# Covert Surveillance Video Transmission with QAM Constellations Modulation
## 1 Introduction
In summary, the proposed phase constellations, whether 16\(-\)QAM or 64\(-\)QAM, represent a sophisticated amalgamation of innovative design principles, ensuring adaptability, reliability, and efficiency within the ever-evolving landscape of communication systems. While ensuring the transmission reliability of surveillance systems, the security of the surveillance systems should also be well considered. Besides preventing information content from being eavesdropped, we can even hide the existence of the information transmission process. Both conventional encryption and physical-layer security techniques aim to prevent transmission content from being eavesdropped [20; 21]. To enhance the security of wireless surveillance systems, covert communication technologies have attracted substantial attention. Covert communication aims not only to protect the content of surveillance transmission but also hide the very existence of the surveillance transmission. Within the realm of covert communication, the paramount objective extends beyond securing the content of communication from adversarial interception: the imperative to hide the very occurrence of communication activities from potential adversaries is equally crucial to ensure the covert  
Figure 1: Some QAM constellation sets adopted in surveillance video transmission. In previous works, covert communication has been a focal point for governmental and military entities aiming to regulate the activities of specific organizations or conceal the intentions of operations within defined geographical areas [23; 24]. Early wireless covert channels were predominantly explored through spread spectrum techniques [25]. However, the foundational limits of covert communication within the realm of information theory remained largely unexplored until the investigation of the _square root law_ (SRL) within channels affected by additive white Gaussian noise (AWGN) [26]. Subsequently, the SRL was extended to diverse communication systems, including binary symmetric channels [27; 28], discrete memoryless channels [29; 30], and multiple access channels [31; 32]. It is noteworthy that the SRL posits that if more than \(\mathcal{O}(\sqrt{n})\) bits are transmitted through \(n\) channels, then as \(n\) approaches infinity, there is a high probability of the transmitter being detected or the receiver incurring a nonzero probability of decoding error [22]. Furthermore, the covert rate approaches zero as \(n\) grows to infinity, i.e., \(\lim_{n\rightarrow\infty}\frac{\mathcal{O}(\sqrt{n})}{n}=0\). This finding has spurred researchers to investigate methods for achieving positive covert rates [33]. Various strategies have been proposed to attain positive covert rates, including utilizing uniformed jammers [34], introducing noise uncertainty to adversaries, enlisting external friendly helpers, and manipulating the timing of covert communications [24]. However, sustaining the functionality of these energy-intensive communication devices poses a challenge, especially in unsafe environments or complex, sensitive areas that are challenging to access. The presence of communication devices or conspicuous electricity consumption may attract the attention of adversaries, underscoring the intricacies of maintaining covert operations in such contexts [35]. To covertly transmit surveillance videos to a designated recipient, the overall process encompasses the following procedural steps. Surveillance cameras capture monitoring data to generate surveillance videos. Subsequently, these videos are subjected to compression using an appropriate protocol, such as H.264/AVC. The compressed surveillance videos then undergo a covert transmission phase, comprising three steps: (1) adopting an appropriate encoding method, such as 16\(-\)QAM, 64\(-\)QAM, or 256\(-\)QAM, based on channel conditions; (2) configuring suitable transmission power for the covert transmission of the surveillance videos; (3) the receiver decoding the videos according to the selected encoding method.