Open RAN: What should telcos do?

Network Futures, Telco Cloud

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Alongside the roll-out of 5G cores and radios, the Radio Access Network (RAN) is evolving to a more open, virtualised and distributed architecture. What are the opportunities and risks for telcos?

What is the open RAN and why does it matter?

The open RAN’ encompasses a group of technological approaches that are designed to make the radio access network (RAN) more cost effective and flexible. It involves a shift away from traditional, proprietary radio hardware and network architectures, driven by single vendors, towards new, virtualised platforms and a more open vendor ecosystem.

Legacy RAN: single-vendor and inflexible

The traditional, legacy radio access network (RAN) uses dedicated hardware to deliver the baseband function (modulation and management of the frequency range used for cellular network transmission), along with proprietary interfaces (typically based on the Common Public Radio Interface (CPRI) standard) for the fronthaul from the baseband unit (BBU) to the remote radio unit (RRU) at the top of the transmitter mast.

Figure 1: Legacy RAN architecture

Source: STL Partners

This means that, typically, telcos have needed to buy the baseband and the radio from a single vendor, with the market presently dominated largely by the ‘big three’ (Ericsson, Huawei and Nokia), together with a smaller market share for Samsung and ZTE.

The architecture of the legacy RAN – with BBUs typically but not always at every cell site – has many limitations:

  • It is resource-intensive and energy-inefficient – employing a mass of redundant equipment operating at well below capacity most of the time, while consuming a lot of power
  • It is expensive, as telcos are obliged to purchase and operate a large inventory of physical kit from a limited number of suppliers, which keeps the prices high
  • It is inflexible, as telcos are unable to deploy to new and varied sites – e.g. macro-cells, small cells and micro-cells with different radios and frequency ranges – in an agile and cost-effective manner
  • It is more costly to manage and maintain, as there is less automation and more physical kit to support, requiring personnel to be sent out to remote sites
  • It is not very programmable to support the varied frequency, latency and bandwidth demands of different services.

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Moving to the open RAN: C-RAN, vRAN and open-RAN

There are now many distinct technologies and standards emerging in the radio access space that involve a shift away from traditional, proprietary radio hardware and network architectures, driven by single vendors, towards new, virtualised platforms and a more open vendor ecosystem.

We have adopted ‘the open RAN’ as an umbrella term which encompasses all of these technologies. Together, they are expected to make the RAN more cost effective and flexible. The three most important sub-components of the open RAN are C-RAN, vRAN and open-RAN.

Centralised RAN (C-RAN), also known as cloud RAN, involves distributing and centralising the baseband functionality across different telco edge, aggregation and core locations, and in the telco cloud, so that baseband processing for multiple sites can be carried out in different locations, nearer or further to the end user.

This enables more effective control and programming of capacity, latency, spectrum usage and service quality, including in support of 5G core-enabled technologies and services such as network slicing, URLLC, etc. In particular, baseband functionality can be split between more centralised sites (central baseband units – CU) and more distributed sites (distributed unit – DU) in much the same way, and for a similar purpose, as the split between centralised control planes and distributed user planes in the mobile core, as illustrated below:

Figure 2: Centralised RAN (C-RAN) architecture

Cloud RAN architecture

Source: STL Partners

Virtual RAN (vRAN) involves virtualising (and now also containerising) the BBU so that it is run as software on generic hardware (General Purpose Processing – GPP) platforms. This enables the baseband software and hardware, and even different components of them, to be supplied by different vendors.

Figure 3: Virtual RAN (vRAN) architecture

vRAN architecture

Source: STL Partners

Open-RANnote the hyphenation – involves replacing the vendor-proprietary interfaces between the BBU and the RRU with open standards. This enables BBUs (and parts thereof) from one or multiple vendors to interoperate with radios from other vendors, resulting in a fully disaggregated RAN:

Figure 4: Open-RAN architecture

Open-RAN architecture

Source: STL Partners

 

RAN terminology: clearing up confusion

You will have noticed that the technologies above have similar-sounding names and overlapping definitions. To add to potential confusion, they are often deployed together.

Figure 5: The open RAN Venn – How C-RAN, vRAN and open-RAN fit together

Open-RAN venn: open-RAN inside vRAN inside C-RAN

Source: STL Partners

As the above diagram illustrates, all forms of the open RAN involve C-RAN, but only a subset of C-RAN involves virtualisation of the baseband function (vRAN); and only a subset of vRAN involves disaggregation of the BBU and RRU (open-RAN).

To help eliminate ambiguity we are adopting the typographical convention ‘open-RAN’ to convey the narrower meaning: disaggregation of the BBU and RRU facilitated by open interfaces. Similarly, where we are dealing with deployments or architectures that involve vRAN and / or cloud RAN but not open-RAN in the narrower sense, we refer to those examples as ‘vRAN’ or ‘C-RAN’ as appropriate.

In the coming pages, we will investigate why open RAN matters, what telcos are doing about it – and what they should do next.

Table of contents

  • Executive summary
  • What is the open RAN and why does it matter?
    • Legacy RAN: single-vendor and inflexible
    • The open RAN: disaggregated and flexible
    • Terminology, initiatives & standards: clearing up confusion
  • What are the opportunities for open RAN?
    • Deployment in macro networks
    • Deployment in greenfield networks
    • Deployment in geographically-dispersed/under-served areas
    • Deployment to support consolidation of radio generations
    • Deployment to support capacity and coverage build-out
    • Deployment to support private and neutral host networks
  • How have operators deployed open RAN?
    • What are the operators doing?
    • How successful have deployments been?
  • How are vendors approaching open RAN?
    • Challenger RAN vendors: pushing for a revolution
    • Incumbent RAN vendors: resisting the open RAN
    • Are incumbent vendors taking the right approach?
  • How should operators do open RAN?
    • Step 1: Define the roadmap
    • Step 2: Implement
    • Step 3: Measure success
  • Conclusions
    • What next?