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PHY Power Saving Features For 11ac

This paper discusses power saving features for 11ac PHY, including micro-sleep during active state, considerations for power save features in PHY, and signaling options for the micro-sleep feature.

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PHY Power Saving Features For 11ac

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  1. PHY Power Saving Features For 11ac Authors: Date: 2010-07-14 Byeongwoo Kang, LG Electronics

  2. Abstract • Useful Usage Model for efficient power consumption • Consideration aspects for less-overhearing • Potential signaling options for the Micro-Sleep Feature • PHY ID for power saving in detail • VHT-SIG field design aspect • PHY ID compression methods • CRC Fail of VHT-SIG-B • Consideration of MAC ID for power saving Byeongwoo Kang, LG Electronics

  3. Multi-media Streaming at Networked Home • Distributed Consumer Electronics(CE) around the AP • More than one device of the networked home is likely to be communicated with one shared AP • Direct data transmission between distributed CEs to support robust HD video streaming and surveillance (e.g. Direct Link Setup, WiFi Direct) Surveillance Camera DLS MU-MIMO MU-MIMO Data Transfer DLS HD Video Streaming Byeongwoo Kang, LG Electronics

  4. Previous features for power saving • With CSMA/CA based, each STA needs to be enforced to listen to the channel to know about the current status regardless of its own data communication with AP • Some method for power saving to reduce the time required for STA to listen to the channel • Basic power save mode switching between awake state and sleep state with PS-Poll frame from STAs • APSD (Automatic Power Save Delivery) • PSMP (Power Save Multi-Poll) • In case of the high throughput to be supported, less chance to sleep due to a lasting awake state supporting reasonable QoS • Consumer need for efficient power consumption even during awake state for the consumer electronics Byeongwoo Kang, LG Electronics

  5. Considerations for Power Save features in PHY • Information to indicate whether or not to listen and decode the data packet • Data non-reception STAs can switch to sleep state after decoding VHT-SIG (VHT-SIGA or VHT-SIGB) • Consideration aspects • AP and STA have different required power efficiency at the transceiver • Efficient power management of STA is typically more desirable Byeongwoo Kang, LG Electronics

  6. Use cases for Micro-Sleep during Active State • Observation • Data transmission can be categorized into 3 links • Scenario 1 : STA-to-AP • Scenario 2 : AP-to-STA • Scenario 3 : STA-to-STA (DLS, Direct Link Setup) Byeongwoo Kang, LG Electronics

  7. Micro-Sleep during Active State (1/3) • Consideration aspect 1 (STA-to-AP transmission, UL) • Data reception at AP • No need for all STAs to overhear UL data packet (not intended users) • The power save information in VHT-SIG to allow Rx micro sleep for all STAs Byeongwoo Kang, LG Electronics

  8. Micro-Sleep during Active State (2/3) • Consideration aspect 2 (AP-to-STA transmission , DL) • Only a single/subset of STAs (SU-MIMO/MU-MIMO) in BSS require data reception • STA(s) requires information on whether or not to demodulate and decode received signal from AP for power saving • The PHY ID (e.g. Association ID) concept to indicate intended receiving STA(s) which allows Rx micro-sleep on subset of STAs Byeongwoo Kang, LG Electronics

  9. Micro-Sleep during Active State (3/3) • Consideration aspect 3 (STA-to-STA, DLS) • STA1 and STA2 are paired for DLS operation • It is assumed that STA1 transmits data packet to STA2 directly • STA2 requires information on whether or not to demodulate and decode the received signal for power saving • Possibility of indicate PHY ID for DLS • Note : current specification does not support Association ID for DLS Byeongwoo Kang, LG Electronics

  10. Signaling for the Micro-Sleep Feature (1/7) • Link differentiation between DL and UL • Simple and efficient signaling to solve half of the active reception processing waste • 1 bit in VHT-SIG-A • or 1 state taken from Group ID field • Introduce the PHY ID in VHT-SIG • Solves the other half of the active reception processing wastes simply • The potential candidate : Group ID and AID (11bits) of STA(s) • Receiver Behavior Procedure • CRC Fail of VHT-SIG-B Byeongwoo Kang, LG Electronics

  11. Signaling for the Micro-Sleep Feature (2/7) • Use of Group ID as PHY ID • Simple and efficient way to use Group ID included in VHT-SIG-A • Depending on the definition, number of data non-RX STAs with sleep mode might be small than expected • Extend PHY Group ID with (logical) MAC Grouping • Same Group ID is allocated to multiple grouping of STAs • Useful to allow giving possibility for AP to allocate and manage more combination of STAs Byeongwoo Kang, LG Electronics

  12. Signaling for the Micro-Sleep Feature (3/7) • Example of Group ID • STA A, STA B, etc can correspond to MAC Address, Associated ID or some other unique identifier • Refer to the corresponding document dealing with STA Group Management for MU-MIMO from LG Electronics for more details • In that sense, AID signaling might be helpful to assist power saving of MU-MIMO Byeongwoo Kang, LG Electronics

  13. Signaling for the Micro-Sleep Feature (4/7) • To support Association ID for DLS • Even though AID field is included in VHT-SIG, there is no way for Tx DLS STA to know AID of Rx DLS STA • add a new field in DLS Action frame for power saving • Example of DLS request frame Byeongwoo Kang, LG Electronics

  14. Signaling for the Micro-Sleep Feature (5/7) • Use of BSSID part of PHY ID • It may help PHY ID ambiguity potentially in case of OBSS scenario • In a typical OBSS circumstance, each AP assigns AID with 11 bits randomly • The benefits of BSSID inclusion to PHY ID will be limited Byeongwoo Kang, LG Electronics

