Abstract:
A wireless, specifically VHT, system that includes APs and STAs can power save during the TXOP. The AP in the system announces whether STAs in the system do SU or MU TXOP power save in a Beacon/Probe Response, and the STAs in the system transmit to the AP whether the STA is capable and willing to save power during a SU, MU, or SU+MU TXOP. For the AP, the process further involves buffering data frames for STAs that have entered doze mode until the end of TXOP. The AP further transmits to STAs a duration of TXOP in the Duration field of a RTS frame. The STA can inform the AP to enter TXOP PM mode in a bit in the HT Control field.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates, in general, to power saving in a wireless system, and, more particularly, to power saving during a transmit opportunity (TXOP) for very high throughput (VHT) or other wireless devices. 
         [0003]    2. Relevant Background 
         [0004]    There is a further need to save power for wireless and VHT devices. 
       SUMMARY OF THE INVENTION 
       [0005]    Briefly stated, the present invention involves controlling an awake or doze state of wireless and VHT devices during the TXOP. 
         [0006]    According to an embodiment of the invention, a method of power saving for an access point (AP) comprises deciding if power saving is allowed in a TXOP with any combination of DL MU-MIMO and SU-MIMO transmission, and if yes, sending buffered frames indicating TXOP power saving in the TXOP to stations that are not in doze state, and checking if there is no further buffered frames to the first station (STA) that is not in doze state, and if yes, sending buffered frames to a first station (STA) in a first remaining TXOP by setting “More Data” to ‘0’ in a frame to the first STA that is not in doze state, and sending buffered frames to a second STA that is not in doze state in a second remaining TXOP. 
         [0007]    According to another embodiment of the invention, a method of power saving for a non-AP STA comprises checking if a specific TXOP power saving indicating bit in a received frame or PPDU is set such that STAs can do power save during the specific TXOP and going to doze state until the end of the specific TXOP if the STA is not a destination of frames. 
         [0008]    According to another embodiment of the invention, a method of power saving for a non-AP STA comprises checking if a bit in a received frame or PPDU is set such that STAs can do power save during a TXOP and going to doze state until the end of the TXOP if the STA is a destination of frames and there is no more buffered frames with it as the destination. 
         [0009]    According to a further embodiment of the invention, a method of power save for a wireless system comprises, for an AP in the system, announcing whether STAs in the system can do a single user (SU) or multiple user (MU) TXOP power save in a Beacon/Probe Response and for a STA in the system, transmitting to the AP whether the STA is capable and willing to save power during a TXOP with any combination of DL MU-MIMO and SU-MIMO transmission. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows an example of multi-user multiple input and multiple input output (MU-MIMIO) TXOP power save; 
           [0011]      FIG. 2  shows an example of SU-MIMIO TXOP power save according to an embodiment of the invention; 
           [0012]      FIG. 3  shows a method of VHT TXOP power saving for APs according to an embodiment of the invention; and 
           [0013]      FIG. 4  shows a method of VHT TXOP power saving for non-AP STAs according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0014]      FIG. 1  shows an example of MU-MIMIO TXOP power save in the related art. 
         [0015]    During down link (DL) MU TXOP for power save, DL MU-MIMO PW (power save) capable STAs can save power by the following activities: DL MU-MIMO TXOP PW STAs that are not members of a Group ID received in VHT-signal (SIG)-A can save power from the beginning until the end of the DL MU TXOP; DL MU-MIMO TXOP PW STAs that are members of a Group ID received in VHT-signal (SIG)-A can further save power after receiving a frame with NSTS=0 corresponding to it until the end of the DL MU TXOP; and DL MU-MIMO TXOP PW STAs that are members of a Group ID received in VHT-signal (SIG)-A can still further save power after sending a block acknowledgement (BA) for the frame with “More Data” bit=0. 
         [0016]    An AP needs to announce whether or not it allows STAs to do DL MU TXOP power save in Beacon/Probe Response; the “VHT TXOP PS” field, where PS is power save, transmitted by the AP is used for this purpose. However, the AP also needs to know whether a STA is capable and willing to save power during a DL MU-MIMO TXOP. A TXOP Power Management mode is defined in the “VHT TXOP PS” field transmitted by a STA for this purpose. The AP needs to buffer data frames for a STA that has entered doze mode until the end of the DL MU-MIMO TXOP. 
