  We introduce the Fluctuating Two-Ray (FTR) fading model, a new statistical
channel model that consists of two fluctuating specular components with random
phases plus a diffuse component. The FTR model arises as the natural
generalization of the two-wave with diffuse power (TWDP) fading model; this
generalization allows its two specular components to exhibit a random amplitude
fluctuation. Unlike the TWDP model, all the chief probability functions of the
FTR fading model (PDF, CDF and MGF) are expressed in closed-form, having a
functional form similar to other state-of-the-art fading models. We also
provide approximate closed-form expressions for the PDF and CDF in terms of a
finite number of elementary functions, which allow for a simple evaluation of
these statistics to an arbitrary level of precision. We show that the FTR
fading model provides a much better fit than Rician fading for recent
small-scale fading measurements in 28 GHz outdoor millimeter-wave channels.
Finally, the performance of wireless communication systems over FTR fading is
evaluated in terms of the bit error rate and the outage capacity, and the
interplay between the FTR fading model parameters and the system performance is
discussed. Monte Carlo simulations have been carried out in order to validate
the obtained theoretical expressions.
