Patent Publication Number: US-8995406-B2

Title: Systems and methods for reducing collisions after traffic indication map paging

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/595,480, filed on Feb. 6, 2012, and U.S. Provisional Patent Application No. 61/758,000, filed on Jan. 29, 2013, entitled “SYSTEMS AND METHODS FOR REDUCING COLLISIONS AFTER TRAFFIC INDICATION MAP PAGING”, the entire contents of which disclosure is herewith incorporated by reference. 
    
    
     BACKGROUND 
     1. Field 
     The present application relates generally to wireless communications, and more specifically to systems, methods, and devices for performing collision avoidance in a wireless communication network. 
     2. 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. 
     The devices in a wireless network may transmit/receive information between each other. Further, devices that are not actively transmitting/receiving information in the wireless network may enter a doze state, to conserve power, where the devices do not actively transmit/receive information in the doze state. These devices may further utilize paging messages to determine when to wake up from a doze state and enter an awake state in order to transmit/receive data. Thus, improved systems, methods, and devices for reducing collisions are 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 paging for devices in a wireless network. 
     One aspect of this disclosure provides a wireless communications device. The wireless communications device comprises a memory configured to store a value of a counter. The wireless communications device further comprises a processor coupled to the memory. The processor is configured to decrement the value of the counter if a channel of a wireless communications network is idle for at least an extended slot time. A starting value of the counter is based on a position of an index corresponding to the wireless communications device in an information element. The processor is further configured to generate a polling request. The polling request is transmitted to an access point over the wireless communications network when the value of the counter reaches a threshold value. 
     Another aspect of this disclosure provides a method for reducing collisions in a wireless communications network. The method comprises decrementing a value of a counter if a channel of a wireless communications network is idle for at least an extended slot time. A starting value of the counter is based on a position of an index corresponding to a wireless communications device in an information element. The method further comprises generating a polling request. The method further comprises transmitting the polling request to an access point over the wireless communications network when the value of the counter reaches a threshold value. 
     Another aspect of this disclosure provides an apparatus configured to reduce collisions in a wireless communications network. The apparatus comprises means for decrementing a value of a counter if a channel of a wireless communications network is idle for at least an extended slot time. A starting value of the counter is based on a position of an index corresponding to a wireless communications device in an information element. The apparatus further comprises means for generating a polling request. The apparatus further comprises means for transmitting the polling request to an access point over the wireless communications network when the value of the counter reaches a threshold value. 
     Another aspect of this disclosure provides a non-transitory computer readable medium comprising instructions or code that, when executed, causes an apparatus to decrement a value of a counter if a channel of a wireless communications network is idle for at least an extended slot time. A starting value of the counter is based on a position of an index corresponding to a wireless communications device in an information element. The medium further comprises code that, when executed, causes the apparatus to generate a polling request. The medium further comprises code that, when executed, causes the apparatus to transmit the polling request to an access point over the wireless communications network when the value of the counter reaches a threshold value. 
     Another aspect of this disclosure provides a wireless communications device. The wireless communications device comprises a receiver configured to detect messages transmitted on a channel of a wireless communications network. The wireless communications device further comprises a processor coupled to the receiver. The processor is configured to generate a polling request. The processor is further configured to determine an adaptive enhanced inter-frame space (AEIFS) each time the wireless communications device detects another message transmitted on the channel of the wireless communications network in which the wireless communications device communicates. An initial duration of the AEIFS is based on a position of the wireless communication device in an information element. The polling request is transmitted to an access point over the wireless communications network after a time based on a duration of the AEIFS and when the channel of the wireless communications network is open. 
     Another aspect of this disclosure provides a method for reducing collisions in a wireless communications network. The method comprises generating a polling request. The method further comprises determining an adaptive enhanced inter-frame space (AEIFS) each time a wireless communications device detects another message transmitted on a channel of a wireless communications network in which the wireless communications device communicates. An initial duration of the AEIFS is based on a position of the wireless communication device in an information element. The method further comprises transmitting the polling request to an access point over the wireless communications network after a time based on a duration of the AEIFS and when the channel of the wireless communications network is open. 
     Another aspect of this disclosure provides an apparatus configured to reduce collisions in a wireless communications network. The apparatus comprises means for generating a polling request. The apparatus further comprises means for determining an adaptive enhanced inter-frame space (AEIFS) each time a wireless communications device detects another message transmitted on a channel of a wireless communications network in which the wireless communications device communicates. An initial duration of the AEIFS is based on a position of the wireless communication device in an information element. The apparatus further comprises means for transmitting the polling request to an access point over the wireless communications network after a time based on a duration of the AEIFS and when the channel of the wireless communications network is open. 
     Another aspect of this disclosure provides a non-transitory computer readable medium comprising instructions or code that, when executed, causes an apparatus to generate a polling request. The medium further comprises code that, when executed, causes an apparatus to determine an adaptive enhanced inter-frame space (AEIFS) each time a wireless communications device detects another message transmitted on a channel of a wireless communications network in which the wireless communications device communicates. An initial duration of the AEIFS is based on a position of the wireless communication device in an information element. The medium further comprises code that, when executed, causes an apparatus to transmit the polling request to an access point over the wireless communications network after a time based on a duration of the AEIFS and when the channel of the wireless communications network is open. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary wireless communication system in which aspects of the present disclosure may be employed. 
         FIG. 2  shows a functional block diagram of an exemplary wireless device that may be employed within the wireless communication system of  FIG. 1 . 
         FIG. 3  illustrates a plurality of partitioned paging messages transmitted by an access point to wireless stations in the wireless communication system of  FIG. 1 . 
         FIG. 4  illustrates an exemplary polling request mechanism. 
         FIG. 5A  illustrates another polling request mechanism. 
         FIG. 5B  illustrates another exemplary polling request mechanism. 
         FIG. 6  illustrates another exemplary polling request mechanism. 
         FIG. 7  is a flowchart of a process for reducing collisions in the wireless communication system of  FIG. 1 . 
         FIG. 8  is a functional block diagram of an exemplary wireless device that may be employed within the wireless communication system of  FIG. 1 . 
         FIG. 9  is another flowchart of a process for reducing collisions in the wireless communication system of  FIG. 1 . 
         FIG. 10  is another functional block diagram of an exemplary wireless device that may be employed within the wireless communication system of  FIG. 1 . 
     
