Alan A. Bertossi

Learn More
ÐHard-real-time systems require predictable performance despite the occurrence of failures. In this paper, fault tolerance is implemented by using a novel duplication technique where each task scheduled on a processor has either an active backup copy or a passive backup copy scheduled on a different processor. An active copy is always executed, while a(More)
This paper investigates the problem of assigning channels to the stations of a wireless network so that interfering transmitters are assigned channels with a given separation and the number of channels used is minimized. Two versions of the channel assignment problem are considered which are equivalent to two specific coloring problems — called(More)
Broadcast is an efficient and scalable way of transmitting data to an unlimited number of clients that are listening to a channel. Cyclically broadcasting data over the channel is a basic scheduling technique, which is known as flat scheduling. When multiple channels are available, a data allocation technique is needed to assign data to channels.(More)
ÐNew heuristic algorithms are proposed for the Graph Partitioning problem. A greedy construction scheme with an appropriate tie-breaking rule (MIN-MAX-GREEDY) produces initial assignments in a very fast time. For some classes of graphs, independent repetitions of MIN-MAX-GREEDY are sufficient to reproduce solutions found by more complex techniques. When the(More)
In this paper, we investigate the channel assignment problem, that is, the problem of assigning channels (codes) to the cells of a cellular radio network so as to avoid interference and minimize the number of channels used. The problem is formulated as a generalization of the graph coloring problem. We consider the saturation degree heuristic, first(More)
In the Code Division Multiple Access (CDMA) framework, collisions that can occur in wireless networks are eliminated by assigning orthogonal codes to stations, a problem equivalent to that of coloring graphs associated to the physical network. In this paper we present new upper and lower bounds for two versions of the problem (hidden and primary collision(More)