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    Characterization of Terahertz Band Transmittance from Sea-Level to Drone Altitudes
    (Institute of Electrical and Electronics Engineers Inc., 2021) Saeed, Akhtar; Saleem, Ammar; Gurbuz, Ozgur; Akkas, Mustafa Alper
    Terahertz (THz) communications has been recognized as a candidate technology for the next generation networks as the THz band offers large bandwidth and data rates, catering for the problem of spectrum scarcity. However, THz band propagation is highly affected by atmospheric absorption due to water vapor molecules, in addition to the high spread loss. Modeling of the absorption loss is essential for a realistic closed form THz path loss model, which can be employed in link level analysis and formulations. For this purpose, in this paper, we characterize the THz transmittance i.e., absorption gain using the data obtained from Line-by-Line Radiative Transfer Model (LBLRTM) tool, considering the available frequency channels selected via water-filling, altitudes from sea-level to drone altitudes and various transmission ranges. We analyze the modeling of transmittance as a function of: (1) Frequency, (2) Distance and (3) Altitude, using different statistical models including, Polynomial, Exponential and Gaussian models. Numerical results depict that modeling transmittance as a function of distance and altitude are feasible approaches using the exponential and the polynomial models, respectively. This work can be extended to characterize the transmittance for all frequencies over the entire THz band, and also for higher altitudes and longer ranges. © 2021 IEEE.
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    Joint Resource Allocation for Terahertz Band Drone Communications
    (Ieee-Inst Electrical Electronics Engineers Inc, 2024) Saeed, Akhtar; Erdem, Mikail; Saleem, Ammar; Gurbuz, Ozgur; Akkas, Mustafa Alper
    This article proposes a joint resource allocation approach for Terahertz (THz) band (0.75-4.4 THz) drone-to-drone communications, studying spectrum and power allocation together with antenna beamwidth adjustment. Considering various drone (mis)alignment and mobility scenarios under a 3D sectored antenna model, the capacity of the proposed spectrum allocation scheme, MaxActive, is compared to existing Common Flat Band (CFB) and standard (STD) schemes, each with water-filling (WF) and equal power (EP) allocations. Results show that up to 6 orders of magnitude improvements are observed with beamwidth optimization, and MaxActive with EP performs close to CFB and STD schemes with WF in all scenarios, even under realistic beam misalignment fading instances (low and high). For drone-to-drone communications, our results prove that the THz band can provide high capacity, in the order of Tbps, which can be preserved well with beam alignment/adjustment. Evaluating also the complexity of all considered resource allocation techniques, it is concluded that MaxActive with EP allocation stands out as the most feasible scheme in terms of practical implementation with the best performance.
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    Terahertz communications at various atmospheric altitudes
    (Elsevier, 2020) Saeed, Akhtar; Gürbüz, Özgür; Akkaş, Mustafa Alper
    Terahertz communications offers a massive potential for the prospective beyond 5G wireless systems, as the band offers huge bandwidth and data rates as compared to the existing sub 6 GHz bands, which are almost saturated. In this paper, we investigate the feasibility of wireless communications over the Terahertz-band (0.75–10 THz) at various atmospheric altitudes, considering different transmission distances and directions by realistically calculating the absorption loss, which is the major limiting factor affecting the propagation of THz waves through the earth’s atmosphere. Four practical altitudes are considered, corresponding to Drone-to-Drone (D2D), Jet plane-to-Jet plane (J2J), Unmanned Aerial Vehicle (UAV)-to-UAV, and near-space Satellite-to-Satellite (S2S) communications. Following comparison and validation with two real-world experimental results from the literature measured at the sea-level, Line by Line Radiative Transfer Models (LBLRTM) is used to obtain realistic THz-band transmittance values against each altitude case and setting. Subsequently, absorption loss and total path loss values are computed and mean total path loss sensitivity is further observed against a range of transmission directions via zenith angle variations from vertically-up to vertically-down communication. Numerical results show that as the altitude increases, the concentration of the water vapor molecules decreases, enabling the communication over the THz-band (0.75–10 THz) to be more feasible as compared to the sea-level communication. Moreover, the total usable bandwidth results over the THz-band (0.75–10 THz) exhibit that the upper bounds of 8.218 THz, 9.142 THz and 9.25 THz are usable up to the transmission distance of 2 km against the total antenna gains of 80 dBi for J2J, U2U and S2S communication cases, respectively.
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    THz band drone communications with practical antennas: Performance under realistic mobility and misalignment scenarios
    (Elsevier, 2025) Saeed, Akhtar; Erdem, Mikail; Gurbuz, Ozgur; Akkas, Mustafa Alper
    For 6G non-terrestrial communications, drones will offer uninterrupted connectivity for surveillance, sensing, and localization. They will also serve as drone base stations to support terrestrial base stations, providing large bandwidth, high-rate, and ultra-reliable low latency services. In this paper, for the first time in the literature, we depict the true performance of Terahertz (THz) band communications among drones by applying various channel selection and power allocation schemes with practical THz antennas within (0.75-4.4) THz under realistic mobility and misalignment scenarios. Through numerical simulations, we unveil the capacity of drone links under different channel selection and power allocation schemes within 10s to 100s of Gbps at distances (1-100) m, when drones are in motion and subject to (mis)alignment due to mobility and even under beam misalignment fading. However, when exposed to real drone mobility traces, the performance of all channel selection schemes drops significantly, sometimes by up to six orders of magnitude, due to the occasional reverse orientations of antennas. In addition to the capacity analysis, we report available frequency bands (transmission windows) considering all schemes and mobility patterns. We also identify a band that is commonly available under all considered mobility and misalignment settings, and we evaluate its performance in terms of spectral and energy efficiencies, which can be useful in designing THz transceivers for drone communications. Our findings emphasize the essence of active beam control solutions to achieve the desired capacity potential of THz drone communications, while also highlighting the challenges of utilizing the THz band for drone communications.
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    Variable-bandwidth model and capacity analysis for aerial communications in the terahertz band
    (IEEE-Inst Electrical Electronics Engineers Inc, 2021) Saeed, Akhtar; Gürbüz, Özgür; Bicen, Ahmet Ozan; Akkaş, Mustafa Alper
    In this work, 0.75-10 THz band is explored for non-terrestrial communications, by leveraging the improved atmospheric conditions at various altitudes. A channel model for aerial communications at THz band is proposed to calculate the common flat bands for frequency-selective path gain and the colored noise spectrums, both of which are highly affected by the atmospheric conditions. With capacity computation based on common flat bands, we consider aerial vehicles at different altitudes and distances, under realistic weather and channel fading conditions, due to beam misalignment and also multi path fading. An extensive capacity analysis is presented, considering equal and water-filling power allocation. It is shown that, when there is no fading, capacity for aerial links is several orders of magnitude larger than the sea-level capacity. When ergodic capacity is computed for the fading scenarios, it is shown that the impact of fading vanishes with altitude. Sea-level ergodic capacity is increased by an order of magnitude for drone-to-drone communications, providing several Tbps at 10 m range, while 10s of Tbps is achievable among jet planes and UAVs, and several 100s of Tbps is possible for satellites/cubesats at 1 km under fading, suggesting that THz band is a promising alternative for aerial communications.