Analog MIMO Radio-over-Copper: Prototype and Preliminary Experimental Results

Analog Multiple-Input Multiple-Output Radio-over-Copper (A-MIMO-RoC) is an effective all-analog FrontHaul (FH) architecture that exploits any pre-existing Local Area Network (LAN) cabling infrastructure of buildings to distribute Radio-Frequency (RF) signals indoors. A-MIMO-RoC, by leveraging a fully analog implementation, completely avoids any dedicated digital interface by using a transparent end-to-end system, with consequent latency, bandwidth and cost benefits. Usually, LAN cables are exploited mainly in the low-frequency spectrum portion, mostly due to the moderate cable attenuation and crosstalk among twisted-pairs. Unlike current systems based on LAN cables, the key feature of the proposed platform is to exploit more efficiently the huge bandwidth capability offered by LAN cables, that contain 4 twisted-pairs reaching up to 500 MHz bandwidth/pair when the length is below 100 m. Several works proposed numerical simulations that assert the feasibility of employing LAN cables for indoor FH applications up to several hundreds of MHz, but an A-MIMO-RoC experimental evaluation is still missing. Here, we present some preliminary results obtained with an A-MIMO-RoC prototype made by low-cost all-analog/all-passive devices along the signal path. This setup demonstrates experimentally the feasibility of the proposed analog relaying of MIMO RF signals over LAN cables up to 400 MHz, thus enabling an efficient exploitation of the LAN cables transport capabilities for 5G indoor applications.Comment: Part of this work has been accepted as a conference publication to ISWCS 201

Spatial Multiplexing of QPSK Signals with a Single Radio: Antenna Design and Over-the-Air Experiments

The paper describes the implementation and performance analysis of the first fully-operational beam-space MIMO antenna for the spatial multiplexing of two QPSK streams. The antenna is composed of a planar three-port radiator with two varactor diodes terminating the passive ports. Pattern reconfiguration is used to encode the MIMO information onto orthogonal virtual basis patterns in the far-field. A measurement campaign was conducted to compare the performance of the beam-space MIMO system with a conventional 2-by-?2 MIMO system under realistic propagation conditions. Propagation measurements were conducted for both systems and the mutual information and symbol error rates were estimated from Monte-Carlo simulations over the measured channel matrices. The results show the beam-space MIMO system and the conventional MIMO system exhibit similar finite-constellation capacity and error performance in NLOS scenarios when there is sufficient scattering in the channel. In comparison, in LOS channels, the capacity performance is observed to depend on the relative polarization of the receiving antennas.Comment: 31 pages, 23 figure

Efficient DSP and Circuit Architectures for Massive MIMO: State-of-the-Art and Future Directions

Massive MIMO is a compelling wireless access concept that relies on the use of an excess number of base-station antennas, relative to the number of active terminals. This technology is a main component of 5G New Radio (NR) and addresses all important requirements of future wireless standards: a great capacity increase, the support of many simultaneous users, and improvement in energy efficiency. Massive MIMO requires the simultaneous processing of signals from many antenna chains, and computational operations on large matrices. The complexity of the digital processing has been viewed as a fundamental obstacle to the feasibility of Massive MIMO in the past. Recent advances on system-algorithm-hardware co-design have led to extremely energy-efficient implementations. These exploit opportunities in deeply-scaled silicon technologies and perform partly distributed processing to cope with the bottlenecks encountered in the interconnection of many signals. For example, prototype ASIC implementations have demonstrated zero-forcing precoding in real time at a 55 mW power consumption (20 MHz bandwidth, 128 antennas, multiplexing of 8 terminals). Coarse and even error-prone digital processing in the antenna paths permits a reduction of consumption with a factor of 2 to 5. This article summarizes the fundamental technical contributions to efficient digital signal processing for Massive MIMO. The opportunities and constraints on operating on low-complexity RF and analog hardware chains are clarified. It illustrates how terminals can benefit from improved energy efficiency. The status of technology and real-life prototypes discussed. Open challenges and directions for future research are suggested.Comment: submitted to IEEE transactions on signal processin