It would be hard to have missed all the talk about white spaces. During the last year or so, the technology has matured, and it now is on the brink of being implemented at the network level.

In the near future, white spaces will come increasingly to the fore in terms of public consciousness. Communications-technology professionals need to familiarize themselves with what it is, what its applications and markets are likely to be, and to understand the standards question.

In simple terms, white spaces are any vacant spectrum within the Ultra High Frequency (UHF) television band (470 MHz-790 MHz). That could mean either empty channels, of which many are designated in any given location due to the need to avoid cross-channel interference between stations or the spaces between the channels.

As anyone knows, the Federal Communications Commission (FCC) lays down some pretty strict rules about use of this spectrum, but the industry has risen to the challenge. There’s no risk whatsoever that white-spaces devices will end up leaking signal all over an episode of “The Sopranos,” but getting to this point has required considerable technical proficiency and co-operation between interested parties.

It’s easy to see why communications companies have been so interested in white spaces. Companies have the potential to access the same amount of spectrum as was freed by the 3G auction and other spectrum sales (billions of dollars’ worth of them), only completely for free. Like the 2.4 GHz band, white spaces are completely open to the public and free to air.

This means that white-spaces modules don’t have to carry costly royalties to subsidize expensive spectrum, thus lowering the price for both purchase and use, and opening white spaces to a raft of low-cost device applications, particularly within machine-to-machine (M2M) communications.

The United States and the U.K. are ahead of the game when it comes to regulating this spectrum; many successful trials have taken place in both countries. The body overseeing development of the leading M2M communications standard for white spaces, "Weightless," has planted its stake in the ground to say the industry will see white-space network rollouts and M2M utilization sometime in 2013.

A Few Key Properties

The UHF spectrum is somewhat ironically named because, by today’s communications standards, it covers fairly low frequencies and long wavelengths. However, one of the reasons this range was selected for television is that signals travel reasonably long distances (c.10km) and through a considerable number of obstacles. With a powerful-enough transmitter, signals even can be bounced off the Ionosphere. This range and attenuation advantage over cellular bands make white spaces attractive.

As well as being cheap, white-spaces technology can, depending on the application, be run at very low power. For example, there is the looming prospect of smart meters communicating long-range to the power grid while lasting 15 years on a standard, primary battery. "Long range" and "low power" sound almost too good to be true, but these kinds of power-usage figures already have been modeled in products available today.

Of course, there is a flip side all "free spectrum" devices must negotiate: the sheer number of other devices and standards that likely will occupy the same radio space. However, white spaces must do this over a much bigger catchment area than, say, Wi-Fi or Bluetooth.

White-spaces radios have been designed, and must be designed, to cope with strong out-of-band signals. In-band TV transmitters also require that white-spaces radios can tune over an octave. White-spaces radios also are required to know their position, whether via a fixed- or GPS positioning, so that a central database can inform them of the available “free” frequencies left vacant in their area. Thankfully, the amount of such frequencies is vast.

Another attractive aspect is that, according to some accurate modeling, current white-spaces technologies can deliver near-100-percent coverage around the country with a small fraction of the number of base stations required for equivalent cellular coverage and at a tiny part of the cost. And each base station can allow for as many as a million connections per cell. Couple this with the fact that each device module, without cellular royalties to incur, only will cost a couple of dollars to implement and may realistically only use a couple of dollars a year in data. This may be one of the causes of white-spaces excitement.

The Coming M2M Boom

White spaces open up some pretty spectacular applications, but it’s worth saying straight away that voice traffic won’t be one of them — for the same reason people don’t currently guarantee voice traffic over Wi-Fi in the 2.4 GHz spectrum, only on a much larger scale. In any case, voice traffic isn’t presenting a big problem for the mobile operators right now. The money is in data.

Fixed wireless broadband in white spaces is an incredibly attractive proposition for wireless Internet Service Providers (WISPs). Governments around the world currently are undertaking big-money campaigns to bring the economic and social advantages of broadband access to the last few locations that don’t have it — those that are hard-to-reach or uneconomical to serve using fiber from the cabinet.

White-spaces radios offer WISPs the prospect of connecting homes cost-effectively to the cabinet wirelessly. In this capacity, white-spaces technology may be the way to go, due to its better signal penetration and range than cellular solutions. And whites spaces are much less expense than Wi-Fi relays. And while this application has a bright future, the bigger long-term opportunity for white spaces is in M2M communications.

