Subramanian Ramanathan

Scheduling algorithms for multihop radio networks

Algorithms for transmission scheduling in multihop broadcast radio networks are presented. Both link scheduling and broadcast scheduling are considered. In each instance, scheduling algorithms are given that improve upon existing algorithms both theoretically and experimentally. It is shown that tree networks can be scheduled optimally and that arbitrary networks can be scheduled so that the schedule is bounded by a length that is proportional to a function of the network thickness times the optimum. Previous algorithms could guarantee only that the schedules were bounded by a length no worse than the maximum node degree times optimum. Since the thickness is typically several orders of magnitude less than the maximum node degree, the algorithms presented represent a considerable theoretical improvement. Experimentally, a realistic model of a radio network is given and the performance of the new algorithms is studied. These results show that, for both types of scheduling, the new algorithms (experimentally) perform consistently better than earlier methods. >

Scheduling algorithms for multi-hop radio networks

New algorithms for transmission scheduling in multihop broadcast radio networks are presented. Both link scheduling and broadcast scheduling are considered. In each instance scheduling algorithms are given that improve upon existing algorithms both theoretically and experimentally. Theoretically, it is shown that tree networks can be scheduled optimally, and that arbitrary networks can be scheduled so that the schedule is bounded by a length that is proportional to a function of the network thickness times the optimum. Previous algorithms could guarantee only that the schedules were bounded by a length no worse than the maximum node degree, the algorithms presented here represent a considerable theoretical improvement. Experimentally, a realistic model of a radio network is given and the performance of the new algorithms is studied. These results show that, for both types of scheduling, the new algorithms (experimentally) perform consistently better than earlier methods.

On the complexity of distance-2 coloring

The authors study the problem of distance-2 colorings of the vertices of undirected graphs. In such a coloring, vertices separated by a distance of less than or equal to two must receive different colors. This problem has direct application to the problem of broadcast scheduling in multihop radio networks. The authors show that even when restricted to planar graphs, finding a minimum such coloring is NP-complete. They then describe a good (constant times optimal) approximation algorithm for the distance-2 coloring of planar graphs. They also extend this analysis of the algorithm to deal with general graphs. They show that the performance of the algorithm has a worst-case bound that is proportional to the product of the graph arboricity and the maximum vertex degree. Previous algorithms could only guarantee a bound proportional to the square of the maximum degree.<<ETX>>