The ORAN Alliance may have based its initial specifications on AT&T code, but it is Japan’s NTT Docomo which is taking the lead in driving the ORAN platform towards commercial reality.
As so often when it comes to advanced architectures and multivendor networks, Docomo is setting the pace. The pre-commercial 5G service it is launching this week will combine 4G and 5G base stations from multiple suppliers using the ORAN specs. This will represent a major step forward in a world where most operators still define a multivendor RAN as one where different suppliers cover different geographical zones.
Japan’s largest MNO will be switching on a network in Tokyo, offering pre-commercial services as a preparation for 5G support for next year’s Olympic Games. This network will combine 4G and 5G base stations in a disaggregated architecture (with centralized baseband units serving multiple radio units), using equipment from Fujitsu, NEC, and Nokia. Docomo claimed this is the first commercial implementation of interoperable signal transmit and receive between equipment from different vendors in a single RAN. This is not, however, a virtualized RAN – Docomo has implemented some vRANs within its 4G network but only for certain locations and in a heavily customized way. However, it is expected to be among the early movers when 5G vRAN standards stabilize.
“The ability to deploy and interconnect base station equipment from different vendors will make it possible to select the equipment most suitable for deployment in any given environment, such as base stations offering broad coverage in rural areas or small base stations that can be deployed in urban areas where space is limited,” the MNO said in a statement.
The network achieves this interoperability using the ORAN-defined protocol for the fronthaul links between the centralized baseband units and remote radio units. It is also using ORAN’s X2 specification to connect the 4G and 5G base stations to one another. While X2 is a 3GPP standard, it has been implemented slightly differently by each base station vendor, preventing their respective equipment from communicating.
Now ORAN is offering a common implementation and calling on vendors – many of which, including Nokia, Ericsson and Samsung, are ORAN members – to adopt this in future systems. X2 is very important in the first wave of 5G, which relies on Non-Standalone (NSA) 5G RAN and the 4G core. With X2 and Dual Connectivity, both types of base stations can communicate with one another and with the shared core, reducing the cost of the initial 5G upgrade because MNOs only have to add 5G capacity where it is required to augment that of LTE.
Docomo added: “Concurrent with the pre-commercial launch of its 5G services, Docomo will expand 5G coverage by combining 5G networks with existing 4G networks using equipment from diverse vendors. The international standardization of signal transmission specifications that will enable this follows lengthy discussions within the ORAN Alliance, which Docomo is chairing.”
The ability to mix and match network elements is an important MNO goal as the industry seeks new economics for 5G. They need to be able to install, and replace, base stations from different vendors with full interoperability, in order to boost price competition and innovation. In a disaggregated RAN, this also means combining radio units and baseband units from different sources, while a full virtualized RAN will need to rely on multivendor virtual network functions (VNFs) running on common cloud infrastructure in the data center or closer to the cell site.
Multivendor interoperability throughout the network is the objective of TIP, of the Open Networking Foundation, and of the various projects, including ORAN Alliance itself and Open Networking Foundation, which come under the Linux Foundation’s LF Network umbrella. But it has scarcely touched commercial roll-outs as yet, and some operators remain sceptical that the challenges of seamless interoperability can be addressed, fearing they will be forced to adopt a vendor-driven, semi-proprietary compromise again, as they did in using the CPRI interface for fronthaul or with X2.
So Docomo’s deployment will be important to build confidence in a multivendor future, as was its similar breakthrough, back in 2016, when it implemented a Network Functions Virtualization (NFV) platform combining cloud infrastructure, SDN controllers and various VNFs from multiple suppliers (Ericsson, Cisco and NEC).
The ORAN Alliance was formed last year from the merger of two similarly focused efforts, xRAN Forum and C-RAN Alliance. Its founder operators were AT&T, Deutsche Telekom, China Mobile, Verizon, Docomo and Orange. Many other operators have now joined, including Docomo’s largest rivals, KDDI and Softbank.
It now has seven working groups focused on:
use cases and architecture
- radio intelligent controller
- stack reference design
- cloudification and orchestration
- resource information and control
- and white box hardware.
It has published a white paper outlining its high level architecture and detailing key components of that including specs for the open interfaces, white box base station hardware, NFV infrastructure and virtual infrastructure management (VIM). The architecture and interfaces will be placed into open source to drive innovation and adoption, and lower barriers to alternative suppliers.
Earlier this month, the Alliance set up a test and integration process, backed by significant vendors and operators, an important step towards making ORAN-based equipment deployable for operators without the deep pockets and technical knowhow of Docomo.
The new initiative is called Open Test and Integration Center (OTIC) and has been spearheaded by China Mobile and Reliance Jio. Other public backers include China Telecom and China Unicom, plus an array of vendors – Intel, Radisys itself, Samsung Electronics, Airspan, Baicells, CertusNet, Mavenir, Lenovo, Ruijie Network, Inspur, Sylincom, WindRiver, ArrayComm and Chengdu NTS.
These will work together on processes to support multivendor interoperability and validation for ORAN-compliant disaggregated 5G access infrastructure. It will provide verification, integration and testing of disaggregated RAN components with the goal of achieving a plug-and-play model for its architecture.
This is vital to any large-scale operator adoption. At this week’s Open Networking Summit in Antwerp, Belgium, Olivier Simon, director of radio innovation at Orange Labs Networks, said: “We need the right methodology … it’s a massive challenge. The success or failure of an open RAN concept depends on operators’ capacity to find a good test and integration model.”
Now Docomo’s news marks another major milestone on the road to commercial reality, and a full 5G roll-out by a major MNO would be an enormous badge of confidence.
Fujitsu designed Docomo’s ORAN software-defined radio:
One of the first concrete signs that Docomo was close to implementing ORAN for 5G was the news, in August, that Fujitsu had developed a software-defined radio (SDR) for the operator, supporting ORAN specifications.
Fujitsu did not say whether the radio would be more widely commercialized – there is a common pattern in Japan, by which the MNOs, and Docomo in particular, work closely with local suppliers on semi-custom technologies for their very advanced network architectures, as well as with the main suppliers. Fujitsu and NEC have been part of Docomo’s supply chain since 3G, but scarcely sell RAN equipment (except small cells) outside Japan.
Fujitsu hopes that supporting the ORAN specifications will broaden its appeal and allow operators outside Japan to buy its equipment with the reassurance that it will interoperate with others.
Although the SDR is proprietary to Fujitsu, allowing Docomo to implement different radio technologies in a flexible way, it will support fronthaul links to centralized baseband units based on ORAN. Its 5G radio units have built-in antennas equipped with beamforming, which reduces deployment time and site space.
Fujitsu also believes open interfaces will make cellular networks easier and more affordable for non-MNOs to deploy, as spectrum is awarded to more entities, or in shared spectrum. It is targeting 5G private or neutral host network providers in industrial fields, including smart factories and remote medical care.