Energy-Aware TDMA-Based MAC for Sensor Networks

1
Energy-Aware TDMA-Based MAC for Sensor Networks

• K. Arisha
• M. Youssef
• M. Younis
• IMPACCT 2002

2
Outline

• Introduction
• Energy-aware Network Management
• Performance Evaluation
• Conclusion

3
MAC for Wireless Sensor Networks

• After Matthews overall introduction, heres one
  example of MAC for hybrid nodes.
• A TDMA-based MAC protocol designed to achieve
  power efficiency

4
Scenario

• Sensor nodes and gateway node
• Cluster are formed such that its gateway is
  located within the communication range of all of
  its cluster sensors.

5
Outline

• Introduction
• Energy-aware Network Management
• Performance Evaluation
• Conclusion

6
Energy-aware Routing

• Centralized in the gateway node for each cluster
• Dijkstra algorithm used to find the shortest
  paths to a single destination, the gateway.
• The weight of the edges takes energy, routing and
  delay related factors into concern.

7
Energy-aware Routing

• The sensor energy model in the gateway maintained
  through received packet updates
• A refresh phase scheduled periodically to correct
  deviations in the energy model
• Each node turns its receiver on at a
  pre-specified time to hear the gateway routing
  decision during the routing phase

8
Advantages of Using a TDMA MAC

• Clock synchronization built in (authors need
  synchronization for their routing protocol)
• Collision free except a packet containing the
  slot assignment is dropped.
• Even though the packet is dropped, the chance of
  collision is still limited.

9
Protocol Phases

• Four main phases data transfer, refresh,
  event-triggered rerouting, refresh-based
  rerouting.
• In the data transfer phase, sensors send, relays
  forward and inactive nodes remain off.

10
Refresh Phase

• During refresh phase, each node in the network
  uses its pre-assigned time slot to inform the
  gateway of its state.
• The phase periodically occurs after multiple data
  transfer phases, which minimizes the overhead
  compared to the payload data.

11
Rerouting Phases

• Event-based rerouting allows the gateway to react
  to changes in sensor organization and nodes
  energy level drop
• Refresh-based rerouting occurs at once after the
  refresh phase terminates.
• Rerouting also acts as a synchronous event.

12
Rerouting Phases

• During both phases, the gateway runs the routing
  algorithm and sends new routes, new state and
  slot number to each node in its pre-assigned time
  slot.

13
More on Protocol Phases

• During system design the size of the data
  transfer phase should be determined to
  accommodate the largest number of sensors that
  could be active in a cluster.

14
Packet Format
15
Slot Assignment

• Two approaches to handle the slot assignment
• Breadth-first-search assign starting from the
  outmost active nodes
• Depth-first-search assign contiguously over each
  route from the sensing node towards the gateway

16
An Example
17
Outline

• Introduction
• Energy-aware Network Management
• Performance Evaluation
• Conclusion

18
Environment Setup

• A cluster of 100 nodes placed randomly in a
  10001000 meter square area.
• The gateway position determined randomly within
  the cluster boundaries
• Rerouting occurs when a nodes energy level falls
  below 80. The threshold reset to 0.8 of its
  previous value once reached.

19
Packet Drop Count
20
State Change Count
21
State Change Count
22
Outline

• Introduction
• Energy-aware Network Management
• Performance Evaluation
• Conclusion

23
Conclusion

• A centralized approach for energy-aware
  management of sensor networks presented
• Two major techniques for slot assignment
  proposed BFS consumes less energy while DFS
  offers more reliable data packet delivery

24
Shortcomings

• Limited scalability
• Maximum number of nodes must be known before
  deployment due to fixed length of TDMA frame