Small cell is a broad category. For public access, it covers powerful outdoor cells planned into the macro network, and it also covers low-power indoor hotspots.
The fact is that mobile data usage is increasing rapidly, and mobile operators face the challenge of providing many times more data capacity at a reduced cost per byte.
One approach is to augment the macro network with outdoor small cells mounted on street furniture. Recent deployments in London for the Olympics have raised the profile of this approach. But there are drawbacks. Site acquisition is a painstaking and costly affair, as is getting backhaul to these sites. If the new outdoor small cells are on the same frequency as the existing macro cells, which is very often the case, then they need high RF output power and costly planning for the small cells to be effective and so that they don’t adversely affect the user experience, particularly for voice calls. The real problem though is that 75% of mobile data is used inside buildings, not outside on the street where these small cells would be installed, making an “outside-in” approach very inefficient. Much valuable signal is blocked by walls, so this approach does seem counter intuitive. Many mobile operators have now experienced this and have moved to supplementing their outside base stations with targeted indoor cells, fixing both capacity and coverage issues at the same time.
Worse, the ratio of indoor to outdoor data rate is changing, as the graph below from Mobile Experts shows. By 2017, the proportion of indoor data usage will have risen to 85%. It appears that typical “indoor” activities like video, Facebook and photo uploads use more data than typical “outdoor” activities like mapping and SMS.

All of which points to the other way of doing small cells in public spaces – deploying them in indoors in stores, coffee shops, retail malls and transport hubs. As well as providing data capacity precisely where it is needed, there are a number of other benefits:
- Because the building provides some isolation from the macro network, indoor small cells transmit at very low power, enabling a higher density of cells to be deployed.
- Low power small cells with self-managing capabilities do not need to be manually planned into the macro network (similar to residential femtocells). This makes deployment a simple and inexpensive exercise.
- There is an abundance of site owners with power and fixed broadband already in place, often to serve WiFi infrastructure. Many of these owners have a commercial incentive to provide their customers with a better mobile experience.
It is most likely that operators will deploy a mix of indoor and outdoor small cells. But when it comes to the big ramp in mobile data capacity it looks like it will be indoor cells that will make the difference.
