Abstract
We propose a simple, full-range carrier frequency offset (CFO) algorithm for coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems. By applying the Chinese remainder theorem (CRT) to training symbol of single frequency, the proposed CFO algorithm has wide range with shorter training symbol. We numerically and experimentally demonstrate the performance of CRT-based algorithms in a 16-ary quadrature amplitude modulation (QAM) CO-OFDM system. The results show that the estimation range of the CRT-based algorithm is full-range corresponding to the sampling frequency. Also, the bit error ratio (BER) degradation of the proposed algorithm with one training symbol is negligible. These results indicate that the proposed algorithm can be used as a wide range CFO estimator with an increased data rate in high speed CO-OFDM systems.
Highlights
Orthogonal frequency division multiplexing (OFDM) technology has been widely used in various digital communications to combat multipath fading
The simulation was performed for the system with 112 Gbps transmission over an 800 km standard single-mode-fiber (SSMF) with polarization division multiplexing 16 quadrature amplitude modulation (PDM 16-QAM)
Optical link consisted with 10 spans and each span consisted of 80 km SSMF with a dispersion parameter of 17 ps/nm/km, attenuation α of 0.2 dB/km, and nonlinearity coefficient γ of 1.2 /W/km and EDFA with 16 dB gain
Summary
Orthogonal frequency division multiplexing (OFDM) technology has been widely used in various digital communications to combat multipath fading. OFDM is invulnerable against dispersion, the OFDM system consisted of multiple subcarriers is sensitive to phase noise and frequency offset which may cause interchannel interference (ICI) between subcarriers. Carrier frequency offset (CFO) estimation and compensation are important functions of OFDM systems. Wide range CFO estimation is essential in coherent optical OFDM (COOFDM) systems. At the receiver in the communication channel with channel noise η(n), the sampled baseband signal r(n) with carrier frequency offset (CFO) Δf can be represented by: r(n) = e j2π nΔfTs s(n) +η (n) (1). The frequency offset angle is calculated from the phase differences between identical complex samples. M=0 where εis the estimated value of normalized CFO, angle () is the phase difference between identical samples, L is the sample interval, N is the size of the inverse fast Fourier transformation (IFFT), and PL is the correlate function
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