Neighbor-Aware Control in Ad Hoc Networks Lichun (Luke) Bao Dissertation Defense University of California, Santa Cruz

10/18/2002Dissertation Defense2/57 Dissertation Committee Prof. J.J. Garcia-Luna-Aceves (Chair and Advisor) Prof. Katia Obraczka Prof. Patrick Mantey

10/18/2002Dissertation Defense3/57 Presentation Agenda Motivations Neighbor-aware contention resolution MACs using omnidirectional antennas MACs for unidirectional networks MACs using directional antennas Topology management Contributions and future work.

10/18/2002Dissertation Defense4/57 Motivation Contention resolution mechanisms: On-demand (contention-based) MAC protocols (ALOHA, CSMA, CSMA/CA — RTS/CTS schemes) Topology control (random election) Problem: run-time control overhead Scheduled MAC protocol (UxDMA — global topology) Schedule exchanges for setup. Problem: background control overhead NCR with minimum topology

10/18/2002Dissertation Defense5/57 Presentation Progress Motivation Neighbor-aware contention resolution MACs using omnidirectional antennas MACs for unidirectional networks MACs using directional antennas Topology management Contributions and future work.

10/18/2002Dissertation Defense6/57 NCR (Neighbor-aware contention resolution) Assumptions Topology information: contenders (two- hop neighbors in MANETs) Time synchronized between contenders Problem formulation In each time slot, how can an entity elect itself without conflicts from its contenders?

10/18/2002Dissertation Defense7/57 a b c d e Contention Floor 1. Assign a priority to each entity using the message digest of its identifier and the current time slot number. Random, unique to each entity (fairness) 2. An entity is entitled the winner if it has the highest priority among its contenders. Conflict-free (deadlock free) NCR Specification

10/18/2002Dissertation Defense8/57 Presentation Progress Motivations Neighbor-aware contention resolution MACs using omnidirectional antennas MACs for unidirectional networks MACs using directional antennas Topology management Contributions and future work.

10/18/2002Dissertation Defense9/57 Channel Access in Ad Hoc Networks Network modeling Independent identical communicating and computing nodes. Communication happens over multi-hop. Time synchronized, and channel time-slotted. Contention modeling One hop neighbors — directly shared the channel. Two hop neighbors — hidden interfering source. Interference outside transmission range ignored.

10/18/2002Dissertation Defense10/57 Networks with Omni-Directional Antennas Antenna modeling Antennas have fixed transmission range Signal propagation in all directions Circular coverage of one-hop neighborhood Contenders of a node One-hop and two-hop neighbors Channel multiplexing technology Code-division using direct sequence spread spectrum (DSSS)

10/18/2002Dissertation Defense11/57 Channel Access Protocols 1 NAMA: Node activation multiple access Require broadcast to all one-hop neighbors Nodes are the competing entities Contenders are one- and two-hop neighbors A B C D E F H G

10/18/2002Dissertation Defense12/57 A B C D E F H G Channel Access Protocols 2 LAMA: Link activation multiple access Require unicast to a one-hop neighbor Nodes are competing entities Signals are scrambled with codes assigned to the receivers Contenders are one-hop neighbors of a node and its receiver

10/18/2002Dissertation Defense13/57 Channel Access Protocols 3 PAMA: Pair-wise activation multiple access Require unicast to a one-hop neighbor Directional links are competing entities Signals are scrambled with codes assigned to the transmitters Contenders are incident links of the end-points of a link A B C D E F H G

10/18/2002Dissertation Defense14/57 Channel Access Protocols 4 HAMA: Hybrid activation multiple access Allow broadcast to all one-hop neighbors and unicast to a one- hop neighbor Nodes are competing entities Signals are scrambled with codes assigned to the transmitters Contenders are one- and two-hop neighbors A B C D E F H G

10/18/2002Dissertation Defense15/57 Channel Access Protocols > Performance analysis Network modeling Uniformly distributed over infinite plain Node density ρ, transmission range r. The number of nodes k over a given area S follows Poisson Distribution

10/18/2002Dissertation Defense16/57 Channel Access Protocols > Activation probability of a node

10/18/2002Dissertation Defense17/57 Channel Access Protocols > Comparing the activation probabilities

10/18/2002Dissertation Defense18/57 Channel Access Protocols > Comparing with CSMA and CSMA/CA

10/18/2002Dissertation Defense19/57 Simulations Results and Comparison > Throughput in fully-connected networks

10/18/2002Dissertation Defense20/57 Simulations Results and Comparison > Delay in fully-connected networks

10/18/2002Dissertation Defense21/57 Simulations Results and Comparison > Throughput in multi-hop networks

10/18/2002Dissertation Defense22/57 Simulations Results and Comparison > Delay in multi-hop networks

10/18/2002Dissertation Defense23/57 Presentation Progress Motivations Neighbor-aware contention resolution MACs using omnidirectional antennas MACs for unidirectional networks MACs using directional antennas Topology management Contributions and future work.

