Spectral iterative algorithm for RCS computation in electrically large or intermediate perfectly conducting cavities

A novel algorithm designed to compute efficiently and accurately the high-frequency electromagnetic scattering from open-ended waveguide cavities is presented. The cavity is converted into a stepped-waveguide model so that the field spectra are propagated, forward and backward, along each waveguide section. As boundary conditions for perfect electric conductors are applied via image theory, they are of local nature and take into account only the first-order interactions between each pair of waveguide sections. Accordingly, additional forward-backward iterations must be performed if multiple interactions are to be taken into account. Finally, the radar cross section due to the interior irradiation is calculated by a Kirchhoff-based aperture integral. Good agreement with method of moments and hybrid modal solutions is found, as well as with experimental data, for two-dimensional and three-dimensional cavities with rectangular cross section.Peer Reviewe

Spectral efficiency in reference-signal-assisted low-power wireless communication

Comunicació presentada a la IEEE International Conference on Communications (ICC '08), celebrada a Beijing (Xina) els dies 19, 20, 21, 22 i 23 de maig de 2008, organitzada per l'Institute of Electrical and Electronics Engineers (IEEE).Expressions relating spectral efficiency, power and Doppler spectrum are derived for low-power Rayleighfaded wireless channels with proper complex signaling. No/nside information on the state of the channel is assumed at the receiver. Rather, periodic reference signals are postulated in/naccordance with the functioning of most wireless systems. In contrast with most previous studies, which relied on block-fading channel models, a continuous-fading model is adopted. This embeds the Doppler spectrum directly in the/nderived expressions thereby imbuing them with practical significance

Per-antenna rate and power control for MIMO layered architectures in the low- and high-power regimes

In a MIMO layered architecture, several codewords/nare transmitted from a multiplicity of antennas. Although the/nspectral efficiency is maximized if the rates of these codewords/nare separately controlled, the feedback rate within the link/nadaptation loop is reduced if they are constrained to be identical./nThis poses a direct tradeoff between performance and/nfeedback overhead. This paper provides analytical expressions/nthat quantify the difference in spectral efficiency between both/napproaches for arbitrary numbers of antennas. Specifically, the/ncharacterization takes place in the realm of the low- and highpower/nregimes via expansions that are shown to have a wide/nrange of validity./nIn addition, the possibility of adjusting the transmit power/nof each codeword individually is considered as an alternative to/nthe separate control of their rates. Power allocation, however,/nturns out to be inferior to rate control within the context of this/nproblem

1-bit MIMO for terahertz channels

Comunicació presentada a 5th International ITG Workshop on Smart Antennas (WSA 2021), celebrat del 10 al 12 de novembre de 2021 a Costa Blava, França.This paper tackles the problem of multiple-input multiple-output communication with 1-bit digital-to-analog and analog-to-digital converters. With the information-theoretic capacity as benchmark, the complementary strategies of beamforming and equiprobable signaling are contrasted in the regimes of operational interest. Line-of-sight settings under both spherical and planar wavefronts are considered, respectively representative of short and long transmission ranges at mmWave and terahertz frequencies. A judicious combination of beamforming and equiprobable signaling is shown to operate within a modest gap from capacity.Work supported by the European Research Council under grant agreement 694974, by Projects RTI2018- 102112 and 101040, and by ICREA

Capacity-approaching rate function for layered multiantenna architectures

The simultaneous use of multiple transmit and receive antennas can unleash very large capacity increases in rich multipath environments. Although such capacities can be approached by layered multi-antenna architectures with per-antenna rate control, the need for short-term feedback arises as a potential impediment, in particular as the number of antennas—and thus the number of rates to be controlled—increases. What we show, however, is that the need for short-term feedback in fact vanishes as the number of antennas and/or the diversity order increases. Specifically, the rate supported by each transmit antenna becomes deterministic and a sole function of the signal-to-noise, the ratio of transmit and receive antennas, and the decoding order, all of which are either fixed or slowly varying. More generally, we illustrate -through this specific derivation— /nthe relevance of some established random CDMA results to the single-user multi-antenna problem

Spectral efficiency in reference-signal-assisted low-power wireless communication

