Researches On The Impulse Radio Based Cooperative Relaying UWB Communication System

Impulse Radio-Ultra Wide Band (IR-UWB) has been considered as one of the possible candidates for the physical layer of future high-rate and low cost wireless personal area network (WPAN). It transmits the data through the impulse, which has extremely low power spectrum density and extremely wide bandwidth (the absolute bandwidth is more than500MHZ, the relative energy bandwidth is more than0.2-0.5). It has numerous advantages over other short range wireless communication systems, such as low power consumption, low interference to other existed systems for it small power spectrum density (PSD), high data rate and excellent time resolution. However, the low PSD limits the coverage of the UWB system and the high data rate also can be influenced by the extension of the coverage.The main idea of cooperative technology in wireless networks is that the cooperative terminals share their antennas and the other resources to create a "virtual array" through distributed transmission and signal processing. The cooperative relaying scheme has been widely employed in modern communication systems to provide higher quality of service (QoS) and extend communication coverage. To solve the question between power consumption and coverage extension, cooperative technology has been considered in UWB system to improve performance.The mainly work focuses on the research of cooperative IR-UWB communication system, including the design of signal processing algorithm, performance analysis and the joint optimization of the cooperative IR-UWB communication system. New analysis method is proposed to analysis the performance of cooperative UWB system under the indoor multipath fading channel model and the approximate closed form expression of BER is given. And, it is the theoretical basis for the design of cooperative IR-UWB system.The main work of this thesis focuses on the following aspects.Firstly, we research the cluster property in UWB multipath fading channel and analysis the channel model of the cooperative IR-UWB system.Secondly, we have identified a suitable method corresponding to the complex multipath fading channel of UWB communication after the research of some typical performance analysis methods. And we use the MGF (Moment Generating Function) in probability theory to derive the performance analysis results.Thirdly, suitable signal processing algorithms are designed for different cooperative strategies. We also analyze the BER performance of the system using AF, DF and DTF strategy under multipath fading channel. The approximate closed form expression of the BER performance for cooperative UWB system is derived.Finally, In order to increase the throughput and decrease the BER, the relay node and the cooperative protocol are selected based on the approximate closed form expression of the cooperative UWB system. We can realize the joint optimization of relay selection and cooperative protocol switch to improve the system performance and extend the coverage.Our work mainly focuses on the analysis and design of cooperative communication of IR-UWB system. We present the derivation of the approximate closed form expression of the average BER of the system based on the MGF. Then we can provide theoretical basis for system design, reduce the simulation time and observe the change of system performance related to different parameters. The channel state information can be represent by ranging information while considering the UWB unique properties such as fine ranging and immunity to small scale fading.The optimal relay selection based on the ranging information and the cooperative protocol switch based on the approximate closed form expression of the cooperative UWB system can be jointly employed to optimize the system performance, which contributes to the improvement of BER performance and system throughput.