Chuandong Li

Precise, robust and least complexity CD estimation

We demonstrate robust and precise frequency domain chromatic dispersion estimation based on offline data and simulations. The blind, least complexity algorithm allows fast acquisition suitable for digital coherent receivers in switched networks.

Coherent transceiver operating at 61-Gbaud/s.

We use 85-Gs/s digital-to-analog convertor (DAC), 85Gs/s analog-to-digital convertor (ADC), commercial optoelectronic (OE) components with an overall electronic 3dB-bandwidth of less than 15GHz, and novel digital signal processing (DSP) algorithms implemented in CMOS to realize real time coherent transceiver operation at a record baud rate of 61-Gbaud/s. Novel DSP approaches for mitigating narrow filtering effect is critical to acquire data clock, and to improve modem performance. With transmitter pre-emphasis, novel timing recovery, and soft output maximum likelihood sequence estimation (MLSE), we are able to achieve error free operation of single carrier 200-Gbit/s polarization division multiplexed quadrature phase shift keying (PDM-QPSK) after forward error correction (FEC) at 15.2dB OSNR with pre-FEC error rate of 1.4E-2, and single carrier 400-Gbit/s PDM 16-ary quadrature amplitude modulation (16QAM) after FEC at 30.2dB OSNR with pre-FEC error rate of 9.5E-3. Error free transmission for 200-Gbit/s PDM-QPSK and 400-Gbit/s PDM-16QAM was achieved after 1200km propagation with 6dB link margin and 80km propagation respectively.

An adaptive decision-feedback channel estimation for coherent optical OFDM

Adaptive channel estimation methods are proposed for reduced guard-interval (RGI) CO-OFDM. Channel estimation is updated adaptively after decoding a sequence of OFDM symbols using LS or MMSE decision-feedback from demodulator to channel estimator.

Nonlinear Phase Noise Mitigation With Soft-Differential Decoding and Nonredundant Error Correction for Hybrid 10G/100G Transmission

We report experimental results of 112-Gb/s po larization-division-multiplexed return-to-zero quaternary phase-shift-keying (PDM-RZ-QPSK) transmission over dis persion-managed 1200-km links embedded between 10.7-GBaud on-off keying nonreturn-to-zero (OOK-NRZ) neighbors. Taking into account implementation constraints for equalization and synchronization of the digital signal processing (DSP) by means of processing delay and parallelization, the performances without differential decoding, with hard-differential decoding, and with soft-differential decoding are evaluated. The combination of soft-differential decoding with nonredundant error correction is identified to provide the best mitigation of cross-phase modulation (XPM)-induced nonlinear phase noise.

Experimental comparison of terabit nyquist superchannel transmissions based on high and low baud rates

We report experimental results comparing two-types-of terabit Nyquist-pulse-shaped superchannel transmissions. A 50-subcarrier low-baud-rate system with potential of significant DSP simplification has shown similar transmission performance compared with a 10-subcarrier high-baud-rate system.

Polarization-Time Code and 4

A linear polarization-time code in conjunction with an adaptive multi-tap 4 4 joint equalizer-decoder is proposed to average the effects of polarization-dependent impairments on two polarizations. For the first time in the context of polarization-time coding, there is no assumption of polarization-dependent loss (PDL) of knowledge at the receiver. This method compensates the performance loss penalty due to polarization-dependent impairments in polarization division multiplexed coherent optical single-carrier systems. Using the proposed method, a 1.25-dB optical signal-to-noise ratio gain is achieved in the presence of 6-dB PDL. The proposed 44 joint equalizer-decoder has twice the complexity of conventional time-domain equalizers. Further changes at the receiver including the demodulator are not required. Since the outputs of the equalizer are noisy quadrature phase shift keying signals, adoption of the method to work with both hard and soft forward error corrections is straightforward.

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We demonstrate the rate-adaptive coding can improve the capacity of a 100-Gbps direct-detection DMT system. A new loading algorithm is proposed to incorporate rate-adaptive coding into water-filling.

4 Equalizer-Decoder for Coherent Optical Transmission

The algorithm estimates the value of residual chromatic dispersion solely from the spectra of filtered signals of a matched-filter-bank in digital coherent receivers. Robust estimation is demonstrated by extensive simulations with combined impairments.

Rate-Adaptive Coding for Direct-Detection of Discrete Multi-Tones

We reported a real-time single carrier 400Gb/s system with baud rate of 61GHz. The reality challenges and corresponding DSP solutions are discussed. We show back-to-back as well as propagation performance of the system.

Fast and Reliable Frequency-Domain CD Estimation

A blind and adaptive decision-feedback channel estimation method is proposed for optical intensity-modulated direct detection discrete multitone transmissions. Due to the channel state variation nature of the fiber, periodic channel estimation update is required. In previous works, periodic preambles are transmitted to acquire and track the channel state information at the receiver. In the proposed method, instead of using periodic preambles, the estimated channel is updated adaptively after decoding a sequence of orthogonal frequency-division multiplexing symbols using least-squares and minimum mean-square error criteria. The simulation results corroborate that the proposed method increases data-rate by 10%, and at the same time provides 0.24-dB Q-factor gains that can be converted into extra 2% data-rate increase, algorithm simplicity, or cost reduction.