【作者】 赵振山；

【导师】 徐国治；

【作者基本信息】 上海交通大学 ， 电路与系统， 2007， 博士

【摘要】 现代无线通信面临着频谱资源有限,传输环境复杂等诸多困难。随着对更高的数据传输率、更好的服务质量、更大的网络容量和覆盖等需求的增大,许多能够提高频谱效率和传输可靠性的新技术和新方案应运而生。在无线通信系统的发射机和接收机处使用多元天线阵,即无线MIMO技术,就是其中之一。MIMO系统用于分集传输,能更有效的克服各种信道衰落和干扰,提高信号的传输性能。随着对MIMO技术研究的深入,它所能提供的性能增益也越来越引人注目,并且被认为是实现未来高速宽带无线Internet接入网的关键技术之一,在第三代(3G)乃至三代以后(B3G)的移动通信系统中有着广阔的应用前景。目前,MIMO技术已被引入到诸如UMTS和CDMA 2000标准中。在固定无线接入和WLAN应用中,MIMO技术也被IEEE 802.16和802.11标准制订者作为一种重要实现方案进行研究。MIMO系统用于空间多路复用,可以在不增加发射功率和占用带宽的条件下极大地提高数据传输速率。目前已经证明在发射端和接收端都已知信道信息的理想情况下,MIMO系统的容量与发射端和接收端最小天线数目成正比。但是当发射端不能获得信道的准确信息时,系统的容量性能会受很大的影响。在实际的传输系统中,由于信道的快速变化、传输时延或信道估计误差等多种因素的制约,在发射端不可能获得准确的信道信息,而信道的统计信息(如:均值、协方差信息)在一段时间内可以看作是不变的,因此对于快速变化的信道,不需要频繁的将信道信息反馈到发射端,只有当信道的统计信息发生变化时再反馈即可,并且已经证明利用发射端的信道统计信息可以提高MIMO系统的容量,本文主要讨论利用反馈到发射端的信道统计信息对发射端进行最优化设计,主要研究成果如下:分别采用遍历容量、中断概率和误码率作为性能指标来分析发射端获得信道的统计信息时,发射信号的最优化设计问题。首先以遍历容量作为性能准则,在分别介绍了发射端获得信道均值信息或者协方差信息时,最优发射信号形式的基础上,着重介绍了当信道的均值和协方差信息同时反馈到发射端时,系统的最优信号发射形式,推导了信号的最优发射方向,并且给出了功率优化分配的算法。接着以最小化系统的中断概率为性能指标,针对发射端和接收端都存在空间相关性的MIMO系统,讨论了协方差反馈时发射信号的最优发射形式。最后以误码率为性能准则,讨论协方差反馈时系统的最优预编码矩阵设计,推导了一个误码率的上界,给出了最优预编码矩阵的特征向量方向以及功率分配方案,最后通过仿真分析了各种信道因素对系统性能的影响。提出了一种适用于非正交空时分组码的预编码设计方案。空时编码技术将多天线技术和编码技术相结合,可以在不牺牲带宽的条件下起到发射分集和功率增益的作用,是MIMO系统中一项十分重要的信号处理技术,将空时编码技术和预编码技术相结合是MIMO系统研究的一个重要领域。本文在正交空时分组码的基础上进行推广,提出了一种适用于其他非正交结构空时分组码的预编码设计方案,推导出最优预编码矩阵的特征向量与发射相关矩阵的特征向量和空时分组码的结构有关,并且给出了最优预编码矩阵功率分配的公式。分析了接收端的信道估计误差对于系统性能的影响。针对SISO系统,文章以中断容量为性能准则,讨论了Nakagami-m和Rice信道中由于信道估计误差的存在导致系统中断容量的不确定,推导了中断容量的上界和下界。对于MIMO系统,分析了信道估计误差对于系统信道容量的影响,给出了信道容量的边界,着重分析了在接收端存在信道估计误差,发射端具有不同的信道状态信息时,系统发射信号的最优传输策略,并且通过仿真分析了信道估计误差对于MIMO系统性能的影响,同时比较了发射端具有不同的信道信息时,系统的信道容量性能。文章最后对本文的内容进行了总结,展望未来的研究方向。更多还原

