Abstract:
Systems and methods are disclosed herein to provide efficient support for the exchange of trigger information between wireless data communication devices and systems, including Multi-User Multiple Input Multiple Output (MU-MIMO) devices and systems that may utilize Orthogonal Frequency Division Multiple Access (OFDMA). In accordance with one or more embodiments, a trigger information exchange mechanism is disclosed that transfers trigger data as part of a pre-existing data frame handshake. Such a system may offer improved capabilities such as a reduced channel overhead incurred due to the trigger information exchange.

Description:
TECHNICAL FIELD 
       [0001]    The subject matter described herein relates generally to wireless data communication systems; and more particularly to systems and methods for transferring trigger information between wireless devices, including but not limited to multi-user multiple-input multiple-output data communication devices and systems. 
       BACKGROUND 
       [0002]    There is increasing need for higher data rates, better efficiency, and support for larger numbers of users in the sophisticated wireless data communications devices that are deployed worldwide. For example, the IEEE 802.11 Wireless Local Area Network (WLAN) systems that have achieved widespread use utilize Multiple Input Multiple Output (MIMO) techniques to increase communication data rates and hence support greater data traffic to larger numbers of users. Further advances in WLAN systems utilize Multi-User MIMO (MU-MIMO) techniques to allow concurrent transmissions to be made in the downstream direction from IEEE 802.11 Access Points (APs) to client devices. This significantly improves the efficiency of the system and the utilization of the wireless channel. 
         [0003]      FIG. 1  illustratively represents an MU-MIMO data transfer process as may be implemented in an MU-MIMO IEEE 802.11 protocol such as IEEE 802.11ac. For descriptive purposes  FIG. 1  depicts a possible downstream MU-MIMO data transfer by the AP followed by upstream data transfers by the clients. The downstream MU-MIMO frames (Physical layer Protocol Data Units, or PPDUs) simultaneously transmitted by the AP in one block are  1 ,  2 ,  3 ,  4 , with padding  5  being used to pad out the PPDUs to the same transmission duration. PPDUs  1 ,  2 ,  3 ,  4  are transmitted to four different clients at the same time. After the AP transmits these PPDUs, the corresponding clients return Acknowledgements  6 ,  7 ,  8  and  9  respectively, waiting a Short Interframe Space (SIFS) from the AP&#39;s PPDUs. The clients now transmit data upstream to the AP as their own PPDUs  10 ,  12 ,  14 ,  16 , waiting the appropriate Distributed Coordination Function Interframe Spacing (DIFS) and SIFS intervals, and receiving Acknowledgement frames  11 ,  13 ,  15 ,  17 , as dictated by the IEEE 802.11 protocol. As MU-MIMO does not support concurrent upstream transmissions, the clients are forced to send their PPDUs  10 ,  12 ,  14 ,  16  separately. 
         [0004]    It is evident from  FIG. 1  that while substantial efficiency is possible in the downstream direction from the AP to clients by virtue of MU-MIMO, the upstream direction does not enjoy such efficiencies. Current technology improvements in IEEE 802.11 are adopting advanced techniques such as Orthogonal Frequency Division Multiple Access (OFDMA) to permit concurrent transmissions to also be made in the upstream direction from IEEE 802.11 client devices to APs. This further improves the ability of a WLAN system to support many concurrently active client devices on each AP. 
         [0005]      FIG. 2  represents for descriptive purposes an MU-MIMO exchange employing OFDMA in the upstream direction. As in the preceding case, the AP utilizes MU-MIMO techniques to transmit PPDUs  1 ,  2 ,  3 ,  4 , padded with padding  5  (and preceded by Physical Layer Convergence Protocol, or PLCP, header  20 ), to four clients. The clients also return their Acknowledgements  6 ,  7 ,  8 ,  9  after waiting a SIFS in the usual manner. However, in the upstream direction the AP first transmits a special trigger frame  22  (which has a PLCP header  21 ), which triggers a subset of clients to synchronize to each other and simultaneously transmit their PPDUs  26 ,  27 ,  28 ,  29  as a single OFDMA burst. The OFDMA frame has a PLCP header  23 —transmitted by all clients simultaneously—as well as padding  24  to ensure that all clients transmit for an equal amount of time. The AP then returns a composite Acknowledgement  25  to all of the clients, indicating proper reception and acceptance of PPDUS  26 ,  27 ,  28 ,  29 . 
         [0006]    Trigger frame  22  plays several important roles in the OFDMA transmission. Firstly, it provides a common synchronization reference for all of the clients, which is required in order for the clients to align their OFDMA symbols with each other so that the AP can properly receive and decode them. Secondly, the trigger frame allows the AP to control which specific clients must transmit data upstream, thereby ensuring that the AP will be able to decode the client data when it is received. Finally, the trigger frame supplies critical parameters such as Transmit Opportunity (TXOP) duration, buffer state information, QoS state, etc. that the clients will need to know in order to control their OFDMA transmissions. 
