Abstract
In recent years, there has been a noticeable increase in interest in the possibilities of embedding additional data in the constellation of an already existing information signal in radio technology. This solution more precisely is based on adding a low power signal (or signals) to a stronger signal (cover). As will be described in the article, this technique is used in numerous radio communication areas, such as watermarking, covert channel creation, and multiple access techniques. Typically, those areas are considered as independent research topics. Our comparison suggests that these areas are closely related. In this article, a comprehensive survey of the implementation of signal superposition is conducted with an emphasis on the similarities and differences between individual solutions. Since the nature of the signal model entails certain problems in the security area, we provide the reader with a review of the state-of-the-art research on this topic, including the PLS (physical layer security) and LPD (low probability of detection) issues.
Highlights
Nowadays, digital modulations are widely used in wireless communication systems
By watermarking and covert channels, we move to the P-NOMA multiple access techniques, which are combined by the same signal but from different applications
The article presents how, using one solution consisting of creating a radio waveform, which is a superposition of signals, we can watermark the transmission, create covert channels or multi-access systems
Summary
Digital modulations are widely used in wireless communication systems. A modulated signal can be depicted by a constellation diagram. The main advantage of the analyzed method of signal embedding is simplicity (transmitter and receiver) and quite good performance. The simplicity of the receiver can be understood as a post-IC (interference cancellation), where interference constitutes the stronger (strongest) of the signals This method represents the most effective IC-based reception technique in terms of bit-error-rate (BER) performance [2]. We are convinced that it is worth considering applying methods typical for the covert channel in order to increase the security of NOMA system. This should be carried out in our future research. Since this paper deals with a specific solution, the DPC techniques will not be discussed further
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