Low-Complexity Hybrid Beamforming for Massive MIMO Systems in Frequency-Selective Channels

Abstract

Hybrid beamforming for frequency-selective channels is a challenging problem as the phase shifters provide the same phase shift to all of the subcarriers. The existing approaches solely rely on the channel's frequency response and the hybrid beamformers maximize the average spectral efficiency over the whole frequency band. Compared to state-of-the-art, we show that substantial sum-rate gains can be achieved, both for rich and sparse scattering channels, by jointly exploiting the frequency and time domain characteristics of the massive multiple-input multiple-output (MIMO) channels. In our proposed approach, the radio frequency (RF) beamformer coherently combines the received symbols in the time domain and, thus, it concentrates signal's power on a specific time sample. As a result, the RF beamformer flattens the frequency response of the "effective" transmission channel and reduces its root mean square delay spread. Then, a baseband combiner mitigates the residual interference in the frequency domain. We present the closed-form expressions of the proposed beamformer and its performance by leveraging the favorable propagation condition of massive MIMO channels and we prove that our proposed scheme can achieve the performance of fully-digital zero-forcing when number of employed phase shifter networks is twice the resolvable multipath components in the time domain.

Developing the First mmWave Fully-Connected Hybrid Beamformer With a Large Antenna Array

“…The designed beamformer can also be used to further optimize the transmission over frequency-selective channels [14], [34], and provide tradeoffs between diversity and spatial multiplexing gains. Such studies may even motivate the deployment of hybrid beamformers in lower frequency bands, which are generally more frequency-selective.…”

“…The design and performance of such methods also depends on the properties of the propagation channel, performance metric, and the structure of the phase shifter network. For example, the sparsity, richness, or the frequency-selectivity of channel matrix channel directly impacts the choice of the hybrid beamforming algorithms [14], [15], [24]. In addition, the hardware connections within the hybrid beamforming network dictate the degrees of freedom and constraints that are available to the algorithm developers.…”

How to Meet Increased Capacities by Future Green 5G Networks: A Survey

“…The main objective of massive MIMO is to increase throughput, spectrum efficiency, reliability and energy efficiency. Among the most importing massive MIMO techniques that will improve energy performance in future mobile networks is the use of a large number of antenna elements for very selective beam-formed transmission [23].…”

An Optimal Steering Vector Generation Using Chaotic Binary Crow Search Algorithm for MIMO System

“…One of the most important types of radar is the MIMO radar that has influenced many researchers to choose this topic for research in recent years [4,5]. The collocated MIMO radar recognizes number of targets which is having a flexible number of transmit antennas for transmitting beam patterns in both uniform and directional beam patterns [6]. The omnidirectional beam pattern is transmitted for independent orthogonal waveforms, while the generated beam patterns are depending on the transmit wave feature [7,8].…”