Efficient MIMO Transmission of PSK Signals With a Single-Radio Reconfigurable Antenna

Abstract

Crucial developments to the recently introduced signal-space approach for multiplexing multiple data symbols using a single-radio switched antenna are presented. First, we introduce a general framework for expressing the spatial multiplexing relation of the transmit signals only from the antenna scattering parameters and the modulating reactive loading. This not only avoids tedious far-field calculations, but more importantly provides an efficient and practical strategy for spatially multiplexing PSK signals of any modulation order. The proposed approach allows ensuring a constant impedance matching at the input of the driving antenna for all symbol combinations, and as importantly uses only passive reconfigurable loads. This obviates the use of reconfigurable matching networks and active loads, respectively, thereby overcoming stringent limitations of previous single-feed MIMO techniques in terms of complexity, efficiency, and power consumption. The proposed approach is illustrated by the design of a realistic very compact antenna system optimized for multiplexing QPSK signals. The results show that the proposed approach can bring the MIMO benefits to the low-end user terminals at a reduced RF complexity. Index TermsBeam-space MIMO, reduced-complexity MIMO, reconfigurable antenna, phase shift keying (PSK), single-radio MIMO.

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

“…The three-port radiator is fully described by a 3-by-3 scattering matrix, S, and three embedded radiation patterns. a load control system reconfigures the variable loads, so that the antenna instantaneous radiated field becomes E {x1,x2} inst [10]. Taking X {−1} 1 as the free parameter, the required reactance values can be obtained from…”

“…The multiplexing strategy outlined above ensures the reflection coefficient at the antenna active port, Γ tot , (given by (45) in [10]) is a function of only the radiator S-matrix, and therefore remains constant regardless of the symbol combination ratio,x, and the selection of X {−1} 1…”

“…In this paper, the strategy proposed in [10] is extended to design and implement the first fully-operational beamspace MIMO antenna capable of transmitting two QPSK signals. The design procedure is described and the results demonstrating the efficiency of the approach are presented.…”

Random Aerial Beamforming for Underlay Cognitive Radio With Exposed Secondary Users

“…The application of ESPAR and other classes of reconfigurable antennas to wireless communications systems is not actually new. In [15]- [18], the Aerial DoF (ADoF) provided by the orthonormal basis patterns are used to construct single radio Beamspace-Multi-Input Multi-Output (MIMO) systems that can apply spatial multiplexing without the need to deploy multiple antennas. Recently, beamspace-MIMO was applied for millimeter-Wave (mm-Wave) systems using parasitic an- tenna arrays with reconfigurable loads [19].…”

User Effects in Beam-Space MIMO

“…However, translating the beam-space MIMO concept to reality requires dealing with various challenges that are commonly overlooked in purely conceptual designs. Recent works have already addressed some of these challenging aspects such as the compatibility with portable devices [5]- [6], the emulation of higher-order modulation schemes [7], and the adaptation to non-ideal channel propagation conditions [8].…”