【作者】 李国才；

【导师】 龚耀寰；

【作者基本信息】 电子科技大学 ， 信号与信息处理， 2009， 博士

【摘要】 移动通信业务的高速发展，以及移动网络和互联网的加速融合，使得对下一代宽带移动通信系统的需求日益迫切。宽带多输入多输出(MultipleInput Multiple Output，MIMO)技术能够充分开发空间资源，在不增加频谱资源和天线发送功率的情况下，成倍地提高信道容量。因此，宽带MIMO已经被确定为下一代移动通信系统的关键技术。众多研究机构和学者已经投入到宽带MIMO系统相关技术研究中，并已经取得了相当的成果，如宽带MIMO无线传播信道建模、信道测量、宽带MIMO系统容量和系统性能分析、载波同步、信道编码、空-时均衡和空-时检测等。然而，宽带MIMO通信系统中还面临大量实现问题亟待研究解决。为了进一步加快开发高频谱利用率、高可靠性、易实现的宽带MIMO通信系统以满足新一代移动通信需求，本文在及时跟踪宽带MIMO技术研究领域国内外发展动向的基础上，针对宽带MIMO系统的下列四个关键技术进行了深入的研究，并取得了一些新的研究成果。首先，本文研究了多输入多输出-正交频分多工(Multiple Input MultipleOutput-Orthogonal Frequency Division Multiplexing，MIMO-OFDM)系统的容量和发射分集MIMO-OFDM系统方案。在MIMO-OFDM系统信道模型的基础上，分析了MIMO-OFDM空频编码(Space-Frequency Coding，SFC)和复用方案下系统容量和性能。重点讨论了一种适合下一代无线通信系统的级联空频编码系统方案，该方案可以实现从普通MIMO空时编码到宽带MIMO-OFDM空频编码的直接映射扩展。仿真实验结果表明MIMO-OFDM是宽带MIMO的低复杂度、高效率实现。其次，为了提高MIMO-OFDM通信系统的传输性能。本文提出了一种空频分组码的自适应调制方案，并优化了基于天线选择发射分集的自适应功率分配策略。本文首先研究了自适应调制(Adaptive Modulation，AM)MIMO-OFDM系统结构、自适应调制算法在MIMO-OFDM系统中的应用。研究了自适应M阶正交幅度调制(M-ary Quadrature Amplitude Modulation，M-QAM)方案，给出了基于最大频谱效率的最优功率和调制分配的封闭解。在此基础上研究了普通MIMO系统和MIMO-OFDM系统特征波束形成结构的自适应传输方案，并且分别在功率和最大化速率条件下给出比特、功率分配算法。仿真表明自适应调制提高了系统的频谱利用率，优化了系统的性能。然后结合自适应调制技术和发射分集技术，针对MIMO-OFDM系统研究了基于空频分组编码发射分集和基于空间复用的自适应调制系统方案，依靠自适应比特和功率分配算法，达到在平均传输速率约束条件下最小化传输功率。研究表明，自适应调制MIMO-OFDM传输系统可以显著提高传统MIMO-OFDM系统的误比特率性能。与多载波实现方案不同，近年来，单载波宽带均衡技术也因其所固有的优点引起了研究者的注意。本文针对宽带MIMO系统均衡技术，分时域均衡(Time Domain Equalization，TDE)和频域均衡(Frequency DomainEqualization，FDE)两个部分分别进行了研究。对于宽带MIMO时域均衡，本文提出了一种最小均方误差(MinimumMean Square Error，MMSE)类盲均衡算法的凸组合策略。本文首先通过对宽带MIMO系统克服符号间干扰(Inter Symbol Interference,ISI)的自适应时域均衡技术的研究，给出了宽带MIMO系统的均衡方案。本文主要研究了单载波MIMO系统中时域线性均衡器(Time Domain-Linear Equalization，TD-LE)及判决反馈均衡器(Time Domain-Decision Feedback Equalization，TD-DFE)算法及对应的系统结构，并对其进行仿真验证和性能分析。针对恒模均衡(Constant Modulus，CM)算法收敛速度慢，收敛性能好，剩余误差大，而判决引导(Decision Directed，DD)算法的收敛速度快，稳态性能好，启动易发散的特点，我们提出了一种MMSE类盲均衡算法的凸组合策略和其锚定训练过程。同常规算法分析比较表明该方案具有收敛速度快稳态性能好的特点。最后，本文在宽带MIMO系统中对上述自适应均衡算法进行了仿真和比较。研究结果表明，应用自适应时域均衡能利用信道频率分集，降低误码率，提高宽带MIMO系统性能。对于宽带MIMO频域均衡，本文研究了宽带MIMO频域均衡及相关干扰抑制问题，研究了一种基于干扰双向预测的抑制窄带干扰的算法。本文首先研究了单载波频域均衡(SC-FDE)的基本原理、信号块结构。然后分析了单载波频分多址系统(SC-FDMA)原理和结构。接下来分析对比了正交频分多工(OFDM)系统和单载波频域均衡(SC-FDE)系统各自的特点和系统性能。然后针对宽带MIMO系统，研究了MIMO SC-FDE系统结构，特别研究了MIMO系统SC-FDE线性均衡(LE)算法。最后研究了一种基于干扰双向预测的抑制窄带干扰的算法。该算法基于宽带MIMO SC-FDE系统数据块结构，在频域均衡器的输出端，根据窄带干扰波形的相关特性，设计了干扰预测器。该预测器在两个方向上对中间传输数据块中的窄带干扰进行预测，预测的结果用于消除数据叠加的干扰波形，从而达到抑制窄带干扰的目的。研究结果表明，自适应频域均衡技术能够以较低的算法复杂度实现宽带MIMO均衡，是上行链路的较好解决方案。更多还原

