Determining frame size based on feedback

A method, an apparatus, and a computer-readable medium for wireless communication are provided. In one aspect, a first wireless device is configured to receive channel feedback from a second wireless device. The first wireless device is configured to determine a frame size based on the received channel feedback for transmitting a frame to the second wireless device. The first wireless device is configured to transmit the frame to the second wireless device based on the determined frame size.

BACKGROUND

Field

The present disclosure relates generally to communication systems, and more particularly, to determining a frame size based on feedback (e.g., channel feedback).

Background

SUMMARY

The systems, methods, computer-readable medium, and devices of the invention each have several aspects, no single one of which is solely responsible for the invention's 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 for devices in a wireless network.

One aspect of this disclosure provides a wireless device (e.g., an access point or a station) for wireless communication. The wireless device is configured to receive channel feedback from a second wireless device. The wireless device is configured to determine a frame size based on the received channel feedback for transmitting a frame to the second wireless device. The wireless device is configured to transmit the frame or frames to the second wireless device based on the determined frame size.

DETAILED DESCRIPTION

Popular wireless network technologies may include various types of WLANs. A WLAN may be used to interconnect nearby devices together, employing widely used networking protocols. The various aspects described herein may apply to any communication standard, such as a wireless protocol.

In some aspects, wireless signals may be transmitted according to an 802.11 protocol using orthogonal frequency-division multiplexing (OFDM), direct-sequence spread spectrum (DSSS) communications, a combination of OFDM and DSSS communications, or other schemes. Implementations of the 802.11 protocol may be used for sensors, metering, and smart grid networks. Advantageously, aspects of certain devices implementing the 802.11 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 a STA serves as a user of the WLAN. For example, a STA may be a laptop computer, a personal digital assistant (PDA), a mobile phone, etc. In an example, a STA connects to an AP via a Wi-Fi (e.g., IEEE 802.11 protocol) compliant wireless link to obtain general connectivity to the Internet or to other wide area networks. In some implementations a STA may also be used as an AP.

An access point 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, connection point, or some other terminology.

A station 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, a user equipment, or some other terminology. In some implementations, a station 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.

In an aspect, MIMO schemes may be used for wide area WLAN (e.g., Wi-Fi) connectivity. MIMO exploits a radio-wave characteristic called multipath. In multipath, transmitted data may bounce off objects (e.g., walls, doors, furniture), reaching the receiving antenna multiple times through different routes and at different times. A WLAN device that employs MIMO will split a data stream into multiple parts, called spatial streams (or multi-streams), and transmit each spatial stream through separate antennas to corresponding antennas on a receiving WLAN device.

The term “associate,” or “association,” or any variant thereof should be given the broadest meaning possible within the context of the present disclosure. By way of example, when a first apparatus associates with a second apparatus, it should be understood that the two apparatuses may be directly associated or intermediate apparatuses may be present. For purposes of brevity, the process for establishing an association between two apparatuses will be described using a handshake protocol that requires an “association request” by one of the apparatus followed by an “association response” by the other apparatus. It will be understood by those skilled in the art that the handshake protocol may require other signaling, such as by way of example, signaling to provide authentication.

Any reference to an element herein using a designation such as “first,” “second,” and so forth does not generally limit the quantity or order of those elements. Rather, these designations are used herein as a convenient method of distinguishing between two or more elements or instances of an element. Thus, a reference to first and second elements does not mean that only two elements can be employed, or that the first element must precede the second element. In addition, 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, or B, or C, or any combination thereof (e.g., A-B, A-C, B-C, and A-B-C).

As discussed above, certain devices described herein may implement the 802.11 standard, for example. Such devices, whether used as a 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. 1shows an example wireless communication system100in which aspects of the present disclosure may be employed. The wireless communication system100may operate pursuant to a wireless standard, for example current or future 802.11 standards. The wireless communication system100may include an AP104, which communicates with STAs (e.g., STAs112,114,116, and118).

A variety of processes and methods may be used for transmissions in the wireless communication system100between the AP104and the STAs. For example, signals may be sent and received between the AP104and the STAs in accordance with OFDM/OFDMA techniques. If this is the case, the wireless communication system100may be referred to as an OFDM/OFDMA system. Alternatively, signals may be sent and received between the AP104and the STAs in accordance with CDMA techniques. If this is the case, the wireless communication system100may be referred to as a CDMA system.

A communication link that facilitates transmission from the AP104to one or more of the STAs may be referred to as a downlink (DL)108, and a communication link that facilitates transmission from one or more of the STAs to the AP104may be referred to as an uplink (UL)110. Alternatively, a downlink108may be referred to as a forward link or a forward channel, and an uplink110may be referred to as a reverse link or a reverse channel. In some aspects, DL communications may include unicast or multicast traffic indications.

The AP104may suppress adjacent channel interference (ACI) in some aspects so that the AP104may receive UL communications on more than one channel simultaneously without causing significant analog-to-digital conversion (ADC) clipping noise. The AP104may improve suppression of ACI, for example, by having separate finite impulse response (FIR) filters for each channel or having a longer ADC backoff period with increased bit widths.

The AP104may act as a base station and provide wireless communication coverage in a basic service area (BSA)102. A BSA (e.g., the BSA102) is the coverage area of an AP (e.g., the AP104). The AP104along with the STAs associated with the AP104and that use the AP104for communication may be referred to as a basic service set (BSS). It should be noted that the wireless communication system100may not have a central AP (e.g., AP104), but rather may function as a peer-to-peer network between the STAs. Accordingly, the functions of the AP104described herein may alternatively be performed by one or more of the STAs.

The AP104may transmit on one or more channels (e.g., multiple narrowband channels, each channel including a frequency bandwidth) a beacon signal (or simply a “beacon”), via a communication link such as the downlink108, to other nodes (STAs) of the wireless communication system100, which may help the other nodes (STAs) to synchronize their timing with the AP104, 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 that is both common (e.g., shared) amongst several devices and specific to a given device.

In some aspects, a STA (e.g., STA114) may be required to associate with the AP104in order to send communications to and/or to receive communications from the AP104. In one aspect, information for associating is included in a beacon broadcast by the AP104. To receive such a beacon, the STA114may, for example, perform a broad coverage search over a coverage region. A search may also be performed by the STA114by sweeping a coverage region in a lighthouse fashion, for example. After receiving the information for associating, the STA114may transmit a reference signal, such as an association probe or request, to the AP104. In some aspects, the AP104may use backhaul services, for example, to communicate with a larger network, such as the Internet or a public switched telephone network (PSTN).

In an aspect, the AP104may include one or more components for performing various functions. For example, the AP104may include a feedback component124configured to receive channel feedback from a second wireless device (e.g., a STA). The feedback component124may be configured to determine a frame size based on the received channel feedback for transmitting a frame to the second wireless device. The feedback component124may be configured to transmit the frame to the second wireless device based on the determined frame size. In an aspect, the frame size may refer to the size of a physical layer convergence procedure (PLCP) protocol data unit (PPDU) size.