10/18/2002Dissertation Defense24/57 Neighbor Protocol (Need) Purpose propagate neighbor updates, time synchronization Cannot be based on NCR or TSMA Requires a priori topology information. Only efficient way: Random access. Broadcast. No acknowledgement: why? Efficiency, broadcast. Use retransmission to improve reliability.

10/18/2002Dissertation Defense25/57 Neighbor Protocol (Method) Insert random access section after scheduled access Send short signal frames carrying neighbor updates (256 bytes). Problem formulation: How to regulate interval t and number n of retransmissions to deliver a piece of information with given (high) probability p with the least delay.

10/18/2002Dissertation Defense26/57 Neighbor Protocol (Results) Reliability: deliver-probability p =99%. Retransmission interval: t =1.44N — only depends on N (the number of two hop neighbors). Number of retransmission: n =6.7≈7 — only depends on p. Suppose 2Mbps bandwidth, 2 second delay, 20 two-hop neighbors — random access sections cost 9.6% of the channel bandwidth.

10/18/2002Dissertation Defense27/57 Presentation Progress Motivations Neighbor-aware contention resolution MACs using omnidirectional antennas MACs for unidirectional networks MACs using directional antennas Topology management Contributions and future work.

10/18/2002Dissertation Defense28/57 Networks with Unidirectional Links Antennas are omnidirectional with different transmission ranges, capable of code-division channelization (DSSS) Unidirectional network properties Can not provide two-way handshakes Network may still partition — inclusive cycle of unidirectional link is required for two-way communication — ULPC

10/18/2002Dissertation Defense29/57 Link-State Routing with Unidirectional Links Unidirectional link: Link (a,b) is unidirectional if link (b,a) non-exists. ULPC (Unidirectional Link-state Routing Protocol with Propagation Control) Need to maintain the inclusive cycle of a unidirectional link when using it in routing The neighbor protocol for ULPC maintains partial topology graph for the discovery Only utilize links with small inclusive cycles to reduce control overhead — limited propagation

10/18/2002Dissertation Defense30/57 Channel Access Protocols 1. NAMA-UN: NAMA for unidirectional networks Node a is the Upstream-only neighbor of node b if link (a,b) has no inclusive cycle. Node a inadvertently interferes at node b Collision avoidance Code-division channelization: assign codes to transmitters by priority. Don’t transmit to B on A ’s code when node A is possible to transmit. A B C D E F H G Partition

10/18/2002Dissertation Defense31/57 Channel Access Protocols 2. PAMA-UN: PAMA for unidirectional networks Links are the contending entities Avoid colliding with Upstream-only neighbor of a node A B C D E F H G y y w

10/18/2002Dissertation Defense32/57 PANAMA = NAMA-UN+PAMA-UN Provides both broadcast and unicast 25 time slots for NAMA-UN, 95 time slots for PAMA-UN Compare with UxDMA that uses global topology information for scheduling Factors Transmission range variations Ratio of usable unidirectional links Traffic types and portion: unicast and broadcast

10/18/2002Dissertation Defense33/57 Simulations: Delays

10/18/2002Dissertation Defense34/57 Simulations: Throughput

10/18/2002Dissertation Defense35/57 Presentation Progress Motivations Neighbor-aware contention resolution MACs using omnidirectional antennas MACs for unidirectional networks MACs using directional antennas Topology management Contributions and future work.

10/18/2002Dissertation Defense36/57 Networks with Directional Antennas DSP advances enable space-time processing using multiple antenna elements — directional transmission and direction- sensitive reception MIMO (multiple input multiple output) becomes practical — MBAA (Multi-Beam Adaptive Array) motivates MAC research Benefits: reduced CCI, multipath fading, higher throughput.

10/18/2002Dissertation Defense37/57 Communication with MBAA Antennas Issues when using directional antennas: Neighbor tracking for directional transmissions. Who transmits, and who listens — coupling. Node d has two transmissions, node b is ready for two receptions.

10/18/2002Dissertation Defense38/57 Network Assumptions Antenna system: MBAA Beam width: pencil (10°) — fan (120 °) Tx or Rx, not both. K simultaneous Tx or Rx. Neighbor position profiling requirements Accurate for aiming antenna beam Yet holds for a while to avoid volatility

10/18/2002Dissertation Defense39/57 Neighbor Position Profiling Azimuth of a is cut into 360°/(ß/2) = 720°/ß sections. Two adjacent sections form a group. Node c sits in overlapping two groups A c ={2,3}, b in A b ={1,2}, d in A d ={3,4} w.r.t node a. Antenna beam pointing to c interferes at b and d. How? Easy to compute: A c ח A b ≠Φ, and A c ח A d ≠Φ — Cannot activate (a,c) and (a,b) simultaneously.

