As the need for wireless broadband capacity grows, and the supply of virgin spectrum in optimal bands below 6GHz dries up, the need to share spectrum between rising numbers of parties is scarcely challenged any more.
Sharing can be supported in several ways of relevance to the WiFi community – allowing licence-exempt technologies to share frequencies already held by incumbent licensees such as mobile operators or government agencies; opening up unused or underused bands for sharing with tiered levels of access; light licensing, in which spectrum is open to many users and technologies, but with stricter rules than in unlicensed; and the free-for-all of a fully unlicensed band such as 2.4GHz, in which the main constraints are on power output.
The European Commission and several national regulators in Europe are taking an intense interest in sharing, and the opportunity to expand capacity for cellular, WiFi, LPWA (low power wide area) and other technologies.
Sharing will also become more important because the barriers between licensed and unlicensed solutions are blurring. For instance, LTE-LAA would see licence-exempt 5GHz frequencies being used to supplement a licensed 4G network; while some projects like Globalstar’s TLPS implement WiFi-based networks in licensed, controlled bands. Some smart city and internet of things (IoT) applications are using licence-exempt airwaves, but require high levels of reliability and availability, and so are arguing for priority access, or for their own protected frequencies within a more open band. Similarly, some manufacturers argue that they want to operate high-power technologies in unlicensed spectrum, which should be allowed provided the signals do not leak outside the factory walls to interfere with general purpose users.
Amid all these variations and competing requirements, especially in the IoT, European regulators want an approach which maximizes the spectrum available and remains technology neutral, rather than carving bands up into tiny pieces, one for each application; but which can guarantee a certain degree of QoS and performance even for solutions based on traditionally unlicensed technologies such as WiFi. This is arousing interest in tiered levels of access, like those proposed by the US regulator, the FCC, for the 3.5GHz band – simply put, that would involve three tiers, with incumbents receiving full protection, followed by one or more licensed users (such as mobile operators), and a section of the airwaves set aside for unlicensed access.
The EU’s Radio Spectrum Policy Programme (RSPP) sets out the framework for use of the airwaves, and requires member states to encourage collective and shared use of spectrum where appropriate. It has also proposed a common approach to identifying where sharing is appropriate and beneficial. In late 2012, its document ‘Promoting the shared use of radio spectrum resources in the EU’ went into more detail and covered licence-exempt examples – notably with a view to extending these bands, in a harmonized way. The Commission is currently working on a full inventory of spectrum across its 28 member states, and under its SMART program, is studying the future needs for licence-exempt spectrum , as well as the impact of traffic offloading.
WiFi is the most obvious beneficiary of additional unlicensed spectrum, such as expansion in the 5GHz band. It is also pushing down into the ISM frequencies (around 868MHz in Europe) with extensions for white spaces and LPWA. However, in fully licence-exempt bands, of course, there is no one technology which gains special rights and in the IoT, WiFi will have more rivals than it has had in wireless broadband to date (from Sigfox and LoRa in the smart city, to LTE-LAA in 5GHz).
That could cause congestion and interference to rise more quickly than previously anticipated and send WiFi supporters looking for shared access to a previously licensed band – something that could not only increase the spectrum availability for the technology, but also provide it with a more protected environment for certain sensitive applications. The WiFi lobby, led by Google, is fighting hard in the US to see the licence-exempt portion of the 3.5GHz band maximized, and similar debates are arising in Europe, with a rising interest in LSA (licensed shared access) as opposed to fully unlicensed sharing.
The LSA idea gives users shared spectrum access rights that are guaranteed by a regulator, with each organization holding a non-exclusive (and sometimes free) licence, so that predictable quality of service can be assured. Licences come with tougher sharing conditions than in fully unlicensed. Interference management is the responsibility of the spectrum management authority, which sets the access parameters through regulation and licence conditions.
One of the key challenges for the EC and other authorities is to support new technologies which allow spectrum sharing to be more flexible and dynamic, and which therefore support many providers, and multiple technologies, in one band. Techniques like cognitive radios and geolocation databases are helping to open up spectrum to WiFi and other technologies without removing the incumbents – as seen in TV white spaces efforts in the UK and elsewhere.
However, to achieve economies of scale and avoid cross-border issues, the EU has the additional challenge of harmonizing shared spectrum usage and frequencies, and preferably the mechanisms for managing them. The Commission proposes to create a common methodology to identify beneficial sharing opportunities (BSO), and to enable regulators to support shared spectrum access rights in a uniform way. That will take time to have an effect across the region, but the potential benefits are high – extending affordable WiFi and other services to more people, and giving easier access to spectrum for new providers and innovators. There should also be the opportunity, for existing users, to save costs by sharing more infrastructure.
One important example is the 2.3GHz band. This is widely allocated for wireless broadband, most commonly TD-LTE, around the world, but in Europe it is fragmented and employed for a wide range of applications including amateur services, government functions and PMSE (program making and special events).
There is work ongoing to harmonize the band for mobile broadband, and to lay down procedures so regulators can allow shared access, which can encourage new players and services and improve economics.But the process is likely to take several more years, and some companies believe the delay is wasting a golden opportunity. Opening it up as a unified mobile band which could be shared would be worth €12bn to the wireless sector in the region, claimed a December 2013 study commissioned by Ericsson, NSN and Qualcomm from Plum Consulting.
Opening up such bands not just for sharing among conventional licensees, but for the ‘unlicensed’ technologies, could create even greater opportunities for innovation in services and networks, and should become more practicable as dynamic spectrum and flexible radio systems evolve. The US 3.5GHz project, though over-complicated, is a sign of things to come, as is the UK’s work on TV white spaces. These are early steps, but valuable pointers towards the flexible, shared future in which WiFi will play an important role, and for which the European Commission is starting to plan today.