# Covert Surveillance Video Transmission with QAM Constellations Modulation
## 1 Introduction  
The widespread deployment of surveillance systems stands as a cornerstone for bolstering public safety, safeguarding property, and systematically monitoring diverse environments [1; 2]. As the integration of these systems becomes increasingly pervasive, a paramount concern has emerged regarding the security of surveillance video transmissions, prompting the need for sophisticated and resilient solutions. Surveillance technologies, often shrouded in secrecy for operational efficiency [3], encounter distinct challenges, both in wired and wireless domains. Wired surveillance cameras, despite their discreet nature, are susceptible to exposure through the existence of signal lines [4]. On the other hand, the wireless transmission of surveillance videos confronts intricate challenges related to wireless signal detection and potential interruptions [5]. Considering the fact that the majority of existing video compression standards are tailored for relatively benign, nearly error-free environments, their direct applicability to hostile mobile domains, exemplified by standards such as H.265/HEVC (high-efficiency video coding) [6; 7; 8] and AV1 (AOMedia Video 1) [9; 10], is limited. However, certain effective video compression methods, such as H.264/AVC, exhibit the capability of facilitating the transmission of multimedia services, even over channels with very low bit rates [11; 12]. When coupled with advanced modulation schemes in wireless communication, such as Quadrature Amplitude Modulation, the allocation of more bits per transmitted symbol enhances overall transmission capacity [13]. As depicted in Figure 1a, the proposed \(16-\)QAM phase constellation [14] showcases an intricate design strategy, leveraging the sophisticated maximum-minimum distance Gray code methodology presented in [15; 16]. This innovative approach inherently gives rise to the establishment of two subchannels, each characterized by distinct integrities andtailored for specific functionalities within the communication system. The high-priority (HP) subchannel plays a pivotal role in the proposed constellation. It is uniquely characterized by the most significant bit (MSB) of both the in-phase (I) and quadrature-phase (Q) bits. This strategic allocation ensures that critical information is embedded in the most robust part of the signal, enhancing the resilience of the communication system to various environmental challenges. In stark contrast, the low-priority (LP) subchannel is formed by the remaining 2 bits of the 4-bit 16\(-\)QAM symbol; specifically, the least significant bits (LSBs). While inherently carrying less weight in terms of information content, the LP subchannel contributes to the overall versatility of the communication system by accommodating supplementary data and enhancing overall spectral efficiency. The transmission performance of both the HP and LP subchannels is intricately linked to channel conditions and noise characteristics, as highlighted in previous works [17; 18; 19]. The robustness and reliability of the communication system, particularly in scenarios with dynamic channel conditions, are contingent upon the optimization and adaptation of these subchannels. Expanding our exploration to the realm of 64\(-\)QAM, as illustrated in Figure 1b, the complexity of the phase constellation intensifies with the introduction of three subchannels: HP, medium priority (MP), and LP. This multifaceted design aims to strike a delicate balance between increasing transmission rates and ensuring reliability in the communication system [13]. The HP subchannel continues to serve as the backbone for critical information, while the introduction of the medium priority (MP) subchannel provides an additional tier for accommodating diverse data types, thereby enhancing the system's adaptability to a variety of communication scenarios.