According to a forecast from Ericsson, sometime during the next eight years, there will be an explosion in the M2M market, with as many as 50 billion devices entering the market. All that gear is going to need a way to communicate, and that’s where white spaces come in. The fact is, no other wireless technology fits the profile of the majority of M2M applications as well as white-spaces radios do.

Cellular systems simply are too expensive and power-hungry for medium to low-end devices. White spaces, however, open up the prospect of devices as small as an earring and as cheap as a few dollars being able to transmit long-range. The technology also can support 10 times as many devices within a given physical area.

The majority of M2M communications don’t involve massively time-sensitive packet delivery, nor do they generally involve long data packets. Messages might be as short as “I have vended my last chocolate bar and need to be restocked” or “This home has used X amount of power this month.” Such applications sit conveniently in “unguaranteed” free-to-air spectrum. When obstructed by other communications, M2M devices simply can resubmit their data at a later time. The key is to craft a standard that suits this profile.

Raising Standards

With white-spaces equipment already available and network deployment not far off, standards must be considered. Of course, M2M applications over white spaces require a “light-touch” standard to make them work. With short amounts of data to communicate over long distances, and with the potential of “noise” over a wide area, it makes no sense to think of high-overhead transmit packets as those found in the Wi-Fi standard.

There has been a lot of discussion of so-called “Super Wi-Fi” over white spaces in the United States. This has great potential to confuse. Wi-Fi may, in fact, work over shorter distances and for rural broadband applications; one or two Wi-Fi-based standards have been suggested. But when it comes to M2M communications over long distances, Wi-Fi’s transmit characteristics that favor versatility and verbosity over focus and brevity will not be suitable.

White-spaces standards can’t be based on anything related to Wi-Fi, and they can’t be an adaptation of any other standard that carries with it the legacy of the specific application and spectrum for which it was designed. Instead, the industry is choosing to focus its efforts on the purpose-built M2M-optimized standard called “Weightless.”

Going ‘Weightless’

Given the potentially noisy environment of white spaces, any technology working within the space must make use of sophisticated algorithms to oversee changing and uncertain frequency assignment along with the intelligence to understand how to reschedule packets according to the variability of its local radio environment. And with the lack of dedicated upload or download channels, Time Division Duplexing (TDD) is an obvious option.

The “Weightless” standard features flexible data rates, variable spreading factors (from none to 1024, enabling a 30 dB spreading gain and improvement in link budgets to increase range or accommodate low power devices), TDD and intelligent scheduling as well as a number of other features. Weightless also can allow for as many as 1 million terminals per cell.

The Weightless group acts as a de facto Special Interest Group (SIG), representing the interests of all members and the progression of the technology as a whole. In the same way that Bluetooth and Wi-Fi progressed, its founding principle is that the rapid spread of the Weightless protocol, in encouraging competition and the rapid growth and development of the white-spaces M2M industry with the most appropriate communications technology, will be of mutual benefit to everyone involved. (For more information on the Weightless standard/SIG or to join, go to www.weightless.org.)

Luke D’Arcy is vice president/Marketing at Neul Ltd. Contact him at luke.darcy@neul.com.

Sidebar

ABI Research: M2M Services Could Garner $35B By 2016

According to ABI Research, by the end of last year, most major wireless operators in North America, Europe and the Asia-Pacific region had established machine-to-machine (M2M) business units to take advantage of this fast-growing market. The market for cumulative cellular M2M connections will rise from about 110 million connections in 2011 to approximately 365 million connections by 2016, the group adds, representing a compounded annual growth rate of roughly 27 percent by 2016 and translating to about $35 billion in connectivity-services revenue.

The two largest cellular M2M market segments in this the forecast period, by revenue, will be automotive telematics and smart energy. Automotive telematics, including such factory-installed systems as GM’s OnStar service and aftermarket services like usage-based insurance and fleet management systems, together will represent more than $15.5 billion in 2016. Meanwhile, smart energy, specifically cellular connectivity to smart meters and data concentrators, will represent more than $7.5 billion in 2016.

“As mobile operators further develop their M2M service offerings, software platforms and M2M application developer support will feature as increasingly larger components of the operators’ services,” notes Sam Lucero, practice director/M2M Connectivity. “For example, AT&T announced on January 9 that it would be reselling Axeda’s M2M application platform in a U.S. carrier-exclusive deal. This platform will enable AT&T customers to more easily develop and deploy complex M2M applications.”

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