Abstract:
This invention relates to switching power saving modes and rescheduling communication frames for various periods of a beacon interval (BI) defined under WGA Draft Specification 0.8 for the personal basic service set (PBSS) and infrastructure BSS to achieve further power savings and other advantages. Stations can be awake during a contention-based period (CBP) if it is in active state and can schedule frames during a service period (SP) to allow the assigned receiver to transmit to the assigned initiator. Stations in a group can schedule a group address frame to be sent during the CBP and group SP of a specific periodic BI. Stations in peer-to-peer connection may directly notify its peer stations of its power saving mode and wakeup schedule. Stations of an infrastructure basic service set (BSS) can also use the same power saving mechanism as stations of a PBSS noting a difference where each BI will be an access point&#39;s (AP&#39;s) awake BI.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method of saving power in wireless network devices, and more specifically, to a method of transmitting frames and switching the power saving mode of WGA network devices. 
     BACKGROUND OF THE INVENTION 
     The Wireless Gigabit Alliance (WGA) Draft Specification 0.8 (WGA-D08), January 2010, herein incorporated by reference, defines modifications to both the 802.11 physical layers (PHY) and the 802.11 Medium Access Control Layer (MAC) to enable operation in the 60 GHz frequency bank (mmWave) for very high throughput wireless networks. 
     The personal basic service set (PBSS) is a self-contained network which includes one PBSS control point (PCP) and other stations (STAs). Wireless communication is possible to all member STAs of the PBSS. The infrastructure BSS is a network which includes one access point (AP) and set of stations (STAs) that have successfully synchronized with the AP using the JOIN service primitives and one STA that has used the START primitive. Membership in a BSS does not imply that wireless communication with all other members of the BSS is possible. An AP in BSS serves as gateway to access another network, e.g., the Internet. 
     Section 9.23 of WGA-D08 defines the mmWave channel access. Channel access by a mmWave station (mSTA) during the Beacon Intervals (BI) and is coordinated by a schedule. The schedule of the data transfer time (DTT) of a BI is communicated through the Extended Schedule element in the Announce frame or the mmWave Beacon frame. The Extended Schedule element contains the scheduling information of all allocations in the DTT. 
       FIG. 1  shows an example BI structure as defined in WGA-D08. In a BI, the DTT is an access period during which frame exchanges are performed between STAs. The DTT is comprised of the contention-based access periods (CBPs) and service periods (SPs). SPs are allocated to specific transmitting and receiving STAs, and CBPs are not specifically allocated to any STA. 
     Section 11.2 of WGA-D08 defines power management modes for a wireless device working under mmWave channels. Table 44 lists the various power states for PCP and non-PCP STAs during the various access periods of an Awake BI. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 44 
               
             
             
               
                   
               
               
                 Power management states for an Awake BI 
               
               
                 (selected portions reproduced). 
               
             
          
           
               
                   
                   
                 PS 
               
               
                   
                 PPS 
                 non-PCP 
               
               
                 BI Portion 
                 PCP 
                 STA 
               
               
                   
               
               
                 CBP marked as PCP available in the schedule 
                 Awake 
                 Awake 
               
               
                   
                   
                 Doze 
               
               
                 CBP marked as PCP unavailable in the schedule 
                 Doze 
                 Awake 
               
               
                   
                   
                 Doze 
               
               
                 SP with broadcast AID as Destination AID 
                 Awake 
                 Awake 
               
               
                 Non-truncatable or non-extensible SP with non-PCP 
                 Awake 
                 Awake 
               
               
                 STA (excluding the PS STA) as Source AID and 
                 Doze 
                 Doze 
               
               
                 Destination AID 
               
               
                 Truncatable SP or extensible SP with non-PCP STA 
                 Awake 
                 Awake 
               
               
                 (excluding the PS STA) as Source AID and 
                   
                 Doze 
               
               
                 Destination AID 
               
               
                 SPs allocated to itself 
                 Awake 
                 Awake 
               
               
                 All other SPs 
                 Awake 
                 Awake 
               
               
                   
