1. 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

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

3. 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 !

4. 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

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

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

7. 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

8. 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]

9. 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

10. 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

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

12. 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

13. 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

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

15. 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

16. References (1)
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17. References (2)
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