Efficient MAC protocol for JT CoMP in small cells

In this paper, we investigate an efficient MAC protocol for interference coordination in small cells embedded in a macro-cell mobile network. We perform joint transmission (JT)-coordinated multi-point (CoMP), where cells in the cluster include adjacent macro-cells as suggested by the small-cell terminal. Most gains compared to uncoordinated transmission come from selecting the right users in these macro-cells. For minimizing the feedback overhead, we propose successive channel state information (CSI) requests. Thereby we replace users in the set until all of them experience consistently enhanced performance when using JT-CoMP. Gains can be further increased by MIMO mode switching in each cell and frequency-selective scheduling. We tested our algorithms over coherently measured multi-cell channels in the LTE-Advanced testbed in Berlin where small cells were embedded at several places. Using these algorithms, performance becomes comparable to a popular bound assuming no more intra-cluster interference while feedback overhead and complexity are substantially reduced.