    
    
     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 in a sub-gigahertz band may be transmitted according to the 802.11ah 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 802.11ah protocol may be used for sensors, metering, and smart grid networks. Advantageously, aspects of certain devices implementing the 802.11ah protocol may consume less power than devices implementing other wireless protocols, and/or may be used to transmit wireless signals across a relatively long range, for example about one kilometer or longer. 
     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 such as 802.11ah) 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 the 802.11ah 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 the 802.11ah 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 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 . 
     The AP  104  may transmit a beacon signal (or simply a “beacon”), via a communication link such as the downlink  108 , to other nodes STAs  106  of the system  100 , which may help the other nodes STAs  106  to synchronize their timing with the AP  104 , or which may provide other information or functionality. Such beacons may be transmitted periodically. In one aspect, the period between successive transmissions may be referred to as a superframe. Transmission of a beacon may be divided into a number of groups or intervals. In one aspect, the beacon may include, but is not limited to, such information as timestamp information to set a common clock, a peer-to-peer network identifier, a device identifier, capability information, a superframe duration, transmission direction information, reception direction information, a neighbor list, and/or an extended neighbor list, some of which are described in additional detail below. Thus, a beacon may include information both common (e.g. shared) amongst several devices, and information specific to a given device. 
     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 beacon broadcast by the AP  104 . To receive such a beacon, 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). 
       FIG. 2  shows an exemplary functional block diagram of a wireless device  202  that may be employed within the wireless communication system  100  of  FIG. 1 . The wireless device  202  is an example of a device that may be configured to implement the various methods described herein. For example, the wireless device  202  may comprise the AP  104  or one of the STAs  106 . 
     The wireless device  202  may include a processor  204  which controls operation of the wireless device  202 . The processor  204  may also be referred to as a central processing unit (CPU). Memory  206 , which may include both read-only memory (ROM) and random access memory (RAM), may provide instructions and data to the processor  204 . A portion of the memory  206  may also include non-volatile random access memory (NVRAM). The processor  204  typically performs logical and arithmetic operations based on program instructions stored within the memory  206 . The instructions in the memory  206  may be executable to implement the methods described herein. 
     The processor  204  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  202  may also include a housing  208  that may include a transmitter  210  and/or a receiver  212  to allow transmission and reception of data between the wireless device  202  and a remote location. The transmitter  210  and receiver  212  may be combined into a transceiver  214 . An antenna  216  may be attached to the housing  208  and electrically coupled to the transceiver  214 . The wireless device  202  may also include (not shown) multiple transmitters, multiple receivers, multiple transceivers, and/or multiple antennas. 
     The transmitter  210  may be configured to wirelessly transmit messages, which may be referred to as “paging messages” that are configured to indicate to wireless devices whether or not the wireless devices need to wake up from a doze state and enter an awake state as discussed below. For example, the transmitter  210  may be configured to transmit paging messages generated by the processor  204 , discussed above. When the wireless device  202  is implemented or used as a STA  106 , the processor  204  may be configured to process paging messages. When the wireless device  202  is implemented or used as an AP  104 , the processor  204  may also be configured to generate paging messages. 
     The receiver  212  may be configured to wirelessly receive paging messages. 
     The wireless device  202  may also include a signal detector  218  that may be used in an effort to detect and quantify the level of signals received by the transceiver  214 . The signal detector  218  may detect such signals as total energy, energy per subcarrier per symbol, power spectral density and other signals. The wireless device  202  may also include a digital signal processor (DSP)  220  for use in processing signals. The DSP  220  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  202  may further comprise a user interface  222  in some aspects. The user interface  222  may comprise a keypad, a microphone, a speaker, and/or a display. The user interface  222  may include any element or component that conveys information to a user of the wireless device  202  and/or receives input from the user. 
     The various components of the wireless device  202  may be coupled together by a bus system  226 . The bus system  226  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  202  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. 2 , 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  204  may be used to implement not only the functionality described above with respect to the processor  204 , but also to implement the functionality described above with respect to the signal detector  218  and/or the DSP  220 . Further, each of the components illustrated in  FIG. 2  may be implemented using a plurality of separate elements. 
     The wireless device  202  may comprise an AP  104  or an STA  106 , and may be used to transmit and/or receive communications including paging messages. That is, either AP  104  or STA  106  may serve as transmitter or receiver devices of paging messages. Certain aspects contemplate signal detector  218  being used by software running on memory  206  and processor  204  to detect the presence of a transmitter or receiver. 
     The STA  106  may have a plurality of operational modes. For example, the STA  106  may have a first operational mode referred to as an active mode. In the active mode, the STA  106  may always be in an “awake” state and actively transmit/receive data with the AP  104 . Further, the STA  106  may have a second operational mode referred to as a power save mode. In the power save mode, the STA  106  may be in the “awake” state or a “doze” or “sleep” state where the STA  106  does not actively transmit/receive data with the AP  104 . For example, the receiver  212  and possibly DSP  220  and signal detector  218  of the STA  106  may operate using reduced power consumption in the doze state. Further, in the power save mode, the STA  106  may occasionally enter the awake state to listen to messages from the AP  104  (e.g., paging messages) that indicate to the STA  106  whether or not the STA  106  needs to “wake up” (e.g., enter the awake state) at a certain time so as to be able to transmit/receive data with the AP  104 . 
     Accordingly, in certain wireless communication systems  100 , the AP  104  may transmit paging messages to a plurality of STAs  106  in a power save mode in the same network as the AP  104 , indicating whether or not there is data buffered at the AP  104  for the STAs  106 . The STAs  106  may also use this information to determine whether they need to be in an awake state or a doze state. For example, if an STA  106  determines it is not being paged, it may enter a doze state. Alternatively, if the STA  106  determines it may be paged, the STA  106  may enter an awake state for a certain period of time to receive the page and further determine when to be in an awake state based on the page. Further, the STA  106  may stay in the awake state for a certain period of time after receiving the page. In another example, the STA  106  may be configured to function in other ways when being paged or not being paged that are consistent with this disclosure. 
     In some aspects, paging messages may comprise a bitmap (not shown in this figure), such as a traffic identification map (TIM). In certain such aspects, the bitmap may comprise a number of bits. These paging messages may be sent from the AP  104  to STAs  106  in a beacon or a TIM frame. Each bit in the bitmap may correspond to a particular STA  106  of a plurality of STAs  106 , and the value of each bit (e.g., 0 or 1) may indicate the state the corresponding STA  106  should be in (e.g., doze state or awake state). Accordingly, the size of the bitmap may be directly proportional to the number of STAs  106  in the wireless communications system  100 . Therefore, a large number of STAs  106  in the wireless communications system  100  may result in a large bitmap. 
