October 2007 doc.: IEEE 802.11-07/2646r2
Power efficient and unified 802.11s solution
Date: 2007-11-12
Authors:
Name Affiliations Address Phone email
Jarkko Kneckt Nokia Itämerenkatu 11-13, jarkko.kneckt@nokia.com
00180 Helsinki,
Finland
Janne Marin Nokia Itämerenkatu 11-13, janne.marin@nokia.com
00180 Helsinki,
Finland
Mika Kasslin Nokia Itämerenkatu 11-13, mika.kasslin@nokia.com
00180 Helsinki,
Finland
Submission Slide 1 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 2 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Contents
1. Introduction
– The big picture
2. Basic components
– Five basic components of MPs
3. Power save in details
– Two levels of power save
– Power mode transition rules
– Peer service period
Submission Slide 3 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 14 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 15 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 16 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 17 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
MP2
MP1 and MP2 are peer-MPs to each other
= DTIM beacon = TIM beacon = Awake Window
Submission Slide 18 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
The basic rules of light sleep
1. Beaconing MP uses Mesh TIM field in its own beacon to indicate presence of
buffered data to power saving peer MPs
2. 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
3. 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
Submission Slide 19 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 20 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Data transmission between deep sleep
mode MPs
1. 2.
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 = Awake Window = peer service period
= Operation in deep sleep mode = Doze state = Awake state
1. MP1 receives null frame during its Awake window. A peer service period
is triggered.
2. MP1 receives frames during its peer service period.
3. MP1 sends null frame to MP2 during Awake window of MP2 to trigger a
peer service period.
4. MP1 transmits the frames to MP2 during the peer service period.
Submission Slide 21 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 22 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 23 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Mode and level transitions (2/2)
• 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 Power Power Save
• Power management indicated in BC/MC management Management Level bit
frames is set as per the lowest power mode bit
management mode used in the links Active mode 0 -
• The power management mode that is Power Save 1 0
Light Sleep
indicated in BC/MC frames is used also
Power Save 1 1
by non-peer MPs to determine the times Deep Sleep
for scan and link creation frame
exchange
Submission Slide 24 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 25 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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.
– A trigger frame initiates a peer service period, which type is specified in the link
setup. The following slides discusses more on the service period types.
• 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 termination rules discussed in the following slides
Submission Slide 26 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Peer service period types
• Peer service period may be unidirectional or bi-directional
– Unidirectional peer service period enables either 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 enables both MPs to transmit data during the peer
service period. The peer service period is terminated when both data frame and
acknowledgement indicate that all buffered traffic is transmitted.
• Two unidirectional peer service periods may be used to allow for the both
MPs to transmit data
• Bi-directional peer service period shall be used, if both MPs support 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
Submission Slide 27 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Information elements 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 mechansims.
Submission Slide 28 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Termination of the unidirectional peer
service periods
Termination of one unidirectional peer Termination of two unidirectional peer
service period service periods
MP 1 is data transmitter in the peer service period. Both MP 3 and MP4 are data transmitters in the peer
service periods. The peer service period from MP3 is
The peer service period is terminated when MP1 indicates terminated, when MP3 transmits a frame with set EOSP
that it does not have more data to transmit with EOSP. bit. MP4 acts accordingly with its own peer service
period.
Data
Data
Ack
Ack
Data, EOSP=1
Data, EOSP=1
Ack
Ack
Data, EOSP=1
Ack
MP1 MP2 MP3 MP4
= MP may transmit data = MP may receive data EOSP = End of service period bit
Submission Slide 29 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Mesh service period between active mode
MP1
indicates in
and light sleep MPs
beacon that
it has data
pending
Data MP2 • MP1 has data to be sent for
responses
Ack with trigger MP2 and MP1 indicates it in
frame
Data starting its beacon
• MP2 responses with
mesh service
Ack period
Data
appropriate trigger frame
Ack
which initiates mesh service
period
Data, EOSP=1 • Service period is ended with
Ack
setting of EOSP bit after the
MP1 buffers further data for
MP2
• MP2 may trigger a peer
service period at any time
MP1 MP2
= Light sleep mode MP
= MP may transmit data = MP may receive data = Active mode MP
Submission Slide 30 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Peer service period handling (1/2)
MP1 terminates the peer service period and
Data
sets in the termination frame:
Ack
- MD to1 to indicate that it has more data to
Data, PM =0, MD=1, EOSP =1 transmit to the MP2.
