LTV equalization of CPM signals over doubly-selective aeronautical channels

In this paper, transmission of continuous phase modulated (CPM) signals over time- and frequency-selective (i.e., doubly-selective) channels is considered. Leveraging on the well-known Laurent representation for a CPM signal, we design a two-stage receiver, composed of a linear time-varying (LTV) equalizer, followed by a detector: the former one aims at mitigating the channel dispersion and it is synthesized under the zero-forcing (ZF) or minimum mean-square error (MMSE) criterion; the latter one recovers the transmitted symbols from the pseudo-symbols of the Laurent representation in a simple recursive manner. Relying on a Basis Expansion Model (BEM) of the doubly-selective channel, we derive frequency-shift (FRESH) versions of the proposed LTV equalizers, discussing also their complexity issues and proposing simplified implementations. Monte Carlo simulation results, carried out in two typical aeronautical scenarios (arrival/takeoff and en-route), show that the proposed approach is able to work satisfactorily also over rapidly time-varying channels.