Spectral and power efficiency investigation in single- and multi-line-rate optical wavelength division multiplexed (WDM) networks

In order to tackle the increasing heterogeneous global Internet traffic, mixed-line-rate (MLR) optical wavelength division multiplexed (WDM) networks have emerged as the cost- and power-efficient solution. In MLR WDM networks, channels are structured as sub-bands, each of which consists of wavelengths operating at a similar data rate. By reducing the (1) spacing within a sub-band, or (2) spacing between sub-bands operating at different data rates, spectral efficiency can be improved. However, owing to high physical layer impairment levels, decrease in sub-band spacing adversely affects transmission reach of the channels, which results in higher power consumption due to requirement of increased signal regeneration. In this work, we compare power efficiency of various MLR and single-line-rate (SLR) solutions, and also investigate the trade-off that exists between spectral and power efficiency in a WDM network. Simulation results indicate that (1) for high transmission capacities, a combination of 100 Gbps transponders and 40 Gbps regenerators will obtain the highest power efficiency; (2) for long connection distances, a point of merging occurs for various SLR and MLR designs, where power consumption is independent of the frequency band distribution; and (3) for MLR systems, both spectral and power efficiency can be improved by using either shorter links with higher bandwidth assignment to 100 Gbps wavelengths, or longer links with higher bandwidth assignment to 40 Gbps wavelengths. Finally, the results indicate that focusing on spectral efficiency alone results in extra power consumption, since high quality of transmission and spectral efficiency leads to increased regeneration.