Real-time 30-GSa/s Precoded and Partial Pre-emphasized DMT Transceiver for Short-reach IMDD Transmission

The precoding technique has been widely studied in multi-carrier modulation systems such as discrete multi-tone (DMT), due to its ability to equalize subcarrier signal-to-noise (SNR) and reduce signal peak-to-average power ratio. In this work, we implement a low-complexity real-time 30-GSa/s DMT transceiver on a single field programmable gate array chip, enabled by simplified fast Fourier transform (FFT) algorithms and timing synchronization, block precoding (BP) and partial pre-emphasis (PPE) techniques. Four software-selectable BP techniques, i.e., the traditional concatenated BP (CBP) and the interleaved BP (IBP) based on FFT or fast Walsh–Hadamard transform (FWHT), and complete pre-emphasis (CPE) or PPE schemes are implemented in the transceiver. FWHT-CBP/IBP saves 60% on-chip registers and 67% look-up tables and 100% multipliers compared to FFT-CBP/IBP. Besides, more than 35% multipliers for the transceiver are reduced with the simplified FFTs in comparison with Spiral FFTs. The real-time transceiver is investigated in a short-reach intensity modulation and direct detection transmission system. The results exhibit that IBP can afford better SNR equalization and outperform CBP ones, and FWHT-IBP has a similar bit error rate (BER) performance to FFT-IBP. With the help of FWHT-IBP and PPE, the real-time 40-Gbit/s 16-QAM-DMT signals are successfully transmitted over 20-km standard single-mode fiber link with the BER below 3.8e-3 during 5-hour continuous measurements.