【作者】 缪庆育；

【导师】 王文博；

【作者基本信息】 北京邮电大学 ， 信号与信息处理， 2010， 博士

【摘要】 蜂窝网络可以用来覆盖不同的地理区域。一方面,它们可以覆盖有室内用户的高密度楼宇市区,另一方面蜂窝网络又对偏远农村地区的大地理区域提供接入。在这两种情况下覆盖整个服务区都是具有挑战性的。要么离基站的连接距离比较大,要么大部分对基站有阴影,使无线电传播具有挑战性。为了应付不同的电波传播条件,多处文献提出多跳通信。通过中间节点,如中继器,无线电链路分为两跳或多跳,这些比直传连接有更好的传播条件,增强了链路质量,从而增加吞吐量和提高了覆盖范围。本论文首先研究了MIMO中继系统的天线在集中情况和分布情况下的容量增益。在多天线的情况下所有的天线位于同一中继器形成集中式模式,在分布情况下,多天线分布在不同的中继器,形成合作中继器。本文考察了在不同中继器位置情况下,不同天线总数下,以及有无天线相关性下的MIMO中继容量增益,既考虑了编解码转发中继器又考虑了放大转发中继器。当中继离基站较近时,容量主要局限于第二跳,分布式和集中式天线之间没有太大的差异。当中继离终端较近时,容量主要局限于第一跳,第一跳的能力与每个中继器天线的数量相关,这时集中模式性能较好。本文进一步在集中式和分布式下研究了MIMO放大转发中继器的滤波器矩阵。根据第一跳和第二跳的信道状态信息,分别考虑了盲放大转发中继器,匹配滤波放大转发中继器和SVD放大转发中继器。其后提出并讨论了一种基于第一跳信道状态信息和等效的基站到终端信噪比的MIMO放大转发中继器。提出的滤波器矩阵是一个对角线矩阵和第一跳信道矩阵的左奇异的共轭转置矩阵的乘积。这里对角矩阵是通过最大化的遍历信道容量得到的。这样在现有的系统中引入这样的放大转发中继器不需要改变现有系统的基站和终端,保证了中继器对现有的系统是透明的。仿真结果表明,该方法优于没有信道状态信息的方法,尤其是当放大转发中继器天线数量比基站天线数量大的情况。对于多中继器的情况,本论文研究了多中继器中的中继器选择的算法,分别考虑多中继器服务单用户的情况和多中继器服务多用户的情况。提出了基于平均容量(遍历容量)或者中断容量的中继器选择算法。利用泰勒公式分解提出了基于信道的平均状态信息或二阶统计得到平均容量(遍历容量)或者中断容量。对于中继器系统,在中继器中通常只有第二跳的平均信道状态信息,本文考虑基于第二跳信道的平均状态信息或二阶统计为基础的中继器选择。结果显示这种基于信道的二阶统计是一种简单而且准确的方法。最后本文比较两跳编解码中继器和放大转发中继器在蜂窝系统的性能。在蜂窝系统中有多小区干扰,情况相对于单链路复杂,这导致单链路的结论在蜂窝中可能很不一样,本文着重考虑了这两种中继器在蜂窝中的特性。对于编解码中继器主要是L2/L3的中继器,由于编解码中继器不可能同时接收和发送,在蜂窝系统中编解码中继器的容量增益来自于频率复用或空间分集。在蜂窝系统中,同频放大转发中继器可以同时发送和接收,但同频放大转发中继器可以带来更多的干扰,放大信号的同时放大了其它小区的干扰和噪声。结论表明对半径小的小区,放大转发中继器比编解码中继器系统能带来更多的增益。对于半径大的小区,编解码中继器比放大转发中继器能带来更多的增益。本文同时给出了蜂窝系统中部署中继的建议。更多还原

【Abstract】 Cellular network is used to cover different geographical regions. On one hand, they should cover high-density buildings in urban areas with indoor users, on the other hand cellular network should provide wireless access for the rural in a large geographic area. In both cases, to cover the whole service area is challenging. Due to either the shadow or too long of the radio connection from base station, the radio propagation faces more challenge. In order to cope with different radio propagation conditions, multi-hop communications was proposed. Through intermediate nodes, such as relay/repeaters, radio links are divided into two or more hops, which is better than the direct connection, which increases the link quality improves the throughput and cell coverage.In this thesis, the MIMO relay system is first studied with co-located case and distributed case in the context of the relay gain. In the co-located case, all the antennas are located in the same relay mode, while in the distributed case, the antennas can be located in different relay nodes, which can have co-operation. The performance with different relay positions, the performance with different number of relay antennas, and the performance of the antenna with different correlation is investigated. Both decode-and-forward relay and amplified-and-forward relay are considered. When the relay nears the base station, the capacity is limited by the second hop, and there is no large relay gain difference between the co-located case and distributed case. When the relay nears the mobile station, the capacity is limited by the first hop, while the capacity of first hop is related to the number antennas in each relay. In this case, the co-located case has better performance. In most of the case, the relay gain for the co-located case is larger than the gain in the distributed case.The filter matrix design for MIMO AF relay is further investigated in the co-located case and the distributed case. According to channel state information of the first and second hop, the blind relay, the match filter relay and the SVD relay are considered. Further a spatial filter for MIMO repeater is designed based on first-hop CSI and end-to-end SNR. The proposed filter is a product of a diagonal matrix and the conjugate transpose of the left singular matrix of the first-hop channel matrix. The diagonal matrix is obtained by maximizing an upper bound of the ergodic channel capacity. Simulation results indicate that the proposed scheme outperforms the scheme without CSI, especially when the number of repeater antennas is greater than that of the base station antennas. The introduction of such a repeater may not need modifications on the base station nor the mobile station. Hence the transparency property of a repeater can be preserved.For multi-relay case, the thesis investigates the relay selection performance. The relay selection algorithm based on the average capacity (ergodic capacity) or the outage capacity is proposed. The average capacity (ergodic capacity) or outage capacity can be obtained based on the average channel information with Taylor series. For the relay system, the relay can easily obtain the instantaneous channel state information in the first hop and the average channel state information on the second-hop. Here relay selection based on the average channel state information (or the second-order statistics of the channel) in the second hop is investigated. The case for the multi-relay with one user and the case with multi-relay and more users are considered. The simulation results shows that relay selection based on the average channel state information (or the second-order statistics) of the second hop is a simple and accurate method.Finally, the performance of the two-hop decode-and-forward (DF) relay and radio frequency (RF) repeater in the cellular system are compared. In the cellular system, there is inter-cell interference, which is more complicated than the single link, leading that the conclusions of a single link may not be applicable to the cellular system. This thesis focuses on the performance of relay and repeaters in the cellular system. Here the decode-and-forward relay is mainly L2/L3 relay. The current relay can not receive and transmit at the same time with the same resource, and the relay capacity gain mainly comes from frequency multiplexing or spatial diversity. In the cellular system, the RF repeaters can receive and transmit at the same time with the same resource, but it brings more interference since the RF repeater amplifies the inter-cell interference and noise when it amplifies the signal. For the cells with small radius, the RF repeater can bring more gain than the DF relay. For the cells with large radius, the DF relay can bring more gain than the RF repeater. The deployment of the multiple relay/repeater in the cellular system is also proposed.更多还原