In another aspect, the STA114may include one or more components for performing various functions. For example, the STA114may include a feedback component126configured to receive channel feedback from a second wireless device (e.g., an AP or another STA). The feedback component126may be configured to determine a frame size based on the received channel feedback for transmitting a frame to the second wireless device. The feedback component126may be configured to transmit the frame to the second wireless device based on the determined frame size.

Wireless devices within a wireless network (e.g., a Wi-Fi network) may transmit feedback information, such as channel feedback information, to other wireless devices within the network to improve data transmission. For example, APs may transmit channel feedback information to STAs. STAs may transmit channel feedback information to APs (e.g., for a WLAN link) and/or other STAs (e.g., for a peer-to-peer link). Channel feedback information (e.g., channel quality information (CQI)) may be used to determine if a channel is bursty. A bursty channel may have periods of good signal-to-interference noise ratios (SINRs) and bad SINRs. For example, if the SINR for a channel is less than a threshold of 5 dB, then the channel exhibits bad SINR. If the SINR for the channel is greater than 25 dB, then the channel exhibits good SINR. However, the quality of a channel may change frequently. If a channel is bursty, it may be beneficial for a transmitter to have up to date channel quality information before choosing an MCS, a transmission time, and/or frame size. In an aspect, the transmitter may want to utilize a lower MCS and/or smaller frame size if channel conditions are poor and may want to utilize a higher MCS and/or larger frame size if channel conditions are good. In another aspect, the transmitter may want to delay transmissions if channel conditions are poor. In an aspect, if good channel conditions are known to be very brief, then the transmitter may want to use short frames if the channel conditions are good. As such, a need exists for improving the way in which channel feedback is collected and reported in order accurately identify periods during which a channel is most likely to exhibit good SINR. Further, a need exists to identify different uses of the received channel feedback information to improve communications.

FIG. 2is a diagram that illustrates a structure of a frame200. STAs (e.g., the STAs112,114,116,118) and/or APs (e.g., the AP104) may transmit frames with similar structure. Referring toFIG. 2, the frame200may include a preamble210, a set of service bits220, and data field230. The preamble210may be considered a header of the frame200with information identifying a modulation and coding scheme (MCS), a transmission rate, and/or a length/time duration associated with the frame200. In aspect, the preamble210may include a signal (SIG) field, a short training field (STF), and one or more long training field (LTF) symbols. The SIG field may be used to transfer rate and length information. The STF may be used to improve automatic gain control (AGC) in a multi-transmit and multi-receive system. The LTF symbols may be used to provide information that enables a wireless device receiving the frame200to perform channel estimation. The set of service bits220may be a set of 16 bits used for control information (e.g., scrambler information). The data field230may contain user data to be communicated between the STA114and the AP104, for example.

The data field230of the frame200may vary in size or length. In one aspect, the data field230may include one medium access control (MAC) protocol data unit (MPDU)240. In this aspect, the frame200may have a relatively short length (or time duration) such as 0.5 millisecond (ms). In another aspect, the frame200may have a set of MPDUs250, and the set of MPDUs250may include multiple MPDUs (e.g., 6 MPDUs as shown inFIG. 2or some other number of MPDUs). Each MPDU in the set of MPDUs250may include a separate MAC header, payload, and frame check sequence (FCS). In yet another aspect, the frame200may have an aggregated MPDU (A-MPDU)260. The aggregated MPDU260may include multiple MPDUs separated by an MPDU delimiter. The MPDU delimiter may be 32-bits in length and enable a receiving device to parse the A-MPDU structure by using the length in each delimiter to extract the following MPDU.

As further discussed below, the frame size/duration may be adjusted based on channel feedback. If the channel feedback indicates that a channel has good quality, then a longer frame (e.g., a frame with more MPDUs) may be transmitted. If the channel feedback indicates that the channel has poor quality, then a shorter frame (e.g., a frame with a single MPDU) may be transmitted.

FIG. 3is a call flow diagram300illustrating a method of determining a frame size based on channel feedback in acknowledgement (ACK) or block ACK (BACK) frames. Referring toFIG. 3, a first wireless device305may communicate over a connection with a second wireless device310. In one aspect, the first wireless device305may be a STA, and the second wireless device310may be an AP, or vice versa. In another aspect, both the first wireless device305and the second wireless device310may be STAs, and the connection may be a peer-to-peer (P2P) connection.

In this method, the first wireless device305may receive channel feedback through ACK frames and/or block ACK frames. Referring toFIG. 3, the first wireless device305may transmit one or more frames315to the second wireless device310. Each of the one or more frames315may be transmitted at a predetermined MCS and/or have a predetermined length (or time duration) as indicated in a preamble (e.g., the preamble210). The second wireless device310may receive the one or more frames315and determine the channel conditions based on whether the one or more frames315was successfully received. For example, if 15 frames were transmitted, the second wireless device310may determine that the first 5 frames were successfully received, the next 5 frames were not successfully received, and the last 5 frames were successfully received. In another aspect, the second wireless device310may measure the SINR (or signal-to-noise ratio (SNR)) for each of the one or more frames315.

Based on the number of successfully received frames and/or the measured SINR/SNR of each of the frames, the second wireless device may determine320channel feedback on the channel(s) on which the one or more frames315was transmitted. In one aspect, the channel feedback may include the measured SINR associated with each one of the one or more frames315(or subframes) received by the second wireless device310. In another aspect, the channel feedback may include an average SINR over a period of time for all of the one or more frames315. In one another aspect, the channel feedback may be pass/fail ACK information. In another aspect, the channel feedback may include one or more recommended MCSs. For example, if the one or more frames315was transmitted at MCS 8 but the measured SINR associated with the one or more frames was below a threshold (e.g., 5 dB), then the second wireless device310may recommend a lower MCS (e.g., MCS 6). In another example, the recommended MCS may be based on the one or more frames315and on a history of measured SINRs of frames received from the first wireless device305. For example, if the one or more frames315was transmitted at MCS 8, but transmission history reveals that the throughput would be better with MCS 4 or 6, then the second wireless device310may recommend MCS 4 or 6. In another aspect, the channel feedback may include a variance of measured SINRs within one of the received frames (e.g., across subframes, as a function of frame length) or across multiple received frames (as a function of frame length). In yet another aspect, the channel feedback may include a time duration associated with a received MCS for which the SINR of the received one or more frames315was above a threshold. In another aspect, if the second wireless device310recommends an MCS to the first wireless device305, the channel feedback may include a probability that the recommended MCS is the best MCS among other available MCSs (e.g., results in highest SINR compared to other MCSs). In another aspect, the channel feedback may include a probability distribution associated with one or more recommended MCSs. In this aspect, the probability distribution may be a table that links each recommended MCS with a probability that the recommended MCS may result in a highest SINR at the second wireless device310. In another aspect, the channel feedback may include a time duration that the initial SINR remained relatively constant. In another aspect, the channel feedback may include a time duration associated with one or more recommended MCS (e.g., a time duration for which the recommended MCS is valid). In another aspect, the channel feedback may include an average time duration for which the recommended MCS remains constant In another aspect, the channel feedback may include a variance of recommended MCSs. In this aspect, the variance of recommended MCSs may be provided as a function of frame length/size.

