AN MMSE BASED WEIGHTED AGGREGATION SCHEME

FOR EVENT DETECTION

USING WIRELESS SENSOR NETWORK

Bhushan Jagyasi (Presenting)Prof. Bikash K. DeyProf. S. N. Merchant

Prof. U. B. Desai

Overview of Wireless Sensor network (WSN)

• Wireless Sensor Network is a network formed by densely deploying tiny and low power sensor nodes in an application area.

• Application:– Military application– Smart home– Agriculture– Event detection (May be disaster event)

• For eg. Landslide Detection

Aggregation Schemes M1 and M2

• M1:Aggregation using majority rule

10

1

1

11

1

0

0

11

11

1

1

Yi Information transmittedYi Majority decision of children.

1

00

11

H={0,1}P(H=0)=P(H=1)=0.5p Precision of sensor

Aggregation Schemes M1 and M2

• M2: Infinite precision aggregation scheme

10

1

1

11

1

1,0

1,1

0,11, 4

1,2

2,7

0,1

10,1

01,0

10,1

<Zi,Oi> : Information TransmittedZi No. of zero’s in subtree.Oi No. of one’s in a subtree.

H={0,1}P(H=0)=P(H=1)=0.5p Precision of sensor

Link metric for Routing C1 and C2

• Routing : Bellman-Ford Routing Algorithm• Link cost C1

– C1=Ij/Bi

Where, Bi Battery level of node Si.

Ij Number of nodes that can transmit to node Sj.

• Link cost C2– C2=Pij/Bi

Where, Pij Power required to transmit a bit from node Si to node Sj.

SiSj

Steven’s results

• Steven Claims that:-C1 results in balanced tree-Thus M1-C1 is better aggregation-routing pair for event detection application as compared to M2-C2(traditional).

Motivation behind WAS

• We observe– The Spanning obtained by Bellman-Ford

routing algorithm using link cost C1=Ij/Bi is far from balanced.

– So majority rule may not be the optimum way of aggregating the data.

Spanning tree

Spanning tree as a result of Bellman ford routing algorithm with link cost C1

Development of Weighted Aggregation Scheme

Local view of a Network

Weighted Aggregation Scheme

• Assumption– Transmission of one bit from a node to its

parent.– Every node Si knows number of descendent

their children have.

Weighted Aggregation SchemeXi One bit decision made by Si

Ni Number of descendants of node Si

ni Number of descendants of node Si deciding in favor of event.

Information available with node So:

•Decisions made by its children

•Xi for i=1,2,…,k

•Decision made by itself, Xo

•Number of descendants its each child have

•Ni for i=1,2,…,k

Probability Mass Function

MMSE Estimate

Final decision by So

WAS Applicability

• Static Network

• Dynamic Network

Overhead on WAS

• Extra transmission and reception required for descendant update.

Simulation Results

Comparison of accuracy for M1, M2 and WAS

Simulation Results

Comparison of lifetime for M1, M2 and WAS

Conclusion

• Weighted Aggregation Scheme (WAS) has equivalent network lifetime as compared to M1 (majority rule aggregation scheme).

• Both WAS and M1 outscores infinite precision aggregation scheme M2 in terms of network lifetime.

• WAS outscores M1 in terms of accuracy.

References• [1] Bhushan G. Jagyasi, Bikash K. Dey, S. N. Merchant, U. B. Desai, “An

MMSE based Weighted Aggergation Scheme for Event Detection using Wireless Sensor Network,” European Signal Processing Conference, 4-8 September 2006, EUSIPCO 2006.

• [2] A. Sheth, K. Tejaswi, P. Mehta, C. Parekh, R. Bansal, S.N.Merchant, U.B.Desai, C.Thekkhath, K. Toyama and, T.Singh, “Poster Abstract-Senslide: A Sensor network Based Landslide Prediction System,” in ACM Sensys, November 2005.

• [3] Steven A. Borbash, “Design considerations in wireless sensor networks, ” Doctoral thesis submitted to University of Maryland, 2004.

• [4] R. Niu and P. K. Varshney, “Distributed detection and fusion in a large wireless sensor network of random size, ”EURASIP Journal on Wireless Communication and Networking 2005, pp. 462-472.

• [5] I.F. Akyildiz, W. Su, Y. Sankarasubramaniam, and E. Cayirci, “A survey on sensor networks, ” in IEEE Comm. Mag., Vol. 40, No. 8, August 2002, pp. 102-116.

• [6] R. Madan and S. Lall, “Distributed algorithms for maximum lifetime routing in wireless sensor networks, ” in Globecom’04, Volume 2, 29 Nov- 3 Dec 2004, pp.748 -753.

• [7] R. Viswanathan and P. K. Varshney, “Distributeddetection with multiple sensors: part Ifundamentals,” Proceedings of the IEEE, Vol. 85, Issue1, Jan 1997, pp. 54-63.

Many Thanks