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TGah Power Saving

This article discusses power saving features in TGah and TGv, including BSS max idle period management, WNM-Sleep mode, Flexible Multicast Service, Direct Multicast Service, and Proxy ARP capability.

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TGah Power Saving

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  1. Date: Jan, 2012 TGah Power Saving Authors: Date: 2012-01-16 Liwen Chu Etc.

  2. TGv Power Save Features BSS Max idle period management enables an AP to indicate a time period during which the AP does not disassociate a STA due to non-receipt of frames from the STA. WNM-Sleep mode enables a non-AP STA to signal to an AP that it will be sleeping for a specified length of time, defined as the number of DTIM intervals. Flexible Multicast Service (FMS) enables a non-AP STA to wake up at the alternate DTIM interval, rather than every DTIM, and enables significant power saving when a non-AP STA receives group addressed traffic. Direct Multicast Service (DMS) enables a non-AP STA to request the AP to transmit group addressed frames destined to the requesting STA as individually addressed frames. Proxy ARP capability enables an AP to indicate that the non-AP STA will not receive ARP frames and remain in power-save for longer periods of time. Date: Jan, 2012

  3. Why WNM-Sleep is not Good for TGah Almost all STAs in a Smart Grid BSS have the same power save requirement (e.g. long sleep period), but WNM-Sleep is suitable for a small number of STAs in a BSS. If WNM-Sleep is used for such STAs, beacon intervals other than DTIM beacon intervals are rarely used. With WNM-Sleep, TIM in Beacon may be as big as 6000/8 = 750bytes (e.g. when AID1 and AID5998 have the same awake DTIM and buffered frames at the awake DTIM). It is difficult for an AP to group STAs with nearby AID to wake up at the same TBTT (e.g. AID 101 to AID 200). The same usage of the STAs in a Smart Grid BSS means the same wake up intervals of the STAs. A beacon interval can not finish polling all 6000 STAs in one 100ms beacon interval given the lower PHY rate of a Smart Grid BSS (~hundreds kbps): (100bytes MPDU + 14bytes ACK) * 8 /200000= 4.56ms. Actually transmission time is longer since Backoff, PS Poll, PHY overhead and IFS are needed. Date: Jan, 2012 DTIM STA1 wakes up. STA1 and STA5998 wake up. TIM STA with AID1 (STA1) negotiates WNM-Sleep with 2 DTIM intervals. STA with AID5998 (STA5998) negotiates WNM-Sleep with 2 DTIM intervals.

  4. TGah Sleep Mode The AP allocates its associated STAs to different groups and matches each group’s TIM to its awake TBTT. Option 1: nearby AIDs being allocated in a group. AID and enhanced TIM IE (2 bytes Bitmap Control with longer Bitmap Offset) can be used. Option 2: similar power save requirement (or nearby position) being allocated in a group. Group member ID need to be defined and Enhanced Group TIM IE indicates group member’s buffered frame indication per member’s group ID. The AP notifies the TBTT and sleep interval of each group. Each group has a different awake TBTT. Date: Jan, 2012 Group1 Group3 Group5 Group7 Group1 Group3 Group5 Group2 Group4 Group6 Group8 Group2 Group4 Group6 Sleep Interval

  5. Option 1: Nearby AIDs in a group Enhanced TIM element extends Bitmap Control field to 2 bytes. Bit 0 of the field contains the Traffic Indicator bit associated with Association ID 0, In an AP with multiple BSSID, more bits are required for group frames indication. The remaining bits of the field form Bitmap Offset of AID. Date: Jan, 2012 Octets: 1 1 1 1 2 1--251 • A STA needs to know the Group Sleep Interval in beacon intervals, wake up TBTT.

  6. Option 2: Similar power save requirement (nearby position) in a group Group TIM element extends Bitmap Control field to 2 bytes. Bit 0 of the field contains the Traffic Indicator bit associated with Association ID 0, In an AP with multiple BSSID, more bits are required for group frames indication The remaining bits of the field form the group indication and Bitmap Offset of group member id. Date: Jan, 2012 Octets: 1 1 1 1 2 1--251 • A STA needs to know the group that it belongs, group member ID, the Group Sleep Interval in beacon intervals, wake up TBTT. AID 5 AID 13 AID 5 has member ID 1, AID 9 has member ID 2, AID 13 has member ID 3………. Group5 AID bitmap: 000001000100100100110000 AID 9

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