Feb 17, 2021
Qualcomm products mentioned within this post are offered by Qualcomm Technologies, Inc. and/or its subsidiaries.
We’re now seeing the rapid spread of 5G across the world of mobile networking. This comes at a time when over two-thirds of the global population subscribes to services from cellular radio access networks (RAN) built by mobile network operators (MNOs).
A prominent feature of the mobile networks built thus far has been a proprietary system of network components, software, and interfaces that MNOs learn to operate. Over generations of mobile technology from 2G to 5G, proprietary RAN solutions have only offered a few interoperable connections, usually to network functions upstream, such as to the network core or the network management system. The RAN vendor space has also seen much attrition and consolidation over the years, which has driven MNOs to prioritize business assurance over innovation when selecting RAN vendors to partner with. Together, these facets of the mobile networking industry have constrained the hardware and software options available to the MNO, throttled the speed of network evolution, limited their ability to leverage innovation from a broader ecosystem, and made it difficult to differentiate their offerings from the competition.
The desire to leverage commercial off-the-shelf (COTS) hardware with general-purpose processors where possible came from the need to evolve mobile networks with new capabilities faster and scale networks for capacity at short notice. This transformation, which requires a disaggregation of hardware and software network functions, is called network function virtualization (NFV). As we’ll see later, open interfaces between network functions also play a critical role in complementing NFV to accelerate innovation and improve operational agility. Core network infrastructure was the first to be successfully virtualized and running virtual mobile cores on COTS hardware quickly became the de facto model for deploying mobile cores.
Boosting performance with hardware-acceleration for real-time functions
The RAN consists of the digital and analog functional elements, with digital functions being typically executed in the baseband unit (BBU) and analog functions in the radio. After the core network, the RAN BBU became the next point of focus for disaggregating hardware and software. This is a more challenging task due to the complexity of the network functions inherent to the RAN.
The lower layers of the RAN protocol stack are characterized by real-time functions and complex signal processing algorithms which don’t execute efficiently on general purpose processors. This gave rise to the next step in disaggregation – that of splitting layers of the RAN protocol stack in the BBU, between a central unit (CU) and distributed units (DUs). Early experience with NFV also revealed advantages in separating control plane and user plane functions because they need network infrastructure to scale differently in response to network load and end-user applications. For example, a 5G mobile network offering unlimited data or fixed wireless service would be expected to bear a much higher user plane load than a network without those offerings. COTS hardware platforms and NFV make separation of control and user plane software functions straightforward.
Real-time functions and complex algorithms would then feature in the DUs, either in the form of purpose-built network elements or in COTS hardware augmented with purpose-built hardware accelerators as shown in the figure below for physical layer acceleration. Interaction between the COTS central processing unit (CPU) and hardware accelerators could happen via an acceleration abstraction layer (AAL) for standardized interoperability. Non-real time and near real-time CU and DU functions could then be virtualized on separate COTS hardware with general purpose processors.
Broaden the interoperable ecosystem with standardized open interfaces
3GPP standards for 3G, 4G, and now 5G mobile networks have been phenomenally successful in bringing together a thriving ecosystem for mobile technology that keeps stepping up to address the needs of advancing societies all over the world. The cornerstone for 3GPP’s success has been globally standardized end-to-end communication between mobile devices, RAN, and core networks with interoperable interfaces between them. Organizations like the O-RAN Alliance (O-RAN) and the Small Cell Forum (SCF) are taking a global ecosystem of network operators, technology providers, and research institutions further to complement 5G with standardized open interfaces and new performance-enhancing capabilities.
The network functional application platform interface (nFAPI) from the SCF and the O-RAN control, user and synchronization plane (CUS) interface extend the 3GPP 5G standard with scalable distributed RAN architectures and hardware acceleration for the most demanding applications, such as ultra-reliable low latency communications (URLLC). Performance-enhancing features like coordinated multi-point (CoMP) can perform significantly better with one-to-many relationships between digital units and multiple radio units (RUs) using the nFAPI or CUS interfaces. O-RAN also introduces the near-real time RAN Intelligent Controller (RIC), which spans across multiple RAN network functions using standardized open interfaces to bring secure, scalable, and intelligent network control to 5G using the power of hyperscale technologies in edge clouds.
Together, standards from the 3GPP, O-RAN Alliance, and the SCF are helping build a common 5G platform for public networks and the growing private network market by broadening the interoperable ecosystem using standardized open interfaces.