Investigation of optical millimeter-wave and heterodyne techniques in radio-over-fibre systems

Radio over Fibre (RoF) has been proposedasan alternative medium to extend the coverage of radio frequency (RF) millimetre wave (MMW). The main challenges are the fibre attenuation and chromatic dispersion which degrade the signal power and induces inter-symbol interference (ISI), respectively. Two electrical modulation schemes are employed in this paper, namely binary phase shift keying (BPSK) and quadrature phase shift keying (QPSK) at electrical bandwidth of 30 GHz. The proposed technique using optical continuous wave (CW) laser as the optical carrierto transmit BPSK and QPSK signals at 30GHz. The performance of the proposed method than compared to optical MMW carrier at 60 GHz inorder to carry 30 GHz BPSK and QPSK electrical signals. The results indicate the improvement in transmission distance of up to 20 km for both BPSK and QPSK modulation schemesat signaltonoise ratio (SNR) of 11 dB and 16 dB respectively for bit error rate (BER) of 10^-5 in the proposed method. These results compared to 15 kmand 10 km in case of optical MMW using BPSK and MMW QPSK systemsat SNR of 18 dB and 26 dB to achieve the same BER value.