Design And Simulation Of OFDM System Based On MATLAB

With the higher and higher requirements of communication system for information transmission efficiency and reliability, the traditional single carrier system and multi-carrier system cannot meet the demand of communication. Because of unique sub-carrier modulation technique, the OFDM system has many advantages such as anti-frequency selective fading channel, anti-ISI, anti-ICI and high spectrum efficiency etc. And it becomes the core technology in the field of fourth generation of mobile communications and wireless local area network. In order to improve the performance of OFDM system further, the simulation analysis for related technologies of OFDM is operated based on MATLAB in this paper, and the decoding algorithm of LDPC codes is highly researched. A complete OFDM system is built on the Simulink platform to the simulation study. The main work is as follows:(1) Simulation of protection interval between OFDM symbols and signals interleave.The effect of modes and length of protect intervals on the ability of anti-ICI and anti-ISI is simulated and analyzed in multipath channel with a time delay. It finds that a cyclic prefix has more excellent performance than a blank prefix, and protection interval length is greater than the maximum of multipath time delay. And by simulating and analyzing the contact between interleave depth and discrete degree of continuous errors, it is acquired that the burst errors can be dispersed well by interleave, and it can greatly improve the correction capability to burst errors combined with interleave with channel codes.(2) Simulation comparison on sub-carrier modulation modes.The sub-carrier modulation and demodulation algorithms are the key to the realization of OFDM system. By analyzing the characteristics and relations between traditional analog modulation and IFFT modulation, it shows that IFFT algorithm modulation and simulation modulation method are equivalent. Then it is further verified that the output data symbol of IFFT samples the signal superposed after modulation of multiple sub-carrier.(3) Research and improvement on decoding algorithm of LDPC codesLDPC codes have outstanding performance in the current channel coding methods, and its decoding algorithm is easy to realize in hardware because of its sparse in check matrix. The decoding algorithm of LDPC codes are studied in this paper and the signal-to-noise ratios are simulated by comparing the bit error rate produced by different decoding algorithms under the same number of iterations. The min-Sum algorithm is simple but its performance is pool, so it is needed to find the correction factor by simulation to improve the decoding algorithm. And effect on its bit error rate is simulated by comparing the different iterations and interleave and deinterleave.(4) Design and simulation of OFDM system.In the design of OFDM system, key technologies including channel encoding and decoding, insert protection interval, interleave/deinterleave, channel estimation and channel equalization are applied to establish a dynamic OFDM system based on IFFT/FFT. The data generated by simulation support the research and implementation of the core technology F-OFDM and hardware in the fifth generation of mobile communication. The simulation results are as follows:When signal-noise ratio is greater than 3dB, the bit error rate of improved min-sum decoding algorithm is decreased by about two orders of magnitude than that of viterbi soft decision decoding algorithm. Interweave has a great influence on error correction of convolution codes and the limited ability of convolution codes to unexpected error is verified. The bit error rate is high if bit transmission rate of signal modulation is high. When using the LS algorithm for channel estimation, the estimation existing error will rise with the variation of channel parameters. The cyclic prefix with greater length than multipath time delay on multipath channel can effectively eliminate ISI and ICI.