Economic viability of high bit rate and high spectral efficiency transponders

Recent trends in transmission technologies focus on bit rates higher than the state-of-the-art DP-QPSK (Dual Polarization - Quadrature Phase Shift Keying) 100 Gbit/s transmission. High spectral efficiency formats and multi-carrier channels are currently under study. In particular coherent 400 Gbit/s and 1Tbit/s channels are becoming technologically feasible. However, economic viability is a key point in determining how networks will evolve, and which formats are more suitable for a given network scenario. Considering Telecom Italia core network as a case study, different technological scenarios characterized by transponders that use different modulation formats and number of carriers for each channel are analyzed and economically evaluated. It results that optimizing the network design by using highest bit rate transponders only on paths that do not require regeneration, economic viability can be achieved, without any cost per bit reduction on transponders. Only in case of cost advantages deriving from device integration, a noteworthy CAPEX reduction can be achieved.