP  504  may not use the random backoff counter, the PIFS timing, and/or the AIFS timing. In still another embodiment, the AP  504  may not use the PIFS timing and/or the AIFS timing on secondary channels. 
     Channel Allocation 
       FIG. 7  shows another timing diagram in which aspects of the present disclosure may be employed. As illustrated in  FIG. 7 , the AP  504  transmits channel allocation messages  702 ,  704 ,  706 , and  708  on each of the channels  520 ,  522 ,  524 , and  526 , respectively. The channel allocation messages  702 ,  704 ,  706 , and  708  may provide information to the STAs  506 A-E regarding which channel is allocated to which STA. In some embodiments, the channel allocation messages  702 ,  704 ,  706 , and/or  708  may be the MAC message described above. 
     The MAC message may include one or more of the following information: a deferral time for third-party STAs, an identifier of STAs that are recipients of the DL-FDMA, in the form of a list of addresses or a group identifier defined a priori by the AP  504 , and/or an indication of the channel(s) and bandwidth to be used. The MAC message may also include information required for sending acknowledgments by using UL-FDMA, as described below. Such information may include an indication of power to be used and/or an indication of a backoff from the nominal transmit power of the STA, which may be indicated earlier by the STA. If such information is not conveyed in a reference signal, the AP  504  and the STA may agree to such information a priori through the exchange of management messages between each STA and the AP  504 . 
     The MAC message may be a regular clear to send (CTS) message or an extended CTS message. An extended CTS message may reserve combination of bits not used in frames of type control to indicate that this is a special CTS message. The term “special” as used herein may mean that the CTS message includes additional information, but legacy STAs may still be able to interpret the CTS message as a legacy or regular CTS message. For example, a special CTS message may use a control wrapper frame to indicate the presence of an HTC field. The HTC field may provide four bytes that can be used to embed identifiers of target STAs. As another example, a special CTS message may include additional information after the FCS field. 
     In an embodiment, the MAC message may be transmitted at a time of short inter frame space (SIFS), PIFS, or AIFS before the start of data transmissions. In another embodiment, the MAC message may be transmitted at a time longer than SIFS, PIFS, or AIFS, where the time may be the time that allows a STA to finish switching channels. The time may be communicated by the STAs to the AP  504 . The AP  504  may use the longest of the times received by the intended recipient STAs. If the time is longer than PIFS, then the AP  504  may perform a new backoff procedure before sending the data portion of the transmission. 
     In an embodiment, if the new PHY layer preamble  528  is available, the PHY layer preamble  528  includes a group identification field that corresponds to a channel allocation of the STAs of the group. 
     In an embodiment, the channels may be pre-allocated, selected by the STAs  506 A-E, and/or selected by the AP  506 A-E and explicitly messaged via channel allocation messages  702 ,  704 ,  706 , and/or  708 . Messages may be conveyed by management or control frames sent before the data transmission (e.g., these frames may not be transmitted based on SIFS or PIFS as described above). If the channels are pre-allocated, and if the number of STAs is above a threshold and traffic requests from the STAs are similar, then a random static allocation may be used (e.g., each STA is allocated to a channel, semi-statically). The AP  504  may indicate to the STAs  506 A-E which station is allocated to which channel (e.g., via the channel allocation messages  702 ,  704 ,  706 , and/or  708 ). If the channels are selected by the STAs  506 A-E, STAs  506 A-E may select and wait on a channel preferred by the respective STA  506 A-E. The STAs  506 A-E may explicitly or implicitly (e.g., via any transmission) notify the AP  504  of their presence on the respective channel. If the allocation is explicitly messaged, the channel allocation messages  702 ,  704 ,  706 , and/or  708  may be sent on each of the channels or just a primary channel. Note that because the STAs  506 A-E may be listening on one channel and need to switch to another channel to receive the DL communication from the AP  504 , the AP  504  may delay sending DL communications  510 ,  512 ,  514 , and/or  518  for a period of time after transmission of the channel allocation messages  702 ,  704 ,  706 , and/or  708  to allow the STAs  506 A-E to switch to the appropriate channel. If the STAs  506 A-E implicitly notify the AP  504  of their presence, the AP  504  may know of a STA  506 A-E location based on reception of any data, control, and/or management frame transmitted by the STA  506 A-E for regular operation. In other words, the data, control, and/or management frame may not necessarily be designed for channel indication. 
