SuperCell: A New Connectivity Solution to Improve ROI for Rural Area Coverage

According to GSMA's recent analysis, there are approximately 600 million people worldwide without mobile internet connections, especially in rural and remote areas in developing countries. From a Mobile Network Operator (MNO) perspective, these undeveloped areas are not economically attractive because a large number of base stations have to be deployed to cover the sparsely distributed population. The poor cost-to-coverage business scenarios result in low return on investment (ROI) for MNOs. Many Tier One infrastructure vendors conduct research and help MNOs provide cost-efficient site solutions. However, these solutions can hardly offer MNOs a sufficient average revenue per user, especially in lower-income countries.  

In collaboration with its telecom industry partners, Facebook Connectivity recently trialed and analyzed its new SuperCell solution in various rural areas to solve this problem. Instead of providing network coverage with conventional cellular solutions, SuperCell leverages a single base station up to 250 meters high with high-gain radio antennas to provide wide coverage and high-order cell sectorization for sufficient capacity. This novel solution has the potential to bring Total Cost of Ownership (TCO) benefit by replacing multiple small/macro sites with a single site for the same network coverage and capacity. Moreover, Commercial-Off-The-Shelf (COTS) components can be used in this approach to enable faster time-to-market.

The SuperCell trials mainly focused on a typical LTE or GSM system to provide basic communication services in rural and remote areas. According to the Facebook Connectivity team's analysis, with the same kind of base station radio antenna units, increasing the tower's height from 30m to 250m could improve cell coverage by approximately 2.75x compared to a traditional macrocell site. However, the cell radius of the new deployment needs to have at least 5x improvement for a better TCO. This improvement can be achieved by further increasing the gain of transmit antennas. In general, high-gain antennas result in narrow beamwidth. Thus, high-order sectorized antennas on a SuperCell base station are required to offer seamless network coverage. For example, each antenna of a conventional base station can cover 120 degrees of azimuth, while a high gain antenna may only cover an azimuth of 10 degrees. In other words, to provide the same azimuth coverage, a SuperCell base station may require 12 times as many antennas as a conventional base station.

With the ability to provide enough network coverage, another primary concern is to meet the high capacity requirement (i.e., to accommodate more users) with the limited available spectrum. This task can be achieved through heavy frequency reuse within high-order sectorization at the base station. However, without efficient deployment planning or accurate channel modeling, inter-sector interference results in severe capacity degradation. For instance, the side lobes overlap could happen if the antennas are not well placed. Moreover, multipath scattering can cause strong co-channel interference unless propagation channels can be estimated accurately for beamforming design.

The initial idea of SuperCell is to replace multiple small and macrocell sites with a tall tower to provide the same or even better network coverage and capacity, thereby reducing infrastructure deployment cost and network operational complexity. However, apart from the above discussion, several more challenges also need to be overcome promptly:  

• The site location should be well planned due to the size of the SuperCell base station. Once the cell site is decided, moving the base station to another place is almost impossible.
• High-gain antennas tend to have large surface areas. Such antenna deployment requires highly skilled engineers to mount them on a tall tower reliably, mainly due to wind loading effect concerns.
• High-gain antennas also create high power consumption, and a single point of failure could cause a large area effect.

Antenna selection strategy creates another concern. Lens antennas, such as a Luneberg Lens, can provide simplified configuration. However, such a solution limits the communication bandwidth and the flexibility to form a non-uniform sectorization to meet different connectivity needs within a single-cell coverage.

SuperCell offers a potential network deployment solution to reduce TCO in comparison to conventional microcell deployment solutions. However, this solution is still in conceptual and testing phases. Facebook is currently conducting different trials with various network configurations to verify its feasibility and analyze the pros and cons. To exploit its full potential benefit, MNOs should follow Facebook’s footsteps to further refine and evaluate ROI by conducting more trials and analysis in terms of performance, equipment and labor cost, site rental fees, and potential risk of a single point of failure. Using COTS antenna systems with little engineering investment can leverage economies of scale and reduce time-to-market. However, the antenna selection for specific deployment scenarios will be key to guaranteeing network operational efficiency and proving commercial viability. ABI Research expects more field trials and analysis to be conducted to verify the solution across different regions. The success of SuperCell will create enormous benefits to improve the living standard for people in the unconnected world and is a viable alternative to bring connectivity to the unconnected.