Optimal wavelength scheduling for hybrid WDM/TDM passive optical networks

This paper investigates upstream wavelength scheduling in hybrid wavelength division multiplexing and time division multiplexing passive optical networks (WDM/TDM PONs), where the minimum resource allocation unit is a time slot on a wavelength. First, WDM/TDM PONs of three types are introduced with the consideration of network and service evolution: 1) Type-I WDM/TDM PONs, where each optical network unit (ONU) has a single optical transmitter with a tunable wavelength; 2) Type-II WDM/TDM PONs, where each ONU still has a single transmitter, but some are fixed to transmit at a certain wavelength; and 3) Type-III WDM/TDM PONs, where each ONU has one or more transmitters and all transmitters can tune their wavelengths. We propose three periodic lightweight optimal wavelength scheduling algorithms for the three kinds of WDM/TDM PONs. Simulation-based performance evaluation demonstrates that the proposed algorithms lead to optimal schedule length with the minimum number of wasted time slots and in turn achieve the maximum wavelength/channel utilization.