arXiv subjects

Álvaro Pendás-Recondo

Publications and source records attributed to Álvaro Pendás-Recondo.

3 recordsLinked to original sources

arXiv2026

Dual-Polarized Rate-Splitting Multiple Access for mmWave Communications: A Practical Design and Prototype Implementation

This work presents a dual-polarized rate-splitting multiple access (RSMA) design for millimeter-wave (mmWave) or frequency range 2 (FR2) communications. Focusing on a practical implementation, we consider the specific scenario of a single transmitter serving two receivers (users) within the same time, frequency, and code resource block. The transmitter and each receiver are equipped with a pair of dual-polarized antennas. We first present the system formulation and compute the achievable rate expressions for discrete constellations. Based on these expressions, we propose and evaluate two receiver architectures: one based on successive interference cancellation (SIC) and a non-SIC decoder. Both designs exhibit comparable performance, and the combination of polarization diversity and RSMA provides the system with significant flexibility to adapt to different channel conditions when serving both users, while the non-SIC decoder enables a simpler hardware implementation. We then present a prototype implementation of the proposed design, operating at a carrier frequency of 25 GHz, and evaluate it by measuring the symbol error rate (SER) of the different data streams under various signal-to-noise ratio (SNR) and polarization diversity conditions. The obtained measurements show good agreement with software simulations, thereby validating the system implementation. To the best of our knowledge, this is the first mmWave RSMA prototype reported in the literature and the first to exploit polarization diversity. Furthermore, given the selected carrier frequency, the proposed design may also find applicability in the upper portion of the envisioned FR3 band (7-24 GHz).

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arXiv2026

Noncoherent MIMO in the FR3 Upper Mid-Band Using Grassmannian Signaling: Prototype and Experimental Evaluation

This work presents a prototype implementation of a noncoherent multiple-input multiple-output (MIMO) system based on Grassmannian signalling, where neither the transmitter nor receiver requires channel state information (CSI), operating at a carrier frequency of 15 GHz in the frequency range 3 (FR3) upper mid-band envisioned for 6G. To the best of our knowledge, this is the first prototype implementation of Grassmannian signaling reported in the literature beyond sub-6 GHz bands. We identify the motivation of applying Grassmannian signaling, a form of unitary space-time modulation (USTM), in this band for wireless and mobile applications with low spectral-efficiency requirements but strict reliability and power-efficiency demands. With this idea in mind, we present a system design integrated with orthogonal frequency-division multiplexing (OFDM) that addresses the challenges associated with the higher carrier frequencies of FR3 while providing reliable operation across a broad range of scenarios, including urban and rural environments as well as vehicular communications. We then present the prototype implementation of the proposed design, based on software-defined radio (SDR) devices integrated with radio-frequency (RF) mixers, filters, and power amplifiers to ensure adequate operation in the targeted band. Over-the-air (OTA) experiments based on symbol error rate (SER) measurements under non-line-of-sight (NLoS) and line-of-sight (LoS) scenarios, and across different data rates, show good agreement with software simulations, thereby validating the prototype implementation.

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arXiv2026

A Structured Family of Grassmannian Constellations via Geodesic Mapping for MIMO Noncoherent Communications

This work presents a novel structured family of Grassmannian constellations for multiple-input multiple-output (MIMO) noncoherent communications over Rayleigh block-fading channels, where neither the transmitter nor the receiver has channel state information (CSI). The proposed constellation design is built upon the geodesic curves of the Grassmann manifold, thereby exploiting its underlying geometric structure. The resulting solution is limited in spectral efficiency (with a maximum constellation size of $4M^2$ points, where $M$ is the number of transmit antennas), targeting a rate in the range of $0.25$-$1$ bps/Hz. However, all space-time matrices resulting from this design exhibit the remarkable property of having a single nonzero entry per row, meaning that only one transmit antenna is active per time slot. This property significantly reduces hardware complexity and implementation cost, while also lowering power consumption, as only a single radio-frequency (RF) chain and power amplifier are required for transmission. Furthermore, within the constellation size limits, the proposed design achieves error performance comparable to state-of-the-art optimization-based unstructured designs, as validated through symbol error rate (SER) numerical results. It also enables simple yet effective bit labeling, confirmed by comparisons of bit error rate (BER) and SER, and reduces the computational complexity of the maximum-likelihood (ML) detector for Grassmannian constellations by a factor of $M$.

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