The problem of covert communication over Multiple-Input Multiple-Output (MIMO) Additive White Gaussian Noise (AWGN) channels is investigated, in which a transmitter attempts to reliably communicate with a legitimate receiver while avoiding detection by a passive adversary. The covert capacity of the MIMO AWGN channel is characterized under a variational distance covertness constraint when the MIMO channel matrices are static and known. The characterization of the covert capacity is also extended to a class of channels in which the legitimate channel matrix is known but the adversary’s channel matrix is only known up to a rank and a spectral norm constraint.
The problem of covert communication over Multiple-Input Multiple-Output (MIMO) Additive White Gaussian Noise (AWGN) channels is investigated, in which a transmitter attempts to reliably communicate with a legitimate receiver while avoiding detection by a passive adversary. The covert capacity of the MIMO AWGN channel is characterized under a variational distance covertness constraint when the MIMO channel matrices are static and known. The characterization of the covert capacity is also extended to a class of channels in which the legitimate channel matrix is known but the adversary’s channel matrix is only known up to a rank and a spectral norm constraint.
We consider the problem of covert communication over Multiple-Input Multiple-Output (MIMO) Additive White Gaussian Noise (AWGN) channels, in which a transmitter attempts to reliably communicate with a legitimate receiver while ensuring a low probability of detection by an adversary. We exactly characterize the covert capacity under a variational distance covertness constraint when MIMO channel matrices are static and known to all parties. We also characterize the covert capacity for a class of channels in which the legitimate channel matrix is known but the adversary's channel matrix is only known to satisfy a rank and a spectral norm constraint.
As claimed in International Telecommunications Union (ITU) Recommendation ITU-R M.2160, 6G communication systems require extremely high-security and low-latency communication, necessitating the study of covert communication operating at finite blocklengths. In the point-to-point (P2P) setting, covert communication enables a transmitter to send messages reliably over a noisy channel to a legitimate receiver without being detected by any third party. Under the covertness metric of Kullback–Leibler divergence (KLD), we derive exact second-order asymptotics for P2P covert communication over a multiple-input multiple-output (MIMO) additive white Gaussian noise (AWGN) channel. In particular, our theoretical benchmarks refine the first-order asymptotics of Wang and Bloch (TIFS 2021), which is known as the square root law by showing that the non-asymptotic maximal number of transmitted messages has a back off that scales in the order Θ(n41) beyond the first-order term scaling in the order Θ(n21) when the blocklength is n. Thus, our second-order asymptotic bound provides a better approximation to the finite blocklength performance of optimal codes. Furthermore, compared with the single antenna result of Yu et al. (arXiv:2305.17924v3), we demonstrate the impact of the number of antennas m and reveal spatial diversity gains of MIMO, advocating the use of MIMO for covert communication to achieve a high transmission rate. To prove our results, we extend the quasi-η-neighborhood framework from single-antenna real value channels to multi-antenna complex value MIMO channels. To ensure covertness, the transmission power vanishes as the blocklength n increases. Thus, we judiciously analyze the finite blocklength performance of MIMO communication by modifying critical steps concerning the Berry–Esseen Theorem to deal with vanishing second and third absolute moments of information densities that rely on blocklength, which is in stark contrast with the non-covert case.
We consider the problem of covert communication with random slot selection over binary-input Discrete Memoryless Channels (DMCs) and Additive White Gaussian Noise (AWGN) channels, in which a transmitter attempts to reliably communicate with a legitimate receiver while simultaneously maintaining covertness with respect to (w.r.t.) an eavesdropper. Covertness refers to the inability of the eavesdropper to distinguish the transmission of a message from the absence of communication, modeled by the transmission of a fixed channel input. Random slot selection refers to the transmitter’s ability to send a codeword in a time slot with known boundaries selected uniformly at random among a predetermined number of slots. Our main contribution is to develop bounds for the information-theoretic limit of communication in this model, called the covert capacity, when the number of time slots scales sub-exponentially with the codeword length. Our upper and lower bounds for the covert capacity are within a multiplicative factor of2independent of the channel. This result partially fills a characterization gap between the covert capacity without random slot selection and the covert capacity with random selection among an exponential number of slots in the codeword length. Our key technical contributions consist of 1) a tight upper bound for the relative entropy characterizing the effect of random slot selection on the covertness constraint in our achievability proof; 2) a careful converse analysis to characterize the maximum allowable weight or power of codewords to meet the covertness constraint. Our results suggest that, unlike the case without random slot selection, the choice of covertness metric does not change the covert capacity in the presence of random slot selection.
Covert communication has recently been recognized as a highly promising security technology that enables a transmitter Alice to reliably and covertly communicate with a receiver Bob without being detected by a malicious warden. Available works on covert communication mainly focus on scenarios with only one warden, while the fundamental limits of covert communication in more practical multi-warden scenarios remain largely unknown. This paper therefore investigates the fundamental limits of covert communication over an additive white Gaussian noise (AWGN) channel in the presence of multiple wardens. We first consider a scenario with two wardens and derive the maximum number of bits Alice can transmit to Bob over n channel uses while ensuring a negligible detection probability at wardens. We then generalize this result to the multi-warden case and find that the minimal power of wardens has impacts on the scaling law of the performance limits of covert communication over AWGN channels.
We consider a problem of communication over a continuous-time additive Gaussian noise channel. A covertness constraint is imposed on the communication protocol, which says that the channel output must statistically resemble pure noise. When there is no bandwidth constraint on the input, we argue that the covert communication capacity of this channel is positive, in contrast to the band-limited case where covertness requires that the amount of transmission grow at most like the square root of total communication time. This claim is formally proven in the case where the Gaussian noise is white with respect to the bandwidth used by the transmitter.
Covert communication over an additive white Gaussian noise (AWGN) channel with finite block length is investigated in this paper. The attention is on the covert criterion, which has not been considered in finite block length circumstance. As an accurate quantity metric of discrimination, the variation distance with given finite block length n and signal-noise ratio (snr) is obtained. We give both its analytic solution and expansions which can be easily evaluated. It is shown that K-L distance, which is frequently adopted as the metric of discrimination at the adversary in asymptotic regime, is not convincing in finite block length regime compared with the total variation distance. Moreover, the convergence rate of the total variation with different snr is analyzed when the block length tends to infinity. The results will be very helpful for understanding the behavior of the total variation distance and practical covert communication.