Scheduling periodic messages on a shared link
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Cloud-RAN is a recent architecture for mobile networks where the processing units are located in distant data-centers while, until now, they were attached to antennas. The main challenge, to fulfill protocol time constraints, is to guarantee a low latency for the periodic messages sent from each antenna to its processing unit and back. The problem we address is to find a sending scheme of these periodic messages without contention nor buffering. We focus on a simple but common star shaped topology, where all contentions are on a single link shared by all antennas. For messages of arbitrary size, we show that there is always a solution as soon as the load of the network is less than 40%. Moreover, we explain how we can restrict our study to message of size 1 without increasing too much the global latency. For message of size 1, we prove that it is always possible to schedule them, when the load is less than 61% using a polynomial time algorithm. Moreover, using a simple random greedy algorithm, we show that almost all instances of a given load admit a solution, explaining why most greedy algorithms work so well in practice.
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