1. 1 Power Efficient Wireless Sensor Networks with Distributed Transmission-Induced Space Spreading Xiaohua (Edward) Li and N. Eva Wu Department of Electrical and Computer Engineering State University of New York at Binghamton {xli, evawu}@binghamton.edu http://ucesp.ws.binghamton.edu/~xli

2. 2 Major Contributions Resolve the conflict between transmission energy efficiency and fault tolerance Propose distributed space-spreading for 1.Efficient/robust blind signal detection 2.Transmission energy efficiency 3.Network reliability

3. 3 1.1. Sensor Network Challenges How to improve transmission energy efficiency in deep-faded near-ground communications? How to improve fault tolerance and network reliability with low cost sensors suffering from high failure rate? How to resolve the conflict between energy efficiency and fault tolerance? They have contradictory requirements on redundancy. Multi-hop Wireless Sensor Network

4. 4 1.2 Strategies for the Challenges Distributed multi-transmission with space- spreading –Transmission redundancy provides diversity for energy efficiency –Transmission redundancy provides fault tolerance Scrambled Parallel Transmission from J Sensors

5. 5 Why can we use multi-transmission? –Wireless transmission is broadcasting a data packet can be received/retransmitted by multiple sensors –There are always multiple standby sensors ready for multi-transmission Energy in standby state is in the same level as in receiving state How to perform multi-transmission? –Distributed space-spreading: scrambled parallel transmission (the above figure) –Distributed space-time coding: to appear in Electronics Letters, 2003.

6. 6 2. Space Spreading and Blind Symbol Estimation Sensor j in cluster i transmits the same signal s(n) with different PN scrambling: A sensor in cluster i+1 receives (separately) signals from all sensors j:

7. 7

8. 8 3. Energy Efficiency Analysis Transmission energy efficiency comes from the diversity of the scrambled parallel transmission Major results:

9. 9 Power ratio of single-transmission to multi-transmission for 15 dB SNR with Probability B. Multi-transmission can be more than 30 dB more energy efficient.

10. 10 4. Fault-Tolerance Analysis

11. 11 Example: For design life T D =2000 packets, J=2 is better and has reliability 0.89. However, for reliability 0.99, J=10 is better, though with a shorter design life T D =1000 packets.

12. 12 5. Simulations Multi-transmission: New batch & adaptive algorithms: J=8 sensors. Single-transmission: DSSS with Rake receiver: processing gain 8. Blind CMA Training MMSE equalization

13. 13 Compare space-spreading with spectrum-spreading (DSSS)

14. 14 Transmission power (normalized with that of the new batch algorithm) required to achieve symbol-error-rate (SER) 0.01 Multi-transmission-based space-spreading has higher energy efficiency, longer sensor lifetime, and higher reliability. New Batch New Adaptive Training MMSE Blind CMA DSSS/ Rake Transmi ssion Power 11.1214.1>897.1

15. 15 6. Conclusions Propose a new space-spreading scheme for wireless sensor networks to achieve –transmission energy efficiency –blind symbol estimation –transmission/network reliability Resolve the conflict between energy efficiency and fault tolerance via transmission redundancy