  15. Signaling for the Micro-Sleep Feature (6/7) • CRC Fail of VHT-SIG-B • VHT-SIG-B is precoded (beamformed) in MU-MIMO transmission • Reception SINR for non-intended STA is expected to be low • This may cause CRC FAIL of VHT-SIG-B for non-intended STA regardless of AID inclusion in VHT-SIG-B • Receiver behavior when CRC FAIL of VHT-SIG-B • VHT-SIG-B contains MCS, [FEC] information which is necessary for decoding of received packet. • STAs with decoded L-SIG & VHT-SIG-A correctly already has Channel Sense of busy information. • STAs with CRC FAIL of VHT-SIG-B may go into RX micro-sleep Byeongwoo Kang, LG Electronics

  16. Signaling for the Micro-Sleep Feature (7/7) • Example of Receiver Behavior Procedure Byeongwoo Kang, LG Electronics

  17. VHT-SIG design aspects for PHY ID (1/2) • AID in VHT-SIG-A • STAs can start micro sleep as early as possible • Possibility of reinterpreting portions of NSTS field for AID in SU-MIMO transmission • Impossible to signal multiple AID for MU-MIMO (4 time 11 bits is already 44 bits, where SIG-A has 48 bit limitation) • AID in VHT-SIG-B • Easier to support AID for each STA in MU-MIMO • STAs can start micro sleep before actual data demodulation & decoding • AID in VHT-SIG-B can be an unified solution for SU-MIMO and MU-MIMO Byeongwoo Kang, LG Electronics

  18. VHT-SIG design aspects for PHY ID (2/2) • Bit width restrictions in VHT-SIG-B • VHT-SIG-B (26bits) may contain following fields • MCS : 3~4bits • [FEC : 1bit] (whether or not to include this is TBD) • CRC : 8 bits • Tail : 6 bits • Having full 11 bits as PHY ID may not be possible if other bits are included in VHT-SIG-B Byeongwoo Kang, LG Electronics

  19. PHY ID compression methods (1/2) • Partial AID with N bits (where N < 11) • The practical number of STA associated with a single AP will be limited • Compressing AID may not help power save utilization in OBSS cases • Example : AP transmits data packets to STA3 • STA1 & 2 switch into micro sleeps after decoding of the partial AID • STA 3 keeps decoding data packet STA3: AID = 1075 Partial AID = 51 Partial AID =51* STA2: AID = 1052 Partial AID =28 STA1: AID = 1054 Partial AID =30 Byeongwoo Kang, LG Electronics

  20. PHY ID compression methods (2/2) • AID compression by utilizing CRC field space • Partial AID with N bits and CRC with (11-N) bits in VHT-SIG-B • CRC masking with the last (11-N) bits of AID • STAs with different AID will result in CRC value mismatch and FAIL of CRC checking Byeongwoo Kang, LG Electronics

  21. Problems with MAC ID power saving • MAC ID in MAC header • Considering AP transmitting A-MPDUto STA(s) • More long receiver processing time with active state for non-intended STAs • Data non-reception STAs can start micro sleep only after decoding the first MPDU • In case of the first MPDU with error , data non- reception STAs keep receiver processing until they can identify the MAC ID of next MPDU • It is safe and beneficial to use PHY ID in VHT-SIG with the low data rate such as (Q)BPSK • It might be beneficial for MAC ID to assist power saving feature as the last stage Byeongwoo Kang, LG Electronics

  22. Summary • In general, support of power saving during active state seems important. • Potential PHY power saving features in different circumstance • 1 bit or 1 state information in VHT-SIG-A is preferred for an efficient way to solve half of the active reception processing waste • Additional consideration to support potential power saving • CRC checking receiver behavior procedure Byeongwoo Kang, LG Electronics

  23. Strawpoll • Do you support adopting Link differentiation information (e.g. UL and DL) in VHT-SIG-A field as described in slide 10 and adding the following item into the specification framework document, 11-09/0992? • R3.2.1.H: VHT-SIG-A includes the fields listed in Table 1. Byeongwoo Kang, LG Electronics

  24. Annex Byeongwoo Kang, LG Electronics

  25. Annex. CRC masking (1/2) • CRC Match • Partial AID with N bits and CRC with (11-N) bits in VHT-SIG-B • CRC masking with the last (11-N) bits of AID RX TX CRC 1 0 1 1 1 1 0 1 0 0 0 0 0 0 1 0 0 1 0 1 0 1 Always 000 XOR XOR AID AID 1 0 1 0 1 1 1 1 1 0 1 1 0 1 0 1 1 1 1 1 0 1 || || CRC Match (PASS) 1 0 1 1 1 1 0 1 0 0 0 0 0 0 1 0 0 1 0 1 0 1 CRC Field AID MSB Field CRC Field AID MSB Field Byeongwoo Kang, LG Electronics

  26. Annex. CRC masking (2/2) • CRC Mismatch • STAs with different AID will result in CRC value mismatch and FAIL of CRC checking RX TX CRC 1 0 1 1 1 1 0 1 0 0 0 0 0 0 1 0 0 1 0 1 0 1 Always 000 XOR XOR AID AID 0 1 1 1 0 0 1 0 1 1 1 1 0 1 0 1 1 1 1 1 0 1 || || CRC Mismatch (FAIL) 1 0 1 1 1 1 0 1 0 0 0 1 1 0 0 1 1 1 1 1 1 1 CRC Field CRC Field AID MSB Field AID MSB Field Byeongwoo Kang, LG Electronics

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