Quadratically Constrained Myopic Adversarial Channels

We study communication in the presence of a jamming adversary where quadratic power constraints are imposed on the transmitter and the jammer. The jamming signal is assumed to be a function of the codebook, and a noncausal but noisy observation of the transmitted codeword. For a certain range of the noise-to-signal ratios (NSRs) of the transmitter and the jammer, we are able to characterize the capacity of this channel under deterministic encoding. For the remaining NSR regimes, we determine the capacity under the assumption of a small amount of common randomness (at most $\mathcal{O}(\log(n))$ bits in one sub-regime, and at most $\mathcal{O}(n)$ bits in the other sub-regime) available to the encoder-decoder pair. Our proof techniques include a novel myopic list-decoding result for achievability and a Plotkin-type push attack for the converse in a subregion of the NSRs, which may be of independent interest. A short video explaining our work is available at https://youtu.be/0015_W_xhLM.