Patent Publication Number: US-2013242916-A1

Title: Scheduling with reverse direction grant in wireless communication systems

Description:
CLAIM OF PRIORITY UNDER 35 U.S.C. §119 
     The present Application for Patent claims priority to Provisional Application No. 60/716,449 entitled “SCHEDULING WITH REVERSE DIRECTION GRANT IN WIRELESS COMMUNICATION SYSTEMS” filed Sep. 12, 2005, and assigned to the assignee hereof and hereby expressly incorporated by reference herein. 
     Claim of Priority under 35 U.S.C. §120 
     The present application for patent is a Divisional and claims priority to patent application Ser. No. 11/312,187 entitled “Scheduling with Reverse Direction Grant in Wireless Communication Systems” filed Dec. 19, 2005, and assigned to the assignee hereof and hereby expressly incorporated by reference herein. 
    
    
     BACKGROUND 
     I. Field 
     The following description relates generally to wireless communications, and more particularly to utilizing a reverse direction grant in a wireless communication system. 
     II. Background 
     Wireless communication systems are widely deployed to provide various types of communication; for instance, voice and/or data may be provided via such wireless communication systems. A typical wireless data system, or network, provides multiple users access to one or more shared resources. A system may use a variety of multiple access techniques such as Frequency Division Multiplexing (FDM), Time Division Multiplexing (TDM), Code Division Multiplexing (CDM), and others. 
     Examples of wireless systems that enable various types of communication include Wireless Local Area Networks (WLANs) such as WLANs that comply with one or more of the IEEE 802.11 standards (e.g., 802.11 (a), (b), or (g)). Additionally, IEEE 802.11(e) has been introduced to improve some of the shortcomings of previous 802.11 standards. For example, 802.11(e) may provide Quality of Service improvements. 
     Conventional wireless systems that utilize techniques to provide channel access may allow a particular station (e.g., access point, base station, user terminal, mobile terminal, . . . ) to transmit data during a specified period of time. However, such allocation can result in inefficient use of the channel when the station completes its associated transmission prior to the end of the allocated transmission time period. Thus, there exists a need in the art for a system and/or methodology of improving efficiency in such scheduled wireless systems. 
     SUMMARY 
     The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of such embodiments. This summary is not an extensive overview of all contemplated embodiments, and is intended to neither identify key or critical elements of all embodiments nor delineate the scope of any or all embodiments. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later. 
     In accordance with one or more embodiments and corresponding disclosure thereof, various aspects are described in connection with reducing waste of communication channel bandwidth in association with scheduled time periods that allocate channel access to particular stations. According to various aspects, systems and methods are described that facilitate providing and/or utilizing reverse direction grants in connection with scheduled channel access. Such systems and/or methods can mitigate an amount of unused channel time after a station completes data transmission prior to an end of the allocated period. 
     According to related aspects, a method of wireless communication can comprise receiving a multi-poll frame that schedules transmissions for a number of time periods associated with transmission opportunities, communicating data during a particular one of the scheduled time periods associated with a particular transmission opportunity in a first direction according to the multi-poll frame, transmitting a reverse direction grant during the particular scheduled time period associated with the particular transmission opportunity in the first direction, the reverse direction grant enables a recipient to transmit data, and receiving data communicated in a second direction during the particular scheduled time period associated with the particular transmission opportunity. The method can further comprise evaluating whether to transmit the reverse direction grant, determining an amount of time remaining in the particular scheduled time period associated with the particular transmission opportunity, and/or determining whether a station indicated to be a transmitter in the multi-poll frame completed an associated transmission. The method can additionally comprise evaluating whether to employ a received reverse direction grant during at least a portion of a remainder of the particular scheduled time period associated with the particular transmission opportunity, evaluating at least one of an amount of time remaining in the particular scheduled time period and an amount of data to be transmitted in the second direction upon obtaining channel access, and/or generating the multi-poll frame which is a frame that indicates, for each of the number of time periods, information associated with a respective, corresponding transmission opportunity, the information includes at least one of an identity of a transmitting station, an identity of a receiving station, a start time, and a duration. 
     Another aspect relates to an apparatus that facilitates utilizing a reverse direction grant in a wireless communication system, which can comprise a memory that stores information associated with a schedule related to access of a channel; and a processor, coupled to the memory, that is configured to transmit a reverse direction grant during a transmission opportunity assigned to the apparatus, according to the information, based upon information to be transmitted from the apparatus. The processor can further be configured to utilize a channel access identifier to determine a time at which the apparatus at least one of receives and transmits data, utilize the channel access identifier to synchronize the apparatus to at least one other apparatus, and/or utilize the channel access identifier to operate in a sleep mode during times in which the apparatus is not identified to be at least one of a receiver and a transmitter. The processor can still further be configured to utilize a received reverse direction grant and alter the apparatus from receiving data during a current transmission opportunity to transmitting data during the current transmission opportunity and/or determine whether to employ the reverse direction grant to alter the apparatus from receiving data to transmitting data based at least in part on one or more of an amount of time remaining in the current transmission opportunity and an amount of data to be transmitted by the apparatus. The processor can also be configured to provide the reverse direction grant when the apparatus completes a transmission during the transmission opportunity prior to an end of an allocated duration and/or determine whether to transmit the reverse direction grant based at least in part on an amount of time remaining in the transmission opportunity. 
     Yet another aspect relates to a wireless communication apparatus, comprising means for receiving data communicated during a particular transmission opportunity in a first direction according to a schedule, means for receiving a reverse direction grant during the particular transmission opportunity in the first direction, and means for transmitting data in a second direction during the particular transmission opportunity via employing the received reverse direction grant. The apparatus can additionally comprise means for identifying a time at which the apparatus is scheduled to at least one of receive and transmit data via a communication channel, means for synchronizing the apparatus to disparate apparatuses, and/or means for enabling the apparatus to utilize a sleep mode to reduce power consumption during transmission opportunities when the apparatus is not communicating via the communication channel. Moreover, the apparatus can comprise means for determining whether to employ a received reverse direction grant during at least a portion of a remainder of the particular transmission opportunity. 