       FIG. 3  illustrates a plurality of partitioned paging messages  302  transmitted by the AP  104  to STAs  106  in the wireless communication system  100  of  FIG. 1 . As shown, time increases horizontally across the page over the time axis  304 . As shown, the AP  104  is configured to transmit a plurality of paging messages  302 . The paging messages  302  may be sent in a TIM frame, a beacon, or using some other appropriate signaling. The STAs  106  may be configured to listen to one or more of the paging messages  302 . Following the one or more paging messages  302 , the STAs  106  may be configured to transmit requests to the AP  104  and receive a response from the AP  104 . 
     The paging process may result in a high number of STAs  106  receiving the one or more paging messages  302 . For example, a high number of STAs  106  in the same TIM may receive the one or more paging messages  302 , which may lead to one or more STAs  106  contending to transmit requests to the AP  104  on the medium after the TIM. Accordingly, collisions resulting in corrupted data received by the AP  104  may occur in situations in which at least two STAs  106  attempt to transmit requests to the AP  104  at or nearly at a same time. 
       FIG. 4  illustrates a polling request mechanism  400 . The polling request mechanism  400  shown may be used by the AP  104  and the STAs  106  in the wireless communication system  100  of  FIG. 1 . As shown, time increases horizontally across the page from slot time  424  to slot time  440 . 
     In general, after the transmission of a paging message, such as TIM  410 , a time interval is reserved for the paged STAs  106 . The reservation may be achieved by transmitting a message (e.g., a paging message, an additional message, etc.) to cause non-paged STAs to defer access to the medium for the duration of the reserved period. In some implementations, the deferred access can be achieved by setting a duration field value of the PPDU of a reserving frame (e.g., the paging message, the additional message, etc.), which prompts the non-paged STAs to set their network allocation vector (NAV). The PPDU of the reserving frame may carry an information element (e.g., the bitmap described above). In other implementations, the deferred access can be achieved by sending an additional frame preceding or following the paging frame, where the additional frame indicates the duration of the reserved period. 
     During the reserved time interval, the paged STAs  106  can send requests to the AP  104  (e.g., Power Saving polls (PS-POLL) requests  412 ,  416 , and  420 ) and receive a response from the AP  104  (e.g., response  414 ,  418 , and  422 ). Multiple paged STAs  106  can contend during the reserved time interval in accordance with various methods, as described herein. In some embodiments, STAs  106  that have not been paged cannot contend during the reserved time interval. Once the reserved time interval is over, STAs  106  can start contending to send the requests to the AP  104 . In an embodiment, the AP  104  may determine the duration of the reserved time interval. The reserved time interval should be sufficient for all the paged STAs  106  to send requests to the AP  104  and receive a response from the AP  104 . By way of example, and not limitation, the duration of the reserved time interval may be a function of the number of paged STAs  106 . 
     The polling request mechanism  400  illustrates an embodiment in which STAs  402 ,  404 , and  406  can transmit requests, like PS-POLLs  412 ,  416 , and  420 , to AP  408  in such a way so as to avoid collisions. STAs  402 ,  404 , and  406  may be similar to STAs  106  as described herein. In some embodiments, the STAs  402 ,  404 , and  406  may transmit requests to the AP  408  in a certain order. AP  408  may be similar to AP  104  as described herein. The paging message, such as TIM  410 , may implicitly or explicitly define an ordering for the STAs  402 ,  404 , and  406 . For example if the TIM  410  bitmap indicates that both STA  402  and STA  404  are paged, then the TIM  410  bitmap also implicitly or explicitly indicates whether STA  402  is before or after STA  404 . In an example, the order could be determined by the order in which the paged STAs appear in the bitmap representation. Consider a bitmap {0, 1, 0, 0, 1, 1}, where the STA associated with the bit in position 2 is assumed to be before the STA associated with the bit in position 5. In some implementations, the compressed bitmap may be expressed as list of STA identifiers. In this case the sequence in which the STA identifiers appear in the list may determine the order. Consider the list {13, 25, 5, 22}, where the STA associated with identifier “13” is assumed to come before STA identified by “5.” In another aspect, the order may be derived from the value of the STA identifier irrespective of the message representation. 
     In some implementations, the position of the STA  402 ,  404 , or  406  within the TIM  410  bitmap sequence may be a function of the position of the STA  402 ,  404 , or  406  as described above. The order may further be dependent on other indications, the indications being either included in the paging message or assumed to be known at the STAs  402 ,  404 , and/or  406 . For example, the indication may include the Timing Synchronization Function (TSF) within the paging message (e.g. TIM  410 ). In such an implementation, the first STA may be the one whose identifier is set to “1” and has a position within the TIM  410  bitmap sequence which is first in the order after the position associated with the 12 least significant bits (LSBs) of the TSF. Many other functions incorporating various indications can be included to achieve a similar result as that based on the TSF. One beneficial result of including the TSF in the computation of the order is that the order may be changed at each transmission, provided that the portion of the used TSF is different at each transmission. 
     In some implementations, the sender of the paging message may determine the order of the paged STAs according to any criteria including the usage of the ordering information. For example the sender, AP  408 , may order the STAs  402 ,  404 , and  406  based on their QoS requirements, power saving requirements, or other performance parameters. It may be desirable in some implementation for the sender of the paging message to include in the message an explicit indication of the order. This explicit indication of the order may not be based on the TIM  410  bitmap, but rather on other factors as described herein. 
     For illustrative purposes only, and not meant to be limiting,  FIG. 4  depicts an order of STA  402 , STA  404 , and then STA  406 . While STA  402  may be the first STA to transmit a request to the AP  408 , the STA  402  may not do so immediately after the TIM  410 . Each of STAs  402 ,  404 , and  406  may be configured to use a carrier sense multiple access with collision avoidance (CSMA/CA) based medium access procedure, such as the distributed coordination function (DCF) or the enhanced distributed channel access (EDCA) as defined in the IEEE 802.11 standard. In such a medium access mechanism, a STA  402 ,  404 , or  406  that wants to access the medium for the transmission of a frame initializes a back-off counter. The back-off counter may be initialized with a random number chosen in an appropriate interval. For example, an appropriate interval may be a value between 0 and a duration of a contention window (CW). The back-off counter may be decremented while the transmission medium (e.g. channel) is idle—in other words, no activity is detected on the transmission medium. The transmission medium may be considered to be idle if no activity is detected for a distributed inter-frame space (DIFS) or an arbitration inter-frame space (AIFS) interval. After the medium has been idle for a DIFS or AIFS interval of time, the back-off counter may be decremented by one unit per each additional consecutive idle interval of a duration equal to a slot time. When activity is detected on the medium, the back-off countdown may be frozen and restarted when the medium becomes idle again, as described herein. The STAs  402 ,  404 , and  406  may transmit a packet on the medium when the back-off counter reaches zero or any other integer that represents a lowest value of the counter. In some implementations the DIFS interval may be defined as
 
