Industry Insights

Why the eCPRI Interface is Critical to 5G

2020-09-30  |  5 min read 

Common Public Radio Interface, better known as CPRI, is an interface standard developed more than tne years ago by network equipment manufacturers (NEMs), including Ericsson, Huawei, NEC, and Nokia. It is commonly used to carry data between 4G cell sites and base stations.

CPRI has served the wireless communications industry well all the way up through Long Term Evolution (LTE). But in the 5G era — and specifically with regard to open radio access networks (open RAN) — things are changing fast.

LTE channels generally have just 10 or 20 MHz of bandwidth. A typical CPRI interface between a baseband unit and remote radio head in an LTE RAN has a line bit rate of between 600 Mb/s and 10 Gb/s, depending on the bandwidth and number of multiple-input / multiple-output (MIMO) channels. One 10-MHz bandwidth channel gives you a line bit rate of 614 Mb/s, while eight 10-MHz channels offer a line bit rate of about 5 Gb/s, and ten 20-MHz channels a line bit rate a little over 10 Gb/s.

This presents no problem in LTE. That’s one of the reasons the CPRI interface has been so successful in LTE.

But 5G is a whole new ballgame. For 5G, the bandwidth is often 100 MHz or more. The interface between the radio unit and the baseband unit requires a line bit rate of 20 Gb/s to 28 Gb/s. As 5G bandwidths increase, you can quickly be looking at a line bit rate requirement of 2 Tb/s or better. For the CPRI interface, this is not realistic.  

Enter enhanced CPRI, or eCPRI, an interface that is substantially more efficient and flexible than its predecessor. This efficiency and flexibility make it possible for operators to deploy millimeter-wave 5G while minimizing the requirement for fiber.

Compared to CPRI, eCPRI reduces both latency and jitter for high-priority traffic and improves the efficiency of 5G fronthaul networks. The bandwidth requirement of the enhanced interface is also about one-tenth of CPRI’s. And, unlike CPRI, eCPRI’s traffic can be moved on Ethernet, an important attribute for the rise of open RAN.

Open RAN is a rapidly growing movement that promises to spur innovation and lower costs by enabling mobile network operators (MNOs) to build multi-vendor RANs for the first time.

O-RAN, the version of open RAN standardized by the O-RAN Alliance, utilizes interfaces built on the eCPRI specification framework. Ethernet enables virtualization by allowing fronthaul traffic to switch between physical nodes using common off-the-shelf networking equipment.

Virtualization is one of the core principles of the O-RAN Alliance. A goal of the O-RAN Alliance reference architecture is maximizing the use of off-the-shelf hardware and minimizing the use of proprietary hardware.   

The eCPRI interface itself is also an open interface, which also fits with the philosophy of the O-RAN Alliance. Another of the group’s core principles is openness, a critical component for allowing MNOs to build multi-vendor O-RANs. Using open interfaces allows the MNOs to mix and match equipment from multiple vendors and link them through interoperable standards and interfaces.

So, if you didn’t know about eCPRI before, you do now. The interface is a critical component for enabling the continued acceleration of 5G deployment. It is also essential for O-RAN, which is proving to be a massive disruption in the wireless communications industry.

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