ONU-wavelength grouping scheme for efficient scheduling in Long Reach-PONs

Long Reach Passive Optical Networks (LR-PON) are capable of supporting upto 2048 subscribers located at a distance of 200 Km from the service provider. The higher propagation delay between the OLT and the ONU (compared to traditional PONs) leads to increased data packet delay. In case of round-robin scheduling among N ONUs, the grant for the first ONU cannot be sent until the N^th ONU has been scheduled. To mitigate this problem, a scheduling approach in which the ONUs and the wavelengths are grouped is proposed in a hybrid TDM/WDM PON environment. A number of ONUs are grouped together and are assigned a set of wavelengths dedicated for the group. The grant scheduling of ONUs in different groups is done simultaneously in parallel by the OLT. Simulation based results indicate that the proposed mechanism provides lower delay when compared to NA+ scheme consistently and performs better than Multi-thread Polling at higher loads.