     Still another aspect relates to a computer-readable medium having stored thereon computer-executable instructions for communicating data during a transmission opportunity in a first direction according to a schedule for channel access, evaluating whether to transmit a reverse direction grant, transmitting a reverse direction grant to a recipient in the first direction during the transmission opportunity, and receiving data from the recipient of the reverse direction grant in a second direction during the transmission opportunity. The computer-readable medium can further comprise instructions for utilizing a sleep mode during a transmission opportunity that allocates channel access to disparate apparatuses and instructions for scheduling a number of transmission opportunities by generating a multi-poll frame which includes a frame that comprises data associated with at least one of a transmitter, a receiver, a start time, and a duration associated with a respective transmission opportunity for each of a plurality of time periods. Additionally, the computer-readable medium can comprise instructions for scheduling a number of transmission opportunities by generating an order in which a token is passed and/or instructions for identifying that an associated station is indicated as a transmitter by the schedule. 
     To the accomplishment of the foregoing and related ends, the one or more embodiments comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative aspects of the one or more embodiments. These aspects are indicative, however, of but a few of the various ways in which the principles of various embodiments may be employed and the described embodiments are intended to include all such aspects and their equivalents. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a wireless communication system in accordance with various aspects set forth herein. 
         FIG. 2  is an illustration of a system that employs reverse direction grants in connection with scheduled times to access a communication channel in accordance with various aspects. 
         FIG. 3  is an illustration of a multi-poll that may be utilized to schedule channel access. 
         FIG. 4  is an illustration of an example that demonstrates utilization of Scheduled Access Periods (SCAPs) with disparate techniques for channel access. 
         FIG. 5  is an illustration of an example of a SCHED frame in accordance with various aspects. 
         FIG. 6  is an illustration of an example of a SCHED message in accordance with various aspects. 
         FIG. 7  is an illustration of an example of a SCAP where scheduling is utilized with reverse direction grants in accordance with various aspects. 
         FIG. 8  illustrates a methodology for utilizing reverse direction grants within an allocated time period for accessing a channel to facilitate reducing an amount of wasted channel bandwidth in a wireless communication system, in accordance with one or more aspects. 
         FIG. 9  is an illustration of a methodology for providing a reverse direction grant in connection with scheduled access to a communication channel in accordance with a plurality of aspects described herein. 
         FIG. 10  is an illustration of a methodology for employing a reverse direction grant in association with scheduled channel access periods in accordance with various aspects. 
         FIG. 11  is an illustration of user device that facilitates generating and/or utilizing a reverse direction grant in association with scheduled channel access periods in accordance with one or more aspects set forth herein. 
         FIG. 12  is an illustration of a system that facilitates scheduling channel access and/or utilizing reverse direction grants to reduce channel bandwidth waste in a wireless communication system in accordance with various aspects. 
         FIG. 13  is an illustration of a wireless network environment that can be employed in conjunction with the various systems and methods described herein. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments are now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of one or more embodiments. It may be evident, however, that such embodiment(s) may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing one or more embodiments. 
     Furthermore, various embodiments are described herein in connection with a subscriber station. A subscriber station can also be called a system, a subscriber unit, mobile station, mobile, remote station, access point, remote terminal, access terminal, user terminal, user agent, a user device, or user equipment. A subscriber station may be 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, computing device, or other processing device connected to a wireless modem. Additionally, in accordance with 802.11 terminology, access points, user terminals, etc. are referred to as stations or STAs herein. 
     Moreover, various aspects or features described herein may be implemented as a method, apparatus, or article of manufacture using standard programming and/or engineering techniques. The term “article of manufacture” as used herein is intended to encompass a computer program accessible from any computer-readable device, carrier, or media. For example, computer-readable media can include but are not limited to magnetic storage devices (e.g., hard disk, floppy disk, magnetic strips . . . ), optical disks (e.g., compact disk (CD), digital versatile disk (DVD) . . . ), smart cards, and flash memory devices (e.g., EPROM, card, stick, key drive . . . ). Additionally, various storage media described herein can represent one or more devices and/or other machine-readable media for storing information. The term “machine-readable medium” can include, without being limited to, wireless channels and various other media capable of storing, containing, and/or carrying instruction(s) and/or data. 
     Conventional fully scheduled time division wireless communication systems may be associated with wasteful utilization of a communication channel. For instance, a particular station may be permitted to transmit data during a particular time period over a communication channel. However, when the station completes a transmission prior to the end of the allocated period, resources associated with the channel are wasted since disparate stations are typically not enabled to access the channel to transmit data during this period. Thus, it becomes desirable to facilitate providing reverse direction grants (RDGs) in association with scheduled channel access periods to mitigate communication channel waste. The reverse direction grant may be utilized by the obtaining station to access the channel during the remainder of the allocated period. 
     Referring now to  FIG. 1 , a wireless communication system  100  is illustrated in accordance with various aspects set forth herein. System  100  includes an Access Point (AP)  104  that is communicatively coupled to one or more User Terminals (UTs)  106 A-N, where N may be any positive integer. In accordance with 802.11 terminology, AP  104  and UTs  106 A-N are also referred to as stations or STAs herein. AP  104  and UTs  106 A-N communicate via Wireless Local Area Network (WLAN)  120 . According to one or more aspects, WLAN  120  is a high speed MIMO OFDM system; however, WLAN  120  may be any wireless LAN. Access point  104  communicates with any number of external devices or processes via network  102 . Network  102  may be the Internet, an intranet, or any other wired, wireless, or optical network. Connection  110  carries signals from the network  102  to the access point  104 . Devices or processes may be connected to network  102  or as UTs  106 A-N (or via connections therewith) on WLAN  120 . Examples of devices that may be connected to either network  102  or WLAN  120  include phones, Personal Digital Assistants (PDAs), computers of various types (laptops, personal computers, workstations, terminals of any type), media devices such as HDTV, DVD player, wireless speakers, cameras, camcorders, webcams, and virtually any other type of data device. Processes may include voice, video, data communications, etc. Various data streams may have varying transmission requirements, which may be accommodated by using varying Quality of Service (QoS) techniques. 
