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Impact of AWGN on Time-of-Arrival Detection Accuracy in IEEE 802.15.4a Networks

Explore the impact of Additive White Gaussian Noise (AWGN) on detecting arrival times of packets in IEEE 802.15.4a networks. Examines narrow-band modulation, UWB differences, time detection, triangulation, signal correlations, averaging methods, and timing accuracy under various SNR levels.

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Impact of AWGN on Time-of-Arrival Detection Accuracy in IEEE 802.15.4a Networks

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  1. The Effect of AWGN on the Accuracy of Time of Arrival Detection Rick Enns IEEE 802.15.4a July 2004 15-04-0335-00-004a

  2. Issues • What effect does AWGN have on the accuracy of measuring a packet’s time-of-arrive? • Can narrow band modulation be used in the presence of AWGN? • What might be some of the issues that differentiate UWB and narrow band time detection? 15-04-0335-00-004a

  3. Position Sensing: Time Detection and Triangulation • Triangulation: n messages for one event detects position in n-1 dimensions • Time stamp data is based on local clocks- clock synchronization is not part of this paper 15-04-0335-00-004a

  4. Basic Time of Arrival Detector • Standard receiver and baseband processing • Time stamp messages are sent to a triangulation processor 15-04-0335-00-004a

  5. Simulation Parameters • Half-sine signal lke a O-QPSK symbol • Zeros allow easy noise level verification • Repeats 1000 times for statistics • Simulation signal with 8dB SNR AWGN • Time unit = 0.5 nsec  15 cm  6” for 802.15.4 in 2.5GHz band 15-04-0335-00-004a

  6. No noise received signal Target half sine symbol Correlation Function Correlation Process time  • Correlated Signal and Target Vertical scale x 200 15-04-0335-00-004a

  7. 8dB SNR received signal Target half sine symbol Correlation Function Correlation Process  • Correlated Signal and Target Vertical scale x 200 15-04-0335-00-004a

  8. Correlation peak for one symbol at 8 dB SNR Based on a 3000 point sliding average Computationally expensive Correlation Peak Detection 15-04-0335-00-004a

  9. Correlation peak for one symbol at 8 dB SNR Based on a 100 point sliding average Computationally less expensive Correlation Peak Detection 15-04-0335-00-004a

  10. Correlation Function • Formula: 15-04-0335-00-004a

  11. Correlation Function Approximation • Signal is the sum of the target and AWG noise: Si = Ti + Ni where N is AWGN • Correlation • Approximation 15-04-0335-00-004a

  12. Central Limit Theorem • When the correlation is done of many sample points the noise averages out 15-04-0335-00-004a

  13. Timing Accuracy – Error Histograms • 8dB SNR, STD = 3.9 time units averaged over one symbol • 8dB SNR, STD = 0.7 time units averaged over 64 symbols • 14dB SNR, STD = 1.9 time units averaged over one symbol 15-04-0335-00-004a

  14. Averaging and Mobility • Increased accuracy can be achieved through averaging • Averaging can be done at the cost of more circuits of and higher operational power within the wireless detector node • Averaging can also be done in the triangulation processor for free but it will lessen support for mobility 15-04-0335-00-004a

  15. Summary • One variable of of timing accuracy is AWGN SNR • Other important variables are: $$ + power and mobility • Existing narrow band systems can support accurate time detection under AWGN under $$ and power constraints • Multipath noise may better differentiate UWB approaches than does AWGN 15-04-0335-00-004a

  16. Recommendations • Consider MAC extensions that allow detection nodes to track existing 802.15.4 targets • Construct the standard to allow wireless detector nodes to be designed with different detection accuracies so power, $$ and accuracy can be optimized to an application • a node’s time stamp accuracy needs to be a reported value 15-04-0335-00-004a

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