After determining the channel feedback, the second wireless device310may transmit the channel feedback in an ACK frame325(or block ACK (BACK) frame) associated with the received one or more frames. The first wireless device305may receive the ACK/BACK frame and determine330a frame size (or PPDU size) for transmitting a frame335to the second wireless device310. By receiving the channel feedback with ACKs or BACKs, the first wireless device305may be able to determine a current channel quality, when and how often channel quality changes, and durations for which the channel quality remains constant at various levels. In an aspect, the first wireless device305may determine, based on the channel feedback included in the ACKs or BACKs, an expected duration for which a channel quality is greater than a threshold (e.g., duration for which a channel may support a particular MCS at the receiver). In an aspect, the first wireless device305may make this determination based on a time duration for which ACKs were received compared to negative ACKs (NACKS). The first wireless device305may select a frame size based on the expected duration for which the channel is greater than the threshold. Upon selecting the frame size, the first wireless device305may determine a number of MPDUs to include within the frame335to be transmitted to the second wireless device310.

In one example, the first wireless device305may transmit 15 frames. Upon receiving the frames, the second wireless device310may transmit ACK/BACKs that include channel feedback. The channel feedback may indicate that the first set of 3 frames has good channel quality (e.g., SINR above a threshold), the second set of 3 frames has poor channel quality (e.g., SINR below threshold), the third set of 3 frames has good channel quality, the fourth set of 3 frames has poor channel quality, and the fifth set of 3 frames has good channel quality. The first wireless device305may determine based on the ACK/BACKs and the channel feedback that the channel is bursty but may still be feasible for data transmission. If the previously transmitted frame had 15 MPDUs, then the first wireless device305may determine that a shorter expected duration (than the an example default of 4 ms) is beneficial. The first wireless device305may select a smaller frame size (e.g., 0.5 ms) based on the expected duration. Based on the smaller frame size, the first wireless device305may select 5 MPDUs instead of 15 MPDUs to transmit in the frame335with the adjusted frame size.

In another example, the first wireless device305may transmit 10 frames, each with 1 MPDU. Upon receiving the frames, the second wireless device310may transmit ACK/BACKs that include channel feedback. The channel feedback may indicate that of the 10 frames, only 1 frame was received with SINR above 10 dB. The channel feedback may include a recommended MCS 1. The first wireless device305may receive the ACK/BACKs and determine a respective SINR for each transmitted frame based on the received channel feedback. The first wireless device may also receive the recommended MCS 1 from the second wireless device310. In this example, the first wireless device305may determine that based on the low SINRs and the inability to reduce the frame size any further, the channel quality is too poor for data transmission even at the recommended MCS 1. Accordingly, the first wireless device305may refrain from transmitting until after a period of time has elapsed, or may transmit frames at the recommended MCS 1.

In another example, the first wireless device305may transmit 10 frames, each with 4 MPDUs. Upon receiving the frames, the second wireless device310may transmit ACK/BACKs that include channel feedback. The channel feedback may indicate that all of the initial MPDUs in the frames were received with SINR above a threshold (e.g., the threshold may be 25 dB). The channel feedback may further include a recommended MCS that is the same as or greater than the MCS as the one previously used for transmission. The first wireless device305may receive the ACK/BACKs and determine the respective SINRs for each transmitted frame and the recommended MCS. The first wireless device305may determine that the latest channel feedback indicates a good channel, but the overall transmission history associated with the channel indicates that good periods do not last long. Accordingly, the first wireless device305may determine to schedule frames with a shorter frame size for transmission (e.g., a frame with 2 MPDUs). On the other hand, if the channel quality is good and previous statistics show that the good channel periods last a long time (e.g., on the order of ms), then the first wireless device305may determine to use a longer frame size (e.g., 64 MPDUs).

In another example, if the channel feedback indicates that the channel quality is poor, and the previous history of feedback information shows that the bad periods do not last very long, then the first wireless device305may send frames with 1 or 2 MPDUs and wait until the second wireless device310transmits feedback that indicates better channel quality before transmitting additional data with longer frame sizes.

In another aspect, the first wireless device305may determine the MCS to transmit the frame335based on the received channel feedback. The first wireless device305may determine the MCS by determining a time period during which a set of MCSs is valid) within a transmission channel. The first wireless device305may select an MCS among the set of MCSs based on which MCS is associated with the highest expected throughput.

Subsequently, the first wireless device305may transmit the frame335to the second wireless device310based on the adjusted frame size. The transmission may also be based on an adjusted MCS.

FIG. 4is a call flow diagram400illustrating a method of determining a frame size based on channel feedback using request to send (RTS) and clear to send (CTS) frames. Referring toFIG. 4, a first wireless device405may communicate over a connection with a second wireless device410. In one aspect, the first wireless device405may be a STA, and the second wireless device410may be an AP, or vice versa. In another aspect, both the first wireless device405and the second wireless device410may be STAs, and the connection may be a P2P connection.

In this method, the first wireless device405may have data to transmit to the second wireless device410. Before transmitting the data, the first wireless device405may transmit an RTS frame415to the second wireless device410. The RTS frame415may be transmitted at a predetermined MCS. Upon receiving the RTS frame415, the second wireless device410may determine420channel feedback based on the received RTS frame415. The second wireless device410may measure the SINR of the received RTS frame415. In one aspect, the channel feedback may include the measured SINR associated with RTS frame415received by the second wireless device310. In another aspect, the channel feedback may include an average SINR over a period of time for frames previously transmitted by the first wireless device405to the second wireless device410. In another aspect, the channel feedback may include one or more recommended MCSs. For example, if the RTS frame415was transmitted at MCS 1 but the measured SINR associated with the RTS frame415was above a threshold (e.g., 25 dB), then the second wireless device410may recommend a higher MCS (e.g., MCS 8). In another example, the recommended MCS may be based on the RTS frame415and a history of measured SINRs of previously received frames from the first wireless device405. For example, if the RTS frame415was transmitted at MCS 8, but transmission history reveals that previous frames transmitted at MCS 4 had a better decode rate, then the second wireless device410may recommend MCS 4. In another aspect, the channel feedback may include a variance of measured SINRs from previously transmitted frames/MPDUs. In yet another aspect, the channel feedback may include a time duration of previously received frames for which the SINR was above a threshold. In another aspect, if the second wireless device410recommends an MCS to the first wireless device405, the channel feedback may include a probability that the recommended MCS is the best MCS among other available MCSs In another aspect, the channel feedback may include a probability distribution associated with one or more recommended MCSs. In this aspect, the probability distribution may be a table that links each recommended MCS with a probability that the recommended MCS may result in the best performance. In another aspect, if the RTS frame415was sent with a first MCS, the channel feedback may indicate the probability that a second MCS is the best MCS, given that previous transmissions were sent with a third MCS. In another aspect, the channel feedback may include a time duration associated with one or more recommended MCS (e.g., a time duration for which the recommended MCS is valid; that is, the measured SINR are above a threshold). In another aspect, the channel feedback may include an average time duration for which the SINR necessary to maintain a received MCS remains constant and/or an average time duration for which the recommended MCS remains valid. In another aspect, the channel feedback may include a variance of recommended MCSs.