     System  100  may be deployed with a centralized AP  104 . All UTs  106 A-N may communicate with AP  104  according to an example. Additionally or alternatively, two or more of the UTs  106 A-N may communicate via direct peer-to-peer communication (e.g., employing Direct Link Set-Up (DLS) associated with 802.11(e)). Access may be managed by AP  104  and/or may be ad hoc (e.g., contention based). 
     In accordance with various aspects, a reverse direction grant can be employed in connection with a wireless communication system, such as system  100 . The reverse direction grant can be utilized with a schedule that allocates channel access for a number of time periods, each of the time periods being associated with a particular station (e.g., AP  104 , one of UTs  106 A-N, etc.) that transmits data via a communication channel (e.g., WLAN  120 ) to a particular second station (e.g., AP  104 , one of UTs  106 A-N, etc.). A multi-poll frame may be utilized to define a schedule of transmissions for a corresponding multi-poll period. Scheduled transmissions during a multi-poll period may include transmissions from AP (e.g., AP  104 ) to STAs (e.g., UTs  106 A-N), from STAs to AP, as well as from STAs to other STAs. For example, the multi-poll frame may be a SCHED frame that defines multiple downlink, multiple uplink, and/or multiple direct link STA-STA transmissions may be provided to the stations (e.g., AP  104 , one of UTs  106 A-N, etc.). The SCHED frame thus may be a single frame that schedules a number of communication periods, wherein the SCHED frame may indicate that a first station is a transmitter, a second station is a receiver, a start time, and a duration for the access to the channel for each of the scheduled periods. It is contemplated that the aspects of the present disclosure is not limited to use of a SCHED frame; for example, the scheduling can be effectuated utilizing a multi-poll, a consolidated poll, and/or a token that is passed between stations in an agreed upon order. Accordingly, it is to be appreciated that any scheduling associated with channel access falls within the scope of the aspects of the present disclosure. 
     The station identified as the transmitter may finish transmitting data over the channel (e.g., WLAN  120 ) prior to the end of the allocated channel access duration. Accordingly, the transmitter can provide a reverse direction grant to the receiver, thereby enabling the receiver to transmit data over the channel (e.g., WLAN  120 ). The receiver that obtains the reverse direction grant can thereafter transmit data to the transmitter during the remaining portion of the duration, for instance. According to another illustration, the transmitter can provide a reverse direction grant to AP  104 , such as, for example, during a scheduled period for direct link STA-STA communication (e.g., UT  106 A scheduled to transmit and UT  106 N scheduled to receive). Thus, AP  104  can communicate with the transmitter (e.g., UT  106 A) via the channel (e.g., WLAN  120 ) during the remainder of the allocated time period. 
     UTs  106 A-N and AP  104  may employ synchronized clocks to enable transmitting and/or receiving data at respective scheduled times in accordance with a received and/or generated multi-poll frame (and/or SCHED frame, consolidated poll, token passed according to a schedule, . . . ). The multi-poll frame enables stations to access the channel during allocated times, and provides an amount of time during which the transmitting station can transmit data via the channel. The schedule provides notification to each transmitter STA related to times a transmission opportunity (TXOP) starts and ends. Thus, the transmitting station can transmit any amount of data that fits into the allocated time slot. Additionally, the schedule may also inform the receiver STA when to be awake to receive traffic. 
     802.11e provides the concept of a TXOP. Instead of accessing the channel to send a single frame of data, a STA is provided a period of time during which it is allowed to use the channel to transmit as many frames as fit within that period. TXOP reduces overhead associated with channel access; for instance, idle time and collisions are reduced in connection with Enhanced Distributed Channel Access (EDCA) and polling overhead is mitigated in relation to HCF Controlled Channel Access (HCCA). 
     By way of a further example, the multi-poll frame can indicate that UT  106 A is a transmitter at a time associated with a first time period (e.g., first poll) and AP  104  is a receiver at that time. UT  106 A is provided with a TXOP at the allocated time. During the TXOP, UT  106 A may transmit any amount of data to AP  104 . For instance, UT  106 A may transmit any number of MAC Protocol Data Units (MPDUs) separated by Short Interframe Spacing (SIFS) to AP  104 . Additionally or alternatively, UT  106 A may aggregate the MDPUs and remove the SIFS that separate MPDUs, and thus transmit an Aggregated MPDU (A-MPDU). Further, a block ACK request can be transmitted by UT  106 A and/or can be aggregated as part of the A-MPDU. If the multi-poll frame allocates an amount of time for UT  106 A to transmit data over the communication channel such that additional time remains in the TXOP subsequent to UT  106 A completing the transmission, UT  106 A may transmit a reverse direction grant to AP  104 . AP  104  may employ the reverse direction grant to transmit data over the communication channel, for instance, to UT  106 A for the remaining time within the TXOP. Upon receipt of the reverse direction grant, AP  104  may evaluate the remaining time in the allocated period and/or data stored in buffer(s) associated with AP  104  that is to be transmitted. Based at least in part on this evaluation, AP  104  may utilize and/or not employ the reverse direction grant to transmit data via the channel. It is to be appreciated that this example is merely for illustration purposes, and the aspects of the present disclosure is not so limited. 
     Example embodiments are disclosed herein that support efficient operation in conjunction with very high rate physical layers for a wireless LAN (or similar applications that use newly emerging transmission technologies). Various example embodiments preserve the simplicity and robustness of legacy WLAN systems, examples of which are found in 802.11(a-e). The advantages of the various embodiments may be achieved while maintaining backward compatibility with such legacy systems. (Note that, in the description below, 802.11 systems are described as example legacy systems. It should be noted, that one or more of the improvements discussed herein are also compatible with alternate systems and standards.) 
