No Rate Code Based On Channel Coding

Rateless codes have drawn much attention in recent years as they can approach channel capacity without requiring channel information at the transmitter. These are forward error correcting schemes i.e., they do not require an acknowledgement for each packet, as against ARQ schemes where the receiver has to request retransmission when packets are dropped or acknowledge when packets are received. These codes have to be rateless i.e., they must produce an endless stream of coded packets from a finite number of data fragments and also achieve optimal performance for any erasure rate. Hence, design of such near optimal, rateless and low complexity coding schemes are of great importance to applications involving transmission of large files such as digital video broadcasts, which cannot tolerate packet losses.Luby Transform Codes were the first class of universal erasure codes, like com-puter networks, also called Digital Fountain. Later Raptor codes, a generalization of the LT codes were introduced to trade off complexity with performance.In this thesis, we first introduce the rateless codes and the present research do-mestic and overseas. The Tanner graph and degree distribution, like ideal soliton distri-bution and robust soliton distribution, are also included. With BPSK modulating and BP decoding, we expatiate the principle of LT codes for the erasure channel and AWGN channel, and also introduce the encoding and decoding methods of Raptor codes and RC-LDPC codes. This thesis focuses on the decoding process of LT codes, which con-tains MP decoding and BP decoding based on the information from generation matrix. After, we firstly propose an improved LT code to get a better performance. UEP rateless code is proposed in this thesis for the communication system needs to protect some part of information which is more important. Based on MATLAB, we structure the simula-tion system model of four kinds of rateless codes for erasure channel and AWGN chan-nel and analyze the performance of LT codes and Raptor codes. How the performance is affected by degree distributions, the length of codes and the quality of channel is ulti-mately concluded. Finally, the LT encoder is realized by FPGA and test. The correctness of LT encoder is validated by serial interface communication tools, by comparing with the results from MATLAB emulator.