Femtocell Operator News and Opinons

AT&T case studies of outdoor small cells in the suburbs

David Orloff ATTYou may think that Urban Small Cells are only for those ultra-busy downtown city districts, and that green, leafy suburbs would continue to be served by traditional macrocell towers with a few residential/in-building femtocells thrown in.

If so, you need to rethink that perception.

David Orloff, AT&T's Director for Small Cells Platforms, speaking at Small Cell World Summit, explained three use cases where AT&T has deployed groups of small cells in the suburbs. We followed up directly with him with some questions to clarify some of the issues they faced and problems solved.


AT&T is in the vanguard of small cell adoption, visibly chairing the Small Cell Forum, publicly promoting their use at events and even in TV advertisements, but most demonstrably through aggressive deployment. Over 50% of its network densification program will use small cells by 2015.

When will Urban Small Cells become a reality on our street lampposts?

ATT-Small-Cell-LamppostWe see that's happening already. There are many outdoor locations that are difficult to get site permission for larger sites, or which don't justify the full cost of a macro. In many cases – including school areas, suburban, residential – we are actively installing urban small cells now.

In the picture on the right, you can see a typical street deployment on a light pole/lamp post. The bottom-most white box is the DC power cabinet including backhaul and surge protection. The box below the street light is the small cell itself. The white box in the middle is not related to the small cell installation.

How do you determine where to deploy small cells?

Our customers would like to have good service everywhere, so we engineer small cells for customer experience. We focus on a set of KPIs which will be familiar to many network engineers: coverage, capacity, voice retainability, packet accessibility, throughput and mobility. I look at these figures every day.

We've developed analysis tools that take several inputs from RF design, social data, transport data and performance data to pinpoint where and when to deploy small cells efficiently. This allows us to prioritise and plan our rollout both strategically and tactically.

Can you describe some typical suburban small cell deployments?

There's no single use case. Here are three different examples and some of the issues we found:

1) A residential neighbourhood at the edge of macrocell coverage


We installed 15 3G metrocells in a residential neighbourhood, located at the edge of multiple macrocells. This configuration dramatically improved coverage throughout the neighbourhood.

There were a limited number of entrance and egress points to which we paid particular attention. We also closely monitored how these edge-point small cells interact with the macrocells, and made some optimisations to deal with the overlap to avoid dropped calls.

2) A mixed suburban environment with a raised suburban road running through the middle, with dense foliage throughout


We deployed 22 small cells in this cluster to great effect. At first, we found that the signal level dropped off fairly quickly between the macro and small cell clusters. The relatively high speed of the traffic on the highway created a challenge when interacting with the small cell layer.

Specifically, the handover success rate from small cell to macro wasn't as good as we expected. When we dug deeper, we found the handover transition wasn't fast enough due to terrain and foliage. So we optimised the handover by adjusting signal thresholds and quality, adding a couple of blind handovers (i.e. adding extra cells into the neighbor lists), and this gave us an immediate improvement in call retainability. However, I would caution that blind handover really only works best when you have very predictable target cells to handover into.

We also minimized the inter-layer transitions, avoiding unnecessary handovers between the macrocells and small cells cluster. Minimizing the transition in this way keeps the traffic on the preferred layer and simplifies the neighbor lists.

3) A residential environment with difficult terrain


We installed 13 metrocells in an area of poor macro coverage and saw an instant improvement in customer experience. This scenario involved a higher number of small cells in the cluster that actively interact with the macrocell layer. It's not about the total number of cell sites, just those that handover to and from the small cells.

Once optimised, we saw significant improvement in call retainability.

How much is SON (Self Organising Networks) being used to simplify the configuration process?

SON is already extremely valuable with small cell implementations during both initial deployment as well as ongoing operation. The Centralized Auto PSC PCI and Distributed (Node Level) Auto PSC PCI functions allow for small cell clusters to initialize and maintain an interference optimized environment.

We also heavily use Auto Neighbor Relation (ANR) functions to maintain interoperability and reciprocal neighbor relation management with the Macro environment.

Any final thoughts?

50% of AT&T densification efforts will use small cells. We are in an aggressive deployment mode right now. If we continue to engineer our network based on customers' experience, then customers will have the service they need and the quality they expect.

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#1 Mike Racine said: 
Our business is located at a small airport in rural New Mexico. For the last 6 years, we've had reasonable cell service from a tower that is about 2 miles away, located near Interstate 25. When AT&T upgraded the tower from 3G to 4G LTE, our cell service was all but gone. We rarely get text messages, are lucky if we can get 1 bar of service, and if we do get a call to come through it usually drops as soon as we answer it. There are 6 of us in the office that have AT&T service, and three other companies on the field that use AT&T wireless, and we're all having the same issues. It seems like our airport would be the perfect place for an AT&T small cell. The problem is, whenever I call technical support, talk to the folks in an AT&T store, or even talk to the field reps in AT&T trucks that I've seen around town, nobody knows how to contact anyone that could possibly deploy a small cell at our airport. Can anyone provide me with contact information so that I can talk to someone about deploying a small cell?
+2 Quote 2015-01-28 17:14
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