A wide range of applications for wireless ad hoc networks are time-critical and impose stringent requirement on the communication latency. This paper studies the problem Minimum-Latency Broadcast Scheduling (MLBS) in wireless ad hoc networks represented by unit-disk graphs. This problem is NP-hard. A trivial lower bound on the minimum broadcast latency is the radius R of the network with respect to the source of the broadcast, which is the maximum distance of all the nodes from the source of the broadcast. The previously best-known approximation algorithm for MLBS produces a broadcast schedule with latency at most 648R. In this paper, we present three progressively improved approximation algorithms for MLBS. They produce broadcast schedules with latency at most 24R - 23, 16R - 15, and R + O (log R) respectively.
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