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Power efficient and unified 802.11s solution

Power efficient and unified 802.11s solution. Authors:. Date: 2007-11-12. Abstract.

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Power efficient and unified 802.11s solution

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  1. Power efficient and unified 802.11s solution Authors: Date: 2007-11-12 Jarkko Kneckt, Nokia

  2. Abstract This presentation provides a high level view of the 802.11s mesh network as seen by the authors. Detailed proposal is given on power save mechanisms. In general the objective has been to have a standard amendment with a feature set meeting the following main objectives: • suitable for both backbone and ad hoc type of mesh networks • power save mechanisms defined to allow for battery powered MPs • one solution to one problem Jarkko Kneckt, Nokia

  3. Contents • Introduction • The big picture • Basic components • Five basic components of MPs • Power save in details • Two levels of power save • Power mode transition rules • Peer service period Jarkko Kneckt, Nokia

  4. Power save in Mesh • The power save consists on 2 capabilities: • Support of power save to enable power save for peer MPs • Operation in power save mode and save power by shutting down the receiver • The support for power save does not enable the power save supporting MP itself to operate in power save mode • The support for power save enables operation in power save for peer MPs • The operation in power save is optional capability • The power save enables MP to operate in doze state and to reduce power consumption Jarkko Kneckt, Nokia

  5. Support for power save • The support for power save contains capabilities to: • keep track of the power modes of the peer MPs • buffer unicast frames for the power saving peer MPs • transmit data according to the power mode of the peer MP; by using service periods or as soon as possible • The mechanisms to transmit data according to power mode of the peer MP are presented in the following slides Jarkko Kneckt, Nokia

  6. Power save proposal in nutshell • The proposal builds upon the current two power management modes • Active mode • Power save mode • Two levels of power save proposed • Light sleep designed for battery powered active MPs • Deep sleep provides a low duty cycle mode for all the MPs • Light sleep power save operations are based on wake-up signaling in beacons and a U-APSD –like operations • Deep sleep MP can be woken up only after its own mesh DTIM beacons for short data exchange periods Jarkko Kneckt, Nokia

  7. Power management modes • Active mode • The MP is awake all the time • Power save mode • Light sleep – “Diet sleep” • The MP is awake during the time needed to send own mesh beacon, receive the peer MP mesh beacons, and to serve peer links as per the mesh service period rules • Designed to be used when the MP desires to reduce the power consumption and the full bandwidth is not needed for data from/to the peer MPs • Deep sleep • The MP is awake during the own mesh DTIM beacon and the following Awake Window, and to serve any subsequent mesh service periods • Designed to be used when there is no or very limited amount of traffic from/to the peer MPs Jarkko Kneckt, Nokia

  8. Minimum activity in power saving MP MP1 = Minimum activity of active mode MP1 =Minimum activity of light sleep mode MP1 = Minimum activity of deep sleep mode MP1 MP1 and MP2 are peer-MPs to each other MP2 = Awake Window = TIM beacon = DTIM beacon Jarkko Kneckt, Nokia

  9. The basic rules of light sleep • Beaconing MP uses Mesh TIM field in its own beacon to indicate presence of buffered data to power saving peer MPs • Power saving MP checks if the peer MP indicates presence of buffered data for it • If the bit is set, the MP triggers a peer service period • Beaconing MP serves power saving peer MPs to which it has buffered data during peer service periods • Doze state can be entered only when all the peer service periods have been closed • The peer service period handling rules are described later in the slide set Beacon Beacon Trigger frame ACK Peer service period Jarkko Kneckt, Nokia

  10. The basic rules of deep sleep • Power saving MP in deep sleep shall be active at least during its mesh DTIM beacon and the following Awake Window • The Awake Window is used for two purposes • MPs can request specific actions from the power saving MP • The MP in deep sleep transmits multicast and broadcast frames to peer MPs • Specific actions one can request during the Awake Window depend on the requesters role • Peer MP can use the Awake Window to initiate a mesh service period with the power saving MP • Non-peer MP can use the Awake Window to transmit a mesh management frame related to mesh discovery or peer link establishment Jarkko Kneckt, Nokia