Ack - Power management mode to 1 to indicate
null, operation in active mode.
Ack
Data, PM=1,MD=0, EOSP=1
MP2 may trigger MP1 at any time when MP1
Ack
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
MP1 MP2 return to doze state.
= Light sleep mode MP
= MP may transmit data = MP may receive data = Active mode MP
Submission Slide 31 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Peer service period handling (2/2)
MP1 terminates the peer service period and
Data
sets in the termination frame:
Ack
- MD to1 to indicate that it has more data to
Data, PM =0, MD=1, EOSP =1 transmit to the MP2.
Ack
MP2 may trigger MP1 after the beacon
…
Beacon.Tim set for MP2 transmission from MP1.
null
New peer service period is triggered after the
Ack
beacon from MP1 and the termination of the
Data, MD=0, EOSP=1
peer service period enables both MPs to
Ack
return to doze state.
MP1 MP2
= Light sleep mode MP
= MP may transmit data = MP may receive data
Submission Slide 32 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Bi-directional peer service period
Operation during the bi-
directional mesh service period
Both MPs are in light sleep mode
Data Both MPs indicate that they have transmitted
Ack all frames. After data frame transmission,
which contains more data bit set to 0 and ack
Data, EOSP=1 with more data bit set to 0, the peer service
Ack, MD=1 period is terminated.
Data, EOSP=1
Ack, MD=0
MP3 MP4
= MP may transmit data = MP may receive data
Submission Slide 33 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Active mode to light sleep transition
(complicated case)
• The MP3 indicates that it
MP indicates
does not have any data to be
that is does not Data sent and it is going to power
have data to be Ack
sent anymore
MP initiates
mesh service
save mode.
and it moves to
power save
period, • MP4 has data in its buffers
Data, PM=1 receiving MP
mode waits until and it initiates mesh service
Ack mesh service
period has period which keeps MP3 in
Data
Ack
ended before
going to
active mode until end of mesh
Data, EOSP=1
service period.
Ack • MP3 may send any additional
data it has during the mesh
MP3 MP4 service period
= Light sleep mode MP
= MP may transmit data = MP may receive data = Active mode MP
Submission Slide 34 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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.
Submission Slide 35 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Appendix, power consumption calculations in different power management modes
Submission Slide 36 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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.
Submission Slide 37 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
A quantitative analysis of benefit derived
from power management mechanism
• Some calculation:
– Assumption on the
power consumption
captured from [1]
– Operational parameter setting Take this parameters for example
• 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
Submission Slide 38 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 39 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Analysis on benefits derived from power
save capabilities
IBSS beaconing power consumption results
IBSS ATIM = 10ms ATIM = 5ms ATIM = 2,5ms
Time [s] Wakeup 0,001 0,001 0,001
Idle 0,0098 0,0048 0,0023
Total RX 0,000171 0,000171 0,000171
Total TX 2,86E-05 2,86E-05 2,86E-05
Sleep 0,989 0,994 0,9965
C [mA_s] Idle 1,6848 0,9048 0,5148
Total RX 0,032571 0,032571 0,032571
Total TX 0,008114 0,008114 0,008114
Sleep 9,89 9,940 9,965
Power [mW] Idle 7,986 4,289 2,440
Total RX 0,154 0,154 0,154
Total TX 0,038 0,038 0,038
Sleep 46,879 47,116 47,234
Total Power Power, 1 beacon /
[mW] 1 second 55,06 51,60 49,87 Note,
Power, power for The time consumption
sleep is not is given for 1
included 8,18 4,48 2,63 beacon/second case.