     Protection Stage 
     In an embodiment, request to send (RTS) and CTS messages are used by the AP  504  and the STAs  506 A-E to ensure that a given channel is free.  FIGS. 8A-C  show another timing diagram in which aspects of the present disclosure may be employed. In particular,  FIGS. 8A-C  illustrate the use of RTS and CTS messages. 
     In an embodiment, the AP  504  performs a backoff procedure in the primary channel (e.g., channel  526 ) and, once backoff expires, the AP  504  determines whether channels  520 ,  522 ,  524 , and/or  526  are idle (e.g., using PIFS timing as described above). If a channel is idle, the AP  504  may transmit a RTS message  802  on the idle channel(s) to the STA(s)  506 A-E associated with the idle channel(s). In an embodiment, the RTS message  802  may be directed to a single STA  506 A-E and simply duplicated across the transmission channels (e.g., as in IEEE 802.11ac). In this case, the recipient STA  506 A-E may respond with a CTS message on the primary channel and/or on one or more of the secondary channels. High-efficiency data transmission may then follow the CTS message. In some embodiments, each RTS message  802  transmitted on a channel may be addressed to a different STA  506 A-E. In particular, each RTS message  802  may be addressed to the STA  506 A-E that is the intended recipient of the data transmission that will follow on that channel. In this case, the STA  506 A-E may already be allocated to the channel a priori. In other embodiments, each RTS message  802  transmitted on a channel may be exactly or nearly exactly the same. For example, as illustrated in  FIG. 8A , the AP  504  transmits RTS message  802 A to the STA  506 C on channel  520  if the channel  520  is idle, RTS message  802 B to the STA  506 B on channel  522  if the channel  522  is idle, RTS message  802 C to the STA  506 A on channel  524  if the channel  524  is idle, and/or RTS message  802 D to the STA  506 E on channel  526  if the channel  526  is idle. The AP  504  may transmit multiple RTS messages if the STAs  506 A-E are only able to detect messages on the channel allocated to the respective STA  506 A-E. 
     Alternatively, an RTS message  802 E may be transmitted by the AP  504  on the primary channel only (e.g., channel  526 ), as illustrated in  FIG. 8B . The AP  504  may transmit RTS message  802 E if the STAs  806 A-E are able to detect messages on the primary channel. The RTS message  802 E may be addressed to a group of STAs involved in DL frequency division multiple access (FDMA), such as the STAs  506 A-E. The group of STAs may be identified by a multicast MAC receiver address previously assigned to a certain group of STAs and/or may be identified by additional signaling added to the RTS message  802 . A management exchange may have taken place to associate the multicast address with a certain group of STAs. In an embodiment, the RTS message  802  may have the same format as in the IEEE 802.11 specifications. In another embodiment, the RTS message  802  may have a new control and/or management frame format that includes one or more of the information that may be included in the MAC message as discussed above. 
     If a STA  506 A-E is available to accept packets from the AP  504 , the STA  506 A-E may respond to the RTS message  802  with a CTS message  804 . The STA  506 A-E may respond to the RTS message  802  on an available channel (e.g., the channel that the STA  506 A-E desires or expects the AP  504  to use to transmit the DL communications, the channel indicated in the RTS message  802 , the channel that is known by the AP  504  and/or the STA  506 A-E a priori, etc.). For example, STA  506 C may be allocated to channel  520  and transmit a CTS  804 A to the AP  504  on the channel  520  if the STA  506 C is available. Likewise, STA  506 B may be allocated to channel  522  and transmit a CTS  804 B to the AP  504  on the channel  522  if the STA  506 B is available, STA  506 A may be allocated to channel  524  and transmit a CTS  804 C to the AP  504  on the channel  524  if the STA  506 C is available, and/or STA  506 E may be allocated to channel  526  and transmit a CTS  804 D to the AP  504  on the channel  526  if the STA  506 E is available. 
