How Much Bandpass Filtering is Required in Massive MIMO Base Stations?

In this paper, we study the impact of aliased out-of-band (OOB) interference signals on the information sum rate of the maximum ratio combining receiver in massive multiple-input multiple-output (MIMO) uplink, with both perfect and imperfect channel estimates, in order to determine the required out-of-band attenuation in radio-frequency (RF) bandpass filters (BPFs). With imperfect channel estimates, our study reveals that as the number of base-station (BS) antennas ( M) increases, the required attenuation at the BPFs increases as O(√M) with M → ∞, provided the desired information sum rate (both in the presence and in the absence of aliased OOB interferers) remains fixed. This implies a practical limit on the number of BS antennas due to the increase in BPF design complexity and power consumption with increasing M.