                 Doze 
                 Doze 
               
               
                   
               
             
          
         
       
     
     However, the power management states are generically defined. There are many inefficiencies when working together with transmitting frames. Thus, there is a need for optimizing the switching of power management modes and transmitting frames. 
     Further, a mSTA may additionally work in an infrastructure BSS beyond the PBSS. An infrastructure BSS contains an AP providing access to another network, e.g., the Internet. All STAs within an infrastructure are required to be associated with the AP. WGA-D08 does not define a power saving mechanism for the infrastructure BSS; therefore, only 802.11 baseline power saving mechanism will be used in 60 GHz infrastructure BSS. Thus, there is a further need to implement a power saving mechanism for mSTAs that can work with both PBSS and 802.11 baseline power saving mechanisms. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method of saving power in wireless network devices by switching power saving modes and transmitting frames of a BI. 
     In one embodiment of the present invention, stations can switch to awake during a CBP. Stations can further eliminate an Announcement Traffic Indication Message (ATIM) frame from the BI. 
     In another embodiment of the present invention, stations in a group can schedule a group address frame to be sent during the CBP and group address SP of an active group BI when all stations in the group are in active mode. 
     In yet another embodiment of the present invention, stations can change the transmission of frames during a SP to allow for the assigned service period receiver to transmit to the assigned service period initiator. 
     In further yet another embodiment of the present invention, stations in peer-to-peer connection can directly notify their peer stations upon switching back to active mode after switching to doze mode of its wakeup schedule and power saving mode. 
     In another embodiment of the present invention, stations of an infrastructure BSS may use the same method of saving power as stations of a PBSS noting a difference where each BI is AP&#39;s awake BI. 
     The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of an embodiment of the invention as illustrated in the accompanying drawings. 
     In addition, the features and advantages described in this disclosure and in the following detailed description are not all-inclusive. Many additional features and advantages will be apparent to one of ordinary skill in the relevant art in view of the drawings, specification, and claims hereof. Moreover, it should be noted that the language used in the specification has been principally selected for readability and instructional purposes and may not have been selected to delineate or circumscribe the inventive subject matter; reference to the claims is necessary to determine such inventive subject matter. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows the BI structure as defined in WGA-D08; 
         FIG. 2  shows a Delivery Traffic Indication Message (DTIM) BI with a group address frame in a CBP according to another embodiment of the invention; 
         FIG. 3  shows a BI with a SP according to another embodiment of the invention; and 
         FIGS. 4A and 4B  show a PBSS under direct peer notification according to another embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention are hereafter described in detail with reference to the accompanying figures. 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. 
     The following description with reference to the accompanying drawings is provided to assist in a comprehensive understanding of exemplary embodiments of the present invention as defined by the claims and their equivalents. It includes various specific details to assist in that understanding, but these are to be regarded as merely exemplary. Accordingly, those of ordinary skill in the art will recognize that various changes and modifications of the embodiments described herein can be made without departing from the scope and spirit of the invention. Also, descriptions of well-known functions and constructions are omitted for clarity and conciseness. 
     The invention relates to a novel method for saving power in wireless network devices. Embodiments of the invention are directed towards saving power in WGA network devices by re-scheduling communication frames and switching power saving modes for periods of inactivity. The method has added advantages of reducing retransmission, increasing the duration of the doze state for a device, and other advantages that may be learned in practice by one of ordinary skill in the art. 
