At a recent GTI event in Japan, Huawei demonstrated 770 Mbps peak throughput in a market trial of LTE-Advanced in 3.5 GHz spectrum. This was achieved with TD-LTE access mode with carrier aggregation. The trial showed 500 Mbps average throughput over multiple sites. Furthermore, Softbank demonstrated the ability to provide 1.2 Gbps peak throughput using 5-carrier aggregation in 3.5 GHz spectrum using TD-LTE.
Now, I think this is a significant demonstration for different reasons. It clearly shows the maturity level of TD-LTE technology and the thrust to implement carrier aggregation to achieve super fast wireless connectivity. It also demonstrates interest in using the abundant bandwidth in 3.5 GHz band to significantly grow the capacity of mobile networks.
I like to take this issue further to suggest that there is real value and business proposition in using the 3.5 GHz band for LTE small cells. The fact that 3.5 GHz band is licensed in most parts of the world and is readily available bodes well to position it as a source of supplementary capacity. In fact, even in the US where this band will be available as shared spectrum, the small cell use case fits well with the proposed spectrum licensing scheme. (The UK recently announced intent to auction 150 MHz of 3.5 GHz band in addition to 40 MHz in 2.3 GHz).
The high path loss properties of the 3.5 GHz band results in short coverage. Small cells are a perfect application in this scenario where high-reuse and low interference will allow the operator to scale the network to provide very high average, not peak, but average throughput. Small cells can be placed outdoors or indoors, irrespective of the case, to cover high-subscriber density areas.
From a business perspective, the small cell network can be operated by a neutral host service provider which leases capacity to multiple mobile network operators. This is an important point because it mitigates a few of practical issues associated with small cells. For instance, the small cell can support a single band (3.5 GHz) without being disadvantaged. As long as the mobile unit supports multi-band, multi-mode operation with 3.5 GHz TD-LTE, the base station does not need to support multiple frequency bands which the lack thereof has the potential to shut out small cells from many markets and deployments scenarios.
The plan therefore requires mobile handsets to support 3.5 GHz band whether TD-LTE or FD-LTE is chosen. We already have RFIC companies providing solutions that support this band as well as baseband modems that support dual TD-LTE and FD-LTE modes. It will take some work to get the full integration commercially ready with a certain capabilities of carrier aggregation as I can imagine implementing a full 100 MHz on a handset can be very power-consuming.
I also think this model will provide much superior performance to Wi-Fi 802.11ac despite using lower bandwidth and modulation scheme because interference can be better managed in LTE. Never mind that 802.11ac headlines 6.9 Gbps peak throughput: in reality only a fraction of that will be provided consistently. In the meantime, LTE-Advanced small cells can provide hundreds of Mbps consistently.
To summarize, the use of 3.5 GHz for LTE-Advanced small cells and implementing a neutral host business model can unlock a tremendous amount of capacity to address the medium and long term needs of mobile network operators. It is an opportunity for many 3.5 GHz spectrum holders to investigate this prospect to stimulate a phase of real and strong growth.