TO MY PARENTS AND YI.

c Copyright by Yuan Xue,2002CROSS-LAYER DESIGN FOR POWER AWARE COMMUNICATION IN MULTIHOP WIRELESS NETWORKSBYYUAN XUEB.S.,Harbin Institute of Technology,1998THESISSubmitted in partial fulfillment of the requirementsfor the degree of Master of Science in Computer Sciencein the Graduate College of theUniversity of Illinois at Urbana-Champaign,2002Urbana,IllinoisTO MY PARENTS AND YI.iiiAcknowledgmentsI sincerely thank my advisor Professor Klara Nahrstedt for her continuous help and invaluable guidance.I would also like to thank Professor Baochun Li from University of Toronto for helping me understand the background knowledge of mobile ad hoc networks.I would like to extend my thanks to Rong Zheng for her advice on power efficient communication designs.I would like to thank MONET research group for all the support.I also thank my family for all their support,love and encouragement.This research was supported by the ONR MURI grant under grant number1-5-21394,and the NSF EIA99-72884EQ grant under grant number1-5-31744.Any opinions,findings,and conclu-sions are those of the authors and do not necessarily reflect the views of the above agencies.ivTable of ContentsChapter1Introduction (1)1.1Background (1)1.2Preliminaries (2)1.2.1Power Consumption Mode (2)1.2.2Power Consumption Model (3)1.2.3Energy Saving Mechanisms (4)1.3Motivation (6)1.4Approach (8)1.5Thesis Outline (11)Chapter2Related Work (12)2.1Power Efficient Designs (12)2.1.1Power Management (12)2.1.2Power Control (16)2.1.3Summary (18)2.2Ad Hoc Routing Protocols (19)2.2.1Proactive Approach (19)2.2.2Reactive Approach (20)2.2.3Hybrid Approach (20)2.2.4Geographical Approach (21)2.3Location Service in MANET (22)Chapter3Cross-Layer Design for Power-Efficient Communication (24)3.1Overview (24)3.2Energy-Efficient Geographical Grid (26)3.2.1Model (26)3.2.2EGGRID Construction (27)3.3Energy-Efficient Location Service (28)3.3.1Address Model (29)3.3.2Location Service Design (32)3.4Location-Aided Power-Aware Routing (42)3.4.1Power Consumption Model (42)3.4.2Protocol (47)vChapter4Performance Evaluation (54)4.1Theoretical Analysis (54)4.1.1Full Length Address Policy (55)4.1.2Partial Address Policy (56)4.2Simulation (57)4.2.1Scalability (57)4.2.2Power Efficiency (60)Chapter5Conclusion and Future Work (62)5.1Conclusion (62)5.2Future Work (63)References (64)viList of Tables1.1Power Consumption Distribution for Toshiba410CDT laptop (2)1.2Power Consumption Comparison among different wireless network adaptors.Datafor WaveLAN PCMCIA card is from the measurement result of[8].Data forProxim RangeLAN2card and Smart Spread is from their specification[4][1] (3)2.1Comparison of topology control algorithms (18)2.2Summary of power-efficient designs (19)3.1Key Notations (31)3.2Selection algorithm for location server regions (34)3.3Merge algorithm (46)3.4Forwarding algorithm (48)3.5Power Efficient Planar Graph Construction (51)4.1Simulation Environment Parameter (60)viiList of Figures1.1Conserving power by power management (4)1.2Saving transmission power by power control (5)1.3Network protocol stack for power management (6)1.4An example that shows how EELS works.In the example,A’s location servers aremarked as (9)2.1Basic Operation of IEEE802.11Power Saving Mode for IBSS (15)3.1Cross Layer Design for Power-Efficient Wireless Communication (25)3.2Global network partitioning (26)3.3Relationship between the transmission range of a node and the minimum partitionof the network (27)3.4An example of EEGRID (28)3.5Location server distribution of node (35)3.6Location updates under the full length address policy (36)3.7Location information storage format under the full length address policy (36)3.8Location information update packet format under the full length address policy..363.9Location updates under the partial address policy (37)3.10Location information storage format under the partial address policy (38)3.11Location information update packet format under the partial address policy (39)3.12Node B queries A’s location information under the full length address policy (40)3.13Location information query packet format under the full length address policy (40)3.14Node B queries A’s location information under partial address policy (41)3.15Relay region with a path loss model of(a)(b) (44)3.16Relationship among,and (44)3.17Relay regions of nodes in (46)3.18Relay regions of after the merge algorithm (47)3.19node can not determine its next hop by greedy search (50)4.1Node Density vs.Cost of Location Queries (58)4.2Node Density vs.Cost of Location Updates (58)4.3Node Mobility vs.Cost of Location Queries (59)4.4Node Mobility vs.Cost of Location Updates (59)4.5Fraction of survived nodes (61)viiiList of AbbreviationsMANET Mobile Ad-hoc NetworkMAC Media Access ControlPSM Power Saving ModeLAPAR Location-Aided