Tragedies of the Spectrum Commons
The Wi-Fi vs. LTE-U disagreement continues to rage, despite efforts by both sides to reach a détente. The Wi-Fi Alliance and the LTE-U Forum held an event last Friday on Capitol Hill that was meant to bring some comity and understanding, but reports from attendees indicate it degenerated into a food fight. This is not good, of course.
The international picture is decidedly different, with formal cooperation underway between 3GPP and IEEE 802.11 (Wi-Fi) and 802.19 (Wireless Coexistence Working Group) on coexistence measures and even coexistence testing and certification.
The happy stuff involves Licensed Assisted Access (LAA). The parties have shared detailed engineering specifications and have conducted some real-world testing of actual devices. The testing has revealed some issues, and they’ve been resolved. With any luck, the final specification for LAA will be approved by 3GPP by March or so, and vendors will commence to stamping out chips that allow LAA to perform quite happily alongside Wi-Fi systems internationally, even sharing the same channel.
But there’s still poor cooperation and communication between LTE-U and the Wi-Fi Alliance. The specifications that have been shared seem to be light on some of the details the Wi-Fi people regard as important, and while members of the LTE-U Forum have given a couple of presentations to the Wi-Fi people, the latter feel they need more information.
The issues that were identified in the LAA testing were of the sort that require close examination of running systems to detect, and it’s likely that LTE-U testing will disclose similarly obscure details that will need adjustment. Wi-Fi systems are also quite diverse, as the specification allows a range of parameters in some of the innards of the protocol, which is quite complex.
The issues that are likely to be discovered are on the order of “this could work better” rather than “LTE-U stomps all over Wi-Fi and kills it dead,” but there are still some rather overblown emotional reactions. So it would be beneficial to get some of the more skilled Wi-Fi engineers in the same room with some LTE-U systems running tests in a variety of configurations to tamp down the fears and find areas of potential friction. Dialog among engineers is helpful, especially when it takes place far from the madding crowd of fear-mongering advocates and loud politicians with no stake in a successful outcome.
Toward that end, the former LTE-U Forum is giving way to a successor organization know as Evolve that has launched a web site and launched an educational initiative. Evolve’s membership includes all the major wireless carriers except Sprint, as well as trade associations CTIA and CCA and equipment vendors Alcatel-Lucent and Qualcomm. The LTE-U Forum was mainly Verizon and Qualcomm, so this is quite an expansion.
One of the questions that comes up in the contrast between LAA and LTE-U is why the US carriers don’t simply use LAA, given its smooth glide path to operation. The reason is that LAA is a much less ambitious system than LTE-U, given the range of restrictive regulatory environments in which it has to run. So that suggestion reprises the public interest complaint of the 2G cellular era when they urged the US to adopt Europe’s GSM technology mandate. There’s no question that standardizing on GSM across Europe helped jump-start the cellular market in Europe and enabled the continent to enjoy a more advantageous position than the US.
But Europe’s GSM mandate lost its luster when the clock struck midnight and 3G came along. 3G was based on Qualcomm’s CDMA technology, and more flexible and efficient means of tapping the potential of spectrum to facilitate data applications such as Internet use. GSM lacked these capabilities initially, and as they were added it was necessary for GSM to license Qualcomm’s intellectual property as the Europeans had none of their own. They had overlooked the fact that technology doesn’t stand still.
The European situation was so contrived that regulators had to license new spectrum bands in which it was lawful to use 3G before it could be used. The technology mandate called for 2G GSM, and only 2G GSM. Oops.
Europe has, not surprisingly, adopted regulations for its unlicensed spectrum that limit its use to systems that behave like Bluetooth and Wi-Fi. LAA is designed for this scenario, so effectively it’s the GSM of unlicensed technology. This has forced LAA into a humble role of supplemental download capability for LTE phones. That’s nice, but it leaves the US problem – not enough licensed spectrum for our large smartphone base – unsolved.
LTE-U is in some ways analogous to White Spaces in the duplex gap, which is to say it’s a system that harvests dead air time and puts it to use. This comes about in two ways for LTE-U: it attempts to use a single channel with low Wi-Fi traffic (or none at all, ideally) and is also eliminates some of the dead air time between Wi-Fi packets from different transmitters.
The legitimate concern for the Wi-Fi folks can be addressed by letting them see how well – or how poorly – Wi-Fi works around LTE-U. I can’t say this for a certainty, but I believe we’re dealing more with perception that reality here.
It’s curious that the brouhaha over LTE-U and Wi-Fi coexistence is taking place at a time when fans of open source Wi-Fi routers are exercised over new FCC rules that regulate and certify the software than can be run in home routers. Rules are necessary because 5 GHz Wi-Fi systems share channels with a number of other systems such as military radar that require low power on some channels. Power limits vary by country, so Wi-Fi chip makers allow them to be programmed.
When companies such as Netgear and Linksys submit devices to the FCC (or its agents) for certification, the hardware and software form an integrated whole and are tested together, but when a user downloads OpenWRT and installs it in her own home router, there’s a possibility of exceeding power limits if the code was modified improperly. Since the whole point of open source is to make modifications, this is a real problem.
Consequently, some sort of licensing process will need to be created for things like OpenWRT and that has the open source people hopping mad. So the lovers of wireless software freedom are miffed that sharing the wireless commons requires some discipline. Gee.
It seems to me that there’s a fairly easy way to resolve this problem that’s similar to the way the LTE-U problem will be resolved: distributors of OpenWRT and similar packages need to prove to the FCC that their packages include non-modifiable code that limits the transmit levels of Wi-Fi radios to the regulatory maximums, and there will need to be some substantial penalties for violating the rules. The FCC’s rules in this area are (essentially) fine, so it’s simply a question of ensuring compliance.
The driving force that will solve both of these Wi-Fi issues is the same: the desire of responsible parties to ensure a functional spectrum environment, the development of trust, and a reasonable verification routine.
This isn’t too much to ask in either case.
For a discussion of spectrum rights, check this podcast by the Congressional Internet Caucus. For a more detail on the Evolve initiative, see this video with Tom Sawanobori, the CTO of CTIA, the wireless industry’s trade group. Tom will be our guest on next week’s High Tech Forum podcast. I hope to follow up on that podcast with a conversation with one of the leading skeptics of LTE-U. We believe in equal time here at High Tech Forum.