         [0007]    A possible example of trigger frame  22  is shown in  FIG. 3 . As represented, trigger frame  22  may comprise an IEEE 802.11 frame header  30 , followed by a block of common data  31 . This data may provide parameters such as TXOP duration and buffer state information that is required by all clients wishing to send upstream data. Following common data block  31 , individual client information blocks  32 ,  33  may encode per-client data. The per-client data may indicate the specific client that is required to transmit upstream data at a specified time after the receipt of this trigger frame, as well as any client-specific parameters or control information that may be needed. Finally, a standard IEEE 802.11 frame trailer  34  may be located at the end of the trigger frame. 
         [0008]    It will be apparent from  FIG. 2  that a significant improvement in efficiency is obtained by the use of OFDMA in the upstream direction. Instead of each client having to transmit its PPDU individually, and also insert SIFS and DIFS spacings between the various PPDUs, it is possible for the clients to concurrently use the same radio channel to send all their PPDUs at the same time. Also, the AP can transmit a single Acknowledgement packet  25  concurrently acknowledging receipt of the four PPDUs to all four clients in one frame, further improving the efficiency and eliminating much of the delays due to the SIFS gaps. 
         [0009]    However, the use of trigger frame  22  still has some significant limitations on efficiency. According to the IEEE 802.11 protocol, the AP must wait for at least a DIFS time before attempting to regain the medium after the clients return their Acknowledgement frames  6 ,  7 ,  8 ,  9 . Further, the transmission of trigger frame  22  has its own overhead in terms of a PLOP header, and the transmission of the OFDMA frames by the clients cannot occur until at least a SIFS time after the trigger frame is received. When a large number of frame exchanges are occurring over a relatively short period, as would be common for high-bandwidth exchanges between the AP and its clients, these overheads can become substantial, resulting in a significant drop in efficiency and a reduction in usable channel capacity. The known prior art therefore suffers from serious shortcomings with regard to attaining the best efficiency for OFDMA operations. There is hence a need for improved wireless data communication test systems and methods. A system that is capable of reducing the overhead of trigger frames is desirable. 
       SUMMARY 
       [0010]    One aspect of the subject matter described herein includes a method for communicating trigger information for time overlapping multiple access uplink wireless communications. The method includes steps performed at a wireless access point including at least one processor. The method includes generating trigger information for triggering clients to transmit uplink data units with overlapping timing to the wireless access point over a multiple access wireless medium. The method further includes generating downlink data units and inserting the trigger information in the downlink data units. The method further includes transmitting the downlink data units including the trigger information to the clients over the multiple access wireless medium. The method further includes receiving the uplink data units transmitted by the clients over the multiple access wireless medium with overlapping timing determined using the trigger information. 
         [0011]    As used herein, the term “uplink data units” refers to frames to be transmitted from client devices to a wireless access point over the air interface. The term “downlink data units” refers to frames to be transmitted from a wireless access point to one or more clients over the air interface. 
         [0012]    According to another aspect of the subject matter described herein, A system for communicating trigger information for time overlapping multiple access uplink wireless communications is provided. The system includes a wireless access point. The wireless access point includes at least one processor. The wireless access point includes a trigger information generator implemented by the at least one processor for generating trigger information for triggering clients to transmit uplink data units with overlapping timing to the wireless access point over a multiple access wireless medium. The wireless access point includes a downlink data unit generator for generating downlink data units and inserting the trigger information in the downlink data units. The wireless access point further includes a wireless transceiver for transmitting the downlink data units including the trigger information to the clients over the multiple access wireless medium and for receiving the uplink data units transmitted by the clients over the multiple access wireless medium with overlapping timing determined using the trigger information. 
         [0013]    The subject matter described herein can be implemented in software in combination with hardware and/or firmware. For example, the subject matter described herein can be implemented in software executed by a processor. In one exemplary implementation, the subject matter described herein can be implemented using a non-transitory computer readable medium having stored thereon computer executable instructions that when executed by the processor of a computer control the computer to perform steps. Exemplary computer readable media suitable for implementing the subject matter described herein include non-transitory computer-readable media, such as disk memory devices, chip memory devices, programmable logic devices, and application specific integrated circuits. In addition, a computer readable medium that implements the subject matter described herein may be located on a single device or computing platform or may be distributed across multiple devices or computing platforms. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1 —representative packet exchange sequence for an exemplary MU-MIMO downstream and upstream transmission. 
           [0015]      FIG. 2 —representative packet exchange sequence for an exemplary MU-MIMO downstream and OFDMA upstream transmission. 
