Multiuser Detection Of TH-UWB Systems

Ultrawide Band (UWB) communication technique has attracted great interests in both academia and industry for applications in short-range wireless communications from the early 1990s. It has been proposed as a viable solution for high speed indoor range wireless communication systems because of its low power, high rate, immunity to multipath propagation, and less complex transceiver hardware.As in the CDMA systems, the MAI (Multiple Access Interference) is the main interference in the TH-UWB (Time-Hopping UWB) systems, and MUD (Multiuser Detection) is the key anti-MAI technology. By adopting multiuser detection technology, TH-UWB systems can solve the near-far problem and enhance the capacity of the system.From the view of the signal structure of TH-UWB, the different characteristics of MAI between the TH-UWB and CDMA systems are researched, and some low complexity multiuser detectors are proposed. The main achievements include:1. Taking advantage of the time diversity theory, some low complexity multiuser detectors are proposed. The fundamental of these detectors is different from that of the CDMA systems, and the computation complexity is reduced. Firstly, the time diversity detector based on pulse confliction can mitigate the MAI entirely; secondly, in order to be applied to the asynchronous channel, a modified time diversity detector is presented to enhance the performance; finally, a detector adopting Maximal Ratio Combined technology (MRC) is presented.2. Using for reference of the SIC (Successive Interference Cancellation) in CDMA systems, the SIC detectors based on pulse confiction is given. The detector ranks the users according to the interference of the users'pulses: the one with minimal interference is the first to be detected. The time diversity detector based on pulse confliction is used at each stage. Because it increases the processing gain of the user at each stage, the detector could achieve good performance. 3. Combined with the MMSE, the SIC detector based on MMSE is presented. This detector ranks the users by the number of colliding users: the one with minimal colliding users is detected first; and the MMSE detector is used at each stage. Due to the reduction of the size of the matrix to be inversed at each stage, the detector embodies low complexity.4. According to the relevant knowledge of PIC (Parallel Interference Cancellation) and PPIC (Partial PIC), the PIC and PPIC detectors are introduced to TH-UWB systems. And then, an iterative multiuser detection algorithm applying PIC to TH-UWB that follows the turbo principle is obtained. The complexity of this iterative detector is lowered by utilizing the special structure of TH-UWB signal. Based on the iterative process, the PPIC iterative detector is designed to choose the appropriate factor according to the bit error rate. The performance of the detector is further improved compared with the PIC iterative detector. Besides, the computer simulations demonstrate that the algorithms presented in this dissertation improve the performance of the receivers, and furthermore, they can be applied in the TH-UWB systems because of its low complexity.