  11. Data transmission between deep sleep mode MPs 1. 2. • MP1 receives null frame during its Awake window. A peer service period is triggered. • MP1 receives frames during its peer service period. • MP1 sends null frame to MP2 during Awake window of MP2 to trigger a peer service period. • MP1 transmits the frames to MP2 during the peer service period. Power mode of MP1 seen by MP2 Operation state of MP1 3. 4. Power mode of MP2 seen by MP1 Operation state of MP2 = DTIM beacon = peer service period = Awake Window = Operation in deep sleep mode = Doze state = Awake state Jarkko Kneckt, Nokia

  12. Deep sleep mode summary • Deep Sleep offers low duty-cycle power save for MPs • The deep sleep mode should be used, when network has little or no data to transmit • Data transmission between MPs in deep sleep is possible, but may introduce delays • The deep sleep mode MP has low power consumption that is independent from the amount of the peer MPs Jarkko Kneckt, Nokia

  13. Mode and level transitions (1/2) • Power save mechanisms are link specific • In some traffic models or network topologies it may make sense to raise the local MP to operate in higher power save level (or power management mode) for only one or few peer links • Transition to lower power save level needs to be unicasted because only those are acknowledged • Robust and reliable power management state transitions from higher power save level to lower power save level require acknowledgement from the peer MP • Transition to higher power save level may use unicast, multicast and broadcast transmissions • The transition from a lower power save level to a higher one is robust • Even if MP assumes that the peer MP operates on the lower power save level, it will not cause failure to frame transmission Jarkko Kneckt, Nokia

  14. Two bits in the MAC header indicate the power management mode Power management bit indicates whether the MP operates in active or power save mode The power save level bit indicates the level of the power save, when the MP has set the power management bit to 1 Power management indicated in BC/MC frames is set as per the lowest power management mode used in the links The power management mode that is indicated in BC/MC frames is used also by non-peer MPs to determine the times for scan and link creation frame exchange Mode and level transitions (2/2) Jarkko Kneckt, Nokia

  15. Power save support for different power modes • The power save supporting MP sets indication of the buffered traffic to beacons it transmits for light sleep MPs. • The power save supporting MP transmits null frame during the Awake window of the deep sleep mode MP to indicate buffered frames. • Mesh DTIM Beacon frame from deep sleep mode MP triggers the null frame creation to the transmission buffer • The lifetime of the null frame is set to the end of the Awake window. • Power save supporting MP may indicate buffered traffic for the deep sleep MP in the beacons it transmits. • The support for power save does not require synchronization. • The operation in power save mode requires some level of synchronization to wake up to listen to beacons from peer MPs Jarkko Kneckt, Nokia

  16. Peer service periods – enabling transmissions while MP operates in power save mode • The MP may use peer service periods for data transmission, when it is operating in power save mode, i.e. have power management bit set to 1 • A peer service period is initiated by acknowledged trigger frame • Unicasted and acknowledged PS-POLL, QoS-Null, data and management frame may be used as a trigger frame. • Peer service periods are link specific • The peer MP shall be active for the duration of the peer service period • During a peer service period, frames from all ACs may be transmitted • Trigger frame’s AC does NOT limit the ACs of the frames transmitted during the peer service period • Peer service period may contain one or more TXOPs. Jarkko Kneckt, Nokia

  17. Peer service period types • MPs use peer link creation signaling to signal the used service period type for the link. • If both MPs set Bi-directional Peer Service Periods bit in Mesh Capability field to 1 in Peer Link Open and Confirm frames bi-directional peer service periods are used for the link • Otherwise unidirectional service periods are used for the link • Peer service period type: • Unidirectional peer service period enable: • An MP to transmit data during the peer service period • The peer service period is terminated when the MP indicates that the last frame is transmitted and receives acknowledgement for the frame. • Bi-directional peer service period enable: • Both MPs to transmit data during the peer service period • Triggering a bi-directional peer service period, in power mode transitions, if peer MP has buffered frames • The peer service period is terminated when both data frame and acknowledgement indicate that all buffered traffic is transmitted Jarkko Kneckt, Nokia

  18. MAC frame header bits used in peer service periods • More Data (MD) bit in unicast data frames • Indicates the status of the buffered unicast frames for the receiver • MD bit in multicast and broadcast frames and bit 0 in Mesh TIM element • Indicates if more multicast or broadcast will be transmitted by the MP • End of Service Period (EOSP) Bit in unicast frames • Indicates termination of the service period • The separation of MD bit and EOSP enables the separate transmission buffer status information passing and control for service periods. See slides at the end of the presentation (30->) • By using both MD and EOSP the indication of the buffered traffic and termination of the peer service period. • 802.11e and U-APSD uses both MD and EOSP bits. By using the same fields, the 802.11s power save mechanisms are compatible with infrastructure mode mechanisms. Jarkko Kneckt, Nokia