     In an embodiment, the CTS messages  804 A-D may be transmitted to the AP  504  simultaneously (e.g., if the AP  504  and/or the STAs  506 A-E support UL FDMA or UL spatial division multiple access (SDMA)), as illustrated in  FIGS. 8A-B . In another embodiment, the CTS messages  804 A-D may be transmitted to the AP  504  in a staggered fashion such that no CTS message  804 A-D is transmitted at the same time (e.g., if the AP  504  and/or the STAs  506 A-E do not support UL FDMA or UL SDMA), as illustrated in  FIG. 8C . The CTS messages  804 A-D may be transmitted based on a schedule provided in the RTS messages  802 A-D and/or based on a schedule provided in a previous message. 
     The DL communications  510 ,  512 ,  514 , and/or  518  may be only be transmitted by the AP  504  if a CTS message is received on the respective channel. In an embodiment, upon expiration of the random backoff counter, the AP  504  may send a CTS message on the primary channel and/or on one or more of the secondary channels (e.g., on secondary channels detected to be idle for a PIFS time), and follow the CTS message with the high-efficiency DL-OFDMA transmission. The CTS message may be a CTS-to-self message (e.g., including the MAC address of the sender AP  504 ) or may be addressed to one or more STAs. The CTS message may be identical across multiple channels or may be different across channels (e.g., having a different MAC address). The CTS message may be sent on the primary channel and may include information identifying the start of the high-efficiency transmission. The information may be in a format that does not compromise the legacy format of the frame (e.g., either in the PHY layer preamble or in the MAC payload). 
     Acknowledgment Stage 
     In an embodiment, restrictions can be placed on the duration of a packet. In some embodiments, transmissions by the AP  504  have different lengths. In other embodiments, transmissions by the AP  504  have the same length. 
     Following the DL communications  510 ,  512 ,  514 , and/or  518 , the STAs  506 A-E may respond with a block acknowledgment (BA) acknowledging that the DL communication was received. The STAs  506 A-E may respond with the BA on their own volition or may be prompted to by the AP  504  (e.g., via a block acknowledgment request (BAR)). 
       FIGS. 9A-E  shows another timing diagram in which aspects of the present disclosure may be employed. In particular,  FIGS. 9A-E  illustrate the use of BAs and BARs as described herein. In an embodiment, if the AP  504  and/or the STAs  506 A-E cannot handle simultaneous UL communications (e.g., do not operate using UL FDMA), one of the STAs  506 A-E responds immediately with a BA after the DL communication is complete. The remaining STAs  506 A-E then respond with a BA after receiving a BAR. The BAR may be transmitted on the channel that the DL communication was transmitted on, the primary channel, and/or the high-efficiency primary channel. 
     For example, as illustrated in  FIG. 9A , STA  506 C may respond with a BA  904 A after the DL communication  514  is complete. After the BA  904 A has been transmitted to the AP  504 , the AP  504  may transmit a BAR  902 B to the STA  506 B on the channel  522 , which is the channel that the DL communication  512  was received by the STA  506 B. Once the STA  506 B receives the BAR  902 B, the STA  506 B may respond with a BA  904 B. The BAR and BA cycle then continues for the remaining STAs (e.g., STA  506 A and STA  506 E). The AP  504  may set the acknowledgment policy of the data transmitted to multiple STAs  506 A-E such that no more than one STA  506 A-E responds with an immediate acknowledgment or BA. The STA  506 A-E receiving an immediate acknowledgment request or BAR may transmit the acknowledgment or BA on the same channel where data was received and/or on the primary channel. An additional BAR may be sent by the AP  504  to other STAs  506 A-E on the primary channel and/or on one or more of the secondary channels, such as the same channel where data was transmitted to the corresponding STAs  506 A-E. In this case, the STA  506 A-E may transmit the acknowledgment or BA on the same channel where the BAR was received and/or on the primary channel. 