DIFS=SIFS+(2*slot time)  (1)
 
where SIFS is a short inter-frame space. The AIFS interval may be defined as
 
AIFS=SIFS+( n *slot time)  (2)
 
where n is greater than or equal to 2.
 
     Each of STAs  402 ,  404 , and  406  may be configured to use a deterministic back-off value to initialize a back-off counter, where an initial value of the back-off counter may be based on the order of the paged STAs  402 ,  404 , and  406 . For example, an initial value of the back-off counter for STA  402  may be 1, an initial value of the back-off counter for STA  404  may be 2, and an initial value of the back-off counter for STA  406  may be 3. In this way, an initial value of the back-off counter may be different for each STA  402 ,  404 , and  406  so as to allow each STA  402 ,  404 , and  406  to access the medium in different time instants. 
     In some implementations, the back-off counter for each STA  402 ,  404 , and  406  may decrement the back-off value when the channel over which the STAs  402 ,  404 , and  406  communicate with the AP  408  is idle for the duration of a slot time  424 ,  426 ,  428 ,  430 ,  432 ,  434 ,  436 ,  438 , and  440 . As an example, a regular slot time may be a slot time defined in the IEEE 802.11 standard or a similar CSMA/CA protocol. The STAs  402 ,  404 , and/or  406  may be configured to transmit a PS-POLL request  412 ,  416 , and/or  420  when their respective back-off value reaches zero or any other integer that represents a lowest value of the counter. 
     In some implementations, the paged STAs  402 ,  404 , and/or  406  may perform the back-off procedure by using a DIFS, an AIFS, and a slot time that are defined differently than the definitions found in the IEEE 802.11 standard. In an embodiment, slot times  424 ,  426 ,  428 ,  430 ,  432 ,  434 ,  436 ,  438 , and  440  may be defined as extended slot times (hereinafter referred to as “slot times”). Extended slot times may be at least as long in duration as the time it takes for a STA  402 ,  404 , or  406  to transmit a PS-POLL request  412 ,  416 , or  420  and for the STA  402 ,  404 , or  406  to receive a beginning of a response  414 ,  418 , or  422 . For example, an extended slot time may be the sum of the time it takes for a STA  402 ,  404 , or  406  to transmit a PS-POLL request  412 ,  416 , or  420 , the SIFS time, and the clear channel assessment (CCA) time. In other words, the extended slot may be defined as
 
