Title: Topology Management for Sensor Networks: Exploiting Latency and Density
1Topology Management for Sensor NetworksExploitin
g Latency and Density
- Curt Schurgers, Vlasios Tsiatsis,
- Saurabh Ganeriwal, UCLA-EE
- Mobihoc2002
- ??? ???
2Contents
- Introduction
- Sparse Topology and Energy Management
- Theoretical Analysis
- Setup Latency and Energy Saving
- Combining STEM and GAF
- Behavior of GAF
- Performance Evaluation
- Conclusion
3Introduction
- Sensor networks
- Efficient power saving protocol
- Topology management
- Coordinate the sleep transitions of sensor nodes
- Best way to save power consumption
- Related work
- Density dimension
- SPIN, GAF
- Time dimension
- S-MAC, SMACS
4Sparse Topology Management (1/6)
- STEM (Sparse Topology and Energy Management)
- Transfer state
- Turn on the radio of sensor node
- There is data to forward
- Monitoring state
- Just monitoring and turning off the radio
- Periodically turns on radio for a short time to
listen - Initiator node
- The node that wants to communicate
- Sends out beacons with the ID of target node
- Target node
- Responds to the initiator node
- Both nodes keep their radio on during
communication
5Sparse Topology Management (2/6)
- Dual frequency setup
- In order for actual data not to interfere with
the wakeup protocol - Initiator node wake up target node using radio f1
wakeup plane - Both nodes turn on radio f2 data plane
- Different frequency bands using a separate radio
- Using one radio that switches between two
frequencies
6Sparse Topology Management (3/6)
- STEM operation
- T Time interval of periodical listen
- TRX time of listening
7Sparse Topology Management (4/6)
- Minimum length of TRX
- The worst case where the radio is turned on just
too late to receive the first beacon - TRX time of listening
- TB Beacon interval
- B1 Beacon length
8Sparse Topology Management (5/6)
- Reasons of dual frequency
- There is no interference between the wakeup and
the transfer plane - One radio with one frequency
- One radio with two frequency switching
9Sparse Topology Management (6/6)
- Collisions in the wakeup plane
- A, B simultaneously wake up node C
- C, D can detect the signal (carrier sensing)
- Node E can receive the beacon
- Carrier sensing node just turn on the radio
- After time T
- Node A, B start communication
- Regular MAC handles collision
- Node D turns off the data radio
10Theoretical Analysis
- Average Setup latency
- Energy saving
B1 time of beacon transmission B2 time of
beacon ack. TB beacon interval TRX time of
listening T Interval of periodic listening
11Combining STEM and GAF
- GAF (Geographical Adaptive fidelity)
- Leverages the network density to conserve energy,
while leaving the data forwarding capacity - STEM (Sparse Topology and Energy Management)
- Saves energy by trading it off with path setup
latency - STEM and GAF are orthogonal to each other
- Full energy gains of both techniques
12Behavior 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
13Behavior of GAF (2/3)
r size of virtual grid R radio transmission
range
14Behavior 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
15Combining STEM and GAF
- Hybrid scheme
- A grid can be viewed as one virtual node
- Virtual node runs STEM in the same way
- Modified leader election
- In GAF, leader election procedure uses
broadcasting discovery message - If readers run STEM, they turned off data radio
- A node that wants to be leader
- Sets up a link to the current leader using STEM
- Necessary information is exchanged in the data
plane - Higher ranking node becomes leader
- If a node cannot contact the any leader, it
becomes leader
16Performance Evaluation
- Environment
- Size 80m x 80m
- Transmission range 20 m
- Node 100 nodes
- MAC protocol CSMA-type MAC similar to 802.11
17Performance Evaluation (1/2)
- E0 energy consumption without STEM
- TS/TRX Setup latency
- a tdata/t total time of data transmission
(data rate)
18Performance Evaluation (2/2)
19Conclusion
- STEM
- Topology management technique
- Trade off power savings versus path setup latency
- Hybrid scheme
- STEM is integrated with GAF in an orthogonal
fashion - Reduce the energy consumption to 10 or less