A base station is provided for communicating data to a mobile terminal unit by means of at least one antenna unit, wherein the at least one antenna unit is linked to the base station by means of at least one optical fibre and the at least one antenna unit is operable to communicate wirelessly with the mobile terminal unit. The base station comprises an optical transmitter for transmitting modulated data signals to the at least one antenna unit for wireless transmission, an optical receiver for receiving modulated data signals forwarded by the at least one antenna unit and a demodulator for demodulating received modulated data signals. The optical transmitter comprises a first optical modulator arranged to modulate an optical carrier with a radio frequency oscillator signal to generate an optical oscillator signal, a second optical modulator, coupled optically to the first optical modulator, operable to modulate the optical oscillator signal with an input data signal of a predetermined frequency to generate a downlink optical data signal and an optical output for directing the downlink optical data signal to the at least one antenna unit by means of the at least one optical fibre.