Information Bytes

Matthieu Bloch
School of Electrical and Computer Engineering
Georgia Institute of Technology

Recent works

  1. M. Tahmasbi, A. Savard, and M. R. Bloch, “Covert Capacity of Non-Coherent Rayleigh-Fading Channels.” submitted to IEEE Transactions on Information Theory, Oct. 2018.
    arXiv

    The covert capacity is characterized for a non-coherent fast Rayleigh-fading wireless channel, in which a legitimate user wishes to communicate reliably with a legitimate receiver while escaping detection from a warden. It is shown that the covert capacity is achieved with an amplitude-constrained input distribution that consists of a finite number of mass points including one at zero and numerically tractable bounds are provided. It is also conjectured that distributions with two mass points in fixed locations are optimal.

    @misc{Tahmasbi2018a,
      author = {Tahmasbi, Mehrdad and Savard, Anne and Bloch, Matthieu R},
      title = {Covert Capacity of Non-Coherent Rayleigh-Fading Channels},
      howpublished = {submitted to \emph{IEEE Transactions on Information Theory}},
      month = oct,
      year = {2018},
      eprint = {1810.07687},
      groups = {Steganography and covert communications}
    }
    

  2. M. Tahmasbi and M. R. Bloch, “First and Second Order Asymptotics in Covert Communication.” accepted to IEEE Transactions on Information Theory, Oct. 2018.
    DOI arXiv

    We study the first- and second-order asymptotics of covert communication over binary-input DMC for three different covertness metrics and under maximum probability of error constraint. When covertness is measured in terms of the relative entropy between the channel output distributions induced with and without communication, we characterize the exact first- and second-order asymptotics of the number of bits that can be reliably transmitted with a maximum probability of error less than εand a relative entropy less than δ. When covertness is measured in terms of the variational distance between the channel output distributions or in terms of the probability of missed detection for fixed probability of false alarm, we establish the exact first-order asymptotics and bound the second-order asymptotics. PPM achieves the optimal first-order asymptotics for all three metrics, as well as the optimal second-order asymptotics for relative entropy. The main conceptual contribution of this paper is to clarify how the choice of a covertness metric impacts the information-theoretic limits of covert communications. The main technical contribution underlying our results is a detailed expurgation argument to show the existence of a code satisfying the reliability and covertness criteria.

    @misc{Tahmasbi2017,
      author = {Tahmasbi, Mehrdad and Bloch, Matthieu R},
      title = {First and Second Order Asymptotics in Covert Communication},
      howpublished = {accepted to \emph{IEEE Transactions on Information Theory}},
      month = oct,
      year = {2018},
      doi = {10.1109/TIT.2018.2878526},
      eprint = {1703.01362},
      groups = {Steganography and covert communications}
    }
    

  3. K. S. K. Arumugam and M. R. Bloch, “Embedding Covert Information in Broadcast Communications.” submitted to IEEE Transactions on Information Forensics and Security, Aug. 2018.
    arXiv

    We analyze a two-receiver binary-input discrete memoryless broadcast channel, in which the transmitter communicates a common message simultaneously to both receivers and a covert message to only one of them. The unintended recipient of the covert message is treated as an adversary who attempts to detect the covert transmission. This model captures the problem of embedding covert messages in an innocent codebook and generalizes previous covert communication models in which the innocent behavior corresponds to the absence of communication between legitimate users. We identify the exact asymptotic behavior of the number of covert bits that can be transmitted when the rate of the innocent codebook is close to the capacity of the channel to the adversary. Our results also identify the dependence of the number of covert bits on the channel parameters and the characteristics of the innocent codebook.

    @misc{Arumugam2018b,
      author = {Arumugam, Keerthi Suria Kumar and Bloch, Matthieu R.},
      title = {Embedding Covert Information in Broadcast Communications},
      howpublished = {submitted to \emph{IEEE Transactions on Information Forensics and Security}},
      month = aug,
      year = {2018},
      eprint = {1808.09556},
      groups = {Steganography and covert communications}
    }
    

  4. G. Cervia, L. Luzzi, M. Le Treust, and M. R. Bloch, “Strong coordination over noisy channels with strictly causal encoding.” accepted to Allerton Conference on Communication, Control, and Computing, Aug. 2018.
    arXiv

    We consider a network of two nodes separated by a noisy channel, in which the input and output signals have to be coordinated with the source and its reconstruction. In the case of strictly causal encoding and non-causal decoding, we prove inner and outer bounds for the strong coordination region and show that the inner bound is achievable with polar codes.

    @misc{Cervia2018a,
      author = {Cervia, Giulia and Luzzi, Laura and {Le Treust}, Mael and Bloch, Matthieu R},
      title = {Strong coordination over noisy channels with strictly causal encoding},
      howpublished = {accepted to \emph{Allerton Conference on Communication, Control, and Computing}},
      month = aug,
      year = {2018},
      eprint = {1809.10934},
      groups = {Coordination of networks}
    }
    


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