Power-Aware Routing DSR Dynamic Source RoutingAODV Ad hoc On demand Distance Vector Routing GPSR Geographical Perimeter Stateless Routing LAR Location Aided RoutingEGGRID Energy-Efficient Geographical GRID LAPAR Location-Aided Power-Aware Routing EELS Energy-Efficient Location ServiceSTA Mobile StationBSS Basic Service SetIBSS Independent BSSAP Access PointixMSDU MAC Service Data UnitTSF Time Synchronization FunctionTIM Traffic Indication MapATIM Announcement Traffic Information Message PCMA Power Controlled MACPARO Power-Aware Routing Optimization RPTS Request-Power-To-SendAPTS Acceptable-Power-To-Sendcbr constant bit ratexChapter1Introduction1.1BackgroundAd hoc networks are multi-hop wireless networks composed of mobile hosts.In order to provide end-to-end communication throughout the network,mobile nodes cooperate to handle network functions,such as packet routing.The general principle is that two hosts communicate with each other directly,if they are close enough;Otherwise,communication session is achieved through relaying by intermediate peer hosts.Such wireless networks could be rapidly deployed without the support offixed infrastructure.They can be used in any situation where temporary network connectivity is needed.For instance,consider the problem of establishing a temporary wireless network in a region hit by some natural disaster.An ad hoc network would enable the patient history retrieved from hospital databases or allow insurance companies tofile claims from the field.Other examples of such ad hoc networks include internetworking participants in a meeting or enabling message exchanging in military operations.Mobile ad hoc networks have the potential to dramatically simplify the deployment of the data networks,when the wireless devices are used“anywhere at anytime”.However,the limited power supplies of mobile devices pose great constraint to achieving this goal.Therefore,power management and energy-efficient designs are becoming a critical problem in wireless networks. Studies show that the significant consumers of power in a typical laptop are the microprocessor (CPU),liquid crystal display(LCD),hard disk,system memory(DRAM)and the wireless network1power consumption 36%21%18%18%Power Supply Receive Sleep4.74V190mA10mA4.74V204mA14mA5V130mA2mA5V80mA5mA, where and denote the transmission and received signal power,respectively.is the distance between the transmitter and receiver antennas.is a constant determined fromfield measurements for the particular network.Let denote gain between sender and receiver due to channel path loss.Then from the path loss model,andandThe received power at must at least equal to the minimum received power threshold, .The observed signal to noise ratio for the transmission at must at lease be equal tothen the underlining MAC protocol needs to have the capability to buffer the data and wake up the sleeping nodes.IEEE802.11defines MAC layer functions for power management and provides such capability.We will present in detail the IEEE802.11power saving mode(PSM)in the related 2.work in ChapterFigure1.2illustrates an example of saving transmission power by power control.In thefigure, if communicates with,there is no need for to transmit at,since can be reached with power.In this way,battery power can be saved.Moreover,suppose that also wishes to communicate with at the same time at.If transmit to at,then both transmissions can be successfully received simultaneously,since neither nor are within the interference range of each other.Otherwise,if transmit to at,then falls into the transmission range of.Therefore,it can not successfully receive packets from due to the interference.Thus,power control can also enable the network to allow a greater number of simultaneous transmissions(so called spatial reuse)and enhance the network capacity1.1.3MotivationFigure1.3:Network protocol stack for power managementExisting works address the problem of power-efficient design in the network protocol stack as shown in Figure1.3.Power-aware MAC layer protocols deal with the problem of collision-free media access when nodal transmission power is adjustable.Power-efficient routing protocols use energy consumption as routing metrics andfind a route between source and destination which consumes the least energy instead of the smallest number of hops.In addition to the layers in the existing network designs,like routing layer and MAC layer,power-efficient design introduces a new layer topology control,which works under the routing layer and above the MAC layer. Topology control constructs an energy-efficient topology on the underlining ad hoc network by adjusting the transmission range or shuting down idle nodes.Topology control also ensures that the energy saving strategy does not affect the data