A subspace method for channel estimation has been recently proposed [1] fortackling the pilot contamination effect, which is regarded by some researchersas a bottleneck in massive MIMO systems. It was shown in [1] that if the powerratio between the desired signal and interference is kept above a certainvalue, the received signal spectrum splits into signal and interferenceeigenvalues, namely, the "pilot contamination" effect can be completelyeliminated. However, [1] assumes an independently distributed (i.d.) channel,which is actually not much the case in practice. Considering this, a moresensible finite-dimensional physical channel model (i.e., a finite scatteringenvironment, where signals impinge on the base station (BS) from a finitenumber of angles of arrival (AoA)) is employed in this paper. Via asymptoticspectral analysis, it is demonstrated that, compared with the i.d. channel, thephysical channel imposes a penalty in the form of an increased power ratiobetween the useful signal and the interference. Furthermore, we demonstrate aninteresting "antenna saturation" effect, i.e., when the number of the BSantennas approaches infinity, the performance under the physical channel with PAoAs is limited by and nearly the same as the performance under the i.d.channel with P receive antennas.
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