RAN, O-RAN, ns-O-RAN and Traffic Steering in 5G Networks.

RAN (Radio Access Network)

RAN is a key component of a cellular network that provides radio connectivity between mobile devices (such as smartphones, tablets, or IoT devices) and the core network infrastructure. The RAN encompasses the equipment, protocols, and technologies that enable wireless communication over the air interface. The image at the right from[9] shows the architecture of a typical RAN.

The primary function of the RAN is to transmit and receive wireless signals between mobile devices and the network infrastructure. It consists of a set of base stations (also known as cell sites or radio transceivers) strategically placed to provide coverage over a specific geographical area called a cell. Each base station typically consists of antennas, radio frequency (RF) equipment, and signal processing components.

When a mobile device communicates with the network, it establishes a wireless connection with the nearest base station within its coverage area. The base station then relays the signals to the core network, which handles tasks such as call routing, data transfer, and network management.

The RAN is responsible for several critical functions, including:

Signal transmission: The RAN transmits and receives radio signals to establish and maintain wireless connections with mobile devices.
Signal modulation and demodulation: It converts digital signals from the core network into analog signals suitable for wireless transmission and vice versa.
Handover management: The RAN manages the seamless transfer of mobile devices’ connections as they move between different base stations or cells.
Radio resource management: It allocates and manages radio resources, such as frequencies and bandwidth, to ensure efficient utilization and optimal performance.
Interference mitigation: The RAN employs techniques to mitigate interference and improve signal quality, such as adaptive antenna systems and interference cancellation algorithms.

RAN technologies have evolved over the years, from analog systems (1G) to digital systems (2G, 3G) and the current generation of Long-Term Evolution (LTE) and 5G networks. The RAN plays a crucial role in providing wireless connectivity, enabling voice calls, data services, and various applications to mobile devices across a wide area.

Open RAN

Open RAN refers to a disaggregated approach to building and operating cellular networks. Open RAN is a new approach to building the RAN that is the foundation of cellular networks. Traditional cellular networks or RAN are typically built using proprietary, integrated hardware and software solutions from a single vendor, which can make it difficult and expensive for operators to upgrade their networks. Open RAN aims to create an open and interoperable ecosystem by separating the hardware and software components of the RAN, which allows operators to choose from a wider range of suppliers and to easily upgrade their networks.

In an Open RAN architecture, the hardware and software functions of the RAN are decoupled, allowing operators to mix and match components from different vendors. This approach promotes vendor diversity, innovation, and competition, as operators are not locked into a single vendor’s solutions. It enables operators to select best-of-breed components and deploy them in a more flexible and cost-effective manner.

Open RAN is seen as a way to promote competition, innovation, and cost reduction in the telecommunications industry. It has gained significant attention and support from operators, governments, and industry organizations worldwide. The ultimate goal of Open RAN is to create an open and interoperable ecosystem that encourages multiple vendors to participate in the network infrastructure market, fostering innovation and driving the evolution of cellular networks.

The key principles of Open RAN include:

Disaggregation: Open RAN separates the different functional components of the RAN into different modules, which can be provided by different vendors. This makes it easier for operators to mix and match components from different suppliers, and it also makes it easier to upgrade the network.
Standardization: Open RAN relies on open interfaces and standards that enable interoperability between different vendors’ equipment. This allows for seamless integration and avoids vendor lock-in.
Virtualization: Open RAN leverages virtualization technologies to separate software functions from hardware, enabling more flexibility and scalability. Virtualized functions can be deployed on general-purpose hardware or in cloud-based environments.
Centralization and intelligence: Open RAN introduces a centralized software-defined control framework that enables dynamic resource allocation, optimization, and intelligent management of the RAN. This centralized approach improves network efficiency and performance.
Open interfaces: Open RAN components communicate with each other using open interfaces. This makes it easier for different components from different vendors to work together, and it also makes it easier for operators to upgrade the network.

Open RAN has a number of potential benefits for operators, including:

Reduced costs: Open RAN can help operators to reduce the cost of their networks by giving them more choices in terms of hardware and software suppliers.
Increased flexibility: Open RAN can help operators to be more flexible in how they deploy their networks, by allowing them to mix and match different components from different suppliers.
Improved performance: Open RAN can help operators to improve the performance of their networks by making it easier to upgrade and manage them.