【Abstract】 Modern wireless communications must cope with critical performance limiting challenges that include limited availability of radio frequency spectrum and a complex time-varying wireless environment (fading and multipath). Meeting the increasing demand for higher data rates, better quality of service, higher network capacity and user coverage calls for innovative techniques that improve spectral efficiency and link reliability. The use of multiple antennas at receiver and transmitter in a wireless system, popularly known as MIMO wireless is an emerging cost-effective technology that promises significant improvement in these measures. It is believed that the wireless MIMO technology will be one of the key ones that realize the high-speed broadband wireless Internet access networks in the future and has wide application prospect in the third generation (3G) or beyond third generation (B3G) mobile communications. A growing acknowledgment of the performance gains from MIMO technology has spurred the insertion of this technology into wireless standards, notably the mobile standards such as UMTS and CDMA 2000. MIMO techniques are also under study in IEEE 802.16 and 802.11 standards for fixed and WLAN applications respectively.MIMO technology can increase data rate without increasing transmission power and bandwidth. It has been proved that the capacity of MIMO system increases as the minimum number of transmit and receive antennas when the channel state information (CSI) is perfectly known at transmitter and receiver. The capacity will degrade greatly when the CSI is not known at transmitter. But in real transmission environment, the perfect CSI can not be obtained at transmitter because of fast change of fading channel, transmission delay and channel estimation error. The channel statistical information can be taken as stationary in a long time. The channel statistical information need to be fed back to the transmitter only when it is changed. It has been proved that the channel statistical information is beneficial to capacity. The optimal design of transmitter with channel statistical information is analyzed in this paper. The main contribution of this paper is listed as follows.Shannon capacity, outage probability and system error probability are taken as performance criterion separately to study the optimal transmitter design when the channel statistical information is fed back to transmitter. When Shannon capacity is taken as the performance criterion, the optimal transmitter design with channel mean information or channel covariance information is introduced firstly. Then the optimal design is studied in detail when both of these two statistical information can be obtained simultaneously. The optimal transmission direction is derived and the optimal power allocation algorithm is given. When outage probability is taken as the performance criterion, the optimal transmitter design of MIMO system with spatial correlation at both transmitter and receiver is discussed. Finally, an upper bound of SEP is derived and the optimal precoder design is analyzed when the system error probability is taken as the performance criterion.A new precoder structure which suits to non-orthogonal STBC with covariance feedback to the transmitter is presented. STBC is often designed for i.i.d. Rayleigh fading channels, assuming no CSI at transmitter. A linear precoder functions as a multi-mode beamformer matching the channel, based on the CSI at transmitter. The precoder and STBC combination, therefore, can exploit the available CSI and is robust to channel fading at the same time. Based on the OSTBC, a new precoder design method which suits to non-orthogonal STBC with covariance information at the transmitter is presented. The optimal eigen-vectors of this precoder are proved to be related to the transmit correlation matrix and STBC, and the optimal power allocation method is also given.The effect of channel estimation error on the system performance is analyzed. For SISO system, the effects of channel estimation error on the outage capacity in Nakagami-m and Rice fading channels are discussed. The upper and lower bounds on outage capacity are derived. For MIMO system, the channel capacity is taken as the performance and the effect of channel estimation error is analyzed. The optimal transmission strategy is studied when there is channel estimation error at receiver and different channel state information can be obtained at transmitter. The effect of channel estimation error on the channel capacity is analyzed by simulation and the system performance with different transmission strategies is compared.At the last part of this dissertation, the whole work of the dissertation is outlined and the future research issues are discussed.更多还原