Challenges with Implementing Centralized Radio Access Networks

Although Centralized Radio Access Networks (C-RAN) are a significant technological step forward for telecoms companies, there are some challenges with implementing and managing them.

A complete overhaul of existing networks cannot be done overnight. Therefore, C-RAN needs to integrate with and work alongside the existing Distributed Radio Access Networks (D-RAN) equipment and standards. There are several standard constraints for C-RAN, but the most significant ones are the network protocols currently in use.

The digital protocols used for the communication between Remote Radio Heads (RRH) and Baseband Units (BBUs) rely on certain connection standards and configurations to work effectively. Failing to meet these standards can damage the performance of the entire network.

However, the two main protocols currently in use – CPRI and OBSAI – were designed with D-RAN in mind, and currently do not present a good solution to the challenges presented by C-RAN.

CPRI

The Common Public Radio Interface (CPRI) is the most commonly used communications protocol in the 4G era.

It came from an agreement between some of the largest telecom manufacturers in the world, including Ericsson, Huawei Tech, Alcatel-Lucent, NEC corporation and Nokia Networks. These manufacturers maintain strict control of CPRI definitions and interoperability.

OBSAI

The Open Base Station Architecture Initiative (OBSAI) is a year older than CPRI and was created to introduce an open market communications protocol. This ensured more telecoms companies would help with its development. The companies that took the initative to create OBSAI were Hyundai, LG, Nokia, Samsung, and ZTE.

Because these protocols were not designed for C-RAN, meeting CPRI and OBSAI requirements can become a challenge. Both CPRI and OBSAI assumed that the BBU and RRH would be close together in the same BTS. For this reason, their requirements become more difficult to achieve as the connections between the RRHs and the BBUs get longer and more complex.

As a result, Bit Rate, Latency, and Jitter all need to be carefully managed when using C-RAN with these protocols.

Bit Rate

Both CPRI and OBSAI require the network to operate at very specific bit rates. CPRI allows for eleven bit rate options: