Generation and transmission of high frequency radio signals through fiber links up to 125 km by means of the optical frequency multiplication technique

The transmission of 64 QAM radio data signals with a data rate up to 150 Mb/s through long single mode fiber links at different frequencies has been experimentally evaluated. The system under study uses the optical frequency multiplication technique for the generation of carriers in the microwave and millimeter-wave bands. Transmission using frequencies of 18.7 GHz, 19.5 GHz, 19.7 GHz and 29 GHz is demonstrated for fiber links up to 125 km, and up to 100 km for transmission frequencies of 32.5 GHz and 36.9 GHz. A careful adjustment of the filter characteristics is crucial to fulfill the performance requirements.

I. Introduction

The increase of subscribers in wireless access networks in the oncoming years drives the need for new infrastructures, supporting the large amount of data traffic expected. Enhancing the capacity of wireless communications can be achieved by means of deploying smaller radio cells as well as carrying the information at higher carrier frequencies. Both approaches impose considerable costs in the infrastructure which may be reduced using Radio over Fiber technologies (RoF). In such systems, the radio signals at high frequencies are generated at a single remote central station and distributed to several simplified base station antennas using the optical fiber as physical link [1]. Here, the Optical Frequency Multiplication (OFM) technique is considered for the generation of the microwave and millimeter-wave frequencies at the remote central station. This technique allows the generation of radio frequencies (RF) from a local oscillator with a lower frequency (typically less than 10GHz), and its transmission through long fiber links, partially overcoming the dispersion of the link for both single-mode fiber (SMF) [2][3] and multi-mode fiber [4].