Open RAN  






You might have been hearing about Open RAN for many years (as of Jan 2022). It has been a buzz word especially in 2019, 2020, 2021 and it is likely to see more and more cases of Open RAN-based deployment in coming years.




What is it ?


What is OpenRAN ? There are many different definition and the scope of definition keep changing and expanding, so it gets more and more difficult to clearly define it. I just want to define it by sticking to the literal meaning of the name.  Literally OpenRAN mean 'Open' the 'RAN(Radio Access Network)'. If you know what RAN is, OpenRAN can be illustrated as below. The issue is to figure out the meaning of 'OPEN' in this context.



The meaning of 'OPEN' in this context can be summarized by a few keywords as listed below.

  • Virtualization of RAN components ==> Implementing the components in software
  • COTS(Commercial Off-The-Shelf) hardware

OpenRAN is not a thing that is invented overnight. It is the result of gradual evolution of the RAN architecture. This RAN evolution process can be summarized in illustration as shown below. The architecture shown at stage (E) is what we call OpenRAN.



In the illustration shown above, I used the term 'RAN : Upper' and 'RAN : Lower'. There are many options to split RAN protocol stack into two parts. By 'RAN Upper', I meant the higher layer of RAN protocol stack and by 'RAN Lower' I mean the lower layer of RAN protocol stack. One example of this kind of split is CU-DU split which is defined in 3GPP NR specification which can be illustrated below. The RAN Upper corresponds to CU and RAN Lower corresponds to DU (NOTE : Check this page for the details of CU-DU separation)





Does OpenRAN mean all Software ?


I think a few keywords for OpenRAN are 'OpenInterface' and 'COTS' hardware. I think as long as a system can provides all the open interface as specified in industry standards and that can be implemented / supported by general purpose hardwares, I don't think it should be done all in the software. Theoretically, every components except ADC/DAC and Antenna can be implemented purely by software. Some of the SDR solutions already implements all the components except ADC/DAC and Antenna purely by software. Even though software only solution is not mandatory for OpenRAN, it looks pretty obvious that OpenRAN solution would adopt much more components in software solution comparing to legacy implementation/deployment.




Why OpenRAN ?


What is the motivation for OpenRAN ? The answer would vary depending on who you ask. One example list of the motivation is as shown below. To me, this seems to be more with respect to business side. There would be different list of motivation with focus on technical aspect as well.

I think the ranking for items in the list may also vary depending on who you ask to and when you survey, but the list itself well captured the most of the reasons / motivations for Open RAN.


Source : Open RAN and 5G: Deployment Options and Key Issues for Operators




Challenges for OpenRAN


Even though OpenRAN solution evolves rapidelny and is getting stronger attention, there are some challenges for OpenRAN.


Performance Issue : Whenever you are trying to talke about OpenRAN implementation, one of the most common challenges you would get would be performance issue. But depending on specific use case and deployment type, you may say 'we don't have performance issue any more' or you should say 'we still have way to go before the openRAN system meets the performance requirement'.

==> As of end of 2021, it seems that OpenRAN performance already reaches to the point to support LTE network with relatively small number of frequency support and not much requirement of density like rural area, and we even see the working example like Rakuten. But it is not yet at the point of meeting the performance requirement that are needed for multi carrier aggregation, Massive MIMO capability (e.g, 5G).


Lack of Common Standard : I think Open RAN specification has been matured greatly, but I don't think it is as mature as or as agreed upon in the industry as 3GPP.

==> As of end of 2021, I think OpenRAN specification from O-RAN Allience would be at the leading position in terms of specification but I am not sure if it is the only specification that every players are following like 3GPP. For Fronthaual specification, it seems most of OpenRAN players tries to support the O-RAN allience specification(7.2x split).  I think most of the players would be likely to agree upon O-RAN allience specification on CU/DU definition and interface since the same specification are adopted by both O-RAN allience and 3GPP. But I am not sure how most of industry players are thinking of other components of OpenRAN architecture.




Any OpenRAN Already Deployed?


Followings are a list of mobile service provider who already deployed Open ran based network or known to deploy in near future.


Rakuten Mobile : Japan, In 2019, Rakuten was the first to implement a multi-vendor RAN, using products from  Altiostar, Airspan, Nokia and  others. Rakuten’s  network  began  as  an  LTE  network consisting of both macro and small cells. The company has evolved its network to deploy 5G NR using sub 6 GHz radios from NEC and a container-based solution from Altiostar. See this.


Inland Mobile :  US. See this.


DISH Network : US. Dish will begin roll out of the world’s second (after Rakuten) large, greenfield network based entirely on O-RAN technology. With a commitment to cover 70% of the U.S. population by June 2023. See this.


Vodafone : U.K., announced a 2,600-site OpenRAN deployment with a commitment to have 1,150 of these sites live by 2023. See this.

==> According to this video (Jan 2022), Vodafone just powered on one OpenRAN cell site.


1&1 : Germany. See this.








Readings on already deploid networks




Reference : Specification and Other Readings