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Modulation Characteristics of Simultaneous Multi-Channel OFDM TV Signal Conversion System

This paper describes for the first time the experimental results of 3-channel simultaneous OFDM television signal modulation by using external optical modulators. In the experiment, carrier suppression was performed to improve the modulation characteristics. Furthermore, this paper describes the modulation characteristics such as the effect of the change in the modulation index of the optical modulator on the signal quality. In this experiment, although the 3-channel simultaneous modulation experiment was successful, in order to succeed in the simultaneous OFDM modulation experiment with a larger number of channels, it is necessary to obtain the maximum extinction ratio with a larger modulation index. At present, the optical modulator with sine curve characteristics used in the experiment increases the nonlinear distortion as the modulation index increases. Therefore, in this experiment, the modulation index was limited to about 10%. In the future, in order to increase the modulation index of the optical modulator, it will be necessary to reduce the non-linear distortion generated by the optical modulator with a predistortion circuit or the like.