Comunicació presentada a la IEEE International Conference on Communications (ICC '08), celebrada a Beijing (Xina) els dies 19, 20, 21, 22 i 23 de maig de 2008, organitzada per l'Institute of Electrical and Electronics Engineers (IEEE).Expressions relating spectral efficiency, power and Doppler spectrum are derived for low-power Rayleighfaded wireless channels with proper complex signaling. No/nside information on the state of the channel is assumed at the receiver. Rather, periodic reference signals are postulated in/naccordance with the functioning of most wireless systems. In contrast with most previous studies, which relied on block-fading channel models, a continuous-fading model is adopted. This embeds the Doppler spectrum directly in the/nderived expressions thereby imbuing them with practical significance

Per-antenna rate and power control for MIMO layered architectures in the low- and high-power regimes

In a MIMO layered architecture, several codewords/nare transmitted from a multiplicity of antennas. Although the/nspectral efficiency is maximized if the rates of these codewords/nare separately controlled, the feedback rate within the link/nadaptation loop is reduced if they are constrained to be identical./nThis poses a direct tradeoff between performance and/nfeedback overhead. This paper provides analytical expressions/nthat quantify the difference in spectral efficiency between both/napproaches for arbitrary numbers of antennas. Specifically, the/ncharacterization takes place in the realm of the low- and highpower/nregimes via expansions that are shown to have a wide/nrange of validity./nIn addition, the possibility of adjusting the transmit power/nof each codeword individually is considered as an alternative to/nthe separate control of their rates. Power allocation, however,/nturns out to be inferior to rate control within the context of this/nproblem

Interplay of spectral efficiency, power and doppler spectrum for reference-signal-assisted wireless communication

Expressions relating spectral efficiency, power, and Doppler spectrum, are derived for Rayleigh-faded wireless channels with Gaussian signal transmission. No side information on the state of the channel is assumed at the receiver. Rather, periodic reference signals are postulated in accordance with the functioning of most wireless systems. The analysis relies on a well-established lower bound, generally tight and asymptotically /nexact at low SNR. In contrast with most previous studies, which relied on block-fading channel /nmodels, a continuous-fading model is adopted. This embeds the Doppler spectrum directly in the derived expressions, imbuing them with practical significance. /nClosed-form relationships are obtained for the popular Clarke-Jakes spectrum and informative expansions, valid for arbitrary spectra, are found for the low- and high-power regimes. While the paper focuses on scalar channels, the extension to multiantenna settings is also discussed

Capacity-approaching rate function for layered multiantenna architectures

The simultaneous use of multiple transmit and receive antennas can unleash very large capacity increases in rich multipath environments. Although such capacities can be approached by layered multi-antenna architectures with per-antenna rate control, the need for short-term feedback arises as a potential impediment, in particular as the number of antennas—and thus the number of rates to be controlled—increases. What we show, however, is that the need for short-term feedback in fact vanishes as the number of antennas and/or the diversity order increases. Specifically, the rate supported by each transmit antenna becomes deterministic and a sole function of the signal-to-noise, the ratio of transmit and receive antennas, and the decoding order, all of which are either fixed or slowly varying. More generally, we illustrate -through this specific derivation— /nthe relevance of some established random CDMA results to the single-user multi-antenna problem

Terahertz transmit beamforming with 1-Bit DACs and ADCs

This paper tackles the problem of transmit beamforming with 1-bit digital-to-analog and analog-to-digital converters. While, at frequencies above 100 GHz, such 1-bit converters are instrumental to restrain the power consumption and enable transmissions spanning many gigahertz of bandwidth, they fundamentally alter the nature of the communication problem. Transmit beamforming, a key task when communicating at these high frequencies, then amounts to identifying the quartet of channel-dependent transmit vectors that maximizes the mutual information. This problem, which becomes unwieldy for even modest numbers of antennas, is herein tackled by means of an unsupervised learning approach that proves effective for very large arrays.Comunicació presentada a: 29th European Signal Processing Conference (EUSIPCO) celebrat del 23 al 27 d'agost de 2021 a Dublin, Irlanda.This work was supported by the European Research Council under the H2020 Framework Programme/ERC grant agreement 694974, by MINECO's Projects RTI2018-102112 and 101040, and by the ICREA Academia program