The defense of PhD thesis of Tania Alhajj will be held on May 17th, 2023 at 10:00 in the Rennes campus of IMT Atlantique (Petit amphi). It will be accessible with a conf call. The thesis is entitled “Impact of centralized-radio access network architecture on 5G performances”. It was partially funded by Région Bretagne.
Fifth Generation (5G) mobile networks are paving the way for a new Radio Access Network (RAN) architecture. This is the Centralized-RAN (C-RAN) which groups some of the Base Station (BS) functions in a Central Unit (CU) connected to Radio Units (RU) distributed in different sites where the other BS functions are implemented. This thesis studies how to take advantage of C-RAN to combine high reliability and low latency on the one hand and to minimize the power consumption of the BS on the other hand. Both single and multi-RU transmissions, as well as a mixture of both, are evaluated. We compare a single-RU approach where the Hybrid Automatic Repeat reQuest (HARQ) mechanism, which combines all the ARQ re-transmissions, is located in the RU to a multi-RU transmission with an HARQ centralized in the CU. We show that multi-RU transmissions provide high reliability and low latency due to spatial diversity, even though centralization increases the round trip time. We then consider radio resource allocation. We evaluate the energy consumed by the BSs using a consumption model that integrates both the transmission power and the energy consumed for processing. At low load, multi-RU transmissions in a C-RAN, where all RUs serve one user, save BS energy consumption, without coverage degradation, compared to serving a user with a single RU. We pose and solve an optimization problem to minimize the energy consumption and increase the capacity to moderate load by reusing radio resources between RUs.