Encoding And Decoding Algorithm Of Fountain Codes And Their Applications To Wireless Communication

Fountain codes are an kind of rateless codes which have the advantages of therobustness, high reliability and strong adaptation to channel, which make them be usedwidely to the radio, Mobile Communication, Wireless Local Area Network (WLAN)and so on. In this paper, we begin work based on the analysis and research of theFountain codes in the following aspects: decoding principle, joint soft decoding,reducing the decoding complexity and the application of Fountain codes in WirelessSensor Network (WSN).Firstly, the third chapter point out that the traditional simple cascade codemodulation system may lost their soft information when decoding in the wirelesscommunication. A kind of joint soft decoding algorithm of the LT-MSK codemodulation system is proposed in this chapter. Then the LT soft decoding and the MSKSISO decoding algorithm are deduced in detail. The algorithm system model is builttoo. The simulation results show that the algorithm system proposed in the chapter hasabout1.5dB coding gain better than the simple cascade code modulation system.Secondly, the belief propagation algorithm of LT codes not only has highcomplexity also has oscillation effect due to present of short loop in the tanner graph.To solve the two problems, a new oscillating iteration algorithm based on soft-bitdomains is proposed. Firstly, the hyperbolic tangent function is transformed andquantified to soft bit domain (-1,1). Then the information update algorithm of variablenodes is transferred to soft bit domains. Thus, computational complex is reducedgreatly. In LT codes, some outer information of variable nodes exist oscillating effectdue to short loops, the decoding performance is affected badly. A new criterion ispresented to judge the oscillate effect. When the sign of variable node flips betweentwo adjacent iterations and the soft bit values are higher than a given threshold, theoscillate effect exists. The simulation results show that the proposed algorithm get75%lower than the BP algorithm in the amount of computation and the decoding performance of soft-bit domains decoding algorithm is very close to the traditional BPalgorithm.Finally, the fifth chapter put forward a kind of improved performancedistributed coding algorithm with high priority coding degree distribution to overcomethe " steep hills effect".The distributed Fountain coding algorithm and random walkalgorithm method are analyzed in the chapter. The simulation results show that theproposed algorithm get a high recovery rate by setting "priority areas" in WSN.