Modeling and performance analysis of the OFDM scheme for radio over fiber system

Abstract

Radio over fiber (ROF) is an hybrid system that having both a fiber optic link and free-space radio path. In such RoF systems using, broadband microwave data signals are modulated onto an optical carrier at a central station, and then transported to remote sites or base station using optical fiber. The base-stations then transmit the RF signals over small areas using microwave antennas. Such system is important in a number of applications, including mobile and satellite communications, wireless local area networks (WLANs), wireless local loop and mobile broadband service, etc. Orthogonal Frequency Division Multiplexing (OFDM) technique distributes the data over a large number of carriers that are spaced apart at precise frequencies with overlapping bands. The use of FFT for modulation provides orthogonality to the subcarriers, which prevents the demodulators from seeing frequencies other than their own. Hence by incorporating OFDM along with the optical fiber, the RoF system can be used for both short distance as well as long-haul transmission at very high data rate. This improves the system flexibility and provides a very large coverage area without increasing the cost and complexity of the system very much. In this project author investigates the feasibility of OFDM as modulation technique for a RoF based on WLAN system in consistency with IEEE 802.11g. Result from Optisystem model shows the performance of OFDM signal through the RoF networks. The system was utilized to carry data rates 20Mbps, using carrier frequency 2.4 GHz and the modulation type for OFDM is 16QAM 4 bit per symbol. Total power of the signal was decreasing while the fiber length of the RoF networks was increased from 10 – 50 km.