1 / 21

When Target Motion Matters: Doppler Coverage in Radar Sensor Networks

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. Outline. Introduction

bowen
Download Presentation

When Target Motion Matters: Doppler Coverage in Radar Sensor Networks

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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) • 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) • Most radar literature focus on single radar systems • Radars have a number of advantages over passive sensors • Typically have larger sensing ranges • Can work under severe conditions (e.g. darkness, haze, rain, snow)

  4. Radar Sensing Model • Range-basedsensing: SNR model • Received target signal power: (SNR contour is circle) • Radar constant K captures physical characteristics (e.g., transmit power, radar cross section) • Angle-basedsensing: Doppler frequency shift (DFS) model • DFS is the frequency difference between the emitted and received radar signals due to the relative velocity between a radar and a moving target Δ

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

  6. Doppler Processing for Sensing • Moving target indication (MTI): An effective technique for exploiting the DFS • 1. Apply high-pass filter in the DFS domain to suppress clutter • 2. Perform SNR-based detection (e.g. energy detection) in the filtered signal • Simple to implement with low computational cost • The filtered signal contains the target signal if and only if Δis large enough (Δ) clutter moving target moving target noise DFS cutoff frequency high-pass filter DFS

  7. Networked Radars • Radar network is a promising paradigm for sensor network applications • Networked radars offer diversity in both range (SNR) and angle (DFS) for potential better sensing capability • Modern radar is becoming more affordable and more efficient, possible for larger-scale networked deployment • Little attention has been paid to radar networks, especially coverage problems no target target detected! no target • A coverage model is lacking for radar networks that exploit the DFS • Existing coverage model based on range (SNR) only: A point is covered by a sensor if and only if is in the sensing range of (i.e., ) • DFS has been studied mostly for single radar systems but NOT for coverage of radar networks

  8. Doppler Coverage Model • We propose Doppler coverage model based on bothrange and angle • If a target is Doppler-covered (D-covered), then there exists some radar that can observe both high SNR and large DFS • Effective Doppler angle is determined by the cutoff frequency • 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 E.g.: is not D-covered is down-D-covered DEFINITION: A target at a point moving in direction is Doppler-covered by a radar if and only if and or ; A point is Doppler-covered if and only if any direction from is Doppler-covered by some radar.

  9. Coverage List • Question 1: How to find all the Doppler-covered points (regions) for arbitrarily deployed sensors? • How to check if a point is D-covered? Coverage list for a point • 1. Construct an image point for each in the set of sensors that cover (“cover” in the range sense, i.e., ) such that • 2. Order all the points and based on their angular positions with respect to E.g.: , (or for short) LEMMA 1: A point is Doppler-covered by if and only if for any pair of neighbor points and in constructed from .

  10. Safe/Complementary Safe Regions • How to check the condition in Lemma 1 for all points? Safe and complementary safe regions for a pair of radars • Safe region: outside the circumscribed circles of where • Complementary safe (c-safe) region: inside the circumscribed circles ofwhere LEMMA 2: for any in the safe region of and ; for any in the complementary safe region of and .

  11. Sub-Region Partition • How to find a sub-region in which all points have the same coverage list? Sub-region partition • Two points covered by the same set of sensors may have different coverage list E.g.: LEMMA 3: For a region covered by , is partitioned by all the lines each passing through a pair of sensors in into a set of sub-regions such that all the points in a sub-region have the same coverage list constructed from .

  12. Doppler-Covered Regions • Answer 1: We develop an efficient method for characterizing Doppler-covered regions • 1: Partition the entire region into sub-regions such that all points in a sub-region have the same coverage list • 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) , , The shaded regions are D-covered by }

  13. Critical Sensor Density • Question 2: What is the critical sensor density (minimum number of sensors) under a particular deployment patternsuch that the entire region is Doppler-covered? • A natural question when we can control the deployment locations • Ignore boundary effect and focus on asymptotic case (typical in sensor coverage literature) • Optimal deployment pattern is difficult to find even for passive sensor networks • We consider a deployment pattern consisting of polygons (e.g., triangles, rectangles, hexagons) • There exists a unit region such that is D-covered if and only if the entire region is D-covered

  14. Critical Sensing Range • Critical pattern size : maximumpattern sizegiven and such that the unit region is D-covered • pattern size : a parameter characterizing the sensor density of a deployment pattern (e.g., side length of a regular triangle for regular triangle pattern) • is increasing in and increasing in • Critical sensing range : minimumsensing range given and such that the unit region is D-covered • is decreasingin and increasing in • Critical sensor density critical pattern size critical sensing range • If we find the closed-form of as a function of parameterized by , • then is the inverse function of • Answer 2: We design CSR Algorithm (find Critical Sensing Range): input output

  15. Numerical Results • Doppler-covered percentage: percentage of D-covered areas • An entire region of 100 X 100 under uniformly random deployment of sensors • Averaged results of 100 runs • Sensing range (a) (b) We observe that 1) Performance is better for a larger 2) A larger sensing range significantly improves performance

  16. Conclusion • Contribution • Introduced a novel Doppler coverage model to study the coverage of radar networks that exploit both SNR and DFS for moving target detection • 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 • 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 • Extending the coverage model: Barrier coverage, k-degree coverage … • Extending the Doppler model: Information of target’s motion … • Bistatic/multistaticradar networks

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

  18. Range-based Detection: SNR Model • Monostatic radar: co-located radar transmitter and receiver • Received target signal power : (SNR contour is circle) • K: depends on physical layer characteristics, e.g., transmit power, antenna gains, radar cross section radar Tx and Rx • Bistatic radar: separated radar transmitter and receiver • Received target signal power : radar Tx radar Rx

  19. CSR Algorithm • CSR Algorithm (find Critical Sensing Range): input output • Phase 1: coarse-grained search : lower bound of : upper bound of : set of sensors that must cover all points in when : set of sensors that must or possibly cover some points in when : set of sensors that must not cover any points in when • Phase 2: divide and conquer approach Split a coverage list into partial coverage lists , , , ,, Sub-routinePCSR Algorithm : PCSR[, ] finds the minimum sensing rangerequired to Doppler-cover all the directions (if any) from any point and between and that can not be Doppler-covered by or

  20. CSR Algorithm: Case Study • CSR Algorithm applied for regular triangle pattern • (a) (unit region) can be Doppler-covered by • (b) can be Doppler-covered by but not by ) )

More Related