| Along with the fast development of the communication industry, the requirement of the communication service increases. People hope the system to provide higher data rate and better quality with low cost. Whereas the frequency resource of the wireless communication is gradually tight, it's necessary to develop new generation system. With the attractive features of high data rate transmission, low power waste, high security, fine time resolution, multipath immunity, low complexity and low cost, ultra-wide band (UWB) systems can be widely applied into high-speed short-range indoor wireless communications, and can also be applied in low-speed long-range communication or location. In addition, UWB systems don't monopolize the frequency resource but share with other wireless communication systems, so it becomes the focus in research of wireless communication field and be considered to be the key technology of next generation wireless communication. The early UWB technology is mainly used in military radar, however in recent years UWB has had large development in civil commerce. In 2002, the Federal Communications Commission (FCC) in the United States permitted the operation of UWB devices in short-range wireless communication, regulated the definition of UWB and characterized the UWB transmission systems with a instantaneous spectral occupancy in excess of 500 MHz or a tractional bandwidth of more than 20%. Also, FCC assigned spectral masks for different applications of UWB devices to avoid the interference to other systems. Since the performance of UWB systems is affected by the strict limit of transmitted power, to enhance the performance of UWB system without increasing the transmitted power is very important.Multi-Input and Multi-Output (MIMO) can improve the system capacity without increasing the frequency resource and transmitted power. It has sharp effect in resolving the capacity bottleneck in the future wireless network which develop rapidly. MIMO systems applying space-time coding can achieve transmit diversity and power gain over spatially uncoded systems, and can also enhance the system performance. So space-time coding can be applied to UWB systems to realize highspeed and effective transmission.Recently, researches on space-time coding for UWB focus on Space-Time block codes (STBC). Space-time trellis codes (STTC) can achieve better performance than STBC, though it is more complex. To select appropriate modulation and decoding algorithm for STTC is difficult. In view of these problems, we research of STTC for UWB with different modulations.Beamforming is a technology which can be applied into all the antenna array and MIMO systems to create antenna array radiation. It is a closed-loop approach which can achieve better performance compared with the open-loop approaches. To further enhance the performance of MIMO-UWB system, we research STTC combined with beamforming for MIMO-UWB system.Main content of this thesisChapter 1 summarizes the characteristic and application of UWB, and analyzes the researching actuality. Finally introduces the main content of this thesis.Chapter 2 introduces the key technology of UWB, including transmit and receive technology and channel model. Simulates the performance of PPM, BPSK and OOK modulation and describes the signal models of TH and DS. Then we simulate the IEEE channel model which divides into CM1~CM4 and the performance of Rake receiver which contains Arake, Srake and Prake.Chapter 3 introduces the basic theory of MIMO and common space-time coding including STBC, STTC, Layered Space-Time Codes (LSTC) and Differential Space-time Block Codes (DSTBC). Mainly analyzes the encoder and decoder of STBC and STTC. Simulation results show that STTC can simultaneously offer a substantial coding gain and diversity improvement, so it can be applied to UWB system to enhance the system performance.Chapter 4 proposes STTC algorithm for MIMO-UWB with PPM, PAM and biorthogonal modulation under analyzing the transmitter and receiver model of MIMO-UWB space-time coding system. Set up the system model when the interference of multipath and multiuser exist and evaluate the performances of these STTC schemes. Simulations show that on both Gaussian channel and multipath channel STTC-UWB with PPM can achieve much better performancethan the schemes employing PAM or biorthogonal modulation and the performance degrades when the number of the users increases.Chapter 5 presents a joint STTC and beamforming algorithm for MIMO-UWB system. This algorithm weights the signals which take the code information with proper weighting matrix before transmission from different antennas, and the weighting matrix base on the feedback channel information from the receiver. It has been shown through the simulation that such algorithm can improve the performance of MIMO-UWB system on Gaussian and multipath channel.Chapter 6 summarizes this thesis and suggests the work to do next. The innovative work of this thesis(1) To combine the advantage of MIMO and space-time coding with UWB, apply STTC into UWB system. Set up the system model of STTC for MIMO-UWB system with PPM, PAM and biorthogonal modulation and derivate the algorithm of encoding and decoding. The simulations show, using STTC can improve the performance of MIMO-UWB system. Also contrast the performances of three STTC schemes on Gaussian and IEEE multipath channel and the results show that STTC with PPM can obtain better performance. In addition, when the interference of multiuser exists, the performance of STTC for MIMO-UWB system degrades when the number of the users increases.(2) To further enhance the performance of MIMO-UWB system, set up a joint space-time coding and beamforming model, and present the encoding and decoding algorithm. The information bits are first encoded by a STTC encoder, and then modulated to UWB waveform signal. The UWB signal is weighted by the transmit weighting matrix based on the feedback channel information from the receiver. Simulation results show that this algorithm enhance the performance of MIMO-UWB system effectively.This paper has some groping action to the following two questions(1) Research on the code design criteria of STTC for MIMO-UWB system.(2) The best algorithm of weighting matrix in beamforming. |
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