Accurate Position Location in TDS-OFDM Based Digital Television (DTV) Broadcasting Networks Linglong Dai, Zhaocheng Wang, Jun Wang, Jintao Wang, and Yu Zhang Tsinghua University, Beijing, China

Time-Frequency Positioning Algorithm Contents 1 Background 2 Time-Frequency Positioning Algorithm 3 Simulation Results 4 Conclusion

DTV Based Positioning Advantage over GPS [1] Current Solutions Low Doppler effect due to fixed transmitter location DTV signal has a power advantage of more than 40 dB Reception in the presence of blockage and indoor environments OFDM: robust to multi-path effect Current Solutions American DTV standard ATSC [2] Correlation based scheme using the synchronization signals The positioning accuracy was about several meters European DTV standard DVB-T [3] Correlation based scheme using frequency-domain pilots The positioning accuracy is in the order of decimeters Chinese DTV standard TDS-OFDM [4] No solution !

State-of-The-Art Positioning with OFDM Signals Correlation Based Timing Synchronization Algorithms [5-8] Traditional or improved timing synchronization Locate the boundaries of OFDM blocks Complexity is low The accuracy limited by sampling rate several meters Super Resolution Algorithms Based [9-10] Adopt Super resolution algorithms on estimated channel frequency response multiple signal classification (MUSIC) [9] maximum likelihood (ML) [10] matrix pencil (MP) [11] Positioning accuracy is higher Complexity is unacceptably high for commercial receivers

Time-Frequency Positioning Algorithm Contents 1 Background 2 Time-Frequency Positioning Algorithm 3 Simulation Results 4 Conclusion

PN-MC training sequence TDS-OFDM signal frame structure Multi-Carrier PN (PN-MC) Sequence Good Channel Estimation Performance [13] Ideal Autocorrelation for Synchronization

Time-Frequency Positioning Algorithm Received PN-MC over the kth subcarrier Transmission delay normalized by sampling period Ts integral fractional is the channel frequency response (CFR) Impact of the transmission delay Time shift by samples in the time domain Phase rotation by in the frequency domain

Time-Frequency Positioning Algorithm Integral Delay Estimation Using Time-Domain Correlation Equivalent to timing synchronization in TDS-OFDM receiver Timing Accuracy within Insufficient for accurate positioning Sampling rate of 7.56 MHz Over-sampled by four (30.24 MHz) Ranging error of 20 m Ranging error of 5 m Fractional Delay Estimation in Frequency-Domain The received PN-MC can be simplified to be [16]

Time-Frequency Positioning Algorithm Step 1: Remove index k by G-lag autocorrelation Step 2: Avoid phase ambiguity problem [17] by differential correlation Step 3: Fractional delay by averaging Ranging Result for Positioning

Computational Complexity Performance Analysis Positioning Accuracy Cramer-Rao lower bound (CRLB) of the fractional delay estimator [18] Thus, the positioning accuracy is is SNR Computational Complexity

Joint Code Acquisition and DFS Estimation Contents 1 Background 2 Joint Code Acquisition and DFS Estimation 3 Simulation Results 4 Conclusion

Positioning Accuracy over AWGN Parameters: PN-MC length 255 cyclic extension length 165 Sampling rate 30.24 MHz Channel AWGN The proposed scheme has the best positioning accuracy When SNR is 15 dB, Estimation error is about 5 m for Mensing’s method [6] 0.35 m for MP scheme [11] 0.06 m for the proposed method Simulated RMSE approaches the CRLB when SNR>10 dB

Positioning Accuracy over Multi-path Channel Parameters: PN-MC length 255 cyclic extension length 165 Sampling rate 30.24 MHz Channel Brazil A & Brazil B Positioning accuracy deteriorates a little 0.06 m over AWGN channel 0.096 m over Brazil A channel 0.10 m over Brazil B channel

Joint Code Acquisition and DFS Estimation Contents 1 Background 2 Joint Code Acquisition and DFS Estimation 3 Simulation Results 4 Conclusion

Conclusions This paper proposes a novel positioning scheme for Chinese DTV systems by using PN-MC training sequence in the guard interval of the time domain synchronous OFDM (TDS-OFDM) signal frame The joint time-frequency positioning algorithm utilizes the properties of the received PN-MC sequence both in the time and frequency domain with respect to transmission delay Distance estimation with high accuracy can be achieved The positioning accuracy of less than 0.1 m when SNR is greater than 15 dB is achieved over both AWGN and the simulated multi-path channels The complexity of the proposed scheme is low

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