Abstract: In this letter, we first present the theoretical basis for coherent optical OFDM systems in direct up/down conversion architecture. We then demonstrate the transmission performance through simulation for WDM systems with coherent optical OFDM (CO-OFDM) including the fiber nonlinearity effect. The results show that the system Q of the WDM channels at 10 Gb/s is over 13.0 dB for a transmission up to 4800 km of standard-single-mode-fiber (SSMF) without dispersion compensation. A novel technique of partial carrier filling (PCF) for improving the non- linearity performance of the transmission is also presented. The system Q of the WDM channels with a filling factor of 50 % at 10 Gb/s is improved from 15.1 dB to 16.8 dB for a transmission up to 3200 km of SSMF without dispersion compensation.
1. Introduction
Orthogonal frequency division multiplexing (OFDM) has been widely employed into numerous digital standards for broad-range of applications such as digital audio/video broadcasting and wireline/wireless communication systems [1]. Recently it has been shown that OFDM can be applied in optical long haul transmission systems and had many advantages over conventional single-carrier modulation format [2-4]. Many key merits of the OFDM techniques have been studied and proven in the communications industry. Firstly, the frequency spectra of OFDM subcarriers are partially overlapped, resulting in high spectral efficiency. Secondly, the channel dispersion of the transmission system is easily estimated and removed, and thirdly, the signal processing in the OFDM transceiver can take advantage of the efficient algorithm of FFT/IFFT with low computation complexity. Recently, an equivalent optical-domain multi-carrier format, called coherent optical OFDM (CO-OFDM) has been proposed for long haul transmission [2]. In the mean time, incoherent optical OFDM (IO-OFDM) has also been proposed independently, and has been shown to have similar dispersion tolerance with a much simpler detection scheme [3]. However, the CO-OFDM is superior to IO-OFDM in spectral efficiency, OSNR requirement, and PMD insensitivity. It is well-known that OFDM is generally susceptible to nonlinearity and phase noise owing to high peak to average power ratio (PAPR) [1]. Therefore it is critical to investigate and improve the CO-OFDM system transmission performance including fiber nonlinearity, in order to ascertain its suitability for optical transmission. In this letter, we intend to answer two important questions for CO-OFDM WDM system, (i) what is the achievable system Q value ?, and (ii) what is the optimal launch power at various transmission distances ?. We first present the theoretical basis for coherent optical OFDM systems in direct up/down conversion architecture. We then demonstrate the transmission performance through simulation for WDM systems with coherent optical OFDM (CO-OFDM) including the fiber nonlinearity effect. The results show that the system Q of the WDM channels at 10 Gb/s is over 13.0 dB for a transmission up to 4800 km of standard-single-mode-fiber (SSMF) without dispersion compensation. A novel technique of partial carrier filling (PCF) for improving the non- linearity performance of the transmission is also presented. The system Q of the WDM channels with a filling factor of 50 % at 10 Gb/s is improved from 15.1 dB to 16.8 dB for a transmission up to 3200 km of SSMF without dispersion compensation.
DOWNLOAD....
Hongchun Bao and William Shieh
ARC Special Research Centre for Ultra-Broadband Information Networks, Department of Electrical and Electronic Engineering, University of Melbourne, Melbourne VIC 3010, Australia
h.bao@ee.unimelb.edu.au; w.shieh@ee.unimelb.edu.au
No comments:
Post a Comment