Space-time Diversity Soft Processing In Mobile Multiuser Communication

Wireless mobile radio communication equipments and techniques have been becoming more and more important for modern life and growing greatly. Techniques in the fields of both mobile radio communication and computer network are the most attractive fields for researchers and the industries for their enormous trade markets. With the application of multimedia in wireless, the conflicts between the resource availability and the quality of integrated service have been becoming more and more acute.In the fields of mobile radio communication, the power of mobile terminals is limited and makes the high-rate multimedia transmission difficult. New adaptive allocation techniques are required for mitigating the influences of multi-path fading, interference of multiple-access and near-far effects. New techniques are required for managing mobile networks for the increasing users and services. B reakthroughs in the research fields of the mobile communication system instruments, coding and decoding mechanism, signal detection, and other receiving techniques should be performed for more effectively dealing with the disadvantageous effects of mobile fading channels and improving the frequency spectrum resource availability.Direct-sequence code-division-multiple-access (DS-CDMA) is the most popular of CDMA techniques because of its many attractive properties for the applications in the third-generation mobile communication. Its frequency can be flexibly reused. It resists multi-path fading and jam-up. RAKE receiver can be used to combine the received signal energy from different radio propagation paths in order to combat the effect of multi-path fading. Soft handover, soft capacity, soft feed-forward error-correcting code, sectored antenna array and adaptive beamforming, multi-rate, multi-system overlay can be used. Radio resource can be effectively managed and the transmission information is difficult to be detected and eavesdropped by others. Such all are the reasons why we choose the DS-CDMA wireless multi-user communication system and the relevant techniques that can be used to improve the system performance as the research subjects of this dissertation.Multiple access interference (MAI) and inter-symbol interference (ISI) are the two main factors that affect the capacity and performance of DS-CDMA mobile multi-user communication systems.The utilization of multi-user detection can provide significant additional benefits than conventional single-user detection by mitigating the influence of multiple access interference.The utilization of efficient soft coding and decoding techniques can greatly reduce the effects of Doppler frequency shift and significantly increase the performance of receivers.The utilization of diversity techniques can improve the link gain of wireless communication systems. In scattering radio environment, the spatial diversity in both the transmitter and the receivers can effectively resist fading and can provide choicesfor interference mitigating and equalizing. Adaptive antenna array techniques can jointly make use of the information in both the temporal domain and spatial domain and significantly improve the capacity of wireless communication systems.The acquisition of amplitude and phase information of channel in good time and accurately is important for the adaptive power control and other advanced signal processing of transmitting and receiving. The acquisition of amplitude and phase information of channel in good time and accurately can also make the coherent demodulation and optimal combining receiving at the receiver.According to following analysis, we can see that it is of great value to both theories and applications for us to continually study channel estimation, multi-user detection, space-time diversity processing, soft coding and decoding for coded communication systems, and to propose various efficient algorithms.In sum, we summarize the newest research results in such fields, thoroughly study in both up-link and down-link cases of mobile multi-user communication systems, develop various new algorithms, and carry out computer simulating and mathematical proving to validate the efficiency and performance of these new algorithms in this dissertation.Firstly, the necessity of jointly mobile multi-user detection and space-time processing is analyzed, space-time diversity multi-user detection algorithm is developed for the up-link of DS-CDMA communication systems. By considering the influence of interference from neighboring cells, the combining strategy of space-time diversity multi-user detection and single-user interference cancellation is derived. The system performances are compared between single-user space-time interference cancellation and space-time diversity multi-user detection. Comparing the performances between iterative space-time diversity multi-user detection receiving and iterative combining receiving of space-time diversity multi-user detection and single-user interference cancellation provides simulation results.A structure of jointly space-time diversity interference mapping and signal multi-user detecting is proposed, and the corresponding algorithm is derived in detail for mitigating interference signals from both other cells and other users of local cell in the DS-CDMA up-link communication case. The direct and iterative solutions of signal multi-user detection after space-time diversity interference mapping are given. Comparing the performances between combining receiving of space-time diversity multi-user detection and single-user interference cancellation and combining receiving of jointly space-time diversity interference mapping and signal multi-user detecting provides simulation and analytical results.A structure of space-time diversity virtual double-route weighting interference mitigating is proposed, and the corresponding practical algorithm is derived in detail using block matrix inversion formula and matrix inversion theory for mitigating interference signals from both other cells and other users of local cell in the DS-CDMA up-link communication case. Performances of such algorithm are thoroughly analyzed through simulation and analytical results.The up-link and down-link channel characters and their relationship of DS-CDMA communication system are thoroughly analyzed, and the relationship ofspace-time diversity weighting matrix between time division duplexing (TDD) and frequency division duplexing (FDD) these two different transmission ways is derived. Thus, the down-link space-time diversity transmission weighting matrix can be directly computed using the information about the up-link space-time diversity transmission weighting matrix and other information held at the base-station. Optimal combining weight of multi-path receiver at the mobile terminal in the down-link case is derived. The system performances of both time division duplexing and frequency division duplexing these two different transmission ways in the down-link case are thoroughly analyzed through simulation and analytical results.The up-link model and down-link model of DS-CAMD communication systems is compared. A common expression is used to express the receiving signals (receiving at the base-station in the up-link case or receiving at the mobile terminal at the down-link case) after the chip-matched sampling. Then, a common channel estimation algorithm is proposed. Based on these, a common space-time diversity beamforming weighting matrix algorithm suitable for both up-link case and down-link case is proposed. Also, a common optimal receiving algorithm combining multi-path signals suitable for both up-link case and down-link case is proposed. The performances for both estimated channel and noise parameters and known channel and noise parameters are compared for the proposed common algorithms.The up-link model and down-link model of DS-CAMD communication systems is thoroughly analyzed, and a Gaussian approximating expression is proposed to express the interference. Based on these, an efficient iterative soft decoding method is derived. The performances of different effects under different doppler frequency shift is provided for the proposed method.Finally, an adaptive scheme of information feedback and power control is proposed for both up-link case and down-link case.Base on all the above proposed algorithms, an integrated scheme of space-time diversity soft processing is proposed for the mobile multi-user communication systems.