Research And Implementation On Joint Demodulation/Decoding Technique Of COFDM

OFDM (Orthogonal Frequency Division Multiplexing) is a modulation technique dealing with multi-path with efficient use of the available bandwidth. OFDM can protect high-speed data transmissions under the environment with serious multi-path interferences. Due to its effective utilization of spectrum and the ability of combating multi-path interference, OFDM becomes one of the main current solutions to support the data transformation with very high speed. Therefore, OFDM has been widely used in many communication systems. This thesis is based on the Project of National High Tech Development (863 Project) named Research on 3G-Based Mobile Ad hoc Networks, and makes research on modulation and demodulation techniques in the physical layer.Based on the assumption that the receiver of the COFDM communication system has already achieved perfect synchronizations, demodulations and channel estimates, this thesis discusses the joint demodulation and decoding in the receiver. By combining the demodulation and decoding in the digital base-band model of COFDM system, we propose two novel algorithms for optimizing the communication system as a whole. One is the iterative decoding algorithm, named COFDM-ID algorithm, which is derived by the modification of original reseived symbol with the one after demodulated and decoded in the receiver which have some errors been corrected. The other one is the so-called over-sampling algorithm, which is obtained by using the Turbo-decoding principle, that is, exchanging the reliability information of the real and imagine parts from the received signal. Computer simulations indicate that the COFDM-ID and over-sampling algorithms are valid, and the joint demodulation and decoding technique can reduce the BER performance in receiver greatly.Finally, the thesis proposes a scheme that uses FPGA with IP-CORE according to the COFDM-ID and over sampling algorithms.