The Research Of Synchronization Technique In OFDM Wireless Communication System

Currently the marine-engineering oriented wireless communiation technique is facing the urgent challenge of high-bandwidth,high-capacity,low-cost and high spectral efficiency,which the traditional single-carrier modulation technique has been unable to fulfill. The Orthogonal Frequency-Division Multiplexing (OFDM) technique has become the mainstream among mainly wireless system, which uses various parallel and orthogonal subcarriers to modulate data, and allows the sub-carrier spectrum overlapping, thus improving its spectral efficiency. And with longer symbol period and cyclic prefix, it can withstand against multi-path fading channel effectively without complex equalization process in receiver.However, OFDM is extremely sensitive to synchronization offset errors, which will cause severe inter-symbol interference and subchannel interference,and will result in serious floor effects among the system, thus strict synchronization become the foundation and prerequisite of the OFDM baseband signal processing. This thesis mainly focuses on the fairly serious synchronization problems in the wireless communication system oriented at bridging the frogman and the ships based on OFDM modulation technique in the PHY layer. In order to consider the non-ideal factors in the transceiver signal processing chain, an investigation of the OFDM symbol timing offset,the carrier frequency offset and sampling clock offset in wireless OFDM communication system is presented.Then it proposes estimation algorithm about the offset and deviation based on the Cyclic Prefix,Train Symbol and Pilot signal method,with the offset estimator the compensation algorithm in both the time domain and frequency domain is presented,and finally develops a complete synchronization algorithm in the actual system.In order to verify the synchronization performance,the thesis designs the frame structure in physical layer based on the system parameters and performance indicators, then it elaborates the process of hardware design,with core of XILINX XC6SLX75 FPGA device, based on software defined radio method.The thesis is mainly focusing the digital front-end(DFE) design procedure:the narrowband signal is bandpass sampled firstly, then fed to a digital downconverter to baseband, then fed to a decimation filter chain to fulfill the requirements of baseband signal processing. In order to solver the problem about the unflat passband of the cascade CIC decimation filter, it designs a 15Tap FIR filter to compensate, achieving a passband ripple of 0.03173dB.In order to verify the system performance in the end-to-end transmission situation, the thesis uses the USB 2.0 bus to transfer the modulated BMP data to PC software, followed by restoration and statistical analysis, the case indicates that the OFDM synchronization processing and baseband processing meet the basic performance requirements,the BER of the peer-to-peer transmission procedure is lower than 10-2.