Towards Compact and Frequency-Tunable Antenna Solutions for MIMO Transmission With a Single RF Chain

Abstract

Abstract-Recently, a technique called beam-space MIMO has been demonstrated as an effective approach for transmitting multiple signals while using a single RF-chain. In this work, we present novel design considerations and a compact antenna solution to stimulate the deployment of beam-space MIMO in future wireless applications. Targeting integration in small wireless devices, the novel antenna is made of a single integrated radiator rather than an array of physically-separated dipoles. It also drastically simplifies the implementation of variable loads and DC bias circuits for BPSK modulated signals, and does not require any external reconfigurable matching circuit. Finally, we show that this antenna system could be reconfigured by dynamic adjustment of terminating loads to preserve its beam-space multiplexing capabilities over a 1:2 tuning range, thereby promoting the convergence of MIMO and dynamic spectrum allocation via reduced-complexity hardware. A prototype achieving single-RF-chain multiplexing at a fixed frequency is designed and measured, showing excellent agreement between simulations and measurements.Index Terms-Beam-space MIMO, cognitive radio, dynamic frequency allocation, MIMO antenna, reconfigurable antenna, reduced complexity.

User Effects in Beam-Space MIMO

“…1(a). This is a compact built-in antenna system designed in [6] for optimum single-radio multiplexing of BPSK modulated signals in free space. In order to facilitate the understanding of upcoming results, here we briefly describe the antenna operation and introduce the key performance parameters of beam-space MIMO.…”

“…Moreover, an acceptable level of the total efficiency (product of radiation and matching efficiencies) at the active port is required. Optimum MIMO operation of the antenna system in terms of the power imbalance ratio and/or the total efficiency can be achieved by optimizing either the reactive loads [4] or the three-port radiator [6]. In summary, the performance of a beam-space MIMO antenna can be examined in terms of four key characteristics:…”

“…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].…”

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

“…As radiation pattern reconfiguration is typically achieved by changing the impedance of variable loads embedded in the antenna structure, e.g., [2]- [4], successful data multiplexing in beam-space MIMO requires finding and realizing the correct impedance values. These impedance values not only depend on the symbols to be multiplexed, but are also very dependent on how the basis patterns for the pattern decomposition are defined.…”

“…For the realization of such load the use of passive-only components is preferred, as the complexity and stability concerns of active loads offset the benefits. The most advanced beam-space MIMO antenna demonstrated today only supports BPSK modulation [3], [4].…”