【作者】 张宁波；

【导师】 刘泽民；

【作者基本信息】 北京邮电大学 ， 电路与系统， 2010， 博士

【摘要】 下一代移动通信系统要求大容量和高质量的数据传输。多输入多输出(MIMO)技术被认为是可实现未来高速数据传输的关键技术之一,在第三代(3G)及第四代(4G)的移动通信系统中有着广阔的应用前景。传统的集中式MIMO系统的多根发射天线均集中于基站(BS)端,与集中式MIMO不同,分布式MIMO系统的多根发射天线分布于不同的地理位置,其各对收发链路之间更加独立,具有大容量、低功耗、更好的覆盖、对人体的低电磁损害等优势,被认为是未来无线通信系统的备选方案之一。本论文正是针对分布式MIMO系统发送端的各项关键技术展开研究的。研究内容涉及分布式MIMO系统的信道特征、多小区分布式MIMO系统的信道容量分析、天线选择技术、功率分配技术及多用户预编码技术等多方面的内容。论文的主要研究内容及研究成果如下：针对分布式MIMO系统的信道特征,研究了天线端口配置多天线时天线之间的空间相关性,给出了Kronecker相关信道模型的建模方法。分析了分布式天线端口之间的相关性,得到了天线端口之间的相关性与用户到基站之间的距离成反比的结论。分析了多小区分布式MIMO系统的信道容量。首先考虑天线端口只有一根天线的的情况,推导了多小区各态历经信道容量的表达式,并与多小区蜂窝网系统的信道容量进行了比较,仿真表明,分布式系统在大部分区域内能获得比蜂窝网系统更多的信道容量。而且,选择较少的发送天线会减小邻小区间干扰,进一步提高信道容量。然后将这些结果扩展到天线端口配置多根天线的情况,得到了信道容量表达式。在天线选择方面,本论文首先推导了信道容量上限的闭式表达式,然后以信道容量为标准,提出了一种基于部分信道信息(CSI)的自适应天线选择方法。该方法利用天线端口的大尺度衰落信息进行天线选择,当用户位置发生变化时,基站能够根据用户位置的变化自适应地选择调整发送天线子集,获得最大的信道容量。通过仿真,发现所提出的方法能够比传统的覆盖式传输方法和选择性传输方法获得更大的信道容量。针对功率分配技术,本文提出了一种基于部分CSI的低反馈量的功率分配方法。该方法基于天线端口的大尺度衰落信息及发送相关矩阵的秩信息进行功率分配。由于所需反馈的大尺度衰落信息和发送相关矩阵的秩信息在低速环境下变化缓慢,因此该方法可以设置较长的反馈周期来减小系统的反馈开销。仿真结果证明,该方法与传统的等功率分配方法相比能够大幅度提高系统的容量性能,与需要实时反馈完整CSI的注水功率分配方法相比容量损失不大。在多用户分布式MIMO系统中,研究了一种时变信道下基于信道预测的预编码方案。针对高速移动环境下会信道预测会带来严重的预测误差问题的问题,本文提出了一种基于预测误差补偿的信号泄漏噪声比(SLNR)预编码算法。所提出的预编码方案利用信道预测的归一化均方误差(NMSE)对预编码矩阵进行修正,补偿了信道不匹配带来的性能损失,进一步抑制了用户间的干扰,提高了系统性能。仿真结果表明,在高速移动环境下,该算法能够带来更好的误码率性能和吞吐率性能。更多还原

【Abstract】 The next generation mobile communication systems require large-capacity and high-quality data transmission.It is believed that MIMO technology will be one of the key technologies and has wide application prospect in the third generation (3G) and the fourth generation (4G) mobile communication systems.In traditional centralized MIMO systems,the multiple transmitted antennas are all co-located in the base station (BS).Distributed MIMO systems are different from centralized MIMO systems,in which the multiple transmitted antennas always locate in different areas, the channels between transmitted antennas and received antennas are more independent. Compared with centralized MIMO, it has the advantages of large system capacity, low transmit power, enhanced coverage and low radiation on the human body. Distributed MIMO systems have been promised as one of the candidate systems in the future wireless communication systems.In this dissertation, key techniques in the transmit side related to the distributed MIMO systems are investigated.Detailed research works include:the channel characteristic in distributed MIMO systems,the channel capacity analysis in multi-cell environment, antenna selection technology, power allocation technology, multi-user precoding technology and so on.The detailed research contents and the main contributions of this dissertation are listed as follows:For the channel characteristic in distributed MIMO systems,the correlations between multiple co-located antennas in the same distributed port are analyzed, and the Kronecker correlation channel model is given. This dissertation also investigates the correlations among different distributed ports and draws the conclusion that the correlations are monotonic decreased with the distance between base station (BS) and user equipment.For the channel capacity of distributed MIMO systems, this dissertation first considers that distributed ports only equip one antenna, and the ergodic capacity expression of multi-cell environment is derived. Furthermore, the channel capacities of distributed systems and cellular network systems are simulated.Simulation results show that compared with cellular network systems, distributed systems can improve channel capacity in most areas.It is also shown that selecting fewer antennas for transmission can decrease the interference among neighbor cells and further enhance the channel capacity. Second, when distributed ports equip multiple antennas, the ergodic capacity is also derived and simulated.For the antenna selection, the upper bound expression of channel capacity is derived in this dissertation.Then, with the capacity criterion, an adaptive antenna selection scheme based on partial channel state information (CSI) is proposed.This scheme uses the large scale fading information to select the transmitted distributed port.When the user’s location varies, BS can adaptively adjust the transmitted antenna subset to obtain the maximum channel capacity according to users’position. Simulation results illustrate that compared with tradition blanket transmission scheme and selection diversity scheme, the proposed scheme can achieve more ergodic capacity.For the power allocation technology, a low feedback power allocation scheme based on partial CSI is proposed.The proposed scheme uses the large scale fading information and the rank of transmit correlation matrix to allocate the transmit power. Since the large scale fading information and the transmit correlation matrix vary slowly, the feedback period can be set long. Therefore, the feedback overhead can be reduced.Simulation results verify that the proposed scheme can greatly improve ergodic capacity compared with the average power allocation scheme, and the capacity loss compared with the optimal water-filling scheme is less.For the multiple distributed MIMO systems, a precoding technology based on channel prediction is investigated in time-varying channels. However, in the higher speed mobile environment, channel prediction will result in serious prediction errors. To solve this problem, an improved signal-to-leakage-and-noise rate(SLNR) precoding scheme based on prediction error compensation is proposed. The proposed scheme uses the normalized mean square error (NMSE) of channel prediction to modify the precoding matrix.This compensation reduces the system performance loss due to the unmatched channels.With this scheme, the interferences among multiple users are suppressed efficiently and the system capacity is further enhanced.Simulation results show that the proposed scheme can obtain better bit error rate (BER) and throughput performance in the higher speed mobile scenario.更多还原