a survey of energy efficient network protocols for wireless networks
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A survey of Energy Efficient Network Protocols for Wireless Networks. Christine E. Jones Krishna M. Sivalingam Prathima Agrawal Jyh-Cheng Chen. Issue 1/2. Rapid expansion of wireless services, mobile data and wireless LANs Greatest limitation: finite power supplies. Issue 2/2. - PowerPoint PPT PresentationTRANSCRIPT
A survey of Energy Efficient Network Protocols for Wireless
Networks
Christine E. JonesKrishna M. Sivalingam
Prathima AgrawalJyh-Cheng Chen
Issue 1/2 Rapid expansion of wireless
services, mobile data and wireless LANs
Greatest limitation: finite power supplies
Issue 2/2 Typical example of power consumption
from a mobile computer (Toshiba 410 CDT):
o 36% Displayo 21% CPU/memoryo 18% Wireless interfaceo 18% Hard drive
Goalo Incorporate energy conservation at all layers of
protocol stack
Energy Efficiency Research in Protocol Stack
Physical Layer Two different perspectives Increase battery capacity
o Increase capacity while restricting weighto However battery technology hasn’t
experienced significant advancement in the past 30 years
Decrease of energy consumedo Variable clock speed CPUso Flash memoryo Disk spindown
Sources of Power Consumption
Two typeso Communication relatedo Computation related
Tradeoff between them
Communication related Three modes:
o Transmito Receiveo Standby
Example:o Proxim RangeLAN2 2.4 GHz 1.6 Mbps PCMCIA
card 1.5W transmit, 0.75W receive, 0.01W standby
Turnaround between transmit and receive typically takes 6 to 30 microseconds
Optimize the transceiver usage
Computation related Usage of CPU, main memory and
disk Data compression techniques for
reduction of packet length increase power consumption
General Guidelines and Mechanisms 1/5
Reduce collisions in MACo Retransmissions lead to power
consumption and delayso Cannot be completely eliminated due to
user mobility and varying set of mobiles Change typical broadcast
mechanismo 802.11: Receiver keeps track of channel
status through constant monitoring
General Guidelines and Mechanisms 2/5
Turnaround between transmit and receive mode spends time and powero Allocate contiguous slots for transmission
or receptiono Request multiple transmission slots with a
single reservation packet Computation of transmission schedule
should be relegated to base station
General Guidelines and Mechanisms 3/5
Scheduling algorithm may additionally consider battery power level
Allow mobile to re-arrange allocated slots under low-power conditions
At link layer:o Avoid transmissions when channel
conditions are pooro Combine ARQ and FEC mechanisms
General Guidelines and Mechanisms 4/5
Energy efficient routing protocolso Ensure all nodes equally deplete their power
levelo Avoid routing through nodes with lower
battery power Requires mechanism for dissemination of node
battery powero Periodicity of routing updates can be
reduced May result in inefficient routes
General Guidelines and Mechanisms 5/5
OS levelo Suspend of specific sub-unit (disk,
memory, display etc.) when detect prolonged inactivity
MAC Sublayer Three specific MAC protocols
o IEEE 802.11o EC-MACo PAMAS
IEEE 802.11 Standard 1/2 A mobile that wishes to conserve power
may switch to sleep mode and inform the base station
The base stationo Buffers packets that are destined for the
sleeping mobileo Periodically transmits a beacon that contains
information about such buffered packets When the mobile wakes up, it listens for
this beacon, and responds to the base station which then forwards the packets
IEEE 802.11 Standard 2/2 Conserves power but results in additional
delays and may affect the QoS Experimental measurements of per
packet energy consumptiono Same incremental costs for both unicast and
broadcast traffico Higher fixed costs for unicast transmission
because of MAC coordination and CTS and ACK messages
EC-MAC Protocol 1/7 Energy Conserving-Medium Access
Control Developed with the issue of energy
efficiency as a primary goal Defined for infrastructure network but
can be extended to ad-hoc by allowing mobiles to elect a coordinator
It is based on reservation and scheduling and supports QoS
EC-MAC Protocol 2/7
EC-MAC Protocol 3/7 FSM:
o transmitted at the start of each frame by the base station
o contains synchronization information and uplink transmission order for subsequent reservation phase
Request/Update Phase:o Each registered mobile transmits new
connection requests and status of established queues
o Collisions avoided
EC-MAC Protocol 4/7 New User Phase (Aloha):
o Registration of new userso Collisions occuro Provides time for BS to compute the data
phase transmission schedule Schedule Message:
o Broadcasted by the base stationo Contains the slot permissions for the
subsequent data phase
EC-MAC Protocol 5/7 Data phase (Downlink):
o Transmission from base station to mobiles
o Scheduled considering QoS requirements
Data phase (Uplink):o Slots allocated using a suitable
scheduling algorithm
EC-MAC Protocol 6/7 Collisions are avoided and this
reduces the number of retransmissions
Mobile receivers are not required to monitor the channel because of schedules
Centralized scheduler can optimize schedule so that mobiles transmit and receive within contiguous slots
EC-MAC Protocol 7/7 Scheduling algorithms may consider
also battery power level in addition to packet priority
Frames may be fixed or variable lengtho Fixed are desirable from energy efficient
perspective since a mobile will know when to wake up to receive FSM
o Variable are better for meeting the demands of bursty traffic
PAMAS Protocol 1/3 Designed for ad hoc network, with
energy efficiency as primary goal Provides separate channels for
RTS/CTS control packets and data packets
