Abstract
We consider power efficient scheduling and precoding solutions for multiantenna hybrid digital-analog transmission systems that use Time-Modulated Arrays (TMAs) in the analog domain. TMAs perform beamforming with switches instead of conventional Phase Shifters (PSs). The extremely low insertion losses of switches, together with their reduced power consumption and cost make TMAs attractive in emerging technologies like massive Multiple-Input Multiple-Output (MIMO) and millimeter wave (mmWave) systems. We propose a novel analog processing network based on TMAs and provide an angular scheduling algorithm that overcomes the limitations of conventional approaches. Next, we pose a convex optimization problem to determine the analog precoder. This formulation allows us to account for the Sideband Radiation (SR) effect inherent to TMAs, and achieve remarkable power efficiencies with a very low impact on performance. Computer experiments results show that the proposed design, while presenting a significantly better power efficiency, achieves a throughput similar to that obtained with other strategies based on angular selection for conventional architectures.
Highlights
Massive Multiple-Input Multiple-Output (MIMO) relies on the use of a large number of antennas to take advantage of the wireless channel spatial diversity and achieve high beamforming gains [1]
Massive MIMO is feasible at millimeter wave where the small wavelengths handled allow the integration of large antenna arrays into apertures of reasonable size [2]
NUMERICAL RESULTS we present the results of computer experiments carried out to assess the performance of the proposed analog network with SPDT switches, scheduler, and hybrid precoding designs
Summary
Massive Multiple-Input Multiple-Output (MIMO) relies on the use of a large number of antennas to take advantage of the wireless channel spatial diversity and achieve high beamforming gains [1]. While [8] considers fixed user directions matching the beams of the different harmonics, [9] assumes the unlikely scenario of isotropically distributed users Both approaches employ rigid weighting patterns to design the precoding matrix, leading to inefficient power allocations. Unlike the solutions in [8], [9], we propose in this work an alternative TMA analog network that provides total flexibility in the design of the analog precoder This freedom to design the precoding matrix was achieved in [4], but the approach proposed avoids the power losses caused by the SPST switches during the OFF-state. The ILs of these simple PSs, are significantly lower than those of high-resolution PSs [4], [15]
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