  A simple data-aided scheme for sampling clock synchronisation in
reduced-guard-interval coherent optical orthogonal frequency division
multiplexing (RGI-CO-OFDM) systems is proposed. In the proposed scheme, the
sampling clock offset (SCO) is estimated by using the training symbols reserved
for channel estimation, thus avoiding extra training overhead. The SCO is then
compensated by resampling, using a time-domain interpolation filter. The
feasibility of the proposed scheme is demonstrated by means of numerical
simulations in a 32-Gbaud 16-QAM dual-polarisation RGI-CO-OFDM system.