         [0017]    The AP needs to indicate whether or not DL MU-MIMO TXOP PW STAs can power save during the DL MU TXOP. TXOP_PS_NOT_ALLOWED is used for this indication. A STA that is in TXOP PS mode also needs to know the DL MU-MIMO TXOP duration. This can be done by checking the Duration field of the RTS/CTS frames, by requiring Request to Send/Clear to Send (RTS/CTS) exchange at the beginning of a DL MU-MIMO TXOP. 
         [0018]    The “More Data” bit in the frame control field and the N sTS  field in VHT-SIG-A are used to indicate whether data frames are pending in the AP for transmission. More Data=0 indicates no more data frames are to be transmitted to this STA until the end of this TXOP. N STS =0 indicates no data frames will be transmitted to this STA until the end of this TXOP. 
         [0019]    Referring to the MU-MIMIO TXOP power save example in  FIG. 1 , STA 1 -STA 4  are in TXOP PM (power save mode)=1 mode, indicating that STA 1 -STA 4  are willing and capable of power save, and STA 5  and STA 6  are in TXOP PM=0 mode, indicating STA 5  and STA 6  are either unwilling or not capable of power save. The STAs are in various groups: Group ID  1  has STA 1  and STA 2 ; Group ID  2  has STA 5  and STA 2 ; Group ID  3  has STA 6  and STA 5 . 
         [0020]    During frame  1  of a TXOP duration, frame  1  is used by Group ID  1  (GID=1). Therefore, only STA 1  and STA 2  will transmit or receive during this period, and STA 3 -STA 6  are idle. Since STA 3  and STA 4  can do DL MU-MIMO TXOP power save and frame  1  does not involve them, they will go to sleep. STA 1  has More Bit=0, indicating there are no more data frames pending for STA 1  during the TXOP duration, and STA 1  can go to sleep after sending acknowledge of frame  1 . STA 2  has More Bit=1, indicating there are more data frames pending for STA 2  during the TXOP duration, so STA 2  remains active. 
         [0021]    Frame  2  is used by Group ID  2  (GID= 2 ). The More Bit=0 for STA 2 , indicating there are no more data frames pending for STA 2  during the TXOP duration. STA 2  can go to sleep after sending acknowledge of frame  2 . The More Bit does not matter for STA 5  as STA 5  cannot power save. 
         [0022]    Frame  3  is used by STA 5  only as N STS =1,0 (N STS  for STA 5  is not 0, N STS  for STA 6  is 0) for Group ID  3  (GID=3). Frame is used by both STA 5  and STA 6  as N STS =1,1 (N STS  for STA 5  is not 0, N STS  for STA 6  is not 0) for Group ID  3 . After frame  4 , the TXOP duration ends and all TXOP power save STAs, STA 1 -STA 4 , wake up.  FIG. 2  shows an example of SU-MIMIO TXOP power save according to an embodiment of the invention. 
         [0023]    The issue with DL MU-MIMO TXOP power save is that it can only be used in DL MU-MIMO TXOP. In a VHT TXOP, MU-MIMO is an optional feature. Non-MU-MIMO basic service sets (BSSs) cannot benefit from a MU-MIMO TXOP power save. DL MU-MIMO is more complicated than SU MIMO TXOP so VHT STAs may not implement DL MU-MIMO even in a MU-MIMO BSS. When a TXOP is used for SU MIMO and/or MU-MIMO, a STA cannot go to doze until the end of the TXOP. As SU-MIMO is a mandatory feature, more BSSs will benefit from a TXOP power save feature by allowing SU MIMO TXOP power saving. To implement SU MIMO TXOP power saving, DL MU-MIMO TXOP PW signaling needs to be extended. An AP needs to announce whether or not it allows STAs to do TXOP power save in a TXOP with any combination of DL MU-MIMO and SU MIMO transmission in Beacon/Probe Response frame. However, the AP also needs to know whether a STA is capable and willing to save power during a TXOP with any combination of DL MU-MIMO and SU MIMO transmission. The AP needs to buffer data frames for a STA that has entered doze mode until the end of the TXOP with any combination of DL MU-MIMO and SU MIMO transmission. 
