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Current debates in license-exempt spectrum for wireless broadband communications in Europe

In December 2017, the European Commission issued a Mandate to the European Conference of Postal and Telecommunications Administrations (CEPT) to study feasibility and identify technical conditions for the use of the lower 6 GHz (5925-6425 MHz) band for the provision of wireless broadband communications.

The justification for undertaking the measure was based on the Commission’s broadband connectivity objectives, aiming to achieve internet connections with download/upload speeds of 1 Gigabit of data per second by 2025. The results of the CEPT’s studies would inform the design of EU harmonised technical conditions, to be developed together with the European Telecommunications Standards Institute (ETSI). Those technical specifications are expected to ensure interference-free, technologically neutral, efficient use of spectrum and ‘fair’ coexistence with other technologies in the 6 GHz and neighbouring bands. 

The developments have added a new aspect to the spectrum sharing tensions between the LTE and Wi-Fi industries. A major (incumbent) player in the adjacent 5 GHz band is the Wi-Fi system, utilising the 455 MHz of spectrum available on a license-exempt basis. The Wi-Fi community in the IEEE 802.11 standards committee have thought of the ‘6 GHz as an extension of 5 GHz’. For the dependents of the Wi-Fi ecosystem, ‘the simplest approach’ to any technical conditions for coexistence in this spectrum would be keeping the ‘status quo’; that is, maintaining the Wi-Fi style spectrum accessing mechanism as a reference point. On the other hand, the LTE proponents have approached the 6 GHz spectrum as a ‘greenfield’, which means that it could allow different coexistence mechanisms to be developed vis-à-vis the traditional Wi-Fi system. 

Wi-Fi and LTE stakeholders have just had come out of a prolonged consensus finding process in relation to the adoption of a revised ETSI EN 301 893 harmonised standard, specifying the spectrum access mechanisms and thresholds for sharing in the 5 GHz band. Both stakeholders had pushed for their own solutions for the harmonisation of the technical conditions for spectrum sharing within the EU regulatory and standardisation framework. For the LTE industry members the preferred option was an Energy Detection (ED)-only mechanism with threshold of -72 dBm, while the Wi-Fi dependent sector insisted on the adoption of their legacy method incorporating both ED (threshold of -62 dBm) and Preamble Detection (PD) (threshold of -82 dBm). For the players in the Wi-Fi eco-system the revision was important because they wanted to make sure that the newest update of the Wi-Fi standard (IEEE 802.11ax) would be covered by the EU’s technical conditions for operation in the 5 GHz band. After months of negotiations, it was agreed that both mechanisms would be adopted in the EN 301 893, until further coexistence tests results prompted more revisions. 

The tension, however, has now moved on to the 6 GHz band. In addition to recently announced specifications such as LTE-U, LTE-LAA, MulteFire, developed for the use of the 5 GHz unlicensed spectrum band, cellular stakeholders within the 3GPP standards body have started working on the extension of the LTE-based 5th Generation New Radio (5G NR) standard for operation in unlicensed bands (i.e. 5G NR-U). The spectrum under consideration have included bands both below and above 6 GHz (up to 60 GHz). At a CEPT meeting in March 2018, the key proponents of LTE in unlicensed spectrum – Qualcomm, Nokia, and Ericsson – argued that their solutions would contribute to achieving the European Commission’s strategy on Gigabit Society. The Wi-Fi stakeholders within the IEEE 802.11 Coexistence (Coex) committee were concerned with the proposals presented by those companies, pointing out that the latter were pitching solutions which, in addition to the traditional 5 GHz band spectrum accessing mechanisms, included also suggestions for a ‘revolutionary’ way forward. 

This has brought back the concerns within the IEEE 802 community as regards the methods of access (single-threshold ED vs double-threshold PD/ED mechanism) to shared spectrum between Wi-Fi and LTE. The former has been particularly worried about the interference and inefficiencies a single-threshold system might cause to its latest revision – IEEE 802.11ax, designed to increase traffic throughput in dense user spaces, using spectrum in 5 GHz and above (up to 7.125 GHz). The IEEE 802.11 community has now approached the LTE standardisation body with a proposal to hold a joint Coexistence Workshop and collaborate on coexistence measures between IEEE 802.11ax and NR-U in the 6 GHz band. The response of the 3GPP and the evolution of the developments would be interesting to follow, as previously negotiations on the 5 GHz coexistence parameters between the two forums have ended up in a deadlock.