Realistic and Efficient Multi-Channel Communications in WSN

Transcription

1 Realistic and Efficient Multi-Channel Communications in WSN Miji Kim Andreas Schädeli Silvia Dorotheea Rus Cievoloth Gilber Coca Olmos

2 Content Introduction Problem description Interference problems Time synchronization problems Description of solution TCMP Channel assignment Test settings Results Performance Evaluation Strengths and drawbacks Paper Analysis Conclusion 2

3 Introduction WSN: ad-hoc, multi-hop routing Single-Channel vs. Multi-Channel communication Single-Channel problem: Interferences Multi-Channel problem: Synchronization 3

4 Introduction Only use orthogonal channels (no interference) We are not alone! 4

5 Tree Based Multi-Channel Protocol (TMCP) Channel Detection (CD) Channel Assignment (CA) Data Communication (DC) 5

6 Tree Based Multi-Channel Protocol (TMCP) Channel Detection (CD) Find usable channels 2 motes sample the link quality of each channel in different positions Select non-adjacent channels (eliminates inter-tree interference) Pass through all frequencies.. IR= 1,5 * CR Then find the ones that suit us! Communication Range (CR) Interference Range (IR) 6

7 Tree Based Multi-Channel Protocol (TMCP) Channel Detection (CD) Channel Assignment (CA) Partition the network into k subtrees Assign a unique channel to each subtree Minimal intra-tree interference Now, we are all partitioned into subtrees. 7

8 Tree Based Multi-Channel Protocol (TMCP) Channel Detection (CD) Channel Assignment (CA) Partition the network into k subtrees Assign a unique channel to each subtree Minimal intra-tree interference And we all chose a channel with minimal interference! 8

9 Tree Based Multi-Channel Protocol (TMCP) Channel Detection (CD) Channel Assignment (CA) Data Communication (DC) No time synchronization needed Base-station is equipped with multiple tranceivers Data reception and dissemination is possible Communication can go on! 9

10 Minimum interference Channel Assignment Goal Minimize intra-tree interferences. Assumption The network is static Define Node interference Number of nodes by which the reception can be disturbed at a given node Tree interference Maximum interference value among all non-leaf nodes 10

11 Minimum interference Channel Assignment Algorithm All interference values are known Build shortest-path tree Channel allocation From top to bottom level of the tree Process nodes with fewer parents first Connect the node to the subtree where adding the node brings the least interference to the subtree Select parent with least interference value among all parents Assign nodes with large interference as leaves 11

12 Test Settings Graph simulation in Java 200mX200m field 250 nodes uniformly distributed Communication range 10 to 35m Interference range is 1.5 times the communication range. Since no other PMIT algorithms exists Prim's algorithms to construct spanning trees (base schema with a single channel) Eavesdropping channel assignment(used by node-base protocols MMSN). lowest bound Maximum interference value/number of channels 12

13 Results PMIT Performance PMIT algorithm 1/3 of Prim s interference PMIT vs Eavesdropping.- when density is high PMIT has less interference. Reason: Eavesdropping.- not enough channels for nodes within two hops neighbors PMIT looks for the local optimal. higher density PMIT assign nodes with large interference as leaves. PMIT - Lower Bound. Algorithm is scalable with different densities. With 8 channels Eavesdropping has 18% less interference. (no explanation why) 13

14 TMCP Performance Evaluation Simulation - Same settings as before TMCP vs. Spanning tree routing (protocol with a single channel). Different network workloads TMCP splits heavy workload into different trees. More tolerant to systems load variations than spanning tree. TMPC performance is unstable. Flow congestion occurs on sub trees 14

15 TMCP Performance Evaluation Performances very close when number of channels is small. TMCP achieves 10% higher throughput with less than 5 channels. When the number of channels increases MMSN outperforms TMCP. 15

16 Strengths and Drawbacks of TMCP Strengths The algorithm doesn't do channels switching so doesn't need time synchronization Every node keeps the shortest path to the base station, partitioning algorithm doesn't require extra transmission and no extra energy consumption. Interference can be reduced by setting nodes with higher interference rate as a leaf nodes Drawbacks The algorithm is not dynamic, what if we add a new node? The solution is not necessarily the best one since is an heuristic, maybe a better one can be implemented (i.e. combination between tree base and node base). (hardware Limitation) base station with multiple radio transceiver limitation Intra sub tree interference(proven to be a problem even in the test flow congestions in sub trees). 16

17 Paper Analysis Strengths Few unstated assumptions Presents realistic scenarios Algorithm well understandable Weaknesses No details about other protocols Very optimistic conclusion based on few results Orthographic faults and bad graph labeling in one case 17

18 Paper Analysis What the paper says: It can be seen that without time errors, the node-based scheme always has higher packet reception ratios than the single channel scheme. What the figure says: 18

19 Conclusions Tree-based algorithm improves the throughput of the WSN. Performed tests are not necessarily the best, Some real tests should be performed(existents are not relevant). Maybe a combination of tree-based Node based could be implemented to improve the sub-tree flow congestion problem. Fast Data Collection in Tree-Based Wireless Sensor Networks Paper makes comparisons of TMCP with other algorithms. 19

20 Thank you for your attention! 20