         [0024]    Further, in a proposed enhanced TXOP power save, the “More Data” bit in the frame control field can be used to indicate whether data frames are pending in the AP for DL MU-MIMO and/or SU MIMO transmission. More Data=0 indicates no more data frames are to be transmitted to this STA until the end of this TXOP with any combination of DL MU-MIMO and SU MIMO transmission. Further, the N STS  field in VHT-SIG-A of MU-MIMO PPDU can be used to indicate whether data frames are pending in the AP for transmission. N STS =0 indicates no data frames will be transmitted to this MU-MIMO capable STA until the end of this TXOP with any combination of DL MU-MIMO and SU MIMO transmission. 
         [0025]    Referring to the SU-MIMO TXOP power save example in  FIG. 2 , according to an embodiment of the invention, STA 1 -STA 4  are in TXOP PM=1 mode, indicating STA 1 -STA 4  are willing and capable of power save, and STA 5 -STA 6  are in TXOP PM=0 mode, indicating STA 5 -STA 6  are either unwilling or not capable of power save. 
         [0026]    In aggregated media access control protocol data unit  1  (A-MPDU 1 ), STA 1  has More Bit=1 so STA 1  remains active after sending acknowledge of A-MPDU 1 . When STA 2 -STA 4  receive A-MPDU 1 , they can realize that the A-MPDU 1  does not involve them. Since STA 2 -STA 4  are TXOP PM STAs and the AP allows TXOP power saving in the TXOP, STA 2 -STA 4  can go to sleep until the end of the TXOP. STA 5 -STA 6  do not go to sleep since they are active STAs. 
         [0027]    In A-MPDU 2 , STA 1  has More Bit=0 so STA 1  goes to sleep after sending acknowledge of A-MPDU 2 , since STA 1  is TXOP PM STA and the AP will not transmit further frames to it during the remaining TXOP. Similar to A-MPDU 1 , STA 5 -STA 6  do not go to sleep since they are active STAs. A-MPDU 3  and A-MPDU 4  relates to STA 5  and STA 6 . STA 1 -STA 4  wakes up at the end of the TXOP duration. 
         [0028]      FIG. 3  shows a method of VHT TXOP power saving for APs according to an embodiment of the invention. 
         [0029]    In the related art, TXOP power save capable VHT STA during TXOP for power save can save power by the following. If a VHT TXOP PW STA that implements DL MU-MIMO is not a member of the Group of the received A-MPDU as indicated in VHT-SIG-A, it can save power enduring the remaining TXOP. The STA that implements DL MU-MIMO saves power after receiving a frame with NSTS=0 corresponding to it until the end of DL MU TXOP. The VHT TXOP PW STA saves power after sending the BA for the frame with “More Data” bit=0. 
         [0030]    According to an embodiment of the invention, TXOP power save capable VHT STA during TXOP for power save can save power by the following activity. If a VHT TXOP PW STA that implements SU MIMO and/or DL MU-MIMO is not a member of the Group of the received A-MPDU as indicated in VHT-SIG-A, it can save power during the remaining TXOP. A VHT TXOP PW STA that is not the destination of the SU-MIMO frame saves power during the remaining TXOP; if Partial AID in the PHY header of the receiving PPDU (PLCP protocol data unit) is not same as a STA&#39;s Partial AID, the STA is not the destination of the MPDU(s) of the PPDU; if the Partial AID in the PHY header is the same as a STA&#39;s Partial AID but the RA is not the same as STA&#39;s MAC address, the STA is not the destination of the MPDU(s) of the PPDU. The VHT TXOP PW STA that implements SU MIMO and/or DL MU-MIMO saves power after receiving a frame with N STS =0 corresponding to it until the end of DL MU TXOP. The VHT TXOP PW STA saves power after sending the acknowledge for the frame with “More Data” bit=0. 
