How Much Bandpass Filtering is Required in Massive MIMO Basestations?

TL;DR

This paper investigates how much out-of-band attenuation is necessary in RF bandpass filters for massive MIMO base stations to mitigate aliased interference, revealing that required attenuation grows with the square root of the number of antennas, impacting system design.

Contribution

It provides a quantitative analysis of the relationship between antenna count and BPF attenuation needs in massive MIMO systems, highlighting practical limitations.

Findings

Required BPF attenuation scales as √M with increasing antennas.

There is a practical limit on the number of antennas due to BPF complexity.

Sum-rate remains fixed despite increasing BPF attenuation requirements.

Abstract

In this paper, we study the impact of aliased out-of-band 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 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 $\mathcal{O}(\sqrt{M})$ with $M \to \infty$, provided the desired information sum-rate (both in the presence and in the absence of AOOBIs (aliased out-of-band 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 $M$.