10/18/2002Dissertation Defense40/57 Channel Access Protocol > ROMA: Receiver-Oriented Multiple Access Require unicast s to multiple one-hop neighbors Links are competing entities Contenders are incoming links at the receivers Steps: Receiver: Sort incoming links according to their priorities. Select top K of the sorted links for reception. Transmitter i : Compute top K active incoming links of each one-hop receiver, from which derive all active outgoing links of itself. Select K of the active outgoing links for packet transmissions.

10/18/2002Dissertation Defense41/57 Simulations (Assumptions) Static topology for algorithm scheduling performance only. Two topology scenarios: Fully connected (5, 10 nodes); Randomly generated topology (100 nodes on 1000X1000 square torus with Tx range: 200, 400). MBAA beam width: 30°. Number of beams: 1, 2, 4. Packet arrival: Poisson. Buffer per neighbor: 20 packets.

10/18/2002Dissertation Defense42/57 Simulations (Throughput) Polygons —ROMA Others — UxDMA: Unified framework for graph coloring. Polynomial algo. Adapted to handle MBAA. ROMA has higher throughput: Why?

10/18/2002Dissertation Defense43/57 Simulations (Delay) ROMA has lower delay in any scenario because of its higher throughput.

10/18/2002Dissertation Defense44/57 Simulations (Packet Drop-rate) Maximum drop rate is one. The drop rate rises up later in ROMA than in UxDMA.

10/18/2002Dissertation Defense45/57 Presentation Progress Motivations Neighbor-aware contention resolution MACs using omnidirectional antennas MACs for unidirectional networks MACs using directional antennas Topology management Contributions and future work.

10/18/2002Dissertation Defense46/57 Topology Management in Ad Hoc Networks: Goals Virtual Overlay Topology Maintenance Less topology information presented to routing. Less topology updates due to mobility. Energy-Awareness Less nodes awake for communication. Load-balancing: the higher the energy left, the more responsibilities for data forwarding. Basic Approach: Clustering and interconnecting. Why not power control? Interference. Election via dynamic nodal priority assignment.

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10/18/2002Dissertation Defense48/57 Topology Management by Priority Ordering : Assumptions Time synchronized Time counted by time slot and epoch Each time slot = 100 millisecond. Each epoch = 600 time slots = 1 minute. Each node knows Topology within two hops — clusterhead, doorway and gateway elections. Nodal speed — stability. Nodal energy level — energy-awareness.

10/18/2002Dissertation Defense49/57 Topology Management by Priority Ordering: Priority Willingness to join virtual topology: Low energy, high mobility ~ less willingness. Nodal priority for a node: Is the message digest of the node identifier and the current time epoch, multiplied by its willingness value. Changes every epoch at unique starting point. Election Algorithms: Nodes with higher priorities than their contenders compose virtual topology.

10/18/2002Dissertation Defense50/57 Topology Management by Priority Ordering: Election Clusterhead election: a node that has the highest priority among The one-hop neighbors of itself The one-hop neighbors of one of its one-hop neighbors Gateway: a node connecting clusterheads The maximum distance between clusterheads are three. Gateways are insufficient for connectivity. Doorway election: a node extending the reach of a clusterhead

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10/18/2002Dissertation Defense52/57 Simulation and Comparison Other clustering heuristics: OPTIMUM: least clusterheads. Lowest ID: use ID instead of priority. Max Degree: select nodes with high degree. MOBIC: least neighbor signal strength variation. Load balance: based on Lowest ID Compare: Simulation duration. Combined metric: the product of energy utilization (awareness), the number and the change rate of clusterheads (stability).

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10/18/2002Dissertation Defense54/57 Presentation Progress Motivations Neighbor-aware contention resolution MACs using omnidirectional antennas MACs for unidirectional networks MACs using directional antennas Topology management Contributions and future work.

10/18/2002Dissertation Defense55/57 Contributions NCR algorithm using local topology information, and derived: Four MACs for networks with omnidirectional antennas One routing protocol and two MACs for networks with unidirectional antennas One MAC for networks with directional antennas Topology management mechanism Neighbor protocol

10/18/2002Dissertation Defense56/57 Publications Two MOBICOM papers MACs using omnidirectional antennas (2001) MAC using directional antennas (2002) One ICNP paper Hybrid MAC using omnidirectional antennas (2002) Two journal papers JPDC 2002, MONET 2002 Six other conference/workshop papers IC3N99,MoMuC00,MILCOM00/01,DialM01,NET02

10/18/2002Dissertation Defense57/57 Future Work Apply the neighbor protocol in wireless sensor networks Compare with TSMA, CSMA, Explore TMPO derivatives Unicast routing Multicast routing Power saving radio and MACs Flow oriented MAC

10/18/2002Dissertation Defense58/57 Acknowledgement My appreciations for the work of the dissertation committee Fellow CCRG members (Marc, Chane, Yu, Soumya, Long …) The support from my wife and parents The funding from various agencies through J.J.