An incremental algorithm for TDM switching assignments in satellite and terrestrial networks

The authors present an incremental algorithm for scheduling traffic in a general class of time-division multiplexed (TDM) switching systems used in satellite and terrestrial communication networks. Instead of recomputing the time slot assignment (TSA) for each frame of traffic, this algorithm computes a TSA for a new frame by modifying the known TSA of the previous frame. The algorithm takes O(M ²+cM) time for finding an optimal TSA in a hierarchical switching system, where M is the number of users and c is the number of changes between the traffic demands of two consecutive frames. The algorithm uses a two-step process. The first step transforms the TSA problem in the hierarchical switching system (HSS) into an equivalent TSA problem in a simple TDM switching system. The second step uses an incremental algorithm to find a TSA for the latter. The second step exploits the correspondence between the TSA problem and the rearrangement problem in a Clos three-stage network. When the traffic demands in consecutive frames overlap to a significant extent, the incremental algorithm provides considerable speedup over previous algorithms