O-RAN: An Open Ecosystem to Power 5G Applications – Viavi
Open Radio Access Network (O-RAN) is being adopted by operators and equipment manufacturers worldwide to reduce infrastructure deployment costs and lower the barrier to entry for new product innovation. This article provides an overview of this technology, industry initiatives to standardize and validate it, and the ecosystem developing around it.
The expectations of 5G will place enormous demands on the network infrastructure to deliver massive volumes of data over swathes of the spectrum to multitudes of users at challenging latencies. To meet this challenge necessitates the possibility for the different logical functions of the network to be flexibly placed at different physical locations and for them to be coordinated by a new RAN Intelligent Controller function.
Traditionally, as shown in Figure 1 (see 5G Magazine), RAN components such as radio and the digital baseband have been built on proprietary hardware, and these components typically use vendor-specific protocols for communications. Software functions and interfaces between the different RAN components are designed for optimal performance for that proprietary hardware. For example, Common Public Radio Interface (CPRI) is commonly used for LTE fronthaul (the link between radio unit and baseband unit). However, vendor-specific implementation often restricts multi-vendor operability.
For the introduction of RAN functions disaggregation and open interfaces in 5G, 3GPP has in Release 15 specified a Higher Layer Split (HLS) option of the gNB, which is also known as the Option 2 NR-PDCP split option. In this option, the gNB may consist of a Central Unit (gNB-CU) and one or more gNB Distributed Unit (gNB-DU) connected through the F1 interface. 3GPP has delivered a set of specifications for the F1 interface, however realizing multivendor interoperability over the F1 interface can be very challenging as these specifications have been defined with options that can be used in different manners depending on vendors’ implementations.
3GPP started a study on Lower Layer Split (LLS) in Release 15, during which multiple lower layer split options were identified. But it has proven difficult for the 3GPP community to converge on specifying a single split option in 3GPP, and that study item has been completed with no further actions planned. Many vendor-specific implementations of lower-layer splits exist today. Even though they have been optimized to take advantage of the benefits of the lower-layer split, such as improved radio performance due to coordination gains, these closed systems do not support multi-vendor interoperability.
O-RAN is delivering well-defined specifications to the industry to enable deployments of O-RAN-based programmable networks consisting of fully-disaggregated modular O-RAN network functions.