After determining the channel feedback, the second wireless device410may transmit the channel feedback in a CTS frame425associated with the RTS frame415. The first wireless device405may receive the CTS frame425and determine430a frame/PPDU size for transmitting a frame435to the second wireless device410. By receiving the channel feedback in the CTS frame425, the first wireless device405may be able to determine a current channel quality, when and how often channel quality changes, and durations for which the channel quality is good or bad. In an aspect, the first wireless device405may determine, based on the channel feedback included in the CTS frame425, an expected duration for which a channel quality is greater than a threshold (e.g., duration for which a channel may support a particular MCS above a particular SINR threshold at the receiver). The first wireless device405may select a frame size based on the expected duration for which the channel is greater than the threshold. Upon selecting the frame size, the first wireless device405may determine a number of MPDUs to include within the frame to be transmitted to the second wireless device410.

In one example, the first wireless device405may transmit the RTS frame415with MCS 1. Upon receiving the RTS frame415, the second wireless device410may transmit the CTS frame425that may include channel feedback. The channel feedback may indicate that of the RTS frame415was received with SINR below 10 dB. The channel feedback may include a recommended MCS 0. The first wireless device405may receive the CTS frame425and the recommended MCS 0 from the second wireless device410. In this example, the first wireless device405may determine an expected duration for which the channel may have acceptable channel quality. For example, the first wireless device405may determine that the channel has a good enough quality for to support MCS 0 for 10 ms. As such, the first wireless device405may select a frame size of 4 ms and determine to include as may MPDUs as possible in the frame435to be transmitted to the second wireless device410at MCS 4.

In another example, the first wireless device405may transmit the RTS frame415. Upon receiving the RTS frame415, the second wireless device410may transmit the CTS frame425that may include channel feedback. The channel feedback may indicate that the RTS frame415was received with SINR above a threshold indicating good channel quality (e.g., 25 dB). The channel feedback may further include a recommended MCS that is the same as or greater than the MCS as the one previously used for transmitting the RTS frame415. The first wireless device405may receive the CTS frame425and determine to use the recommended MCS. The first wireless device305may determine that the latest channel feedback indicates a good channel, but the overall transmission history indicates that good periods do not last long. Accordingly, the first wireless device405may determine to schedule the frame435with a shorter frame size for transmission (e.g., a frame with 2 MPDUs). On the other hand, if the channel quality is good and previous statistics show that the good channel periods last a long time, then the first wireless device405may determine to use a longer frame size (e.g., 64 MPDUs).

In another example, if the channel feedback indicates that the channel quality is poor, and the previous history shows that the bad periods do not last very long, then the first wireless device405may send frames with 1 or 2 MPDUs and wait until the second wireless device410transmits feedback that indicates better channel quality before transmitting additional data with longer frame sizes.

In another aspect, the first wireless device405may determine the MCS to transmit the frame435based on the received channel feedback. The first wireless device405may determine the MCS by determining a time period during which a set of MCSs is valid (e.g., expected to result in a received frame above a SINR threshold) within a transmission channel. The first wireless device405may select an MCS among the set of MCSs based on which MCS is associated with the highest expected throughput given the expected valid time periods.

Subsequently, based on the determined frame size, the first wireless device405may transmit the frame435to the second wireless device410using a frame size determined based on the channel feedback.

FIG. 5is a call flow diagram500illustrating a method of determining a frame size based on channel feedback using trigger and response frames. Referring toFIG. 5, a first wireless device505may communicate over a connection with a second wireless device510. In one aspect, the first wireless device505may be a STA, and the second wireless device510may be an AP, or vice versa. In another aspect, both the first wireless device505and the second wireless device510may be STAs, and the connection may be a P2P connection.

In this method, the first wireless device505may have data to transmit to the second wireless device510. Before transmitting the data, the first wireless device505may transmit a trigger frame515to the second wireless device510. The trigger frame515may be transmitted at a predetermined MCS. Upon receiving the trigger frame515, the second wireless device510may determine520channel feedback based on the received trigger frame515. The second wireless device510may measure the SINR of the trigger frame515. In one aspect, the channel feedback may include the measured SINR associated with trigger frame515received by the second wireless device510. In another aspect, the channel feedback may include an average SINR over a period of time for frames previously transmitted by the first wireless device505to the second wireless device510. In another aspect, the channel feedback may include one or more recommended MCSs. For example, if the trigger frame515was transmitted at MCS 8 but the measured SINR associated with the trigger frame515was below a threshold (e.g., 5 dB), then the second wireless device510may recommend a lower MCS (e.g., MCS 4). In another aspect, the recommended MCS may also be based on the trigger frame515and a history of measured SINRs of frames received from the first wireless device505. For example, if the trigger frame515was transmitted at MCS 8, but transmission history reveals that previous frames transmitted at MCS 6 had better packet error rates (PERs), then the second wireless device510may recommend MCS 6. In another aspect, the channel feedback may include a variance of measured SINRs within the trigger frame515and/or one of a previously transmitted frame (e.g., across subframes) and/or across multiple transmitted frames from the first wireless device505. In yet another aspect, the channel feedback may include a time duration associated with an MCS for which the MCS is expected to remain valid (e.g., packets sent at that MCS would be decodable for a given amount of time). In another aspect, if the second wireless device510recommends an MCS to the first wireless device505, the channel feedback may include a probability that the recommended MCS is the best MCS among other available MCSs. In another aspect, the channel feedback may include a probability distribution associated with one or more recommended MCSs. In this aspect, the probability distribution may be a table that links each recommended MCS with a probability that the recommended MCS may result in a better PER. In another aspect, the channel feedback may include a time duration associated with one or more recommended MCS (e.g., a time duration for which the recommended MCS is valid). In another aspect, the channel feedback may include an average time duration for which the received MCS remains constant (e.g., a time duration for which the MCS would result in measured PERs below a threshold). In another aspect, the channel feedback may include a variance of recommended MCSs.

After determining the channel feedback, the second wireless device510may transmit the channel feedback in a response frame525associated with the trigger frame515. The first wireless device505may receive the response frame525and determine530a frame/PPDU size for transmitting a frame535to the second wireless device510. By receiving the channel feedback in the response frame525, the first wireless device505may be able to determine a current channel quality, when and how often channel quality changes, and durations for which the channel quality is good or bad. In an aspect, the first wireless device505may determine, based on the channel feedback included in the response frame525, an expected duration for which a channel quality is greater than a threshold (e.g., duration for which a channel may support a particular MCS). The first wireless device505may select a frame size based on the expected duration for which the channel is greater than the threshold. Upon determining the frame size, the first wireless device505may determine a number of MPDUs to include within the frame to be transmitted to the second wireless device510.