communication to a great extent.For example, each node may adjust its transmission power by a local algorithm to save power.However,the power control decisions on all nodes need to collectively guarantee global network connectivity so that communication routes between hosts will not be disconnected due to the power control.There are a list of problems that previous works have not addressed.1.Most existing works for power-efficient design only consider the problem of conserving en-ergy in separate layers and limit their solution spaces within each individual protocol layer.However,to be useful in a larger context,power-efficient designs at different layers need6to cooperate with each other.Moreover,simple stacking the power-efficient designs at dif-ferent layers is not feasible.First,uni-directional wireless links between nodes are natural side-effects of many topology control algorithms,due to asymmetric power configurations in neighboring nodes.However,existing power-aware MAC protocols either do not sup-port uni-directional links or have problems in fully solving the problem of hidden terminals.Thus,they can not directly be used underlying those power-efficient topology control algo-rithms.Asymmetric links may also significantly affect the design of routing protocols.Most existing ad hoc routing protocols are designed for bi-directional wireless links.When asym-metric links are introduced,they may suffer from either performance degradation or do not function at all.2.The power-efficient topology control schemes usually assume a static networks,where theconstruction of a global power-efficient network is feasible.However,when node mobility is considered,existing algorithms become less efficient,since the energy-efficient graph needs to be dynamically maintained whenever nodes move.In networks where nodes are of high mobility,maintaining such a power-efficient topology may cost more energy than it could save.3.Power control and power management are two complementary approaches in saving energyfor wireless communication.They both take advantage of network redundancy in dense networks to achieve the goal of power saving and retaining the network connectivity simul-taneously.Particularly,power control makes use of link/route redundancy and saves power by adjusting transmission power so that only power-efficient route will be chosen for packet delivery;Power management uses node redundancy and reduces power usages by shutting down some idle nodes.However,both power conserving approaches have their pros and cons in data communication.On one hand,power control improves the network capacity through spatial reuse;On the other hand,it also increases the end-to-end delay for the packet deliv-ery,since it prefers routes with large number of hops,each of which has small distance,over7the short paths.Power management may reduce the network capacity when a small number of nodes are alive2.It may also introduce long route establishment delay,when a sleeping node needs to be woken up for packet transmission.Current power-efficient schemes only employ one of them.Whether it will further reduce the energy consumption and how it will affect the data communication,when both approaches are used,are still open questions.Such observation leaves great space for further research in power-efficient designs.1.4ApproachTo address above open questions,we employ both power control and power management to achieve maximum power saving and retaining the network capacity at the same time.We propose a cross-layer design for power-efficient wireless communication so that routing protocol,topology con-trol and MAC protocol could work in an integrated manner.Location information is used in our power-aware design to accommodate node mobility so that efficient and stateless routing could be achieved.We also explicitly considers the link asymmetry problem in our design.In our design,the entire network is partitioned into a hierarchical grid.In each minimum partitioned region,one node is chosen to be key node,which needs to be alive.Thus,these key nodes collectively form an energy-efficient geographical grid skeleton(EGGRID)on the deployed ad hoc network.Such a skeleton network serves two purposes:(1)providing location service for the location-aided routing protocol;(2)power management by allowing other nodes to sleep and still providing connectivity for the whole network.The selection of the key node is dynamic, based on nodes’remaining battery power.Thus it could balance the load,thereafter the power consumption of each node.The selection algorithm is fully distributed and scales well in large networks.It could also meet the challenges presented by node mobility.Based on EEGRID,we build a novel Location-Aided Power-Aware Routing protocol(LAPAR)and its underlining