Optimal electrical power distribution among coexisting OFDM-based signals in LR-PONs: Theoretical and experimental analyses
The provision of a quintuple-play service (fixed Internet and telephony, mobile telephony/Internet, security/control applications, and wireless high-definition audio/video distribution) along wavelength division multiplexing long-reach passive optical networks has been proposed recently. Five coexisting orthogonal frequency division multiplexing based signals have been used to deliver the quintuple-play service to each user. In this paper, the electrical power distribution (EPD) among those five coexisting signals is studied using numerical simulation. The need for EPD optimization is stressed, as the optimum EPD (OEPD) enables the maximization of the signal and network performances. The OEPD is achieved by setting optimized gains (OG) in the electrical amplifiers used to impose the electrical power level of each one of the coexisting signals. For practicability, the gains are optimized only for a specific fiber length. For other fiber lengths, the use of those OG may cause performance degradation. This degradation can be mitigated if a predistortion (PD) scheme, which compensates for the frequency-dependent losses (FDLs) of the transmission channel, is used with proper OG. It is shown that the main advantage of using OG + PD over using OG only is to enable the reduction of the performance degradation that occurs for other fiber lengths than the one considered in the OG optimization. The capability to mitigate the FDLs is more limited in the absence of PD. Therefore, the advantage of using OG + PD over OG increases with the magnitude of the variation of the FDLs inside the band of the signals. However, under the conditions considered in this work, the impact of the use of OG + PD on the maximum transmission reach (MTR) is determined to be reduced (less than 1% relative to the MTR obtained with OG only, 126.5 km of standard single-mode fiber).