In one example, the first wireless device505may transmit the trigger frame515with MCS 0. Upon receiving the trigger frame515, the second wireless device510may transmit the response frame525that may include channel feedback. The channel feedback may indicate that the trigger frame515was received with SINR below 10 dB. The channel feedback may include a recommended MCS 1. The first wireless device505may receive the response frame525and the recommended MCS 1 from the second wireless device510. In this example, the first wireless device505may determine an expected duration for which the channel may support MCS 1. For example, the first wireless device505may determine that the channel may support MCS 1 for 10 ms. As such, the first wireless device505may select a frame size of 4 ms and determine to include as many MPDUs as possible in the frame535to be transmitted to the second wireless device510at MCS 4.

In another example, the first wireless device505may transmit the trigger frame515. Upon receiving the trigger frame515, the second wireless device510may transmit the response frame525that may include channel feedback. The channel feedback may indicate that the trigger frame515was received with SINR above a threshold indicating good channel quality (e.g., 25 dB). The channel feedback may further include a recommended MCS that is the same as or greater than the MCS as the one previously used for transmitting the trigger frame515. The first wireless device505may receive the response frame525and determine to use the recommended MCS. The first wireless device505may determine that the latest channel feedback indicates a good channel, but the overall transmission history indicates that good periods do not last long. Accordingly, the first wireless device505may determine to schedule the frame535with a shorter frame size for transmission). On the other hand, if the channel quality is good and previous statistics show that the good channel periods last a long time, then the first wireless device505may determine to use a longer frame size (e.g., 4 ms).

In another example, if the channel feedback indicates that the channel quality is poor, and the previous history shows that the bad periods do not last very long, then the first wireless device505may send frames with 1 or 2 MPDUs and wait until the second wireless device510transmits feedback that indicates better channel quality before transmitting additional data with longer frame sizes.

In another aspect, the first wireless device505may determine the MCS to transmit the frame535based on the received channel feedback. The first wireless device505may determine the MCS by determining a time period during which a set of MCSs is valid within a transmission channel. The first wireless device505may select an MCS among the set of MCSs based on which MCS is associated with the highest expected throughput given the expected valid time periods.

In another aspect, the first wireless device505and the second wireless device510may be engaged in a sounding procedure to initiate beam forming. The first and second wireless devices505,510may employ a null data packet (NDP) sounding procedure. The first wireless device505may be the beamformer and the second wireless device510may be the beamformee. In this process, the beamformer may transmit an NDP announcement frame to gain control of the channel and identify beamformees. Beamformees may respond to the NDP announcement. The beamformer may follow the NDP announcement with a null data packet. Based on the NDP, the beamformee may calculate the channel response/feedback matrix. The beamformee may also calculate or measure the above-mentioned forms of channel feedback information and transmit the feedback matrix and channel feedback (e.g., SINR, recommended MCS, durations that MCSs would be valid, etc.) to the beamformer. The beamformer may utilize the received channel feedback to adjust the frame size and/or MCS for transmitting subsequent frames. In another aspect, the first wireless device505and the second wireless device510may use a short sounding procedure to transmit feedback information. That is, the first wireless device505may ask the second wireless device510to send a compressed or reduced set of information that may not include all the beam forming information but includes the channel feedback information for adjusting frame size (e.g., no feedback matrix but includes recommended MCS).

In another aspect, the channel feedback may be included a control field (e.g., a high throughput (HT or HE) control field) of a frame. The control field may be sent in a frame with data (e.g., in a quality of service frame). In another aspect, the control field may be included in a control frame if a control wrapper is used. In another aspect, the control field may be sent in a stand-alone frame.

FIG. 6is a functional block diagram of a wireless device602that may be employed within the wireless communication system100ofFIG. 1for determining a frame size based on channel feedback. The wireless device602is an example of a device that may be configured to implement the various methods described herein. For example, the wireless device602may be the AP104, the STAs112,114,116,118, the first wireless devices305,405,505, or the second wireless devices310,410,510.

The wireless device602may include a processor604which controls operation of the wireless device602. The processor604may also be referred to as a central processing unit (CPU). Memory606, which may include both read-only memory (ROM) and random access memory (RAM), may provide instructions and data to the processor604. A portion of the memory606may also include non-volatile random access memory (NVRAM). The processor604typically performs logical and arithmetic operations based on program instructions stored within the memory606. The instructions in the memory606may be executable (by the processor604, for example) to implement the methods described herein.

The wireless device602may also include a housing608, and the wireless device602may include a transmitter610and/or a receiver612to allow transmission and reception of data between the wireless device602and a remote device. The transmitter610and the receiver612may be combined into a transceiver614. An antenna616may be attached to the housing608and electrically coupled to the transceiver614. The wireless device602may also include multiple transmitters, multiple receivers, multiple transceivers, and/or multiple antennas.

The wireless device602may also include a signal detector618that may be used to detect and quantify the level of signals received by the transceiver614or the receiver612. The signal detector618may detect such signals as total energy, energy per subcarrier per symbol, power spectral density, and other signals. The wireless device602may also include a DSP620for use in processing signals. The DSP620may be configured to generate a packet for transmission. In some aspects, the packet may comprise a PPDU.

The wireless device602may further comprise a user interface622in some aspects. The user interface622may comprise a keypad, a microphone, a speaker, and/or a display. The user interface622may include any element or component that conveys information to a user of the wireless device602and/or receives input from the user.

