A Coordinated Approach To Channel Estimation In Massive MIMO Systems

Over the past decade, multiple antenna techniques have been adopted in wirelesscellular systems. In today’s wireless systems, inter-cell interference has become a limitingfactor when trying to achieve higher performance in term of network capacity. To alleviatethe inter-cell interference, extensive research has been done. The multiuser MIMO,interference alignment, and cooperative network have been proved to be effective ways tomitigate the interference. Nevertheless, as there has been an explosive increase in demandfor wireless connectivity, driven by cellular telephony and ever increasing wireless dataapplications, it seems unlikely that these techniques would be able to carry theexponentially growing data traffic.An unprecedented spectral efficiency was achieved by a newly proposed "MassiveMIMO" scheme where the base station is equipped with a large excess of antennascompared with the number of single antenna terminals which the base station serves in aTime-Division Duplexing (TDD) manner. However, an impairment named "pilotcontamination" cased by the re-use of pilot sequences in different cells imposes restrictionon the potential capacity gain from a large number of base station antennas. Statistically,the magnitude of pilot contamination is only bound up with the path loss.In this paper, we propose a Bayes estimator and further more, a scheduling method forchannel estimation based on the long term statistical information of the users’ channels, i.e.,the channels’ covariance matrices. Useful information lies untapped in the covariancematrix, such as the angle of arrival and its variance. We can exploit this information toreduce the pilot contamination. Today, uplink channel estimation is done in each cellindependently. But now the idea of this paper is that we estimate the channel only of usersin multiple cells which we know are "compatible" from the point of view of theircovariance matrices information. We show that significant reduction of pilot contaminationand over100%performance gain in term of sum rate can be achieved by our schedulingmethod.