Cognitive radio's fate 'uncertain' as the spectrum battle plays out
The U.S. Federal Communications Commission (FCC) is attempting to find a regulatory fix – striking a balance between national defense and economics – to eliminate electromagnetic spectrum inefficiencies. For now, this is making the exact role cognitive radio technology will play in the U.S. military’s future unclear.
During the past few years, there’s been a lot of talk about an impending “electromagnetic spectrum scarcity” within the U.S. But what’s actually happening is that mobile operators aren’t able to keep up with the demand generated by the rapid proliferation of smartphones, tablets, laptops, and other wireless gadgets – so these devices are hitting wireless traffic jams that could be avoided in the future by tapping cognitive radio technology to exploit the unused or underused parts of the electromagnetic spectrum.
In the U.S., the vast majority of spectrum designated to specific users is either used lightly, around 10 percent, or not at all – a gigantic utilization problem. Federal agencies have exclusive use of 18.1 percent (629 MHz) of the “beachfront” frequencies between 225 MHz and 3700 MHz, according to the FCC’s Office of Spectrum Management, while non-federal users have exclusive licenses to 30.4 percent (1058 MHz). The remaining 51.5 percent is shared, with federal use primary and private sector use secondary.
With the transition from analog to digital television, white space “channel guards” within the UHF spectrum (~500 to 700 MHz) are no longer needed to prevent interference between channels. Unlike analog signals, digital signals can be cut off or filtered precisely, so the FCC is proposing to “repack” or essentially eliminate the white spaces between the channels, freeing up and consolidating all the available white space into a single, highly desirable block of spectrum to be auctioned off.
This is all playing out as a cognitive radio battlefield, but this war is political and regulatory in nature. It is a big deal for the U.S. military, because its different forces all make use of different parts of the spectrum, not only for radio but also radar. But the military’s spectrum needs aren’t the only ones at stake. Other government agencies, mobile operators – such as AT&T and Verizon – and all of the various television broadcasters also want more spectrum, so there are many big stakeholders involved, billions of dollars at stake, and everyone is vying for the same spectrum.
“It’s a fascinating battle – essentially a spectrum war,” says Manuel Uhm, vice president of marketing for Coherent Logix (Austin, Texas; www.coherentlogix.com), as well as a board member of the Wireless Innovation Forum (Reston, VA; www.wirelessinnovation.org), a nonprofit international industry association dedicated to driving the future of radio communications and systems worldwide. “How this all plays out will ultimately determine how fast and effective cognitive radio technology will roll out,” he continues.
Cognitive radio technology was developed many years ago, with an initial goal of providing flexible channels that could ensure high bandwidth, inference-free communications – mainly for military radio applications – over software-defined radio platforms.
The U.S. Department of Defense’s (DoD) military forces maneuver within the electromagnetic spectrum to gain tactical, operational, and strategic advantages, and their stated vision is to have spectrum access “when and where needed to achieve mission success. To support this goal, DoD has stated that its future systems must become “more spectrally efficient, flexible, and adaptable.” In short: cognitive radios.
So, what exactly are cognitive or “smart” radios? “Intelligent wireless devices that can dynamically access radio spectrum, rather than waiting for statistically assigned frequencies, cognitive radios can detect locally unused spectrum ranges and intelligently share them with nearby peers based on their instantaneous demands,” explains Heather Zheng, a wireless networking and cognitive radio expert, as well as computer science professor at the University of California, Santa Barbara.
One of the key benefits cognitive radio provides the military is “the ability to access spectrum in a versatile manner, especially within hostile environments,” Zheng says. “Usable spectrum within these environments are unpredictable and can change dynamically on-the-fly. Cognitive radios are capable of adapting spectrum usage on-the-fly to maintain reliable communication despite such dynamics.”
There are still challenges ahead for the technology, and a big one is how to “realize cognitive radios that are both affordable and energy efficient so that they can be mobile portable devices,” she adds.
That’s not to say primitive forms of cognitive radio aren’t already in use; they are. “An example is the automated cellular offload to WiFi,” says Lee Pucker, chief executive officer of the Wireless Innovation Forum.
While cognitive radio and dynamic spectrum access define an entire set of technologies, the application of these technologies tends to be band specific. “Leaders of providing database/spectrum access system services, for example, include Federated Wireless, Google, Spectrum Bridge, and KeyBridge Global,” Pucker says.
