Abstract
Due to the air-to-ground line-of-sight communication links, it is challenging to deal with the security threats in the wireless system with unmanned aerial vehicles (UAVs) integrated. In a UAV-enabled mobile relay system, the paper proposes a novel cooperative communication scheme from a physical layer security perspective to address the security issue. Specifically, in a mobile relay system where a UAV relay is employed to forward confidential information between two ground users, an eavesdropper exists on the ground wiretapping the relay UAV. To enhance the security performance of the system, we introduce a friendly UAV jammer transmitting interference signals and confusing the eavesdropper. A secrecy rate maximization problem is then formulated, subject to mobility constraints, power constraints on both UAVs and the information-causality constraint on the relay UAV. To solve the non-convex optimization problem with closely coupled variables, we decouple the problem into more tractable subproblems. An iterative algorithm is thus proposed to optimize the transmit power and flight trajectory of both UAVs alternately via the update-rate-assisted block coordinate descent and successive convex approximation techniques. Simulation results demonstrate that proposed cooperative design can significantly improve the secrecy rate of the UAV-enabled mobile relay system compared to benchmark schemes.
Highlights
Unmanned aerial vehicles (UAVs) have the characteristics of high mobility and line-of-sight (LoS) dominated unmanned aerial vehicle (UAV)-ground communication links
With the evolution of the 5G standard, the non-terrestrial network (NTN) will be the hot spot in the future, where UAVs will continue to play an essential role in providing ubiquitous access
To fill the vacancy in the research on the secure UAV-enabled mobile relay system, we propose a novel scheme where two UAVs are cooperatively deployed to improve the security performance of the UAV-enabled relay communication system with a ground eavesdropper
Summary
Unmanned aerial vehicles (UAVs) have the characteristics of high mobility and line-of-sight (LoS) dominated UAV-ground communication links. B. PROBLEM FORMULATION Taking the information-causality constraint (6) into account, we aim to maximize the average achievable secrecy rate (7) by jointly optimizing trajectory and transmit power for both the relay UAV and the jammer UAV over all time slots. The details of the proposed joint trajectory and transmit power optimization algorithm in the cooperative UAV-enabled secure mobile relay scheme are summarized in Algorithm 1. In (31), (d) holds since the first-order Taylor expansions in (20), (22), (23), and (27) are tight at given local points, respectively, which means that problem (P5.2) at QkR has the same objective value as that of problem (P5); (e) holds since in step 5 of Algorithm 1 with given QkJ+1, PkJ , and PkR, problem (P5.2) is solved optimally with solution QkR+1; (c) holds since the objective value of problem (P5.2) is the lower bound of that of its original problem (P5) at QkR+1. Algorithm 1 can be practically implemented with relatively fast convergence for wireless networks containing a moderate number of devices
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