Transmit Optimization for Symbol-Level Spoofing

With recent developments in wireless communication technologies, malicious users can use them to commit crimes or launch terror attacks, thus imposing new threats on public security. To quickly respond to these attacks, authorized parities need to intervene in the malicious communication links over the air. This paper investigates the emerging wireless communication intervention problem at the physical layer. Unlike prior studies using jamming to disrupt or disable the targeted wireless communications, we propose a new physical-layer spoofing approach to change their communicated information. Consider an abstract three-node model over additive white Gaussian noise channels, in which a legitimate spoofer aims to spoof a malicious communication link from a malicious transmitter to a malicious receiver, such that the received message at the receiver is changed from the transmitter's originally sent message to the one desired by the spoofer. We propose a new symbol-level spoofing scheme, where the spoofer designs the spoofing signal by exploiting the symbol-level relationship between each original constellation point of the transmitter and the desirable one of the spoofer. In particular, the spoofer aims to minimize the average spoofing-symbol-error-rate (SSER), which is defined as the average probability that the symbols decoded by the malicious receiver fail to be changed or spoofed, by designing its spoofing signals over symbols subject to the average transmit power constraint. By considering two cases when the malicious transmitter employs the widely-used binary phase-shift keying and quadrature phase-shift keying modulations, we obtain the respective optimal solutions to the two average SSER minimization problems. Numerical results show that the symbol-level spoofing scheme with optimized transmission achieves a much lower average SSER, as compared with other benchmark schemes.