Research On LDPC Codes And The Applications In UWB System

Compared with wireline networks, wireless networks is more mobile, however, they have problems of bad communication environment and limited spectrum resource. Meanwhile, people demand more from wireless communication systems, expecting higher data rate, lower cost, and less energy. Under such background, Ultra-Wideband (UWB) technology attracts much attention around the world. UWB is an important technology for indoor high rate wireless communications and now it is regarded as one of the key technologies for the next generation wireless communication systems.Characterized by high frequency band efficiency, low requirement of channel equalization and high endurance for multi-path fading, OFDM(Orthogonal Frequency Division Multiplexing )technology is especially suitable for wideband system.Low-Density Parity-Check Codes, first introduced by Gallager in 1963, is a special kind of parity check codes which can be defined by a very sparse parity check matrix. LDPC codes can achieve performance approaching the Shannon limit when decoded using an iterative probabilistic algorithm. In addition to their simple descriptions of code structure and fully parallelizable decoding implementations, such codes have attracted much attention particularly in the field of coding theory.The technology of LDPC codes, including the encoding , decoding , constructing method are studied.Simulations of different decoding algorithms in AWGN and UWB environment are performed.Chapter one gives a brief introduction to UWB, OFDM and channel coding.The principles of OFDM as well as the details of the UWB channels and the simulation model are introduced in Chapter two.Chapter three gives the principles of LDPC codes and introduces different constructing type for LDPC codes. Simulations are performed to verify the performance of LDPC codes in AWGN environment. A new kind of algorithm to calculate the girth of every symbols nodes and the quantity of the cycles which have the same length of the girth is put forward and realized.Different decoding algorithm for LDPC codes are introduced in chapter four, including the Belief Propagation algorithm in probability domain as well as in log domain, Min-Sum algorithm, Normalized BP_based algorithm, Offset BP_based algorithm, Oscillation_based algorithm, the Normalized_based algorithm in the symbol node side, the Offset_based algorithm in symbol nodes side, and also a kind of algorithm called Corrected BP_based algorithm here. then the probability schedule decoding algorithm is introduced.Simulation are performed to compare the performance of some decoding algorithm given above.