Throughput Analysis of Massive MIMO Uplink With Low-Resolution ADCs

Abstract

Abstract-We investigate the uplink throughput achievable by a multiple-user (MU) massive multiple-input multiple-output (MIMO) system in which the base station is equipped with a large number of low-resolution analog-to-digital converters (ADCs). Our focus is on the case where neither the transmitter nor the receiver have any a priori channel state information. This implies that the fading realizations have to be learned through pilot transmission followed by channel estimation at the receiver, based on coarsely quantized observations. We propose a novel channel estimator, based on Bussgang's decomposition, and a novel approximation to the rate achievable with finite-resolution ADCs, both for the case of finite-cardinality constellations and of Gaussian inputs, that is accurate for a broad range of system parameters. Through numerical results, we illustrate that, for the 1-bit quantized case, pilot-based channel estimation together with maximal-ratio combing or zero-forcing detection enables reliable multi-user communication with high-order constellations in spite of the severe nonlinearity introduced by the ADCs. Furthermore, we show that the rate achievable in the infinite-resolution (no quantization) case can be approached using ADCs with only a few bits of resolution. We finally investigate the robustness of low-ADC-resolution MU-MIMO uplink against receive power imbalances between the different users, caused for example by imperfect power control.Index Terms-Analog-to-digital converter (ADC), channel capacity, linear minimum mean square error (LMMSE) channel estimation, low-resolution quantization, multi-user massive multiple-input multiple-output (MIMO).

Achievable uplink rates for massive MIMO with coarse quantization

“…Several system simulations have been performed to analyze low-resolution adcs, e.g. [18,19], where the conclusions coincide with the conclusions in this paper: that three-bit adcs are sufficient to obtain a performance close to an unquantized system.…”

“…In [18], it is pointed out that low-resolution adcs create a near-far problem, where users with relatively weak received power drown in the interference from stronger users. This is illustrated with a zero-forcing combiner in Figure 4, where it can be seen how the performance of the weak users degrades if there is a stronger user in the system.…”

Analysis of Alternative Massive MIMO Designs : Superimposed Pilots and Mixed-ADCs

“…The number of quantization levels is given by the ADC bit resolution such that the distortion decreases whereas the power consumption and complexity increase with the ADC bit resolution. In [28][29][30][31] the selection of ADC bit resolution is studied to maximize performance in terms of BER, SE, and power consumption, showing that Massive MIMO can provide high SE with low-resolution ADCs. Here, low ADC bit resolution refers to values of up to 4-5 bits which is considerably lower than standard ADCs used in current BS deployments which have around 15 bits.…”

“…Here, low ADC bit resolution refers to values of up to 4-5 bits which is considerably lower than standard ADCs used in current BS deployments which have around 15 bits. The works [30,32] show that Massive MIMO can even operate with one-bit ADCs. However, it is not clear whether operating with such low hardware precision is preferable in terms of SE and EE.…”

Robust full-dimension MIMO transmission based on limited feedback angular-domain CSIT

“…Such high-resolution AD converters are, however, among the most power hungry devices of the receiver chain. This motivates the use of low-resolution energy efficient AD converters in FD-MIMO systems to achieve energy-efficient operation [12][13][14][15]. At the transmit side, on the other hand, power expenditure is dominated by power amplifiers, which are usually required to operate within the high linearity regime to avoid signal distortion.…”