Data throughput tripling by Feed-Forward Equalization and photonic QPSK in a 7 Gbps single-carrier RoF link at 60 GHz

This paper investigates the use of feed-forward equalization (FFE) to combat performance limitations imposed by non-uniform channel characteristics in a wideband vector signal-modulated single-carrier radio-over-fiber (RoF) system at 60 GHz. A direct photonic QPSK modulator was implemented at 60 GHz and used in the system experiments. By combining photonic QPSK modulation and FFE, 7 Gbps data throughput was achieved over a channel bandwidth of less than 2 GHz, representing a bit-rate increase of three times over simple amplitude shift keying (ASK) modulation. The photonic QPSK modulator incorporates frequency doubling, leading to the simplification of the transmitter. In addition, frequency doubling extends the fiber length limit imposed by signal fading due to chromatic dispersion. FFE is simpler to implement and is less computation intensive than, for instance OFDM. Transmission experiments over 2 km of fiber were conducted.