     Turning to  FIG. 2 , illustrated is a system  200  that employs reverse direction grants in connection with scheduled times to access a communication channel in accordance with various aspects. The system  200  includes an Access Point (AP)  204 , a first User Terminal (UT)  204 , and a second User Terminal (UT)  206 . It is to be appreciated that the system  200  may include any number of additional APs and/or UTs. AP  204  and UTs  204 - 206  communicate via Wireless Local Area Network (WLAN)  208 . AP  204  may provide a schedule to UTs  204 - 206  associated with access to WLAN  208 . For instance, a multi-poll frame (e.g., SCHED frame) may be transmitted, an order may be predetermined for a token to pass between stations, etc. 
     According to an example, the schedule may indicate that during a particular time segment, UT  204  is a transmitter and UT  206  is a receiver. Thus, UT  204  and UT  206  communicate via connection  210  which is associated with WLAN  208 . If UT  204  completes transmission of data prior to the end of the allocated time segment as provided by the schedule, UT  204  may transmit a reverse direction grant to UT  206  via connection  210 . UT  206  may utilize the reverse direction grant to transmit data via WLAN  208 . For instance, UT  206  may transmit data to UT  204  and/or AP  202  during the remaining portion of the allocated time segment. By way of illustration, disparate UTs other than UT  204  and UT  206  (not shown) may be sleeping during this particular time segment. 
     With reference to  FIG. 3 , illustrated is a multi-poll frame  300  (e.g., consolidated poll) that may be utilized to schedule channel access. Multi-poll frame  300  may be provided according to 802.11n. Multi-poll frame  300  includes a header  310  that may comprise synchronization data. Multi-poll frame  300  may also include a sequence of any number of polls (e.g., poll 1  320 , poll 2  330 , poll N  340 , where N is any positive integer). Each of the polls (e.g., poll 1) may include data identifying a station as a transmitter  350 , data identifying a disparate station as a receiver  360 , data indicating a start time  370 , and data indicating a duration  380 . 
     According to various aspects, multi-poll frame  300  is transmitted to the stations and the stations are awake to receive multi-poll frame  300 . Each station may identify and store a time when the station is a receiver or a transmitter by reviewing the received multi-poll frame  300 . During the times when the station is not a receiver or a transmitter, the station may be in sleep mode. Thus, power consumption associated with the stations is reduced. Additionally, polling overhead is mitigated via utilizing header  310  with a sequence of polls (e.g., polls  320 - 340 ) rather than a separate header with a single poll. 
     Turning to  FIG. 4 , illustrated is an example that demonstrates utilization of Scheduled Access Periods (SCAPs) with disparate techniques for channel access. Within a beacon interval (e.g., between two Beacons  402 ), several channel access methods can be interspersed. For instance EDCA, HCCA and/or SCHED can be present. 802.11e introduced the Transmission Opportunity (TXOP). To improve efficiency, when a STA acquires the medium through Enhanced Distributed Channel Access (EDCA) or through a polled access in HCF Controlled Channel Access (HCCA), the STA may be permitted to transmit more than a single frame, which is referred to as the TXOP. 
     During Beacon intervals (e.g., Beacon  402 ), an AP has flexibility to adaptively intersperse durations of EDCA contention-based access (e.g., EDCA  404 ), 802.11e controlled access phase (CAP) (e.g., CAP  406 ), and Scheduled Access Period (SCAP) (e.g., SCAP  408 ). EDCA  404  may include one or more EDCA TXOPs  410 . During EDCA TXOP  410 , an acquiring STA may be permitted to transmit one or more frames. The maximum length of each EDCA TXOP  410  depends on the Traffic Class and may be established by the AP. A STA may gain access to a channel after sensing the channel to be idle for at least an amount of time corresponding to an associated Interframe Spacing. 
     CAP  406 , which may be associated with HCCA, is a bounded time interval and may be formed by concatenating a series of HCCA TXOPs  412 . An AP may establish a Contention-Free Period (CFP) during which the AP can provide polled access to associated STAs. The contention-free poll (CF-Poll), or poll  414 , is transmitted by the AP and is followed by a transmission from the polled STA. The Direct Link Set-Up (DLS) associated with 802.11e allows a STA to forward frames directly to another destination STA with a Basic Service Set (BSS). The AP may make a polled TXOP available for this direct transfer of frames between STAs. Additionally, during polled access, the destination of frames from the polled STA may be the AP. 
     An Adaptive Coordination Function (ACF) may be utilized as an extension of the HCCA and EDCA that permits flexible, highly efficient, low latency scheduled operation suitable for operation with high data rates enabled by the MIMO Physical layer (PHY). Using a SCHED message  416  as part of the SCAP  408 , the AP may simultaneously schedule one or more AP-STA, STA-AP and STA-STA TXOPs over a period known as a Scheduled Access Period (SCAP). The maximum permitted value of the SCAP may vary, and according to an aspect may be 4 ms. Pursuant to another example, the maximum value of the SCAP may be 2.048 ms; however, the aspects of the present disclosure are not so limited. 
     MIMO STAs obey the SCAP boundary. The last STA to transmit in a SCAP  408  terminates its transmission no later than the end of its allocated TXOP. MIMO STAs obey the scheduled TXOP boundaries and complete their transmission prior to the end of the assigned TXOP. This reduces the chance of collisions and allows the subsequent scheduled STA to start its TXOP without sensing the channel to be idle. 
