Abstract :
RoF technology is an engineering system that can transmit microwave waves through optical fiber for long distance
using Orthogonal Frequency Division Multiplexing (OFDM) multiplexing technique) OFDM-RoF system will be very
related to modulation and demodulation mechanism in both transmitter and receiver side, it is influenced by several
parameters The mechanism of mapping modulation, the mechanism of up-conversion E / O (optical modulator, fiber
characteristics, and down-conversion O / E (optical to electrical conversion). This study will focus on digital
modulation performance of 4 QAM, 16 QAM, QPSK, 8-PSK and 16 QAM using external optical modulation with
coherent detection on baseband over fiber using Software optisystem 14.1. With variations in fiber length from 10 km
to 50 km for receiving power, constellation and signal spectrum. In the results of this study both on the receiving
power of the spectrum form, the most well-modulated signal constellation 16 QAM with the amplitude value in the
signal constellation 8909 a.u, and the power subsystem at 98 dBm. Then it can be concluded the higher the modulation
then the received power is high, and the longer the distance traveled in the lower power.
Keywords: RoF, OFDM, M-QAM and M-PSK