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Sensor Network Capacity Enhancement Through Spatial Concurrency Bharat B. Madan and Shashi Phoha Applied Research Lab, P

Sensor Network Capacity Enhancement Through Spatial Concurrency Bharat B. Madan and Shashi Phoha Applied Research Lab, Penn State University. Sensor Network Communication. CH. Nodes need to send their data to the CH (Cluster Head, Fusion Center).

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Sensor Network Capacity Enhancement Through Spatial Concurrency Bharat B. Madan and Shashi Phoha Applied Research Lab, P

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  1. Sensor Network Capacity Enhancement Through Spatial Concurrency Bharat B. Madan and Shashi Phoha Applied Research Lab, Penn State University

  2. Sensor Network Communication CH • Nodes need to send their data to the CH (Cluster Head, Fusion Center). • Single wireless channel (e.g., 802.11) – need to time multiplex a single channel to service multiple sensors. • Need for concurrency – so that CH can receive data concurrently from high data rate multiple sensors. • Multiple frequency channels – CH deploys multiple frequency channels. • Spatial concurrency – create multiple channels in space (via beam forming). q1 s1 s2 sN CH Array BF1 BF2 BFN y1 y2 yN

  3. 2 3 1 4 q1 ti i 0 1 N-1 di Space Diversity Processing • Space diversity requires multiple element array antenna. • Duality between time sampling and space sampling. • Optimally control the link (or channel) gain Gij • Assumptions: • CH knows the location (direction) of each sensor node • Sources lie in the far field • Problem formulation: Steer null in the direction of nodes 2,3,4 while maintaining constant gain in the direction of node 1 • Possible Solutions • Constrained optimization • Synthesize array response CH • Mathematical Model

  4. Constrained Optimization CH • Minimize total output power subject to C1*W=1 wN-1 w0 w1 S • In the process of minimizing total power, the array would null out all nodes (except for the contribution of node 1 due to the constraint) • Spatial parallelism: Have multiple beam-formers running in parallel • The ith beam-former will maintain contribution of the ith node, while nulling out all other nodes.

  5. Beam Pattern Synthesis • BF1:Maintain fixed response towards the direction of θ1while simultaneously generating nulls in the directions θ2, θ3 ,.., θM-1 • Design BF2, BF3, ..,BFM-1in a similar manner to deal with (M-1) sensor nodes of a cluster • Computational Issues • In general, C may not be square and existence of unique solution can not be guaranteed • Pair wise multi-stage algorithm BF1 y1 BF2 y2 Antenna array CH BFM-1 yM-1

  6. w1 w1 w1 w1 w2 w2 w2 w2 w1 w2 S S S S S Pair Wise Multi-stage Algorithm • Consider only 2-element array and two directional sources q1 q2 • 2-element array that constrains output due to source1 to a constant level, while simultaneously nulling out source2

  7. Receive Side Concurrent Beam-forming CH 3 2 1 ti 4 i 0 1 1 N-1 CH BF2 BF3 BF4

  8. + + + + + + + + + tw Transmit Side Concurrent Beam-forming • Wireless communication: effectively half-duplex, i.e., not possible to simultaneously receive and transmit (unlike in wired communication  collision detection is feasible). • Antenna array (a node) is not capable of transmitting and receiving at the same time (on the same channel). • How to exploit available concurrency? • Accumulate requests for a finite time, i.e., batch processing s1 BF1 s2 BF2 s3 BF3 2 1 3 Array Manifold : Channel gain offered by ith element to signal sj

  9. Beam Pattern Synthesis • Let u = sin(θ) • Initializebeam pattern  • Synthesis problem: Control the pattern Ps(u), such that is minimized, subject to N=17, M=4

  10. Applications • Wireless Ethernet Switch • Single hop sensor fusion P2,j2 2’ P1,f1 1 CH RTS 3’ P2, f2 P3, j3 1 2 2 4 P1,j1 1’ 3 P3,f3 3 • Receive/Transmit concurrent beam-former makes the wireless router behave like a wireless Ethernet switch. • Each nodes sends RTS (in some arbitrary order). • Mobile command and control. • Concurrent Jamming CH CTS CTS T2,j2 2’ 1 Jamming waveform synthesizer Concurrent Transmit Side Beam-former 2 4 3’ T3,j3 3 T1,j1 1’ • CH accumulates RTSs and sends CTS concurrently to all nodes. • Above scenario: node 3 is enemy; 1 and 2 are friends • Alternately, 1, 2 and 3: enemy nodes being suppressed concurrently • CH, Wireless router/switch, C2 center, Jammer, etc. not constrained to be stationary

  11. Accumulate RTS/CTS Protocol • k=0,1,..,N number of requests (arrivals) in time window tw f(k) tw k’ N k • Associate a reward (penalty) function f(k) with event k • Linear f(k)

  12. Simulation Results • New MAC protocol, Accumulated RTS/CTS (A-RTS/CTS) • N: # array elements • Reward versus arrival rate λ • Concave function behavior • For a given N, as λ increases, R first increases (due to N degrees of concurrency) • Beyond certain point, higher value of λ leads to reduced performance (due to the request accumulation window getting filled up quickly  hence higher idle time)

  13. Conclusions • Concurrent beam-forming is a powerful concept for providing spatial concurrency. • Several possible applications: • Sensor network traffic capacity enhancement. • Wireless Ethernet switch for high speed routing. • Mobile Control & Command Center • Concurrent jamming. • Cellular phone network – cell capacity enhancement.

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