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Safeguarding Wireless Network with UAVs: A Physical Layer Security Perspective

Qingqing Wu, Weidong Mei, Rui Zhang

arXiv:1902.02472v2cs.IT

TL;DR

Strong ground-to-air line-of-sight links enable more powerful UAV-related jamming, creating a challenging security problem for future wireless networks. The article identifies these UAV security challenges and proposes physical-layer approaches, including signal nulling and UAV-assisted techniques, to secure UAV-ground and terrestrial communications.

  • Problem

    Strong ground-to-air LoS links allow jammers to launch more powerful attacks, making UAV security in future wireless networks a challenging problem.

  • Method

    The article proposes approaches to secure UAV-ground communications against terrestrial attackers and terrestrial communications against malicious UAVs.

  • Results

    Beamforming at a ground base station achieves efficient signal nulling and secure communication, while UAV-BS locations can provide significant secrecy-rate gains.

  • Takeaways & Limitations

    The proposed approaches address security against both terrestrial eavesdroppers or jammers and malicious UAV attacks in future wireless networks.

Abstract

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Integrating unmanned aerial vehicles (UAVs) into future wireless systems such as the fifth-generation (5G) cellular network is anticipated to bring significant benefits for both UAV and telecommunication industries. Generally speaking, UAVs can be used as new aerial platforms in the cellular network to provide communication services for terrestrial users, or become new aerial users of the cellular network served by the terrestrial base stations. Due to their high altitude, UAVs usually have dominant line-of-sight (LoS) channels with the ground nodes, which, however, pose new security challenges to future wireless networks with widely deployed UAVs. On one hand, UAV-ground communications are more prone than terrestrial communications to eavesdropping and jamming attacks by malicious nodes on the ground. On the other hand, compared to malicious ground nodes, malicious UAVs can launch more effective eavesdropping and jamming attacks to terrestrial communications. Motivated by the above, in this article, we aim to identify such new issues from a physical-layer security viewpoint and propose novel solutions to tackle them efficiently. Numerical results are provided to validate their effectiveness and promising directions for future research are also discussed.

I. INTRODUCTION

Integrating UAVs into 5G creates new physical-layer security challenges because LoS-dominant channels expose UAV-ground and terrestrial communications to stronger eavesdropping and jamming. The article identifies these issues and proposes PHY-layer approaches for safeguarding both communication directions.

  • I. INTRODUCTION: UAVs can serve as aerial base stations, relays, or users in future 5G networks.They may provide or enhance communication services for terrestrial users or receive service from terrestrial base stations.
  • I. INTRODUCTION: High-altitude UAVs generally have dominant LoS channels with ground nodes, improving communication performance but increasing interference and security risks.The LoS links can strengthen both legitimate reception and unintended reception or interference.
  • I. INTRODUCTION: A2G and G2A communications are more susceptible than terrestrial communications to terrestrial eavesdropping and jamming, respectively.Ground eavesdroppers can exploit strong LoS reception, while ground jammers can significantly degrade UAV reception or cause communication failure.
  • I. INTRODUCTION: Malicious UAVs can more effectively eavesdrop on wide-area terrestrial communications and disrupt uplink and downlink traffic than conventional ground attackers.Their LoS links, mobility, and ability to track moving targets increase the effectiveness and spread of attacks.
  • I. INTRODUCTION: The article identifies these two UAV-related security problems and proposes physical-layer solutions because conventional terrestrial techniques may be ineffective against LoS-induced UAV threats.The discussion revisits techniques such as artificial noise, cooperative jamming, beamforming, DSSS, and FHSS for UAV security.

II. SECURING LEGITIMATE UAV COMMUNICATIONS IN WIRELESS NETWORK

Legitimate UAV communications are especially vulnerable to terrestrial eavesdropping and jamming because their channels are LoS-dominant. The section presents countermeasures intended to improve UAV communication security and reliability.

  • II. SECURING LEGITIMATE UAV COMMUNICATIONS IN WIRELESS NETWORK: Legitimate A2G and G2A communications are more susceptible to ground eavesdropping and jamming than terrestrial communications because of LoS-dominant channels.
  • II. SECURING LEGITIMATE UAV COMMUNICATIONS IN WIRELESS NETWORK: The section proposes countermeasures to improve the security and reliability of legitimate UAV communications.