Open RAN is a promising new technology that has the potential to revolutionize the way that cellular networks are built and operated. It is still in its early stages of development, but it is gaining momentum and it is likely to play a major role in the future of cellular networks.

The right side image is an illustration of O-RAN from O-RAN ALLIANCE [8]. O-RAN ALLIANCE is committed to evolving Radio Access Networks with its core principles being intelligence and openness. It aims to drive the mobile industry towards an ecosystem of innovative, multi-vendor, interoperable, and autonomous RAN, with reduced cost, improved performance, and greater agility[8].

ns-O-RAN

ns-O-RAN is the first open-source simulation platform that combines a functional 4G/5G protocol stack in ns-3 with an O-RAN-compliant E2 interface[1]. ns-O-RAN builds on ns-3 and the ns3-mmWave[4] module, which is developed and maintained by the University of Padova and NYU.

The tutorial page at[3] says, “ns-O-RAN has been designed and implemented to enable the integration of O-RAN software such as the O-RAN Software Community Near-RT RIC with large-scale 5G simulations based on 3GPP channel models and detailed modeling of the full 3GPP RAN protocol stack. This allows data collection of RAN Key Performance Metrics (KPMs) at scale, in different simulated scenarios, and with different applications (e.g., multimedia streaming, web browsing, wireless virtual reality, etc). ns-O-RAN supports an O-RAN-compliant E2 interface and implements two E2 service models (E2SM), E2SM-Key Performance Metrics (KPM) monitoring and E2SM-RAN Control (RC), that enable a closed-loop control (for example, of traffic steering and mobility)”.

The image at [3] presents the architecture of ns-O-RAN as follows:

ns-O-RAN Architecture

In [2], the authors introduce ns-O-RAN, a software framework that integrates a real-world, production-grade nearRT RIC with a 3GPP-based simulated environment on ns-3.

E2 Interface

The E2 interface is a standardized interface used in the context of Open RAN architecture. It facilitates communication and coordination between different functional entities within the Radio Access Network (RAN). The E2 interface enables the exchange of control plane and management plane information, allowing for efficient operation and optimization of the RAN.

The E2 interface is part of the overall O-RAN (Open Radio Access Network) architecture, which promotes interoperability and openness in RAN deployments. It is defined by the O-RAN Alliance, a global industry consortium that develops specifications and promotes the adoption of Open RAN principles.

The E2 interface serves several purposes within the RAN, including:

Coordination between RAN components: The E2 interface enables coordination between various RAN components, such as baseband units (BBUs), remote radio units (RRUs), and centralized control functions. It allows for the exchange of information related to resource management, scheduling, handover, and other RAN-specific functions.
Dynamic RAN optimization: Through the E2 interface, the RAN components can exchange real-time information, such as radio conditions, traffic load, and network status. This information can be used to optimize resource allocation, adapt radio parameters, and enhance overall network performance.
Interoperability between vendors: The E2 interface follows open standards, allowing RAN components from different vendors to interoperate seamlessly. It promotes vendor diversity and fosters competition by enabling operators to choose components from multiple suppliers without being locked into a single vendor’s proprietary solutions.

The E2 interface is specific to Open RAN deployments and is part of the broader efforts to create a more open and flexible RAN architecture.

E2 is a bi-directional interface that splits the RRM between the E2 nodes and the near-RT RIC. With this architecture, the call processing and signaling procedures are implemented in the E2 nodes, but the RRM decisions for these procedures are controlled by the RIC through xApps. For example, the handover procedures for a UE are executed by the E2 node, but the UE’s target cell for handover is decided and controlled by the RIC [2].

RAN Intelligent Controller

RIC is a key component in the Open RAN architecture that plays a crucial role in managing and optimizing the Radio Access Network (RAN). The RIC acts as a centralized and intelligent control function that oversees and orchestrates various RAN operations.

