The gNB applies maximal ratio combining to separate the signal transmitted by each terminal from the interfering signals, using the channel estimate of a terminal to maximize the signal power of that terminal by coherently adding the signal components. This results in a signal amplification proportional to NRX, which is known as the array gain. Alternatively, ZF combining can be used, which suppresses inter-cell interference at the cost of reducing the array gain to NRX - Nuser + 1, or MMSE combining can be utilized that balances between amplifying signals and suppressing interference. Receive combining cre- ates one effective scalar channel per terminal where the intended signal is amplified, and/or the interference is suppressed. The performance of the received combining methods will be improved by adding more gNB antennas, since there are more channel observations to uti- lize. The remaining interference is typically treated as additive noise; thus, conventional single-user detection algorithms can be applied. Another benefit of the combining is that small-scale fading averages over the array, in the sense that its variance decreases with NRX. This is known as channel hardening and is a consequence of the law of large numbers. Since the uplink and downlink channels are ideally reciprocal in TDD systems, there is a strong connection between receive combining in the uplink and transmit precoding in the downlink. This is known as uplink-downlink duality. Linear precoding based on MRC, ZF, or MMSE principles can be applied to focus each signal on its target user and possibly to minimize interference toward other users [16,52]. It can be shown that the achievable spectral efficiency per cell of massive MIMO systems under ideal conditions and independent identically distributed Rayleigh fading can be expressed in the following form [16,52]: bps/Hz/Cell, where (1 - Nuser/T) is the loss due to pilot transmission, V is the downlink/uplink SNR, and ECSI is the quality of the estimated CSI, proportional to the mean-squar