Presentation on theme: "CS710 : Special issues in Computer Architecture 1/22 Power-Saving Protocols for IEEE 802.11-Based Multi-Hop Ad Hoc Networks Yu-chee tseng et. al National."— Presentation transcript:
CS710 : Special issues in Computer Architecture 1/22 Power-Saving Protocols for IEEE 802.11-Based Multi-Hop Ad Hoc Networks Yu-chee tseng et. al National Chio Tung University, Taiwan INFOCOM ‘02 Presented by Joo, Jaikwan
CS710 : Special issues in Computer Architecture 2/22 Contents Introduction General power saving Power saving modes in IEEE 802.11 Three asynchronous power saving protocols for MANET Dominating-awake-interval Periodically-fully-awake-interval Quorum-based Simulations Conclusions
CS710 : Special issues in Computer Architecture 3/22 Introduction The critical issue of MANET(Mobile Ad hoc NETwork) : power saving Battery technology is not likely progress as fast as computing and communication technologies. The category of power-saving solution Transmission power control Topology control Power aware routing Base on mobile host power level Low-power mode IEEE 802.11 has power saving mode which is a radio only needs to be awake periodically. Bluetooth : park, hold, sniff mode.
CS710 : Special issues in Computer Architecture 4/22 Introduction MANET Multi-hop, unpredictable mobility, no plug-in power, no clock synchronization Two challenge of power saving Clock synchronization No central control, variable packet delay due to unpredictable mobility and radio interference. Neighbor discovery Because PS host will reduce its transmitting/receiving activity Routing problem
CS710 : Special issues in Computer Architecture 5/22 Introduction Basic idea of protocol Enforces PS hosts send more beacon packets than the original IEEE 802.11 standard Arrange the wake-up and sleep patterns of PS hosts such that any two hosts are guaranteed to detect each other in finite time even under PS mode
CS710 : Special issues in Computer Architecture 6/22 Introduction Power saving modes in IEEE 802.11 Two power modes : active and power saving(PS) Under infrastructure(with AP) AP monitors the mode of each mobile host. A host in PS mode only awakes up periodically to check for possible incoming packet from AP. A host always notifies its AP when changing mode. Periodically AP transmit beacon frames. In each beacon frame, a Traffic Indication Map(TIM) will be delivered, which contains ID’s of those PS host with buffered unicast packet in the AP. A PS host, on hearing its ID, should stay awake remaining beacon interval. On DCF, awake PS host issue PS-POLL On PCF, awake PS wait for AP Poll To send Buffered broadcast packet, AP send DTIM(Delivery TIM), after that, buffered broadcast packet will be sent.
CS710 : Special issues in Computer Architecture 7/22 Introduction Under an ad hoc network PS hosts also wake up periodically ATIM window : short interval that PS hosts wake up. Assuming that hosts are fully connected and all synchronized. In the beginning of each ATIM window, each mobile host will contend to send a beacon frame. Successful beacon serve for synchronizing mobile host’s clock. This beacon also inhibits other hosts from sending their beacon To avoid collisions among beacons, use random back-off [0- 2*CW min –1]
CS710 : Special issues in Computer Architecture 8/22 Introduction - After the beacon, host can send a direct ATIM frame to each of its intended receivers in PS mode. - After transmitted an ATIM frame, keep remaining awake - On reception of the ATIM frame, reply with an ACK and remain active for the remaining period - Data is sent based on the normal DCF access.
CS710 : Special issues in Computer Architecture 9/22 Introduction Problem statement PS mode of 802.11 is designed for single hop(fully connected) ad hoc network. If applied for multi-hop Clock synchronization Communication delay and mobility are all unpredictable Neighbor discovery A host in PS mode is reduced its chance to transmit Network partitioning Inaccurate neighbor information may lead to long packet delay or even network partitioning problem.
CS710 : Special issues in Computer Architecture 10/22 Three asynchronous power saving protocols for MANET Guidelines in designing protocol More beacon To prevent the inaccurate-neighbor problem A PS host should not inhibit its beacon in ATIM window even if it has heard other beacons. Allow multiple beacon in a ATIM window Overlapping Awake interval Since protocol don’t count on clock synchronization The wake-up pattern of two PS host must overlap with each other. Wake-up prediction To drive PS host’s wake-up pattern based on their time difference.
CS710 : Special issues in Computer Architecture 11/22 Three asynchronous power saving protocols for MANET Three power-saving protocols, each with a different wakeup pattern for PS host Beacon interval For each PS host, it divides its time axis into a number of fixed length interval Active window On state Beacon window PS hosts send its beacon MTIM window Other hosts send their MTIM frames to the PS host. Excluding these three windows, PS host with no packet to send or receive may go to the sleep mode.