PAMAS Protocol 2/3 A mobile with a packet to transmit sends a
RTS over the control channel, and awaits the CTS
If no CTS arrives the mobile enters a backoff state
However, if CTS is received, then the mobile transmits the packet over the data channel
The receiving mobile transmits a “busy tone” over the control channel for the others to determine that the data channel is busy
PAMAS Protocol 3/3 The use of control channel allows mobiles
to determine when and for how long to power off
A mobile can power off when:o It has no packets to transmit and a neighbor
begins transmitting a packet not destined for ito It does have packets to transmit but at least
one neighbor-pair is communicating The length of power off time is determined
through the use of a probe protocol (Singh and Raghavendra, 1998)
LLC Sublayer Is responsible for the error control The two most common techniques
for the error control are Automatic Repeat Request (ARQ) and Forward Error Correction (FEC)
Both waste network bandwidth and power resources due to retransmissions and greater overhead
LLC Sublayer Recent research has addressed
low-power error control and several energy efficient link layer protocols have been proposed:o Adaptive Error Control with ARQo Adaptive Error Control with ARQ/FEC
Combinationo Adaptive Power Control and Coding
Scheme
Adaptive Error Control with ARQ 1/3
Three guidelines:o Avoid persistence in retransmitting
datao Trade off number of retransmission
attempts for probability of successful transmission
o Inhibit transmission when channel conditions are poor
Adaptive Error Control with ARQ 2/3
Works as normal until the transmitter detects an error due to the lack of a received ACK.
Then the protocol enters a probing mode in which a probing packet is transmitted every t slots. Probe packet contains only header
This mode continues until an ACK is received. Then the protocol returns to normal mode and continues transmission from where it was interrupted
Adaptive Error Control with ARQ 3/3
Analysis results show that under slow fading channel conditions it is superior to standard ARQ in terms of energy efficiency
There is an optimal transmission power in respect to energy efficiency
o Decreasing the transmission power results in an increased number of transmission attempts but may be more efficient than attempting to maximize the throughput
Adaptive Error Control withARQ/FEC Combination
Each packet streamo is associated with service quality parameters
(packet size, QoS requirements)o maintains its own time-adaptive customized
error control scheme Error control scheme
o is a combination of an ARQ scheme (Go-Back-N, CACK, SACK, etc.) and a FEC scheme
o modifies as channel conditions change over time
Adaptive Power Control andCoding Scheme
Each transmitter operates at a power-code pair
o Power level lies between a specified minimum and maximum
o The error code is chosen from a finite set At each iteration (timeframe):
o Receiver checks the word error rate (WER)o If the WER lies within an acceptable range,
power-code is retained, otherwise a new power-code pair is computed by the transmitter
Variations of algorithm include average WER
Network Layer Energy efficient routing algorithms for ad
hoc networks Does not apply to infrastructure networks
because all traffic is routed through BS Two different approaches:
o Frequent topology updates Improved routing Consumes bandwidth
o Infrequent topology updates Decreased update messages Inefficient routing and occasional missed packets
Network Layer Typical metrics for ad hoc routing
protocolso Shortest-hopo Shortest-delayo Locality-stability
However they may result in the overuse of energy resources of a small set of mobiles decreasing mobile and network life
Network Layer example Using shortest-hop
routing, traffic from A to D will always be routed through E
E’s energy reserves will be drained faster and then F will be disconnected from network
A to D traffic should also use the B-C path extending networks life
Network Layer: Unicast Traffic 1/6
Five different metricso Energy consumed per packeto Time to network partition
Given a network topology, a minimal set of mobiles exist such that their removal will cause the network to partition
The traffic in that mobiles should be divided in such a way that they drain their power at equal rates
Network Layer: Unicast Traffic 2/6
o Variance in power level across mobiles All mobiles are equal and remain powered-on
together for as long as possibleo Cost per packet
Routes should be created such that mobiles with depleted energy reserves do not lie on many routes
o Maximum mobile cost By minimizing the cost experienced by a mobile
when routing a packet through it significant reductions in the maximum mobile cost result
Network Layer: Unicast Traffic 3/6
The goal is to minimize all the metrics except for the second which should be maximized
Shortest-cost routing protocol is more appropriate instead of shortest-hop
So although packets may be routed through longer paths, the paths contain mobiles that have greater amounts of energy reserves
Also routing traffic through lightly loaded mobiles conserves energy because it minimizes contention and retransmission
Network Layer: Unicast Traffic 4/6
Simulation results showed no extra delay over the traditional shortest-hop metric
This is true because congested paths are often avoided
However this approach requires that every mobile have knowledge of every other mobile and the links between them
This creates significant communication overhead and increased delay
Network Layer: Unicast Traffic 5/6
Stojmenovic and Lin proposed localized routing algorithms
These algorithms depend only on information about the source location, the location of neighbors and location of the destination
