| Impulse Radio Ultra-wideband (IR-UWB) technology has recently attracted considerable interests in the research and standardization communities, due to its high data rate, large capacity and immunity to multipath fading. IR-UWB can implement high data rate transmission at low power consumption, low complexity and low cost, which makes it a promising technology for wireless personal area networks(WPAN). However, in the dense multipath indoor channel, the high data rate UWB signal suffers from frequency selective fading, which spreads the signal energy over several symbols. This phenomenon makes it difficult to collect multipah energy and meanwhile brings interference to the detection of symbols, which affects the performance of UWB system severely.In this paper, starting from the two kinds of impacts caused by dense multipath channel, we studied the performance of Rake receiver in IEEE 802.15.3a channel, and discussed multipath interference suppression by the means of time domain equalization and receiver algorithm and structure improvement.Firstly, by considering the finiteness of clusters and multipath components in each cluster, a mathematical model is proposed for the IEEE 802.15.3a channel model, which makes the channel model not only straightforward to simulation but also amendable to theoretical analysis. The obtained mathematical model is constructed by four statistically independent components including one invariable component, two finite two-dimensional Poisson processes and one finite two-dimensional Poisson cluster process. Closed form expressions for the mean number of paths arrived in a time window, mean number of paths density distribution and power decay profile for the IEEE 802.15.3a channel are found through the proposed mathematical model, which makes it intuitive and accurate to analyze channel characteristics.Secondly, the number of Rake fingers used to capture a given percentage of energy is analyzed by utilizing the mathematical model proposed above. In the absence of multipath interference, the relationship between Rake error performance and observation time is derived from the proposed mathematical model. In the presence of multipath interference, by studying the signal model of multipath interference, a semi-analytical approach is proposed to analyze Rake receiver performance. This approach is efficient in CM4 channel and its results accord with waveform level simulation results.Thirdly, multipath interference suppression is studied by the means of time domain equalization. An approximation method for the Ungerboeck MLSE is proposed under Rake reception. In the proposed method, channel impulse response used in sequence estimation is replaced with the Rake receiver impulse response, which efficiently reduces the complexity of sequence estimation. In CM1 channel, comparing with other time domain equalization methods, our method is the closest to the lower bound of Rake symbol error rate.Finally, multipath interference suppression is considered by improving receiver algorithm and structure. By investigating the signal model of chip level samples of each Rake finger, a chip level optimal combining method is proposed based on symbol level optimal combining, which is capable of utilizing the potential repetition diversity in DS-UWB signals. Then based on similarities between the signals of asynchronous CDMA systems and the signals received by PRake receivers, decorrelating algorithm is introduced to PRake receiver to combat multipath interference. Additionally, by changing signal model, the multipath interference suppression capability of linear multiuser detection receiver is studied in the single user environment. Two kinds of reduced rank linear filtering schemes, multistage Wiener filter and eigencanceler, are introduced to multipath interference suppression to mitigate the complexity and to improve convergency of the linear multiuser detection receiver.It can be summarized that, this paper discusses energy spreading and multipath interference issues brought by dense multipath channel to high data rate UWB system. Many analysis methods and solutions are proposed. Besides the theoretical analysis many simulations are carried out to support the effectiveness of our methods.
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