Waveforms for the Massive MIMO Downlink: Amplifier Efficiency, Distortion, and Performance

Abstract

Abstract-In massive MIMO, most precoders result in downlink signals that suffer from high PAR, independently of modulation order and whether single-carrier or OFDM transmission is used. The high PAR lowers the power efficiency of the base station amplifiers. To increase power efficiency, low-PAR precoders have been proposed. In this article, we compare different transmission methods for massive MIMO in terms of the power consumed by the amplifiers. It is found that: 1) OFDM and single-carrier transmission have the same performance over a hardened massive MIMO channel and 2) when the higher amplifier power efficiency of low-PAR precoding is taken into account, conventional and low-PAR precoders lead to approximately the same power consumption. Since downlink signals with low PAR allow for simpler and cheaper hardware, than signals with high PAR, therefore, the results suggest that low-PAR precoding with either single-carrier or OFDM transmission should be used in a massive MIMO base station.

On the Energy Efficiency of MIMO Hybrid Beamforming for Millimeter-Wave Systems With Nonlinear Power Amplifiers

“…Furthermore, we assume that the PAs in the different antenna branches follow the same inputoutput relation. This assumption is widely used in the literature [20], [40], [44]. In this case, the equivalent baseband output signal of the n th PA is…”

Spatial Characteristics of Distortion Radiated From Antenna Arrays With Transceiver Nonlinearities

“…Because of multiple carriers in (5), multiuser precoding in (10) and (13), and the central limit theorem, the distribution of the digital transmit signals x[n, ν] is close to circularly symmetric Gaussian. Note that this is true independently of whether OFDM or single-carrier transmission is used and independently of the order of the symbol constellations used for the data symbols s[n, ν] when either the number of users or number of filter taps in the precoding is large [29]. We therefore assume that the digital transmit signals, and thus the analog transmit signals, are circularly symmetric Gaussian.…”

“…The partitioning in (29) can also be obtained using Bussgang's theorem. The Hermite expansion, however, simplifies the derivation of the cross-correlation of the output signals, which is easily obtained from the orthogonality property in (28).…”

Nonlinear Precoding for Phase-Quantized Constant-Envelope Massive MU-MIMO-OFDM

“…2b shows the SQUID-OFDM output for the problem (P 2 ∞ ) before and after 2-phase-bit quantization. 3 We see that the ∞norm constrains the SQUID-OFDM output to a box in the complex plane, which limits the error caused by the quantizer. Fig.…”

“…In this case, the ∞ -norm constrains 2 The simulation parameters are given in Section IV-A. 3 By setting S = 1 and N = 1 for the problem (P 2 ∞ ), Algorithm 1 reduces to the SQUID precoder for single-carrier transmission [11, Sec. IV-B].…”