One interesting embedded system

Transcription

1 One interesting embedded system Intel Vaunt small glass Key: AR over devices that look normal More details at: ECE 6/6 Embedded Computer System Design

2 ECE 6/6 Embedded Computer System Design Sensing - Wei Gao Spring 8

3 Indoor Localization GPS-free methods Primary approach: range-based localization Multiple anchors Distances between nodes to anchors measured wirelessly Metrics: TOA (Time of Arrival ) TDOA (Time Difference of Arrival) AOA (Angle of Arrival ) RSSI (Receive Signal Strength Indicator) ECE 6/6 Embedded Computer System Design 3

4 Time of Arrival (ToA) Example: GPS Satellites broadcast precise time Estimate distance to satellite using signal TOA Trilateration ECE 6/6 Embedded Computer System Design 4

5 Acoustic measurement Slower propagation speed -> easier measurement Limitations: Require line of sight Short detection rage ECE 6/6 Embedded Computer System Design 5

6 Available device Wireless Cricket Indoor range ~-m Ranging precision: cm 3cm Modes: active beaconing & passive listening ECE 6/6 Embedded Computer System Design 6

7 Angle of Arrival (AoA) Use antenna array to measure direction of neighbors Flood beacons, update bearing along the way Once bearing of three landmarks is known, calculate position ECE 6/6 Embedded Computer System Design 7

8 RF Signal Strength Distance measurement using RF signals Problematic Susceptible to different signal propagation characteristics Graph from Bahl, Padmadabhan: RADAR: An In-Building RF-Based User Location and Tracking System ECE 6/6 Embedded Computer System Design 8

9 More on RSSI Path loss characteristics depend on environment (/r n ) Shadowing depends on environment Short-scale fading due to multipath adds random high frequency component with huge amplitude (3-6dB) very bad indoors RSSI Path loss Shadowing Fading Distance ECE 6/6 Embedded Computer System Design 9

10 Range-free Approaches Limitations of range-based localization Expensive hardware deployment Limited detection range Range-free localization Simple hardware But less accuracy ECE 6/6 Embedded Computer System Design

11 Centroid Idea: Do not use any ranging at all, simply deploy enough beacons Anchors periodically broadcast their location Anchors Localization:. Listen for beacons. Average locations of all anchors in range 3. Result is location estimate Good anchor placement is crucial! ECE 6/6 Embedded Computer System Design

12 Hop-Count Techniques r Works well with a few, well-located seeds and regular, static node distribution. Works poorly if nodes move or are unevenly distributed. ECE 6/6 Embedded Computer System Design

13 Approximate Point In Triangle Area-based approach Anchors divide terrain into triangular regions A node s presence inside or outside of these triangular regions allows a node to narrow the area in which it can potentially reside. ECE 6/6 Embedded Computer System Design 3

14 Algorithm Pseudo Code: Receive beacons (X i,y i ) from N anchors N anchors form N 3 triangles. For ( each triangle T i Є 3 ){ InsideSet Point-In-Triangle-Test (T i ) } Position = COG ( Ti InsideSet); N ECE 6/6 Embedded Computer System Design 4

15 Perfect Point in Triangle (PIT) If there exists a direction in which M is departure from points A, B, and C simultaneously, then M is outside of ABC. Otherwise, M is inside ABC. Require approximation for practical use Nodes can t move, how to recognize direction of departure Exhaustive test on all directions is impractical A M A M B C B C Inside Case Outside Case ECE 6/6 Embedded Computer System Design 5

16 Departure testing Recognize directions of departure via neighbor exchange RSSI N A M Anchor Receiving nodes Signal Strength (mv) Foot 5 Feet Feet 5 Feet Beacon Sequence Number ECE 6/6 Embedded Computer System Design 6

17 Approximate PIT Test only directions towards neighbors Error in individual test exists, may be masked by APIT aggregation. A A 3 M 3 M 4 4 B C A. Inside Case B. OutSide Case B C ECE 6/6 Embedded Computer System Design 7

18 Sources of Possible Errors Exhaustive testing on all possible directions is impossible False positive: M is near the edge of triangle False negative: A A 3 M M 4 4 B C B C A. InToOut Error B. OutToIn Error PIT = IN while APIT = OUT PIT = OUT while APIT = IN ECE 6/6 Embedded Computer System Design 8

19 APIT aggregation ECE 6/6 Embedded Computer System Design 9 Grid-Based Aggregation High Possibility area Low possibility area

20 Applications Location-based services ECE 6/6 Embedded Computer System Design

21 Applications Augmented and Virtual Reality ECE 6/6 Embedded Computer System Design