Pilot based single user frequency offset estimation in spectrally-overlapping FDMA CPM systems

The spectral efficiency of a frequency division multiple access system can be increased by allowing some spectral overlap of adjacent user signals, at the expense of higher interuser interference. We derive the linearized mean square error of pilot based single user maximum likelihood frequency offset estimation in such a system, assuming continuous phase modulation. We consider synchronous as well as asynchronous reception of the pilot signals from the various users. Moreover, the pilot signals are assumed to be either constant and equal to 1, or pseudo-random and independent for all users. In spite of the presence of interuser interference, we obtain relatively simple closed-form expressions, from which the effect of the modulation parameters, the pilot signal structure and the number of users is easily derived.