Factor Graph Based Iterative Receiver Design And Optimization

Iterative receiver technology can improve the system performance dramatically. Factor graph is a powful tool to analyze and design iterative receiver. In this thesis, several iterative systems are analyzed intensively. The main topics include:1．IDMA systems are studied intensively. The main contributions include: (l)The problem of iterative multiuser detection for IDMA system is analyzed by using factor graph. The factor graph representation of IDMA system is compared with that of CDMA system. The reason for that IDMA can use low complexity detection algorithm is analyzed. (2) The detection algorithm of IDMA system is derived by using the universal rule of sum-product algorithm and the inner relationship between the IDMA detection algorithm and the sum-product on factor graph is also discovered. (3) EXIT charts technology is used to analyze the performance of uncoded IDMA and convolutional coded IDMA systems. The effect of channel coding scheme on IDMA systems is studied.2．IDMA system with equal power constrains is optimized. The main contributions include: (1) Correlation among the messeges in uncoded IDMA systems is analyzed. A kind of interleavers, named by PEG interleavers is designed for uncoded IDMA system. (2) LDPC codes are used to multiple access channel. Two schemes, named by multiuser LDPC coding and LDPC-coded IDMA, respectively, are proposed and the corresponding message update rules for three kinds of nodes are designed. A Gaussian approximation method is designed these update rule. Differential evolution, combined with Gaussian approximation technology, is used to optimize the irregular LDPC codes for these schemes.3．An IDMA based one step random access channel structure is designed for B3G systems. IDMA is used as the transportation mode for the resource request message part. The whole RACH channel structure, including preamble part and message part, is designed for one-step random access. The preamble detection algorithm is designed and analyzed. By inserting several bits in the message part as addition ID, the IDMA-based one step access scheme has lower collision probility than conventional schemes.4．Three problems about iterative acquisition for m sequence are studied. The main contributions include: (1) Non-coherent differential iterative acquisition for m sequence. By using the differential property of m sequence, a differential iterative sum-product acquisition algorithm is designed. A simple method to find original sequence phase with known differential sequence phase is designed. (2) The problem of parallelized iterative acquisition for multiple access. By combining the low complexity multiuser detection algorithm for IDMA and the sum-product iterative acquisition algorithm for m sequences, a parallelized iterative acquisition algorithm is proposed for multiple m sequences. (3) The problem of iterative acquisition for m sequence with non-sparse generating polynomial. By using the sampling property and the phase difference constrains property of m sequenece, aided by the LDPC codes optimization theory, the factor graph representation of m sequenece with "non-sparse" generating polynomial is optimized and good acquisition performance is acquired.