@conference {1054, title = {Frequency-selective hybrid beamforming for mmWave full-duplex}, booktitle = {IEEE Int. Conf. Acoustics, Speech and Signal Processing (ICASSP)}, year = {2023}, address = {Rhodes, Greece}, abstract = {
We study beamforming cancellation for a full-duplex (FD) wideband millimeter wave (mmWave) point-to-point bidirectional link in which both multicarrier-based nodes transmit and receive simultaneously and on the same frequency. The focus is on hybrid architectures in which the analog subblock of the beamformer, common to all subcarriers, is fully-connected and based on phase shifters with finite resolution, to avoid frontend saturation by mitigating FD-induced self-interference in the analog domain.
}, keywords = {full-duplex, mmWave, rodin}, doi = {10.1109/ICASSP49357.2023.10094826}, author = {Andrea Guamo-Morocho and R. L{\'o}pez-Valcarce} } @article {1024, title = {Full-duplex mmWave MIMO with finite-resolution phase shifters}, journal = {IEEE Trans. Wireless Communications}, volume = {21}, year = {2022}, month = {11/2022}, pages = {8979-8994}, abstract = {
Enabling simultaneous transmission and reception on the same carrier frequency, i.e., full-duplex (FD) communication, critically requires that the self-interference (SI) be sufficiently suppressed. We investigate the design of precoders and combiners for an FD millimeter wave point-to-point bidirectional link, where dense antenna arrays provide an opportunity for SI suppression via beamforming cancellation. In practice the precoders and combiners are usually implemented in a hybrid digital/analog fashion with a reduced number of radio frequency (RF) chains, and it becomes necessary to overcome a number of limitations imposed by this structure. We focus on a hybrid architecture with a phase shifter-based fully-connected analog stage, assuming finite-resolution phase shifters. To avoid analog-to-digital converter saturation at the receiver, the proposed design aims at cancelling SI at the analog combiner output. Although accurate SI suppression is difficult with low-resolution phase shifters, our design is able to provide reasonable performance, significantly improving upon previous approaches, and allowing to efficiently exploit the availability of RF chains to partially compensate for coarse phase quantization effects.
}, keywords = {full-duplex, mmWave, rodin}, issn = {1536-1276}, doi = {10.1109/TWC.2022.3171664}, author = {R. L{\'o}pez-Valcarce and M. Mart{\'\i}nez-Cotelo} } @article {1028, title = {General Form of the Power Spectral Density of Multicarrier Signals}, journal = {IEEE Communications Letters}, volume = {26}, year = {2022}, month = {08/2022}, pages = {1755-1759}, chapter = {1755}, abstract = {
Multicarrier modulation has been adopted in many modern communication systems because of its many appealing\ 
properties. Its relatively high out-of-band radiation has spurred many techniques to shape the power spectral density (PSD)\ 
of multicarrier signals, including spectral precoding and pulse shaping. We derive a general expression for the PSD which is\ 
valid for subcarrier-specific pulses and for spectral precoders operating over multiple blocks. The only statistical assumptions\ 
on the vector-valued sequence modulating the active subcarriers are wide-sense cyclostationarity and properness. The applicability\ 
of the result to a number of popular multicarrier formats is discussed.
}, keywords = {rodin, spectrum shaping}, doi = {10.1109/LCOMM.2022.3181728}, author = {R. L{\'o}pez-Valcarce} } @article {1009, title = {Hybrid Beamforming Designs for Frequency-Selective mmWave MIMO Systems with Per-RF chain or Per-antenna Power Constraints}, journal = {IEEE Trans. Wireless Communications}, volume = {21}, year = {2022}, month = {08/2022}, pages = {5770-5784}, chapter = {5770}, abstract = {
Configuring precoders and combiners is a major
challenge to deploy practical multiple-input multiple-output
(MIMO) millimeter wave (mmWave) communication systems
with large antenna arrays. Most prior work addresses the problem
focusing on a total transmit power constraint. In practical
transmitters, however, power amplifiers must operate within their
linear range, so that a power constraint applies to each one
of the input signals to these devices. Therefore, precoder and
combiner designs should incorporate per-antenna or per-radio
frequency (RF) chain transmit power constraints. We focus on
such problem for frequency-selective channels with multicarrier
modulation, and assuming hybrid analog/digital architectures
based on fully connected analog blocks implemented with finite resolution
phase shifters. We first derive an all-digital solution
which aims to maximize spectral efficiency. Then, we develop
hybrid precoders and combiners by approximately matching
the corresponding all-digital matrices while still enforcing the
power constraints. Numerical results show that the proposed
all-digital design performs close to the upper bound given
by the standard waterfilling-based solution with a total power
constraint. Additionally, the hybrid designs exhibit a moderate
loss even when low-resolution phase shifters are considered.
