The author is a former Advisor, Department of Telecommunications (DoT), Government of India
The mobile network comprises two domains: The Radio Access Network (RAN) and the Core Network. The RAN is the final link between the network and the phone. It includes an antenna on the tower plus the base station. Though it was possible for the operators to have one vendor for the core and a separate vendor for the RAN, the same was not done because of interoperability issues.
Open RAN is the hot topic now-a-days and most talked about technology, both in diplomatic and technical circles. This is a three year old technology and fifty operators in more than two fifty countries have deployed open RAN. First it was deployed in the network of Rakuten mobile, a Japanese telecom service provider. This technology makes RAN agnostic to vendors, programmable and converts it to plug & play type. Open RAN is at the epicentre of the digital transformation and plays a critical role in bringing more diversity to the 5G ecosystem. It is required for faster 5G rollout. Domestic (India) vendors may get the opportunity to supply the building blocks of RAN and so it is an initiative towards ‘self-reliant India.’
The RAN accounts for 60 per cent of capex/opex of mobile networks and so a lot of focus is there to reduce RAN costs. 5G signals have a shorter range than previous generation signals. As a result 5G networks require more base stations to provide the required coverage. So in 5G networks this percentage may be still higher.
Open RAN implementation reduces RAN costs. Instead of concentrating on making end-to-end open, opening the RAN ecosystem is given priority by the operators. The open RAN standards aim to undo the siloed nature of the RAN market where a handful of RAN vendors only offer equipment and software that is totally proprietary. Proprietary products are typically more expensive than their generic counterparts. Cellular networks have been evolving with various innovations. It has evolved from 1G to 5G. With these evolutions networks are evolving towards open networks having open interface and interoperability. Open RAN is a term used for industry wide standards for RAN interfaces that support interoperation between different vendor’s equipment and offer network flexibility at a lower cost. The main purpose of open RAN is to have an interoperability standard for RAN elements including non-proprietary hardware and software from different vendors. An open environment means an expanded ecosystem, with more vendors providing the building blocks. Open RAN helps the operators to overcome “Vendor lock in” introducing ‘best of breed’ network solutions.
There will be more innovations and more options for the operators. With a multi -vendor catalog of technologies, network operators have the flexibility to tailor the functionality of their RANs to the operators’ needs. They can add new services easily. Open RAN gives new equipment vendors the chance to enter the market with Commercial off the shelf (COTS) hardware. An influx of new vendors will spur competition. Cell site deployment will be faster. Third Party products can communicate with the main RAN vendor’s infrastructure. New features can be added more quickly for end users.
Current RAN technology is provided as a hardware and software integrated platform. The aim of open RAN is to create a multi supplier RAN solution that allows for the separation or disaggregation between hardware and software with open interface. Open RAN is about disaggregated RAN functionality built using open interface specifications between blocks. It can be implemented in vendor neutral hardware and software based on open interfaces and community developed standards.
In an open RAN environment, the RAN is disaggregated into three main building blocks:
- Radio Unit (RU)
- Distribution unit (DU)
- Centralized unit(CU)
The RU is where the radiofrequency signals are transmitted, received, amplified and digitized. It is located near or integrated into the antenna. The DU and CU are parts of the base station that send the digitized radio signal into the network. The DU is physically located at or near the RU whereas the CU can be located nearer the Core. DU is connected with RU on Optical Fiber cable. The concept of open RAN is opening the protocols and interfaces between these building blocks (radio, hardware and software) in the RAN.
Another feature of Open RAN is the RAN Intelligent Controller (RIC) which adds programmability to the RAN. For example, Artificial Intelligence can be introduced via the RIC to optimise the performance of the network in the vicinity of a cricket stadium on a match day. The RIC works by exposing an API (Application Programming Interface) which lets software talk to each other. There are two types of RIC: near-real time and non real time. Both perform logical functions for controlling and optimizing the elements and resources of open RAN. A near-real time RIC (response time on the order of 10’s of milliseconds) controls and optimizes elements and resources with data collection and communication. A non-real time RIC (response time greater than one second) uses AI and Machine Learning (ML) workflows that include model training, where the workflows learn how to better control and optimize the RAN elements and resources.
The O-RAN alliance has defined eleven different interfaces within the RAN including those for:
Front haul between RU and DU Mid haul between DU and CU Backhaul connecting the RAN to the Core (also called as transport network)
O-RAN alliance is a specification group defining next generation RAN infrastructures, empowered by principles of intelligence and openness. Openness allows smaller players in the RAN market to launch their own services. It was founded in 2018.
O-RAN alliance is a worldwide community of around two hundred mobile operators, vendors and research and academic institutions operating in the Radio Access Network industry. Its goals include to build mechanisms for enabling AI and ML for more efficient network management and orchestration. It supports its members in testing and implementation of their open RAN implementation. O-RAN conducts world wide plug tests to demonstrate the functionality as well as the multi vendor interoperability of open network equipment. O-RAN alliance develops, drives and enforces standards to ensure that equipment from multiple vendors interoperate with each other. It creates standards where none are available, for example Front haul and creates profiles for interoperability testing where standards are available.
Open RAN challenges:
1. Integration of equipment from multiple vendors
2. Since equipment is from different vendors, operators have to have multiple Service Level Agreements (SLAs)
3. Network latency may increase
4. Reliability and availability may be a challenge
5. Staff has to acquire multiple skill sets
6. Security Concerns
Open RAN offers a golden opportunity for software developers to become a global hub for offering RAN solutions. This technology leads to a great disruption to the traditional ecosystem and accelerates the adoption of more innovative technologies. The disaggregation of RAN has also added further advantages by enabling better network slicing and edge compute capabilities.