Page 11 - ITU Journal Future and evolving technologies Volume 2 (2021), Issue 7 – Terahertz communications

ITU Journal on Future and Evolving Technologies, Volume 2 (2021), Issue 7

Self-configuring asynchronous sleeping in heterogeneous networks

Pages 51–62
Ali Medlej, Eugen Dedu, Kamal Beydoun, Dominique Dhoutaut

Nowadays, the heterogeneous wireless nano‑network topology becomes a need for diverse applications
based on heterogeneous networks composed of regions of different node densities. In Wireless
Nano‑networks (WNNs), nodes are of nano‑metric size and can be potentially dense in terms of
neighbouring nodes. Nano‑nodes have limited resources in terms of processing, energy and memory
capabilities. In nano‑network(s), even in a communication range limited to tens of centimeters,
thousands of neighbours can be found. We proposed a fine‑grained duty‑cycling method (sleeping
mechanism), appropriate to nanonodes, which aims to reduce the number of receptions seen by a node
during data packet routing. The present study reveals the usefulness of implementing the sleeping
mechanism in heterogeneous networks, as well as configuring a dynamic awaken duration for nodes
based on a density estimation algorithm. We also proposed an algorithm that helps in increasing the
reliability of the packet received by the destination node.
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Hierarchical beam alignment in SU-MIMO terahertz communications

Pages 63–80
Yifei Wu, Johannes Koch, Martin Vossiek, Wolfgang Gerstacker

Single‑Carrier Frequency Division Multiple Access (SC‑FDMA) is a promising technique for high data
rate indoor Terahertz (THz) communications in future beyond 5G systems. In an indoor propagation
scenario, the Line‑Of‑Sight (LOS) component may be blocked by the obstacles. Thus, efficient THz
SC‑FDMA communications require a fast and reliable Beam Alignment (BA) method for both LOS
and Non‑Line‑Of‑Sight (NLOS) scenarios. In this paper, we first adopt the hierarchical discrete Fourier
transform codebook for LOS BA, and introduce the hierarchical k‑means codebook for NLOS BA to
improve the beamforming gain. Simulation results illustrate that the hierarchical DFT codebook and the
hierarchical k‑means codebook can achieve the beamforming gain close to that of the maximum ratio
transmission in LOS and NLOS cases, respectively. Based on these two codebooks, we propose a
Multi‑Armed Bandit (MAB) algorithm named Hierarchical Beam Alignment (HBA) for single‑user
SC‑FDMA THz systems to reduce the BA latency. HBA utilizes a hierarchical structure in the adopted
codebook and prior knowledge regarding the noise power to speed up the BA process. Both theoretical
analysis and simulation results indicate that the proposed BA method converges to the optimal beam
with high probability for both the hierarchical DFT codebook and the hierarchical k‑means codebook
in the LOS and NLOS scenarios, respectively. The latency introduced by HBA is significantly lower
when compared to an exhaustive search method and other MAB‑based methods.
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