Research On The Key Technologies Of TC-OFDM Indoor Positioning Receiver Baseband Signal Processing

In recent years,as a kind of new strategic industry,location based services(LBS)have been widely used in people’s daily lives.With the rapid development of society and economy,the number of large buildings is fast increasing.The requirement of high precision indoor positioning is wide and urgent in area like public security,emergency rescuing,warehousing,logistics and Internet of Things.This paper focuses on the key technologies of TC-OFDM(Time&Code Division-Orthogonal Frequency Division Multiplexing)baseband signal processing.An SOPC(System on Programmable Chip)is also designed,which is used and verified in the positioning prototype receiving terminal.The detailed research contents and achievements are as follow:(1)The signal system of TC-OFDM is researched in detail.The ranging performance of TXID made up of pure PN sequence and mixed OFDM-PN signal during the time slot is analyzed.Both spreading gain and cross-correlation performance are analyzed.The signal-to-noise ratio and carrier-to-noise ratio are also given.The signal-to-noise ratio of CDMA component in weak signal which is interference by nearby strong TC-OFDM signal is given.The TC-OFDM positioning signal GNSS signals are compared and analyzed to find out the common ground and differences between them,which can be referenced during the design of TC-OFDM processing.The influence of ground mobile channel on TC-OFDM signal is analyzed and expressions of system model are given.(2)According to the characters of TC-OFDM signal system,the TXID capture method with matched filter is proposed to realize PN code synchronization.The probability density functions of correlation value when PN phase match or mismatch are given to derive the capture threshold.A new simplified method for TXID acquisition is proposed to save the channel for floor noise measuring.The probability density function of correlation value and equation for calculating missing capturing probability with the new method are derived.Through the simulation,the probabilities of successful capturing,mistake capturing,missing capturing and time to first successful capturing is got.(3)The reason that the performance of weak signal capturing with matched filter becomes worse is analyzed.Aiming at the low successful capturing probability of weak signals,new PN code capturing method for weak signals using time and phase prior information of strong signals is proposed.The structure diagram of the new method is given.The new method can increase the ability of weak signal detection by 7.4dB.The method and principle expression for TC-OFDM frequency acquisition is proposed.The problems of TC-OFDM frequency acquisition in multipath fading channel are analyzed.Parallel frequency acquisition method is proposed to deal with the fading channel and expressions for searching result fitting are derived.The parallel frequency acquisition method is then verified by actual data.(4)The structure of tracking loop for TC-OFDM signal is proposed.The carrier tracking loop and method of navigation message demodulation are given.The code tracking loop and method of pseudo-range measuring are given.The performance of pseudo-range measuring using tracking loop is analyzed.The error of pseudo-range measuring under signal-to-noise ratio of ideal TC-OFDM signal is researched.The pseudo-range measuring error caused by integration time and interval of integrator is analyzed.The problems that pseudo-range measuring with tracking loop under multipath fading channel are analyzed.New pseudo-range measuring method of snapshot-replay is proposed.The equations used for pseudo-range resolving under infinite bandwidth and limited bandwidth are derived.The approximate equations used for pseudo-range measuring under limited bandwidth are derived.Simulations are done to analyze the performance and error of pseudo-range measuring under different signal-to-noise ratio.The approximate error caused by approximate equations used for pseudo-range measuring under limited bandwidth is simulated.The TXID multiple access interference between different TC-OFDM base stations are research.The expressions of interference are derived.A method of anti multiple access interference is proposed to increase the ability of weak TXID detecting by 15dB.Simulations are done to analyze the affection by quantification.(5)The architecture of system on programmable chip for TC-OFDM baseband signal processing is proposed.The baseband signal processing module is designed and an optimized structure of digital matched filter is designed and realized,saving 50%combinational logic resources.The structure of parallel frequency searching module is also optimized to share hardware resource with tracking module.The software for baseband signal processing is also designed.The actual performance of TC-OFDM baseband processor is tested.