Patent Document

[0001]    This application is a continuation of U.S. patent application Ser. No. 12/842,239, filed on Jul. 23, 2010, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    Embodiments pertain to wireless communications including wireless-fidelity (WiFi) communications. Some embodiments relate to multi-user multiple-input multiple-output (MU-MIMO) communications. Some embodiments pertain to MU-MIMO systems that use a downlink space-division multiple access (DL-SDMA) technique. Some embodiments pertain to MU-MIMO systems that operate in accordance with one of the IEEE 802.11 standards, such as the 802.11ac standard. 
       BACKGROUND 
       [0003]    MU-MIMO systems use multiple spatial channels to transmit and receive signals to/from multiple stations at the same time using two or more antennas. In a MU-MIMO system, the signals for the different stations are precoded for transmission on different spatial channels, allowing the stations to separate out the data intended for a particular station. One issue with MU-MIMO systems is managing and maintaining groups of stations. 
         [0004]    Thus there are general needs for access points configured for station group management and methods for managing station-management groups. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]      FIG. 1  illustrates a basic service set (BSS) in accordance with some embodiments; 
           [0006]      FIG. 2A  illustrates the frame format of a group allocation message configured for explicit deletion of station-management groups in accordance with some embodiments; 
           [0007]      FIG. 2B  illustrates the frame format of a group deletion message in accordance with some embodiments; 
           [0008]      FIG. 2C  illustrates a DL MU-MIMO transmission in accordance with some embodiments; 
           [0009]      FIG. 3  is a state diagram for an access point configured for explicit deletion of station-management groups in accordance with some embodiments; 
           [0010]      FIG. 4  is a state diagram for a station configured for explicit deletion of station-management groups in accordance with some embodiments; 
           [0011]      FIG. 5  illustrates the frame format of a group allocation message configured for implicit deletion of station-management groups in accordance with some embodiments; 
           [0012]      FIG. 6  is a state diagram for an access point configured for implicit deletion of station-management groups in accordance with some embodiments; and 
           [0013]      FIG. 7  is a state diagram for a station configured for implicit deletion of station-management groups in accordance with some embodiments. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The following description and the drawings sufficiently illustrate specific embodiments to enable those skilled in the art to practice them. Other embodiments may incorporate structural, logical, electrical, process, and other changes. Portions and features of some embodiments may be included in, or substituted for, those of other embodiments. Embodiments set forth in the claims encompass all available equivalents of those claims. 
         [0015]      FIG. 1  illustrates a basic service set (BSS) in accordance with some embodiments. BSS  100  includes an access point (AP)  102  and a plurality of associated communication stations (STA)  104 . In accordance with embodiments, the access point  102  is configured to transmit data frames to the stations  104  that are part of a station-management group using a MU-MIMO technique. As described in more detail below, the access point  102  may establish, maintain and delete one or more station-management groups, such as station-management group  105  and station-management group  115 , within the BSS  100 . Stations  104  may also maintain non-interfering peer link groups with peer-to-peer links  107 . 
         [0016]    As illustrated in  FIG. 1 , the access point  102  is configured to transmit data frames  103  to the stations  104  that are part of station-management group  105  using a MU-MIMO technique. The access point  102  may also be configured to transmit data frames  113  to the stations  104  that are part of station-management group  115  using a MU-MIMO technique. Data frames  103  transmitted to the stations  104  of the station-management group  105 , and data frames  113  transmitted to the stations  104  of the station-management group  115  may be referred to as downlink (DL) MU-MIMO transmissions, which are described in more detail below. 
         [0017]    In accordance with embodiments, the access point  102  may select stations  104  for a station-management group  105  and transmit a group allocation message to the selected stations  104 . The access point  102  may also establish a station-management group  105  that includes stations  104  from which response frames were received. A response frame may be an acknowledge (ACK) frame or a frame that includes channel-state information (CSI) feedback. While the station-management group  105  is established, the access point  102  may transmit data frames  103  to the stations  104  of the station-management group  105  using a MU-MIMO technique. 
