Mobile operators are currently focused primarily on deploying eICIC and MIMO. Relay nodes add additional complexity to the network and will be rolled out at a later date.

Carrier aggregation aggregates mobile operators’ 3G spectrum freed up by LTE roll-outs along with LTE and LTE-Advanced spectrum to add increased throughput to the network. The scarcity of spectrum has led to faster adoption of carrier aggregation by mobile operators as compared to other LTE-Advanced capabilities. Carrier aggregation is also being used for both LTE-FDD and LTE-TDD modes, allowing mobile operators with both network assets to adopt the technology to gain even more performance.

Carrier Aggregation and LTE-Unlicensed

One of the biggest innovations in driving the return of the small cells is LTE-Unlicensed technology, also known as LTE-LAA (LTE-License Assisted Access). Mobile operators are beginning to aggregate unlicensed spectrum in the 5 GHz band with their available licensed spectrum to add even more bandwidth.  

As LTE-LAA is an extension of LTE-Advanced and is based on carrier aggregation, it’s no surprise that small cells remain central to its deployment. Leveraging small cells for LTE-LAA provides a localized approach to carrier aggregation that helps mobile operators co-exist with the Wi-Fi community, while being able to further maximize their spectrum to increase capacity and coverage and ease network strain. Small cells are also suited to deployment in the LTE-LAA 5 GHz band as they are better suited to the band's low power requirements as opposed to macrocells. 

LTE-LAA is expected to be fully standardized in 3GPP Release 13, currently planned to be finalized in 2016.

Breaking Down the Numbers

Dell’Oro Group has forecast that small cell RAN revenues will account for 16% of the total RAN market by 2020. According to Pongratz, “the indoor enterprise/public access market improved significantly in 2015, though outdoor revenues still account for the greatest portion of revenue. We expect the indoor segment to grow at a quicker pace and expect the revenue split between indoor and outdoor to be closer to 50/50 by 2020.” And 5G small cells will account for close to 5% of the small cell market by 2020.

Deployments Around the World

A large proportion of the world’s small cells have been deployed in Asia Pacific in Korea and Japan, with volumes picking up in China and India. In dense environments, mobile operators are deploying enterprise and residential small cells in indoor venues to add capacity locally, with the potential for a 1-to-4 ratio of macrocells to small cells.

Outdoor picocells will most likely leverage a Cloud-RAN architecture and will roll out in 2017. Cloud-RAN deployments are now out of the proof of concept stage and are currently in trials. These cloud-based access points, which are also known as virtual base stations or C-RANs, will form the base of a 5G network architecture. They will handle not only the voice and data traffic for consumers, but will also support the M2M and IoT applications that form the ‘connected network’ of the future.

The majority of small cells will be multi-mode, supporting both LTE and Wi-Fi in the 5GHz band, allowing operators to take advantage of cost savings due to leveraging unlicensed spectrum. By supporting the 5GHz band, mobile operators can also deploy LTE-LAA on the same small cell. 

Critical Lessons Learned

Each small cell deployment is unique – and what happens in the lab is never replicated exactly in the field. In addition, we learned that focusing on data speeds in trials wasn’t enough. In real-world deployments, it’s more important to make sure that the small cells gel with the network from all angles and not just provide the required data speeds.

Mobile operators also need to plan for more than just mitigating interference between small cells and macrocells. They also need to mitigate issues associated with small cell placement and acquiring the necessary real estate. This needs to happen early in the planning process to ensure a smooth roll-out. 

Small cells have returned in a big way. From a role of just filling coverage gaps in 3G networks, small cells now form a major part of mobile operators’ strategy as they contend with exploding mobile data traffic on their networks and chart their path towards 5G. It’s all about adding capacity efficiently and economically. Now that the small cell force has awakened, we can’t wait for the next sequel.