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A radio over fiber (RoF) communication system is considered for cable television (CATV) channels over wavelength division multiplexing (WDM) network using an optical direct modulator (DM). Since the DM bandwidth is limited, increasing bandwidth efficiency of the system using M-ary quadrature amplitude modulation (MQAM) schemes will improve the link symbol error rate (SER) performance. Radio frequency (RF) signals with constellations of 16-64-256 QAM were simulated for CATV channels and the effect of using higher bit per symbol on the link performance was studied in order to reduce the cost of the network through utilizing financially feasible optical modulator. The 64-QAM scheme which is the most appropriate is used for the system of CATV channels. The link performance is studied for different combinations of effective parameters such as AC electrical power and Module to Bias ratio, which are crucial to be set properly, and SER is obtained at the front end of the receiver. The best setting options are proposed for 30 CATV channels with 64-QAM constellation with direct modulation transmitted over the 4-WDM link. Moreover, communication system is modeled by fuzzy logic using data-base obtained from simulation. Fuzzy reverse modeling of the system is also implemented in order to provide reasonable estimate of electrical power required to achieve a desired SER. Characteristics of forward and reverse fuzzy modeling are discussed. Simulation results represent satisfactory performance of the models.