         [0018]    The access point  102  may also either explicitly delete a station  104  from the station-management group  105  by transmitting a group deletion message to the station  104 , or implicitly delete a station  104  from the station-management group  105  by refraining from transmitting DL MU-MIMO transmissions or group update messages to the station  104 . These embodiments are described in more detail below. 
         [0019]    The access point  102  and the stations  104  of BSS  100  may implement a carrier-sense multiple access technique (CSMA) for accessing the wireless medium, such as the carrier-sense multiple access with collision avoidance (CSMA/CA) technique of IEEE 802.11. The access point  102  and the stations  104  may also implement a MU-MIMO technique of IEEE 802.11 
         [0020]    The access point  102  and stations  104  may include several separate functional elements to implement the operations described herein, including a radio transceiver, processing circuitry and memory. One or more of the functional elements may be combined and may be implemented by combinations of software-configured elements, such as processing elements including digital signal processors (DSPs), and/or other hardware elements. For example, some elements may comprise one or more microprocessors, DSPs, application specific integrated circuits (ASICs), radio-frequency integrated circuits (RFICs) and combinations of various hardware and logic circuitry for performing at least the functions described herein. 
         [0021]    In some embodiments, stations  104  may be a fixed or mobile wireless communication device, such a personal digital assistant (PDA), a laptop or portable computer with wireless communication capability, a smart phone, a web tablet, a wireless telephone, a wireless headset, a pager, an instant messaging device, a digital camera, an access point, a television, a medical device (e.g., a heart rate monitor, a blood pressure monitor, etc.), or other device that may receive and/or transmit information wirelessly. 
         [0022]      FIG. 2A  illustrates the frame format of a group allocation message configured for explicit deletion of station-management groups in accordance with some embodiments. The group allocation message  202  may be transmitted by the access point  102  ( FIG. 1 ) to indicate to which of stations  104  ( FIG. 1 ) are selected to be part of a station-management group  105  ( FIG. 1 ). The numbers above each field of the group allocation message  202  may indicate the length of each of the fields in octets. 
         [0023]    In accordance with embodiments, the group allocation message  202  includes a group identification (ID) field  204  within the frame body to identify the station-management group  105  and a plurality of associated identifier (AID) fields  206  to identify the associated IDs of the stations  104  that are being selected for the station-management group  105 . The group allocation message  202  may be transmitted in either a broadcast or a unicast fashion. When transmitted in a broadcast fashion, the receiver address (RA) of the group allocation message  202  is the broadcast address. 
         [0024]    The frame body of the group allocation message  202  may also include a category field and an action field indicating that the message is a group allocation message, and a length field indicating the length of the frame body. 
         [0025]      FIG. 2B  illustrates the frame format of a group deletion message in accordance with some embodiments. The group deletion message  232  may be transmitted by an access point  102  ( FIG. 1 ) to delete an established station-management group  105  ( FIG. 1 ) or to remove one or more stations  104  ( FIG. 1 ) from the established station-management group  105 . The numbers above each field of the group allocation message  232  may indicate the length of each of the fields in octets. When configured to remove one or more stations from a station-management group, the group deletion message  232  may be considered a station deletion message. 
         [0026]    The group deletion message  232  may be addressed to the one or more stations  104  of the station-management group  105  that are to be deleted. The group deletion message  232  may include a group ID field  234  in the frame body to identify the station-management group  105 . The group deletion message  232  may be addressed to the stations being removed from the group using the RA field. 
         [0027]    The frame body of the group deletion message  232  may also include a category field and an action field indicating that the message is a group allocation message, and a length field indicating the length of the frame body. 