Energy-Efficient Location Service(EELS),which is able to provide location information of any host at anytime for LAPAR.LAPAR uses location information and makes greedy decision infinding energy-efficient route. Atfirst,Key nodes in EGGRID are used by LAPAR for fast route setup.Then,LAPAR optimizes the route progressively through the local greedy algorithm based on location information.The basic idea of the algorithm is that a forwarding node constructs its relay regions based on the locations of its neighbors.The node forwards a data packet to the specific neighboring node whose relay region covers the destination.If there are more than one neighbors that are able to cover the destination,the algorithm makes greedy choices to determine the energy-efficient next hop to forward the packet.In addition,we also propose an alternative backup algorithm where the greedy algorithm fails to discover a power-efficient route.The algorithm is fully distributed such that only location information of neighboring nodes are exploited in each routing node.Through rigorous theoretical analysis,we are able to derive critical global properties with respect to end-to-end energy-efficient routes.Figure1.4:An example that shows how EELS works.In the example,A’s location servers are marked asTo provide location information for LAPAR,we present EELS,an energy-efficient location service.Actually,the location service in mobile ad hoc networks itself is an inherently hard prob-lem:First,when one node requests the location of another node,it has no prior knowledge beyond the identifier of the requested node.Yet,it is impossible to maintain a static relation between9the node’s identifier and its location,due to node mobility.Second,a location service needs to draw upon the support of geographical ad-hoc routing protocols to distribute location information, which,in turn,require location information in thefirst place,forming a functional deadlock.To address the above issues,in EELS a specific node in the network will chose a small subset of nodes,namely its location servers,from EGGRID and periodically update them with its location as shown in Figure1.4.In particular,a hash function is used to map’s ID directly to a set of minimum partitioned regions in the network,then the key nodes are selected at those regions as the location servers of.Via this approach,’s location can be queried solely by its identifier,solving the functional deadlock.More importantly,EELS operates upon EGGRID,since only key nodes will be used as location servers.Thus the goal of power-saving can be achieved at no additional cost.We also introduce a hierarchical addressing model based on logical network partitions.With this model,locations of nodes could be represented at different accuracy levels.While different location servers may carry location information of different levels of accuracy,only a small set of location servers needs to be updated when the node moves.With less update,we save more power in the location service.Our algorithm addresses existing open problems in previous work in the following two as-pects.First,Our power-efficient design integrates power management and power PAR operates upon EGGRID,which is constructed through power management,while making its own optimization by using power control.Thus,our approach can maximize the power saving without much influence on data transmission;Second,our algorithm does not attempt to construct a global power-efficient sub-network through topology control before making routing decisions.By using a cross-layer design,all power adjustment and routing decisions are made at the same time locally within the nodes,based solely on local information about locations of neighboring nodes.As a result,our algorithm not only scales well to larger ad-hoc networks,but also requires no additional overhead in maintaining the topology of a global power-efficient subgraph when node mobility is present.Third,throughout the design of our power-efficient scheme,we have explicitly taken uni-directional wireless links into consideration.10The main contributions of this thesis are:1.To our best knowledge,this is thefirst work that integrates two power saving approaches,namely power management and power control.2.Our power-efficient solution employs a cross-layer power-efficient design so that it can ac-commodate node mobility and asymmetric links.3.As a part of the cross layer design,we present a novel location-aided power-aware proto-col(LAPAR),which is scalable and efficient.4.We design an energy-efficient location service(EELS),which is able to provide locationinformation for LAPAR in a power-conserving way.5.We evaluate our design through solid theoretical analysis as well as extensive simulation.1.5Thesis OutlineThe outline of the thesis is