     The AP may use the following procedures for recovery from SCHED receive errors. If a STA is unable to decode a SCHED message it will not be able to utilize its TXOP. If a scheduled TXOP does not begin at the assigned start time, the AP may initiate recovery by transmitting at a PIFS after the start of the unused scheduled TXOP. The AP may use the period of the unused scheduled TXOP as a CAP. During the CAP, the AP may transmit to one or more STA (e.g., STA(s) that are awake) or poll the STA that missed the scheduled TXOP or another STA. The CAP is terminated prior to the next scheduled TXOP. The same procedures may also be used when a scheduled TXOP terminates early. The AP may initiate recovery by transmitting at a PIFS after the end of the last transmission in the scheduled TXOP. The AP may use the unused period of a scheduled TXOP as a CAP. 
     Turning to  FIG. 5 , illustrated is an example of a SCHED frame  500  in accordance with various aspects. SCHED message  500  may be transmitted as a special SCHED Physical (PHY) Protocol Data Unit (PPDU); however, the aspects of the present disclosure are not so limited. A MAC Header  510  field of SCHED frame  500  may be 15 octets in length; however, the aspects of the present disclosure are not so limited. The presence and length of the CTRL 0 , CTRL 1 , CTRL 2  and CTRL 3  segments are indicated in the SIGNAL field of the SCHED PPDU. The transmission rate of CTRL 0  may, or may not, be lower than the transmission rate of CTRL 1  and so on. Hence, CTRL 0  may signal STA(s) that have a poor radio link with the AP, and may allow maximal transmission range. Additionally, CTRL 3  may be transmitted at a high rate and minimizes the transmission time for signaling STA(s) with a good radio link to the AP. Bits  13 - 0  of the Duration field  520  may specify the length of the SCAP, e.g. in microseconds. The Duration field  520  is used by STAs capable of MIMO OFDM transmissions to set a network allocation vector (NAV) for the duration of the SCAP. NAV may be utilized to determine a length of time the channel will be busy in the future. NAV may be set by a request-to-send (RTS) and/or a clear-to-send (CTS) frame. A Basic Service Set Identifier (BSSID)  530  may be a media access control (MAC) address of a station or an AP. 
     With reference to  FIG. 6 , illustrated is another example of a SCHED message  600  in accordance with various aspects. The SCHED message  600  defines the schedule for the SCAP. Each of the CTRL 0 , CTRL 1 , CTRL 2  and CTRL 3  segments are of variable length and may be transmitted at 6, 12, 18 and 24 Mbps, respectively. A number of assignment elements  610  may be included in each CTRLJ segment. Each assignment element  610  specifies the transmitting STA association identity (AID), the receiving STA AID, the start time of the scheduled TXOP and the maximum permitted length of the scheduled TXOP. Inclusion of the transmitting and receiving STA in the assignment elements permits efficient power-save at STAs that are not scheduled to transmit or receive during the SCAP. When legacy STAs are present in the BSS, the AP may utilize additional means to protect the SCAP, e.g., a legacy CTS-to-Self. SCHED message  600  additionally includes frame check sequences (FCSs)  620 . 
     With reference to  FIG. 7 , illustrated is an example of a SCAP  700  where scheduling is utilized with reverse direction grants in accordance with various aspects. The reverse direction grants may be available to both an access point and a station. Additionally, a reverse direction grant may be employed when a Direct Link (DL) is established between two stations. A number of transmissions may be scheduled  702 . For example, transmissions may be scheduled from an AP to a STA (e.g., AT to STA B assignment  704 ), from a STA to an AP (e.g., STA C to AP assignment  706 ), from a STA to a STA (e.g., STA D to STA E assignment  708 ), etc. Assuming a transmitter (e.g., AP, STA) completes transmission of data during a TXOP with time remaining in the TXOP (e.g., AP to STA B Tx  710 ), the transmitter may use a reverse direction grant (e.g., RDG  712 ) to a provide access to the channel to a disparate STA active during that interval. Thus, the transmitting STA may transmit an RGD in a first direction to a receiving STA. 
     In response to the RDG, the responder may have an opportunity to transmit traffic (e.g., STA B to AP Tx  714 ) in a second direction without having to perform random channel access. Thus, the probability of collision with another STA accessing the channel at the same time is mitigated provided all the other STA decoded the SCHED frame and set their NAV appropriately. Also, the responder is permitted to transmit traffic related to the data just received, hence reducing the round-trip delay. Examples of traffic that can benefit from lower round trip time are TCP ACKS, VoIP traffic, Block Acks, etc. 
     A number of variations of reverse direction grants are contemplated. For instance, the transmitter may provide a reverse direction grant to a receiver. According to another example, the transmitter may provide a reverse direction grant to a receiver and/or an AP (assuming that the receiver was a STA other than the AP). Pursuant to a further illustration, the transmitter may transmit a reverse direction grant to any third party STA. 
     The signaling utilized to perform the defined RDG with EDCA may be simplified for ease of implementation. For example in the case of EDCA the following could be used: (i) one bit may be used to let the responder know that an RDG is granted; (ii) three bits may be used to let the responder know which class of QoS traffic is permitted in the RDG; and (iii) one bit may be used to terminate the responder&#39;s response and give the TXOP back to the initiator. In a TXOP, it is not required to transmit a particular class of QoS traffic, hence the data associated with QoS may not be utilized. Further, additional information may be used. Also, the number of bits for each message type may vary and is application dependent. 
     SCHED frame  716  defines how the STAs are allowed to access the channel for a future period of time. SCHED frame  716  signals when a transmitter STA is to start and/or stop transmitting. Additionally, SCHED frame  716  indicates when a receiver STA is to awaken to start receiving data and when that period ends, which may be adjacent to a transmission period for the STA. A STA whose address does not appear as a transmitter or receiver in the SCHED frame  716  may go into sleep mode to maximize power savings. A clear-to-send (CTS) to self  718  may be employed to set a NAV associated with the SCHED frame  716 . The CTS (and/or RTS)  718  can be sent using one of the rates decodable by all legacy STA and may be used to improve protection for data frame transmission. The CTS to self  718  may include duration information associated with SCHED  716  and/or a scheduled access period  720 . 
