| With the rapid growth of business in wireless communication network, the existing spectrum resources become more and more scarce. CRAHN(cognitive radio ad hoc networks) as a distributed cognitive network combines cognitive radio technology and Ad-hoc network. It not only uses spectrum effectively, but also is suitable for temporary and emergency communication. OFDM is a multicarrier digital modulation techniques.The technology can realize high bandwidth utilization and high-rate data transmission.The channel condition has great influence to quality of communications. According to the channel status and communication tasks of different needs, combined with the characteristics of various codes, find out the channel error correcting coding scheme suitable to improve the anti-jamming capability of the communication system has become an important research direction.This paper first gives a introduction to the CRAHN technology and OFDM network. Details the characteristics and work principle of BCH code, convolutional code, LDPC and other common error correcting codes. I researched above error correction coding methods on the MATLAB platform and obtained the different codec parameters and algorithm complexity of error correction performance. At the same time for the research background of this issue--the characteristics of the channel error correcting CRAHN network based on OFDM modulation system, research on the combination of communication task demand for error correction scheme. Under the premise of ensuring the communication performance requirements, considering the cost of hardware equipment, and other factors, finally found the channel error correction scheme for this system. The BCH code can correct no more than 2bit error bits, i use a simplified decoding method, and reduce the decoding complexity. LDPC uses its parity check matrix characteristics of quasi cyclic structure to realize fast encoding. I use the minimum sum decoding algorithm as decoding algorithm of LDPC, with appropriate parameters, its performance is close to belief propagation decoding algorithm.This paper implemented BCH-CC concatenated codec and LDPC encoder on FPGA of Cyclone III series Altera chip. I use the Verilog hardware description language(HDL) as programming language. |
