Use of 1‐bit digital‐to‐analogue converters in massive MIMO systems

et al. 2017

IEEE Trans. Commun.

317

355

Abstract-Massive multiuser (MU) multiple-input multipleoutput (MIMO) is foreseen to be one of the key technologies in fifth-generation wireless communication systems. In this paper, we investigate the problem of downlink precoding for a narrowband massive MU-MIMO system with low-resolution digital-toanalog converters (DACs) at the base station (BS). We analyze the performance of linear precoders, such as maximal-ratio transmission and zero-forcing, subject to coarse quantization. Using Bussgang's theorem, we derive a closed-form approximation on the rate achievable under such coarse quantization. Our results reveal that the performance attainable with infinite-resolution DACs can be approached using DACs having only 3 to 4 bits of resolution, depending on the number of BS antennas and the number of user equipments (UEs). For the case of 1-bit DACs, we also propose novel nonlinear precoding algorithms that significantly outperform linear precoders at the cost of an increased computational complexity. Specifically, we show that nonlinear precoding incurs only a 3 dB penalty compared to the infinite-resolution case for an uncoded bit error rate of 10 −3 , in a system with 128 BS antennas that uses 1-bit DACs and serves 16 single-antenna UEs. In contrast, the penalty for linear precoders is about 8 dB.Index Terms-Massive multi-user multiple-input multipleoutput, digital-to-analog converter, Bussgang's theorem, minimum mean-square error precoding, convex optimization, semidefinite relaxation, Douglas-Rachford splitting, sphere precoding.

Section: Signal Decomposition Using Bussgang's Theoremmentioning

confidence: 99%

Quantized Precoding for Massive MU-MIMO

et al. 2017

IEEE Trans. Commun.

317

355

“…The work of CS was supported by Xilinx, Inc. and by the US National Science Foundation (NSF) under grants ECCS-1408006, CCF-1535897, CAREER CCF-1652065, and CNS-1717559. performance. For frequency-selective channels, the performance achievable by using OFDM in combination with 1-bit DACs was recently studied in [9]- [11]. For linear precoding, the analysis in [10] was extended in [12] to multi-bit DACs.…”

Section: A Previous Workmentioning

confidence: 99%

On out-of-band emissions of quantized precoding in massive MU-MIMO-OFDM

2017 51st Asilomar Conference on Signals, Systems, and Computers

et al. 2017

We analyze out-of-band (OOB) emissions in the massive multi-user (MU) multiple-input multiple-output (MIMO) downlink. We focus on systems in which the base station (BS) is equipped with low-resolution digital-to-analog converters (DACs) and orthogonal frequency-division multiplexing (OFDM) is used to communicate to the user equipments (UEs) over frequencyselective channels. We demonstrate that analog filtering in combination with simple frequency-domain digital predistortion (DPD) at the BS enables a significant reduction of OOB emissions, but degrades the signal-to-interference-noise-and-distortion ratio (SINDR) at the UEs and increases the peak-to-average power ratio (PAR) at the BS. We use Bussgang's theorem to characterize the tradeoffs between OOB emissions, SINDR, and PAR, and to study the impact of analog filters and DPD on the error-rate performance of the massive MU-MIMO-OFDM downlink. Our results show that by carefully tuning the parameters of the analog filters, one can achieve a significant reduction in OOB emissions with only a moderate degradation of error-rate performance and PAR.

“…All existing results on low-resolution DACs reviewed so far dealt with the frequency-flat case. The first work to consider 1-bit DACs combined with (OFDM) for massive MU-MIMO over frequency-selective channels is [40]. There, by using an approximate model that treats the 1-bit-DAC distortion as white, it is shown that simple MRT precoding results in high signalto-interference-noise-and-distortion ratio (SINDR) at the UEs provided that the number of BS antennas is significantly larger than the number of UEs.…”

Section: ) Transmitter Impairments and Out-of-band Emissionsmentioning

confidence: 99%

Linear Precoding With Low-Resolution DACs for Massive MU-MIMO-OFDM Downlink

IEEE Trans. Wireless Commun.

et al. 2019

We consider the downlink of a massive multiuser (MU) multiple-input multiple-output (MIMO) system in which the base station (BS) is equipped with low-resolution digital-toanalog converters (DACs). In contrast to most existing results, we assume that the system operates over a frequency-selective wideband channel and uses orthogonal frequency division multiplexing (OFDM) to simplify equalization at the user equipments (UEs). Furthermore, we consider the practically relevant case of oversampling DACs. We theoretically analyze the uncoded bit error rate (BER) performance with linear precoders (e.g., zero forcing) and quadrature phase-shift keying using Bussgang's theorem. We also develop a lower bound on the informationtheoretic sum-rate throughput achievable with Gaussian inputs, which can be evaluated in closed form for the case of 1-bit DACs. For the case of multi-bit DACs, we derive approximate, yet accurate, expressions for the distortion caused by low-precision DACs, which can be used to establish lower bounds on the corresponding sum-rate throughput. Our results demonstrate that, for a massive MU-MIMO-OFDM system with a 128-antenna BS serving 16 UEs, only 3-4 DAC bits are required to achieve an uncoded BER of 10 −4 with a negligible performance loss compared to the infinite-resolution case at the cost of additional out-of-band emissions. Furthermore, our results highlight the importance of taking into account the inherent spatial and temporal correlations caused by low-precision DACs.