Competitive analysis of on-line algorithms for on-demand data broadcast scheduling

We consider a communication problem, in which requests for data items arrive from time to time via a terrestrial network and at each broadcast tick the single server chooses a data item to broadcast via a satellite downlink to satisfy all the requests for the item. The goal of the server to minimize the total wait time of the requests. In this paper, we examine two well-known on-line algorithms used by the server to decide which data item to broadcast at each broadcast tick. In particular, we present complete competitive analysis of the algorithms, a research aspect of the problem which had not been studied before. Our results are consistent with observations obtained by simulation experiments reported in past literature. In addition, we prove a general lower bound to the competitive ratios of all online algorithms. The competitive ratios obtained for the two on-line algorithms in fact match our general lower bound, indicating the optimality of the algorithms.