Research On Frame Syschronization And Channel Estimation Algorithm For Ofdm Systems

With the advantages of high frequency spectrum utilization efficiency and resistance to multipath interference, it is imperative for orthogonal frequency division multiplexing (OFDM) technology on the application of mobile communication development field, in the future. So It is more and more popular that we combine OFDM technology with multiple access technologies.We target to realize high transmission rate of data service and multimedia in wireless communication transmission system. While owing to the wireless environment caused by multipath characteristic, in addition to its special frame structure. So it is important to how to realize symbol synchronization and channel estimation OFDM system accurately and rapidly. In this thesis we will be aimed at these two problems. In addition, the symbol timing deviation system will have an effect on the performance of OFDM system. We will also carry on the simulation test. The paper is fruit of subject research achievement, and according to the emphases, It is be divided into four parts generally.First, we discuss about the OFDM system subcarrier number and cycle prefix. Due to the time discreteness of channel, this can cause to between the interference between symbols, the purpose of cycle prefix is to reduce the interference, the length of the cycle prefix choice also follows a certain principle, the thesis gives a lot of simulation experiments, subcarrier number is decided by data throughput, symbol duration time and channel bandwidth, the paper also gives the suitable range of proper choice through the different subcarrier number system performance.Second, we propose some frame synchronization algorithms. This paper first elaborates the basic principle of orthogonal frequency-division multiplexing (OFDM) systems and the key technology, then we introduces two kinds of algorithm:one is ML algorithm based on cycle prefix, and the other is an algorithm based on the training symbol, we perform the simulation experiment to compare this two kinds of algorithm. And a simplified algorithm was proposed to simplify the hardware implementation based on cycle prefix method.Third, the algorithm research about channel estimation in the OFDM system. We compare two kind of channel estimation way in this paper: coherent demodulation and differential demodulation. The two key problems have been studied in the design of channel estimator:the choice of pilot frequency and channel estimation rule, we conduct the simulation about two kinds of pilot and three kinds of channel estimation methods.Last, the research about timing deviation problem. We premise that the frequency and phase is consistent in the of the oscillation frequency of receiver and transmitter, with the passage of time in actual situation, the cumulative deviation will be more and more. This article through the theoretical analysis and simulation, this paper focuses on the effect of symbol timing deviation on the system under the AWGN channel and simple multipath channel, so this thesis lays the foundation for the synchronous algorithm.