Securing wireless relaying communication for dual unmanned aerial vehicles with unknown eavesdropper

Highlights

• We consider a new optimization problem for dual UAVs that one UAV is utilized as a mobile wireless relay and the other auxiliary UAV is used to interfere with the eavesdropper. Here, the eavesdropper whose actual position is unknown attempts to eavesdrop on information illegally.

• We formulate a critical problem that how to maximize the average secrecy rate with the constraints of trajectories and transmit power of dual UAVs as well as the information causality. This optimization problem is thorny because of the characteristic of non-convex.

• We propose an iterative algorithm that jointly optimize the trajectories and transmit power for dual UAVs with multiple constraints. We decompose the original problem into three tractable subproblems by applying the successive convex approximation technique. Then, we alternately optimize the trajectories and transmit power for dual UAVs through a method of block coordinate descent to make the average secrecy rate maximized.

Abstract

Unmanned aerial vehicles (UAVs) face a lot of security challenges due to the openness of their wireless communication. In this paper, we investigate how to improve the security of wireless communication when the UAV is utilized as a wireless relay. We consider a new scenario where the dual UAVs are employed cooperatively to transmit confidential information and an eavesdropper whose actual position is unknown attempts to eavesdrop on the information illegally. We propose an optimization problem for the average secrecy rate under multiple constraints. The optimization problem we proposed is non-convex and complicated. We design an iterative algorithm that jointly optimizes the trajectories and transmit power to make the average secrecy rate maximized via the block coordinate descent and successive convex approximation techniques. The feasibility of this method is verified by numerical simulation.

Introduction

Unmanned aerial vehicles (UAVs) have been expanded from the military domain into civilian markets, with the growing interest in unmanned technology [1], [2], [3], [4], [5], [6], [7], [8]. Especially, they play an important role in wireless communications thanks to their low operation cost, fast placement speed, extremely flexible deployment, and the ability to quickly adapt to special scenarios. They can easily change their positions dynamically and provide users with communication in an emergency situation. When a region needs to quickly restore communication, UAVs can be usually served as an onboard communication platform to provide temporary communication [9]. Apart from this, when the direct communication link between two or more remote users is blocked, it can also be used as a mobile relay to resume wireless communication [10]. The communication system composed of UAVs can communicate through line-of-sight (LoS) links so that the communication performance between the source point and the target points can be greatly improved [11].

Although the above-mentioned UAV-based communication systems have numerous advantages, it often faces new challenges in actual design and operation. In reality, UAVs have to collect, process, and transmit a large amount of private data. It is clear that UAV communication links are vulnerable to malicious attacks and eavesdropping [12], [13]. Therefore, security is a critical issue in the construction and operation of UAV networks. When eavesdroppers exist, it is important to design effective methods to improve the secrecy rate of UAV networks[14], [15], [16].

The problem of improving the secrecy rate of UAV when the eavesdroppers exist has received a great deal of attention in the past. To improve the secrecy rate of data transmission, Shen et al. proposed a algorithm that iteratively optimize the trajectory of a relay UAV [17]. In [18], Li et al. researched the secrecy communication issue where dual UAVs were cooperatively applied. They maximized the secrecy rate by jointly optimizing the trajectories and transmit power of both source UAV and jammer UAV. In [19], Lee et al. also designed the scene of dual UAVs where the source UAV transmitted data to multiple users. They maximized the minimum secrecy rate among the targets by jointly optimizing the trajectories and the transmit power of the UAVs along with the scheduling of the targets. Apart from this, many researchers have also studied the security of UAV networks from different angles [20], [21], [22], [23], [24]. The above work mainly has the following defects,

• The similarity in the existing literature is that the position of the eavesdropper was assumed to be known in their scenarios. In practice, because the eavesdropper may remain silent to hide his location [25], [26], it is difficult for us to achieve the precise position coordinates.

• Most existing literature considers the UAV with transmitting function rather than a transceiver [18], [19]. However, to restore long distance communication between two users, UAVs had to act as a relay platform that they can receive and forward data [17].

To overcome these defects, in this paper, we consider a new scenario where dual UAVs are employed cooperatively to improve the quality of information transmission. One UAV is utilized as a mobile relay and the other is a jammer that tends to disturb eavesdroppers who can illegally eavesdrop on the information between the relaying UAV and the user. It is worth noting that the interference of user’s legitimate communications is also inevitable. Therefore, we take this interference into account when designing the achievable rate of the user. During the process of trajectory optimization, the jammer UAV is kept as far away as possible from user and close to the eavesdropper. In this scenario, the actual position of the eavesdropper is unknown. Meanwhile, when the relaying UAV can receive and forward data, it will be subject to the information causality from the transmitter.

The secrecy rate is an important index to measure the security of the scenario considered above. The critical issue in this scenario is that how to maximize the average secrecy rate. In this paper, we propose an iterative algorithm that jointly optimizes the trajectories and transmit power to maximize the average secrecy rate. The main contributions of this paper are as follows:

• We consider a new optimization problem for dual UAVs that one UAV is utilized as a mobile wireless relay and the other auxiliary UAV is used to interfere with the eavesdropper. Here, the eavesdropper whose actual position is unknown attempts to eavesdrop on information illegally.

• We propose an iterative algorithm that jointly optimize the trajectories and transmit power for dual UAVs with multiple constraints. The original optimization problem is thorny because of the characteristic of non-convex. We decompose the original problem into three tractable subproblems by applying the successive convex approximation technique. Then, we alternately optimize the trajectories and transmit power for dual UAVs through a method of block coordinate descent to make the average secrecy rate maximized.

This paper is organized as follows: Section 2 is an introduction of system model for UAV system and the critical problem to be addressed. Section 3 introduces the iterative algorithm that jointly optimizes the trajectories and transmit power to maximize the average secrecy rate. We validate the efficacy of the proposed optimization algorithm in Section 4. In the end, we have a conclusion in Section 5.