Transcript Power Save Topics for Mobile Battery Powered

IEEE 802.21 MEDIA INDEPENDENT HANDOVER
Title: Power Save Topics for Mobile Battery Powered
Wireless Devices
Date Submitted: July 15, 2008
Presented at IEEE 802.21 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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IEEE 802.21 presentation release statements
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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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System related power drains
• Always-on applications and services are the current main cause
of battery drain where 802.21 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 email
• IM
• Voice, video (CoIP)
• VPN
• MIP
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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
• Email 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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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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Typical Cellular Internet
Access Scenario
GGSN, SAE GW,
CSN GW
RAN
Internet or
corporate
service
Internet
NAT/FW
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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Multi Radio Power Consumption
(relative measurements with SIP)
• Figures from 2006 implementations, for comparison only
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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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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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WLAN Power Save Overview
• WLAN supports power save mode (PSM) and Unscheduled Automatic
Power Save Delivery (U-APSD) scheme, part of the WLAN QoS
802.11e/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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WLAN Power Save Overview
A high-level state diagram of IEEE 802.11 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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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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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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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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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 e-mails) will consume a lot more
power
• Some networks support the state transition from idle mode directly to
CELL_FACH
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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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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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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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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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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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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
HSPA R6
User reading
web page
User moved to
FACH/PCH
HS-DSCH
DPCCH
Continuous packet
connectivity
HSPA R7
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HS-DSCH
DPCCH
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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 802.21
• 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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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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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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