Survey on 5G Second Phase RAN Architectures and Functional splits

Abstract

<p>The Radio Access Network (RAN) architecture evolves with different generations of mobile communication technologies and forms an indispensable component of the mobile network architecture. The main component of the RAN infrastructure is the base station, which includes a Radio Frequency unit and a baseband unit. The RAN is a collection of base stations connected to the core network to provide coverage through one or more radio access technologies. The advancement towards cloudnative networks has led to centralizing the baseband processing of radio signals. There is a trade-off between the advantages of RAN centralization (energy efficiency, power cost reduction, and the cost of the fronthaul) and the complexity of carrying traffic between the data processing unit and distributed antennas. 5G networks hold high potential for adopting the centralized architecture to reduce maintenance costs while reducing deployment costs and improving resilience, reliability, and coordination. Incorporating the concept of virtualization and centralized RAN architecture enables to meet the overall requirements for both the customer and Mobile Network Operator. Functional splitting is one of the key enablers for 5G networks. It supports Centralized RAN, virtualized Radio Access Network, and the recent Open Radio Access Networks. This survey provides a comprehensive tutorial on the paradigms of the RAN architecture evolution, its key features, and implementation challenges. It provides a thorough review of the 3rd Generation Partnership Project functional splitting complemented by associated challenges and potential solutions. The survey also presents an overview of the fronthaul and its requirements and possible solutions for implementation, algorithms, and required tools whilst providinga vision of the evaluation beyond 5G second phase.</p>

A Tutorial on the Characterisation and Modelling of Low Layer Functional Splits for Flexible Radio Access Networks in 5G and Beyond

“…In relation to previous surveys [5][8] [9] that have also considered the functional splits, their focus and their survey nature make them fundamentally different from this tutorial paper, which targets a characterization, modelling and assessment exercise of functional splits rather than a comprehensive survey. In this respect, although the analysis of the functional splits proposed by industrial initiatives is also covered by these papers, none of them presents the analysis of the BB PHY layer functionalities and the associated complexity/performance for different algorithms.…”

“…Similarly, a comprehensive overview of C-RAN with optical fronthaul is presented in [8], discussing the split options considered by the 3GPP and providing an overview of some references for each case. Recently, a survey [9] presented a literature review of the functional splits proposed by the 3GPP and by O-RAN Alliance and overviewed the fronthaul requirements and implementation solutions. The idea of a flexible functional split was introduced by the iJOIN project in [10] [11] [12] via the RAN as a Service (RANaaS) concept, which consists of partially centralizing functionalities of the RAN depending on the actual needs and network characteristics.…”