C-RAN . . . But to Where?

How Network Evolution Demands Enclosure Flexibility —

While cellular network architectures have evolved from 3G to 4G on their way to 5G, cell sites have changed as well: from RAN to D-RAN to the emerging C-RAN model. It’s tempting to assume one leads the way for the other, but it isn’t that simple. There was and is overlap, and the current move toward C-RAN architectures is happening without any clear consensus on what 5G eventually will be.

Simply put, C-RAN architectures take equipment from the base of the tower and centralize it elsewhere to serve multiple sites. This reduces the physical footprint at the tower and provides other benefits related to equipment monitoring and service. There are plenty of good reasons for this, but support for a 5G network that doesn’t exist yet isn’t among them.

Before we dive into 5G speculation and what the move to C-RAN architectures may mean for those next-gen networks, let’s look at how we reached this point — and what we can learn from those experiences.

RAN to C-RAN
A traditional macro base station with radio access network (RAN) architecture consists of a cell tower and antenna with all associated equipment at the base of the tower, connected to the antenna via coaxial cable. These types of sites require multiple enclosures or, in some cases, shelters housing all the required equipment.

Distributed radio access network (D-RAN) moves the radios (RRH – remote radio heads) from the base of the tower to the top of the tower alongside the antenna and replaces the coaxial cable with fiber. The rest of the equipment remains at the base of the tower. D-RAN architecture reduces the power required, and increases network capacity, by reducing the distance between the antenna and the radio (reducing signal loss). The use of RRHs also translates into a decreased equipment footprint at the base of the tower.

The recent move to centralized radio access network (C-RAN) is more disruptive. C-RAN architecture moves the baseband processing unit (BBU) to a central location to support multiple towers. Instead of each tower having BBUs at its base, multiple towers share a pool of BBUs at a separate location. This moves much of the intelligence associated with a cell site away from the tower. The remaining equipment, along with power and batteries, potentially can be consolidated to a single cabinet to further reduce the physical footprint at the base of the tower. Centralizing BBUs also makes it easier and less expensive to power, monitor, and service them.

Figure 1. Cell Site Architecture Evolution: From RAN to Cloud-RAN

The Path to 5G
The evolution from RAN to D-RAN to C-RAN has been fairly straightforward, but the move from 4G to whatever 5G becomes is far less clear-cut. 3G enabled the modern smartphone with basic data and Internet capabilities. 4G increased the speed of the network and made mobile video viable. 5G will enable further consumer applications as well as innovations related to the Internet of Things (IoT), like autonomous automobiles, telemedicine, and applications we can’t even imagine.

But how do we get there, and what impact do 5G and IoT have on network architecture and infrastructure? Let’s start with some safe assumptions.

We can be certain we’ll see further densification of the wireless network. Providers will deploy more and more sites to meet the requirements of 5G. This will change network architectures in some meaningful ways.

It’s likely we’ll see battery backup de-emphasized as providers rely on overlapping coverage from these dense networks to cover power outages at a given site. If batteries are reduced or eliminated, that decreases the enclosure requirements at a traditional macro tower site.

On the other hand, another requirement of 5G networks is decreased latency. This is mandatory to support applications like self-driving cars where a lag in the network can be a matter of life and death.

These applications are going to require more computing equipment at the edge of the network — most likely increasing equipment infrastructure needs at the tower site.

We also can’t forget that computing equipment has different operating parameters with greater thermal management needs than traditional telecom gear.

The Enclosure Paradox
Let’s consider the implications of 5G on what’s happening now with C-RAN architectures. C-RAN is removing equipment and intelligence from the cell site. Likely, 5G and mobile edge computing will remove some batteries, but require additional equipment and intelligence at the tower site. It raises the question of what type(s) of enclosure should be deployed in support of the ever-changing network requirements. It’s a question providers are wrestling with daily.

The solution, if there is one when so much uncertainty is involved, seems to be a compromise favoring enclosure flexibility at tower sites. Forward-thinking providers are deploying configurable enclosure solutions that enable the benefits C-RAN offers today while maintaining options to support 5G when it’s needed. The Vertiv™ XTE 601E is one of these models that provides for increasingly flexible enclosures.

These solutions can consolidate equipment and batteries in a single enclosure with the capability to add or remove battery boxes and space for electronic equipment. (See Figure 2.)