This paper addresses the effect of timing synchronization errors for two different multicarrier techniques CP-OFDM and FBMC. Such errors degrade the performance of the reference receiver by causing multi user interference. This interference occurs when the signals from different transmitters arrive at a given receiver with arbitrary timing misalignments, leading to the destruction of orthogonality between subcarriers. In this paper, we propose a model of interference that provides a useful computational tool in order to analyze the performance of an OFDM/FBMC receiver in frequency selective fading environment. Finally, simulation results confirmed the accuracy of the proposed model.