         [0028]      FIG. 2C  illustrates a DL MU MIMO transmission in accordance with some embodiments. The DL MU MIMO transmission  240  may be transmitted by an access point to stations that are part of an established station-management group. The DL MU MIMO transmission  240  may correspond to data frames  103  ( FIG. 1 ) that are transmitted in accordance with a MU-MIMO technique to station management group  105  ( FIG. 1 ), or data frames  113  ( FIG. 1 ) that are transmitted in accordance with a MU-MIMO technique to station management group  115  ( FIG. 1 ). The DL MU MIMO transmission  240  may comprise a concurrent transmission of spatially-separated data packets  250  to at least some of the stations  104  of a station-management group. 
         [0029]    As illustrated in  FIG. 2C , the spatially-separated data packets  250  may comprise a plurality of individual data packets, such as data packet  251 , data packet  252  and data packet  253 , transmitted concurrently within the same frequency spectrum. Data packet  251  may be intended for a first station (STAT), data packet  252  may be intended for a second station (STA 2 ) and data packet  253  may be intended for a third station (STA 3 ). Although individual data packets  251 ,  252 ,  253  are separately illustrated in  FIG. 2C , this does not imply that they are transmitted on separate frequency channels. 
         [0030]    In some embodiments, each data packet  250  may be separately precoded for receipt by the receiving stations. These embodiments are described in more detail below. 
         [0031]    The spatially-separated individual data packets  250  may be transmitted concurrently on the same frequency channel, which may comprise the same set of orthogonal frequency division multiplexed (OFDM) frequency subcarriers. Each of the individual data packets  250  may be addressed to and precoded for receipt by one of the stations  104  of the station-management group  105 . In these embodiments, the individual data packets may be transmitted at the same time and each data packet  250  may be transmitted on a different spatial channel. In these embodiments, a DL MU MIMO or a DL SDMA technique may be employed. 
         [0032]    In some embodiments, a single frequency channel may be used to transmit the DL MU MIMO transmission  240 . In some IEEE 802.11embodiments, a primary frequency channel and up to seven secondary frequency channels may be used to transmit the DL MU-MIMO transmissions  240 . Each frequency channel may be a 20-MHZ frequency channel and may use a plurality of OFDM subcarriers. 
         [0033]    The plurality of individual data packets  250  of the DL MU-MIMO transmission  240  may be transmitted as a single frame by the access point  102  in accordance with a CSMA/CA technique. After transmission of the individual data packets  250 , the access point  102  may receive individual acknowledgements  255 , such as block acknowledgements (BA)  255 , from the stations  104  of the station-management group  105 . The acknowledgements  255  may be transmitted by the stations in accordance with a CSMA/CA technique on the same frequency channel in response to receipt of the DL MU-MIMO transmission  240 . Although block acknowledgements  255  are illustrated in  FIG. 2C , this does not imply that they are transmitted on different frequency channels. 
         [0034]    A DL MU-MIMO transmission  240  may be a single frame that may include, among other things, one or more training fields and one or more signaling fields. A DL MU-MIMO transmission  240  may be configured in accordance with an IEEE 802.11 standard. 
         [0035]      FIG. 3  is a state diagram for an access point configured for explicit deletion of station-management groups in accordance with some embodiments. An access point, such as access point  102  ( FIG. 1 ), may operate in accordance with state diagram  300 . During idle state  301 , the access point  102  is idle with respect to station group management activities. After transmitting a group allocation message, such as group allocation message  202  ( FIG. 2A ), to selected stations  104  ( FIG. 1 ), the access point  102  may enter the group setup wait state  302 . When response frames are received from one or more of the selected stations  104 , the access point  102  may establish a station-management group  105  to include stations  104  from which response frames are received and enter the established state  304 . While in the established state  304 , the access point  102  may transmit a DL MU-MIMO transmission  240  to the stations  104  of the established station-management group  105  using a MU-MIMO technique. While in the established state  304 , the access point  102  may explicitly delete the station-management group  105  by transmitting a group deletion message  232  ( FIG. 2B ) or a station deletion message and enter the deletion wait state  306 . During the deletion wait state  306 , the access point  102  may wait for stations to acknowledge receipt of the group deletion message  232 . After all stations  104  are deleted from the station-management group  105  or a retry limit is reached, the access point  102  may return to the idle state  301 . 
