4D PAM-7 Trellis Coded Modulation for Data Centers

We propose a novel seven-level pulse amplitude modulation (PAM-7) combined with trellis coded modulation (TCM) for data center applications. Four symbols are combined in the 4D space to encode ten information bits. The novel scheme called 4D PAM-7 TCM is experimentally demonstrated with commercially available devices at 1550 nm at rates of 210/225 Gbit/s. Excellent performance is achieved by employing advanced digital signal processing algorithms both at transmitter and receiver. The TCM scheme is compared with the PAM-6 modulation format which has the same spectral efficiency. The 4D PAM-7 TCM format improves the sensitivity by 5.5 dB compared to the best PAM-6 results assuming that the system works with the KP4 FEC. The TCM solution may transport the next Ethernet data rate of 800G using 4 × 200G transceivers.