Beyond government-funded R&D programs such as DARPA’s xG and WNaN, and NSF’s EARS, Pucker is seeing “limited investment in dynamic spectrum sharing technologies in advance of FCC regulation. Regulatory uncertainty in already-existing spectrum sharing bands is also inhibiting growth.”
More efficient management of the spectrum will help enable cognitive radio. Government agencies, the military, research communities, and companies interested in the technology are all exploring methods to efficiently monitor and enforce spectrum usage.
“An increasingly difficult challenge in spectrum management is how to perform real-time spectrum monitoring with strong coverage of deployed regions,” points out Zheng. Today’s spectrum measurements are basically “carried out by government employees driving around with specialized hardware that’s bulky and expensive – making the task of gathering real-time, large-scale, spectrum-monitoring data extremely difficult and cost prohibitive,” she explains.
One solution to the spectrum-monitoring problem, proposed by Zheng and colleagues, is to leverage the power of the masses – in the form of millions of wireless users – using low-cost, commoditized spectrum-monitoring hardware. “We envision an ecosystem in which crowd-sourced smartphone users perform automated and continuous spectrum measurements using their mobile devices to report the results to a monitoring agency in real-time,” she says.
Spectrum monitoring and enforcement are critical problems frequently cited as being the main obstacles facing widespread deployment of dynamic spectrum systems, according to Zheng. “Without monitoring and enforcement, cognitive radio users could potentially ‘misuse’ spectrum without authorization, and such transmissions could disrupt legacy users and break the safety guarantees necessary for deploying dynamic spectrum access,” she adds.
Emerging spectrum sharing trends
“The biggest spectrum sharing trend to emerge so far is the FCC’s 3550 Citizen’s Band Radio Service Proceeding, which proposes a three-tier model with federal users at the top tier as the protected incumbent, followed by a priority access tier, and a general authorized access tier,” Pucker says.
This supports the model proposed by the President’s Council of Advisors on Science and Technology in a spectrum sharing report, which states that the relocation/reallocation of federal users’ spectrum for use by the commercial sector isn’t a sustainable model. Instead, they propose spectrum sharing between federal and commercial users as the way forward in many bands.
“At the same time, new regulations for dynamic spectrum sharing can’t be made unless there’s a clear understanding that incumbents – commercial, civil, or defense – can be protected by the spectrum-sharing technology used and there’s a valid business model under which investment can occur,” Pucker says. “New business model development is driven by an understanding of the technology’s potential and limitations, as well as the regulatory environment under which they’ll operate.”
The industry is “incrementally winding its way around the technology, regulatory, and business circle – aided by government-funded R&D programs – and this evolution will continue,” Pucker says.
Timeline for cognitive radio
The POTUS Wireless Broadband Initiative to free up 500 MHz of spectrum, initiated back in 2010, is driving some activity in cognitive radio, with a 2020 deadline.
Cognitive radio is expected to happen for the military in one form or another. The U.S. military is at the leading edge with cognitive radio and continues to make substantial investments in the technology. For example, earlier this year, University at Buffalo engineers received a $2.7 million grant from the Air Force to further develop cognitive radio, with a goal of making wireless 10 times faster.
“While regulatory uncertainty is one of the biggest concerns right now, another factor to consider is the possibility of needing to replace all of the associated radio-based equipment being used within a particular band today if it has to move to another band, which could happen if the FCC opts not to take a sharing approach and licenses all of the spectrum,” Uhm says. “And, of course, no incumbent wants to take on that cost or effort.” (See Figure 1.)
If spectrum “continues to be viewed as an asset to be allocated and not shared, then we will run out. But if, instead, it’s viewed as an asset to be shared, everyone will need to learn to play nicely with others,” he adds. Using inexpensive receivers that don’t stay within band is a classic example of not playing well with others. This occurred with LightSquared and GPS receivers in the U.S.
For this reason, the Wireless Innovation Forum is advocating receiver specifications, not just transmitter specifications. Today, all the specs are on the transmit side in terms of how much power can be radiated. This is one more change that will need to happen before cognitive radio can truly take off.
Ultimately, cognitive radio’s real beauty is that it “enables all of these new and efficient ways of using the spectrum, but at a level of flexibility that can also be viewed as a drawback if it makes it too difficult to map out a course forward or reach an agreement between users,” Uhm says. “A spectrum-sharing friendly regulatory environment can help to ensure the creation of successful business models that will enable cognitive radio technology to transform how we use spectrum.”