         [0036]    As illustrated in state diagram  300 , the access point  102  may return to the idle state  301  from the group setup wait state  302  when no response frames are received from any of the selected stations  104  within a predetermined period of time. The access point  102  may also retry sending a station deletion message while in the deletion wait state  306  and return to the established state  304  if there is station remaining in the group. 
         [0037]      FIG. 4  is a state diagram for a station configured for explicit deletion of station-management groups in accordance with some embodiments. A communication station, such as one of communication stations  104  ( FIG. 1 ), may operate in accordance with state diagram  400 . During idle state  402 , the communication station  104  may receive a group allocation message  202  ( FIG. 2A ) from an access point  102  ( FIG. 1 ) and enter group setup wait state  404 . In response to the group allocation message  202 , the communication station  104  may send a response frame, such as an ACK frame or a frame that includes CSI feedback, to indicate that it will join a station-management group  105  ( FIG. 1 ) indicated in the group allocation message  202  and enter the established state  406 . During the established state  406 , the communication station  104  is a member of the station-management group  105  and may receive DL MU-MIMO transmission  240  (FIG.  2 C) from the access point  102 . In these explicit group deletion embodiments, the communication station  104  may remain in the established state  406  until it receives a group deletion message from the access point. 
         [0038]      FIG. 5  illustrates the frame format of a group allocation message configured for implicit deletion of station-management groups in accordance with some embodiments. The group allocation message  502  may be transmitted by the access point  102  ( FIG. 1 ) to stations  104  ( FIG. 1 ) that are selected to be part of a station-management group  105  ( FIG. 1 ). The numbers above each field of the group allocation message  502  may indicate the length of each of the fields in octets. 
         [0039]    In accordance with embodiments, the group allocation message  502  includes a group ID field  504  within the frame body to identify the station-management group  105  and a plurality of AID fields  506  to identify the associated IDs of the stations  104  that are being selected for the station-management group  105 . The frame body of the group allocation message  502  may also include a timeout field  514  to indicate a maximum duration of group membership. In these embodiments, the access point  102  will automatically delete the station-management group when no group update messages or no DL MU-MIMO transmissions  240  are sent after the predetermined period of time indicated in timeout field  514  to the stations of the established station-management group  105 . These embodiments are discussed in more detail below. In some embodiments, timeout field  514  may indicate a timeout interval in milliseconds. 
         [0040]    The frame body of the group allocation message  502  may also include a category field indicating that the message is a group allocation message configured for implicit group deletion, an action field, and a length field indicating the length of the frame body. Other fields may be included in the frame body of the group allocation message  502 , group allocation message  202  ( FIG. 2A ), and group deletion message  232  ( FIG. 2B ). 
         [0041]    In these embodiments, station-management groups may be established for time periods ranging from 10 milliseconds to a much longer period such as hours. The establishment and reestablishment of station-management groups in both the explicit group deletion and implicit group deletion embodiments allows an access point to dynamically update and change members of a station-management group based on, among other things, traffic patterns of the individual stations and changing channel conditions. 
         [0042]      FIG. 6  is a state diagram for an access point configured for implicit deletion of station-management groups in accordance with some embodiments. An access point, such as access point  102  ( FIG. 1 ) may operate in accordance with state diagram  600 . During idle state  601 , the access point  102  is idle with respect to station group management activities. After transmitting a group allocation message, such as group allocation message  502  ( FIG. 5 ), to selected stations  104  ( FIG. 1 ), the access point  102  may enter the group setup wait state  602 . When response frames are received from one or more of the selected stations  104 , the access point  102  may establish the station-management group  105  to include stations  104  from which response frames are received and enter the established state  604  and establish a station-management group  105  ( FIG. 1 ). While in the established state  604 , the access point  102  may transmit a DL MU-MIMO transmission  240  ( FIG. 2C ) to the stations  104  of the station-management group  105 . While in the established state  604 , the access point  102  may implicitly delete the station-management group  105  by refraining from transmitting DL MU-MIMO transmissions  240  or group update messages to the stations  104  of the established station-management group  105  after a predetermined period of time indicated in timeout field  514  ( FIG. 5 ) and return to idle state  601 . While in the established state  604 , the access point  102  may enter maintenance wait state  606  while waiting for acknowledgement frames or CSI feedback from stations  104  in response to a DL MU-MIMO transmission  240 . Data packets may be retransmitted when acknowledgements are not received in accordance with conventional techniques. 
