A novel joint symbol timing and carrier frequency offset (CFO) estimation algorithm is proposed for reduced-guard-interval coherent optical orthogonal frequency-division multiplexing (RGI-CO-OFDM) systems. The proposed algorithm is based on a constant amplitude zero autocorrelation (CAZAC) sequence weighted by a pseudo-random noise (PN) sequence. The symbol timing is accomplished by using only one training symbol of two identical halves, with the weighting applied to the second half. The special structure of the training symbol is also utilized in estimating the CFO. The performance of the proposed algorithm is demonstrated by means of numerical simulations in a 115.8-Gb/s 16-QAM RGI-CO-OFDM system. 1800-1805 (1997). 13. X. Zhou, X. Yang, R. Li, and K. Long, "Efficient joint carrier frequency offset and phase noise compensation scheme for high-speed coherent optical OFDM systems," J. Lightwave Technol. 31(11), 1755-1761 (2013). 14. Y. Huang, X. Zhang, and L. Xi, "Modified synchronization scheme for coherent optical OFDM systems," J. Opt.Commun. Netw. 5(6), 584-592 (2013 7350-7361 (2012). 16. X. Zhou, X. Chen, and K. Long, "Wide-range frequency offset estimation algorithm for optical coherent systems using training sequence," IEEE Photon.

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