CBRS is a US scheme that dynamically allocates 3.5GHz spectrum on demand to anyone, such as a building owner, for their exclusive use. A similar scheme is being developed by ETSI for use in Europe in the 2.3 and 2.4GHz band. Both have huge potential for standalone or neutral host small cell networks, and incorporate strategies to avoid incumbent users being disadvantaged.
A new type of spectrum assignment
Spectrum management has up to now tended to be either licence exempt (e.g. Wi-Fi) or assigned on a long-term exclusive basis. Cellular operators might buy a 25 years lease on a nationwide basis but would rarely use their entire allocation throughout all geographic areas. Other wireless applications can be very location specific – you’ll find US naval radar stations at the coast but rarely further inland.
Shared access measures the active use of spectrum and models the interference to and from existing systems and other known users. Central servers can then allocate spectrum blocks with well-defined RF power levels for both temporary and longer term use.
Examples include issuing additional spectrum for operators to provide localised service for special events without needing to buy a long term licence for the entire area. These schemes also extend the range of potential market players for mobile services beyond the traditional mobile operators.
Quick recap on CBRS
CBRS (Citizens Broadband Radio System) allows almost anyone in the US to operates TD-LTE in the 3.5GHz to 3.65GHz band. Spectrum blocks of 10MHz are automatically assigned on request from the 150MHz band available.
The scheme is ideally suited for Small Cells, whether used as a private standalone enterprise system, directly linked to cellular operators to boost data speeds and capacity or indirectly roaming to provide a fully multi-operator neutral host solution.
We’ve explained CBRS details in more depth >here and interviewed Iyad Tarazi, CEO of Federated Wireless, about the wider ecosystem involved. We can expect to see the first private systems deployed later this year, followed by more widespread commercial rollouts during 2018 when compatible handsets are introduced.
ETSI publishes specifications for Licenced Shared Access at 2.3GHz
Elsewhere, regulators and others have been taking a strong interest and are considering similar schemes.
An ETSI (European Technical Standards Institute) committee has just published its initial specification for Licenced Shared Access (LSA). This is very similar but slightly different to the US scheme, called Authorised Shared Access (ASA).
Their focus has been on the 2300 to 2400MHz band using TD-LTE although extensions to other frequencies are not excluded. A new protocol, LSA1, is defined which co-ordinates spectrum allocation between the LSA controller and the LSA Repository.
One advantage of using this frequency is that it’s already well defined as Band 40 and many smartphones and handsets already support it. Disadvantages include that the spectrum is already partially occupied for other purposes and is adjacent to the popular ISM band (2400 to 2483MHz) used for Wi-Fi.
An earlier ETSI technical report documented various concerns from regulators about other users including telemetry, cordless cameras and defence applications. Cisco highlighted concerns about disruption of Wi-Fi.
LSA is not restricted to the very lowest power levels. One deployment scenario would be to use it in high power macrocell towers. However, the smaller footprint of small cells of all types creates greater opportunities for sharing in areas with other incumbent users as well as delivering much greater spectrum reuse opportunities.
Band 40 defines the permitted channel bandwidth assignments, which can be in steps of 5, 10, 15 or 20MHz. This gives greater flexibility and potentially greater capacity than the fixed 10MHz blocks of CBRS.
Different countries may have different views
France seems to be the place with the most activity on LSA. Rethink Research reports that the first LSA tests were conducted in France in 2016 by Ericsson, Qualcomm and RED technologies. RED provided the spectrum allocation server which incorporated live radio environment maps and SON algorithms to determine the most efficient frequencies to assign. Ericsson used a Radio Dot system with Carrier Aggregation to bond across licensed and shared spectrum channels. RED also demonstrated their SAS in the 3.5GHz band at an ETSI workshop and claim to be the first company capable of supporting both variants.
In the UK, a 2015 report from Plum Consulting on behalf of the UK Spectrum Policy Forum noted that there were no proposals for implementation of LSA in the UK. They even felt there was some uncertainty over whether LSA could become mandated at European level. Instead, Ofcom plan to auction off 40MHz of 2.3GHz spectrum this year alongside 150MHz of 3.5GHz although last year held a consultation about opening up shared spectrum at 3.8GHz to 4.2GHz bands.
It’s good to see regulators and standards bodies thinking “out of the box” about how to make more spectrum available to both operators and new entrants. There’s still a lack of clarity of which bands, modes and options will be adopted outside the US.
ETSI’s initial focus on Band 40 could accelerate development timescales since there won’t be a need to wait for compatible handsets to be developed. But not all European countries see this spectrum as their first choice.
Incumbent users of that spectrum will want to be assured of minimal impact to existing systems.
These schemes have huge potential to re-energise the small cell market, driven both by existing network operators and new entrants including cable/wired broadband providers and MVNOs.
ETSI TR 103 113 – A technical report from 2013 discussing the market requirements and spectrum interference issues.
ETSI TS 103 379 – A technical specification newly published which standardises the interface between the Repository and Controller elements of an LSA ecosystem.