Throughput Comparison between 50GHz and 37.5GHz-grid Transparent Networks

With the introduction of Nyquist pulse shaping, it is possible to transmit a channel in a spectral window comparable to its baud-rate. To increase the overall network spectral efficiency the most promising solution seems the reduction of the channel spacing. Standardization bodies have proposed a flexible grid with 12.5GHz of granularity. Hence, 100Gb/s signals can be transported in a 37.5GHz-grid network. But if 37.5GHz channel spacing brings an ideal extra-throughput of 33% compared to 50GHz one, this value ignore filtering-induced impairments occurring when narrower channel spacing is adopted. In this paper we investigate the filtering penalty stemming from optical filters and its implications on the extra-throughput provided by 37.5 vs. 50GHz-grid WDM networks for two different networks with two diverse traffic distributions. We show scenarios for which the ideal 33% extra-throughput of 37.5GHz channel spacing is drastically reduced or even vanishes because of filtering penalties.