     In an embodiment, if the AP  504  and/or the STAs  506 A-E can handle simultaneous UL communications (e.g., do operate using UL FDMA), all of the STAs  506 A-E may respond with a BA after the DL communications are complete (e.g., end of transmission is a trigger for all STAs  506 A-E to send the BAs). The BAs may be transmitted on the same channel as the channel where the DL communication was received. For example, as illustrated in  FIG. 9B , STAs  506 A-C and  506 E each respond with a BA  904 A-D immediately after the DL communications  510 ,  512 ,  514 , and  518  are complete. The BAs  904 A-D may be transmitted concurrently. 
     In an embodiment, the AP  504  transmits BARs  902 A-D to the STAs  506 A-C and  506 E to trigger the transmission of the BAs  904 A-D. For example, as illustrated in  FIG. 9C , the BARs  902 A-D may each be transmitted on a separate channel simultaneously. The BARs  902 A-D may be transmitted after the end of the transmission of the longest DL communication (e.g., DL communication  512  in  FIG. 9C ). The STAs  506 A-C and  506 E may then respond to the BARs  902 A-D with BAs  904 A-D using the channel upon which the respective BARs  902 A-D were received. 
     In an embodiment, the AP  504  broadcasts a single BAR  902 E to the STAs  506 A-C and  506 E to trigger the transmission of the BAs  904 A-D. The single BAR  902 E may be transmitted over the primary channel. For example, as illustrated in  FIG. 9D , BAR  902 E is transmitted by the AP  504  on the channel  526  after the end of the transmission of the longest DL communication, DL communication  512 . The BAR  902 E is received by the STAs  506 A-C and  506 E. The STAs  506 A-C and  506 E then respond with BAs  904 A-D on the channel that the DL communication was received on. 
     In an embodiment, UL multiuser multiple input multiple output (MU-MIMO) is used to deliver BAs in a parallel manner to the AP  504 . For example, as illustrated in  FIG. 9E , each of the STAs  506 A-C and  506 E may transmit a BA on the same frequency (e.g., the primary frequency) at the same time. Such UL communications is represented as BA  904 E, which includes the BAs transmitted by each of the STAs  506 A-C and  506 E. 
     Note that in any or all of the above embodiments, BARs and/or BAs may be transmitting in a legacy or high-efficiency PPDU format. When the BARs and/or BAs are transmitted in high-efficiency PPDU format, the bandwidth may be smaller than 20 MHz. Different BARs and/or BAs may have a different duration, which may depend on the bandwidth used for transmission (not shown). 
     Use Cases 
     In an embodiment, the DL FDM protocol described herein with respect to  FIGS. 5A-9E  is implemented in several applications. For example, a BSA may include legacy STAs and high-efficiency STAs. The DL FDM protocol may use otherwise unused bandwidth in the communication medium by assigning some of the STAs to a portion of the otherwise unused bandwidth. This may allow the legacy STAs and/or the high-efficiency STAs to communicate concurrently. This may be beneficial if the BSS range of the wireless network is restricted to high rate users. 