CS710 : Special issues in Computer Architecture 12/22 Three asynchronous power saving protocols for MANET Access procedure Back-off delay [0 ~ 2*CW min –1 slot] Notation used in this paper BI : length of a beacon interval AW : length of an active window BW : length of a beacon window MW : length of an MTIM window
CS710 : Special issues in Computer Architecture 13/22 Dominating-awake-interval PS host stay awake sufficiently long so as to ensure that neighboring host can know each other. Dominating awake property AW >= BI/2 + BW This guarantees any PS host’s beacon window to overlap with any neighboring PS host’s active window. In every two beacon interval, PS host can receive all its neighbor’s beacon short response time suitable for highly mobile The sequence of beacon intervals are alternatively labeled as odd and even interval
CS710 : Special issues in Computer Architecture 14/22 Periodically–fully-awake-interval Two types of beacon interval Low power intervals AW is reduced to the minimum PS host send out its beacon to inform others its existence AW = BW + MW, in the rest of the time, the host can go to the sleep mode. Fully awake intervals AW is extended to the maximum Arrives periodically every T intervals AW = BI, rest of the time must remain awake PS hosts discover who are in its neighborhood. By collecting other host’s beacons, hosts predict when its neighboring host will wake up. a lot of power, so they only appear periodically and are interleaved by low power intervals. Response time to get aware of a newly appearing host T beacon interval Suitable for slowly mobile environments
CS710 : Special issues in Computer Architecture 15/22 BI Quorum-based PS host only needs to send beacon O(1/n) of the all beacon intervals. Design PS host’s wakeup pattern so as to guarantee a PS host’s beacons can always be heard by other’s active windows. Quorum interval Beacon + MTIM, AW = BI Non quorum intervals Start with an MTIM window, after that, host may go to sleep mode, AW=MW As long as n=>4, this amount of awaking time is less than 50% Suitable for expensive transmission cost
CS710 : Special issues in Computer Architecture 16/22 Communication protocols for power- saving hosts Since the PS host is not always active, the sending host has to predict when the PS host will wake up. Beacon packet has to carry the clock value of the sending host so as for other hosts to calculate their time differences. S predict the receiving side’s MTIM window, S contends to MTIM packets to notify the receiver, after which the buffered data packet can be send. Unicast During the receiver’s MTIM window, sender contends to send its MTIM packet to the receiver. Receivers will reply an ACK after SIFS, stay awake in the remaining of the beacon interval. After the MTIM window, sender will contend to send the buffered packet to the receiver based on the DCF procedure.
CS710 : Special issues in Computer Architecture 17/22 Broadcast To reduce the number of transmissions, divide these asynchronous neighbors into group and notify them separately in multiple runs. When S intends broadcast a packet, it first check the arrival time of the MTIM windows of all neighbors. S picks the host, whose first MTIM window arrives earliest, S picks those MTIM window have overlapping with Y’s first MTIM. After the these notification, S repeats the same process. A neighbor, on receiving a MTIM carrying a broadcast indication, should remain awake until broadcast received or time value expires. Broadcast packet should send based on DCF procedure.
CS710 : Special issues in Computer Architecture 18/22 Simulation experiments Environment Implemented by C Transmission radius : 250m Rate : 2Mbps Traffic load : Poisson distribution 5~30pkts/sec “On-off model” to simulate mobility(in every 5 sec) On probability : uniform distribution 50%~100% Beacon interval : 100ms~500ms Simulation time : 100sec Assume all hosts are in the PS mode Metric Power consumption The average power consumption per mobile host thru one simulation run Power efficiency average power consumption for each successful packet transmission Neighbor discovery time Average time to discover a newly approaching neighbor
CS710 : Special issues in Computer Architecture 19/22 Impact of beacon interval length [Traffic load=10pkts/sec, “ON” probability=80%][For unicast Traffic load=10pkts/sec, “ON” probability=80%] [For broadcast Traffic load=10pkts/sec, “ON” probability=80%] P(4) is good for both
CS710 : Special issues in Computer Architecture 20/22 Impact of mobility For unicast(traffic load=10pkts/sec, Beacon interval=300ms) In case of broadcast Broadcast packet is counted as successful as long as some neighbors are there to receive the packet.
CS710 : Special issues in Computer Architecture 21/22 Impact of traffic load For unicast(“on”=80%, Beacon interval=300ms) Higher traffic load incurs higher power consumption since hosts have less chance to sleep. Higher load makes transmitting a packet less costly because multiple packets may be transmitted in one beacon interval.
CS710 : Special issues in Computer Architecture 22/22 Conclusions Three power saving protocol based on IEEE802.11, multi-hop, asynchronous MANETs. Dominating awake interval Most power consumption, the lowest neighbor discovery time. Quorum based The most power saving, the longest neighbor discovery time. Periodically-fully-awake interval Balance both power consumption and neighbor discovery time.