         [0043]    As illustrated in state diagram  600 , the access point  102  may return to the idle state  601  from the group setup wait state  602  when no response frames are received from any of the selected stations  104  within a predetermined period of time. The access point  102  may also return to the idle state  601  after a predetermined period of time after a retry limit is reached for stations that do not respond with to the a DL MU-MIMO transmission  240 . 
         [0044]      FIG. 7  is a state diagram for a communication station configured for implicit deletion of station-management groups in accordance with some embodiments. A communication station, such as one of communication stations  104  ( FIG. 1 ), may operate in accordance with state diagram  700 . During idle state  702 , the communication station  104  may receive a group allocation message  502  ( FIG. 5 ) from an access point  102  ( FIG. 1 ) and enter group setup wait state  704 . In response to the group allocation message  502 , the communication station  104  may send a response frame, such as an ACK frame or a frame including CSI feedback, to indicate that it will join the indicated station-management group and enter the established state  706 . During the established state  706 , the communication station  104  may receive DL MU-MIMO transmissions  240  ( FIG. 2C ) from the access point  102 . The communication station  104  may remain in the established state  706  until it no longer receives any DL MU-MIMO transmissions  240  or group update messages for the predetermined period of time indicated in timeout field  514  ( FIG. 5 ) of the group allocation message  502 . 
         [0045]    Referring to  FIGS. 1 ,  2 A,  2 B,  2 C, and  5  as discussed above, the access point  102  is configured to set up and manage one or more station-management groups  105  by transmitting a group allocation message to selected stations  104 . Group allocation message  202  ( FIG. 2A ) may be transmitted when the access point  102  employs explicit group deletion, and group allocation message  502  ( FIG. 5 ) may be transmitted when the access point  102  employs implicit group deletion. The access point  102  may establish the station-management group  105  to include stations from which response frames are received. The access point  102  may transmit DL MU-MIMO transmissions  240  to the stations of the station-management group  105  using a MU-MIMO technique. The access point  102  may either explicitly delete the station-management group by transmitting a group deletion message  232  to the stations of the group or implicitly delete the station-management group by refraining from transmitting DL MU-MIMO transmissions  240  or group update messages to the stations of the group for a predetermined period of time. In some embodiments, the access point  102  may concurrently establish more than one station-management group. 
         [0046]    In some embodiments, the response frames are transmitted by at least some of the selected stations  104  in response to receipt of a group allocation message  202  or  502 , and the access point  102  establishes the station-management group  105  to include stations  104  from which response frames are received within a predetermined period of time. In these embodiments, the response frames are acknowledge frames, and all stations that receive a group allocation message send back an acknowledge frame. Based on the receipt of acknowledge frames, the access point  102  may decide which of the stations to include in the station management group. 
         [0047]    In some embodiments, the access point  102  may attempt to establish a station-management group  105  within a predetermined period of time. During this period of time, the access point  102  may transmit one or more group allocation messages to selected stations  104 . Stations  104  that respond within this period of time may become part of the indicated station-management group  105 . 