     As another example, the DL FDM protocol may allow for multiplexing STAs at different ranges with different power allocations. For example, the AP  504  may have a finite amount of power available for transmitting packets. Some STAs, such as STA  506 D and STA  506 E may be located far away from the AP  504  as compared to other STAs. Thus, more power may be needed to transmit to these far away STAs. However, the power used to transmit to the far away STAs can be reduced slightly (e.g., enough so as to not compromise connectivity) in order to enable low power transmissions to STAs (e.g., STAs  506 A-C) located near the AP  504 . If the AP  504  has a total power allotment of 20 dB for transmissions, instead of 20 dB, 19 dB could be allocated for transmitting packets to the STA  506 E. The remaining 1 dB could be split into three parts so that the AP  504  can then also transmit packets to the STAs  506 A-C, which are closer to the AP  504 . This mechanism may require signaling from the STA  506 E to the AP  504  indicating what is the “margin” in power reduction that can be tolerated by the STA  506 E. 
     As another example, frequency diversity can be achieved if the PHY layer uses a tone interleaved approach. With frequency diversity, a frequency hopping system is created that requires minimal interference coordination. Tones may be divided into two or more subsets. A first STA may transmit and/or receive data via tones in the first subset and a second STA may transmit and/or receive data via tones in the second subset. As long as the first subset and the second subset do not overlap, interference may be avoided. 
     Flowcharts 
       FIG. 10  is a flowchart of a process  1000  for high-efficiency wireless frequency division multiplexing. In an embodiment, the process  1000  may be performed by an AP, such as the AP  504 . At block  1002 , the process  1000  determines a performance characteristic for each wireless device in a first BSS. In an embodiment, the performance characteristic can include physical and/or RF characteristics such as, for example, an SINR, an RF geometry, an RSSI, an MCS value, an interference level, a signal level, a transmission capability, and/or the like. 
     At block  1004 , the process  1000  categorizes each wireless device in the first BSS into a first subset of wireless devices or a second subset of wireless devices based on the performance characteristic. At block  1006 , the process  1000  transmits packets to the first subset of wireless devices using a primary frequency channel. At block  1008 , the process  1000  transmits packets to the second subset of wireless devices using a secondary frequency channel. 
     At block  1010 , the process  1000  transmits a coordination packet to an AP in a second BSS indicating that the secondary frequency channel is used to communicate with the second subset of wireless devices. In an embodiment, the AP in the second BSS transmits packets to a first set of wireless devices in the second BSS using the primary frequency channel and transmits a packet to a second set of wireless devices in the second BSS using a ternary frequency channel in response to receiving the coordination packet. After block  1010 , the process  1000  ends. 
       FIG. 11  is a flowchart of a process  1100  for transmitting data. In an embodiment, the process  1100  may be performed by an AP, such as the AP  504 . At block  1102 , the process  1100  generates a first packet. In an embodiment, the first packet comprises a physical layer and a MAC layer. In a further embodiment, the MAC layer allocates a first STA to a primary frequency channel and a second STA to a secondary frequency channel. At block  1104 , the process  1100  transmits the first packet to the first STA and the second STA. At block  1106 , the process  1100  transmits a second packet to the first STA using the primary frequency channel. At block  1108 , the process  1100  transmits a third packet to the second STA using the secondary frequency channel. After block  1108 , the process  1100  ends. 
       FIG. 12  is a flowchart of a process  1200  for transmitting data. In an embodiment, the process  1200  may be performed by an AP, such as the AP  504 . At block  1202 , the process  1200  generates a first packet. In an embodiment, the first packet comprises a physical layer preamble. In a further embodiment, the physical layer preamble comprises an allocation of a first STA to a primary frequency channel and a second STA to a secondary frequency channel. At block  1204 , the process  1200  transmits the first packet over the primary frequency channel and the secondary frequency channel. At block  1206 , the process  1200  transmits a second packet to the first STA using the primary frequency channel. In an embodiment, the second packet is transmitted after the first packet. At block  1208 , the process  1200  transmits a third packet to the second STA using the secondary frequency channel. In an embodiment, the third packet is transmitted after the first packet. After block  1208 , the process  1200  ends. 
