Positioning in Chinese Digital Television Network Using TDS-OFDM Signals Linglong Dai, Zhaocheng Wang, Changyong Pan, and Sheng Chen Tsinghua University, Beijing, China University of Southampton, Southampton SO17 1BJ, U.K.

基于TDS-OFDM信号的时频二维定位算法 提纲 1 研究背景 2 基于TDS-OFDM信号的时频二维定位算法 3 仿真结果 4 结论

DTV-Based Positioning Global Positioning System (GPS) [Kaplan05] Worldwide (Oceans, desert) Hard to use in indoors, dense urban areas National security Compass Digital Television (DTV)-Based Positioning Advantages [Spilker05] Much higher received power : 40 dB (10000 times) Wider signal bandwidth Lower Doppler effect DTV-Based Positioning: a promising complementary to GPS

Positioning Using OFDM Positioning Using OFDM Signals Correlation-based timing synchronization algorithms [Shalom09] [Mensing07] [Martin09] Low complexity Low Accuracy Super-resolution algorithms (e.g., MUSIC) [Khanzada08] [Li04] High accuracy High complexity Current DTV-Based Positioning Solutions ATSC: Correlation based on the SYNC signal [Spilker05] ATSC/ASTC-M/H: orthogonal Kasami sequences ssuperimposed on the normal TV signals [Wang06] DVB-T: Correlation based on the frequency-domain pilots [Kovar08] DVB-H: Artificial delays in single frequency network (SFN) [Thevenon09] Positioning based on Chinese DTV standard (TDS-OFDM signal) Very few ! 4

Positioning Using TDS-OFDM Signal Contents 1 Background 2 Positioning Using TDS-OFDM Signal 3 Simulation Results 4 Conclusion 5 5

TDOA-Based Positioning Model in SFN Single Frequency Network (SFN) Most DTV systems are deployed in SFN mode 6 SFN transmitters in Hongkong Better coverage and higher spectral efficiency Synchronicity among different transmitters in SFN Time Difference of Arrival (TDOA) Remove the common TOA estimation error Receiver location: intersection of hyperbolic curves Two fundamental issues Accurate TOA estimation Transmitter identification 6

Positioning Using TDS-OFDM Signals (1) Regarding TPS as Frequency-Domain Pilots Transmission parameter signaling (TPS) Inform the coding rate, modulation schemes, etc. 36 TPS out of the 3780 subcarriers [DTMB06] Invariant property of TPS regarded as known pilots Training information: time-domain onlytime-frequency domains 7

Positioning Using TDS-OFDM Signals (2) TDM of TPS as Orthogonal Frequency-Domain Pilots Time-division multiplexing (TDM) of TPS for transmitter identification Provide the orthogonality in the time domain No impact on normal TV program 8

Positioning Using TDS-OFDM Signals (3) Impact of the transmission delay on the received OFDM signal Integral delay: time shift by samples in the time domain Fractional delay: phase rotation of in the frequency domain Transmission delay: Integral delay Fractional delay Received signal: 9

Positioning Using TDS-OFDM Signals (3) Time-Frequency Positioning Algorithm Integral TOA estimation using time-domain PN sequence Time-domain correlation to find the correlation peaks Timing accuracy: Several meters 10

Positioning Using TDS-OFDM Signals (3) Fractional TOA estimation using frequency-domain TPS Firstly: facilitate correlation peaks identification Secondly: fractional delay estimation 11

Performance Analysis Ranging Accuracy Average ranging time Computational Complexity High accuracy Fast Method Complexity Correlation-based Super-resolution-based Proposed time-frequency method acceptable 12

Positioning Using TDS-OFDM Signal Contents 1 Background 2 Positioning Using TDS-OFDM Signal 3 Simulation Results 4 Conclusion 13 13

Simulation Results (1) Main parameters 1. Higher accuracy Central carrier：UHF (770 MHz) Signal bandwidth： 7.56 MHz Channel：ITU Indoor A SARFT 8 M = 4 Modulation：QPSK/16QAM Sampling rate：7.56 MHz*4 N=3780, K=420 1. Higher accuracy 2. Coincides with the theoretical bound 14 14

Simulation Results (2) Accuracy in multi-path channels is also high 15

Simulation Results (3) No impact on normal TV program reception 16 16

Positioning Using TDS-OFDM Signal Contents 1 Background 2 Positioning Using TDS-OFDM Signal 3 Simulation Results 4 Conclusion 17 17

Brief Conclusions The positioning solution using TDS-OFDM signals for Chinese DTV standard in SFN is proposed in this paper; The TPS embedded in the TDS-OFDM signal is time-division multiplexed as orthogonal frequency-domain pilots; The proposed time-frequency positioning scheme jointly utilizes the time-domain PN sequence and frequency-domain TPS (pilots) for accurate TOA estimation of each transmitter; Results obtained have shown that the proposed positioning scheme achieves a higher positioning accuracy compared with the state-of-the-art methods, while imposing a low complexity.

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