System Simulations Of OFDM Synchronization And Hardware Design Of Symbol Synchronization

One of the requirements of next generation of wireless mobile communication system is to provide the transmission of the multimedia services with higher speed and wider bandwidth.In the wireless environment,the frequency resources,power and multi-path fading channel etc limit higher data transmission.In theses years,OFDM(Orthogonal Frequency Division Multiplexing)technique has been paid more and more attention because it has strong transmission ability in wireless channels,which comes from its own parallel transmission mechanism,inherited robustness to inter symbol interference(ISI)and the diversity with the multi-path channel.Meanwhile,OFDM system has very high channel utilization ratio because of the orthogonal properties among its sub carriers.While the OFDM technique also has some shortcomings,first,in the wireless environment, the receiver has no knowledge about the time delay between the transmitter and itself in general situation.In the OFDM system,the OFDM data is transmitted as one symbol,so in order to do the correct demodulation,the correct start of symbol should be got from the received signals to reduce the effect of ISI.Secondly,the high frequency utilization and the robust transmission of OFDM are founded on the orthogonal properties of the sub carriers,so if the frequency offset is generated and the orthogonal properties among sub carriers is lost,that will cause the inter carrier interference(ICI).As a result,this paper studies the synchronization technique in the OFDM system,which is to do efficient estimation and compensation of time and frequency offset to enhance the system performance.Firstly,the paper discusses characters of the wireless channel and the mathematical model, then the paper analyzes the structure of OFDM system and the influence of timing,frequency offset on the OFDM system.In the following chapters,the paper separately discuses the timing and frequency offset estimation algorithms of OFDM transmission systems.This thesis studies, analyses and compares some synchronization methods which have been proposed.Many simulations are taken,the performances are given by simulation results.Modified methods which based on the methods of Schmidl &Cox,H.Minn and ML synchronization algorithms have been proposed here to estimate timing offset and frequency offset.The results of Matlab simulations show that the modified methods are feasible and efficient to reduce the timing offset which can maintain good system performance.Finally,the paper discuss the hardware circuit design of OFDM symbol synchronization module.Considering some factors such as the complexity and operation quantity and so on,the CMOS chip,Stratix-EPIS40F780C5 is choose as the hardware platform.After the hardware chip and the exploitation software are selected,we can write the corresponding module of Schmidl&Cox symbol synchronization by verilog languag and carry on circuit synthesize by QuartusⅡ.Finally,the paper gives functional simulation and timing simulation figure.