Junfan Hu

In this paper, we analyse the reliability performance for the orthogonal time frequency space (OTFS) based low earth orbit (LEO)-satellite-air-terrestrial (LSAT) communication system. To facilitate the downlink transmission from the LEO satellite to the terrestrial node, a group of randomly distributed mobile unmanned aerial vehicles (UAVs) are employed to serve as the relays with decode-and-forward (DF) scheme. With the aid of stochastic geometry approach, the distribution of mobile UAVs is modeled by Poisson point processes (PPP) process with two motion modes: user dependent model (UDM) and user independent model (UIM). We derive the approximate closed-form expressions for the outage probabilities of the LSAT system under two UAV motion modes. Finally, the simulation results demonstrate that the reliability of the LSAT system can be significantly enhanced by using OTFS scheme, and by properly adjusting the UAV deployment parameters, corroborating the theoretical derivation.

Orthogonal Time Frequency Space (OTFS) technique has received significant research attentions as a potential solution for ensuring robust and reliable communication in high-mobility mobile communication scenarios in recent years. In this paper, we propose a model-driven deep learning based orthogonal approximate message passing (OAMP) detector to harvest the time and frequency diversity promised by OTFS modulation and improve the detection performance in the presence of channel estimation error. The intelligent detector is designed by unfolding the OAMP detector with adding several learnable parameters. Simulation results demonstrate that, with much reduced complexity and much fewer parameters, the proposed detector can achieve better error performance under channel estimation errors compared with other nonlinear detectors.

With the aim of ensuring secure transmission in high-mobility wireless scenarios, this paper proposes a 2D permutation-aided Orthogonal Time Frequency Space (OTFS) secure transmission scheme, which uses the Gosudarstvennyi Standard (GOST) algorithm to perform disturbance control on the OTFS modulation domain. Furthermore, we develop an improved SeLective Mapping (SLM) algorithm, which can significantly improve the Peak-to-Average Power Ratio (PAPR) problem with very low complexity. In addition, we carry out the security analysis, investigating the proposed scheme’s resistance performance to a range of effective attacks. Finally, our numerical results show that our proposed transmission scheme can guarantee the underlying security property of OTFS.

As an important technique of enabling global access for 6G, low earth orbit satellite (LEO-Sat) communication is still facing the challenges of large path-loss, and severe Doppler effect. This paper studies the reliability performance of a downlink LEO-Sat communication system, where the orthogonal time frequency space (OTFS) scheme is employed to combat severe Doppler effect. Further, the unmanned aerial vehicle (UAV) based cooperative transmission is developed, in order to compensate for the large margin of path-loss caused by the long transmission distance. In particular, the closed-form expression for the outage probability of the OTFS based LEO-Sat transmission is derived, where the novel moment matching approach is used to closely approximate the PDF of a sum of shadowing Rician (SR) variables. Further, the condition of using UAV cooperation is obtained so that the positive reliability gain is guaranteed. Finally, both the theoretical analysis and simulation results show that, the OTFS scheme can significantly outperform the traditional OFDM scheme, while demanding to carefully address the trade-off between reliability improvement and implementation complexity determined by modulation size.

Recently, satellite communication (Sat-Com) has developed rapidly, and its security is critical. In this letter, we investigate the security performance for an uplink low earth orbit (LEO) Sat-Com system, where the cooperative UAV is employed to send jamming signals against the reconnaissance satellite. In particular, the uplink transmission is based on the orthogonal time frequency space (OTFS) technique, in order to combat the severe Doppler effect caused by the high mobility of the LEO satellite. As a pioneer work, we derive the closed-form expression for the security outage probability (SOP) at the legitimate receiver, where a novel moment matching approach is used for finding a summed probability distribution function (PDF) of the shadowed-Rician (SR) distributed terms. Furthermore, we analyze the SOP advantage achieved by the OTFS scheme over the traditional orthogonal frequency division multiplexing (OFDM) scheme. Simulation results validate the theoretical results for SOP performance of the uplink LEO Sat-Com, and show the effectiveness of employing UAV jammer in terms of enhancing secrecy transmission.