1. PHY Power Saving Features For 11ac
July 2010
doc.: IEEE /0785r0
July 2010
PHY Power Saving Features For 11ac
Date:
Authors:
Yujin Noh, LG Electronics
Yujin Noh, LG Electronics

2. Abstract Useful Usage Model for efficient power consumption
July 2010
doc.: IEEE /0785r0
July 2010
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
Yujin Noh, LG Electronics
Yujin Noh, LG Electronics

3. Multi-media Streaming at Networked Home
July 2010
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
HD Video Streaming
Data Transfer
DLS
MU-MIMO
Yujin Noh, LG Electronics

4. Previous features for power saving
July 2010
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
Yujin Noh, LG Electronics

5. Considerations for Power Save features in PHY
July 2010
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
Yujin Noh, LG Electronics

6. Use cases for Micro-Sleep during Active State
July 2010
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)
Yujin Noh, LG Electronics

7. Micro-Sleep during Active State (1/3)
July 2010
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
Yujin Noh, LG Electronics

8. Micro-Sleep during Active State (2/3)
July 2010
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
Yujin Noh, LG Electronics

9. Micro-Sleep during Active State (3/3)
July 2010
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
Yujin Noh, LG Electronics

10. Signaling for the Micro-Sleep Feature (1/7)
July 2010
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
Yujin Noh, LG Electronics

11. Signaling for the Micro-Sleep Feature (2/7)
July 2010
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
Yujin Noh, LG Electronics

12. Signaling for the Micro-Sleep Feature (3/7)
July 2010
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
Yujin Noh, LG Electronics

13. Signaling for the Micro-Sleep Feature (4/7)
July 2010
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
Order
Information 1
Category 2
Action 3
Destination MAC Address 4
Source MAC Address 5
Capability Information 6
DLS Timeout Value 7
Supported rates 8
Extended Supported Rates 9
Destination PHY ID
Yujin Noh, LG Electronics

14. Signaling for the Micro-Sleep Feature (5/7)
July 2010
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
Yujin Noh, LG Electronics

15. Signaling for the Micro-Sleep Feature (6/7)
July 2010
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
Yujin Noh, LG Electronics

16. Signaling for the Micro-Sleep Feature (7/7)
July 2010
Signaling for the Micro-Sleep Feature (7/7)
Example of Receiver Behavior Procedure
Yujin Noh, LG Electronics

17. VHT-SIG design aspects for PHY ID (1/2)
July 2010
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
Yujin Noh, LG Electronics

18. VHT-SIG design aspects for PHY ID (2/2)
July 2010
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
Yujin Noh, LG Electronics

19. PHY ID compression methods (1/2)
July 2010
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
STA1: AID = 1054
Partial AID =28
Partial AID =30
Yujin Noh, LG Electronics

20. PHY ID compression methods (2/2)
July 2010
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
Yujin Noh, LG Electronics

21. Problems with MAC ID power saving
July 2010
Problems with MAC ID power saving
MAC ID in MAC header
Considering AP transmitting A-MPDU to 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
Yujin Noh, LG Electronics

22. Potential information for power saving
July 2010
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
Type
Potential information for power saving UL
1 bit or 1 state indication in VHT-SIG A
DL MU-MIMO
Group ID and (partial) AID in VHT-SIG B
DL SU-MIMO
(partial) AID in VHT-SIG B
DLS
Yujin Noh, LG Electronics

23. July 2010
doc.: IEEE /0785r0
July 2010
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.
Field
Bits
Description
Bandwidth
TBD
STBC
1 [10/382r2]
Group ID [10/0582r1]
A value of zero indicates [10/0382r2]:
A single user transmission
A transmission where the group membership has not yet been established
A transmission that needs to bypass a group (e.g. broadcast)
NSTS [10/0582r1]
Link differentiation
Yujin Noh, LG Electronics
Yujin Noh, LG Electronics

24. Annex July 2010 July 2010 doc.: IEEE 802.11-10/0785r0
Yujin Noh, LG Electronics
Yujin Noh, LG Electronics

25. Annex. CRC masking (1/2) CRC Match
July 2010
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
CRC Field
AID MSB Field
XOR ||
AID
Always 000
CRC
CRC Match (PASS) TX RX
Yujin Noh, LG Electronics

26. Annex. CRC masking (2/2) CRC Mismatch
July 2010
Annex. CRC masking (2/2)
CRC Mismatch
STAs with different AID will result in CRC value mismatch and FAIL of CRC checking
CRC Field
AID MSB Field
XOR ||
AID
Always 000
CRC
CRC Mismatch (FAIL) TX RX
Yujin Noh, LG Electronics