When the wireless device602is implemented as an AP (e.g., AP104) or as a STA (e.g., the STA114), the wireless device602may also include a feedback component624. The feedback component624may be configured to receive channel feedback (e.g., channel feedback628) from a second wireless device. The feedback component624may be configured to determine a frame size (e.g., determined frame size630) based on the received channel feedback for transmitting a frame (e.g., frame based on feedback642) to the second wireless device. The feedback component624may be configured to transmit the frame to the second wireless device based on the determined frame size. In one configuration, the feedback component624may be configured to transmit at least one frame (e.g., frame632) to the second wireless device and to receive an ACK frame (e.g., ACK frame636) or block ACK frame from the second wireless device based on the transmitted at least one frame. In this configuration, the ACK frame or block ACK frame may include the channel feedback. In another configuration, the feedback component624may be configured to transmit an RTS frame to the second wireless device and to receive a CTS frame (e.g., CTS frame638) from the second wireless device. In this configuration, the channel feedback may be received in the CTS frame. In another configuration, the channel feedback may be received during a sounding procedure (or based on a sounding procedure). In yet another configuration, the feedback component624may be configured to transmit a trigger frame to the second wireless device and to receive a response frame (e.g., response frame640) from the second wireless device based on the transmitted trigger frame. In this configuration, the channel feedback may be received in the response frame. In an aspect, the received channel feedback may include a SINR associated with one or more frames or subframes received by the second wireless device from the wireless device602, a recommended MCS (e.g., MCS634), a variance of SINRs within a second frame or across multiple frames, and/or a time duration associated with a received MCS. In another aspect, the received channel feedback may further include a probability associated with the recommended MCS, a probability distribution associated with the recommended MCS, a time duration associated with the recommended MCS, an average time duration for which the recommended MCS or the received MCS remains constant, and/or a variance of recommended MCSs. In another configuration, the feedback component624may be configured to determine the frame size by determining, based on the received channel feedback, an expected duration for which a channel quality is greater than a threshold and by selecting the frame size based on the determined expected duration for which the channel quality is greater than the threshold. In an aspect, the expected duration may be further based on a history of received channel feedback information. In this configuration, the feedback component624may also be configured to determine the frame size by determining a number of MPDUs to include within the frame for transmission to the second wireless device based on the determined expected duration and the selected frame size. In another configuration, the feedback component624may be configured to determine an MCS (e.g., determined MCS646) for transmitting the frame based on the received channel feedback. In this configuration, the feedback component624may be configured to determine the MCS by determining a time period during which one or more MCSs is valid within a transmission channel and by selecting the MCS based on which of the one or more MCSs is associated with a highest expected throughput given the expected valid time periods.

The various components of the wireless device602may be coupled together by a bus system626. The bus system626may 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. Components of the wireless device602may be coupled together or accept or provide inputs to each other using some other mechanism.

Although a number of separate components are illustrated inFIG. 6, one or more of the components may be combined or commonly implemented. For example, the processor604may be used to implement not only the functionality described above with respect to the processor604, but also to implement the functionality described above with respect to the signal detector618, the DSP620, the user interface622, and/or the feedback component624. Further, each of the components illustrated inFIG. 6may be implemented using a plurality of separate elements.

FIG. 7is a flowchart of an exemplary method700of determining a frame size based on channel feedback in ACK or block ACK frames. The method700may be performed using an apparatus (e.g., the AP104, the STA114, the first wireless device305, or the wireless device602, for example). Although the method700is described below with respect to the elements of wireless device602ofFIG. 6, other components may be used to implement one or more of the steps described herein. InFIG. 7, blocks denoted with dotted lines indicate optional operations.

At block705, an apparatus may transmit at least one frame to a second wireless device. For example, referring toFIG. 3, the apparatus may correspond to the first wireless device305, and the second wireless device may correspond to the second wireless device310. The first wireless device305may transmit one or more frames315to the second wireless device310.

At block710, the apparatus may receive an ACK frame or block ACK frame from the second wireless device based on the transmitted at least one frame. The ACK frame or block ACK frame may include channel feedback from the second wireless device. In an aspect, the channel feedback may include a SINR associated with one or more frames or subframes received by the second wireless device from the apparatus, a recommended MCS, a variance of SINRs within a second frame or across multiple frames, a time duration associated with a received MCS (e.g., the MCS used to transmit the at least one or more frames), a probability associated with the recommended MCS, a probability distribution associated with the recommended MCS, a time duration associated with the recommended MCS, an average time duration for which the recommended MCS or the received MCS remains constant, and/or a variance of recommended MCSs. For example, referring toFIG. 3, the first wireless device305may receive the ACK frame325(or block ACK frame) from the second wireless device310. The ACK frame325may include channel feedback from the second wireless device310that is based on the one or more frames315transmitted to the second wireless device310. The channel feedback may include measured SINRs associated with each of the one or more frames315.

At block715, the apparatus may determine a frame size based on the received channel feedback for transmitting a frame to the second wireless device. In one configuration, the apparatus may determine the frame size by determining, based on the received channel feedback, an expected duration for which a channel quality is greater than a threshold (at block720), by selecting the frame size based on the determined expected duration for which the channel quality is greater than the threshold (at block725), and by determining a number of MPDUs to include within the frame for transmission to the second wireless device based on the determined expected duration and the selected frame size (at block730). In an aspect, the expected duration may be determined based on a history of received channel feedback information. For example, referring toFIG. 3, the first wireless device305may determine the frame size based on the measured SINRs for each of the one or more frames315and on the recommended MCS. In an aspect, if ACK frames are transmitted, each ACK frame may include a recommended MCS. In another aspect, if a block ACK frame is transmitted, then the block ACK frame may include a bitmap with SINRs for each of the received MPDUs (or may include a single SINR based on all of the received frames). The measured SINRs may average 20 dB and the recommended MCSs may be 4-6. Based on this feedback information, the first wireless device305may determine that the channel quality is good. The previously received channel feedback history may also indicate that the connection typically experiences long periods of good channel quality. Accordingly, the first wireless device305may determine that the expected duration in which channel quality is greater than 20 dB will be at least 10 ms. The first wireless device305may determine to use a longer frame size (e.g., 4 ms) based on the expected duration for which the channel quality is expected to support 20 dB SINRs. Based on the 10 milliseconds for which the channel quality is expected to be greater than 20 dB and the 4 ms frame duration, the first wireless device305may determine to include as many MPDUs as can fit in 4 ms in the frame335to be transmitted to the second wireless device310.

At block735, the apparatus may determine an MCS for transmitting the frame based on the received channel feedback. In one configuration, the apparatus may determine the MCS by determining the recommended MCS received from the second wireless device and by selecting the MCS based on the recommended MCS. In another configuration, the apparatus may determine the MCS by determining a time period during which one or more MCSs is valid within a transmission channel (at block740) and by selecting the MCS based on which of the one or more MCSs is associated with a highest expected throughput given the expected valid time periods (at block745). In one example, referring toFIG. 3, the first wireless device305may determine the MCS for transmitting the frame335based on the measured SINRS and/or the recommended MCS. The first wireless device305may use the recommended MCS for transmitting the frame335. In another example, based on the received feedback, the first wireless device305may determine a time period during which one or more MCSs is valid within a transmission channel (e.g., expected to result in messages transmitted with SINR above a threshold) and select the MCS based on which of the one or more MCSs is associated with a longest valid time period. In another example, the first wireless device305may choose the MCS and PPDU size based on which combination of MCS and PPDU size will successfully transmit the most bits.

At block750, the apparatus may transmit the frame to the second wireless device based on the determined frame size. For example, referring toFIG. 3, the first wireless device305may transmit the frame335to the second wireless device310based on the determined frame size (or PPDU size).

FIG. 8is a flowchart of an exemplary method800of determining a frame size based on channel feedback in CTS frames. The method800may be performed using an apparatus (e.g., the AP104, the STA114, the first wireless device405, or the wireless device602, for example). Although the method800is described below with respect to the elements of wireless device602ofFIG. 6, other components may be used to implement one or more of the steps described herein. InFIG. 8, blocks denoted with dotted lines indicate optional operations.