       FIG. 13  is a flowchart of a process  1300  for transmitting data. In an embodiment, the process  1300  may be performed by an AP, such as the AP  504 . At block  1302 , the process  1300  generates a first packet for transmission to a first STA over a primary frequency channel. At block  1304 , the process  1300  generates a second packet. In an embodiment, the second packet comprises a physical layer preamble. In a further embodiment, the physical layer preamble comprises an allocation of a second STA to a secondary frequency channel and a third STA to a ternary frequency channel. At block  1306 , the process  1300  transmits the first packet over the primary frequency channel to the first STA. In an embodiment, the first STA is not configured to communicate over the secondary frequency channel or the ternary frequency channel. At block  1308 , the process  1300  transmits the second packet over the secondary frequency channel and the ternary frequency channel. 
     At block  1310 , the process  1300  transmits a third packet to the second STA using the secondary frequency channel. In an embodiment, the third packet is transmitted after the second packet. At block  1312 , the process  1300  transmits a fourth packet to the third STA using the ternary frequency channel. In an embodiment, the fourth packet is transmitted after the second packet. After block  1312 , the process  1300  ends. 
       FIG. 14  is a flowchart of a process  1400  for transmitting data. In an embodiment, the process  1400  may be performed by an AP, such as the AP  504 . At block  1402 , the process  1400  operates a random backoff counter associated with a primary frequency channel. At block  1404 , the process  1400  transmits a first data packet over the primary frequency channel after the random backoff counter expires. In an embodiment, the first data packet is transmitted to a first STA. 
     At block  1406 , the process  1400  determines, after the random backoff counter expires, whether a secondary frequency channel has been idle for a duration of time based on a point coordination function inter frame space (PIFS) before a time that the random backoff counter expired. At block  1408 , the process  1400  transmits a second data packet over the secondary frequency channel if the secondary frequency channel has been idle for the duration of time based on the PIFS before the time that the random backoff counter expired. In an embodiment, the second data packet is transmitted to a second station. After block  1408 , the process  1400  ends. 
       FIG. 15  is a flowchart of a process  1500  for transmitting data. In an embodiment, the process  1500  may be performed by an AP, such as the AP  504 . At block  1502 , the process  1500  operates a first random backoff counter associated with a primary frequency channel and a second random backoff counter associated with a secondary frequency channel. At block  1504 , the process  1500  transmits a first data packet over a frequency channel associated with a random backoff counter that expires first. In an embodiment, the first data packet is transmitted to a first station over the primary frequency channel if the first random backoff counter expires before the second random backoff counter. In a further embodiment, the second data packet is transmitted to a second station over the secondary frequency channel if the second random backoff counter expires before the first random backoff counter. 
     At block  1506 , the process  1500  determines, after the first of the first random backoff counter or the second random backoff counter expires, whether a frequency channel associated with a random backoff counter that has not expired has been idle for a duration of time based on a point coordination function inter frame space (PIFS) before a time that the respective random backoff counter expired. At block  1508 , the process  1500  transmits a second data packet over a frequency channel associated with a random backoff counter that has not expired if the respective frequency channel has been idle for the duration of time based on the PIFS before the time that the respective random backoff counter expired. After block  1508 , the process  1500  ends. 
       FIG. 16  is a flowchart of a process  1600  for transmitting data. In an embodiment, the process  1600  may be performed by an AP, such as the AP  504 . At block  1602 , the process  1600  transmits a request to send message to a first station and a second station. At block  1604 , the process  1600  receives at least one clear to send message from at least one of the first station or the second station. 
     At block  1606 , the process  1600  transmits, in response to reception of a clear to send message from the first station over a primary frequency channel, a first data packet to the first station over the primary frequency channel. At block  1608 , the process  1600  transmits, in response to reception of a clear to send message from the second station over a secondary frequency channel, a second data packet to the second station over the secondary frequency channel. After block  1608 , the process  1600  ends. 
     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. 
     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.