}, keywords = {mmWave, rodin}, doi = {10.1109/TWC.2022.3142959}, author = {R. L{\'o}pez-Valcarce and Nuria Gonz{\'a}lez-Prelcic} } @article {1030, title = {Joint Precoder and Window Design for OFDM Sidelobe Suppression}, journal = {IEEE Communications Letters}, volume = {26}, year = {2022}, month = {12/2022}, pages = {3044-3048}, abstract = {

Spectral precoding and windowing are two effective approaches to reduce out-of-band radiation (OBR) in multicarrier systems. Their performance comes at the price of reduced throughput and additional computational complexity, so there is strong motivation for simultaneously using both techniques. We present a novel design that jointly optimizes the precoder and window coefficients to minimize radiated power within a user-selectable frequency region. Results show that the proposed design achieves a better OBR/throughput/complexity tradeoff than either of these individual techniques separately.

}, keywords = {rodin, spectrum shaping}, doi = {10.1109/LCOMM.2022.3203521}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {1025, title = {Orthogonal precoding with memory for sidelobe suppression in OFDM}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2022}, abstract = {
Orthogonal precoding is a very effective approach to reduce out-of-band radiation (OBR) in multicarrier systems in order to avoid adjacent channel interference. This is achieved at the cost of introducing precoder redundancy, which results in throughput loss. Introducing memory in the precoding operation has the potential to improve performance without sacrificing additional spectral efficiency, in exchange for extra computational complexity. We present a novel orthogonal memory precoder which minimizes OBR within a user-selectable frequency region and allows for controlling spectral overshoot. Decision-feedback decoding avoids symbol error rate degradation at the receiver.
}, keywords = {rodin, spectrum shaping}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {996, title = {Analog beamforming for full-duplex mmWave communication with low-resolution phase shifters}, booktitle = {IEEE International Conference on Communications (ICC)}, year = {2021}, month = {06/2021}, address = {Montreal, Canada (Virtual event)}, abstract = {
Full-Duplex (FD) communication has been the object of recent attention, particularly in sub-6 GHz bands. By enabling in-band simultaneous transmission and reception, these techniques present great potential in terms of spectral efficiency, latency, and medium access flexibility, and their extension to millimeter wave (mmWave) bands can be expected to benefit similarly. The dense antenna arrays available in mmWave offer a large number of degrees of freedom which could be exploited towards self-interference (SI) mitigation in FD. However, analog beamforming architectures based on practical phase shifters make this task quite challenging due to the lack of amplitude
control and finite phase resolution. In this context, we consider a single-stream bidirectional point-to-point mmWave FD link, and develop a new analog beamforming design requiring a single radio frequency chain in each direction, explicitly taking into account such hardware-related constraints. Simulation results show that the proposed scheme significantly outperforms previous methods for practical phase shifter resolution values of a few bits.
}, keywords = {full-duplex, mmWave, rodin}, author = {R. L{\'o}pez-Valcarce and M. Mart{\'\i}nez-Cotelo} } @article {995, title = {Mask-Compliant Orthogonal Precoding for Spectrally Efficient OFDM}, journal = {IEEE Transactions on Communications}, volume = {69}, year = {2021}, month = {03/2021}, pages = {1990-2001}, abstract = {
Orthogonal precoding constitutes a powerful technique to reduce spectrum sidelobes of multicarrier signals. This reduction is bought at the cost of introducing precoder redundancy, which results in some throughput loss and additional precoding/decoding complexity. When the goal is to meet some spectral emission mask constraints, it is desirable to avoid unnecessary sidelobe suppression in order to keep precoder redundancy at a minimum. In this context, we introduce a general framework under which we develop a novel Lagrange multiplier-based mask-compliant orthogonal precoder design targeting minimal redundancy. We also adapt to this framework two previously proposed
designs based on spectral notches and minimum out-of-band emission, respectively, to explicitly incorporate mask constraints. Simulation results are provided to show the effectiveness of the proposed designs under different practical masks for multicarrier wireless systems.
