Key Technologies Of Ffh System Of Concatenated Codes

Frequency-hopping communication technology is one important branch of spread-spectrum technology. Because of its excellent capability in anti-jamming, Anti-interception and anti-blocking, it's widely employed in both commercial and military areas.Channel coding is one important mean to improve the reliability of digital communication. Turbo codes became hot research field in error-correcting codes since been proposed, for its excellent performance that close to Shannon limit. Turbo codes are a class of parallel concatenated convolutional code system. Through the clever design of the encoder, a number of sub-yards through the interleaver for parallel concatenated coding output isolation, increasing the code distance; while the decoder is introduced in a soft input soft output decoding and iterative On behalf of the decoding method, resulting in superior error correction capability.In this paper, through theoretical analysis, Log-MAP decoding method for the FFH/BFSK system,which select Turbo codes as its Channel coding scheme, are given.Then,a novel parallel concatenated code is proposed, based on the existing Turbo coding scheme and PCGC (Parallel Concatenated Gallager Code) scheme. The proposed scheme is encoded in parallel by an RSC encoder and an LDPC encoder without interleavers between them.The second chapter introduces the structure of Turbo encoder and decoder, then discusses several common decoding algorithms and makes the corresponding contrast of its performance and decoding complexity. Then the principle of concatenated codes is briefly discussed, and then makes a comparison of performance among several given concatenated codes.Chapter three reserch the decoding method of Turbo codes in FFH/BFSK system. According to the different methods of soft demodulation respectively, we obtain the two Log-MAP decoding algorithm through theoretical analysis and mathematical deduction, under the AWGN and Rayleigh channel. For the Rayleigh channel, each decoding algorithms are given specific decoding algorithm, under blind channel estimation and ideal channel estimation.Chapter IV presents a novel parallel concatenated code:An iterative decoding technique is used to enhance the performance of the proposed concatenated code. We also modify the BP (belief propagation) algorithm to solve the following two problems: how to use the a priori probabilities and how to derive the posterior probabilities, which play a key role in the iterative decoding technique. Simulation result shows that the proposed scheme outperforms the original LDPC schemes in terms of BER.The last chapter summaries the paper, and points out future research work and future research directions.