Simulation And FPGA-Based Implementation Of OFDM Demodulation In China Mobile Multimedia Broadcasting Standard

With the growing needs of people for digital video information, cellphone television broadcasting is developing rapidly in China and China Mobile Multimedia Broadcasting (CMMB) standards was formally tabled on October 24th, 2006. It realizes the coordinated seamless coverage between satellite transmission and terrestrial network by mainly providing digital broadcasting television programmes, integrated information and urgent broadcasting service to portable terminals which have small screens.CMMB cellphone has been widely used during the Beijing Olympic Games and received good reputations from its users. As Chinese 3G mobile telephone licences have been issued, the coordination of cellphone television and 3G mobile terminals is of tremendous practical value and broad market prospects, which means the simulation and implementation for CMMB systems should be paid much attention to.In OFDM modulation module of CMMB standard, the frequency band is divided into several sub-bands and orthogonal sub-carriers are used to transmit data. By superimposing these signals on sub-carriers, the modulated symbol which is sampled in time domain is the result of IFFT transform. After IFFT, the transmitted data has been fully randomized in frequency domain and can be considered as a linear combination of a series of independent identically destributed varibles which means it subjects to Gaussian destribution. In order to deal with multi-path fading, cyclic prefix should be added between OFDM symbols, which can avoid inter-symbol-interference effectively.This paper firstly analyzes the role and related principle of OFDM technology in CMMB system, and then simulates the fix point performance of OFDM demodulation module in accordance with CMMB standard technical requirements. At last, the realization scheme of OFDM demodulation module is demonstrated in this paper, which uses Altera's Stratix II series EP2S180F1020C3 chip hardware implementation in Quartus II 6.0 simulation environment.As the key part of OFDM demodulation, FFT sub-module adopts radix4/2 butterfly algorithm which is simple and effective, speedy, and occupies little hardware resources space and improves the performance of FFT. At present, the design has achieved the pre-determined experiment objective and it works stably and realizes the module function in FPGA.