## 2 Related Work  
Our project is intended to create an alternative to radio communication in WSN by using covert communication using audio steganography techniques. In the literature, various studies have focused on concealing information in audio for covert communication. For instance, [PERSON] et al. [23] used Discrete Wavelet Transform (DWT) and Singular Value Decomposition (SVD) to hide dialogue within musical audio. They applied SVD to the approximation coefficients, effectively embedding secret audio signals. Similarly, [PERSON] et al. [24] proposed Adaptive Multi-Level Phase Coding (AMPC) to address performance and security issues, achieving 24 kbps at 32 dB SNR using Interval-Centered Quantization (ICQ). [PERSON] et al. [25] developed a robust method against LSB removal and resampling attacks, demonstrating that their approach maintains audio quality and withstands Gaussian white noise. In terrestrial environments, researchers have explored two natural sounds for covert communication. [PERSON] et al. [8] used cricket sounds, achieving a rate of 46.9 bit/s by encoding information into pulse sequences. Additionally, [PERSON] et al. [16] proposed a method for covert communication by mimicking the songs of the Verditer Flycatcher, achieving a transmission rate of about 58 bps with high covertness and low bit error rates in forest environments. However, they did not consider specific _On/Off_ periods. Bird songs, particularly from Passeriform birds, offer a higher frequency range (2-7 kHz) compared to cricket sounds (around 4.3 kHz), making them suitable for our purposes [26, 27, 28, 29]. In underwater scenarios, researchers have used aquatic animal sounds for covert communication. [PERSON] et al. [10] mimicked dolphin whistles and clicks for synchronization and information encoding, achieving 37 bit/s. They also used whale sounds in a Direct Sequence Spread Spectrum (DSS) signal for covert communication [12]. [PERSON] et al. [11] used sea lion sounds, achieving a baud rate of 20 bit/s. [PERSON] et al. [9] and [PERSON] et al. [17] used sperm-whale call pulses, achieving transmission rates of 37.5 bit/s and 27 bit/s. These works focused on synchronization and information codes, while our approach modifies the entire spectrum of bird songs during _On_ periods. [PERSON] et al. [18] also proposed a method to enhance underwater communication security by mimicking dolphin whistles, achieving a rate of 45.28 bps. [PERSON] et al. [13] used machine learning to classify dolphin whistles for covert communication, achieving low Bit Error Rates (BER). They later modeled Right Humpback Whales' whistles for information hiding [15]. [PERSON] et al. [18] used Time-Frequency Contour techniques to improve signal-to-noise ratios in dolphin whistles. Unlike these works, we use real bird sounds and modify original recordings to insert information. The jamming attack disrupts communication channels by introducing external electromagnetic energy. [PERSON] et al. [30] showed how jamming attacks affect WSNs using MAC protocols. [PERSON] et al. [31] highlighted the vulnerability of wireless networks to jamming attacks due to open wireless channels. Our work proposes an alternative communication method to avoid electromagnetic jamming attacks. [PERSON] et al. [32] proposed an energy-saving method in the MAC layer using sleep/awake schedules, synchronizing nodes only with their parent and child nodes. Our approach proposes a statistical behavior of sleep/awake periods based on the natural behavior of bird sounds to better conceal the covert channel. In summary, while significant progress has been made in the field of covert communication using various natural sounds across different environments, our approach stands out by leveraging real bird songs for terrestrial wireless sensor networks. Unlike in previous works, that have focused on synthetic signals or water environments, our method changes original bird recordings by inserting information into them, thus enhancing the covert nature of the communication channel.