Research On MIMO-UWB Wrieless Communication Techniqhe

Ultra-wideband (UWB) is a new-style wireless communication technique which employs ultra short analog pulses to transmit information without carrier. It has been considered as the main solution for short-range indoor wireless communication. UWB possesses several attractive features, including low power consumption, low implementation complexity, strong multiple access ability, capabilities to support high data-rate connectivity as well as the high definition ranging. Although the UWB systems enjoy so many merits, it is still confronted with plenty of technological challenges. In order to avoid interfering with other coexist systems in the wide bandwidth, the power spectrum of UWB system is limited to a lower level. Accordingly, this imposes a limitation on the communication range of UWB. Due to the wide bandwidth, UWB channel is a high frequency-selective channel which usually contains more than one hundred multi-paths, and the maximum multi-path delay can achieve several hundreds nanoseconds. This imposes a limitation on the actual data rate of UWB. Multi-Input Multi-Output (MIMO) technique can increase data rate by transmitting/receiving parallel data streams (multiplexing) and enhance the signal-to-noise ratio by transmitting/receiving multiple copies of the same data (diversity). Owning to these advantages, MIMO will be the most extensively adopted physical-layer technique in future wireless network. In this paper, we mainly focus on MIMO-UWB systems and research on how to use MIMO technique to solve the technological challenges of UWB. For MIMO-UWB system, we propose two preprocessing schemes, one detection scheme and its two improved schemes. Besides, we propose a new modulation scheme for noncoherent single-input single-output UWB system.Firstly, this paper proposes a time reverse (TR) technique based preprocessing scheme for multiplexing MIMO-UWB system. The existing TR preprocessing scheme can suppress the multi-stream interference (MSI) to some extent, however, it requires the estimations of all UWB channels between transmit and receive antennas which are very complex. The proposed scheme reduces the complexity of channel estimation and the requirement of preprocessing filters. This enables our proposal more feasible.Secondly, an ultra-high data rate TR MIMO-UWB communication system with space-time pre-equalizer is proposed. When the symbol duration is set to approach the duration of UWB monocycles, the data rate is close to the limit, resulting in the severe intersymbol interference (ISI). The zero-forcing (ZF) criterion based space-time pre-equalizer presented in this paper eliminates both ISI and MSI caused by spatial multiplexing at the sampling time. With less demand for degree of freedom (the number of antenna) than other existing schemes, the proposed scheme enables the data rate to reach the order of Gbps without losing bit error rate (BER) performance. Since TR signal preprocessing and the proposed precoding both require the channel state information (CSI), a simple but effective channel estimation algorithm is also proposed to evaluate the impact of channel estimation on the proposed scheme.Then, this paper investigates noncoherent MIMO-UWB systems where the signal is encoded by Differential Space-Time Block Code (DSTBC). Considering the specific signal format of DSTBC-UWB system and employing the property of DSTBC, a noncoherent multiple symbol detection (MSD) scheme is developed by generalized likelihood ratio testing (GLRT) approach. Although the proposed MSD scheme can enhance the performance of DSTBC-UWB system, the complexity of the exhaustive search based MSD exponentially increases with observation window size. To decrease the computational complexity, the original MSD metric is transformed into another equivalent form which can be implemented by sphere decoding (SD) for DSTBC-UWB system. Moreover, a suboptimal Decision-Feedback (DF) based MSD with lower complexity than SD based MSD is proposed to further reduce the computational complexity.Finally, a multi-layer orthogonal block coded transmission scheme is proposed in this paper to enhance the performance of the noncoherent Single-Input Single-Output (SISO) UWB system. The design employs a novel Multiple Orthogonal Block Coded Modulation (MOBCM), which transmits multiple information-bearing orthogonal codewords with an ingenious layered structure. At the receiver side, a correspondent noncoherent multiple codeword detection technique is developed to jointly detect multiple codewords and exploit the high energy efficiency inherent in MOBCM. Solid performance gain is achieved and our design narrows the general performance gap between noncoherent and coherent receiver for UWB system.