Deterministic Scheduling of Periodic Messages for Low Latency in Cloud RAN

Abstract

Cloud-RAN (C-RAN) is an architecture for cellular networks, where processing units, previously attached to antennas, are centralized in data centers. The main challenge, to fulfill protocol time constraints, is to minimize the latency of the periodic messages sent from the antennas to their processing units and back. We show that statistical multiplexing suffers from high logical latency, due to buffering at nodes to avoid collisions. Hence, we propose to use a deterministic scheme for sending periodic messages without collision in the network, thus saving the latency incurred by buffering. We propose several algorithms to compute such schemes for star routed networks, a common topology where one link is shared by all antennas. First, we show there exist deterministic sending schemes without any buffering when the routes are short or the load is small. When the load is high, we allow buffering in processing units, and we propose the PMLS algorithm adapted from a classical scheduling method. Experimental results show that, even under full load, PMLS finds a deterministic sending scheme with no logical latency most of the time, while using statistical multiplexing adds very large latency. Moreover, PMLS runs in polynomial time and scales well to hundreds of antennas. Building on this algorithm, we also obtain very low latency periodic sending schemes that do not disrupt additional random traffic on the network. This article is an extended version of previous work presented at ICT[1].