Abstract: The aim of this study, is to investigate and evaluate the performance of various techniques for suppression of co channel interference in GSM. In mobile communication networks, the system capacity is often limited by co channel interference because of the surrounding cells using the same carrier frequency. Therefore, to cancel or suppress co channel interference, some methods and algorithms are proposed. These methods are, optimum distribution of the transmitter power, lowering the antenna height, joint demodulation of co channel signals, dual antenna interference suppression technique, tilted base station antenna. In optimum distribution of transmitter powers, applied the complex algorithm and used regular and irregular model of the cellular system for simulation and assessed the algorithm efficiency. In lowering the antenna height, by half than the original, the efficiency is very much improved than with normal antenna height. In joint demodulation of the co channel signals, find�s the dominant interferer (DI), which occurred because of the number of near by co channel interferers and its probability is investigated by network simulation and observerd the improved receiver performance. In dual antenna interference suppression technique, applied a filter based single antenna interference suppression for downlink GSM with 8PSK modulation by assuming the terminal is equipped with 2 antennas and evaluated the performance using correlation based spatial channel model and showed the potential of suppressing the co channel interference.