Optical links for installation of a GSM base transceiver station

The coaxial cables that are used in the GSM system for mobile communication to transport the RF signals to and from the antenna in the base transceiver station, are very bulky and heavy. When installing new base stations in existing buildings, these cables cause several problems. The authors therefore propose to use optical transmission links for these signals. An optical fibre is small, very light, offers low attenuation, electrical insulation an low EMI problems. The problems that arise when using RF optical links are the relatively high insertion losses and the noise. In order to lower the electrical insertion loss of these links, the authors design active impedance matching networks for the transmitting laserdiode and the receiving photodiode. These active networks however introduce extra noise that should be limited as well. Care must be taken to design these networks for optimum noise performance. The first practical realisations show that this approach is promising and will be even more advantageous for the future DCS system.