According to the latest GSMA mobile economy report 2020, although 4G is the dominating technology today, the adoption of 5G will get closer to 4G in the coming 5 years while 2G and 3G will still remain in the most part of the world. Even in the developed region like Europe, 2G and 3G are critical for the mandatory voice service. They are even more important in some less developed regions such as the Middle East, Africa and Latin America. The report predicts that about 25% to 60% of the mobile subscribers will still be using these legacy services in 2025 .
Source: GSMA’s The Mobile Economy 2020
This technology trend poses a dilemma to adopt Open RAN solution. From the operator’s perspective, a RAN solution which supports 2G/3G/4G and is easily upgradable to 5G is more justified than the 4G/5G only solution. On the other hand, the existing 2G/3G systems are also facing end-of-life deadline in most operator’s network, that gives a good opportunity to bring in the future proof Open RAN solution to break the vendor lock-in and reduce the TCO.
To solve the dilemma, besides focusing on 4G and 5G technologies, the Open RAN solution should also be able to support legacy technologies of 2G and 3G. It is an innovative and interoperable RAN solution for brownfield operators to deploy RAN systems with an open interface without interrupting the legacy services nor the hassle to manage two separate RAN systems.
In order to have an end-to-end Open RAN system to support legacy technologies, a multi-RAT remote radio unit (RRU) is very critical. A multi-RAT capable RRU can transmit different radio access technologies, e.g. 2G, 3G and 4G, in a single unit that will greatly reduce the site complexity and cost. On the DU side, software vendor also has to develop the multi-RAT support in DU. Both the software and RRU vendors have to work closely to make sure the interoperability in such Multi-RAT RAN system.
In some recent industry news and announcements, the vendors of the Open RAN ecosystem are responding to this market requirement which lots of efforts and investments have been put into this area. We can expect the commercial multi-RAN solution will be available in the coming year taking this new technology to the next level of success.
 Source: The Mobile Economy 2020, 2020, GSM Association, https://www.gsma.com/mobileeconomy/wp-content/uploads/2020/03/GSMA_MobileEconomy2020_Global.pdf