Researches On Key Techniques Of Iterative Detection And Decoding In Wireless Communications

Iterative decoding algorithm has been introduced in advanced forward-error-correct-ing codes,which is just the reason why Turbo and LDPC codes have performanceclose to Shannon limits.Turbo principle can be used not only to offer the potential ofhigh spectral efficiency,but also to decrease the effect of fading and jamming.Therefore,iterative detection algorthim is one of the key candidate techniques of thenext generation broadband mobile communication system.Firstly,the researches of iterative decoding and detection are surveyed,a variety offundamental problems needed to be solved are investigated,and the main contents ofthis dissertation are list.In the area of Turbo equalization,the effect of SNR mismatch on bit error rateperformance is investigated.Through the comparative study between log maximum aposteriori probability (Log-MAP) and suboptimal Max-Log-MAP algorithm,a newiterative equalization algorithm called scaled Max-Log-MAP algorithm is proposed,which not only performs almost the same as that of Log-MAP over low-loss channels,but also is insensitive to a SNR estimation error.Over high-loss channels,a new SNRestimation method is proposed based on the reliability information of soft output fromscaled Max-Log-MAP equalizer.By using the estimated SNR,a new switchingiterative equalization algorithm between Max-Log-MAP and Log-MAP is alsoproposed.In the area of frequency-domain equalization,a novel parallel concatenated frequ-ency-domain equalization structure is proposed.By exploiting minimum mean squareerror decision-feedback equalization criterion,a new iterative frequency-domainequalization algorithm with hard-decision feedback and soft-decision feedback isderived,respectively.The performance of our new scheme is also investigated overboth static channels and Rayleigh channels.Moreover,the influence of a SNRmismatch on this new scheme is also analyzed.In the area of resisting man-made jamming,a slow frequency-hopping CPM system is considered.With the MAP demodulation algorithm,a new branch metricscalculation method which makes it insensitive to the SNR offset is presented.Thisalgorithm is also improved so that it can perform close to optimum MAP demodulationalgorithm.In aspect of anti-jamming,an iterative jamming estimation method isderived.The performance of the iterative CPM demodulation and decoding algorithmwith jamming estimation algorithm is analyzed.Simulation results demonstrate that theproposed jamming estimation method can improve dramatically the performance ofiterative CPM demodulation and decoding algorithm.Finally,some important issues of LDPC codes applicated in B3G/4G mobilesystems are discussed.A semirandom construction method of quasi-cyclic LDPC codesis proposed.With this method,a LDPC code with more flexible parameters is obtained.And the fixed-point implementation of LDPC decoding algorithm have been analyzed.Due to the rate-compatible property ofπ-rotation LDPC codes,a new adaptive LDPCscheme is designed,and its performance over fading channels is investigated.Furthermore,an iterative multiple-input multiple-output detection and LDPC decodingalgorithm in a B3G/4G TDD downlink is derived,and the performance over COST207channels are also shown.