Kittipong Piyawanno

DSP for Coherent Single-Carrier Receivers

In this paper, we outline the design of signal processing (DSP) algorithms with blind estimation for 100-G coherent optical polarization-diversity receivers in single-carrier systems. As main degrading optical propagation effects, we considered chromatic dispersion (CD), polarization-mode dispersion (PMD), polarization-dependent loss (PDL), and cross-phase modulation (XPM). In the context of this work, we developed algorithms to increase the robustness of the single DSP receiver modules against the aforesaid propagation effects. In particular, we first present a new and fast algorithm to perform blind adaptive CD compensation through frequency-domain equalization. This low complexity equalizer component inherits a highly precise estimation of residual dispersion independent from previous or subsequent blocks. Next, we introduce an original dispersion-tolerant timing recovery and illustrate the derivation of blind polarization demultiplexing, capable to operate also in condition of high PDL. At last, we propose an XPM-mitigating carrier phase recovery as an extension of the standard Viterbi-Viterbi algorithm.

Data-Aided Versus Blind Single-Carrier Coherent Receivers

Fiber-optic research in signal processing for the first generation of coherent communication systems was dominated by receivers with blind adaptation. Next-generation systems will require a scalable and modular design for higher order modulation formats. Due to the nature of the fiber channel and the required parallelization in high-speed receivers, data-aided and blind algorithms call for a general reassessment when used in coherent optic receivers employing higher order modulation formats. In this paper, blind and data-aided receivers are compared for coherent single-carrier optical systems in terms of complexity, tracking ability, and convergence speed. Methods for equalization are discussed for time-domain- and frequency-domain-based receivers covering the most important algorithms. The general superiority of data-aided frequency-domain equalization is demonstrated.

Digital Timing Recovery for Coherent Fiber Optic Systems

We present a novel, low-complexity, non-data aided (NDA) digital timing recovery algorithm operating at a rate of two samples per symbol. Exceeding performance improvements over standard methods are demonstrated for higher distortions.

Impact of Mechanical Vibrations on Laser Stability and Carrier Phase Estimation in Coherent Receivers

Coherent communication systems are largely limited by the laser linewidth of the local oscillator. In addition to phase noise, large frequency deviations can occur if the laser is mechanically vibrated. The detrimental effect of the frequency instability is measured for coherent optical receivers on a typical laser and numerically analyzed for quadrature phase-shift keying and 16-quadrature amplitude modulation using common feed-forward carrier phase recovery algorithms.

Correlation-Based Carrier Phase Estimation for WDM DP-QPSK Transmission

A novel algorithm for frequency offset compensation and carrier phase estimation in systems with 40 or 111 Gb/s coherent dual-polarization quadrature phase-shift keying (DP-QPSK) with on-off keying or DP-QPSK neighbors is demonstrated. The algorithm, which applies correlation phase adjustment embedded between digital differential demodulation and nonredundant error correction, leads to a significant performance improvement over standard algorithms.

On the Performance of Coherent Systems in the Presence of Polarization-Dependent Loss for Linear and Maximum Likelihood Receivers

The performance of coherent polarization- multiplexed optical systems is evaluated in the presence of polarization-dependent loss (PDL) for linear and maximum- likelihood receivers and lumped noise at the receiver. The boundaries of PDL mitigation methods are discussed.

Nonlinearity mitigation with carrier phase estimation for coherent receivers with higher-order modulation formats

We investigate the nonlinearity mitigation with carrier phase estimation for coherent PolMux-16QAM and PolMux-16ASK-PSK using carrier phase estimation. The performance is demonstrated for various transmission rates, neighbor channels as well as compensated and uncompensated links.

Optimal Symbol Rate for Optical Transmission Systems with Coherent Receivers

We investigate the nonlinear impairments for future 1Tbit/s transmission in multi-band systems with coherent reception. The optimal baud rate for the sub-band is derived for higher-order QAM and varying dispersion management.

Data-aided single-carrier coherent receivers

Data-aided algorithms for coherent optic receivers are discussed as an extension of existing non-data aided methods. The concept presents a scalable approach with low implementation complexity and limited overhead for higher-order modulation formats.

Data-aided vs. blind single-carrier coherent receivers

Blind and data-aided single-carrier receivers are discussed for high-speed optical coherent receivers. Equalization concepts are presented and evaluated regarding the implementation complexity and overhead for time-domain and frequency-domain equalization techniques.