         [0031]    The AP needs to announce whether or not it allows STAs to do (SU and MU) TXOP power save in Beacon/Probe Response; the “VHT TXOP PS” field in VHT Capabilities IE (Information Element) transmitted by the AP is used for this purpose. Additionally, to give an AP more flexible design, e.g., for buffer management, an AP can select if TXOP power saving is allowed in each individual TXOP with any combination of DL MU-MIMO and SU-MIMO transmission. Therefore, the AP needs to indicate whether or not VHT STAs can be in a doze state during the TXOP with any combination of DL MU-MIMO and SU-MIMO transmission. TXOP_PS_NOT_ALLOWED in PHY header is used for this indication. A STA that is in TXOP PS mode needs to know the TXOP duration. This is done by checking the Duration field of the RTS/CTS frames, and requires RTS/CTS exchange at the beginning of a TXOP with any combination of DL MU-MIMO and SU-MIMO transmission. 
         [0032]    Also, the AP needs to know whether a STA is capable and willing to save power during a TXOP with any combination of DL MU-MIMO and SU MIMO transmission. A TXOP Power Management mode is defined for a STA. One bit “VHT TXOP PS” field in the VHT capabilities IE transmitted by STA can be used. A STA use “VHT TXOP PS” to inform the AP to enter TXOP PM mode. The AP needs to buffer data frames for a STA that has entered doze mode until the end of the TXOP. 
         [0033]    Referring to  FIG. 3 , the VHT TXOP power saving algorithm for APs  300  starts with checking if VHT TXOP power saving is allowed in the TXOP  310 . If no, normal TXOP transmission is performed  311  and process  300  terminates thereafter. If yes, the process checks if an acknowledge frame is received from an STA  320 . If yes, the process checks if “More Data” is set to 0 in the acknowledged frame  330 . If yes, the process labels the STA being in doze state in the remaining TXOP  331  then stops; if no, process  300  stops. 
         [0034]    If the process gets no in  320 , the process checks if there are frame(s) to send  340 . If no, process  300  stops. If yes, a bit in transmitted frames is set to indicate that TXOP PW STAs can go to sleep during the TXOP  341 . Then the process fetches a frame from its buffer and obtains the frame&#39;s receiver address (RA)  350 . Then the process checks if the STA identified by RA is in doze state in the remaining TXOP  360 . If yes, the process puts the frame to the buffer  361 , then fetches a frame from its buffer and get the frame&#39;s receiver address (RA)  350 . If no, the process checks if the frame is the last one to the STA identified by RA  370 . If yes, the process sets “More Data” indication of the frame to 0  371 . The process then checks if there are enough frames for the transmission  380 . If no, the process fetches a frame from its buffer and gets the frame&#39;s receiver address (RA)  350 . If yes, the process labels the TXOP PW STA as a member of a DL MU transmission to be in doze state in the remaining TXOP if there are no frames for it  381 . Then the process labels the TXOP PW STA to be in doze state in the remaining TXOP if the STA is not the receiver of the selected frames  382 . The process sends the frames out  391 , and process  300  terminates. 
         [0035]      FIG. 4  shows a method of VHT TXOP power saving for non-AP STAs according to an embodiment of the invention. 
         [0036]    Referring to  FIG. 4 , a VHT TXOP power saving algorithm for non-APs  400  starts with checking if a bit in received frame/PPDU is set such that STAs can do a power save during the TXOP  410 . If no, normal TXOP reception is performed  450  and process  400  terminates. If yes, the process checks if the TXOP PW STA is the destination (receiver) of the frame(s)  420 . If no, the process goes to a doze state until the end of the TXOP  450 . If yes, the process sends acknowledge to the AP  421  then checks if the received frame is for the TXOP PW STA and “More Data” is set to ‘0’  430 . If yes, the process goes to a doze state until the end of the TXOP  450 . If no, check if N STS  in the received PPDU for the TXOP PW STA is set to ‘0’  440 . If yes, the process goes to a doze state until the end of the TXOP  450 . If no, the process stops. 
         [0037]    Although the invention has been described and illustrated with a certain degree of particularity, it is understood that the present disclosure has been made only by way of example, and that numerous changes in the combination and arrangement of parts can be resorted to by those skilled in the art without departing from the spirit and scope of the invention, as hereinafter claimed.