     An active STA or a power save STA in its awake BI is switched to the active power management state during all CBP periods according to one embodiment of the invention. 
     Referring to Table 44, a STA in active mode and a power save STA in its awake BI can switch to doze mode in an awake BI during the CBP for a non-PCP STA. If a STA, e.g., STA 1 , transmits frames in a CBP to another STA in active mode, e.g., STA 2 , the frame transmission cannot be received correctly by STA 2  if STA 2  is in doze state. STA 1  may have to retransmit frames several times before the frames are received correctly by STA 2 , thereby wasting power. 
     Section 11.2.3.1.3 of WGA-D08 further defines an Announcement Traffic Indication Message (ATIM) frame for an ATIM sender to notify that there are buffered frames for ATIM destination. Before transmitting frames to a STA in active mode in the CBP, a directed ATIM frame to the active STA may be required. This is not a good requirement, as explained in the following example. In each BI, a STA, e.g., STA 1 , needs to send an ATIM frame to each STA, e.g., STA 2 , for which STA 1  has buffered frames in active mode so that STA 2  will be awake in the CBPs. This makes the CBP transmission complicated. However, if the protocol mandates that each active STA is to be awake in each CBP, then if a STA has frames for an active STA, it can transmit frames to the active STA in each CBP without transmitting ATIM to the active STA. 
     Therefore, by mandating an active STA to be in awake state during all CBP periods, the complexity of power management is reduced by eliminating the need of transmitting the directed ATIM frame to the active STA before transmitting frames to a STA in an active mode in the CBP. The result is increased bandwidth and power saving as well as simplifying the CBP frame transmission protocol. 
       FIG. 2  shows a DTIM BI with a group address frame in a CBP or SP according to another embodiment of the invention. 
     Group address frames are multiple destination broadcast frames that a STA can send to a group of STAs in its group SP or a CBP in its active BIs. However, with power saving mode considerations, other STAs may be in doze mode during such BIs. Thus, other STAs may not receive the group address frame sent by the STA. In other words, if a STA wants to receive group address frames, it has to be active in each BI. This is not good for saving power, thus a need for improvement exists. 
     Specific periodic BI is defined according to one embodiment of the invention. During such BIs, group address frames can be transmitted. During other BIs, group address frames are not transmitted. One example of a specific periodic BI can be a DTIM BI according to another embodiment of the invention. BI schedule  200  shows an example BI schedule consisting of normal beacon (NB) intervals  210 ,  220 ,  230 , and a DTIM BI  240 . Here, the group SP  241  is allocated in DTIM BI  240 . The group address frames are transmitted in the group SP  241 . The group address frames are transmitted in CBP  242  which is also allocated in DTIM BI  240 . In normal beacon intervals  210 ,  220 ,  230 , group address frames are not transmitted. 
       FIG. 3  shows a BI with a SP according to yet another embodiment of the invention. 
     Normally, a SP in a BI is assigned exclusively to the SP&#39;s initiator and the SP&#39;s responder. Only the SP&#39;s initiator is allowed to transmit data and/or management frames, and only the SP&#39;s responder is allowed to receive such data and/or management frames if the reverse direction (RD) protocol is not supported. Therefore, bandwidth and power are wasted when the SP&#39;s initiator has nothing to transmit resulting in an idle channel in the SP. 
     BI  300  shows an example BI consisting of SP  310  assigned to a SP&#39;s initiator STA 1  and a SP&#39;s responder STA 2  according to one embodiment of the invention. During a first period  320  of SP  310 , STA 1  may send data and/or management frames exclusively, and STA 2  may receive such frames from STA 1  exclusively. When STA 1  no longer has frames to transmit during the second period  330  of SP  310 , it may be detected that the channel medium is idle for a point (coordination function) interframe space (PIFS) in the SP. According to another embodiment of the invention, the More Data bit in the frame control field of a data frame from SP initiator STA 1  can be set to ‘0’ to indicate that it has no more frames to transmit. Thereafter, the SP responder STA 2  is allowed to transmit data and/or management frames to SP initiator STA 1  during the third period  340  of SP  310 . According to yet another embodiment of the invention, STA 1  and STA 2  can also choose to go to doze state if the More Data bit from SP initiator STA 1  is set to ‘0’ to indicate that it has no more frames to transmit. 
