1. Adaptive Topology Control for Ad-hoc Sensor Networks
팀원 : 나종근, 박상하
정보통신연구실(INCLAB)

2. 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

3. 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

4. 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.

5. Connectivity Measurements*

6. 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.

7. 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)

9. Some definition Routing fidelity Fidelity
Uninterrupted connectivity between communicating nodes
Fidelity
MSE
PSNR

12. 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

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

14. 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

15. 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

16. 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

17. 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

18. Simulation - Network Lifetime

19. Simulation –Data Delivery