           [0016]      FIG. 3 —representative example of a possible trigger frame used to trigger one or more clients to perform an OFDMA upstream transmission. 
           [0017]      FIG. 4 —packet exchange sequence for an OFDMA upstream transmission where the trigger information is integrated into the trailer of the downstream data frame. 
           [0018]      FIG. 5 —representative example of a trigger information element used as trigger information integrated into the downstream data frame. 
           [0019]      FIG. 6 —packet exchange sequence for an OFDMA upstream transmission where the trigger information is integrated into the PLOP header of the downstream data frame. 
           [0020]      FIG. 7 —block diagram of system for trigger information exchange for multiple access wireless communications according to an embodiment of the subject matter described herein. 
           [0021]      FIG. 8 —flow chart of process for trigger information exchange for multiple access wireless communications according to an embodiment of the subject matter described herein. 
       
    
    
       [0022]    Note that like reference numbers are used to identify like elements illustrated in the different drawings. 
       DETAILED DESCRIPTION 
       [0023]      FIG. 4  shows an illustrative depiction of a frame exchange sequence wherein the downstream data transferred from the AP to four clients is performed using MU-MIMO and the upstream data transferred from four clients to the AP is performed using OFDMA. As shown, the downstream data frame set begins with PLOP header  20  followed by four data PPDUs  1 ,  2 ,  3 ,  4 , each padded out to the same transmission duration by padding  5 . Padding  5  is then followed by trigger information element  40 , which triggers a subsequent upstream transmission by some selected set of clients. After the downstream data transmission by the AP has terminated, the target clients wait for a SIFS time and return their Acknowledgements  6 ,  7 ,  8 ,  9 . In response to trigger information  40 , the selected clients transmit OFDMA PPDUs  10 ,  11 ,  12 ,  13  to the AP a SIFS time after the last Acknowledgement, including padding  24 . Another SIFS time after the upstream frame transmission completes, the AP returns a composite Acknowledgement for all upstream PPDUs as frame  25 , thereby terminating the handshake. 
         [0024]    Trigger information element  40  in  FIG. 4  comprises one or more symbols encoding trigger data that are placed within the downstream MU-MIMO frame by the AP. The trigger information element performs the same synchronization and control parameter notification that trigger frame  22  in  FIG. 2  performs. Synchronization is achieved by encoding data that instructs all of the clients selected for upstream data transfer to begin their transmissions at a predetermined time relative to the start of trigger information element  40 . As all clients receive and decode the trigger information element, all of the selected clients are able to synchronize their transmissions precisely relative to each other. Further, trigger information element  40  can be encoded with all of the necessary information such as TXOP duration and client selection that was previously encoded by trigger frame  22  in  FIG. 2 . Therefore, the arrangement of  FIG. 4  accomplishes the same functions as that of  FIG. 2 . 
         [0025]    The transmission of trigger information element  40  in  FIG. 4  clearly incurs much less overhead than the transmission of an entirely separate trigger frame as in  FIG. 2 . For example, the AP is not required to transmit the trigger data as an entirely separate frame, thereby avoiding the need to wait for a DIFS time period and potentially losing control of the medium to another 802.11 device. Also, the trigger frame contains its own PLOP header, and there must be a gap of at least one SIFS time between the trigger frame and the succeeding data frames. All of these overhead items are eliminated by the transmission of trigger information element  40  as part of a preceding downstream data frame, rather than as a separate trigger frame  22 . Clearly this can result in a substantially enhanced data throughput and increased channel utilization. 
         [0026]      FIG. 5  shows a possible format for trigger information element  40  of  FIG. 4 . As seen, it may consist of a common data block  50  and one or more per-client blocks  51 ,  52 . These correspond to common data block  31  and per-client information blocks  32 ,  33  of  FIG. 3 ; however, as this is an information element within a frame and not a separate frame, there is no requirement for a frame header or frame trailer. Again, common data block  50  encodes information such as TXOP duration that is required by all clients, and per-client data blocks  51 ,  52  encode client-specific transmit control data as well as per-client parameters. 
         [0027]      FIG. 6  depicts an alternative method of transmitting trigger data from the AP to the clients. In this case, trigger information element  40 , again comprising one or more symbols encoding trigger data, immediately succeeds the PLOP header  20  of a preceding downstream MU-MIMO data frame set. Four data PPDUs  1 ,  2 ,  3 ,  4  then succeed trigger information element  40 , conveying downstream data to some set of clients. Again, these data PPDUs are padded out to the same length by padding  5 , and are followed by Acknowledgements  6 ,  7 ,  8 ,  9  from the recipient clients. One SIFS time following the last Acknowledgement frame  9 , the set of clients selected to perform upstream data transfer by trigger information element  40  transmit their OFDMA PPDUs  10 ,  11 ,  12 ,  13 , padded as usual to the same length by padding  24 , after which the AP returns a composite Acknowledgement  25 . 
