Robust cooperative spatial processing and power control for interference mitigation in cellular networks

原则上，不同通信链路之间的干扰可以通过各自的介质接入方案在时间和频率上进行正交传输来消除。然而，最先进的干扰缓解技术能够通过结合线性空间处理和功率控制来优化链路集合，从而提供更高的频谱效率。在这方面，最突出的方法是优化单个用户传输的信号干扰和噪声比（SINRs），均方误差（MSEs），相对于发射功率的限制，反之亦然。这两个指标可以相互关联，同时它们都与可实现的数据速率有关，这是网络运营商特别感兴趣的。由于在这些设置中增加了空间自由度，因此这些技术非常适合与利用合作基站的新型蜂窝技术结合使用。但是，上述干扰缓解技术需要了解底层无线电信道。虽然它们的性能在完全了解信道的假设下得到了很好的研究，但在实际设置中几乎无法获得完整的信道状态信息（CSI）。除了诸如频分双工（FDD）系统中的有限速率反馈等经典的CSI损伤源之外，协作方案还引入了新的恶化源，例如速率和延迟的回程限制。此外，每组天线的多个发射功率约束的集成导致了特别具有挑战性的优化问题。在本文件中，我们首先介绍了自上次项目报告以来我们取得的最新成果。我们解释了我们的新型鲁棒合作干扰缓解技术，其中信道信息仅是不完全可用的。针对分布式协同传输的最新项目阶段，提出了w.r.t. CSI精度和干扰抑制的解决方案。此外，我们提出了一个新的项目阶段，该阶段涵盖了在不完善的CSI条件下存在的进一步方面。我们认为，这一额外阶段的调查完成了该项目，从而解决了在不完善的CSI条件下合作减少干扰的主要挑战。

Interference between different communication links can in principle be combated by orthogonalizing transmissions in time and frequency through respective medium access schemes. However, state of the art interference mitigation techniques are able to provide much higher spectral efficiencies by optimizing a collection of links jointly through combined linear spatial processing and power control. In this regard, the most prominent approaches optimize signal-to-interference-and-noise-ratios (SINRs), mean-square-errors (MSEs) of individual user transmissions with respect to limits on the transmit powers or vice versa. Both metrics can be linked among each other, while they are both connected to the achievable data rate, which is of particular interest for network operators. These techniques lend themselves very well for use in conjunction with novel cellular technologies utilizing cooperative base stations due to the increased number of spatial degrees of freedom in these setups.However, the interference mitigation techniques mentioned above require knowledge of the underlying radio channel. While their performance has been well investigated under the assumption of perfect knowledge of the channel, complete channel state information (CSI) is barely available in practical setups. Besides the classical sources of impairments of CSI such as, e.g., limited rate feedback in frequency division duplex (FDD) systems, cooperative schemes introduce new sources of deterioration, such as backhaul restrictions in rate and latency. Additionally, the integration of multiple transmit power constraints per group of antennas lead to particularly challenging optimization problems.In this document, we first give an update on our latest achievements since our last project report. We account for our novel robust cooperative interference mitigation techniques where channel information is only imperfectly available. According to the latest project phase which addresses distributed cooperative transmission we present solutions w.r.t. CSI accuracy and interference mitigation . In addition we propose a new project phase which covers further aspects present in the context of imperfect CSI conditions. We belief that the investigations in this additional phase complete the project, such that the main challenges of cooperative interference mitigation under imperfect CSI conditions have been addressed.