At block805, an apparatus may transmit an RTS frame to a second wireless device. For example, referring toFIG. 4, the apparatus may correspond to the first wireless device405and the second wireless device may correspond to the second wireless device410. The first wireless device405may transmit an RTS frame415to the second wireless device410.

At block810, the apparatus may receive a CTS frame from the second wireless device. The CTS frame may include channel feedback based on the transmitted RTS frame. In an aspect, the channel feedback may include a SINR associated with the RTS frame received by the second wireless device from the apparatus, a recommended MCS, a variance of SINRs across multiple frames previously transmitted by the apparatus, a time duration associated with a received MCS (e.g., the MCS used to transmit the at least one or more frames), a probability associated with the recommended MCS, a probability distribution associated with the recommended MCS, a time duration associated with the recommended MCS, an average time duration for which the recommended MCS or the received MCS remains constant, and/or a variance of recommended MCSs. For example, referring toFIG. 4, the first wireless device405may receive the CTS frame425from the second wireless device410. The CTS frame may include channel feedback based on the RTS frame415. The channel feedback may include a recommended MCS.

At block815, the apparatus may determine a frame size based on the received channel feedback for transmitting a frame to the second wireless device. In one configuration, the apparatus may determine the frame size by determining, based on the received channel feedback, an expected duration for which a channel quality is greater than a threshold (at block820), by selecting the frame size based on the determined expected duration for which the channel quality is greater than the threshold (at block825), and by determining a number of MPDUs to include within the frame for transmission to the second wireless device based on the determined expected duration and the selected frame size (at block830). In an aspect, the expected duration may be determined based on a history of received channel feedback information. For example, referring toFIG. 4, the first wireless device405may determine the frame size based on the recommended MCS received in the CTS frame425. The recommended MCS may indicate an MCS 2. Based on this feedback information, the first wireless device405may determine that the channel quality is poor (e.g., an MCS greater than or equal to 5 may indicate good channel quality). Additionally, the first wireless device405may determine that the expected duration in which channel quality is poor is only about 1 ms. The first wireless device305may determine to use a shorter frame size (e.g., 1 ms) based on the expected duration for which the channel quality is expected to remain poor. Based on the 1 ms for which the channel quality is expected to remain poor and the 1 ms frame duration, the first wireless device405may determine to include 1 MPDU in the frame435to be transmitted to the second wireless device410and attempt to transmit longer frames later when channel quality improves.

At block835, the apparatus may determine an MCS for transmitting the frame based on the received channel feedback. In one configuration, the apparatus may determine the MCS by determining the recommended MCS received from the second wireless device and by selecting the MCS based on the recommended MCS. In another configuration, the apparatus may determine the MCS by determining a time period during which one or more MCSs is valid within a transmission channel (at block840) and by selecting the MCS based on which of the one or more MCSs is associated with a longest valid time period (at block845). In one example, referring toFIG. 4, the first wireless device405may determine the MCS for transmitting the frame435based on the measured SINRS and/or the recommended MCS. The first wireless device405may use the recommended MCS for transmitting the frame435. In another example, based on the received feedback, the first wireless device405may determine a time period during which one or more MCSs is valid within a transmission channel (e.g., expected to result in messages transmitted with SINR above a threshold) and select the MCS based on which of the MCS and PPDU duration combinations has the maximum expected number of successfully transmitted bits.

At block850, the apparatus may transmit the frame to the second wireless device based on the determined frame size. For example, referring toFIG. 4, the first wireless device405may transmit the frame435to the second wireless device410based on the determined frame size (or PPDU size).

FIG. 9is a flowchart of an exemplary method900of determining a frame size based on channel feedback using trigger and response frames. The method900may be performed using an apparatus (e.g., the AP104, the STA114, the first wireless device505, or the wireless device602, for example). Although the method900is described below with respect to the elements of wireless device602ofFIG. 6, other components may be used to implement one or more of the steps described herein. InFIG. 9, blocks denoted with dotted lines indicate optional operations.

At block905, an apparatus may transmit a trigger frame to a second wireless device. For example, referring toFIG. 5, the apparatus may be the first wireless device505, and the second wireless device may be the second wireless device510. The first wireless device505may transmit the trigger frame515to the second wireless device510.

At block910, the apparatus may receive a response frame from the second wireless device based on the transmitted trigger frame. The response frame may include channel feedback. In an aspect, the channel feedback may include a SINR associated with the trigger frame received by the second wireless device from the apparatus, a recommended MCS, a variance of SINRs within the trigger frame or across multiple frames previously transmitted by the apparatus, a time duration associated with a received MCS (e.g., the MCS used to transmit the at least one or more frames), a probability associated with the recommended MCS, a probability distribution associated with the recommended MCS, a time duration associated with the recommended MCS, an average time duration for which the recommended MCS or the received MCS remains constant, and/or a variance of recommended MCSs. For example, referring toFIG. 5, the first wireless device505may receive the response frame525from the second wireless device510based on the trigger frame515. The response frame525may include channel feedback such as a recommended MCS.

At block915, the apparatus may determine a frame size based on the received channel feedback for transmitting a frame to the second wireless device. In one configuration, the apparatus may determine the frame size by determining, based on the received channel feedback, an expected duration for which a channel quality is greater than a threshold (at block920), by selecting the frame size based on the determined expected duration for which the channel quality is greater than the threshold (at block925), and by determining a number of MPDUs to include within the frame for transmission to the second wireless device based on the determined expected duration and the selected frame size (at block930). In an aspect, the expected duration may be determined based on a history of received channel feedback information. For example, referring toFIG. 5, the first wireless device505may determine the frame size based on the recommended MCS received in the response frame525. The recommended MCS may indicate an MCS 8. Based on this feedback information, the first wireless device505may determine that the channel quality is good (e.g., an MCS greater than or equal to 5 may indicate good channel quality). Additionally, the first wireless device505may determine that the expected duration in which channel quality is greater than 20 dB may be 10 ms. The first wireless device505may determine to use a longer frame size (e.g., 3 ms) based on the expected duration for which the channel quality is expected to support 20 dB SINRs. Based on the 10 ms for which the channel quality is expected to be greater than 20 dB and the 3 ms frame duration, the first wireless device505may determine to include 64 MPDUs in the frame535to be transmitted to the second wireless device510.

At block935, the apparatus may determine an MCS for transmitting the frame based on the received channel feedback. In one configuration, the apparatus may determine the MCS by determining the recommended MCS received from the second wireless device and by selecting the MCS based on the recommended MCS. In another configuration, the apparatus may determine the MCS by determining a time period during which one or more MCSs is valid within a transmission channel (at block940) and by selecting the MCS based on which of the one or more MCSs and its corresponding duration is expected to result in the maximum amount of bits transferred successfully (at block945). In one example, referring toFIG. 5, the first wireless device505may determine the MCS for transmitting the frame535based on the recommended MCS. The first wireless device505may use the recommended MCS for transmitting the frame535. In another example, based on the received feedback, the first wireless device505may determine a time period during which one or more MCSs is valid within a transmission channel (e.g., expected to result in messages transmitted with SINR above a threshold) and select the MCS based on which of the one or more MCSs is expected to result in the maximum number of successful bits transferred.

