Interference alignment and the generalized degrees of freedom of the X channel

  • Authors:
  • Chiachi Huang;Viveck R. Cadambe;Syed A. Jafar

  • Affiliations:
  • Electrical Engineering and Computer Science, University of California Irvine, Irvine, California;Electrical Engineering and Computer Science, University of California Irvine, Irvine, California;Electrical Engineering and Computer Science, University of California Irvine, Irvine, California

  • Venue:
  • ISIT'09 Proceedings of the 2009 IEEE international conference on Symposium on Information Theory - Volume 3
  • Year:
  • 2009

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Abstract

We study the sum capacity of the X channel generalization of the symmetric 2-user interference channel. In this X channel, there are 4 independent messages, one from each transmitter to each receiver. We characterize the sum capacity of a deterministic version of this channel, and obtain the generalized degrees of freedom characterization for the Gaussian version. The regime where the X channel outperforms the underlying interference channel is explicitly identified, and an interesting interference alignment scheme based on a cyclic decomposition of the signal space is shown to be optimal in this regime.