     One potential drawback of a conventional scheduling mode of operation is the risk to waste the channel if the assigned transmission duration is excessive. Indeed once sent, the schedule is fixed and cannot be modified until another SCHED frame is sent. Without the use of a reverse direction grant, if a transmitter runs out of traffic to send to the assigned receiver during the assigned time, no other STA can use the channel and the resource is wasted. 
     Reverse direction grants may allow a transmitter to provide remaining scheduled time to the receiver. When a reverse direction grant is employed with HCCA, a number of polls transmitted by an AP may be reduced in half. For example, instead of scheduling a time for STA 1  to transmit with STA 2  to receive and another time with STA 2  to transmit and STA 1  to receives, the scheduler can group them together. The multiplexing of these two flows may allow for simpler and more efficient scheduling algorithms. It is to be appreciated that the aspects of the present disclosure is not limited to these examples. 
     Referring to  FIGS. 8-10 , methodologies relating to utilizing a reverse direction grant in connection with scheduled transmission periods are illustrated. For example, methodologies can relate to employing reverse direction grants in an FDMA environment, an OFDMA environment, a CDMA environment, a WCDMA environment, a TDMA environment, an SDMA environment, or any other suitable wireless environment. While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the methodologies are not limited by the order of acts, as some acts may, in accordance with one or more embodiments, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with one or more embodiments. 
       FIG. 8  illustrates a methodology  800  for utilizing reverse direction grants within an allocated time period for accessing a channel to facilitate reducing an amount of wasted channel bandwidth in a wireless communication system, in accordance with one or more aspects. At  802 , a multi-poll frame (e.g., SCHED frame) that is utilized to schedule channel access during a number of time periods is received. For instance, the multi-poll frame may indicate a transmitting station, a receiving station, a start time, and/or a duration of channel access for each of the time periods. Pursuant to an example, the multi-poll frame may be generated by an access point and transmitted to disparate stations; however, the aspects of the present disclosure are not so limited. Additionally or alternatively, consolidated poll, SCHED frame, token, etc. may be employed in connection with scheduling transmissions associated with a number of time periods. At  804 , communication of data occurs in a first direction during a particular one of the scheduled time periods. The multi-poll frame may be employed to identify a transmitter and/or receiver at a particular time. Thus, the transmitter may access the channel to transmit data to the receiver (in the first direction) in accordance with the multi-poll frame. At  806 , a reverse direction grant is transmitted during the particular scheduled time period. If the transmitter completes its transmission prior to the end of the scheduled time period, a reverse direction grant may be transmitted to the receiver. At  808 , data that is transmitted in a second direction (e.g., from the station indicated as the receiver by the multi-poll frame to the station indicated as the transmitter, from the station indicated as the receiver by the multi-poll frame to an access point, . . . ) is received during the particular scheduled time period after transmitting the reverse direction grant. 
     Turning to  FIG. 9 , illustrated is a methodology  900  for providing a reverse direction grant in connection with scheduled access to a communication channel in accordance with a plurality of aspects described herein. At  902 , a multi-poll frame that schedules channel transmissions for a number of time periods is received. The multi-poll frame may provide indications related to which stations are to communicate via a communication channel and/or when the communication is to occur. It is to be appreciated that the aspects of the present disclosure is not limited to use of a multi-poll frame. An access point may obtain a multi-poll frame via producing a schedule associated with a particular scheduled access period and generating the multi-poll frame. Further, the access point may transmit the multi-poll frame to user terminal(s), thereby enabling the user terminal(s) to obtain the multi-poll frame. At  904 , data is transmitted in a first direction during a scheduled time period. The transmission of data may be in accordance with the multi-poll frame. At  906 , an evaluation is performed to determine whether to transmit a reverse direction grant. For example, an evaluation is made as to an amount of time remaining in the scheduled time period and/or whether the transmitting station as indicated in the multi-poll frame completed its transmission. If it is determined that the reverse direction grant should be provided, at  908 , a reverse direction grant is transmitted to a recipient in the first direction during the scheduled time period. At  910 , data is received from the recipient of the reverse direction grant which is transmitted in a second direction during the scheduled time period. Pursuant to an example, the second direction may be from the original receiver to the original transmitter; however, the aspects of the present disclosure are not so limited. 
     With reference to  FIG. 10 , illustrated is a methodology  1000  for employing a reverse direction grant in association with scheduled channel access periods in accordance with various aspects. At  1002 , a multi-poll frame that schedules channel transmissions and/or access for a number of time periods is received. At  1004 , data that is communicated in a first direction from a scheduled transmitter (e.g., as indicated via the multi-poll frame) is received during an allocated time period. At  1006 , a reverse direction grant is received from the scheduled transmitter during the allocated time period. At  1008 , an evaluation is performed to determine whether to employ the reverse direction grant during at least a portion of the remainder of the allocated time period. The amount of time remaining within the allocated time period may be considered. Additionally or alternatively, the amount of data stored in buffers associated with the station that obtains the reverse direction grant that is to be transmitted may be considered as part of the evaluation. If it is determined that the reverse direction grant should be utilized, at  1010 , data is transmitted to the station scheduled to be the transmitter in a second direction during the allocated time period. The second direction may be opposite to the first direction. Additionally or alternatively, the second direction may be from the station indicated to be the receiver to an access point. However, the aspects of the present disclosure are not limited to such illustrations. 
     It will be appreciated that, in accordance with one or more aspects described herein, inferences can be made regarding transmitting reverse direction grants, utilizing reverse direction grants to transmit data in a second direction, etc. As used herein, the term to “infer” or “inference” refers generally to the process of reasoning about or inferring states of the system, environment, and/or user from a set of observations as captured via events and/or data. Inference can be employed to identify a specific context or action, or can generate a probability distribution over states, for example. The inference can be probabilistic—that is, the computation of a probability distribution over states of interest based on a consideration of data and events. Inference can also refer to techniques employed for composing higher-level events from a set of events and/or data. Such inference results in the construction of new events or actions from a set of observed events and/or stored event data, whether or not the events are correlated in close temporal proximity, and whether the events and data come from one or several event and data sources. 
