Abstract
We study the delay over virtual RAN (vRAN) topologies, entailing base stations that are divided into centralized and distributed units, as well as the packet-switched fronthaul network that connects them. We consider the use of flexible functional split, where the functions that are executed at each of these two entities can be dynamically shifted. We propose a queuing-based model, which is able to precisely mimic the behavior of such nodes, and we validate it by means of extensive simulations. We also exploit Jackson Networks theory to establish the end-to-end delay over the fronthaul network, allowing us to assess the impact of having different networking policies and conditions (for instance, background traffic or heterogeneous technologies). Thanks to the simulator we can also broaden the analysis, by studying the delay variability. In addition, we conduct an in-depth analysis of the performance exhibited by a realistic network setup, whose particular characteristics might hinder the services performance, due to the longer dwell times at each split configuration. The results evince the validity of the proposed model, even under realistic conditions. We show that it might not be enough to guarantee an average stable operation of the centralized/distributed units, but the traffic load should remain below the slowest service rate, to avoid reaching unacceptable delays. An increase of $> 100 \times $ is observed in the delay, using the realistic network setup, when these conditions do not hold.
Highlights
It is well known that one of the most stringent requirements for forthcoming cellular systems (5G and Beyond 5G) comes from the so-called Ultra-Reliable Low Latency Communication (URLLC)
Considering an architectural look, Radio Access Networks (RAN) have witnessed a strong shift, and thanks to the SDN and NFV paradigms, operators are deploying many of the functions that were traditionally co-located in the base station (BS) in centralized controllers
In order to overcome the limitations coming from fully centralized solutions, functional-split architectures were proposed to permit the use of multiple centralization levels [5], which could be adapted to the particular network characteristics, traffic features and service requirements
Summary
It is well known that one of the most stringent requirements for forthcoming cellular systems (5G and Beyond 5G) comes from the so-called Ultra-Reliable Low Latency Communication (URLLC). The new RAN is made of physical and virtual entities, leading to the so called virtual RAN (vRAN) [9] These architectural changes have imposed new challenges on the fronthaul network that connects such entities, since it needs to provide quality of service (QoS) levels aligned with the configured split. Recent studies consider the dynamic, or flexible, shifting of the selected functional split, to adapt the network to the varying environment [11] (i.e. new services, traffic changes). To the best of our knowledge, this is the first work that exploits queuing theory to study the delay for vRAN architecture with Flexible Functional Split, embracing the fronthaul network.
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