International. Current wireless networks, e.g. WiFi, LTE-Advanced, etc., operate on the lower band of the radio spectrum, below 6 GHz. Experts warn that soon this band will become congested due to the explosive growth of data traffic. An estimated 17.722 million connected devices are in 2024.
To meet the increasingly large and ubiquitous demand for broadband wireless connectivity, communication over the terahertz (THz) band (0.1-10 THz) is seen as a necessary option for 6G networks and beyond, due to the large amount of spectrum available on these frequencies.
A paper published in the IEEE Journal on Selected Areas in Communications presents a new communication design that improves wireless broadband connectivity. Konstantinos Dovelos and Boris Bellalta from the Wireless Networking research group, the Department of Information and Communications Technologies (DTIC) of UPF and the IoT Lab have participated, with the collaboration of Michail Matthaiou and Hien Quoc Ngo, researchers at Queen's University belfast (United Kingdom).
Mitigate propagation losses of THz signals
Despite the potential of wireless links in the THz band to achieve bandwidths of terabits per second, THz signals suffer severe propagation losses due to their short wavelength. However, the use of multiple transmission and reception antennas following Massive Multiple-Input Multiple-Output (MIMO) techniques allows to compensate for these losses, while expanding the communication range through beamforming.
Ultra-large bandwidths of transmissions in the THz band make standard beamforming and channel estimation techniques ineffective
Beamforming basically consists of concentrating and directing the radiated electromagnetic signal optimally between the sender and the receiver. To be able to use beamforming, it is necessary to know precisely the channel between the sender and the receiver, which is why there are different techniques for estimating it.
A new design that mitigates signal lag
The ultra-large bandwidths of transmissions in the THz band render standard beamforming and channel estimation techniques ineffective. In the article published in the IEEE Journal on Selected Areas in Communications (JSAC), "we have shown that when the signal propagation time between the transmitter's own antennas exceeds the symbol time of the data to be sent, the response of the antenna array ceases to be homogeneous. This aspect, typically assumed in the design of current beamforming techniques, makes them ineffective to be used in the THz band, which our proposal solves by adjusting these delays in a controlled manner, "says Konstantinos Dovelos, first author of the article.
And adds Dovelos: "In addition, with the subtle design of the channel estimator that we have presented, the transmitter can obtain reliable information on the state of the channel with a low estimation cost, minimizing the impact on the gain in capacity of the link."
The numerical results obtained in this work show the performance gains offered by the design proposed by these researchers compared to the use of techniques developed without taking into account the essential characteristics of the THz band, opening the way for the achievement of multi-Gbps speeds at distances of several meters.
Reference work
Konstantinos Dovelos, Michail Matthaiou, Hien Quoc Ngo, and Boris Bellalta (2021), "Channel Estimation and Hybrid Combining for Wideband Terahertz Massive MIMO Systems", IEEE Journal on Selected Areas in Communications, advanced online edition, doi: 10.1109/JSAC.2021.3071851.
Source: Universitat Pompeu Fabra.
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