A. Protecting A2G Communication from Terrestrial Eavesdropping

Secure A2G communication can exploit UAV altitude, mobility, three-dimensional beamforming, artificial noise, and joint positioning or trajectory design to reduce terrestrial eavesdropping.

  • A. Protecting A2G Communication from Terrestrial Eavesdropping: Strong A2G LoS reception over a large ground area makes preventing terrestrial eavesdropping difficult.
  • 1) UAV 3D Beamforming:: Compared with low-altitude ground BSs, UAV transmitters can use elevation-angle separation to avoid information leakage when legitimate users and eavesdroppers differ spatially.
  • 1) UAV 3D Beamforming:: UAV altitude enables 3D beamforming to exploit different elevation angles and use ZF precoding or artificial noise against ground eavesdroppers.
  • 2) Joint UAV Positioning/Trajectory and Communication Design:: UAV positioning, trajectory, scheduling, and power control can be jointly designed to improve secrecy performance.Altitude and movement can alter blockage, communication distances, and relative legitimate and wiretap channel strengths.
  • 2) Joint UAV Positioning/Trajectory and Communication Design:: Trajectory and communication co-design can adapt in real time to moving eavesdroppers and mission-constrained flight paths.

3) Multi-UAV Cooperation:

A single UAV may lack sufficient communication and maneuvering capability in challenging scenarios, motivating collaborative multi-UAV deployment and aerial jamming for improved secrecy.

  • 3) Multi-UAV Cooperation:: A single UAV may fail to achieve desired secure communication performance against multiple collusive eavesdroppers over a large area.
  • 3) Multi-UAV Cooperation:: Multiple collaborative UAVs can serve separate ground-user clusters, reducing the need to fly over eavesdroppers and thereby reducing information leakage.
  • 3) Multi-UAV Cooperation:: Some UAVs can act as aerial jammers deployed above nearby eavesdroppers to degrade their signal reception.
  • 3) Multi-UAV Cooperation:: Collaborative deployment and trajectory design provide greater flexibility for UAV transmitters seeking better secrecy communication performance.

B. Securing G2A Communication Against Terrestrial Jamming

G2A communications are vulnerable to terrestrial jamming because ground adversaries can reduce legitimate UAV receivers’ SINR over LoS-dominant channels. The paper discusses 3D beamforming, mobility, and D2D forwarding as countermeasures.

  • Ground adversaries can transmit artificial noise to reduce a legitimate UAV receiver’s SINR for decoding.
  • DSSS and FHSS may have low spectrum efficiency and may be insufficient against strong G2A jamming over LoS-dominant channels.
  • 3D receive beamforming at a legitimate UAV provides higher spatial resolution than 2D beamforming for interference suppression.
  • Joint 3D transmit and receive beamforming at the BS and UAV can maximize the legitimate-link SINR.
  • UAV mobility can optimize position or trajectory relative to legitimate transmitters and malicious jammers.
  • D2D forwarding can move data through an unjammed channel from ground nodes near the UAV trajectory to improve uploading reliability.

III. SAFEGUARDING TERRESTRIAL NETWORK AGAINST MALICIOUS UAV ATTACKS

LoS-dominant air-ground channels expose terrestrial communications to malicious UAV eavesdropping across multiple cells. The paper proposes multi-hop D2D relaying and cooperative remote jamming to improve secrecy while managing delay, spectrum, and interference trade-offs.

  • A malicious UAV can wiretap or contaminate transmissions within multiple terrestrial cells.
  • Terrestrial signals are more likely to be wiretapped by a UAV than by a ground receiver under the same link distance.
  • Multi-hop D2D Relaying: Multi-hop D2D relaying uses selected ground nodes and cooperative transmission to exploit spatial or multipath diversity and enhance secrecy rate.
  • Multi-hop D2D Relaying: Excessive relaying hops can increase end-to-end delay, lower spectrum efficiency, and increase eavesdropping exposure.
  • Cooperative Remote Jamming: Cooperative remote jamming selects terrestrial BSs with strong LoS channels to UAV eavesdroppers but favorable separation from legitimate users.
  • Cooperative Remote Jamming: The selected BSs can severely degrade UAV reception while causing negligible interference at the legitimate ground receiver.

B. Anti-UAV Jamming to Terrestrial Communication

Malicious UAVs can strongly jam terrestrial communications, creating particular difficulties for single-antenna downlink receivers. The paper discusses 3D receive beamforming, cooperative cancellation, and D2D relaying over unjammed paths.

