Superimposed Training Sequence Of Ofdm Frequency Synchronization And Channel Estimation,

With the rapid development of mobile communications business evolving from the traditional voice service to those mainly based on Internet access and multimedia technologies, how to use the limited available wireless spectrum resources to provide mobile broadband multimedia services and thus meet the material and cultural needs of human beings, has become a huge challenge to the development of future mobile communications technologies. Compared with the traditional ways, which transmit training sequence first and then send the data symbols, OFDM system using superimposed training sequence transmits the training sequence, which is used for time and frequency synchronization, and OFDM data symbol simultaneously. This new scheme improves the efficiency of the frequency spectrum, and has broad application prospects in the future mobile communications systems.For practical wireless communications systems, time and frequency synchronization between the transmitter and receiver, and the estimation of the time-varying channel are two key technologies. Synchronization is the premise for the correct signal demodulation and restoration, while the performance of channel estimation has a direct impact on the overall performance of the system. Because the training sequence is arithmetically added on the OFDM data symbols, the separation issue of the training sequence and data symbols should be resolved in OFDM system using superimposed training sequence; besides, to further enhance system efficiency, the method of utilizing the known training sequence to do synchronization and channel estimation must be considered. In addition, since there are various types of interference or jamming in wireless channels, it is necessary to study the anti-jamming performance of the system. This article did some researches on the above-mentioned aspects of OFDM system using superimposed training sequence:Aiming at coping with the sensitivity of OFDM system using superimposed training sequence to frequency offset, a frequency synchronization method based on pilot subcarriers and cyclic prefix is proposed in this paper. The time-domain periodic property of the pilot subcarriers, which are used for channel estimation, is exploited for coarse frequency synchronization, and the redundant information of the cyclic prefix is used for fine frequency synchronization. Then, an iterative frequency synchronization algorithm is given to realize high performance data detection and the improvement of system efficiency. This paper describes in detail the system models, specific algorithms, and simulation results and their analysis of these two types of synchronization methods. Simulation results show that the performance of these two algorithms can meet the frequency synchronization requirements of next generation mobile communications.This paper proposes a method of iterative channel estimation, based on minimum mean square error algorithm, for OFDM system using superimposed training sequence with iterative receiver. High performance data detection is realized at the receiver, with further improvement of system efficiency. Computer simulations show that the bit error rate performance of the system becomes better when the number of iteration increases, which approaches the performance under ideal channel state information. There is about 1.5dB gap to the ideal performance when the bit error rate performance of the system is about 1.5×10?3.This paper investigates the performance of the time-frequency two-dimensional spread spectrum system in multi-tone jamming environment and points out the significance of this investigation to the further research on the anti-jamming performance of OFDM system using superimposed training sequence. The system model of the time-frequency two-dimensional spread spectrum system is given, the theoretical bit error rate of the system under multi-tone jamming environment is analyzed, and a kind of special anti-jamming parameter is derived. Computer simulations show agreement between the theoretical analysis and simulation results.The research results of the synchronization, channel estimation and anti-jamming performance of OFDM system using superimposed training sequence in this paper can be applied in the air interface of wireless local access network, next generation mobile communications systems, next generation high resolution digital television, and etc, and bring flexibility to the design of air interface for wireless communications, which are of great theoretical importance and economic value.