Why the need for Cloudifying Radio Access Network? Journey from D-RAN to C-RAN, vRAN and O-RAN

Before starting the article here is common acronyms: D-RAN (Distributed RAN), C-RAN (Centralized-RAN), vRAN (Virtual-RAN), Open-RAN (O-RAN)

Radio Access Network (RAN) is the interface of mobile network with subscribers and is distributed across targeted coverage area. RAN is the most source of expenditure and the most expensive part of any mobile network in term of both CAPEX and OPEX. Technically, due to the nature of vast and distant distribution of sites across the network and air interface limitations, RAN is the source of almost 80% of network performance issues that impact customer experience. Therefore, RAN is the focus area of any mobile network operator in term of technical and financial investment. Thus, vendors and operators are continuously developing new approaches to increase RAN efficiency to meet surging demands while reducing CAPEX, OPEX and TCO simultaneously.

The current architecture of RAN is mostly distributed RAN (D-RAN), for 4G, 3G and 2G technologies, where base stations consists of the Baseband Processing Unit (BBU) and the RF processing unit (Remote Radio Unit-RRU) from the same vendor due to propriety interfaces and no interoperability support. In a normal architecture, BBU and RRU are both placed in the equipment room and connected with the RRU via short optical fiber with CPRI interface and RRU connected with antennas with long feeders. In a split architecture, the RRU is located at the top of the tower near antennas and connected to the BBU via long fiber connection and connected to antennas with short jumper, which incur more cost for long fiber connection. However, this RAN architecture is limited in service agility, capacity increase, cost reduction, scalability and performance efficiency.

In the new decade and the emergence of new communication generation (5G) and advancement in IR4.0 technologies and applications, there are tremendous surge of demands on mobile broadband, critical communication, IoT connectivity, and other different service-based connectivity. Which operators will race toward seizing as much of those customer they can and thus need to be ready for such increasing market demands. Statistically, number of mobile and FWA subscribers are forecasted to reach 8.8 billion subscribers worldwide by 2026, while IoT connections are forecasted to reach 6 billion by the same year, Ericsson mobility report. This surging demands represents a challenging hurdle for operators to meet such extremely high demands with such RAN architecture. Therefore, there must be an evolution toward new RAN architecture that meet capacity demand, scalability, agility, cost and performance efficiency.

C-RAN is moving BBUs from sites and relocate them to central location between the edge of the network and the core network creating a pool of BBUs (data centers) to increase scalability and prepare RAN for virtualization (cloudification). The evolution from D-RAN to vRAN requires this move toward C-RAN before virtualizing those pool of BBUs. vRAN is the solution that meet capacity scalability and efficiency by virtualizing those centralized BBUs functions. vBBUs are deployed on multiple NFV platforms using industry-standard x86 hardware and aggregated in centralized data centers, while Remote Radio Heads (RRHs) are left at the cell site at the edge of the network. That means that dedicated BBUs hardware built by vendors, i.e. Ericsson, Huawei or Nokia, to specifically run their own RRUs/antenna are now replaced with Commercial Off-The-Shelf (COTS) hardware running standard inexpensive computing architectures like x86. vRAN leverages a standard server hardware that can be cost effectively scaled up or down of processing, memory, and input/output resources with demand and leverage the RAN capacity for application intelligence which significantly improve service quality and reliability.

Disaggregating software from hardware in RAN adjourns the proprietary oligopoly of RAN network’s elements and protocols market and open competition for innovation in RAN software and hardware solutions while reducing costs for operators. O-RAN is a concept based on interoperability and standardization of RAN elements including a unified interconnection standard for COTS hardware and open source software elements from different vendors Thus, ORAN Alliance was formed and pushed seriously forward by 26 leading international operators, i.e. Deutsch Telecom, BT, Telefonica, Vodafone; vendors will eventually have to join to maintain their partnership with CSPs and stay innovative and competitive in this evolved market.

The idea is that if operators force all vendors to move software, focusing on SDN, and operators can source COTS (commercial-off-the-shelf) hardware. As a result, operators gain CAPEX cost efficiency and more control because COTS are always cheaper than proprietary. And if operators virtualize all their RAN software then they gain OPEX cost efficiency because they can ideally software manage RAN operation, which means on demand usage and spending, as well as vendor independence if those proprietary interfaces are open. O-RAN alliance aims to make RAN open, intelligent, virtualized and interoperable RAN to meet operators’ vision and surging customer demands. We can see the result of ORAN effort that leading vendors shifted their focus toward advancing their network software development (SDN and NFV) to compensate the expected loss from long propriety-based revenue. 

In conclusion, Centralized RAN (C-RAN), Cloud RAN (CRAN not to be confused with C-RAN), Virtualized RAN (vRAN) and Open-RAN (O-RAN) are all concepts that have emerged in the last few years to describe the evolution of RAN architecture. O-RAN is the umbrella concept which include C-RAN and vRAN will enable a more competitive and vibrant RAN supplier value chain with faster innovation and time to market. O-RAN is the move from vendor defined RAN toward operator defined RAN, which result improved CAPEX and OPEX efficiency as well as improving RAN deployment and operation with more flexible and innovative solutions. While most operators would rather continue purchasing from their traditional vendors, to reduce operational and financial risks, the race toward 5G and the pressure on margins and operators stock prices is forcing them to reevaluate the RAN value chain.

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Some additional sources

https://www.o-ran.org/

https://www.nokia.com/networks/portfolio/radio-access-networks-ran/open-ran/

https://www.ericsson.com/4adc87/assets/local/mobility-report/documents/2020/november-2020-ericsson-mobility-report.pdf