  • Malicious UAV jamming is a challenging threat to terrestrial communications because of strong LoS interference.
  • Ground BSs can use receive 3D beamforming to mitigate UAV jamming signals in uplink transmissions.
  • A neighboring idle BS can forward received jamming signals over a high-speed backhaul for cooperative cancellation at the serving BS.
  • For single-antenna downlink receivers, the preceding approaches become infeasible and anti-UAV jamming becomes more challenging.
  • Cooperative D2D communication can relay messages through ground nodes with blocked LoS links to the UAV jammer and onward over an unjammed channel.

IV. NUMERICAL RESULTS AND DISCUSSION

The paper reports numerical results to demonstrate the effectiveness of techniques proposed in the preceding sections.

  • Numerical results demonstrate the effectiveness of techniques proposed in the previous two sections.

A. UAV-assisted Jamming

UAV-assisted jamming improves secrecy by jointly optimizing UAV placement and cooperative interference, but its benefit depends on the UAV-BS transmit-power regime.

  • Placement optimization: Optimizing the UAV-BS location significantly increases secrecy rate compared with hovering at a fixed location, even without a UAV jammer.Proper placement enlarges the receive-SNR difference between the legitimate user and eavesdropper.
  • Jamming-power regime: With fixed jamming power, a UAV jammer can reduce secrecy rate at low UAV-BS transmit power but substantially improve it at high transmit power.At low power, the jammer harms the legitimate receiver more than the eavesdropper; at high power, it disrupts eavesdropper reception and supports closer UAV-BS placement.
  • Joint optimization: Jointly optimizing the UAV jammer’s power and location with the UAV-BS location can make jamming outperform no-jamming operation.The reported design optimizes all three variables rather than fixing the jammer configuration.

B. Cooperative Remote Jamming

Cooperative remote jamming protects terrestrial downlink communication against a UAV eavesdropper by having multiple remote base stations transmit independent jamming signals.

  • Remote-jamming effectiveness: Without cooperative jamming base stations, secrecy rate is approximately zero regardless of the base station transmit power.The UAV’s dominant-LoS eavesdropping channel is much stronger than the legitimate terrestrial fading channel.
  • Remote-jamming effectiveness: Secrecy rate increases rapidly as the number of cooperative base stations increases.Additional jamming base stations create more interference at the UAV eavesdropper while causing negligible interference to the legitimate receiver.
  • Transmit-power effects: Increasing P_T further improves secrecy rate because the legitimate-link rate grows faster than the UAV-eavesdropping rate.The eavesdropping link is increasingly limited by higher G2A interference as P_T rises.

V. CONCLUSIONS AND FUTURE WORK

The paper addresses physical-layer security challenges created by LoS-dominant UAV-ground channels, proposing protections for both aerial and terrestrial communications while identifying detection and spoofing issues for future work.

  • Conclusions: The proposed approaches target secure UAV-ground communications against terrestrial eavesdropping and jamming, and secure terrestrial communications against malicious UAV attacks.The paper frames both aerial and terrestrial links as requiring protection from sophisticated attacks.
  • Limitations and future work: The proposed approaches require further investigation in more challenging practical scenarios involving collusive eavesdroppers and jammers on the ground and in the air.This is identified as a scope boundary for the paper’s physical-layer security designs.
  • Future research directions: UAV-assisted terrestrial adversary detection can use optical cameras and the UAV’s favorable LoS-dominant sensing conditions to improve terrestrial jamming detection.UAVs are described as platforms for detecting, identifying, and tracking malicious ground nodes.
  • Future research directions: Malicious UAV detection must address both active UAVs, which can use signal sensing and ranging, and passive UAVs, which may require radar or computer-vision methods.The paper distinguishes detection of UAV jammers from detection of UAV eavesdroppers.
  • Future research directions: UAV spoofing is an additional threat in which ground adversaries send counterfeit GPS signals to deceive a UAV’s navigation system.This extends the security problem beyond eavesdropping and jamming.
  • Future research directions: UAV mobility and LoS channels also enable legitimate UAVs to perform wireless surveillance and intervention against suspicious or malicious ground communications.This reverses the objective from defending against UAV attacks to designing eavesdropping and jamming schemes for legitimate UAVs.
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