A survey of Energy Efficient Network Protocols for Wireless .ppt
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1、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,Typical example of power co
2、nsumption from a mobile computer (Toshiba 410 CDT): 36% Display 21% CPU/memory 18% Wireless interface 18% Hard drive Goal Incorporate energy conservation at all layers of protocol stack,Energy Efficiency Research in Protocol Stack,Physical Layer,Two different perspectives Increase battery capacity I
3、ncrease capacity while restricting weight However battery technology hasnt experienced significant advancement in the past 30 years Decrease of energy consumed Variable clock speed CPUs Flash memory Disk spindown,Sources of Power Consumption,Two types Communication related Computation related Tradeo
4、ff between them,Communication related,Three modes: Transmit Receive Standby Example: 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 relat
5、ed,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 MAC Retransmissions lead to power consumption and delays Cannot be completely eliminated due to user mobility and var
6、ying set of mobiles Change typical broadcast mechanism 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 power Allocate contiguous slots for transmission or reception Request m
7、ultiple 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 con
8、ditions At link layer: Avoid transmissions when channel conditions are poor Combine ARQ and FEC mechanisms,General Guidelines and Mechanisms 4/5,Energy efficient routing protocols Ensure all nodes equally deplete their power level Avoid routing through nodes with lower battery power Requires mechani
9、sm for dissemination of node battery power Periodicity of routing updates can be reduced May result in inefficient routes,General Guidelines and Mechanisms 5/5,OS level Suspend of specific sub-unit (disk, memory, display etc.) when detect prolonged inactivity,MAC Sublayer,Three specific MAC protocol
10、s IEEE 802.11 EC-MAC 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 station Buffers packets that are destined for the sleeping mobile Periodically transmits a beacon that contains information about such buffered pac
11、kets 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 consumption Same incremental cos
12、ts for both unicast and broadcast traffic 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 bu
13、t 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: transmitted at the start of each frame by the base station contains synchronization information and uplink transmission order
14、 for subsequent reservation phase Request/Update Phase: Each registered mobile transmits new connection requests and status of established queues Collisions avoided,EC-MAC Protocol 4/7,New User Phase (Aloha): Registration of new users Collisions occur Provides time for BS to compute the data phase t
15、ransmission schedule Schedule Message: Broadcasted by the base station Contains the slot permissions for the subsequent data phase,EC-MAC Protocol 5/7,Data phase (Downlink): Transmission from base station to mobiles Scheduled considering QoS requirements Data phase (Uplink): Slots allocated using a
16、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 slo
17、ts,EC-MAC Protocol 7/7,Scheduling algorithms may consider also battery power level in addition to packet priority Frames may be fixed or variable length Fixed are desirable from energy efficient perspective since a mobile will know when to wake up to receive FSM Variable are better for meeting the d
18、emands 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
19、 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
20、 channel allows mobiles to determine when and for how long to power off A mobile can power off when: It has no packets to transmit and a neighbor begins transmitting a packet not destined for it It does have packets to transmit but at least one neighbor-pair is communicating The length of power off
21、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 res
22、ources 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: Adaptive Error Control with ARQ Adaptive Error Control with ARQ/FEC Combination Adaptive Power Control and Codin
23、g Scheme,Adaptive Error Control with ARQ 1/3,Three guidelines: Avoid persistence in retransmitting data Trade off number of retransmission attempts for probability of successful transmission Inhibit transmission when channel conditions are poor,Adaptive Error Control with ARQ 2/3,Works as normal unt
24、il 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 continue
25、s 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 Decreasing the transmis
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