Fountain Code And Its Application In The Cooperative Communication System

Fountain codes are a new class of rateless codes with low encoding and decoding complexity. Moreover, due to the rateless property, Fountain code are able to naturally adapt to the channel conditions without requiring the channel state knowledge at the transmitter, which makes Fountain codes more suitable for collaborative communication than other codes with fixed code rate. Based on the disscuss of the algorithms, realization and performance of LT codes and Raptor codes, a coded cooperation scheme in wireless relay network based on fountain codes is studied.Firstly, the algorithms of encoding and hard-decision decoding of LT codes on erasure channels are introduced. Then the details of simulation realization are introduced. Later an iterative decoding algorithm, the belief propagation algorithm, is introduced. Based on that, a soft-decision decoding algorithm for AWGN channels by constructing a pseudo parity-check matrix is proposed. At last, the performance of LT codes on erasure channels and AWGN channels are simulated and the results show that the proposed soft-decision decoding algorithm of LT codes is available. Moreover, the influences of degree distribution and the number of source symbols to LT codes' performance are compared and analyzed.Secondly, the construction of Raptor codes and two different pre-code, LDPC codes and LDGM codes are introduced. Then a Raptor codes realization scheme is presented: a LDPC code or LDGM code as outer code and a weakened LT code as inner code. Finally, the performance of Raptor codes using LDPC codes as pre-code and Raptor codes using LDGM codes as pre-code are compared. The simulation results show that both of the Raptor codes have better performance than LT codes, and the Raptor codes using LDPC codes as pre-code has better performance than the Raptor codes using LDGM codes as pre-code, as a result of the high "error floor" of LDGM codes. But in aspect of the complexity, the latter is better.Finally, a coded cooperation scheme in wireless relay network based on fountain codes is discussed. Based on the introduction of the cooperation communication system model and the common cooperative communication schmes, the influences of the location of relay nodes to the cooperative communication system when relay nodes work on half-duplex model is discussed mainly. Finally, the performance of the entire cooperative communication system was simulated and the results show that coded cooperation using fountain codes can adapt to the tiume-varying channel and the reliability of the cooperative communication system is improved.