The 3.5GHz band is currently the dark horse of LTE. Traditionally used for fixed local loop and WiMAX services, it has many potential benefits for more modern applications, notably small cells, especially as it is a near-global band. Some companies are placing high hopes on a future flourishing of this spectrum, including small cell start-up Accelleran.
The Belgium-based company points to the importance of the FCC’s support for 3.5GHz as an international small cell band, which could be valuable to add a layer of dense capacity to LTE services. It has upgraded its M101 TD-LTE small cell to support the US spectrum, even though the rules are not yet finalized. The product is in line with the FCC proposal, issued on April 23 and labelled US Citizens Broadband Radio, to earmark 3.5GHz as an ‘innovative band’ for small cells. It claims its design has sufficient flexibility to adapt as the FCC decides on the specifics of its licensing scheme and band plan.
This is only at the preliminary stage, and the FCC still has to finalize many details, but the general objective is to open up 3.5GHz via a flexible spectrum sharing model, which could be the model for other frequencies too.
As first-wave LTE deployments, most of them in paired FDD spectrum such as 1.8GHz, start to reach capacity, many operators plan to ‘densify’ using small cells and TDD spectrum, which is particularly suited to downlink-heavy applications and for minimizing interference in multilayer HetNets. In the US, this prospect, and pressure from spectrum reformers, has led to moves to open up 3.5GHz, even though much of it is occupied by government users.
The FCC supports a three-tiered model, with spectrum sharing in the government frequencies, to open up a total of 150MHz for consumer access (including mobile), carrier small cells, backhaul and fixed wireless. The agency initially targeted the frequencies from 3550MHz to 3650MHz back in 2012. These are used by federal and other bodies and would require spectrum sharing, with the incumbents having some form of priority access. In April the regulator sought comments on adding a further tranche in 3650MHz to 3700MHz, which is used by WISPs to provide rural broadband. Interoperability would be required across all three tiers within the 150MHz, to help drive economies of scale.
The idea is to have a tier of unlicensed spectrum for ‘opportunistic’ use plus priority access tiers, some of which could be auctioned or lightly licensed. The FCC wants a flexible licensing system with low administrative costs, short terms of engagement, an unlicensed portion, and support for micro-targeted deployments wbich could also be easily aggregated into larger footprints. That system would encourage all kinds of participants from large carriers (always needed to inject funds into a new band) to localized operators or single-application service providers.
‘At Accelleran we are very aware that one of the key requirements for operators is to have a small cell platform in 3.5GHz that can reduce the TCO’, said Jeff Land, director of business development at Accelleran. ‘That is why we designed the M101 small cell platform to allow OEMs and operators to take advantage of this new LTE TDD global capacity band. With the latest events unfolding in the US, our M101 is in a strong position to support different industry stakeholders to target the Priority Access and General Access tiers of the US 3.5GHz Citizens Broadband Radio’.
Over in Europe, CEPT has agreed to harmonize spectrum between 3400MHz and 3600MHz for ‘TDD-preferred’ allocation and 3600MHz to 3800MHz as TDD-only, while there will be auctions in Japan this year. The four Japanese operators plan to bid and to launch services in 2016.