  19. Triggering of peer service period • null, data, management or ps-poll frame may be used as a trigger frame. • Unidirectional peer service period: • Null and ps-poll trigger frames initiate a peer service period that is owned by the receiver of the trigger frame. The receiver may send data and management frames during the service period. • Management and data trigger frames initiate two peer service periods so that both the transmitting MP and the receiving MP own a peer service period. • Bi-directional service period: • All trigger frames trigger a bi-directional service period, which enable both MPs to transmit frames. Jarkko Kneckt, Nokia

  20. Termination of the unidirectional peer service periods Termination of one unidirectional peer service period Termination of two unidirectional peer service periods Both MP 3 and MP4 are data transmitters in the peer service periods. The peer service period from MP3 is terminated, when MP3 transmits a frame with set EOSP bit. MP4 acts accordingly with its own peer service period. MP 1 is data transmitter in the peer service period. The peer service period is terminated when MP1 indicates that it does not have more data to transmit with EOSP. Data Data Ack Ack Data, EOSP=1 Data, EOSP=1 Ack Ack Data, EOSP=1 Ack MP1 MP3 MP2 MP4 = MP may transmit data = MP may receive data EOSP = End of service period bit Jarkko Kneckt, Nokia

  21. Mesh service period between active mode and light sleep MPs MP1 indicates in beacon that it has data pending • MP1 has data to be sent for MP2 and MP1 indicates it in its beacon • MP2 responses with appropriate trigger frame which initiates mesh service period • Service period is ended with setting of EOSP bit after the MP1 buffers further data for MP2 • MP2 may trigger a peer service period at any time Beacon MP2 responses with trigger frame starting mesh service period Data Ack Data Ack Data, EOSP=1 Ack MP1 MP2 = Light sleep mode MP = Active mode MP = MP may transmit data = MP may receive data Jarkko Kneckt, Nokia

  22. Peer service period handling (1/2) • MP1 and MP2 have a peer service period. • MP1 terminates the peer service period and sets in the termination frame: • MD to1 to indicate that it has more data to transmit to the MP2. • Power management mode to 1 to indicate operation in active mode. • MP2 may trigger MP1 at any time when MP1 is active. • New peer service period is triggered and the termination of the peer service period sets MP1 to power save mode and both MPs may return to doze state. Data Ack Data, PM =0, MD=1, EOSP =1 Ack null, Ack Data, PM=1,MD=0, EOSP=1 Ack MP1 MP2 = Light sleep mode MP = Active mode MP = MP may transmit data = MP may receive data Jarkko Kneckt, Nokia

  23. Peer service period handling (2/2) • MP1 and MP2 have a peer service period ongoing. • MP1 terminates the peer service period and sets in the termination frame: • MD to1 to indicate that it has more data to transmit to the MP2. • MP2 may trigger MP1 after the beacon transmission from MP1. • New peer service period is triggered after the beacon from MP1 and the termination of the peer service period enables both MPs to return to doze state. Data Ack Data, MD=1, EOSP =1 Ack … Beacon.Tim set for MP2 null Ack Data, MD=0, EOSP=1 Ack MP1 MP2 = Light sleep mode MP = MP may transmit data = MP may receive data Jarkko Kneckt, Nokia

  24. Bi-directional peer service periods • Bi-directional peer service periods enable: • better efficiency and controllability of the mesh service period, because both sides may actively transmit data and other MP is not forced to receive only • Better coordination to transition from active mode to power save, no lost frames in power mode transition • Efficient termination, one frame and ack transmission to terminate a peer service period • Signaling examples are shown in the following slides. Jarkko Kneckt, Nokia

  25. Bi-directional peer service period Operation during the bi- directional mesh service period Both MPs are in light sleep mode Both MPs indicate that they have transmitted all frames. After data frame transmission, which contains more data bit set to 0 and ack with more data bit set to 0, the peer service period is terminated. Data Ack Data, EOSP=1 Ack, MD=1 Data, EOSP=1 Ack, MD=0 MP3 MP4 = MP may transmit data = MP may receive data Jarkko Kneckt, Nokia

