Spatial multiplexing in heterogeneous networks with MMSE receiver

In this paper, we analyze the downlink of a multi-antenna heterogeneous cellular network with distance-dependent interference. In particular, we consider open-loop spatial multiplexing (SM) with minimum mean-square estimation (MMSE) receiver for suppressing self-interference as well as other cell interference. Coverage probability and rate distribution are obtained with biased user association rule and inter-cell interference. The results show that using full rate SM at the macro base stations (BSs) degrades the data rate for a large percentage of cell-edge users compared to a low rate SM transmission. Therefore, the cell edge data rate can be improved substantially by reducing the SM rate at the macro BSs while maintaining full SM rate at the pico BSs. The loss in mean spectrum efficiency (SE) caused by the SM rate reduction is shown to be acceptable for the cases of interest.