Power 10beacons /
1second 123,97 89,37 72,07
Power, power for
sleep is not
Submission included Slide 40
81,78 44,82 26,33 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 41 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Analysis on benefits derived from power
save capabilities
Light Sleep beaconing power consumption results
Light Sleep ATIM = 10ms ATIM = 5ms ATIM = 2,5ms
Time [s] Wakeup 0,007 0,007 0,007
Idle 0,0098 0,0048 0,0023
Total RX 0,0012 0,0012 0,0012
Total TX 2,00E-04 0,0002 0,0002
Sleep 0,9818 0,9868 0,9893
C [mA_s] Idle 2,6208 1,8408 1,4508
Total RX 0,228 0,228 0,228
Total TX 0,0568 0,0568 0,0568
Sleep 9,818 9,868 9,893
Power [mW] Idle 12,422592 8,725 6,877
Total RX 1,08072 1,081 1,081
Total TX 0,269232 0,269 0,269
Sleep 46,53732 46,774 46,893
Total Power Power, 1 beacon /
[mW] 1 second 60,31 56,85 55,12 Note,
Power, power for The time consumption
sleep is not is given for 1
included 13,77 10,08 8,23 beacon/second case.
Power 10beacons /
1second 176,50 141,90 124,60
Power, power for
sleep is not
Submission included 42
Slide 137,73 100,75 82,27 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
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
Submission Slide 43 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Analysis on benefits derived from power
save capabilities
Deep Sleep beaconing power consumption results
Deep Sleep ATIM = 10ms ATIM = 5ms ATIM = 2,5ms
Time [s] Wakeup 0,0016 0,0016 0,0016
Idle 0,0098 0,0048 0,0023
Total RX 0,00012 0,00012 0,00012
Total TX 2,00E-04 0,0002 0,0002
Sleep 0,98828 0,99328 0,99578
C [mA_s] Idle 1,7784 0,9984 0,6084
Total RX 0,0228 0,0228 0,0228
Total TX 0,0568 0,0568 0,0568
Sleep 9,8828 9,933 9,958
Power [mW] Idle 8,429616 4,732 2,884
Total RX 0,108072 0,108 0,108
Total TX 0,269232 0,269 0,269
Sleep 46,844472 47,081 47,200
Total Power Power, 1 beacon /
[mW] 1 second 55,65 52,19 50,46 Note,
Power, power for The time consumption
sleep is not is given for 1
included 8,81 5,11 3,26 beacon/second case.
Power 10beacons /
1second 129,91 95,31 78,01
Power, power for
sleep is not
Submission included Slide 44
88,07 51,10 32,61 Jarkko Kneckt, Nokia
October 2007 doc.: IEEE 802.11-07/2646r2
Analysis on benefits derived from power
save capabilities
Total stand-by power consumption, excluding the sleep
Total stand-by power consumption mode power consumption
Beaconing ATIM
interval duration Light Deep IBSS
[ms] [ms] Sleep Sleep network
Beaconin ATIM IBSS
g interval duratio Light Deep networ
[ms] n [ms] Sleep Sleep k 1000 10 13,77 8,81 8,18
1000 10 60,31 55,65 55,06 1000 5 10,08 5,11 4,48
1000 5 56,85 52,19 51,60 1000 2,5 8,23 3,26 2,63
1000 2,5 55,12 50,46 49,87 100 10 137,73 88,07 81,79
176,5
100 5 100,75 51,10 44,82
100 10 0 129,91 123,97
141,9 100 2,5 82,27 32,61 26,33
100 5 0 95,31 89,37
124,6
100
Submission 2,5 0 78,01 72,07 Slide 45 Jarkko Kneckt, Nokia