The battle between the cable industry and cellular providers over the use of unlicensed spectrum for LTE (LTE-U) has been the subject of tests. The tests were interpreted differently by the players and the issue appears closer to resolution.
To recap the situation: Cellular providers use spectrum that is licensed to them by the government, while Wi-Fi operators use free spectrum. The continuing acceleration of demand has pushed the cellular providers to covet that free spectrum. In addition to providing them with more capacity, the price – nothing – is enticing.
The key question is if the cellular players can act as good neighbors when using unlicensed spectrum. Since their technology evolved in a landscape in which they had full control over the spectrum they used – they paid a pretty penny for it, after all – their technology was not designed to share. What is there belongs to them. Wi-Fi approaches, on the other hand, have such sharing built in. To exist in the fractious world of unlicensed spectrum, sophisticated ways of using the system that don’t impinge on others is table stakes.
Jon Gold writes at Network World on the tests by cable industry consortium CableLabs and Qualcomm, summing up what was found, with a dose of irony:
Recent tests to see whether LTE-U technology interferes with Wi-Fi signals prove conclusively that LTE-U poses no problems whatsoever for Wi-Fi networks, and also that LTE-U (Long-term evolution in Unlicensed spectrum) will drown out Wi-Fi, depending on which party is to be believed.
Qualcomm, which said it used guidelines set by CableLabs, found that LTE on unlicensed spectrum is even less intrusive to Wi-Fi than Wi-Fi is to itself. CableLabs’ testing, Network World said, led the consortium to maintain the opposite: that an LTE-U station, even if it cedes half its time to Wi-Fi, “decreased throughput [of the Wi-Fi station] by more than half.” LTE-U, CableLabs found, interrupts Wi-Fi when it is in the middle of transmitting.
Of course, Qualcomm and CableLabs were not shy in voicing their interpretations. Qualcomm, which perhaps is the main driver of LTE-U, focused on the rather inconvenient fact for Wi-Fi (if, of course, it is true) that cellular is nicer to Wi-Fi than Wi-Fi is to Wi-Fi:
The tests, which used a large collection of user devices connected to the test Wi-Fi Access Point (“AP”), showed that Wi-Fi throughput improves when a second interfering Wi-Fi AP is replaced by LTE-U equipment.
Believe it or not, CableLabs disagreed. In a blog post at the organization’s site, Vice President of Technology Policy Rob Alderfer described tests that CableLabs – after long negotiations, according to the post – did at Qualcomm facilities:
In brief, we observed that current LTE-U prototype equipment is quite primitive — it is really just in mock-up state at this point — and incapable of demonstrating important coexistence features. The vendor-promised features, most of which are not required or even identified by the LTE-U Forum in its latest specifications, are not yet working to enable fair and reliable coexistence and confidence in testing. In addition, we found that claims of its ability to share fairly rest on a seemingly faulty understanding of how Wi-Fi shares spectrum. For CableLabs, this reinforces the need for a collaborative and open standards development process.
Clearly, the jury is still out. Craig Mathias, a wireless analyst, essentially said in the Network World piece that details so far are too scarce to determine which side has the best of the argument. At the end of the day, this is an important issue with which the Federal Communications Commission will have to deal.
Carl Weinschenk covers telecom for IT Business Edge. He writes about wireless technology, disaster recovery/business continuity, cellular services, the Internet of Things, machine-to-machine communications and other emerging technologies and platforms. He also covers net neutrality and related regulatory issues. Weinschenk has written about the phone companies, cable operators and related companies for decades and is senior editor of Broadband Technology Report. He can be reached at firstname.lastname@example.org and via twitter at @DailyMusicBrk.