The defense of PhD thesis of Flavien Ronteix–Jacquet will be held on December 13th, 2022 at 10:00. It will be accessible with a conf call. The thesis is entitled “Reducing Latency and Jitter in 5G Radio Access Networks”. It was made in the framework of a CIFRE contract within Orange.
Cellular networks present high latencies, especially in the Radio Acccess Network (RAN). The new generation of cellular technology 5G, in addition to increasing transmission throughput, must offer low latency in mobile connectivity.The objective of this thesis is to propose mechanisms for reducing latency in the RAN. In this perspective, we set up a software-defined RAN experimentation platform based on the OpenAirInterface project and designed a tool for fine-grained measurement of RAN internal latencies called LatSeq. We show that the round-time trip latency typically reaches 30 ms in LTE divided between processing, queueing, retransmission and medium acquisition delays. We also measure a significant jitter on the uplink that affects the RAN latency but also the performance of TCP traffics, which are very common on the Internet. LatSeq highlights the role of the radio resource allocation mechanism in the jitter and latency of the uplink channel. We show how the partial knowledge of the transmission buffer length by the scheduling algorithm from Buffer Status Reports (BSRs) and Scheduling Requests (SRs) induces bursts of transmissions, significant jitter and under-utilization of the radio channel capacity. We then propose a new mechanism for estimating the terminal transmission buffer length compatible with 3GPP LTE and 5G standards. We demonstrate that this method makes it possible to reduce the latency of the uplink channel and even more the jitter experienced by packet flows.