     According to an example, one or more methods presented above can include making inferences regarding when to transmit a reverse direction grant, when to employ reverse direction grants to transmit data, etc. For instance, a reverse direction grant may be received while time remains in an allocated time period subsequent to a station transmitting data to a receiving station. Upon receiving a reverse direction grant at the receiving station, an inference may be made as to the whether the receiving station would be able to transmit all or some portion of data over the access channel prior to the end of the allocated time period. It will be appreciated that the foregoing examples are illustrative in nature and are not intended to limit the number of inferences that can be made or the manner in which such inferences are made in conjunction with the various embodiments and/or methods described herein. 
       FIG. 11  is an illustration of a user device  1100  that facilitates generating and/or utilizing a reverse direction grant in association with scheduled channel access periods in accordance with one or more aspects set forth herein. User device  1100  comprises a receiver  1102  that receives a signal from, for instance, a receive antenna (not shown), and performs typical actions thereon (e.g., filters, amplifies, downconverts, etc.) the received signal and digitizes the conditioned signal to obtain samples. Receiver  1102  can be, for example, an MMSE receiver, and can comprise a demodulator  1104  that can demodulate received symbols and provide them to a processor  1106  for channel estimation. Processor  1106  can be a processor dedicated to analyzing information received by receiver  1102  and/or generating information for transmission by a transmitter  1116 , a processor that controls one or more components of user device  1100 , and/or a processor that both analyzes information received by receiver  1102 , generates information for transmission by transmitter  1116 , and controls one or more components of user device  1100 . 
     User device  1100  can additionally comprise memory  1108  that is operatively coupled to processor  1106  and that stores information related to channel access schedules for various time periods, data to be transmitted via the transmitter  1116 , multi-polls, and any other suitable information for mitigating communication channel waste in a wireless communication system as described with regard to various figures herein. Memory  1108  can additionally store protocols associated with providing and/or utilizing reverse direction grants (e.g., performance based, capacity based, . . . ), such that user device  1100  can employ stored protocols and/or algorithms related to generating and/or utilizing reverse direction grants to enable communication in a second direction during an allocated time period during which communication was to occur in a first direction as described herein. 
     It will be appreciated that the data store (e.g., memories) components described herein can be either volatile memory or nonvolatile memory, or can include both volatile and nonvolatile memory. By way of illustration, and not limitation, nonvolatile memory can include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable PROM (EEPROM), or flash memory. Volatile memory can include random access memory (RAM), which acts as external cache memory. By way of illustration and not limitation, RAM is available in many forms such as synchronous RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), and direct Rambus RAM (DRRAM). The memory  1108  of the subject systems and methods is intended to comprise, without being limited to, these and any other suitable types of memory. 
     Receiver  1102  is further operatively coupled to a channel access identifier  1110  that utilizes a received schedule (e.g., multi-poll frame, SCHED frame, . . . ) to determine a time at which user device  1100  is to receive and/or transmit data via a communication channel. The channel access identifier  1110  may also utilize a received reverse direction grant to enable the user device  1100  to transmit data via a communication channel. During times when user device  1100  is not scheduled to receive and/or transmit data, user device  1100  may be in sleep mode to reduce power consumption. Channel access identifier  1110  can be further coupled to a reverse direction grant (RDG) generator  1112  that may provide a reverse direction grant when user device  1100  completes a transmission during a scheduled time prior to the end of the allocated duration. The reverse direction grant may be utilized by a disparate apparatus to access the channel. For instance, the reverse direction grant may be employed by a station that is receiving data transmitted by user device  1100 ; the receiving station may then utilize the reverse direction grant to transmit data over the communication channel. User device  1100  still further comprises a modulator  1114  and a transmitter  1116  that transmits the signal to, for instance, an access point, another user device, etc. Although depicted as being separate from the processor  1106 , it is to be appreciated that channel access identifier  1110 , RDG generator  1112  and/or modulator  1114  may be part of processor  1106  or a number of processors (not shown). 
       FIG. 12  is an illustration of a system  1200  that facilitates scheduling channel access and/or utilizing reverse direction grants to reduce channel bandwidth waste in a wireless communication system in accordance with various aspects. System  1200  comprises an access point  1202  with a receiver  1210  that receives signal(s) from one or more user devices  1204  through a plurality of receive antennas  1206 , and a transmitter  1224  that transmits to the one or more user devices  1204  through a transmit antenna  1208 . Receiver  1210  can receive information from receive antennas  1206  and is operatively associated with a demodulator  1212  that demodulates received information. Demodulated symbols are analyzed by a processor  1214  that can be similar to the processor described above with regard to  FIG. 11 , and which is coupled to a memory  1216  that stores information related scheduling data, data to be transmitted to user device(s)  1204 , and/or any other suitable information related to performing the various actions and functions set forth herein. Processor  1214  is further coupled to a scheduler  1218  that generates a schedule for channel access. For example, scheduler  1218  may generate a multi-poll that includes a number of polls, and each of the polls may indicate a start time for a particular transmission, a duration for the transmission, a particular station which transmits the data, and/or a particular station that receives the data. The scheduler  1218  may append information related to the schedule (e.g., multi-poll) to a signal generated by processor  1214  for transmission to user device(s)  1204 . A modulator  1224  can multiplex the signal for transmission by a transmitter  1226  through transmit antenna  1208  to user device(s)  1204 . 
