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

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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.