5G: Open RAN Vs vRAN

 

Next came Virtual RAN, or vRAN. Does Open RAN equal Virtual RAN? Not exactly. Let us explain. With vRAN, the proprietary hardware remains as it is, but the BBU gets replaced by a COTS server rather than proprietary hardware. The software that runs on the BBU is virtualized to run on any COTS server. The proprietary interfaces remain as they are. Here’s a picture that illustrates how we see it. 

he point to emphasize here is that vRAN is not Open RAN as it is not completely open; it still contains proprietary interfaces and purpose-built hardware. Open RAN is, instead, a movement to define and build 2G, 3G, 4G and 5G RAN solutions based on a general-purpose, vendor-neutral hardware and software-defined technology. Open RAN Is the disaggregation of hardware and software: the RRU / RRH hardware becomes a GPP-based or COTS hardware that can be purchased from any ODM, OEM or RAN hardware vendor. The BBU is the same as in the case of vRAN: COTS server + vendor’s proprietary software with virtualized functions.

The main thing with Open RAN is that the interface between the BBU and RRU / RRH is an open interface, so, any vendor’s software can work on any open RRU / RRH. With Open RAN and the “virtualization” it brings, operators should be able to run software-based network functions on standard servers. More open interfaces enable them to use one supplier’s radios with another’s processors — something not currently possible with traditional solutions.

The OpenRAN vision is that the RAN is open within all aspects, with the interfaces and operating software separating the RAN control plane from the user plane, building a modular base station software stack that operates on commercial-off-the-shelf (COTS) hardware, with open north- and south-bound interfaces. This software enabled Open RAN network architecture enables a “white box” RAN hardware – meaning that baseband units, radio units and remote radio heads can be assembled from any vendor and managed by Open RAN software to form a truly interoperable and open network. This way, the underlying hardware layer (radios and servers) stay on site; the only thing that gets replaced is the software as shown in the graphic below.

Example scenario: OpenRAN deployment model

How?

3GPP considered the split concept (DU and CU) from the beginning for 5G. In a 5G cloud RAN architecture, the BBU functionality is split into two functional units: a distributed unit (DU), responsible for real time L1 and L2 scheduling functions, and a centralized unit (CU) responsible for non-real time, higher L2 and L3. In a centralized 5G cloud RAN, the DU physical layer and software layer are hosted in an Edge cloud datacenter or central office, and the CU physical layer and software can be collocated with the DU or hosted in a regional cloud data center. While CUs will maintain BBU-like functionalities, DUs will be more than RRH in terms of processing capacities. And this is where the Open RAN concept comes in: from COTS-based servers for DU and CU software to RU from any vendor. Open RAN is the key to next-generation mobile network infrastructure and as a result of vendor interoperability, it offers: 

Open RAN is about horizontal openness – with open interfaces enabling functions of the RAN to connect with other functions, from a radio unit (RU) to a baseband (DU-CU), to the controller to the NMS/orchestrator. 

And though the functional split concept was introduced for 5G, to get full interoperability and cost benefit, it must be applied to RAN for 2G 3G 4G as well. 

The main takeaway: When RAN is opened up horizontally, it could bring in a new range of low-cost radio players, and it gives mobile operators a choice to optimize deployment options for specific performance requirements at much better cost.