extended slot time=PS-POLL time+SIFS+CCA time  (3)
 
As an example, the extended slot time may be a multiple of a regular slot time, where the regular slot time is defined by the IEEE 802.11 standard. For example,
 
                       extended   ⁢           ⁢   slot   ⁢           ⁢   time       regular   ⁢           ⁢   slot   ⁢           ⁢   time       =   K           (   4   )               
where K is an integer. In an embodiment, the DIFS or AIFS interval duration used by the paged STAs  402 ,  404 , and/or  406  may be the same or nearly the same as the duration as defined by the IEEE 802.11 standard. For example, the DIFS or AIFS interval duration used by the paged STAs  402 ,  404 , and/or  406  may be defined as in Equations (1) and (2) above. In another embodiment, the DIFS or AIFS interval duration used by the paged STAs  402 ,  404 , and/or  406  may be equal to zero. In this case, the back-off counter may be decremented by one unit per each consecutive idle interval of a duration equal to an extended slot time, without waiting for a DIFS or AIFS interval. In another embodiment, the DIFS or AIFS interval duration used by the paged STAs  402 ,  404 , and/or  406  may be defined in terms of the extended slot time. For example,
 
AIFS=SIFS+( n *extended slot time)  (5)
 
DIFS=SIFS+(2*extended slot time)  (6)
 
In this way, the wireless communications system may be able to reduce the likelihood of collisions, even if the system contains hidden nodes. Hidden nodes are those STAs that are not within range of each other, and so are not aware of the other STAs&#39; existence, yet are in range of the AP. While a hidden node may not sense a PS-POLL request transmitted by one STA, the hidden node will sense a response transmitted by the AP  408 . By ensuring that the extended slot time is at least as long in duration as described herein, even hidden nodes will not decrement their back-off values until the appropriate time, thereby increasing the likelihood of avoiding collisions.
 
     As described herein, the extended slot time may be defined as a multiple of a regular slot time, and the DIFS or AIFS interval may be the same as is defined in the IEEE 802.11 standard. As an example, the back-off procedure used by a paged STA  402 ,  404 , and/or  406  may be implemented by using a regular back-off procedure. A STA  402 ,  404 , and/or  406  may set the initial value, i, of the regular back-off counter as follows:
 
 i=K*N   i   (7)
 
where K is as defined in Equation (4) and N i  may be a random integer between 0 and a duration of a CW or may be deterministically assigned based on the STA  402 ,  404 , and/or  406  position in the paging messaged as described herein. After the medium has been idle for a DIFS or AIFS interval of time, the back-off counter is decremented by K units per each additional consecutive idle interval of a duration equal to an extended slot time. When activity is detected on the medium, the back-off countdown is frozen and is restarted when the medium becomes idle again, as described herein. The STA  402 ,  404 , or  406  transmits a packet on the medium when the back-off reaches zero or any other integer that represents a lowest value of the counter.
 
     As shown in  FIG. 4 , AP  408  may complete the transmission of TIM  410  just before the beginning of slot time  424  (e.g., an enhanced slot time as defined herein). Because the channel is idle for the duration of slot time  424 , the back-off counter for each of STAs  402 ,  404 , and  406  may decrease the back-off value. For example, the back-off counter for each of STAs  402 ,  404 , and  406  may decrement their back-off value by 1, such that the back-off value of STA  402  is 0, the back-off value of STA  404  is 1, and the back-off value of STA  406  is 2. Since the back-off value for STA  402  is 0, STA  402  may transmit a PS-POLL request  412  in the next slot time, slot time  426 . Since STA  402  transmits a PS-POLL request and the AP  408  transmits a response  414 , neither the STA  404  back-off counter nor the STA  406  back-off counter decrements the back-off value. Note further that a detection of a PS-POLL request or a detection of an AP response may be sufficient to cause the STA  404  back-off counter and the STA  406  back-off counter to maintain their respective back-off values. In this way, even if STA  404  and/or STA  406  is a hidden node, the back-off values will not be decremented. 
     STAs  404  and  406  maintain the back-off values during slot time  428  as well because both STAs detect the transmission of response  414  by AP  408 . During slot time  430 , the channel is once again idle. Both the STA  404  back-off counter and the STA  406  back-off counter decrement their respective back-off values, such that the back-off value for STA  404  is now 0 and the back-off value for STA  406  is now 1. 
     In slot time  432 , STA  404  transmits a PS-POLL request  416  to the AP  408  and the process repeats as described herein until the STA  406  back-off value reaches 0 and it transmits a PS-POLL request  420 . If a STA  402 ,  404 , and/or  406  fails to transmit a PS-POLL  412 ,  416 , and/or  420  during its allotted time, the subsequent STAs later in the order of STAs may continue to decrement their back-off value since the channel will instead be idle for at least a duration of the extended slot time. In this way, delay of the wireless communications system may be reduced or minimized. 
     In other implementations, not shown, each STA  402 ,  404 , and  406  may be in a sleep mode for a period of time before waking. The sleep time may be determined based on a position of the STA  402 ,  404 , and  406  in the TIM  410  bitmap sequence and/or an estimation of data sent by the AP  408 . After the STA  402 ,  404 , or  406  has waken and the medium has been idle for a DIFS or AIFS interval of time, the back-off counter is decremented by K units per each additional consecutive idle interval of a duration equal to an extended slot time. When activity is detected on the medium, the back-off countdown is frozen and is restarted when the medium becomes idle again, as described herein. The STA  402 ,  404 , or  406  transmits a packet on the medium when the back-off reaches zero or any other integer that represents a lowest value of the counter. In another implementation, not shown, each STA  402 ,  404 , and  406  may start the back-off counter at a time randomly selected over a given time interval. In still another implementation, not shown, each STA  402 ,  404 , and  406  may transmit at a time n*X where n identifies a particular STA and X is a function of the TIM  410  bitmap sequence. 
       FIG. 5A  illustrates a polling request mechanism  500 . The polling request mechanism  500  shown may be used by the AP  104  and the STAs  106  in the wireless communication system  100  of  FIG. 1 . The polling request mechanism  500  is similar to the polling request mechanism  400  of  FIG. 4 . However, in the polling request mechanism  500 , an overlapping basic service set (OBSS) transmission  516  occurs. An OBSS transmission  516  may occur if a STA, such as STA  404 , identifies with two or more basic service sets, where each basic service set include an AP and associated STAs. The OBSS transmission  516  may originate from an AP other than AP  508 . 
     In some implementations, if STA  504  receives an OBSS transmission  516 , the STA  504  back-off counter may not decrement the back-off value until the OBSS transmission  516  is complete. For example, as illustrated in  FIG. 5 , OBSS transmission  516  may not be complete until during slot time  534  such that the STA  504  back-off counter decrements the back-off value during slot time  536 , the next slot time in which the channel is idle. However, the STA  506  back-off counter may decrement the back-off value during slot time  530  because STA  506  does not detect any transmission on the channel. For example, STA  506  may determine that the channel is idle for the duration of slot time  530  because it is not part of the basic service set for which the OBSS transmission  516  was intended. This may result in a situation in which two or more STAs, like STA  504  and STA  506 , attempt to transmit a PS-POLL request  519  and  520  at or nearly at a same time and cause a collision. 
       FIG. 5B  illustrates a polling request mechanism  550 . The polling request mechanism  550  may reduce the likelihood of a collision occurring as illustrated in  FIG. 5A  with respect to the polling request mechanism  500 . The polling request mechanism  550  is similar to the polling request mechanism  400  of  FIG. 4  and the polling request mechanism  500  of  FIG. 5A . However, in the polling request mechanism  550 , the STAs  552  and  556  do not transmit a PS-POLL request  562  and  568  at the end of extended slot time  574  or  586 . Rather, at the end of the slot times  574  and  586 , the STAs  552  and  556  start an additional short back-off procedure. The additional short back-off procedure is based on regular (non-extended) slot times such that a maximum back-off time if the medium was idle would be shorter than an extended slot time. For example, like STA  504 , STA  554  may receive an OBSS transmission  566 . While both STA  554  and STA  556  may have a back-off value equal to zero during extended slot time  586 , a collision may be avoided. 
     In some implementations, the additional back-off counter may be initialized with a random number or it may be based on a deterministic value, like a deterministic back-off value as described herein. Thus, the duration may be based on how the STAs  552 ,  554 , and  556  are ordered in the TIM  560  bitmap sequence. As an example, the back-off procedure used by a paged STA  552 ,  554 , and/or  556  may be implemented by using the regular back-off procedure. A STA  552 ,  554 , or  556  may set the initial value, i, of the regular back-off counter as follows:
 
 i =( K*N   i )+ M   i   (8)
 
where K is as defined in Equation (4), N i  may be a random integer between 0 and a duration of a CW or may be deterministically assigned based on the STA  402 ,  404 , and/or  406  position in the paging messaged as described herein, and M i  may be a random integer between 0 and a duration of a CW′ or may be deterministically determined based on the STA  402 ,  404 , and/or  406  position in the paging message as described herein. After the medium has been idle for a DIFS or AIFS interval of time, the back-off may be decremented by K units per each additional consecutive idle interval of a duration equal to an extended slot time. In an embodiment, if the back-off counter value is less than or equal to M i , then the back-off counter is decremented by 1 unit per each additional consecutive idle interval of a duration equal to a regular slot time. When activity is detected on the medium, the back-off countdown is frozen and is restarted once the medium becomes idle again, as described herein. The STA  402 ,  404 , or  406  transmits a packet on the medium when the back-off counter reaches zero or any other integer that represents a lowest value of the counter.
 
     In some implementations, the extended slot time may be the sum of the time it takes for a STA  552 ,  554 , or  556  to transmit a PS-POLL request  562 ,  568 , or  572 , the short inter-frame space (SIFS) time, the clear channel assessment (CCA) time, and a maximum contention window time. In an embodiment, the maximum contention window time may be a maximum number of regular slot times that a residual back-off may have (i.e., a maximum value of M i ). 
     Because STA  554  and STA  556  may have different additional back-off periods (e.g. because both STAs may have different initial residual back-off values), one of STA  554  and STA  556  may transmit a PS-POLL request before the other. As shown in  FIG. 5B , STA  556  transmits PS-POLL request  568  during slot time  588  after the additional back-off period has passed, where the additional back-off period begins at the beginning of slot time  588 . The additional back-off period for STA  554  also passes during slot time  588 . However, because STA  554  detects the PS-POLL request  568  transmitted by STA  556 , STA  554  waits at least an additional slot time before attempting to transmit the PS-POLL request  572  once again. Since the channel is busy until after slot time  590 , STA  554  transmits PS-POLL request  572  after slot time  590  and after its additional back-off period has passed. 
     In other implementations, collisions may still occur. In such situations, a STA may transition into a sleep mode and attempt to transmit a request to the AP during the next reserved time interval or after the current reserved time interval has expired. In this way, while a delay of the wireless communications system may be increased, energy consumption may be decreased. 
       FIG. 6  illustrates a polling request mechanism  600 . The polling request mechanism  600  shown may be used by the AP  104  and the STAs  106  in the wireless communication system  100  of  FIG. 1 . Unlike the polling request mechanisms  400 ,  500 , and  550 , an extended slot time may not be defined, yet the likelihood of collisions may still be reduced. 
     As shown in  FIG. 6 , each STA  602 ,  604 , and  606  waits at least an adaptive enhanced inter-frame space (AEIFS) before attempting to transmit a PS-POLL request  612 ,  616 , or  620  to AP  608 . A calculated AEIFS may prevent each STA  602 ,  604 , and  606  from transmitting a request until the AEIFS duration has expired. Once the AEIFS has passed, the STA  602 ,  604 , and/or  606  may transmit the request if the channel is idle. If the channel is not idle, the STA  602 ,  604 , and/or  606  may recalculate the AEIFS and repeat the above process. The STAs  602 ,  604 , and/or  606  may not begin the AEIFS countdown until the channel is idle. 
     In some implementations, an initial duration of an AEIFS may be based on a position of the respective STA in the STA ordering. The duration of the AEIFS for a particular STA may change as other STAs transmit polling requests and/or as the AP transmits responses addressed to other STAs. For example, an initial duration of the AEIFS may be calculated by first summing a SIFS time, a maximum CW time, and a time it takes a STA  602 ,  604 , or  606  to transmit a PS-POLL request  612 ,  616 , or  620  to the AP  608 . This sum may then be multiplied by the position of the respective STA in the STA ordering as may be defined in the TIM  610  bitmap sequence. The product is then summed with the DIFS time to generate the initial AEIFS duration. Once a channel is idle, the STA at issue may wait for the initial AEIFS period before determining whether to transmit a request. 
     In some implementations, once a STA detects a PS-POLL request from another STA that comes earlier in the STA ordering than the STA at issue or detects a response addressed to another STA that comes earlier in the STA ordering than the STA at issue, the STA at issue decrements the multiplication factor so as to reduce a duration of the AEIFS. In some embodiments, the decrement of the multiplication factor may also be determined by a special indication send by the AP  608  to all of the STAs  602 ,  604 , and  606 . The indication may be included in the response addressed to a STA  602 ,  604 , and/or  606  or may be included in a dedicated frame sent for this purpose. For example, if the position of the STA at issue in the STA ordering is 3, the initial duration of the AEIFS may be based on the sum as described above multiplied by 3, and the product summed by the DIFS time. If the STA at issue detects either the PS-POLL request from a STA identified earlier in the TIM  610  bitmap sequence or a response address to a STA identified earlier in the TIM  610  bitmap sequence, then the STA at issue may decrement the 3 to a value of 2 and recalculate the AEIFS. In this way, a STA at issue may wait for the initial AEIFS period before determining whether to transmit a request. Once the initial AEIFS period has passed, if the channel is idle, then the STA at issue transmits the request. If the channel is not idle and the STA at issue detects one of the two messages as described above, then the STA at issue recalculates the AEIFS. Once the channel is again idle, the STA at issue then waits the recalculated AEIFS duration before determining whether to transmit the request and the process repeats until the STA at issue is able to transmit the request. In other embodiments, the STA may wait an additional period of time after the AEIFS duration has passed before attempting to transmit the request. 
     As shown in  FIG. 6 , after the AP  608  has completed transmitting the TIM  610 , STAs  602 ,  604 , and  606  begin to wait for the respective calculated AEIFS duration. Because STA  602  is first in the order of the three STAs, its AEIFS duration may be shorter than the others. For example, the AEIFS time  624  for STA  602  may be equal to the DIFS time because a position of the STA  602  in the order of STAs may be represented by a 0. Likewise, the AEIFS time  626  for STA  604  may be calculated with its position in the order of STAs represented by 1. The AEIFS time  628  for STA  606  may be calculated with its position in the order of STAs represented by 2. Since STAs  604  and  606  are still waiting when AEIFS time  624  passes, the channel is idle and STA  602  may transmit PS-POLL request  612  after its AEIFS time  624  has passed. The PS-POLL request  612  causes the AP  608  to generate and transmit a response  614 . Because AEIFS time  626  and AEIFS time  628  passes while the response  614  is being transmitted, STAs  604  and  606  do not attempt to transmit a request to the AP  608 . If STA  604  or  606  is a hidden node, then the STA may not detect the PS-POLL request  612  transmitted by STA  602 . However, the STA will detect the response  614  and will thus recalculate its AEIFS duration according to the embodiments described herein. Likewise, if STA  604  or  606  is not a hidden node, then the STA may detect both the PS-POLL request  612  and the response  614 , and may adjust its AEIFS accordingly. 