         [0048]    In some embodiments, the access point  102  may explicitly delete one or more stations  104  from the established station-management group  105  by transmitting a group deletion message  232  to one or more of the stations  104  of the established station-management group  105 . In some embodiments, the access point  102  may implicitly delete one or more stations  104  from an established station-management group  105  by refraining from transmitting a DL MU-MIMO transmission  240  or group update messages to one or more stations  104  for a predetermined period of time. Stations  104  that are deleted from the station-management group may be deleted from a memory of the access point  102  that identifies stations currently part of a station-management group. 
         [0049]    When the access point  102  is configured for implicit group deletion, no explicit messages need to be transmitted to the stations  104  of an established station-management group  105  to indicate that stations are being removed or the station-management group  105  is being deleted. The stations of the station-management group  105  are automatically deleted as discussed above by refraining from transmitting DL MU-MIMO transmissions  240  or group update messages for a predetermined period of time. 
         [0050]    When the access point  102  is configured for explicit deletion, stations  104  may respond to the group deletion message  232  with an acknowledgement frame. These responding stations  104  may be deleted from the station-management group  105  after the acknowledgement frame is received by the access point  102 . 
         [0051]    As discussed above, a DL MU-MIMO transmission  240  may comprise a concurrent transmission of spatially-separated data packets  250  to at least some of the stations  104  of the station management group  105  employing a DL MU MIMO or DL SDMA technique. In some embodiments, beamforming may be employed by the access point  102  as well as the stations  104  for transmitting and receiving. In some embodiments, a station-management group may be a DL SDMA group when an SDMA technique is used to transmit DL MU-MIMO transmissions  240 . 
         [0052]    In embodiments that employ DL-SDMA, the individual data packets  251 ,  252 , and  253  may be precoded based on a CSI matrix for the stations  104  of the station-management group  105 . In these embodiments, the precoding matrix may be generated from the CSI for each station  104 , and the precoding matrix may be used to precode the individual data packets for concurrent transmission within a DL MU-MIMO transmission  240 . The stations  104  include processing circuitry to separate their packet from packets intended for other stations based on the station&#39;s CSI or the CSI matrix. In some of these embodiments, the group allocation message  202  may be used as a sounding frame by the stations  104  to determine their CSI. 
         [0053]    The access point  102  may be configured to select stations  104  for the station-management group  105  based on the CSI of the stations  104  associated with the access point within the BSS  100 . Stations  104  having a greatest difference between their CSI&#39;s may be selected for a station-management group  105 , although this is not a requirement. In these embodiments, the greater difference in CSI&#39;s between stations  104  of a station-management group  105  may provide for a greater spatial channel separation by precoding, making it easier for a station  104  to separate out its data packet from the other data packets within a DL MU-MIMO transmission  240 . In some embodiments, based on interfering patterns of different peer-to-peer links  107  between peer stations  104 , the access point  102  may select stations  104  for different station-management groups  105  and  115  so that peer-to-peer links  107  within a group can be used to communicate simultaneously without causing interference to each other&#39;s directional transmissions. Although  FIG. 1  illustrates stations  104  of station-management group  105  being located together and stations of station-management group  115  being located together, this may not be the case when stations  104  are selected for a station-management group based on their CSI. 
         [0054]    In some embodiments, when the access point  102  has buffered traffic for a station  104  after the station  104  is removed from a station-management group  105  (either explicitly or implicitly), the access point  102  may transmit the buffered traffic as unicast traffic to the station rather than transmitting the traffic as part of a DL MU-MIMO transmission  240 . 
         [0055]    In some embodiments, a station  104  may be removed from a group if the station&#39;s CSI has changed (e.g., if the CSI of the station  104  is not sufficiently different from the CSI of other stations to allow for sufficient signal separation by precoding) or if there has been no traffic for the station  104 . 
         [0056]    The Abstract is provided to comply with 37 C.F.R. Section 1.72(b) requiring an abstract that will allow the reader to ascertain the nature and gist of the technical disclosure. It is submitted with the understanding that it will not be used to limit or interpret the scope or meaning of the claims. The following claims are hereby incorporated into the detailed description, with each claim standing on its own as a separate embodiment.

Technology Category: h