A Framework for Optimizing the Downlink Performance of Distributed Antenna Systems under a Constrained Backhaul

Recent work has shown that multi-cell co-operations in cellular networks, enabling distributed antenna systems and joint transmission or joint detection across cell boundaries, can significantly increase system capacity and user fairness. Most publications in this field assume that an infinite amount of information can be exchanged between the co-operating base stations, neglecting the main downside of such systems, namely the need for an additional network backhaul. In a recent publication [1], we have proposed an optimization framework and algorithm that applies joint detection to a subset of users for scenarios of constrained backhaul. In this paper, we will now observe joint transmission in the downlink, which can be described in a similar way, but allows for an additional degree of freedom in the way the backhaul infrastructure is used. Different schemes are compared, yielding that linear multi-user beamforming to selected users can significantly improve the downlink performance of cellular systems under a strongly limited backhaul.