# Total Energy Efficiency of TD- and FD-MRC Receivers for Massive MIMO Uplink

## TL;DR

This paper compares the total energy efficiency of time-reversal MRC with single-carrier waveform and frequency-domain MRC with OFDM in massive MIMO uplink, revealing conditions where each scheme is preferable.

## Contribution

It provides a systematic comparison of energy efficiency between TRMRC and FDMRC in massive MIMO uplink, considering current and potential future computational efficiencies.

## Key findings

- FDMRC/OFDM generally achieves higher energy efficiency with current parameters.
- TRMRC becomes more attractive for small cell radii (<300m) with improved computational efficiency.
- The choice between TRMRC and FDMRC depends on cell size and processing power improvements.

## Abstract

This paper proposes a detailed investigation on the uplink (UL) performance of massive multiple-input-multiple-output (maMIMO) systems employing maximum-ratio combining at the receiver. While most papers in maMIMO literature assume orthogonal frequency-division multiplexing (OFDM), current standards like LTE employ single-carrier (SC) waveform in the UL due to several benefits. We thus perform a systemic comparison between two fundamental schemes: the time-reversal MRC (TRMRC) operating under SC, and the frequency-domain MRC (FDMRC) employed with OFDM. It was recently shown that TRMRC outperforms FDMRC in terms of achievable rates, since SC systems do not require the cyclic prefix (CP) of OFDM. On the other hand, the computational complexity of TRMRC algorithm is higher than that of FDMRC, even when efficient solutions are employed (e.g., fast convolution with the overlap-and-add method). Hence, the best scheme for the UL maMIMO systems still remains an open question. The main contribution of this paper is the comparison of the total energy efficiency of both TRMRC and FDMRC when used in the UL of maMIMO systems. Our results show that, for current typical system parameters, FDMRC/OFDM achieves a higher total energy efficiency than TRMRC/SC. However, if the cell radius is below 300m and/or the computational efficiency increases by 30% regarding the current processors, the TRMRC under SC waveform becomes more attractive for the UL of maMIMO systems.