Linear MIMO Techniques in Multiuser Wireless Communications

最近对无线通信系统中MIMO系统的研究一直集中在Costa的Dirty Paper编码上，它是一种优雅的方法，至少在主要上实现了矢量BC和MIMO BC信道的两个重要性能指标的理论界限，即总和容量和加权总和速率。虽然DPC技术在理论上非常吸引人，但它存在两个缺点：非常复杂的实现，如果考虑次优的THP解决方案，则性能损失，以及在许多相关场景中甚至可能禁止实际实现，以及在相应通信链路的发射机侧需要非常精确的信道状态信息。特别是，后者在例如具有高移动性应用的网络中的替换通信场景中被证明是严重缺陷，或者可替换地对于干扰信道场景，其中多个空间分布的MIMO系统在网络会话期间或在蜂窝网络的边界彼此干扰。为此，不依赖于DPC的线性MIMO技术是非常有吸引力的候选技术，可以在无线通信网络中利用空间信号处理来挖掘潜在的性能增强，而不需要与DPC和THP相关的挑战性要求。然而，足够有趣的是，尽管线性MIMO技术似乎是基本波束形成技术的自然扩展，甚至开始于空时处理的成功发展，但基本的优化通常被证明是相当复杂的，甚至比理论上要求更高的DPC更复杂，并且线性MIMO的一些问题到目前为止仍然没有解决。考虑到线性MIMO信号处理的本质挑战，现有的工作主要集中在基于底层多用户MIMO信道的(块)对角化的次最优方案，或者通过施加单独解码的数据流的约束而不开发在各自的数据接收器处的多个协作接收器的潜力。在这个提议的项目中，不会强加这样的限制，因为其目标是利用最近发现的具有线性预编码的MIMO BC和具有线性用户分离的MIMO MAC之间的对偶结果。这一新的对偶结果将作为在多用户通信场景中系统地处理线性MIMO系统和设计相应算法的基本框架。

The recent research on MIMO systems in wireless communication systems has been concentrating on Costa’s Dirty Paper Coding, which is an elegant approach for – at least principally – achieving the theoretically bounds of two important performance measures for the vector BC and MIMO BC channel, namely the sum capacity and the weighted sum rate. Although theoretically very appealing, the DPC technique suffers from a couple of drawbacks; that are the very complex implementation, the performance loss if considering the suboptimal THP solution, and, which in many relevent scenarios might even be prohibitive for practical implementation, the requirement of very precise channel state information at the transmitter side of the respective communication links. Especially, the latter turns out to be a severe drawback in alternative communication scenarios, e.g. as in networks with high mobility applications, or alternatively for the interference channel scenario, where multiple spatially distributed MIMO systems interfere with each other during a network session or at the border of a cellular network. To this end, linear MIMO techniques which do not resort to DPC are very attractive candidates for the exploitation of the potential performance enhancements by spatial signal processing in wireless communication networks without the challenging requirements related with DPC and THP. However, interestingly enough, although linear MIMO techniques appear to be the natural extension of the fundamental beamforming techniques, which the successful evolution of space time processing even started with, the underlying optimizations generally turn out to be rather complicated, even more complicated than for the theoretically more demanding DPC, and a couple of problems with linear MIMO have remained unsolved until now. Taking into account the intrinsical challenges of linear MIMO signal processing the existing previous work mainly concentrates on suboptimal schemes based on the (block) diagonalization of the underlying multiuser MIMO channels or by imposing the constraint of separately decoded data streams without exploiting the potential of multiple cooperating receivers at the respective data sinks. In this proposed project, such restrictions will not be imposed, since the goal is rather to exploit the recently discovered duality results between the MIMO BC with Linear Precoding and the MIMO MAC with linear user separation. This new duality results will serve as the fundamental framework for a methodical treatment of linear MIMO systems in multiuser communication scenario and the design of respective algorithms.