This information is collected through GPS receivers which are included in every mobile
Network Layer: Unicast Traffic 6/6
They proposed a new power-cost metrico Incorporates both a mobile’s lifetime and
distance based power metrics Three power-aware localized routing
algorithms were developedo Power
Minimize total amount of power utilized when transmitting a packet
o Cost Avoid mobiles with low battery reserves
o Power-cost Combination of the other two
Network Layer: Broadcast Traffic 1/4
Each mobile needs to receive a packet only once
Intermediate mobiles are required to retransmit the packet
Key idea: allow each mobile’s radio to turn off after receiving a packet if its neighbors have already received a copy of the packet
Network Layer: Broadcast Traffic 2/4
In traditional networks broadcast technique is a simple flooding algorithm
o No global information topology gatheredo Requires little control overheado Completes with minimum number of hops
Not suitable for wireless networks because many intermediate nodes must retransmit packets needlessly
It is more beneficial to spend some energy in gathering topology information in order to determine the most efficient broadcast tree
Network Layer: Broadcast Traffic 3/4
A broadcast approach is presented in (Singh et al., 1999)
The tree is constructed starting from the source and expanding to the neighbor that has the lowest cost per outgoing degree
Mobile costs continuously change so broadcast transmissions may traverse different trees
Simulations showed very little difference in delay but 20% or better in energy consumption
Network Layer: Broadcast Traffic 4/4
In (Wieselthier et al., 2000) is presented an algorithm for determining the minimum-energy tree
There exists an optimal point in the trade-off between reaching greater number of mobiles in a single hop by using higher transmission power versus reaching fewer mobiles but using lower power levels
Transport Layer TCP was designed initially for wired networks
o Physical links are fairly reliableo Packet loss is random in nature
Over a wireless link it degrades significantlyo It resorts to a larger number of retransmissions
and frequently invoke congestion control measures because it confuses link errors and loss as channel congestion
The increased retransmissions consume battery energy and bandwidth
Transport Layer Various schemes have been
proposedo Split connection protocolso Link-layer protocolso End-to-end protocols
Split connection protocols 1/2
Split connection protocols 2/2
Completely hide the wireless link from the wired network by splitting each TCP connection into two separate connections at the BS
The second one may use modified versions of TCP that enhance performance over the wireless channel
Link-layer protocols 1/2
Link-layer protocols 2/2 Hides link related losses from the
TCP source Uses a combination of local
retransmissions and FEC over the wireless link
Local retransmissions use techniques that are tuned to the characteristics of the wireless channel
End-to-end protocols Include modified versions of TCP that
are more sensitive to the wireless environment
Uses mechanisms such as o SACK
allow the TCP source to recover from multiple packet losses
o ELN Aid the TCP source to distinguish between
congestion and other forms of loss
Energy Consumption Analysis of TCP 1/4
The energy consumption of Tahoe, Reno and New Reno is analyzed in (Zorzi and Rao, 2000)
Efficiency is defined as the average number of successful transmissions per energy unit
Results demonstrate thato error correlation affects the energy performanceo congestion control algorithms of TCP allow for
greater energy savings by backing off and wait during error bursts
o energy efficiency is sensitive to the version of TCP
Energy Consumption Analysis of TCP 2/4
The same versions of TCP were studied in (Tsaoussidis et al., 2000a) in terms of energy/throughput tradeoffs
Results showed thato no single version is most appropriate within
wired/wireless heterogeneous networkso the key to balancing energy and throughput is
through the error control mechanism They proposed a modified version of TCP,
referred to as TCP-Probing in (Tsaoussidis and Badr, 2000)
Energy Consumption Analysis of TCP 3/4
In TCP-Probing when a segment is delayed or lost, instead of invoking congestion control, transmission is suspended and a probe cycle is initiated
Probe cycle:o exchange of probe segments (TCP header
with no payload) between sender and receiver
o terminates when two consecutive RTT are successfully measured
Energy Consumption Analysis of TCP 4/4
The sender invokes standard TCP congestion control if persistent error conditions are detected
However, if conditions indicate transient random error, then the sender resume transmissions according to available network bandwidth
OS/Middleware The main functions of an operating system
is to manage access to physical resources like CPU, memory and disk space
CPUs can be operated at lower speeds by scaling down the supply voltage (quadratic relationship between power and supply voltage)
Predictive shutdown Different page placement algorithms exploit
the new power management features of memory technology
Application Layer 1/2 Load Partitioning
o Applications may be selectively partitioned between the mobile and base station
o Most of the power intensive computations of an application are executed at the BS
Proxieso Middleware that automatically adapt the
applications to changes in battery power and bandwidth
o Either on the mobile or BS side of wireless link
Application Layer 2/2 Databases
o Minimize power consumed per transaction through embedded indexing
Video Processingo Reduce effective bit rate of videoo Carefully discard video frames