1. IEEE 802.21 MEDIA INDEPENDENT HANDOVER
Title: Power Save Topics for Mobile Battery Powered Wireless Devices
Date Submitted: July 15, 2008
Presented at IEEE session #27 in Denver
Authors or Source(s): Michael G. Williams, Padam Kafle (Nokia)
Abstract: Discussion topics of power save at the network and lower layers. Discuss potential improvements through enhancements to MIH services.
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2. IEEE 802.21 presentation release statements
This document has been prepared to assist the IEEE Working Group. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein.
The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE
The contributor is familiar with IEEE patent policy, as outlined in Section 6.3 of the IEEE-SA Standards Board Operations Manual < and in Understanding Patent Issues During IEEE Standards Development
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3. Power save related topics
Outline
Review of today’s system related power issues for mobile battery powered devices
WLAN power save overview
WCDMA power save overview
Can .21 help ?
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4. System related power drains
Always-on applications and services are the current main cause of battery drain where might help
.21 cannot modify WCDMA or WLAN power save modes
Applications require keep-alives from the terminal
To refresh the application server
To keep open the NATs or FWs in the network
‘Push’ apps and services require the terminal must be reachable
Mobile IM
Voice, video (CoIP)
VPN
MIP
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5. System related power drains
Unified messaging / instant messaging services
fring, gizmo, MSN, etc (not preinstalled in devices)
large buddy groups and presence updates
Peer-to-peer networks with variety of services increases traffic, power demands
Location based applications
Apps using low GPS fix rate
Navigation use case is standard
Music, Video services
Streaming or download
Youtube and other video services
Watching and uploading
to become an obvious item to haveh
With push when needed or liked
Browser Asynchronous Javascript (AJAX) et al
Browser based apps utilize frequent messaging
VPN usage
intranet access, Internet through intranet
Network and session layer mobility related traffic, keep-alives
Understanding the power save features in use today can help to show the way for future improvements
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6. NAT, FW, VPN, MIP Keep-alives
Timers are used to close connections through these devices to help network devices conserve resources and improve security
Commonly used in residential broadband connections, WLAN hotspot, 3G internet connections (almost everywhere for IPv4)
Terminal can usually discover the presence of these, but still must send keep-alives within the timer interval to keep the session continuity
The more mobility services that are running on the terminal, the more keep-alives are sent
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7. Typical Cellular Internet Access Scenario
RAN
Internet
NAT/FW
GGSN, SAE GW,
CSN GW
Internet or
corporate
service
Private addresses
Public addresses
In cellular/wireless network architectures (3GPP, 3GPP2, WMF) NAT/FW is typically located at the “access router”, i.e. the first IP level network element from the mobile host point of view
Inbound traffic for a certain IP:port pair is allowed only after outbound traffic sent first. The state expires (for UDP ~30 seconds, TCP 5-60 min.)
There is often only a single layer of NAT/FW
If this NAT/FW bindings/pinholes could be explicitly controlled from the mobile host, excessive keep-alive traffic would not be needed
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8. Multi Radio Power Consumption (relative measurements with SIP)
Figures from 2006 implementations, for comparison only
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9. NAT, FW, VPN, MIP Keep-alives
UDP-based solutions used by e.g. VPNs and by most SIP services really power-consuming.
TCP works better, but not a generic solution.
Problem can’t be solved in devices/hosts alone, but it requires special support in the access networks (and in some cases servers)
Perhaps MIH MRPM could help?
New MIH SAP local services for coordination and control of keep-alive transmissions?
Discover presence of timer values for NAT/FW/VPN/MIP via IS or ES?
Configure timers to synchronize them, via CS or new service?
Proxy keep-alive services up or downstream?
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10. Power save related topics
Outline
Review of today’s system related power issues for mobile battery powered devices
WLAN power save overview
WCDMA power save overview
Can .21 help ?
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11. WLAN Power Save Overview
WLAN supports power save mode (PSM) and Unscheduled Automatic Power Save Delivery (U-APSD) scheme, part of the WLAN QoS e/WMM work
.11n will also support Power Save Multi Poll (PSMP)
STA signals to AP it is going to from constant awake mode (CAM) to PSM
STA goes to low power
AP buffers downstream traffic, indicates the awaiting traffic via beacon Delivery Traffic Indicator Map (DTIM)
STA wakes up periodically to check beacon DTIM from AP for traffic
U-APSD STA wakes up anytime,
PSM wakes up at scheduled time (typically awakes every 1-5 DTIMs)
If DTIM indicates traffic, STA sends trigger frame to AP requesting delivery
AP receives trigger frame and delivers data according to delivery mode in use
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12. WLAN Power Save Overview
A high-level state diagram of IEEE power save
Implementation of PSM and U-APSD is not consistent
Some APs don’t buffer multicast or broadcast so these can be dropped (e.g. DHCP and ARP)
Typically three behavioral modes in implementations:
Never PS
Sometimes PS on receive, never when transmit needed
Always attempt to PS
UI and applications aren’t coordinated.
No standard MAC SAP services to indicate or control modes
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13. WLAN Power Drain Causes
Scanning contributes substantially to power drain
Background scanning, even if no network, is common
Hidden SSIDs take more power to scan due to probing
Broadcast and Multicast traffic downstream can be large power drain for STAs
NetBIOS, DHCP, UPnP
control protocols of local bridges, switches, and access points
AP encrypts and forwards traffic downstream, STA decrypts and drops unwanted traffic
AP implementations often do proxy ARP, so hopefully no ARP traffic
Small DTIM timer values
Perhaps MIH MRPM could help?
New MIH SAP local services for coordination and control?
