The Study Of Synchronization Technique In OFDM System And Its FPGA Realization

OFDM (Orthogonal Frequency Division Multiplexing) technique has become aresearch hotspot in the field of wireless communication recently, because it has theadvantage of high bandwidth efficiency, good performance in anti multi-path fading andso on. Synchronous is an important problem in OFDM system, which affects theperformance of the whole system greatly. Some typical symbol timing, carrierfrequency and sampling error estimation algorithm are researched in this paper. on thatbasis,the whole synchronous system is designed and realized on FPGA.The development, advantages and disadvantage of OFDM technology areintroduced briefly. The mathematical model, modulation and demodulation principle,and characteristic are discussed in detail.Under the background of high speed data chainon uavs, the whole data chain scheme is designed, which stipulates the model of systemtransceiver machine, the specific parameters of the system, the format of frame andpreamble, the pilot insertion pattern and so on.The effects of synchronization error on OFDM system are deduced in theory andsimulated on MATLAB. A deep research on timing, the carrier frequency and samplingsynchronization algorithms are researched deeply both on time and frequency domain.Based on the delay auto-correlation of training sequences and cross-correlation ofreceving symbols and training sequences, an improved rough timing synchronizationalgorithm on time domain is proposed. The algorithm can guarantee the beginning ofFFT window is in the range of CP to avoid ISI, and meets the demands of timingsynchronization algorithm on frequency domain. Using the training sequences, thetiming and frequency information on time domain can be estimated, and the range of theactual carrier frequency is±192kHz.Using the information of pilot, the timingestimatation, the frequency estimation and phase tracking on frequency domain can befinished. The FFT window can be adjusted accurately by timing estimatation onfrequency domain. The range of the actual carrier frequency using frequency estimationon frequency domain is±38.4kHz.The irreducible phase errors can be compensated byphase tracking. Through the MATLAB simulation, the synchronization algorithms areanalyzed and the simulation diagram is get. After the theoretical discussion of OFDMsystem on different mapping way, the OFDM-CPM system based on CPM mappingway is proposed. In addition, the OFDM-CPM, OFDM-QPSK and OFDM-16QAM system are analyzed through MATLAB simulation.Considering the theory and realization complexity of synchronization algorithmand mapping way, a whole synchronization implementation scheme of time andfrequency domain is designed. The hardware structure is described usingVerilog HDL language. As the hardware structure of the rough timing synchronizationalgorithm of time domain saving a lot of multiplying and summing units, the realizationcomplexity is reduced. The synchronization modules and the whole system are tesed onModelsim, then the Logic circuit is synthesized in FPGA chip. Combined with thewhole OFDM transceiver prototype, the whole synchronization system is tested and thehardware timing waves of various synchronization modules are geted. The tests showthat the whole OFDM synchronization system is operated correctly, and meets therequirements of pratical project basicly.