On multi-carrier systems robustness to Doppler in fast varying flat fading wireless channel

Abstract

In this paper, the performance of a generalized multi-carrier Frequency Division Multiplexing (FDM) system - including Orthogonal Frequency Division Multiplexing (OFDM) and Filter-Bank Multi-Carrier (FBMC) - is analyzed in terms of normalized interference power in a fast-varying flat-fading downlink channel. The analysis is done assuming a conventional correlator-based receiver using three families of pulse shapes: orthogonal time-limited pulse shapes, orthogonal frequency-limited pulse shapes, and non-orthogonal pulse shapes. The analysis is done for the Rayleigh random channel with different Doppler spreads, and interference distribution over sub-carriers and symbols is analyzed per pulse shape. Interference reduction by reducing the bandwidth efficiency through turning off some sub-carriers and reducing symbol density is then analyzed. After that, the special ability of non-orthogonal pulse shapes to have more flexible density reduction is indexed and studied. The theoretical study, validated by Monte Carlo simulations, showed that for low, high, and extreme Doppler spreads, the appropriate pulse shapes (resp. system density) to be used are respectively time or frequency limited orthogonal pulse shapes (resp. 100%), short-tail frequency-limited pulse shapes (resp. 50%), and time and frequency limited non-orthogonal pulse shapes (resp. 25%).