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.
Highlights
Coherent optical orthogonal frequency division multiplexing (CO-OFDM) is regarded as a potential candidate for high capacity spectrally efficient optical transmission systems attributed to its inherent compact spectrum [1,2,3]
We propose a decision-aided sampling frequency offset (SFO) compensation (DA-SFOC) method for RGI-coherent optical (CO)-OFDM, which is suitable for directly compensating the standard SFO or for compensating residual SFO due to estimation errors with other estimation methods
We have presented a decision aided sampling frequency offset compensation method for RGI CO-OFDM systems and studied its performance for various conditions
Summary
Coherent optical orthogonal frequency division multiplexing (CO-OFDM) is regarded as a potential candidate for high capacity spectrally efficient optical transmission systems attributed to its inherent compact spectrum [1,2,3]. The reduced-guard-interval (RGI) CO-OFDM system was proposed to compensate CD with an overlapped frequency domain equalizer (OFDE) [5] This novel scheme enables the use of a small OFDM symbol size while maintaining a reduced CP overhead (≤5%). The typical method used in experiments to combat SFO is to manually synchronize the clock both at the Tx and Rx, or to use an external clock to drive DAC and ADC at the same time Both approaches are not applicable for real optical transmission systems with a standard 200 ppm SFO since the Tx and Rx are physically separated [8,9]. Both numerical and experimental results demonstrate that the standard SFO (200 ppm) for optical transmission system can be compensated with a negligible performance penalty.
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