The Research On Anti-interference Performance For MIMO-UWB Systems

The ultra-wideband (UWB) system has some advantages, including low transmitting power, high transmission rate, anti-multipath ability, high system capacity and so on. It causes more and more attention in the wireless communication academia and industry. But the UWB system has many indoor multipath channels, which can bring inter-symbol-interference easily and reduce the BER performance of the UWB system. For multipath interference problems of the UWB system, the system performance can be enhanced through taking many techniques, such as Orthogonal Frequency Division Multiplexing (OFDM), RAKE receiving and Multiple Antenna Diversity.This paper mainly researches on the anti-multipath interference in the UWB system by using the RAKE receiver and MIMO technologies. The primary contents of the thesis are as following:The modulation and multiple access techniques of the UWB systems are introduced. The multipath channel models of UWB system are introduced briefly and the reason of the multipath interference caused by indoor dense channel is analyzed. The anti-multipath interference performance of the DS-UWB system is compared with that of the MB-UWB system.The anti-multipath interference property for the UWB system is studied from time-domain. From the point of time domain equalization, the anti-multipath interference technology is introduced by utilizing the RAKE receivers under the multipath channels of the UWB system. The performance of the RAKE receivers with different combing methods is analysed. The MRC-based RAKE receiver can make signal-to-noise ratio (SNR) of each multipath component reach the maximum. However, as the multipath interference tends to be stronger, the branch number of the RAKE receiver needs to add and this causes high system complexity. To reduce the complexity of the RAKE receiver, the RAKE receiver based on LMS algorithm is introduced. The anlysis and simulation shows that the RAKE receiver based on LMS algorithm can not only eliminate the multipath interference of the system, but also reduce the complexity of RAKE receiver, and hence the BER performance is improved. On this basis, the RAKE receiver based on wavelet transform is proposed and the simulation results indicate that it can further improve the the multipath interference resistance performance and lower the system complexity.The anti-multipath interference for the UWB system is investigated from the point of antenna diversity. The MIMO-UWB system model and transceiver principle are introduced. The channel model of the MIMO-UWB system is analyzed through using the S-V model modified by IEEE802.15.3a. Based on the traditional STF coding scheme, a new STF coding algorithm based on the rotation matrix is put forward. The simulation and analysis for the UWB system with different antennas number are implemented by using the MMSE-based receiver. The simulation results show that the MIMO technology applied to the UWB system can increase the channel capacity and the anti-multipath interference performance of the system enhances when the antennas number increases.