as follows:In Chapter2,we discuss the related work.In Chapter3,we present our cross-layer design of power-efficient wireless communication.Performance evaluation is shown in Chapter4.Chapter5concludes the thesis and proposes possible future works.11Chapter2Related WorkIn this chapter,we present related work.The problems of power-aware design have been studied by different approaches,namely power management and power control,at different network layers, such as MAC layer and routing layer.We summarize the existing works on power-efficient design in Section2.1.The general problem of ad hoc routing and the location service in mobile ad hoc networks also relate to our work.We present an overview on both topics in Section2.2and Section 2.3,respectively.2.1Power Efficient DesignsThis section gives an overview on the existing works of power efficient designs.First,we present the existing works that employ power management in Section2.1.1.Then,related work that use power control is discussed in Section2.1.2.2.1.1Power ManagementPower management saves energy by allowing nodes which do not participate in communication to switch to sleep mode.Since less energy is consumed at sleep mode than at idle mode.This requires underlining MAC layer protocol able to buffer data for nodes that are asleep temporarily and wake up sleeping nodes for incoming data transmission.IEEE802.11[2]defines MAC layer functions for power management and provides such capability.12IEEE802.11Power Saving ModeIEEE802.11specification describes the functions and services for wireless devices to operate within ad hoc and infrastructure networks.Mobile stations form basic service set(BSS)where they can communicate.In an infrastructure network,BSS can be interconnected to form an extended form of network.Inside each BSS,there is a station called access point(AP)that provides access to mobile devices.By contrast,mobile stations can form an independent BSS(IBSS)in an ad hoc fashion so that no additional infrastructure is needed.In addition to services that support MSDU (MAC service data unit)delivery between stations and control LAN access and confidentiality, IEEE802.11specification also provides the function to do power management in both infrastruc-ture network and IBSS.IEEE802.11support power management function such as buffering data for sleeping stations,synchronize stations to wake up periodically to check if there are packets destined for it etc.In this thesis,we will focus on the power management in IBSS,since we are interested in power management in ad hoc networks.In IEEE802.11,a station(STA)may be one of two different power status:awake when STA is fully powered and doze when the STA is not able to transmit or receive and consume lower power.The basic operations of power management function are:Synchronization:Clock synchronization is essential for rendezvous stations for data trans-mission in power saving mode.To realize synchronization,beacons are sent periodically carrying the TSF(time synchronization function)timer of each STA.In IBSS,there is no timer master(as AP in BSS),so it is up to the implementer to decide when to adopt the TSF in beacon message.All stations including those in doze mode will wake up before each beacon interval.Beacon interval is decided by thefirst STA that initialize the IBSS.At the beginning of each beacon interval,a STA will suspend its back-off timer associated with data transmission and back off a random interval chosen from.TSF timer counted in microsecond is contained in the beacon message.The one whofirst transmits the beacon will silence and cancel neighboring stations’back-off timer.13Traffic indication map(TIM):If a STA has buffered data for another STA in PS mode,it will record the identify of the station in its TIM.ATIM(Announcement Traffic Information Message)window:Every IBSS has a ATIM win-dow size specified at the establishment of the IBSS.If ATIM window is0,no power saving is allowed.Otherwise,ATIM management frame is transmitted following the beacon,con-taining TIM for the corresponding STA.The basic approach of IEEE802.11PSM is that multicast/broadcast message and MSDUs that are transmitted to a power saving station are first announced during the ATIM window when all stations are awake.A station in the PS mode will listen for these announcements to determine if it should remain awake state.If a STA receive a directed ATIM frame during the ATIM window(i.e.it is the designated re-ceiver),it shall acknowledge the directed ATIM and stay awake for the entire beacon interval for the data to be transmitted.Broadcast/multicast messages announced in the ATIM do not need to be acknowledged.Transmission offirst ATIM management frame after the beacon need to follow the same back-off rule as in regular data transmission.Immediately