The capacity of finite Abelian group codes over symmetric memoryless channels

  • Authors:
  • Giacomo Como;Fabio Fagnani

  • Affiliations:
  • Laboratory for Information and Decision Systems, Massachusetts Institute of Technology, Cambridge, MA and Dipartimento di Matematica, Politecnico di Torino, Torino, Italy;Dipartimento di Matematica, Politecnico di Torino, Torino, Italy

  • Venue:
  • IEEE Transactions on Information Theory
  • Year:
  • 2009

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Abstract

The capacity of finite Abelian group codes over symmetric memoryless channels is determined. For certain important examples, such as m-PSK constellations over additive white Gaussian noise (AWGN) channels, with m a prime power, it is shown that this capacity coincides with the Shannon capacity; i.e., there is no loss in capacity using group codes. (This had previously been known for binary-linear codes used over binary-input output-symmetric memoryless channels.) On the other hand, a counterexample involving a three-dimensional geometrically uniform constellation is presented in which the use of Abelian group codes leads to a loss in capacity. The error exponent of the average group code is determined, and it is shown to be bounded away from the random-coding error exponent, at low rates, for finite Abelian groups not admitting Galois field structure.