The RIC is responsible for dynamically controlling and optimizing the RAN based on real-time network conditions, traffic demands, and service requirements. It leverages advanced algorithms, machine learning, and AI techniques to make intelligent decisions and adjustments to improve network performance and efficiency.

Some of the key functions and capabilities of the RIC include:

Policy-based control: The RIC applies policies and rules to govern and control different aspects of the RAN operation, such as radio resource management, interference mitigation, handover optimization, and traffic steering.
Dynamic resource allocation: The RIC optimally allocates and manages radio resources, such as frequency bands, time slots, and power levels, based on the current network conditions and traffic demands. It ensures efficient resource utilization and quality of service for users.
Intelligent network optimization: The RIC continuously monitors the RAN performance, collects data, and performs real-time analysis to identify bottlenecks, congestion points, or areas for improvement. It then takes corrective actions, such as adjusting radio parameters or reconfiguring network elements, to optimize the RAN performance.
Service orchestration: The RIC coordinates and orchestrates the delivery of different services and applications over the RAN. It ensures that the RAN resources are allocated appropriately to meet the service requirements and provide the best possible user experience.

The RIC works in conjunction with other components in the Open RAN architecture, such as the RAN controller (RAN-C) and the RAN dispatcher (RAN-D). These components collaborate to enable dynamic and intelligent control of the RAN, promoting flexibility, interoperability, and innovation in the cellular network environment.

The near-RT RIC is typically deployed as a network function in a virtualized cloud platform at the edge of the RAN. It onboards extensible applications (xApps), apart from O-RAN standardized platform framework functions, to optimize RRM decisions for dedicated RAN functionalities using low-latency control loops at near-RT granularity (from 10 ms to 1 second). The near-RT RIC connects through the E2 interface to the CUCP, CU-UP, DU, and eNB, collectively referred to as the E2 nodes [2].

Traffic Steering (TS)

Traffic Steering is the management of the mobility management of individual UEs served by the RAN. TS involves key RAN procedures, such as handover management, dual connectivity, and carrier aggregation, among others. While handover management is a classic problem, the requirements and deployment scenarios for optimizing handovers keep changing with evolving radio access technologies and use-cases, posing newer challenges and requiring newer optimization strategies [2].

Using ns-O-RAN we can create simulated closed control loops between ns-3 and a Near-RT RIC. Near-RT RIC from the WIoT’s ColO-RAN framework can be installed on a local workstation or can be loaded into any experimental platform such as Colosseum[3].

OpenRAN Gym

OpenRAN Gym is an open-source project fostering collaborative, AI-driven and experimental research in the Open RAN ecosystem[10]. OpenRAN Gym is organized by a team at the Institute for the Wireless Internet of Things, Northeastern University. The goal of OpenRAN Gym is to bring together researchers from academia and industry to create a vibrant, dynamic, evolving and cooperative ecosystem advancing research and development of cutting-edge and groundbreaking solutions for the Open RAN[10]. It is possible to use OpenRAN Gym along with ns-O-RAN to do state-of-the-art ML/RL-based algorithms for Open RAN architecture.

Colosseum

Colosseum is the world’s largest wireless network emulator designed to support research and development of large-scale, next-generation radio network technologies in repeatable and highly configurable Radio-frequency (RF) and traffic environments,[7]. It combines 128 Standard Radio Nodes (SRNs), each equipped with NI USRP X310 Software-defined Radios (SDRs), with a Massive digital Channel Emulator (MCHEM) backed by an extensive FPGA routing fabric. MCHEM emulates in FPGA real-world wireless RF channel between the SRNs and it is able to capture effects such as fading, multipath, etc., for up to 256×256 independently customizable channels. Accessible as a cloud-based platform, Colosseum also provides unique experimentation and data-collection capabilities[6].

Conclusion

ns-O-RAN is an ns-3 module that connects a real-world near-RT RIC with ns-3 simulations, enabling the large-scale collection of RAN KPMs and testing of closed-loop control of simulated cellular networks. So, using ns-O-RAN, it is possible to do experiments and evaluations on state-of-the-art, ML/RL-based Traffic Steering techniques that will revolutionize future 5G Networks. We will see the installation of ns-O-RAN and related software in another article.