Recently there has been a push to make a significant amount of unlicensed white-space spectrum available in the 600 MHz band as part of the Broadcast Television Spectrum Incentive Auction Rulemaking. As reported in BNA, the FCC is considering making an additional 30 MHz of spectrum available for unlicensed use, augmenting existing white-space spectrum. Proponents of this unlicensed band are using the term “Super Wi-Fi” to describe the technology that would use this spectrum. The only problem is that it’s not super for multiple reasons, and it’s definitely not “Wi-Fi.”
The term Wi-Fi refers to interoperability compliance with specific IEEE 802.11 standards, and is a designation controlled by the Wi-Fi Alliance, the organization that certifies Wi-Fi gear. The Wi-Fi Alliance is not happy about the term “Super Wi-Fi” had this to say in a press release last year, “The technology touted as “Super Wi-Fi” does not interoperate with the billions of Wi-Fi devices in use today.” In addition, they state, “Wi-Fi is a registered trademark of the Wi-Fi Alliance and the term ‘Super Wi-Fi’ is not an authorized extension of the brand.” So let’s just call it “white-space” network, which is the origin of this technology.
Since it’s not Wi-Fi, it needs new radios
Because super Wi-Fi isn’t a new band and has a new radio standard, existing Wi-Fi radios in phones, tablets, and laptops won’t work with these white-space networks. Any user wishing to connect over a future white-space network will need entirely new equipment, most likely a USB form-factor modem. Another possibility would be a wireless router that connects to the white-space network and provides Wi-Fi connections as a hot spot; however, that newly created Wi-Fi hotspot is then subject to all the congestion frailties we currently experience on Wi-Fi networks today.
Another important issue is the radio standard itself. There are two different standards being developed for white-space spectrum, IEEE 802.11af and IEEE 802.22. IEEE 802.22 was just recently completed but IEEE 802.11af is still in development. It’s not at all clear which of these standards will prevail in the market, or whether something entirely new will come along. Dueling standards generally serve to confuse and delay markets.
Now let’s try to understand the “super” part of this technology, since I don’t really see anything that “super” about it. First, it’s quite slow compared to existing Wi-Fi technologies, limited to a peak rate of 29 Mbps. In contrast the latest Wi-Fi standard, IEEE 802.11ac which is still under development but available in commercial product, can deliver throughput rates close to 1 Gbps (800 Mbps) in a base configuration, and over 6 Gbps in its most advanced configuration.
Who will build the networks?
Second, claims about its superiority are based on an assumption that as-yet-unidentified service providers will deploy networks to operate on this white space spectrum all over the country and offer wireless broadband service. Policymakers seem to hope that these new networks will somehow alleviate the mobile broadband capacity crunch that we are experiencing.
This notion, however, is flawed. First, it is extremely unlikely that any entity will invest billions of dollars in massive amounts of network infrastructure to use unlicensed spectrum to support commercial wireless broadband services. The carrier’s inability to guarantee service quality, predict and manage capacity, and eliminate or prevent interference render unlicensed spectrum an inferior solution for providers who compete based on quality of service and ability to support bandwidth-hungry apps and devices.
Add to this the possibility of different technologies using this band and it looks like an even less attractive basis for a significant capital expenditure which needs a return on the investment. For example, an IEEE article states that there is likely to be heavy degradation of 802.22 performance if it operates alongside an 802.11af network.
One thing we have learned over the least twenty years of building wireless data networks is that large volumes of users, whether its consumers, business users, or even M2M applications, subscribe to a wireless network technology only if they can obtain really broad coverage. Wireless network technologies with limited coverage have achieved only limited commercial success, including technologies such as Cellular Digital Packet Data (CDPD), Metricom Ricochet, and most recently Sprint/Clearwire’s WiMAX network.
White-space networks will be similarly limited in its coverage, but will further be complicated by being suited only for fixed operations. This is because the technologies currently envisioned to operate in the white space spectrum rely on the modem’s current location to query a database to learn what frequencies it is authorized to use.
Is LTE a better bet for this spectrum?
In contrast, wireless data technologies that have enjoyed wild success, such as EV-DO, HSPA, and LTE are technologies with extremely broad coverage, coverage achieved from tens of thousands of base stations covering almost all of the population. It may seem to be an apples to oranges comparison to compare a commercial LTE network with a white space network, yet it is exactly this comparison that needs to be made, because the spectrum being contemplated will end up being used for LTE networks or for white-space networks. There is no middle ground currently under discussion or development.
I believe one effective basis for such a comparison is to consider the aggregate capacity the two different networks might provide. The math for this is straightforward. Simply consider the number of possible sites, multiplied by the amount of spectrum, and multiply that by the spectral efficiency.
According to CTIA, there are some 285,000 cell sites. Assuming the spectrum was auctioned, cellular operators would likely deploy the spectrum across most of these sites, but a conservative estimate would be half these – 142,000 sites, each with 3 sectors. Taking 30 MHz of spectrum under consideration and average LTE spectral efficiency of 1.4 bps as per my studies and writing on this topic, that amounts to 17,640 gigabits/second (Gbps) of additional national mobile data capacity.
White-space networks could have comparable spectral efficiency and could also be deployed in 3 sector configurations. The only variable in question to determine the total capacity delivered by white-space networks using the same amount of spectrum is the number of sites (access points). Given my previous arguments of interference concerns, it’s inconceivable that anybody would build out white-space networks with density equivalent to cellular network.
White spaces are for local networks, not national ones
Usages are more likely to be adhoc and localized – just as with Wi-Fi. It might make sense to deploy a white space network on a campus, at an oil well, or in a town, but given the lack of control over the spectrum, it won’t make sense for any entity to deploy a national network. As a consequence, my expectation is that the total number of white space sites will be significantly lower than that of today’s cellular networks, and thus the aggregate national data capacity provided by the use of that spectrum will also be significantly lower. This lower data capacity represents a lost opportunity for the spectrum.
It’s all well and good to create experimental networks and to foster innovation, but the 600 MHz band represents a precious resource at a time when providing sufficient capacity to foster the mobile broadband revolution is crucial, and a time when new sources of spectrum seem ever more challenging.
I believe applying that spectrum to technologies that will use it the most fully will provide the greatest societal and economic benefit. Right now, those technologies include LTE and LTE-Advanced. We should continue to foster innovation and experimentation with white space spectrum and Wi-Fi, but not at the expense of also expanding the base and capabilities of our best-in-class, commercial wireless broadband networks that depend on licensed, exclusive use spectrum for their core operations.
Peter Rysavy is President of Rysavy Research, a wireless network engineering firm.