1. When Target Motion Matters: Doppler Coverage in Radar Sensor Networks Presenter: Yin Sun Xiaowen Gong, Junshan Zhang, Douglas Cochran School of Electrical, Computer, and Energy Engineering Arizona State University INFOCOM 2013, Apr. 17th, 2013

2. Outline Introduction Doppler Coverage Model Characterization of Doppler-Covered Regions Critical Sensor Density for Doppler Coverage under A Deployment Pattern Conclusion

3. Passive Sensing vs. Active Sensing Passive sensors, such as thermal, seismic, optical, infrared sensors, detect natural radiation emitted or reflected by an object of interest (i.e., target) o Most sensor network literature consider passive sensors Radars are active sensors that actively emit radio waves and collect the echo reflected by the target (e.g. people, vehicles, aircrafts, ships) o Most radar literature focus on single radar systems Radars have a number of advantages over passive sensors o Typically have larger sensing ranges o Can work under severe conditions (e.g. darkness, haze, rain, snow)

4. Radar Sensing Model Angle-based sensing: Doppler frequency shift (DFS) model o DFS is the frequency difference between the emitted and received radar signals due to the relative velocity between a radar and a moving target

5. Clutter Spoils Radar Sensing Clutters are echoes from undesired objects (e.g., rocks, trees, clouds) o Can be much stronger in magnitude than that from a target o The magnitude depends on physical characteristics of undesired objects (e.g., material, shape) which may not be known o A salient challenge for radar compared to passive sensors Key observation: Clutter objects are typically stationary or slow- moving compared to the target o DFS can be exploited for detection of moving target

6. Doppler Processing for Sensing clutter noise moving target DFS high-pass filter moving target

7. Networked Radars Radar network is a promising paradigm for sensor network applications o Networked radars offer diversity in both range (SNR) and angle (DFS) for potential better sensing capability o Modern radar is becoming more affordable and more efficient, possible for larger-scale networked deployment o Little attention has been paid to radar networks, especially coverage problems target detected! no target

8. Doppler Coverage Model o New challenges: 1) The D-coverage depends on both distances and angular positions of radars from target 2) A radar can contribute two types of D-coverage: up-Doppler and down-Doppler

9. Coverage List Question 1: How to find all the Doppler-covered points (regions) for arbitrarily deployed sensors?

10. Safe/Complementary Safe Regions

11. Sub-Region Partition

12. Doppler-Covered Regions Answer 1: We develop an efficient method for characterizing Doppler-covered regions o 1: Partition the entire region into sub-regions such that all points in a sub- region have the same coverage list o 2: For each sub-region, construct safe or c-safe region for each pair of neighbor points in its coverage list (construct safe region if both are non- image points or both are image points; otherwise, construct c-safe region)

13. Critical Sensor Density Question 2: What is the critical sensor density (minimum number of sensors) under a particular deployment pattern such that the entire region is Doppler- covered? o A natural question when we can control the deployment locations o Ignore boundary effect and focus on asymptotic case (typical in sensor coverage literature) o Optimal deployment pattern is difficult to find even for passive sensor networks

14. Critical Sensing Range

15. Numerical Results

16. Conclusion Contribution o Introduced a novel Doppler coverage model to study the coverage of radar networks that exploit both SNR and DFS for moving target detection o Developed an efficient method for characterizing the Doppler-covered regions for arbitrarily deployed sensors Can be used to evaluate the coverage of any deployed radar networks that exploit DFS for moving target detection o Designed CSR Algorithm for finding the critical sensor density for Doppler coverage under a polygon deployment pattern Can be used to estimate the number of radars needed for Doppler coverage Future Work o Extending the coverage model: Barrier coverage, k-degree coverage … o Extending the Doppler model: Information of target’s motion … o Bistatic/multistatic radar networks

17. Thank You ! Please send any questions to the co-authors at xgong9@asu.edu; junshan.zhang@asu.edu xgong9@asu.edu Questions ?

19. Range-based Detection: SNR Model radar Tx radar Rx radar Tx and Rx

20. CSR Algorithm

21. CSR Algorithm: Case Study