     Additionally, processor  1214  may be coupled to a channel access identifier  1220  that determines times during which access point  1202  transmits and/or receives data via a communication channel. Channel access identifier  1220  may utilize the schedule (e.g., multi-poll frame, SCHED frame, . . . ) provided by scheduler  1218  to determine access times. Additionally or alternatively, channel access identifier  1220  may employ a received reverse direction grant to switch access point  1202  from a receiver during a current scheduled time period to a transmitter. Channel access identifier  1220  is further coupled to a reverse direction grant generator  1222  that evaluates whether to transmit a reverse direction grant when access point  1202  is transmitting data via a communication channel and finishes transmission prior to the completion of the allocated duration of time. If reverse direction grant generator  1222  identifies that a reverse direction grant should be provided, this information may be appended to a signal generated by processor  1214  for transmission to user device(s)  1204 , may be multiplexed by modulator  1224 , and may be transmitted via transmitter  1226 . Although depicted as being separate from the processor  1214 , it is to be appreciated that scheduler  1218 , channel access identifier  1220 , reverse direction grant generator  1222  and/or modulator  1224  may be part of processor  1214  or a number of processors (not shown). 
       FIG. 13  shows an exemplary wireless communication system  1300 . The wireless communication system  1300  depicts one access point and one terminal for sake of brevity. However, it is to be appreciated that the system can include more than one access point and/or more than one terminal, wherein additional access points and/or terminals can be substantially similar or different for the exemplary access point and terminal described below. In addition, it is to be appreciated that the access point and/or the terminal can employ the systems ( FIGS. 1-2  and  11 - 12 ) and/or methods ( FIGS. 8-10 ) described herein to facilitate wireless communication there between. 
     Referring now to  FIG. 13 , on a downlink, at access point  1305 , a transmit (TX) data processor  1310  receives, formats, codes, interleaves, and modulates (or symbol maps) traffic data and provides modulation symbols (“data symbols”). A symbol modulator  1315  receives and processes the data symbols and pilot symbols and provides a stream of symbols. A symbol modulator  1315  multiplexes data and pilot symbols and provides them to a transmitter unit (TMTR)  1320 . Each transmit symbol may be a data symbol, a pilot symbol, or a signal value of zero. The pilot symbols may be sent continuously in each symbol period. The pilot symbols can be frequency division multiplexed (FDM), orthogonal frequency division multiplexed (OFDM), time division multiplexed (TDM), frequency division multiplexed (FDM), or code division multiplexed (CDM). 
     TMTR  1320  receives and converts the stream of symbols into one or more analog signals and further conditions (e.g., amplifies, filters, and frequency upconverts) the analog signals to generate a downlink signal suitable for transmission over the wireless channel. The downlink signal is then transmitted through an antenna  1325  to the terminals. At terminal  1330 , an antenna  1335  receives the downlink signal and provides a received signal to a receiver unit (RCVR)  1340 . Receiver unit  1340  conditions (e.g., filters, amplifies, and frequency downconverts) the received signal and digitizes the conditioned signal to obtain samples. A symbol demodulator  1345  demodulates and provides received pilot symbols to a processor  1350  for channel estimation. Symbol demodulator  1345  further receives a frequency response estimate for the downlink from processor  1350 , performs data demodulation on the received data symbols to obtain data symbol estimates (which are estimates of the transmitted data symbols), and provides the data symbol estimates to an RX data processor  1355 , which demodulates (i.e., symbol demaps), deinterleaves, and decodes the data symbol estimates to recover the transmitted traffic data. The processing by symbol demodulator  1345  and RX data processor  1355  is complementary to the processing by symbol modulator  1315  and TX data processor  1310 , respectively, at access point  1305 . 
     On the uplink, a TX data processor  1360  processes traffic data and provides data symbols. A symbol modulator  1365  receives and multiplexes the data symbols with pilot symbols, performs modulation, and provides a stream of symbols. A transmitter unit  1370  then receives and processes the stream of symbols to generate an uplink signal, which is transmitted by the antenna  1335  to the access point  1305 . 
     At access point  1305 , the uplink signal from terminal  1330  is received by the antenna  1325  and processed by a receiver unit  1375  to obtain samples. A symbol demodulator  1380  then processes the samples and provides received pilot symbols and data symbol estimates for the uplink. An RX data processor  1385  processes the data symbol estimates to recover the traffic data transmitted by terminal  1330 . A processor  1390  performs channel estimation for each active terminal transmitting on the uplink. Multiple terminals may transmit pilot concurrently on the uplink on their respective assigned sets of pilot subbands, where the pilot subband sets may be interlaced. 
     Processors  1390  and  1350  direct (e.g., control, coordinate, manage, etc.) operation at access point  1305  and terminal  1330 , respectively. Respective processors  1390  and  1350  can be associated with memory units (not shown) that store program codes and data. Processors  1390  and  1350  can also perform computations to derive frequency and impulse response estimates for the uplink and downlink, respectively. 
     For a multiple-access system (e.g., FDMA, OFDMA, CDMA, TDMA, etc.), multiple terminals can transmit concurrently on the uplink. For such a system, the pilot subbands may be shared among different terminals. The channel estimation techniques may be used in cases where the pilot subbands for each terminal span the entire operating band (possibly except for the band edges). Such a pilot subband structure would be desirable to obtain frequency diversity for each terminal. The techniques described herein may be implemented by various means. For example, these techniques may be implemented in hardware, software, or a combination thereof. For a hardware implementation, the processing units used for channel estimation may be implemented within one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, micro-controllers, microprocessors, other electronic units designed to perform the functions described herein, or a combination thereof. With software, implementation can be through modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory unit and executed by the processors  1390  and  1350 . 
     For a software implementation, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. The software codes may be stored in memory units and executed by processors. The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled to the processor via various means as is known in the art. 
     What has been described above includes examples of one or more embodiments. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the aforementioned embodiments, and many further combinations and permutations of various embodiments are possible. Accordingly, the described embodiments are intended to embrace all such alterations, modifications and variations that fall within the spirit and scope of the appended claims. Furthermore, to the extent that the term “includes” is used in either the detailed description or the claims, such term is intended to be inclusive in a manner similar to the term “comprising” as “comprising” is interpreted when employed as a transitional word in a claim.