Research Of Key Techniques Of DS-UWB Wireless Communication System

The research on Ultra Wideband (UWB) communication technology shows more significant in resent years. UWB technology has the features of device infrastructure simplest, lower transmission power, higher gain and data rate, multipath resolution capability. It can be deployed for military communications, family entertainment and office. As a new technology, it faces lots of practical questions, such as anti-interference and multiuser accessibility. This thesis mainly discusses the key technologies in UWB communication technology, and it can be divided into four parts: research on channel model and channel estimation algorithm of UWB system; research on synchronization acquisition algorithm of DS-UWB system; research on multi-user detection algorithm and adaptive baseband signal processing technology of DS-UWB receiver system.UWB system has different signal model and channel model. Due to the extremely wide bandwidth, UWB system has a high multipath resolution and the number of the multipath is very large, thus the research of UWB indoor channel model is a chief problem. In this thesis, UWB signal model and channel model are firstly introduced. On the basis of researching the IEEE802.15.3a model, a pilot signal and Maximum-Likelihood based channel estimation algorithm is proposed. Simulation results showed that the algorithm could obtain satisfying performance in typical UWB channels.By analyzing the current acquisition algorithm, acquisition time in theoretic was analyzed .Due to the difficulty of obtaining the chip synchronization and PN code synchronization in multipath channel, a modified model signal based synchronization acquisition scheme is proposed. First, the chip synchronization was achieved by paralleled correlators with equal interval chip waveform energy accumulation algorithm. Once the chip synchronization achieved, PN code synchronization can be achieved by serial correlator easily. The simulation results indicate that the proposed scheme can achieve satisfactory synchronization performance in DS-UWB channel. The simulation showed that the proposed method could achieve synchronization of DS-UWB system fast and accurately in several microseconds. How to restrain the multiple access interference and interference between symbols is a challenge in UWB technology. Multi-user detection is a method which solves the problem with the design of the receiver and is widely used. A DS-UWB system Multi-user Detection scheme is proposed, which is based on one-class SVM Bayesian algorithm. It is proven that the solution of one-class SVM using the Gaussian kernel can be normalized as an estimate of probability density, and the probability density can be used to construct the two-class and multi-class Bayesian classifier. Shown by digital modulation recognization experiment, the classification performance of the proposed algorithm is better than artifical neural net and similar to the traditional SVM algorithm. The simulation results showed that in UWB multi-path channel the BER performance of the proposed scheme was better than liner MUD algorithm such as MMSE detector and decorrelating detector. The size of kernel matrix of the new algorithm is greatly less than traditional multi-class SVM, which lead to less training time and good performance of mitigating of MAI.In addition, an adaptive synchronization rebuilding algorithm of baseband signal processing in DS-UWB receiver is proposed. The baseband signal processing algorithm includes low pass digital signal filtering, infimum measurement based adaptive digital signal frequency estimation algorithm, and synchronization rebuild algorithm. The proposed algorithm can rebuild the baseband signal in high frequency noise condition and modify the bit judge error of the multi-user detector. This performance can improve the demodulation performance of the receiver.