【Abstract】 Rapid development of mobile data communication and the merging of mobile network and Internet have put dramatically growing demands for future broadband wireless communication systems. The broadband Multiple Input Multiple Output(MIMO) systems exploit the spacial resource to improve the channel capacity effectively without additional frequency spectrum and transmission power. Therefore, the broadband MIMO system has been regarded as a potential candidate for future mobile communication system.Many research institutions and researchers have paid much attention to the broadband MIMO techniques, including the measurement and the modeling of the broadband MIMO wireless channel, system capacity, system performance, carrier synchronization, channel coding, space-time equalization and space-time detection, etc.. However, there are lots of technical problems that have to be studied.To expedite the process of developing feasible broadband MIMO communication systems with large capacity and high reliability, the four key technologies on broadband MIMO system have been studied in this dessertation. These research work are based on the latest research results on broadband MIMO system in all over the world.Firstly, we ananlyzed the characteristics and modeling of wideband MIMO channels. We also ananlyzed the channel capacity and the transceiver structure of the Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing(MIMO-OFDM) systems. Then, we proposed a cascade structure to map from Space-Time (ST) codes in narrowband MIMO system to the the Space-Frequency (SF) codes in MIMO-OFDM system. And we investigated the system performance by system simulations. The research results show that the system complexity is reduced and the system performance is improved.Secondly, to improve the system performance in multipath channel, we investigated the Adaptive Modulation (AM) and its applications on the MIMO-OFDM systems. First, we studied the adaptive modulation algorithms for the M-ary quadrature amplitude modulation (M-QAM), and the closed-form solution is derived then. And based on these adaptive modulation algorithms, we investigated the adaptive modulation system structure based on singular value decomposition (SVD) for the narrow band MIMO system and MIMO-OFDM system. Then, we studied the adaptive modulation transceiver structures for MIMO-OFDM system, based on spacial multiplexing(SM) technology and space-time-frequency diversity technology. And we studied the system performance by simulations. The results show that the adaptive modultion MIMO-OFDM system achieves significant performance improvement compared to the conventional systems.Another broadband MIMO realization technique is the Single-Carrier (SC) broadband equalization. The broadband equalization has attracted much attention due to its low complexity and mature theory. Finally, for the equalization algorithms of the broadband MIMO system, we investigated the equalization algorithms in time domain (TDE) and frequency domain (FDE), respectively.For the Single-Carrier Time Domain Equalization(SC-TDE) system, based on the research on the adaptive equalization algorithms to overcome the Inter Symbol Interference(ISI), a convex combination strategy for the blind Minimum Mean Square Error(MMSE) equalization to combine the constant modulus(CM) algorithm with decision directed(DD) algorithm was proposed in this dissertation. We investigated the equalization algorithms of the broadband MIMO system, including Time Domain-Linear Equalization(TD-LE) and Time Domain-Decision Feedback Equalization (TD-DFE). We investigaed the system structure and the system performance of these equlizers. To combine the advantages of convergency property of CM algorithm with the high convergency speed of DD algorithm, a convex combination strategy with its anchoring process was proposed. Comparing with some other methods, our proposed algorithm has the fastest convergence speed and best steady-state performance. Then, adaptive equalization algorithms applied in MIMO system are simulated in fading channels. The study shows that adaptive equalization reduces the ISI and Bit Error Ratio(BER) effectively and improves the performance of broadband MIMO system.For the Single Carrier-Frequency Domain Equalization system (SC-FDE), based on the study on the MIMO SC-FDE and the interference suppression, we proposed a new narrow band interference (NBI) suppression algorithm which is based on the bi-directional interference prediction. We studied the principle of the SC-FDE system, the design of the signal block structure. Then we studied the principle and the system structure of the Single Carrier-Frequency Division Multiple Access (SC-FDMA) system, and studied the performance and the property of peak to average power ratio (PAPR) compared with OFDM system. Then we also invesitigated the structures and the algrithms of the Frequency Domain-Linear Equalization (FD-LE). Then, based on the studied on the NBI in SC-FDE, we proposed an impoved NBI suppression algorithm which is based on the bi-directional interference prediction. This algorithm ultilized the unique word (UW) in the SC-FDE transmit block and the correlation property of NBI to predict the NBI vector on the data vector. Then this information was used to remove NBI part from data vector before symbol detection. Simulations show that the proposed system achieves significant performance improvement.更多还原