Uncertain Location Transmitter and UAV-Aided Warden Based LEO Satellite Covert Communication Systems

TL;DR

This work addresses covert satellite communications under mobility and location-uncertainty by modeling an Alice-to-Bob link assisted by a UAV warden. It develops a formal detection framework based on false-alarm and miss-detection probabilities tied to a detection window $L$, derives the distance distribution between Alice and Willie in a square area, and introduces a practical optimization algorithm to maximize the catch probability $P_{ca}$; it also studies how splitting the message into $n$ chunks influences the overall catching probability $P_{ov}$ and provides an optimization method for $n$. Key contributions include closed-form expressions for $P_{FA}$, $P_{MD}$, and practical expressions for $P_{ca}$ and $P_{ov}$, plus Algorithm 1 for $L^*$ and Algorithm 2 for $n^*$ validated by simulations. The results reveal that both the detection window and chunking significantly affect covert performance, offering design insights for secure NTN (non-terrestrial network) communications with mobility and localization uncertainty. The framework enables principled risk management in satellite-UAV covert channels and points to future work on rapid direction-finding and additional concealment technologies.

Abstract

We propose a novel covert communication system in which a ground user, Alice, transmits unauthorized message fragments to Bob, a low-Earth orbit satellite (LEO), and an unmanned aerial vehicle (UAV) warden (Willie) attempts to detect these transmissions. The key contribution is modeling a scenario where Alice and Willie are unaware of each other's exact locations and move randomly within a specific area. Alice utilizes environmental obstructions to avoid detection and only transmits when the satellite is directly overhead. LEO satellite technology allows users to avoid transmitting messages near a base station. We introduce two key performance metrics: catch probability (Willie detects and locates Alice during a message chunk transmission) and overall catch probability over multiple message chunks. We analyze how two parameters impact these metrics: 1) the size of the detection window and 2) the number of message chunks. The paper proposes two algorithms to optimize these parameters. The simulation results show that the algorithms effectively reduce the detection risks. This work advances the understanding of covert communication under mobility and uncertainty in satellite-aided systems.

Figures (8)

• Figure 1: Covert communication model in the LEO satellite communication systems.
• Figure 2: Definitions of Willie's catching radius and Alice's observation radius.
• Figure 3: The catching probability $P_{ca}$ versus the detection window size $L$ for Alice's transmission power $P_{a}$ (left), the message length $M$ (middle), and the square area size $u$ (right), respectively.
• Figure 4: The optimal detection window size $L^*$ (left) and its corresponding catching probability $P_{ca}$ (right) versus the Alice's transmission power $P_{a}$ (upper), the message length $M$ (middle), and the square area size $u$ (lower), respectively.
• Figure 5: The overall catching probability $P_{ov}$ versus the splitting-chunks quantity $n$ for Alice's transmission power $P_{a}$ (left), the message length $M$ (middle), and the square area size $u$ (right), respectively.