All countries regulate RF spectrum, but the form of regulation differs. In the case of LTE-in-unlicensed-spectrum, the US regulator invites the industry to police itself, while Europeans are more rules-oriented. These forces are shaping the path and future adoption of LTE-U (LTE in Unlicensed spectrum) and LAA (Licensed Assisted Access). This column draws no conclusions as to which is the better approach, but it is indisputable that the future of these technologies will be determined in Europe.
In late 2014, some participants in the cellular industry thought it would be fun to start using the 5GHz unlicensed band, which is widely known as a Wi-Fi band although it is not reserved for Wi-Fi by any regulation. Emerging from the cellular world, they decided the best signal to use would be LTE, as that would require the fewest changes.
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But LTE transmits blindly in accordance with a base-station’s schedule (the licensee is the sole occupant of the spectrum), whereas Wi-Fi uses a packet-by-packet, listen-before-talk protocol to force devices – even on independent, overlapping networks – to take turns to transmit, rather than jamming each other. Thus, LTE as it stands is not a good neighbor for Wi-Fi (or any other wireless communication): an LTE device would transmit over the top of any other signal.
At this point we note that the US FCC (Federal Communications Commission) rules for the 5-GHz band are so thin that unmodified LTE in the 5-GHz band would be completely legal by the letter of existing FCC regulations. Meanwhile, ETSI (the European Telecommunications Standards Institute) is known for a more prescriptive approach to regulation. These two regulatory bodies have global significance because most countries follow the lead of one or the other.
So the LTE-in-unlicensed-spectrum group developed a two-pronged strategy. A hastily-assembled consortium, the LTE-U Forum (LTE-Unlicensed Forum), defined a set of loose rules explaining how LTE could work in 5GHz, with some modifications that they claimed would ensure co-existence with Wi-Fi. The goal of LTE-U was to get product to market quickly in the US, establishing working trials and networks without delay and meeting the commercial requirements of its proponents (selling and deploying new gear as soon as possible).
Meanwhile, work started on the European regulators. The movers behind LTE-U lobbied the global cellular standards body, 3GPP, to develop standards that would satisfy ETSI. Since 3GPP-ETSI is a multi-year exercise, this was envisaged as a slower, parallel path to the LTE-U-FCC work.
For a while, all this seemed to be following the plan. But unsurprisingly, the Wi-Fi industry viewed LTE-U as an existential threat. Cellular operators have many resources, and LTE-U transmitters in celltowers, urban hotspots and large buildings could monopolize much of the spectrum that Wi-Fi uses today. So the Wi-Fi industry approached the FCC with much weeping, gnashing of teeth and rending of raiment, suggesting LTE-U would interfere with Wi-Fi networks.
And the FCC, taking a stance it may yet regret, asked the industry – current and prospective users of the spectrum – to go away and figure it out among themselves. Companies were exhorted to develop rules that would allow the different types of equipment to “fairly” coexist. Both sides found this difficult to accept, being diametrically opposed, but they went through the motions out of respect for the FCC.
Then, a little while later, the FCC dropped a bombshell. It formally expressed concern about the possible effects of LTE-U (primarily vis-a-vis Wi-Fi) and established a requirement for all LTE-U equipment to submit for special approval. This, and silicon development delays, set back the timeline for LTE-U in the USA: we may see a handful of localized trials publicized before the end of 2016, but largely for show.
Meanwhile ETSI is moving, through a series of hearings, to establish explicit rules that all transmitters in the 5-GHz band will be required to follow, rules that will ensure fair coexistence between different wireless technologies. These rules will eventually apply to Wi-Fi, LAA and all new technologies wanting to share the band.
ETSI is stepping into the regulatory void left by the FCC. There are three consequences.
First, the timeline must be readjusted. LTE-U will very likely never see commercial deployment. While there will be small-scale tests and trials in various US cities, it now seems likely that LTE-U is so distant that most operators see its timeline converging with LAA, and will opt to use LAA as it will be the globally-accepted standard.
Second, all devices transmitting in the 5-GHz band will comply with ETSI rules and implement a form of packet-by-packet listen-before-talk technology, similar to Wi-Fi today. This is very desirable, as it will allow independent networks to share common spaces on the same RF channel, with some degree of fairness.
And the third, rather interesting consequence is that ETSI will become a much more influential regulator, setting explicit rules unlicensed wireless protocols must follow and eclipsing the FCC which gave birth to the Wi-Fi industry by opening up the 2.4- and 5-GHz bands. ETSI’s rules are likely to have influence beyond Wi-Fi and LAA, and beyond the 5-GHz band.
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