     Once the AP  608  has completed its transmission of the response  614 , STAs  604  and  606  may begin to wait for their respective AEIFS times  630  and  632 . As described herein, once the AEIFS times  630  and  632  pass, the respective STA  604  and  606  checks the channel to determine whether a request can be transmitted. As illustrated in  FIG. 6 , STA  604  will determine that the channel is idle and transmit PS-POLL request  616 , which may result in a response  618 . The process described herein continues until STA  606  is able to transmit PS-POLL request  620 . The STAs  602 ,  604 , and  606  may wait an additional period of time, such as a contention window time, before attempting to transmit a request (not shown). 
     In this way, the use of the AEIFS may allow the wireless communications system to reduce the likelihood of collisions that may occur because of hidden nodes or other errors. A time that each STA waits before attempting to transmit a request may be independent of whether or not hidden nodes exist in the system. By basing a wait time at least partly on a position of a STA in a TIM bitmap sequence, each STA may wait for a unique time period before attempting to transmit a request. The use of the AEIFS may allow the wireless communications system to achieve reductions in collisions without creating a longer slot time and without increasing power consumption by the STAs and/or AP. 
       FIG. 7  is a flowchart of a process  700  for reducing collisions in the wireless communications system of  FIG. 1 . At block  702 , the process  700  decrements a value of a counter if a channel of a wireless communications network is idle for at least an extended time slot. In an embodiment, a starting value of the counter is based on a position of an index corresponding to a wireless communications device in an information element, such as a TIM. At block  704 , the process  700  generates a polling request, such as a PS-POLL request. At block  706 , the process  700  transmits the polling request to an access point over the wireless communications network when the value of the counter reaches a threshold value. After block  706 , the process  700  ends. 
       FIG. 8  is a functional block diagram of an exemplary wireless device  800  that may be employed within the wireless communication system  100 . The device  800  includes means  802  for decrementing a value of a counter if a channel of a wireless communications network is idle for at least an extended time slot. In an embodiment, means  802  for decrementing a value of a counter if a channel of a wireless communications network is idle for at least an extended time slot may be configured to perform one or more of the functions discussed above with respect to block  702 . The device  800  further includes means  804  for generating a polling request. In an embodiment, means  804  for generating a polling request may be configured to perform one or more of the functions discussed above with respect to block  704 . The device  800  further includes means  806  for transmitting the polling request to an access point over the wireless communications network when the value of the counter reaches a threshold value. In an embodiment, means  806  for transmitting the polling request to an access point over the wireless communications network when the value of the counter reaches a threshold value may be configured to perform one or more of the functions discussed above with respect to block  706 . 
       FIG. 9  is another flowchart of a process  900  for reducing collisions in the wireless communications system of  FIG. 1 . At block  902 , the process  900  generates a polling request, such as a PS-POLL request. At block  904 , the process  900  determines an adaptive enhanced inter-frame space (AEIFS) each time a wireless communications device detects another message transmitted on a channel of a wireless communications network in which the wireless communications device communicates. In an embodiment, an initial duration of the AEIFS is based on a position of the wireless communication device in an information element. At block  906 , the process  900  transmits the polling request to an access point over the wireless communications network after a time based on a duration of the AEIFS and when the channel of the wireless communications network is open. After block  906 , the process  900  ends. 
       FIG. 10  is a functional block diagram of an exemplary wireless device  1000  that may be employed within the wireless communication system  100 . The device  1000  includes means  1002  for generating a polling request. In an embodiment, means  1002  for generating a polling request may be configured to perform one or more of the functions discussed above with respect to block  902 . The device  1000  further includes means  1004  for determining an adaptive enhanced inter-frame space (AEIFS) each time a wireless communications device detects another message transmitted on a channel of a wireless communications network in which the wireless communications device communicates. In an embodiment, means  1004  for determining an AEIFS each time a wireless communications device detects another message transmitted on a channel of a wireless communications network in which the wireless communications device communicates may be configured to perform one or more of the functions discussed above with respect to block  904 . The device  1000  further includes means  1006  for transmitting the polling request to an access point over the wireless communications network after a time based on a duration of the AEIFS and when the channel of the wireless communications network is open. In an embodiment, means  1006  for transmitting the polling request to an access point over the wireless communications network after a time based on a duration of the AEIFS and when the channel of the wireless communications network is open may be configured to perform one or more of the functions discussed above with respect to block  1006 . 
     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. 
     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. 
     The functions described may be implemented in hardware, software, firmware or any combination thereof. If implemented in software, the functions may be stored as one or more instructions on a computer-readable medium. 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. Disk and disc, as used herein, include 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, 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. 
     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.