Decision-aided sampling frequency offset compensation for reduced-guard-interval coherent optical OFDM systems

Abstract

We propose a decision-aided algorithm to compensate the sampling frequency offset (SFO) between the transmitter and receiver for reduced-guard-interval (RGI) coherent optical (CO) OFDM systems. In this paper, we first derive the cyclic prefix (CP) requirement for preventing OFDM symbols from SFO induced inter-symbol interference (ISI). Then we propose a new decision-aided SFO compensation (DA-SFOC) algorithm, which shows a high SFO tolerance and reduces the CP requirement. The performance of DA-SFOC is numerically investigated for various situations. Finally, the proposed algorithm is verified in a single channel 28 Gbaud polarization division multiplexing (PDM) RGI CO-OFDM experiment with QPSK, 8 QAM and 16 QAM modulation formats, respectively. Both numerical and experimental results show that the proposed DA-SFOC method is highly robust against the standard SFO in optical fiber transmission.

Simple sampling clock synchronisation scheme for reduced‐guard‐interval coherent optical OFDM systems

“…Typically, in most existing CO-OFDM work, SCO is avoided by either manually adjusting the arbitrary waveform generator and the scope, or by using a common external reference clock to drive the DAC and ADC. It is obvious that these approaches will not be feasible in real optical transmission systems which have a standard SCO of 200 parts per million (ppm) and physically separated Txs and Rxs [5]. Another approach for sampling clock synchronisation is to transmit a dedicated clock signal to the Rx [6].…”