Cloud RAN (C-RAN)
Commoditization and virtualization of wireless networks are changing the economics of mobile networks to help network providers (e.g., MNO, MVNO) move from proprietary hardware and software platforms toward an open, cost-effective, and flexible cellular ecosystem. In addition, rich and innovative local services can be efficiently created through cloudification by leveraging the existing infrastructure. Consequently, there are proposals such as RANaaS, which is a cloudified radio access network delivered as a service. RANaaS provides the service life-cycle of an on demand, elastic, and pay as you go 3GPP RAN instantiated on top of the cloud infrastructure.
In the last few decades, radio access networks (RANs) have significantly evolved from analog to digital signal processing units, where hardware components are often replaced with flexible and reusable software-defined functions. In a pure software-defined radio (SDR) system, the entire radio function runs on a general-propose processor (GPP) and only requires analog-to-digital and digital-to-analog conversions, power amplifiers, and antennas, whereas in typical cases, the system is based upon a programmable dedicated hardware (e.g. ASIC, ASIP, or DSP) and associated control software. Thus, the flexibility offered by a pure SDR improves service life-cycle and cross-platform portability at the cost of lower power and computational efficiency (i.e. ASIC: 1x, DSP: 10x, GPP: 100x).
Virtual RAN extends this flexibility through abstraction (or virtualization) of the execution environment. Consequently, radio functions become a general-purpose application that operates on top of a virtualized environment and interacts with physical resources either directly or through a full or partial hardware emulation layer. The resulted virtualized software radio application can be delivered as a service and managed through a cloud controller. This changes the economics of mobile networks towards a cheap and easy to manage software platforms. Furthermore, cloud environment enables the creation of new services, such as RAN as a service (RANaaS), and more generally, network as a service (NaaS), such as LTEaaS, associated with the cloud RAN (C-RAN). C-RAN systems replace traditional base stations with distributed (passive) radio elements connected to a centralized baseband processing pool. Decoupling of the radio elements from the processing serves two main purposes. Centralized processing has the benefit of cost reduction due to fewer number of sites, easy software upgrade, performance improvement with coordinated multi-cell signal processing. Also, the remote radio heads have a much smaller footprint than a base station with on site processing, allowing for simpler and cost-effective network densification. C-RAN can be realized in two main steps, namely:
- Commoditization and Softwarization: refers to a software implementation of network functions on top of GPPs with no or little dependency on a dedicated hardware (e.g. DSP, FPGA, or ASIC). In addition, the programmability in RF domain can be achieved with the Field Programmable Radio Frequency (FPRF) technology.
- Virtualization and Cloudification: refers to execution of network functions on top of virtualized (and shared) computing, storage, and networking resources controlled by a cloud OS. I/O resources can be shared among multiple physical servers, and in particular that of radio front-end through multi root I/O virtualization (MR-IOV).
Software Defined Networking (SDN)
Software Defined Networking (SDN) is a new architecture that that has been designed to enable more agile and cost-effective networks. SDN allows dynamic reconfiguration of the network by taking a new approach to the network architecture. In a traditional network device, like a router or switch, it contains both the control and data plane. The control plane determines the route that traffic will take through the network, while the data plane is the part of the network that actually carries the traffic. By separating the control and data plane, network equipment can be configured externally through vendor independent management software and has the potential to transform the network from a closed system to an open system. SDN also helps to enable centralization of network management for different entities within a cellular network. There is still work going on within academia and industry to apply SDN principles to cellular networks.
- Directly Programmable: Decouple network control and data plane enabling network intelligence to reside in software-based SDN controllers.
- Open: Facilitate consensus within the industry for open standard for managing different vendor equipment. Open Standard for SDN is the key to successful adoption of this technology and facilitate SDN based innovation within cellular ecosystem.
- Agile: Enable dynamic configuration, management and optimization of cellular network for operators based on changing traffic scenarios and deployment characteristics.
SDN separates the network into three different layers – application, control and data.
- Application Layer: This layer hosts the SDN applications and communicate with the SDN enabled controller via standardized application programming interface (API), northbound interface. Developers can write the applications for configuring the network and do not have to worry about the details of underlying network. The SDN applications may be network applications, cloud orchestration or business applications.
- Control Layer: SDN decouples control plane from the data plane. The SDN controller is located in control layer and translates application layer requirements and controls the SDN data paths. The SDN controller constructs and presents a logical map of the network for efficient decision making by SDN applications that are sitting inside the application layer.
- Infrastructure Layer: This layer is referred to as the actual network hardware (core network, base-stations, switches, routers, etc) that implement SDN data paths and forward the actual traffic. The infrastructure layer is required to implement open standards-based programmatic access to infrastructure to enable programming from SDN controllers.