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

TL;DR

This paper presents a fully-operational beam-space MIMO antenna capable of spatial multiplexing two QPSK signals, with experimental validation showing comparable performance to conventional MIMO systems in NLOS conditions.

Contribution

It introduces the first fully-operational beam-space MIMO antenna for QPSK signals and provides experimental performance analysis under realistic propagation scenarios.

Findings

Beam-space MIMO achieves similar capacity and error rates as conventional MIMO in NLOS.

Performance depends on polarization in LOS channels.

Experimental validation confirms practical viability.

Abstract

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.