Power Management in MANETs Teddy Framhein CMPE257 Katia Obraczka Presentation March 8th 2010 1 Introduction Yu Chee Tseng Chih Shun Hsu Ten Yueng Hsieh Power saving protocols for IEEE 802 11 based multi hop ad hoc networks Computer Networks Volume 43 Issue 3 22 October 2003 Pages 317 337 ISSN 1389 1286 DOI 10 1016 S1389 1286 03 00284 6 Gomez J Campbell A T Variable Range Transmission Power Control in Wireless Ad Hoc Networks Mobile Computing IEEE Transactions on vol 6 no 1 pp 87 99 Jan 2007 2 Goal Power management is Increasingly important Wireless devices rely on battery power for all operations Savings allow for more capability in other areas longer battery life etc Relatively unexplored Many possible approaches 3 Power saving Protocols for IEEE 802 11based multi hop ad hoc networks Power saving Techniques Transmission power control Modulate transmission power based on need per node Power aware routing Weight possible routes based on energy rather than just delay Either look at minimum power usage or nodes with most remaining power Both addressed in 2 Low power mode Implement power saving states depending on node usage 4 Network Assumptions Some recent works assume nodes are Synchronized Asynchronous operation poses other problems Data transfer to sleeping nodes Neighbor discovery o worst case relaying node asleep no route Fully connected Aided by base station None of these are desirable requirements 5 Other Approaches Use separate signaling channel to relay node state information Power Aware Multi Access protocol with Signaling PA MAS Include separate hardware that can receive wakeup signals Remote Activated Switch RAS Have some hosts serve as coordinators chosen by remaining power location in network always on Use base stations to page nodes when buffered packets are available nodes wake periodically to check can result in long delays when the network is heavily loaded 6 802 11 Power Saving Infrastructure based network Nodes have active and power saving states Access Points Relay packets monitor node states similar to paging from previous slide Periodically transmit beacon frames which include Traffic Indication Maps TIM lets nodes know there is traffic waiting Contention operation nodes poll AP for buffered packets contention free nodes wait for AP to poll Infrastructure less networks PS hosts wake periodically ATIM Announcement Traffic Indication Message frames transmitted during ATIM window Nodes contend to send beacons ATIM frames Beacons for synchronization ATIM frames for traffic notification 7 802 11 Power Saving ATIM Operation 8 802 11 Power Saving Problems Clock synchronization required for correct operation of ATIM traffic scheduling Neighbor discovery may be impeded by contention in beacon transmission This can result in partitioning making Synchronization even harder Proposed fixes More beacons avoid situations arising from contention Overlapping awake intervals without synchronization Wake up prediction beacons contain clock information derive timing differences from this 9 Solution Three protocols proposed Each node divides time into beacon intervals each of which includes an active window beacon window and MTIM window Active window receiver powered on Beacon window beacon transmission MTIM window similar to ATIM frames Outside of the active window if a node has nothing to send it goes to sleep 10 Time Division Notation BI beacon interval AW active window BW beacon window MW BW MTIM window lengths 11 Protocol 1 Dominating Awake Interval Basic idea Each host should stay awake for at least half of their beacon interval guaranteeing some overlap with every other node To satisfy the dominating awake property AW BI 2 BW Problem beacons can be missed depending on timing if a node s BW happens to fall outside of another node s AW 12 Protocol 1 Dominating Awake Interval Solution Beacon intervals divided into odd MW and BW at start of AW and even MW and BW at end of AW Theorem 1 Dominating awake interval protocol guarantees when AW BI 2 BW a PS host s entire beacon window always overlaps with any neighboring PS host s active window in every other beacon interval 13 Protocol 2 Periodically Fully AwakeInterval Problem with Protocol 1 requiring that nodes remain active at least half the time doesn t give much flexibility in energy saved Solution Introduce low power vs fully awake intervals In low power intervals the active window is shortened to include only MW and BW Fully awake intervals inserted periodically every p intervals As long as P 2 more power saving than dominating awake But time taken to discover new hosts increases on average Better for less mobile environments 14 Protocol 2 Periodically Fully AwakeInterval Low power intervals begin with AW BW MW rest of interval spent in sleep state Fully awake intervals also begin with BW and MW but AW BI node is active for entire interval Theorem 2 Periodically fully awake interval protocol guarantees a PS host s beacon window overlaps with any neighboring PS host s fully awake interval once every p beacon intervals 15 Protocol 3 Quorum based Quorums used in distributed system design sets of identities from which a node must obtain permission to transmit in our case Used here to guarantee that a host s beacons can be heard during other hosts active windows n global parameter where beacon intervals are divided into groups of n Each group forms an n x n matrix Within the matrix one row and one column are chosen 2n 1 quorum intervals n 2n 1 non quorum intervals Quorum intervals BW followed by MW AW BI active throughout Non quorum intervals MW at start with AW MW sleep 16 Protocol 3 Quorum based Theorem 3 Quorum based protocol guarantees at a PS host always has at least two beacon windows that are fully covered by another PS host s active windows in every n beacon intervals Hosts only transmit or remain awake in O 1 n intervals O 2 n combined As long as n 4 total awake time is less than 50 Again this comes with the cost of greater latency in node discovery 17 Summary of Protocols 1 3 Number of beacons beacons transmitted per beacon interval Active ratio ratio of active vs passive time Neighbor sensitivity average time for PS host to learn of new neighbor Notes Quorum based uses the least power transmitting beacons Periodically awake and Quorum based use less energy overall depending on p n Dominated awake is most sensitive to neighbor changes 18 Unicast in Power Sensitive Environments PS hosts are not always active when can