At block950, the apparatus may transmit the frame to the second wireless device based on the determined frame size. For example, referring toFIG. 5, the first wireless device505may transmit the frame535to the second wireless device510based on the determined frame size (or PPDU size).

FIG. 10is a functional block diagram of an exemplary wireless communication device1000for modifying a frame size based on channel feedback. The wireless communication device1000may include a receiver1005, a processing system1010, and a transmitter1015. The processing system1010may include a feedback component1024and/or a frame generation component1036. The processing system1010, the feedback component1024, and/or the receiver1005may be configured to receive channel feedback (e.g., channel feedback1026) from a second wireless device. The processing system1010and/or the feedback component1024may be configured to determine a frame size (e.g., a frame size1030) based on the received channel feedback for transmitting a frame (e.g., a frame1028) to the second wireless device. The processing system1010, the feedback component1024, the frame generation component1036, and/or the transmitter1015may be configured to transmit the frame to the second wireless device based on the determined frame size. In one configuration, the processing system1010, the feedback component1024, and/or the transmitter1015may be configured to transmit at least one frame to the second wireless device. In this configuration, the processing system1010, the feedback component1024, and/or the receiver1005may be configured to receive an ACK frame or a block ACK frame from the second wireless device based on the transmitted at least one frame. The ACK frame or the block ACK frame may include the channel feedback. In another configuration, the processing system1010, the feedback component1024, and/or the transmitter1015may be configured to transmit an RTS frame to the second wireless device. In this configuration, the processing system1010, the feedback component1024, and/or the receiver1005may be configured to receive a CTS frame from the second wireless device. In this configuration, the channel feedback may be received in the CTS frame. In an aspect, the channel feedback may be received during a sounding procedure. In another configuration, the processing system1010, the feedback component1024, and/or the transmitter1015may be configured to transmit a trigger frame to the second wireless device. In this configuration, the processing system1010, the feedback component1024, and/or the receiver1005may be configured to receive a response frame from the second wireless device based on the transmitted trigger frame. In this configuration, the channel feedback may be received in the response frame. In another aspect, the received channel feedback may include a SINR associated with one or more frames or subframes received by the second wireless device from the wireless communication device1000, a recommended MCS, a variance of SINRs within a second frame or across multiple frames, a time duration associated with a received MCS, a probability associated with the recommended MCS, a probability distribution associated with the recommended MCS, a time duration associated with the recommended MCS, an average time duration for which the recommended MCS or the received MCS remains constant, and/or a variance of recommended MCSs. In another configuration, the processing system1010and/or the feedback component1024may be configured to determine the frame size by determining, based on the received channel feedback, an expected duration for which a channel quality is greater than a threshold and by selecting the frame size based on the determined expected duration for which the channel quality is greater than the threshold. In an aspect, the expected duration may be further based on a history of received channel feedback information. In this configuration, the processing system1010and/or the feedback component1024may be further configured to determine a number of MPDUs (e.g., MPDUs1034) to include within the frame for transmission to the second wireless device based on the determined expected duration and the selected frame size. In another configuration, the processing system1010and/or the feedback component1024may be configured to determine an MCS (e.g., MCS1032) for transmitting the frame based on the received channel feedback. In this configuration, the processing system1010and/or the feedback component1024may be configured to determine the MCS by determining a time period during which one or more MCSs is valid within a transmission channel and by selecting the MCS based on which of the one or more MCSs is associated with a best expected throughput.

The receiver1005, the processing system1010, the feedback component1024, the frame generation component1036, and/or the transmitter1015may be configured to perform one or more functions discussed above with respect to blocks705,710,715,720,725,730,735,740,745, and750ofFIG. 7, to blocks805,810,815,820,825,830,835,840,845, and850ofFIG. 8, and to blocks905,910,915,920,925,930,935,940,945, and950ofFIG. 9. The receiver1005may correspond to the receiver612. The processing system1010may correspond to the processor604. The transmitter1015may correspond to the transmitter610. The feedback component1024may correspond to the feedback components124,126and/or the feedback component624.

In one configuration, the wireless communication device1000may include means for receiving channel feedback from a second wireless device. The wireless communication device1000may include means for determining a frame size based on the received channel feedback for transmitting a frame to the second wireless device. The wireless communication device1000may include means for transmitting the frame to the second wireless device based on the determined frame size. In another configuration, the wireless communication device1000may include means for transmitting at least one frame to the second wireless device. In this configuration, the wireless communication device1000may include means for receiving an ACK frame or a block ACK frame from the second wireless device based on the transmitted at least one frame. The ACK frame or block ACK frame may include the channel feedback. In another configuration, the wireless communication device1000may include means for transmitting an RTS frame to the second wireless device. In this configuration, the wireless communication device1000may include means for receiving a CTS frame from the second wireless device. The channel feedback may be received in the CTS frame. In another configuration, the channel feedback may be received during a sounding procedure. In another configuration, the wireless communication device1000may include means for transmitting a trigger frame to the second wireless device and means for receiving a response frame from the second wireless device based on the transmitted trigger frame. The channel feedback may be received in the response frame. In another aspect, the received channel feedback may include a SINR associated with one or more frames or subframes received by the second wireless device from the wireless communication device1000, a recommended MCS, a variance of SINRs within a second frame or across multiple frames, a time duration associated with a received MCS, a probability associated with the recommended MCS, a probability distribution associated with the recommended MCS, a time duration associated with the recommended MCS, an average time duration for which the recommended MCS or the received MCS remains constant, and/or a variance of recommended MCSs. In another configuration, the means for determining the frame size may be configured to determine, based on the received channel feedback, an expected duration for which a channel quality is greater than a threshold and to select the frame size based on the determined expected duration for which the channel quality is greater than the threshold. In another aspect, the expected duration may be further based on a history of received channel feedback information. In another configuration, the means for determining the frame size may be further configured to determine a number of MPDUs to include within the frame for transmission to the second wireless device based on the determined expected duration and the selected frame size. In another configuration, the wireless communication device1000may include means for determining an MCS for transmitting the frame based on the received channel feedback. In another configuration, the means for determining the MCS may be configured to determine a time period during which one or more MCSs is valid within a transmission channel and to select the MCS based on which of the one or more MCSs is associated with a highest expected throughput.

For example, means for receiving may include the receiver1005, the processing system1010, and/or the feedback component1024. Means for determining may include the processing system1010, the feedback component1024, and/or the frame generation component1036. Means for transmitting may include the transmitter1015, the processing system1010, the feedback component1024, and/or the frame generation component1036. Means for selecting may include the processing system1010, the feedback component1024, and/or the frame generation component1036.

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. The various figures may depict elements with dotted lines. In some instances, elements depicted with dotted lines may be considered optional features.