# 5G New Radio Open Radio Access Network Implementation in Brazil: Review and Cost Assessment
## 2 Background
### Open RAN Architecture  
The key goals of Open RAN implementation are to bring openness and intelligence and offer flexibility, performance improvement, and cost-efficiency in RAN deployment and operation [18]. The RAN is better known as the base station (BS) or gNodeB. The BS has two central units: the radio unit (RU), which is responsible for transmission and reception through electromagnetic waves to UEs, and the baseband unit (BBU), which is responsible for radio management, resource allocation, and other management operations, interconnecting the core functions to the gNodeB. The RAN architecture has evolved through generations, centralizing, separating, and virtualizing the elements of the RAN network. In d-RAN, the RU and the BBU are vertically integrated, with BBU installed right at the base of the BS using proprietary hardware and software. The RU is located at the top of the tower, providing extensive area coverage, and it does not require a high-speed interface to connect to the BBU. Each BS operates independently and becomes denser as the number of RANs increases. This layout results in high OPEX costs for MNOs due to renting BS site spaces and cooling systems, along with high CAPEX on equipment. The \"Centralized\" or \"Cloud\" RAN architecture reduces site space rental costs and power consumption. The BBU is divided into a CU and a DU. The fronthaul (FH) connects the DU to the remote RU (RRU) using the Common Public Radio Interface (CPRI). The CU manages and distributes traffic from the core to different DUs and from the DUs to several RRUs. This concept requires high bandwidth and low latency due to additional jitter and latency introduced by the equipment needed to reach the RRU. In c-RAN, the BBU's functions are physically pooled, while in cloud RAN, the DU and CU are used in aggregated cloud servers. The cloud server improves baseband processing, improvesnetwork throughput, enables network scalability, and reduces power consumption. Some disadvantages of the c-RAN include FH overhead, trust issues, security concerns, and a single point of failure. A failure in the CU could impact a wide coverage area. By introducing virtualization, the BBU abstracts the physical hardware, creating virtual instances of the RAN elements. Virtualization enables the implementation of new technologies such as software-defined networks (SDNs) and network function virtualization (NFV). It allows for automatic deployment of elements, rapid scaling with service management and orchestration (SMO), reduced energy consumption, improved service reliability, and better service quality through efficient network resource utilization. In v-RAN, the virtualized BBU (vBBU) connects to the RRU through enhanced CPRI (eCPRI), resulting in lower latency. The vBBU houses the DU and CU software running vertically on COTS hardware. A CU can operate several kilometers away from RUs. Specialized hardware can utilize Graphical Process Units (GPUs) to accelerate real-time sensitive processing for radio lower layers, supporting mMIMO technologies and AI processes. Although v-RAN can reduce data-processing resources by around 50% compared to c-RAN, a proprietary interface can lead to vendor lock-in, hindering equipment cost competitiveness. v-RAN allows for multi-vendor interoperability with open APIs and network element virtualization, offering unit flexibility and bringing system processing to the network edge through Mobile Edge Computing (MEC) to meet new application requirements. In addition, shared sites reduce MNO investments in hardware or site rentals, saving space and energy consumed by equipment and cooling systems. This solution can be deployed in public or proprietary data centers, reducing costs by leveraging data center infrastructure without concerns about hardware upgrades or additional security implementations. Open RAN originates from disaggregating hardware and software into segmented and flexible elements along the network fronthaul to the radio antenna [19].