Analog MIMO Research Articles

Optimal beamforming and deployment of millimeter-wave drone base stations

Due to their flexible deployment and line-of-sight channel conditions, using drones as base stations is a promising technology. Recent developments in Massive MIMO transmission with millimeter-wave beamforming also enables high data rates and enables simultaneous transmission to multiple ground users. In this work we consider the problem of deployment (i.e. positioning) of drone base stations for maximizing proportional fairness, along with analog MIMO beamforming that maximizes the Signal to Interference plus Noise Ratio (SINR). Simulation results reveal that careful K-means clustering of ground users and altitude adjustment performs close to a Particle Swarm Optimization (PSO)-based solution. Discrete Fourier Transform (DFT) codebook-based low-complexity beamforming also provides a promising performance, when compared to the Semi-Definite Programming (SDP)-based solution, as the number of antennas is increased.

Analog MIMO Communication for One-Shot Distributed Principal Component Analysis

A fundamental algorithm for data analytics at the edge of wireless networks is distributed principal component analysis (DPCA), which finds the most important information embedded in a distributed high-dimensional dataset by distributed computation of a reduced-dimension data subspace, called principal components (PCs). In this paper, to support one-shot DPCA in wireless systems, we propose a framework of analog MIMO transmission featuring the uncoded analog transmission of local PCs for estimating the global PCs. To cope with channel distortion and noise, two maximum-likelihood (global) PC estimators are presented corresponding to the cases with and without receive channel state information (CSI). The first design, termed coherent PC estimator, is derived by solving a Procrustes problem and reveals the form of regularized channel inversion where the regulation attempts to alleviate the effects of both receiver noise and data noise. The second one, termed blind PC estimator, is designed based on the subspace channel-rotation-invariance property and computes a centroid of received local PCs on a Grassmann manifold. Using the manifold-perturbation theory, tight bounds on the mean square subspace distance (MSSD) of both estimators are derived for performance evaluation. The results reveal simple scaling laws of MSSD concerning device population, data and channel signal-to-noise ratios (SNRs), and array sizes. More importantly, both estimators are found to have identical scaling laws, suggesting the dispensability of CSI to accelerate DPCA. Simulation results validate the derived results and demonstrate the promising latency performance of the proposed analog MIMO

Analog MIMO RoC Passive Relay for Indoor Deployments of Wireless Networks

Most of the indoor coverage issues arise from network deployments that are usually planned for outdoor scenarios. Moreover, the ever-growing number of devices with different Radio Access Technologies (RATs), expected for new 5G scenarios and to maintain compatibility with older cellular standards (mostly 3G/4G), worsen this situation thus calling for novel bandwidth-efficient, low-latency and cost-effective solutions for indoor coverage. To solve this problem, Centralized Radio Access Network (C-RAN) architectures have been proposed to provide dense and controlled coverage inside buildings. However, all-digital C-RAN solutions are complex and expensive when indoor layout constraints and device costs are considered. We discuss here an analog C-RAN architecture, referred to as Analog MIMO Radio-over-Copper (A-MIMO-RoC), that aims at distributing RF signals indoors over distances in the order of 50 m. The all-analog passive-only design presented here proves the feasibility of analog relaying of MIMO radio signals over LAN cables at frequency bandwidth values up to 400 MHz for multi-RAT applications. After asserting the feasibility of the A-MIMO-RoC platform, we present some experimental results obtained with the proposed architecture. These preliminary results show that the A-MIMO-RoC system is a valid solution towards the design of dedicated 4G/5G indoor wireless systems for the billions of buildings which nowadays still suffer from severe indoor coverage issues.

Analog MIMO Radio-Over-Copper Downlink With Space-Frequency to Space-Frequency Multiplexing for Multi-User 5G Indoor Deployments

Radio access network (RAN) centralization is at the basis of current mobile networks, in which BaseBand Units (BBUs) and radio antenna units (RAUs) exchange over the FrontHaul (FH) digitized radio-frequency signals through protocols such as the common public radio interface. However, such architecture, as it stands, does not scale to the demands of multiple-antennas 5G systems, thus leading to drastic RAN paradigm changes. Differently from digital RAN architectures, we propose to overcome bandwidth/latency issues due to digitization by employing an all-analog FH for multiple-antenna RAUs based on the analog radio-over-copper (A-RoC) paradigm. The A-RoC is an alternative/complementary solution to FH for the last 200 m, such as for indoor, to reuse existing local area network (LAN) cables with remarkable economic benefits. Although LAN cables contain 4 twisted-pairs with up to 500 MHz bandwidth/ea., their usage is limited by cable attenuation and crosstalk among pairs. This paper demonstrates that a judicious mapping of each radio-frequency signal of each antenna onto a combination of cable pair-frequency allocations, referred to as space-frequency to space-frequency multiplexing, optimized together with the design of the digital precoding at the BBU, substantially mitigates the cable impairments. The LAN cables can be exploited for last 100–200 m analog transport FH to meet the requirements of 5G indoor networks.

Analog MIMO-RoC Downlink With SF2SF

Analog MIMO radio-over-copper is an alternative/complementary solution to conventional fiber-based mobile-fronthaul suitable for the last 200m with goal to reuse existing indoor LAN cables with remarkable economic benefits. Although LAN cables contain four twisted-pairs with up to 500MHz bandwidth/ea., their usage is limited by cable attenuation and crosstalk among pairs. In this letter, we demonstrate by numerical evaluations that a judicious mapping of each radio-frequency signal of each antenna onto a combination of cable pair-frequency allocations, referred to as space-frequency to space-frequency multiplexing, minimizes the cable impairments. LAN cables bandwidth capabilities are thus exploited to evaluate the radio access requirements of 5G indoor networks.

Low-Complexity and High-Resolution DOA Estimation for Hybrid Analog and Digital Massive MIMO Receive Array

A large-scale fully digital receive antenna array can provide very high-resolution direction of arrival (DOA) estimation, but resulting in a significantly high RF-chain circuit cost. Thus, a hybrid analog and digital (HAD) structure is preferred. Two phase alignment (PA) methods, HAD PA (HADPA) and hybrid digital and analog PA (HDAPA), are proposed to estimate DOA based on the parametric method. Compared to analog PA (APA), they can significantly reduce the complexity in the PA phases. Subsequently, a fast root multiple signal classification HDAPA (root-MUSIC-HDAPA) method is proposed specially for this hybrid structure to implement an approximately analytical solution. Due to the HAD structure, there exists the effect of direction-finding ambiguity. A smart strategy of maximizing the average receive power is adopted to delete those spurious solutions and preserve the true optimal solution by linear searching over a set of limited finite candidate directions. This results in a significant reduction in computational complexity. Eventually, the Cramer–Rao lower bound (CRLB) of finding emitter direction using the HAD structure is derived. Simulation results show that our proposed methods, root-MUSIC-HDAPA and HDAPA, can achieve the hybrid CRLB with their complexities being significantly lower than those of pure linear searching-based methods, such as APA.