Year: 2025
Type: preprint
Abstract: We show two properties of i.i.d. code ensembles over classical-quantum (CQ) channels with arbitrary output states. The first property is that the probability distribution of the error exponent across the ensemble accumulates above a threshold that is strictly larger than the CQ random coding exponent (RCE) at low rates, while coinciding with it at rates close to the mutual information of the channel. This result, combined with the works by Dalai, Renes, Li and Yang and Cheng and Liu, implies that the ensemble distribution of error exponents concentrates around the CQ RCE in the high rate regime. Moreover, in the same rate region the threshold we derive coincides with the ensemble-average of the exponent, that is, the CQ typical random coding (TRC) exponent. The second property we derive is that the probability that a randomly selected code from an ensemble contains a nested code of the same rate such that each of its codewords achieves the CQ expurgated exponent goes to one asymptotically in the codeword length. Such nested code can be obtained by expurgating a vanishingly small fraction of codewords as the codeword length increases. This result refines Holevo's work [5], which proved that the expurgated exponent can be achieved by discarding the worst half of the codewords from at least one code in the ensemble.
Source: arXiv (Cornell University)
Institution: Universitat Politècnica de Catalunya
Language: English
Subfield: Artificial Intelligence
Field: Computer Science
Domain: Physical Sciences
Open Access status: green
Awards: G1175115578, G1561925909, G2038104832, G2064873908, G210041235, G2120394195, G2262748287, G2355262757, G2462415295, G2601397997, G288263039, G3005324705, G300979063, G34346518, G3480869486, G3546882995, G3681454997, G4042783231, G425668148, G4526231891, G5080475149, G5195188938, G5852091828, G69051668, G7084143925, G7181157420
OpenAlex ID: W4416104255
Cites:
Cited by:
Related to: