Optimal WDM schedules for optical star networks

We consider a wavelength division multiplexed, optical network where the nodes are connected in a star topology. In this architecture, each node can be equipped with transmitters and receivers that may be tunable or tuned to a fixed wavelength. To efficiently use the bandwidth, at least one end (at the receiver side or at the transmitter side) must be tunable. However, tunability is an expensive option and it is typically assumed that only one end is tunable and the other end is fixed. In this paper, we assume that each node in the passive-star network is equipped with a fixed receiver and tunable receiver. A transmitter takes a non-zero amount of time (called tuning latency) to tune from one wavelength to another. We assume that time is slotted and the transmission time of each packet is equal to one time slot. We restrict our attention to schedules where collisions are avoided in the broadcast medium, i.e., two transmitters will not transmit in the same wavelength during any time slot.