Noise Performance Comparison: ENRZ, NRZ, PAM3, and PAM4

The noise performances of four line codes, i.e., Ensemble Non-Return-to-Zero (ENRZ), Non-Return-to-Zero (NRZ), Pulse Amplitude Modulation of 3-level (PAM3), and Pulse Amplitude Modulation of 4-level (PAM4) are investigated. The closed-form signal-to-noise ratio (SNR) formulas of the four codes are deduced. The method of injecting noise onto high-speed channels is described. Channel simulation running at 128 Gbps (for NRZ, PAM3, and PAM4) and 256 Gbps (for ENRZ) is performed and the resulting eye diagrams are compared. In addition, a brief categorization of external and internal noise types is also presented. The study shows that ENRZ and NRZ demonstrate less degradation than PAM3 and PAM4 under the influence of Gaussian thermal noise.