         [0028]    The method of  FIG. 6  has certain advantages over that of  FIG. 4 , in that trigger information element  40  (which is intended to be received and processed by all clients which are associated to the AP) is received earlier. It is therefore possible for clients to decode the data in trigger information element  40  sooner, and as a result make the determination of whether they are required to transmit an upstream frame in a succeeding OFDMA data burst much earlier. Clients that are not selected for upstream transmissions may then enter sleep mode or otherwise resort to power-saving measures, instead of having to receive and decode the entire downstream set of PPDUs  1 ,  2 ,  3 ,  4  in order to extract and process a trigger information element at the end of the set. This may increase battery life for battery-powered clients, and may also reduce the average amount of processing power required in a busy network. 
         [0029]      FIG. 7  is a block diagram illustrating an exemplary system for communicating trigger information for multiple access uplink wireless communications according to an embodiment of the subject matter described herein. Referring to  FIG. 7 , a wireless access point  700  communicates with a plurality of clients  702  over a multiple access wireless medium. In one embodiment, wireless access point  700  is an MU-MIMO wireless access point that uses orthogonal frequency division multiple access (OFDMA) communications to communicate with clients  702 . Clients  702  may be any suitable devices that can receive and decode the MU-MIMO OFDMA communications from access point  700 . For example, clients  702  may be mobile handsets, tablet or laptop computers, or any other device with MU-MIMO OFDMA communications capabilities. 
         [0030]    In the illustrated example, wireless access point  700  includes a processor  704  and a memory  706 . Processor  704  may be a general purpose micro-processor or the processing engine of a special purpose ASIC or FPGA. Similarly, memory  706  may be stand alone RAM and/or ROM or on-chip memory. Wireless access point  700  includes a downlink data unit generator  708  that generates the downlink data units to be transmitted to clients  702 . Downlink data unit generator  708  may generate the PPDUs illustrated in  FIGS. 4 and 6 . Wireless access point  700  also includes a trigger information generator  710  for generating the trigger information to be inserted in the downlink data units. Wireless access point  700  further includes a wireless transceiver  712  for transmitting the downlink data units, including the trigger information, to clients  702 . Wireless transceiver  712  also receives time overlapping uplink data units with timing specified by the trigger information from clients  702 . 
         [0031]      FIG. 8  is a flow chart illustrating an exemplary process for communicating trigger information for multiple access uplink wireless communications according to an embodiment of the subject matter described herein. Referring to  FIG. 8 , step  800 , a wireless access point generates trigger information for triggering clients to transmit uplink data units with overlapping timing to the wireless access point. For example, trigger information generator  710  illustrated in  FIG. 7  may generate trigger information, as illustrated in  FIG. 5 , for triggering clients  702  to communicate PPDUs  1 - 4  to access point  700  with overlapping timing, as described above. 
         [0032]    In step  802 , the wireless access point generates downlink data units and inserts the trigger information in the downlink data units. For example, downlink data unit generator  708  may generate PPDUs  1 ,  2 ,  3 , and  4  to be transmitted to clients  702 . Downlink data unit generator  708  may insert the trigger information in the downlink data units, for example, at the end of the data units, as illustrated in  FIG. 4  or at the beginning of the data units, as illustrated in  FIG. 6 . 
         [0033]    In step  804 , the downlink data units including the trigger information are transmitted to the clients over the multiple access wireless medium. For example, wireless transceiver  712  illustrated in  FIG. 7  may transmit PPDUs  1 - 4  with the trigger information, as illustrated in  FIG. 4  or  FIG. 6  to clients  702 . 
         [0034]    In step  806 , uplink data units are received from the clients over the multiple access wireless medium with overlapping timings determined using the trigger information. For example, wireless transceiver  712  may receive PPDUs  10 ,  11 ,  12 , and  13  transmitted over the wireless medium with overlapping timings, as illustrated in  FIG. 4  or  FIG. 6 . 
         [0035]    Thus, by triggering clients to transmit uplink data units over a multiple access communications medium with overlapping timings, the trigger information generator described herein improves the utilization of the multiple access wireless medium by increasing throughput in uplink communications. Such increase throughput increases the efficiency of OFDMA communications, by allowing more information to be transmitted in the uplink direction per unit time. Other embodiments and applications of this arrangement may be apparent to persons skilled in the art. 
         [0036]    It will be understood that various details of the subject matter described herein may be changed without departing from the scope of the subject matter described herein. Furthermore, the foregoing description is for the purpose of illustration only, and not for the purpose of limitation, as the subject matter described herein is defined by the claims as set forth hereinafter.