Adaptive Topology Control for Ad-hoc Sensor Networks 팀원 : 나종근, 박상하 정보통신연구실(INCLAB) 2019-05-04

Contents Adaptive Topology Control 소개 GAF STEM Ya Xu et. al., “Geography-informed Energy Conservation for Ad Hoc Routing,” Mobicom’01 STEM Curt Schurgers et. al., “STEM : Topology Management for Energy Efficient Sensor Networks,” IEEE 2002 2019-05-04

Adaptive Topology Can we do more than shut down radio in between transmissions/receptions? Can we put nodes to sleep for longer periods of time? Goal: Exploit high density (over) deployment to extend system lifetime Provide topology that adapts to the application needs Self-configuring system that adapts to environment without manual configuration 2019-05-04

Adaptive Topology: Problem Description Simple Formulation (Geometric Disk Covering) Given a distribution of N nodes in a plane. Place a minimum number of disks of radius r (centered on the nodes) to cover them. Disk represents the radio connectivity (simple circle model). The problem is NP-hard. 2019-05-04

Connectivity Measurements* 2019-05-04

Tradeoff How many nodes to activate? few active nodes: distance between neighboring nodes high -> increase packet loss and higher transmit power and reduced spatial reuse; need to maintain sensing coverage too many active nodes: at best, expending unnecessary energy; at worst, nodes may interfere with one another by congesting the channel. 2019-05-04

Adaptive Topology Schemes Mechanisms being explored: Empirical adaptation: Each node assesses its connectivity and adapts participation in multi-hop topology based on the measured operating region, ASCENT (Cerpa et al. 2002) Cluster-based, load sharing within clusters, CEC (Xu et al. 2002) Routing/Geographic topology based, eliminate redundant links, SPAN (Chen et al. 2001), GAF (Xu et al. 2001) Data/traffic driven: Trigger nodes on demand using paging channel, STEM (Tsiatsis et al. 2002) 2019-05-04

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Some definition Routing fidelity Fidelity Uninterrupted connectivity between communicating nodes Fidelity MSE PSNR 2019-05-04

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Behavior of GAF (1/3) GAF (Geographical Adaptive fidelity) Virtual grid with GPS or other location information All node in virtual grid are equivalent Who will sleep and how long Virtual grid Divide the whole area into small “virtual grid” For two adjacent grids A and B, all nodes in A can communicate with all nodes in B and vice versa All nodes in each grid are equivalent for routing Nodes exchange grid id to adjust their duty cycle Grid id is determined by its location and grid size 2019-05-04

Behavior of GAF (2/3) 6 What if node 1 dies? r: size of virtual grid R : radio transmission range 2019-05-04

Behavior of GAF (3/3) Three states Sleeping, discovery, active Periodically re-broadcasts its discovery message Discovery message Initial state Node id Grid id Estimated node active time (enat) Node state 2019-05-04

Tuning GAF Estimated node active time (enat) Node active duration (Ta) Node ranking : longer enat  high-ranked node Discovery message interval (Td) A uniform random value between 0 and n Node ranking : larger n  low-ranked node Node sleep duration (Ts) E.g. Uniform(enat/2, enat) Node mobility should be considered 2019-05-04

Mobility adaptation engt: expected node grid time (speed) engt = r/s Sleep duration = min (enat, engt) How about? N highest ranking (e.g., energy, slow speed) nodes per grid are alive Resolution between N nodes 2019-05-04

GAF interactions with ad hoc routing Duty cycle is based on application- and system-level information GAF decision to turn radio on/off is independent of routing protocols Packet loss GAF can inform routing protocol of impending suspension Interaction between clustering (topology control) and routing is important If N nodes per grid are alive, seamless transfer is possible? Kind of grid-wise anycasting MAC header: dest field is broadcast address NWK header: src, dest, next-hop grid-id 2019-05-04

Simulation - Network Lifetime 2019-05-04

Simulation –Data Delivery 2019-05-04