By: Renuka Bhalerao, Tom McQuade

Not a long time ago, in a galaxy not far away – in fact this one – small cells made their first appearance on the scene. In a 3G network, small cells were primarily used for in building coverage where it was needed. It was an important role, but not a glamorous one.

According to Stefan Pongratz, Senior Director of Carrier Economics and Mobile Radio Access Network (RAN) Market Research for Dell’Oro Group, the business case for 3G small cells in 2016 and beyond will remain meager, with 3G small cells expected to account for less than one fifth of the small cell market by 2020.

So what awakening in the force is calling for a return of the small cells now? First, the demand for mobile data took over the world, leaving operators with overloaded networks and scrambling to add both coverage and capacity. Rolling out LTE networks for mobile traffic was the first step, but these networks are already being strained.

Strategy Analytics predicted in its report, Mobile Data Traffic Forecasts 2014-2018, that by 2018 mobile networks will carry 56.2 Exabytes of data, up from 21.3 Exabytes of mobile data traffic in 2014. This growth in traffic is being driven by both strong performance on 4G/LTE networks and rapid growth in smartphone data subscriptions, with future growth driven by tablets, consumer electronics and M2M devices contributing to a larger share of the total data traffic. 

There are a number of ways that operators can add capacity to their networks, including acquiring new spectrum, which leads us to our second point – LTE spectrum is both scarce and expensive. Mobile operators are turning to a Heterogeneous Network model – or HetNet – to maximize their spectrum. A HetNet is composed of a combination of macrocells, Wi-Fi, distributed antenna systems (DAS) and small cells. By using a layered network model with deployed small cells, mobile operators not only address coverage concerns between macrocells and in indoor environments, they can also add much needed capacity to the network and improve the overall end user experience.  

Provisioning Small Cells

The addition of small cells to the mobile network adds complexity when it comes to RF network planning as compared to a macrocell-only network; therefore, efficient and autonomous coordination between macrocells and small cells is key. Self-organizing Networks (SON) techniques provide the real-time self-configuration, self-optimization and self-healing capabilities that are becoming mandatory features for the HetNet to work as a cohesive network. SON offers the promise of reducing costs in initial rollouts, enabling more effective coordination of time and frequency resources, providing dynamic interference management, and adapting to changing network conditions.

Interference Management and Carrier Aggregation

Mobile operators are deploying LTE-Advanced capabilities such as carrier aggregation and interference management techniques to make their networks even more efficient. Here again, small cells remain critical to operators’ overall strategy as they provide additional capacity in dense indoor environments where a majority of data traffic will be generated.

In a HetNet scenario combining small cells with Wi-Fi and macrocells, mobile operators are rolling out a number of interference management techniques to ensure the network is optimized for capacity and coverage.

• Enhanced Inter-cell Interference Coordination (eICIC) works as the interference manager for small cells as part of a HetNet. It uses advanced time domain scheduling to reduce radio interference and increase the coordination between network cells to ensure a streamlined flow of information.
• Multiple Input and Multiple Output (MIMO) is an approach which serves to increase efficiency across the spectrum by leveraging smart antenna technology that analyzes how base stations, antennas and user equipment communicate.
• Coordinated Multi-Point (CoMP) is a technique that ensures that even greater performance is achieved at the edge of the network, by increasing coordination between small cells, and between small cells and macro cells.
• Relay Nodes are low-power base stations that reduce the site-to-site distance in the macro network. They were added to the LTE Release 10 specification.