## 1 Introduction  
With the development of electromagnetic weapons, Electronic Warfare (EW) has been rising as the future form of wars [1, 2]. In EW, the attackers' purposes are to capture military secrets and cause the malfunctioning of core electronic equipment such as radios, radars, or spy satellites using Electromagnetic Pulse (EMP) and High-Power Microwave (HPM) attacks. Leakage of military secrets can directly cause a significant loss of military forces. To defend against message leakage, more complex and robust defense systems are required such as Low Probability of Detection (LPD), Low Probability of Interception (LPI), or Low Probability of Exploitation (LPE) communication algorithms [3, 4, 5, 6]. LPD is defined as a system in which an eavesdropper cannot detect a signal at all. LPI is defined as a system in which an eavesdropper detects the presence of a signal but cannot identify the characteristics of the signal. LPE is defined as a system in which the eavesdropper detects the presence of and identifies the characteristics of a signal but cannot exploit the message. These solutions are processed at the physical-layer level. Physical-layer processing is studied to reduce complexity by hiding signals with dummy noises [7] or by using a dirty constellation algorithm. However, there is a limitation in that such systems cannot create complete noise. Various security methods in the communication field have been proposed. Cryptography methods such as symmetrical and asymmetrical key encryption are used in wireless communication systems [8; 9]. However, these methods may generate additional delays because of complex procedures due to using additional bits for security, but they are not particularly critical in the channel coding process. Physical-layer security processes have been discussed and studied to overcome these disadvantages [10; 11; 12; 13; 14]. However, still, a complex and long sequence, which can occur with additional computational overhead, is required to be used for strong security performances. Therefore, scholars are studying waveform-modifying security methods to achieve lower latency, lower complexity, and higher security [15; 16]. In this paper, we propose a flexible and adaptable covert communication algorithm through a noise-shaping process in the physical layer to overcome the problems of implementation complexity and hardware dependency. The proposed algorithm focuses on modifying In-Phase and Quadrature (I/Q) forms of data. The proposed algorithm is composed of shared noise-shaping modifying factors, which are shared between the designated transmitter and receiver. After the conventional modulation process, the transmitter reshapes a noise shape using the shared noise-shaping modifying factors and the original I/Q data. The receiver or attacker, a third party, will detect the signal as a noisy signal. Since the receiver knows the shared factors, the receiver can recover the correct I/Q data while an attacker cannot. Most previous works have concluded their studies at the simulation level while not considering real implementation. We present a practical implementation of noise signaling through SDR radios which can flexibly function with installed user-customizable software. With the implementation process, we present the realistic possibility to implement a noise-signaling system. As mentioned in [17; 18], ultimate physical-layer security may be achievable when noise shaping is very similar to Additive White Gaussian Noise (AWGN). However, due to the limitations of radio hardware, it is not possible to obtain a perfect AWGN shape; certain boundaries need to be optimized to achieve both good security and recovery performance. Therefore, we decided to form the I/Q constellation data as a ring shape rather than full AWGN. With the implemented ring-shaped signaling system SDR radios, we evaluate the system with the Bit Error Rate (BER) and Probability of Modulation Identification (PMI) performance metrics.