       FIGS. 4A and 4B  show a PBSS under direct peer notification according to further yet another embodiment of the invention. PBSS  400  has PCP  410 , STA 1   420 , and STA 2   430 . 
     Normally, the wakeup schedule (WS) and power saving mode of STA 1   420  and STA 2   430  is stored with PCP  410 . STA 1   420  and STA 2   430  can acquire the peer STA&#39;s WS and power saving mode through PCP  410 . 
     Referring to  FIG. 4A , STA 1   420  and STA 2   430  starts peer-to-peer communication  465 . When STA 2   430  changes from active mode to power saving mode or have a new wakeup schedule, STA 2   430  transmits a power saving configuration to PCP  410  to be recorded. STA 1   420 , upon realizing that STA 2   430  is no longer in active mode by realizing that an unsuccessful transmission threshold has been reached, may transmit an information request  455  to PCP  410  asking for the WS and power saving mode of STA 2   430 . 
     However, a STA may not always know when to acquire such wakeup and power saving schedule of its peer STAs if a STA changes from power saving mode to active mode. If STA 2   430  returns to active mode, it is difficult for peer STA 1   420  to decide when to re-acquire the WS and power saving mode of STA 2   430  from PCP  410 . 
     Direct peer notification, especially when a STA only has one peer STA, makes this notification simple and reasonable. Referring to  FIG. 4B , when STA 2   430  changes its power save state and/or wakeup schedule, STA 2   430  may notify its wakeup schedule and/or power saving mode to peer STA 1   420  directly via action frame  466 . One example of such action frame may be information response frame. An information response frame is defined for the direct peer notification to indicate a new WS. A successful exchange of an information response frame between peer STA can be used to indicate a power saving mode change according to an embodiment of the invention. 
     An infrastructure BSS may also be adapted to use power saving modes and transmission frames of a PBSS with some modification according to another embodiment of the invention. 
     Section 11.2.3 of WGA-D08 discusses power management in a PBSS, but there is no power save protocol defined for a WGA infrastructure BSS. Two possible methods for implementing a power save protocol for a WGA infrastructure are using 802.11 baseline power save protocol defined for 2.4 GHz/5 GHz infrastructure BSS or using PBSS power save protocol. However, neither of these two methods is entirely appropriate. The 2.4 GHz/5 GHz infrastructure BSS does not have SP mechanism, and normally EDCA is the medium access method in all BI. Therefore, the 802.11 baseline power save protocol defined for 2.4 GHz/5 GHz infrastructure BSS is not appropriate for power save in a WGA infrastructure BSS. With the PBSS power save protocol, a PCP can be in doze state for several BIs. Thus, this violates the rules of infrastructure BSS since an AP is always awake in an infrastructure BSS in 2.4 GHZ/5 GHz band. Therefore, the unmodified PBSS power save protocol is also not appropriate for the WGA infrastructure BSS. 
     As such, the following describes power saving modes and transmission frames adapted for an infrastructure BSS according to one embodiment of the invention. 
     An infrastructure BSS necessary consists of an AP and associated non-AP STAs. The AP, similar to the PCP in a PBSS, should operate under rules different from a non-AP STA. The AP can be in doze state in SPs that are neither the SP initiator nor the responder where the SP is not a truncatable or extensible SP, since such a SP is exclusively allocated to SP&#39;s source and SP&#39;s destination. The AP will need to be awake in other periods of the BI. However, it is noted that the AP cannot sleep for several BIs under the conditions. In other words, each BI will be AP&#39;s awake BI. Since the AP should otherwise always be active, CBP power saving for the AP in an infrastructure BSS uses the same methods of CBP power saving in PBSS CBP. 
     A non-AP STA may be in doze state in SPs that the STA is not the SP&#39;s initiator or responder in its active BI. A non-AP STA may also be in doze state in the CBP in its active BI if it is in power saving mode. However, the non-AP STA in active mode shall be awake during all CBP according to one embodiment of the invention. 
     It is further noted that an infrastructure BSS can further adapt the same methods of SP power saving in a PBSS SP as discussed according to one embodiment of the invention. 
     A presently preferred embodiment of the present invention and many of its improvements have been described with a degree of particularity. It should be understood that this description has been made by way of example, and that the invention is defined by the scope of the following claims.