Channel (broadcasting)

Pulse-amplitude modulation

Bandwidth (computing)

Computer network

Digital radio

Bit error rate

Engineering

Electronic engineering

Pulse (music)

Computer science

Transmitter

Data transmission

Fading

Transmission (telecommunications)

Telecommunications

Detector

Intersymbol interference

Journal of Lightwave Technology

Insufficient system bandwidth and chromatic dispersion (CD) of fiber are major limitations for high-speed four-level pulse amplitude modulation (PAM4) direct detection systems. In this article, we investigate C-band 112-Gb/s PAM4 optical transport systems over 10-km and 20-km standard single-mode fiber (SSMF) transmission, which suffers from both bandwidth limitation and CD-induced power fading. Advanced digital signal processing techniques are proposed to handle those channel distortions. At the transmitter, a low-complexity 1 + α Z-1 finite impulse response (FIR) filter coarsely pre-compensates system bandwidth without a preliminary channel estimation. At the receiver, a modified feed-forward equalizer and decision feedback equalizer (FFE-DFE) is employed to compensate residual insufficient bandwidth and CD-induced power fading. Moreover, a novel multi-symbols joint decision is proposed for receiver-side FFE-DFE to mitigate symbol error propagation and correct possible previous error symbols. Experimental results show that the proposed preequalization technique exhibits a better transmission performance, which reduces bit error ratio (BER) from 3.3 × 10 -3 to 5.5 × 10 -4 for optical back to back transmission. As for 10-km transmission case, FFE-DFE with 5-symbols joint decision achieves a BERof 7.3 × 10 -5 , which is betterthanthe BERof 1.6 × 10 -4 with ideal error-propagation-free FFE-DFE (EPF-FFE-DFE). Furthermore, for 20-km transmission scenario, FFE-DFE with 8-symbols joint decision achieves a BER of 6.0 × 10 -4 , which is also a superior result than the BER of 9.1 × 10 -4 with EPF-FFE-DFE.

Digital Pre- and Post-Equalization for C-Band 112-Gb/s PAM4 Short-Reach Transport Systems