Narrow-band Mobile Video Transmission System Based On Ofdm Technology Design And Simulation

Due to the characteristics of the multi-path fading of the wireless mobile communication channel in the mobile communication technology, there exists serious inter-symbol interference (ISI) in the process of high speed transmission. Orthogonal Frequency Division Multiplexing (OFDM), as a multi-carrier modulation technique, can overcome the multi-path fading of wireless effectively. It also has high bandwidth utilization rate, which could save valuable frequency spectrum resource. Therefore, OFDM has wide range of applications, such as the European Digital Video Broadcasting (DVB) and Digital Audio Broadcasting (DAB) and so on.Firstly, the basic theory and characteristics of OFDM are fully analyzed in this paper. Then, the impact of synchronization of OFDM on system performance is analyzed. Meanwhile, the channel coding technology of OFDM is also researched.In the mobile video transmission, the OFDM is mainly used in multi-channel and broadband transmission system. But it only requires a single-channel transmission and a narrow-band compared to the common video transmission system in some application of mobile video surveillance system. In order to solve this problem, a brief introduction of three mobile TV standards of DVB-H, T-DMB and DMB-T which all received widely range of applications is given. After that, their shortages in the application of mobile video surveillance system are pointed out. According to its requirements, a system solution based on DAB is designed. The system parameters, frame structure and channel coding structure are modified to satisfy the system. It can achieve effective data transmission rate of 1.26Mbps~1.89Mbps, but only takes up effective bandwidth of 1.536Mhz. When using MPEG-2 standard, CIF images can be transferred in this system.In the last section, the synchronization algorithm which will be used in the system is simulated with Matlab. Then the result is analysed. Taking the subsequent portability of DSP transplant of the code into account, modular design is adopted in the code. Scrambling/descrambling module, RS coding/RS decoding, convolution coding/Viterbi decoding module, interleaving/de-interleaving, OFDM modulation/demodulation module and the synchronization module are coding with C-MEX S function. Finally, the function of the system is tested and verified. And the BER curve of three kinds of convolution code rate in Gaussian channel, Ricean channel and Rayleigh is given respectively. According to the simulation, the system can achieve the desired function. And when the SNR is low, the system can still reach a lower BER in Gaussian channel and Ricean channel.