Kangarshahi, Ehsan AsadiGuillén i Fábregas, A. (Albert)2023-03-092023-03-092021Kangarshahi EA, Guillén i Fàbregas A. A single-letter upper bound to the mismatch capacity. IEEE Trans Inf Theory. 2021;67(4):2013-33. DOI: 10.1109/TIT.2021.30580700018-9448http://hdl.handle.net/10230/56120We derive a single-letter upper bound to the mismatched-decoding capacity for discrete memoryless channels. The bound is expressed as the mutual information of a transformation of the channel, such that a maximum-likelihood decoding error on the translated channel implies a mismatched-decoding error in the original channel. In particular, it is shown that if the rate exceeds the upper-bound, the probability of error tends to one exponentially when the block-length tends to infinity. We also show that the underlying optimization problem is a convex-concave problem and that an efficient iterative algorithm converges to the optimal solution. In addition, we show that, unlike achievable rates in the literature, the multiletter version of the bound cannot not improve. A number of examples are discussed throughout the paper.application/pdfeng© 2021 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works. http://dx.doi.org/10.1109/TIT.2021.3058070info:eu-repo/semantics/articlehttp://dx.doi.org/10.1109/TIT.2021.3058070d-decoderd-capacitymismatchshannon capacitychannel capacitydecodinginfo:eu-repo/semantics/openAccess