Abstract
We report an adaptive weighted channel equalizer (AWCE) for orthogonal frequency division multiplexing (OFDM) and study its performance for long-haul coherent optical OFDM (CO-OFDM) transmission systems. This equalizer updates the equalization parameters on a symbol-by-symbol basis thus can track slight drifts of the optical channel. This is suitable to combat polarization mode dispersion (PMD) degradation while increasing the periodicity of pilot symbols which can be translated into a significant overhead reduction. Furthermore, AWCE can increase the precision of RF-pilot enabled phase noise estimation in the presence of noise, using data-aided phase noise estimation. Simulation results corroborate the capability of AWCE in both overhead reduction and improving the quality of the phase noise compensation (PNC).
Highlights
orthogonal frequency division multiplexing (OFDM) was originally designed for wireless transmission, recently it has gained a great deal of attention in optical communications considering its ease of equalization and robustness with respect to the fiber transmission impairments such as chromatic dispersion (CD) and polarization mode dispersion (PMD) [1,2]
One of the key features of digital signal processing (DSP) in optical fiber transmission systems is the capability of sending pilot symbols (PSs) which are known to the receiver to provide channel estimation
H e n−1,k where Sn,k is the subcarrier-specific equalized complex value symbol and the term φ ∆ pilot,n is to compensate for the laser phase noise and can be extracted by using RF-pilot [4] or pilot subcarriers [1,2]; in this paper, we focus on the data-aided phase noise compensation (PNC) based on RF-pilot enabled phase noise estimation
Summary
OFDM was originally designed for wireless transmission, recently it has gained a great deal of attention in optical communications considering its ease of equalization and robustness with respect to the fiber transmission impairments such as chromatic dispersion (CD) and polarization mode dispersion (PMD) [1,2]. We introduce a data-aided equalizer, AWCE, for optical OFDM systems and study its performance for the CO-OFDM transmission system via numerical simulations This equalizer updates the equalization parameters on a symbol-by-symbol basis and operates based on decision-directed channel estimation which is an alternative to the pilot-assisted channel estimation: it uses previous demodulator decisions to help estimate channel fading factors, happened during the current symbol period. To overcome the shortcomings of decision-directed and pilot-assisted channel estimators, we combine the two methods as suggested in [12,13], AWCE utilizes both receiver decisions and pilot symbols so can produce better results when the receiver decisions are correct In this way, by updating the equalization parameters on a symbol-by-symbol basis, receiver can track the slight drifts in the optical channel.
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