Multi-cell MMSE data detection for massive MIMO: new simplified bounds

In this study, the authors analyse and provide new insights into the problem of multi-cell minimum mean square error (MMSE) detector in massive multiple-input multiple-output (MIMO) systems. Their system combines pilot hopping and pilot reuse strategy in the multi-cell scenario.They obtain a deterministic expression of rate bounds of the uplink system when MMSE is used for channel estimation and data detection. Their result is different from the existing MMSE bounds in massive MIMO literature in that they obtain an achievable rate that is simply a scaled version of that of the matched filter (MF) detection, i.e. the achievable rate of the MF detection can be scaled with a constant, which is a function of the number of antennas and users as well as the power allocation to directly obtain the achievable rate of the MMSE detection. This new finding saves a significant amount of work needed when analysing MMSE detection in massive MIMO since it reduces the problem to obtaining simpler results (using MF analysis) and then extending the result to the MMSE case in a straightforward manner. Simulation results show how tight the achievable rate bound to the actual one at a large number of BS antennas.