UAV Trajectory Optimization for Directional THz Links Using Deep Reinforcement Learning

As an alternative solution for quick disaster recovery of backhaul/fronthaul links, in this paper, a dynamic unmanned aerial vehicles (UAV)-assisted heterogeneous (HetNet) network equipped with directional terahertz (THz) antennas is studied to solve the problem of transferring traffic of distributed small cells. To this end, we first characterize a detailed three-dimensional modeling of the dynamic UAV-assisted HetNet, and then, we formulate the problem for UAV trajectory to minimize the maximum outage probability of directional THz links. Then, using deep reinforcement learning (DRL) method, we propose an efficient algorithm to learn the optimal trajectory. Finally, using simulations, we investigate the performance of the proposed DRL-based trajectory method

FSO Communication for High Speed Trains: Blind Data Detection and Channel Estimation

International audienceWe consider an free-space optical (FSO) system for high-speed trains where the sampling clock offset is randomly changing and the receiver does not have any information on the instantaneous channel fading coefficient. Based on the use of multiple samplers at the receiver, we propose a novel sequence blind detection method, thus without requiring any pilot symbol. Furthermore, using the detected data, we propose a channel estimation scheme for the considered system

Blind Signal Detection Under Synchronization Errors for FSO Links with High Mobility

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Differential Pulse-Amplitude Modulation Signaling for Free-Space Optical Communications

International audienceTo improve the bandwidth efficiency of free-space optical (FSO) systems and at the same time to reduce the impact of the background noise, we propose a differential M-ary pulse-amplitude modulation (M-PAM) signaling scheme that uses two laser transmitters. We first consider the condition that the receiver perfectly knows the instantaneous channel coefficient and compare the performance of the proposed differential PAM with the conventional PAM signaling and show the improved performance when the background noise level is relatively high. Second, we consider the practical situation where the receiver has to estimate the channel for signal detection. We propose an estimation scheme based on the characteristics of the differential PAM signaling while requiring no pilot symbol transmission. The proposed data-aided channel estimation is performed on a sequence of received PAM symbols. We show that for a sufficiently large observation window, the proposed estimation method allows achieving a performance close to the perfect channel knowledge

Differential Pulse-Amplitude Modulation Signaling for Free-Space Optical Communications

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