Proxy to handle unwanted traffic?
Coordinated use of CS plus location to improve scanning intelligence?
Use of ES over other radio to announce awaiting WLAN traffic ?
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14. Power save related topics
Outline
Review of today’s system related power issues for mobile battery powered devices
WLAN power save overview
WCDMA power save overview
Can .21 help ?
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15. WCDMA Power Save Overview
Overview of basic WCDMA radio resource control (RRC) state machine
CELL_DCH (dedicated channel):
Channel not shared, highest power use, giving maximum throughput and minimum delay
CELL_FACH (forward access channel):
Shared channel used when there is not much uplink traffic, about 50% power of CELL_DCH state.
CELL_PCH (paging channel, optional):
1–2% of CELL_DCH power.
If there are downlink packets for the terminal, the terminal will be paged.
New states in newer releases (e.g. URA PCH)
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16. WCDMA Power Save Overview
Overview of basic WCDMA radio resource control (RRC) state machine
Idle mode:
No RRC connection, only paging can reach terminal
Usually, the terminal will use the CELL_DCH state to send keep-alives
keep-alives and push traffic (e.g. incoming s) will consume a lot more power
Some networks support the state transition from idle mode directly to CELL_FACH
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17. WCDMA Power Save Overview
Overview of basic WCDMA radio resource control (RRC) state machine
Timers T1, T2 and T3 are controlled by radio network controller (RNC) to cause transition
T1 is CELL_DCH state inactivity timer
reset whenever there is traffic
after expiring, terminal enters the CELL_FACH state.
the shorter the T1 timer, the worse the user experience will be
T1 value may depend on the DCH data rate
Typical values used in RNC implementations are:
5 seconds for 8–32 kbit/s
3 seconds for 128 kbit/s
2 seconds for data rates greater than 128 kbit/s
In some networks, significantly longer timers than these may be used
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18. WCDMA Power Save Overview
Overview of basic WCDMA radio resource control (RRC) state machine
Timers T1, T2 and T3 are controlled by radio network controller (RNC) to cause transition
T2 is CELL_FACH state inactivity timer
If CELL PCH is used, terminal state machine will enter the CELL_PCH state after T2 expires
If CELL_PCH is not used, the terminal state machine will enter the idle state
Typical implementation value is 2 seconds
but often significantly longer T2 values are used
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19. WCDMA Power Save Overview
Overview of basic WCDMA radio resource control (RRC) state machine
Timers T1, T2 and T3 are controlled by radio network controller (RNC) to cause transition
T3 is a timer used in CELL_PCH
After staying in the CELL_PCH for T3 seconds, the RRC connection will be released
Typical implementation value is long
Minimum is several minutes
Maximum can be tens of minutes
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20. WCDMA Power Save Overview
T1 and T2 define the time of device transitions from the more power-consuming states to less consuming states
The sum T1+T2 defines the general power consumption behavior of the device
T1 has a significant effect on the perceived performance of several applications
T2 accounts for most of the idle battery performance in networks where CELL_PCH or idle-to-CELL_FACH transitions are available
Short keep-alive packets can be transmitted in CELL_FACH state
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21. WCDMA Power Save Overview
In CELL_PCH state (or URA_PCH) terminal only responds to pages
In CELL_PCH, terminal can use discontinuous reception (DRX) mode
terminal powers off its receiver
DRX mode is used when nothing else is needed to be done
DRX cycle length is interval between two successive power ups
cycle length affects battery performance
Typical DRX cycle length is 1-2 seconds
Increasing the DRX cycle length is a tradeoff:
improves the stand-by battery performance
increases the paging delays
increases the packet roundtrip delays and call setup delays
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22. WCDMA Power Save Overview
3GPP R7 and R8 allows major terminal power savings with Discontinuous transmission (DTX) and reception (DRX)
Release 7 brings Continuous packet connectivity (CPC) which allows DTX and DRX for Cell_DCH state. L1 activity can be decreased by 70% for VoIP and by 85% of inactive terminal
Release 8 brings DRX to FACH state. Lower power consumption for keep alive messages
Web page download
User reading web page
User moved to FACH/PCH
HS-DSCH
HSPA R6
DPCCH
Continuous packet connectivity
HS-DSCH
HSPA R7
DPCCH
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23. WCDMA Power Save Overview
Other aspects of mobility also drain power:
Intersystem reselections
Out-of-coverage conditions
All of these states and intersystem mobility procedures are internal to 3G-2G radio systems, cannot be changed in
Perhaps MIH MRPM could help?
MIH entities will likely not be in the PoA as they could be in IEEE based systems
New MIH SAP local services for coordination and control?
Coordinated use of CS plus location to improve scanning intelligence for multi radio terminals?
Use of ES over other WCDMA radio to announce awaiting WLAN or WiMAX traffic ?
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24. Power save related topics
Outline
Review of today’s system related power issues for mobile battery powered devices
WLAN power save overview
WCDMA power save overview
Can .21 help ?
mrpm

25. Summary of areas for MRPM work
Develop new services and entities in following areas:
(Refer to MRPM documents that describe new entities)
New MIH SAP local services for coordination and control of power states
New MIH SAP local services for coordination and control of keep-alive transmissions
Coordinated use of CS plus location to improve scanning intelligence for multi radio terminals
Use of ES over active radio to announce awaiting WLAN or WiMAX traffic
Discover presence of timer values for NAT/FW/VPN/MIP via IS or ES
Configure timers to synchronize them, via CS or new service
Proxy keep-alive services up or downstream in new PoA entity
Proxy to handle unwanted traffic in new PoA entity
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