On Research And Simulation Of Broad Band OFDM Transmission System And Implementation Of Partial Modules

To meet the demand of high rate datum service such as photo and video grown with days, and at the same time to support datum transmission in mobile environment such as high definition real time photo service, virtual meeting television service and so on, under prerequisite of quality of service, Two trends as "broad band" and "mobility" take on in the development of future communication techniques and systems. And the goal is to realize "Whoever, Wherever, Whenever, Whomever and Whatever communications". For the sake of good immunities to frequency selective and multi-path wireless channel, OFDM (Orthogonal Frequency Division Multiplexing) appeals to researchers in the field of wireless communication. And in this area, it's a common sense that OFDM will be applied to next generation mobile communication system-Beyond 3G and broad band wireless access as a kernel technique.Though OFDM is an excellent broad band transmitting technique, it's weakness is fatal, that it is sensitive to error signals. When carrier frequency offset exists in the received signal and if not compensated, the orthogonality can be broken and ICI (Inter-Channel Interference) can be introduced. And because of channel transmit delay, sample clock phase and frequency errors, symbol timing error is added, and the phases of signal are rotated. More intractably, ISI (Inter Symbol Interference) appears, which brings ICI at the same time. Also when transmitted through wireless channels, signals are attenuated, which results that signals can not be demodulated correctly. Thus research on OFDM system, especially synchronization and channel estimation techniques, is very important.At first the technique background of OFDM is introduced, and the developments of various communication systems are generalized shortly.Chapter 2 as a key part of theory research of the dissertation, mainly focuses on the synchronization of receiver. Firstly, OFDM system model is given, based on which influences of synchronization errors are analyzed in theory, then the problems are pointed out in the stage of synchronization of receiver. At last, an solution of PHY layer synchronization is proposed, and the synchronization algorithms are deduced analytically. Also the simulation figures are given.Chapter 3 studies the methods of channel estimation of OFDM system. The theory model of wireless channel is depicted, then the effect on transmit signals is illuminated. Finally, several different methods of OFDM channel estimation are introduced, performance of which are compared, and the performance compare figures are listed.Chapter 4 is about the digital front end design of base band system. In the transmitter, it includes zeros interpolation, up sample filter design, up sample and digital intermediate frequency up convert. And in the receiver, it includes digital intermediate frequency down convert, decimate, down sample filter design and down sample. At last, spectrums thatsimulated in MATLAB and measured in FPGA base band design with spectrum analyzer instrument are given.Chapter 5 as the end of the dissertation, firstly describes the hardware platform of OFDM base band system, Then fully discussed the design and implementation of the kernel system hardware module - high speed fixed-point pipeline FFT (Fast Fourier Transform) processor in FPGA (Field Programmable Gate Array) .