Approximate Capacity of Fast Fading Interference Channels with no CSIT Shorter versions of this work appeared in Joysonfading,JoysonAFisit with outline of proofs. This version has complete proofs. This work was supported in part by NSF grants 1514531 and 1314937

We develop a characterization of fading models, which assigns a number called logarithmic Jensen’s gap to a given fading model. We show that as a consequence of a finite logarithmic Jensen’s gap, approximate capacity region can be obtained for fast fading interference channels (FF-IC) for several scenarios. We illustrate three instances where a constant capacity gap can be obtained as a function of the logarithmic Jensen’s gap. Firstly for an FF-IC with neither feedback nor channel state information at transmitter (CSIT), if the fading distribution has finite logarithmic Jensen’s gap, we show that a rate-splitting scheme based on average interference-to-noise ratio (inr) can achieve its approximate capacity. Secondly we show that a similar scheme can achieve the approximate capacity of FF-IC with feedback and delayed CSIT, if the fading distribution has finite logarithmic Jensen’s gap. Thirdly, when this condition holds, we show that point-to-point codes can achieve approximate capacity for a class of FF-IC with feedback. We prove that the logarithmic Jensen’s gap is finite for common fading models, including Rayleigh and Nakagami fading, thereby obtaining the approximate capacity region of FF-IC with these fading models.