Research On Hybrid Diversity Combining Techniques In UWB Wireless Communications

Ultra-wideband (UWB) is a novel short-distance wireless communication technology with high transmission rate. UWB shows broad prospect of applications in the high speed WPAN, intelligent transportation system, wireless ethernet interface link, wireless sensor networks and accurate positioning, especially in the application of digital home network. UWB wireless channels show complex time-varying property. UWB signals suffer from multipath fading and serious energy dispersion which degrade the system performance. Therefore, measures must be taken to combat multipath fading so as to improve the signal energy captured. Rake receiver technology, which is based on diversty combining theory, is one of the most effective solution for UWB wireless communications to combat multipath fading. In this thesis, we investigate the modelling of energy capture of hybrid diversity UWB Rake receivers, based on which the system bit error rate and outage probability are analyzed.The main contributions of this thesis are summrized as follows:(1) UWB Rake receivers using different diversity comb inning strategies are analyzed and compared. Based on simulation results over typical channels, we compare ARake, Selective Rake and Partial Rake in terms of BER performance and implementation complexity. It suggests that the hybrid selection maximal ratio combining (HS/MRC) and hybrid selection equal gain combining (HS/EGC) Rake receivers can be used to make satisfactory balance between system performance and complexity.(2) The modelling of energy capture of HS/MRC UWB PRake receivers is studied, based on which analytical methods for BER and outage probability evaluation are investigated. Firstly, taking intra-pulse interference (IPI) into consideration, we derive two ernergy capture models, i.e., continious time model and discrete time model, for HS/MRC UWB PRake receivers. Then, we approximate the distribution of the energy capture with Coxian distribution or lognormal distribution, where least squares fitting algorithm is employed to estimate the distribution parameters prcisely. Finally, the best approximating distribution is used to analyze the BER and outage probability. Numerical reslts show that:the proposed energy capture models can be used to chanracterize the behavior of the corresponding UWB PRake receivers precisely; Coxian and lognormal distributions can be used to approximate the real distribution of energy capture of UWB PRake receivers with high pricision, and therefore the BER and outage probability can be evluated easily by using simple analytical expressions.(3) The modelling of the energy capture of HS/EGC UWB PRake receivers is studied, based on which the BER and outage probability are analyzed. Taking intra-pulse interference (IPI) into consideration, we derive continious time ernergy capture model and discrete time ernergy capture model seperately for HS/EGC UWB PRake receivers. Based on the ernergy capture models, the BER and outage probability are evaluted and compred with those of HS/MRC UWB PRake receivers via simulations. Simulation results show that:the continuous time energy capture model outperforms the discrete model in terms of BER and outage probability; HS/EGC UWB PRake receivers have loss of BER and outage probability in comparison with HS/MRC UWB PRake receivers...