}, keywords = {rodin, spectrum shaping, winter}, doi = {10.1109/TCOMM.2020.3041351}, author = {Ravinder Kumar and Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {1003, title = {Memory Tricks: Improving Active Interference Cancellation for Out-of-Band power reduction in OFDM}, booktitle = {IEEE Int. Workshop Signal Process. Adv. Wireless Commun. (SPAWC)}, year = {2021}, address = {Lucca, Italy (Virtual event)}, abstract = {

Although active interference cancellation (AIC) is an appealing approach to reduce out-of-band radiation (OBR) in multicarrier systems without distorting data subcarriers, it usually requires a large number of reserved subcarriers to be effective. Introducing memory in AIC precoding may help alleviate this drawback in exchange for some increase in computational complexity. We propose a novel memory AIC precoder which, in contrast to previous schemes, minimizes OBR within a user-selectable frequency region and allows for controlling spectral overshoot.

}, keywords = {rodin, spectrum shaping}, author = {Khawar Hussain and R. L{\'o}pez-Valcarce} } @conference {990, title = {Energy-efficient analog beamforming with short packets in millimeter-wave MIMO systems}, booktitle = {2020 54th Asilomar Conference on Signals, Systems, and Computers, California, 2020}, year = {2020}, address = {Virtual event}, abstract = {
The energy-aware design of fully analog precoders and combiners is investigated in this paper. To that aim, we consider a millimeter-wave short-packet communication scenario where power consumption and hardware complexity constitute relevant factors. User terminals employ a single channel encoder and, at hardware level, they implement analog architectures that combine phase shifters and switches. Additionally, transmitting terminals also leverage a power control system. An energy efficiency figure of merit is considered, and its optimization subject to finite packet-length constraints is tackled cyclically over disconnected feasible sets. Numerical results are reported
firstly, to illustrate the advantages of the proposed short-packet fully analog design, secondly, to compare its performance to that of on-off beamforming, and finally, to discuss the optimality of the proposed optimization algorithm.
}, keywords = {mmWave, rodin}, author = {Jordi Borr{\`a}s and Francesc Molina and R. L{\'o}pez-Valcarce and Josep Sala} } @conference {989, title = {Full-Duplex mmWave Communication with Hybrid Precoding and Combining}, booktitle = {European Signal Processing Conference (EUSIPCO)}, year = {2020}, month = {08/2020}, address = {Amsterdam (Netherlands)}, abstract = {
We investigate the design of hybrid precoders and combiners for a millimeter wave (mmWave) point-to-point bidirectional link in which both nodes transmit and receive simultaneously and on the same carrier frequency. In such full-duplex configuration, mitigation of self-interference (SI) becomes critical. Large antenna arrays provide an opportunity for spatial SI suppression in mmWave. We assume a phase-shifter based, fully connected architecture for the analog part of the precoder and combiner. The proposed design, which aims at cancelling SI in the analog domain to avoid frontend saturation, significantly improves on the performance of previous approaches.
}, keywords = {full-duplex, mmWave, rodin, winter}, author = {R. L{\'o}pez-Valcarce and M. Mart{\'\i}nez-Cotelo} } @conference {991, title = {Robustness analysis of beamforming based designs for mmWave Full-Duplex Amplify-and-Forward relays}, booktitle = {2020 14th International Conference on Signal Processing and Communication Systems (ICSPCS)}, year = {2020}, month = {12/2020}, abstract = {
We consider the robust design of a millimeter wave MIMO two-hop system in which source, relay and destination are
equipped with large antenna arrays. The relay implements the amplify-and-forward protocol and operates in full-duplex mode,
thus being subjected to self-interference (SI). Imperfect channel state information (CSI) is assumed in all involved links, including
the SI channel, with a deterministic isotropic bounded model on CSI errors. The proposed robust design seeks to maximize
the worst-case spectral efficiency, accommodates both digital and phase shifter-based analog beamforming, and is computationally
simple; moreover, it does not require knowledge of the size of the CSI uncertainty regions.
}, keywords = {full-duplex, mmWave, rodin}, author = {R. L{\'o}pez-Valcarce and M. Mart{\'\i}nez-Cotelo} }