Deep Unfolding for Fast Linear Massive MIMO Precoders under a PA Consumption Model

Massive multiple-input multiple-output (MIMO) precoders are typically designed by minimizing the transmit power subject to a quality-of-service (QoS) constraint. However, current sustainability goals incentivize more energy-efficient solutions and thus it is of paramount importance to minimize the consumed power directly. Minimizing the consumed power of the power amplifier (PA), one of the most consuming components, gives rise to a convex, non-differentiable optimization problem, which has been solved in the past using conventional convex solvers. Additionally, this problem can be solved using a proximal gradient descent (PGD) algorithm, which suffers from slow convergence. In this work, to overcome the slow convergence, a deep unfolded version of the algorithm is proposed, which can achieve close-to-optimal solutions in only 20 iterations compared to the 3500 plus iterations needed by the PGD algorithm. Results indicate that the deep unfolding algorithm is three orders of magnitude faster than a conventional convex solver and four orders of magnitude faster than the PGD.Comment: This paper is presented at VTC2023-Spring. T. Feys, X. Mestre, E. Peschiera, and F. Rottenberg, "Deep Unfolding for Fast Linear Massive MIMO Precoders under a PA Consumption Model," in 2023 IEEE 97th Vehicular Technology Conference (VTC2023-Spring), Florence, Italy, June 202

Switchable capacitor

A micro electromechanical switchable capacitor is disclosed, comprising a substrate, a bottom elecrode, a dielaectric layer deposited on at least part of sai bottum electrode, a conductive floating electrode deposited on at least part of said dielectric layer, an armature positioned proximate to the floating electrode and a first actiuation area in order to stabilize the down state position of the armature. The device may futhermore comprise a second actuation area. The present invention provides shunt switches and series switches with actuation in zones attached to the floating electrode area of with relay actuation

A 2D pixelated optical beam scanner controlled by the laser wavelength

We present a chip-based optical beam scanner based on a dispersive optical phased array (OPA) that illuminates the far field with a pixelated pattern. To scale up theOPAto a large number of antennas, we break it up intomanageable blocks with acceptable losses. The 2D wavelength scanning within a block is handled by dispersive delay lines. Between blocks, there are no delay lines, and theOPAwill only have constructive interference for a discrete set of wavelengths. This results in the far-field illumination of a pixelated pattern along both x and y directions. The sidelobes and the power in the main lobe can be controlled by the power distribution of the individual OPA antennas

Characterization and modelling of switchable stop-band filters based on RF-MEMS and complementary split ring resonators

In this work, we present the characterization and electrical modelling of a reconfigurable stop-band filter based on RF microelectromechanical systems (RF-MEMS) combined with metamaterial structures. The device consists of a coplanar waveguide (CPW) structure that combines complementary split ring resonators (CSRRs) and RF-MEMS varactor bridges operating at Q-band. A full electrical model for the description of the proposed structure is presented. The circuit model takes into account the electrical characteristics of the RF-MEMS, CSRRs and transmission line as well as the involved electromagnetic coupling and is used for accurate prediction of switchable filter response.Peer ReviewedPostprint (author’s final draft

Reconfigurable RF-MEMS Metamaterials Filters

In this work, the design procedure, modelling and implementation of recon¯gurable ¯lters based on RF microelectromechanical systems metamaterials is presented. Speci¯cally, tunable stop-band and pass-band frequency responses are obtained by combining RF-MEMS with metamaterials based in complementary split rings resonators. These particles, allow for the design of negative e®ective permittivity transmission lines, providing forbidden propagation frequency bands. Moreover, CSRRs properly combined with metal vias in transmission lines, generate a simultaneously " < 0 and ¹ < 0 e®ective media which involves an allowed frequency band. These two phenomenons have been used in order to implement stop-band and pass-band ¯lters. Since CSRRs present a LC-tank behaviour and are electrically coupled to the host line, the tunability is achieved by means of the RF-MEMS, which modify the electrical characteristics of the CSRRs and the electric coupling. A full electrical model for the description of the proposed structures is presented. The circuit model take into account the electrical characteristics of the RF-MEMS, CSRRs and transmission lines as well as the involved electromagnetic coupling and are used for accurate prediction of switchable ¯lters response.Peer ReviewedPostprint (published version

Sensor searches demanding application

SCOPUS: ar.jDecretOANoAutActifinfo:eu-repo/semantics/publishe

Optimal zero forcing precoder and decoder design for multi-user MIMO FBMC under strong channel selectivity

This paper investigates the optimal design of precoders or decoders under a channel inversion criterion for multi-user (MU) MIMO filterbank multicarrier (FBMC) modulations. The base station (BS) is assumed to use a single tap precoding/decoding matrix at each subcarrier in the downlink/uplink, resulting in a low complexity of implementation. The expression of the asymptotic mean squared error (MSE) for this precoding/decoding design in the case of strong channel selectivity is recalled and simplified. Optimizing the MSE under a channel inversion constraint, the expression of the optimal precoding/decoding matrix is found. It is shown that as long as the number of BS antennas is larger than the number of users, the optimized precoder and decoder can compensate for the channel frequency selectivity and even restore the system orthogonality for a large enough number of BS antennas

LINEAR RECEIVERS FOR MASSIVE MIMO FBMC/OQAM UNDER STRONG CHANNEL FREQUENCY SELECTIVITY

Abstract: Filterbank Multicarrier (FBMC) modulations based on OQAM (FBMC/OQAM) have become a promising alternative to conventional OFDM because of their higher spectral efficiency and their improved selectivity in the frequency domain. Unfortunately, the orthogonality of these modulations is lost when the channel presents strong frequency selectivity, meaning that the channel response cannot be approximated as frequency flat within each subcarrier bandwidth. In this paper, this effect is analyzed in the massive MIMO setting, whereby the number of transmit and receive antennas is asymptotically large (but not as large as the number of subcarriers). It is formally shown that, under these asymptotic conditions, the output mean squared error (MSE) at each subcarrier converges to a constant independent of the subcarrier index. This was previously referred to as “self-equalization” principle in the FBMC/OQAM literature. It is demonstrated here that this phenomenon is a direct consequence of channel hardening effect in large scale MIMO configurations

Single-Tap Precoders and Decoders for Multi-User MIMO FBMC-OQAM under Strong Channel Frequency Selectivity

The design of linear precoders or decoders for multiuser multiple-input multiple-output filterbank multicarrier (FBMC) modulations in the case of a strong channel frequency selectivity is presented. The users and the base station (BS) communicate using space division multiple access. The low complexity proposed solution is based on a single tap per-subcarrier precoding/decoding matrix at the BS in the downlink/uplink. As opposed to classical approaches that assume flat channel frequency selectivity at the subcarrier level, the BS does not make this assumption and takes into account the distortion caused by channel frequency selectivity. The expression of the FBMC asymptotic mean squared error (MSE) in the case of strong channel selectivity derived in earlier works is developed and extended. The linear precoders and decoders are found by optimizing the MSE formula under two design criteria, namely zero forcing or minimum MSE. Finally, simulation results demonstrate the performance of the optimized design. As long as the number of BS antennas is larger than the number of users, it is shown that those extra degrees of freedom can be used to compensate for the channel frequency selectivity