after the ATIM window,a STA shall begin transmission of buffered broadcast/multicast frames, any MSDUs and management frames addressed to STAs,for which an acknowledgment for a previously transmitted ATIM frame was received,shall be transmitted.Following the transmission of all buffered MSDUs,a STA may transmit MSDUs without announcement to STAs that are known to be in the awake state for the current beacon interval due to an appro-priate ATIM management or beacon frame having been transmitted or received.If directed ATIM isn’t acknowledged it will be transmitted again in next ATIM window.Data will re-main buffered if they can’t be transmitted successfully.An example of the basic operation of power management in IBSS is shown in Figure2.1.14no cost of setup latency.This approach facilitates efficient data delivery at the same time of power conservation.There are two schemes for power management topology control in the existing literature.They are presented as follows.In GAF[32],geographical information is used to build a“virtual grid”.All nodes in the same grid are equivalent with respect to forwarding packets.They coordinate with each other to deter-mine who can sleep and for how long.For load balancing purpose,sleeping node will wake up periodically to elect himself as active node in the grid.Span[7]uses a distributed and randomized algorithm to form the“virtual backbone”.In the algorithm,nodes exchange HELLO messages and make local decisions on whether they can sleep, or to join a forwarding backbone.The nodes that choose to stay awake serve as the coordinators, which maintain the connectivity and the capacity of the network.The rule for electing coordinators is that if two neighbors of a non-coordinator node can neither directly communicate with each other nor through one or two coordinators,then the node itself will be elected as a coordinator.Both protocols are proactive in constructing the“virtual backbone”without consideration of traffic characteristics.Maintenance of the routing backbone requires local exchange of messages which will consume a significant amount of energy,which is undesired.2.1.2Power ControlNodes can also reduce the power consumption during data transmission by using appropriate trans-mission power.This approach is called power control.Power Controlled MAC protocolsPower controlled MAC protocols are proposed to enable the collision free access of the wireless channel,when nodal transmission range is adjustable.Among the existing power controlled MAC protocols,PCMA[13]presents the most complete solution.PCMA generalizes the transmit-or-defer“on/off”collision avoidance model of current protocols to a moreflexible“variable bounded power”collision suppression model.In particular,PCMA has two main mechanisms:(1)A16request-power-to-send(RPTS)/acceptable-power-to-send(APTS)handshake between the data sender and receiver,which is used to determine the minimum transmission power that will result in a suc-cessful packet reception at the receiver.The RPTS/APTA handshake occurs in the data channel and precedes the data transmission;(2)The noise tolerance advertisement is used by each active receiver to advertise the maximum additional noise power it can tolerate,given its current received signal and noise power level.The noise tolerance advertisement or busy tone is periodically pulsed by each receiver in the busy tone channel,where the signal strength of the pulse indicates the tolerance to additional noise.A potential transmitter can“sense the carrier”by listening to the busy tone for a minimum time period in order to detect the upper bound of its transit power for all control and data packets.Topology ControlWhile power controlled MAC protocols negotiate the transmission power locally,topology control determines the transmission power of each node in the network so that the global minimum energy topology can be constructed.In the work of Rodoplu et al.[28]and its extensions[29,21],each node may adjust its trans-mission power by a local algorithm.The local decisions on all nodes collectively form a subgraph of the minimum-powered network,which guarantees global network connectivity.While[28],[29] and[21]target minimizing the power consumption,the work of[23][22]aim at maximizing the network lifetime,which also considers the balanced power usage in the network.A comparison of different power-aware topology control schemes is presented in Table2.1.Power-Aware RoutingPower-aware routing protocols use energy consumption as routing metrics andfind a route between source and destination which consumes the least energy.PARO proposed by J.Gomez et al.[12]considers the problem of power aware routing in wire-less networks where all nodes are located within the maximum transmission range of each other.17。