The sharing of infrastructure among mobile operators is likely to represent a critical aspect of future radio access networks.
The flattening of ARPU (Average Revenue Per User) and at the same time the need for increasing profits have put operators under tremendous pressure to reduce the costs of network deployment. In this context, sharing infrastructure is a possible solution for lessening the cost burden.
However, the definition of interfaces to the shared network infrastructure has always been a key challenge because each operator typically approves a different equipment vendor. The question is which interfaces can best support multi-vendor deployment? Let’s explore the three main areas where interfaces need to be addressed.
Firstly, the backhaul link connects the core network to radio access network and is intended for transporting control signaling and user data payload. In the 3G world, Radio Network Controllers (RNC) are connected to the base station via the Iub interface, which is proprietary of the different vendors. That has prevented a multi-vendor deployment of 3G base stations and RNCs to occur so far. The first step towards more open interfaces was the standardization of Iuh intended for backhauling home base stations. In the today’s 4G world, Ethernet is the most common standard interface used for connecting LTE E-UTRAN to the Evolved Packet Core Network. In particular, 3GPP has standardized the S1 interface. Even though some specific signaling parameters are still customized by vendors, interoperability tests over S1 have turned out to be significantly easier than in the past.
Secondly, the fronthaul link connects the baseband unit to the radio remote units of a base station and is intended to transport IQ digital samples. CPRI (Common Public Radio Interface) and OBSAI (Open Base Station Architecture Initiative) are two common standards adopted by large OEMs as front-haul interfaces, which allows for multiplexing multiple carriers and MIMO paths on a single digital link. It also introduces flexibility in routing signals to different radio remote units through both star and daisy chain configurations. However, significant effort needs to be spent on customizing the control signaling of different vendors to the point that CPRI and OBSAI cannot be fully regarded as open standards. Moreover, high bandwidth and tight timing requirements need to be met on this interface. So fiber is in most of the cases the only possible physical media supporting this approach.
Last but not least, the RF link connects the radio remote unit to the antenna. Here the widely adopted standard interface is the 50-Ohm coaxial cable. The RF interface has the key advantage of greatly simplifying a multi-vendor deployment. For example, a single DAS infrastructure can accommodate any signal coming from any base station regardless of the radio access technology (e.g. 2G, 3G and 4G) or radio node vendor. On the other hand, some input conditioning is typically required for combining RF signals and to adjust power levels.
CommScope recently announced its new ION-U platform, which is designed to largely simplify the design, commissioning and optimization of DAS based on the RF interface. Among other benefits, the ION-U is ready for infrastructure sharing arrangements at the RF link level.
What are your thoughts about the future of RAN infrastructure sharing? What will help the industry get there?