Abstract
Recently, coherent-detection (CoD) polarization multiplexed (PM) transmission has attracted considerable interest, specifically as a possible solution for next-generation systems transmitting 100 Gb/s per channel and beyond. In this context, enabled by progress in ultra-fast digital signal processing (DSP) electronics, both multilevel phase/amplitude modulated formats (such as QAM) and orthogonal-frequency-division multiplexed (OFDM) formats have been proposed. One specific feature of DSP-supported CoD is the possibility of dealing with fiber chromatic dispersion (CD) electronically, either by post-filtering (PM-QAM) or by appropriately introducing symbol-duration redundancy (PM-OFDM). In both cases, ultra-long-haul fully uncompensated links seem to be possible. In this paper we estimate the computational effort required by CD compensation, when using the PM-QAM or PM-OFDM formats. Such effort, when expressed as number of operations per received bit, was found to be logarithmic with respect to link length, bit rate and fiber dispersion, for both classes of systems. We also found that PM-OFDM may have some advantage over PM-QAM, depending mostly on the over-sampling needed by the two systems. Asymptotically, for large channel memory and small over-sampling, the two systems tend to require the same CD-compensation computational effort. We also showed that the effort required by the mitigation of polarization-related effects can in principle be made small as compared to that of CD over long uncompensated links.
Highlights
Optical system research is currently targeting 100 Gb/s per channel transmission and higher
Our appraisal of the computational complexity involved in dispersion compensation for coherent polarization-multiplexed PM-orthogonal frequency division multiplexing (OFDM) and PM-QAM systems showed that the two classes of systems have similar behaviors
PM-OFDM appears to require a somewhat lower computational effort than PM-QAM, but this relative advantage is independent of bit rate and system accumulated dispersion. It depends on the different oversampling required by the two systems, which currently appears to be lower for PM-OFDM
Summary
Optical system research is currently targeting 100 Gb/s per channel transmission and higher. In this paper we consider optically uncompensated links and we aim at comparing the computational effort required to carry out CD compensation at the Rx using CoD and either PM-QAM or PM-OFDM. As in [25], we chose to express the DSP computational effort in terms of arithmetical operations per transmitted information bit (OPb) Another fundamental assumption that we made is that the same DSP technology is used for both classes of systems and, in particular, the same FFT/IFFT technology is available to both PM-QAM and PM-OFDM. From an implementation viewpoint, additions and multiplications have different complexities With both formats, by far the bulk of the computational effort consists of FFTs/IFFTs, as we shall see later on. M: number of bits per subcarrier and per PM-OFDM symbol, or number of bits per PMQAM symbol
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