  26. Active mode to light sleep transition, bi-directional peer service periods used • The MP3 indicates that it does not have any data to be sent and it is going to power save mode. • MP4 has data in its buffers and it initiates mesh service period which keeps MP3 in active mode until end of mesh service period. • MP3 may send any additional data it has during the mesh service period MP indicates that is does not have data to be sent anymore and it moves to power save mode Data Ack MP initiates mesh service period, receiving MP waits until mesh service period has ended before going to Data, PM=1 Ack, MD=1 Data Ack Data, EOSP=1 Ack, MD = 0 MP3 MP4 = Light sleep mode MP = MP may transmit data = MP may receive data = Active mode MP Jarkko Kneckt, Nokia

  27. Mesh service period summary • Unidirectional Mesh Service Period • Used when link configured to support only unidirectional service periods • Used in between active mode and light sleep mode MPs • Bi-directional Mesh Service Period • Provides efficient method to send data between light sleep MPs when there isn’t equal amount of data to be sent and other MP is not forced to receive only • Better coordination to transition from active mode to power save, no lost frames in power mode transition • Efficient termination through a single frame and ack transmission. Jarkko Kneckt, Nokia

  28. Appendix, power consumption calculations in different power management modes Jarkko Kneckt, Nokia

  29. Calculations on stand-by modes power consumption • 11-07-1996-r2 (Power save and routing) presentation presents radio power consumption parameters and beacon transmission density. • Next slide is copied from the presentation in order to provide power consumption analysis for beaconing mechanisms. • The presentation calculates power consumption estimations for IBSS beaconing, light sleep and deep sleep beaconing modes. Jarkko Kneckt, Nokia

  30. A quantitative analysis of benefit derived from power management mechanism • Some calculation: • Assumption on the power consumption captured from [1] • Operational parameter setting • Beaconing interval : 1000 /100ms • DTIM interval : 0 (every beacon is DTIM beacon, no TIM beacons) • ATIM Window : 10 / 5 / 2,5 ms • Ramp up margin: 1ms • Number of neighbouring peer MPs : 6 • Beacon frame length: 200us Take this parameters for example Jarkko Kneckt, Nokia

  31. Analysis on benefits derived from power save capabilities • Case 1. MP uses IBSS beaconing, all peers are using the same beacon. • MP transmits every seventh (1/7) beacon and receives 6/7 of the beacons. MP stays active during the ATIM period. • Total power consumption per 1[sec] • Amount of beacons per second x (ramp up + 1/7 beacon transmission + 6/7 beacon reception + ATIM Wakeup) + rest of time x Doze State power drain Jarkko Kneckt, Nokia

  32. Analysis on benefits derived from power save capabilities IBSS beaconing power consumption results Note, The time consumption is given for 1 beacon/second case. Jarkko Kneckt, Nokia

  33. Analysis on benefits derived from power save capabilities • Case 2. MP operating in light sleep • Total power consumption per 1[sec] • Amount of beacons per second x [ (ramp up + beacon transmission + ATIM Wakeup) + 6*(ramp up + beacon reception)] + rest of time x Doze State power drain Jarkko Kneckt, Nokia

  34. Analysis on benefits derived from power save capabilities Light Sleep beaconing power consumption results Note, The time consumption is given for 1 beacon/second case. Jarkko Kneckt, Nokia

  35. Analysis on benefits derived from power save capabilities • Case 3. MP operating in Deep sleep • Case assumes that MP using Deep Sleep receives every 10th (1/10) beacon from peer MPs in order to maintain links from timeout. • Total power consumption per 1[sec] • Amount of beacons per second x (ramp up + beacon transmission + ATIM Wakeup) + 6*(ramp up + beacon reception) /10 + rest of time x Doze State power drain Jarkko Kneckt, Nokia

  36. Analysis on benefits derived from power save capabilities Deep Sleep beaconing power consumption results Note, The time consumption is given for 1 beacon/second case. Jarkko Kneckt, Nokia

  37. Analysis on benefits derived from power save capabilities Total stand-by power consumption, excluding the sleep mode power consumption Total stand-by power consumption Jarkko Kneckt, Nokia

  38. Strawpolls • Does 802.11s Mesh networks need power save? • Yes • No • Are you in favour of the power save enhancements presented in this slide set and described in 11-07-2717r2? • Yes • No Jarkko Kneckt, Nokia

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