Interference Alignment and the Generalized Degrees of Freedom.pdfVIP

Interference Alignment and the Generalized Degrees of Freedom of the X Channel Chiachi Huang, Viveck R. Cadambe, Syed A. Jafar Electrical Engineering and Computer Science University of California Irvine Irvine, California, USA Email: {chiachih, vcadambe, syed}@uci.edu Abstract—We study the sum capacity of the X channel equally strong in the dB scale, the GDOF perspective provides generalization of the symmetric 2-user interference channel. In a richer characterization by allowing the full range of relative this X channel, there are 4 independent messages, one from each signal strengths in the dB scale. transmitter to each receiver. We characterize the sum capacity of a deterministic version of this channel, and obtain the generalized A useful technique in the characterization of the GDOF degrees of freedom characterization for the Gaussian version. of a wireless network is the deterministic approach [5]. The The regime where the X channel outperforms the underlying deterministic approach essentially maps a Gaussian network interference channel is explicitly identified, and an interesting to a deterministic channel, i.e, a channel whose outputs are interference alignment scheme based on a cyclic decomposition deterministic functions of its inputs. The deterministic channel of the signal space is shown to be optimal in this regime. captures the essential structure of the Gaussian channel, but I. INTRODUCTION is significantly