With seemingly everyone in the world over the age of six owning a smart phone, the FCC estimates that the demand for wireless services will continue to increase over 50% year-over-year. While the cellular network load due to voice traffic has remained relatively flat, data traffic has soared. Cisco reports that almost half of data traffic is streaming video, and AT&T has discovered that the killer app on its network – as in network killer – is the iPhone, with 4% of its iPhone customers recently accounting for more than half of the data traffic on its 3G network. This is a problem that isn’t going away anytime soon, and cellular network operators are desperately trying to deal with a huge surge in demand they hadn’t anticipated.
Spectrum utilization (Courtesy of the FCC Office of Broadband Development)
Network operators have a number of ways to address the capacity problem, none of them attractive and all of them expensive. First they can buy more spectrum at auction from the FCC or from another company, such as AT&T’s purchase of spectrum from Qualcomm; or they can buy another operator for the same reason—most notably AT&T’s acquisition of Cingular and abortive acquisition of T-Mobile USA. Or operators can just splurge and build their purported 4G networks as quickly as possible – witness the current race between Verizon and AT&T. Finally, they can introduce tiered data pricing plans – and we all know how popular those have proven to be.
A pending move by the FCC could go a long way toward addressing the problem, but not as far as the dynamic spectrum access (DSA) made possible by cognitive radio techniques.
Enter the FCC
The FCC has done its part, selling large blocks of spectrum at auction and opening up TV white spaces for unlicensed portable devices. In addition its National Broadband Plan promises to “find” an additional 300 MHz of spectrum within the next three years and 500 MHz within five years—though it’s unclear where those frequencies are hiding. Since the RF spectrum isn’t getting any larger, this promises to be largely a zero sum game involving moving existing users to less used portions of the spectrum. But not entirely: the FCC has ordered all land mobile radio (LMR) stations below 512 MHz to further narrowband their channels, which could result in up to twice as many available channels below that frequency. Also, opening up the TV white spaces to unlicensed portable devices could have the same dramatic impact that creating the ISM bands did with the introduction of Wi-Fi, Bluetooth, etc. The use of digital frequency hopping techniques plus free spectrum made all this possible.
The economic impact of freeing up spectrum in what was previously thought of as “junk bands” like 2.4 GHz has been considerable. According to FCC Chairman Julius Genachowski, “The economic benefit created by unlicensed spectrum is estimated at up to $37 billion a year.” The reward from selling off licensed spectrum isn’t exactly bupkis, either. Again according to Genachowski, “Spectrum auctions have raised more than $50 billion for the U.S. Treasury, and economists regard the economic value created by FCC auctions as being about 10 times that number, or $500 billion in value.”
Always keen to turn a quick buck, yesterday (February 16) Congress stepped into the act. Assuming that the current bill becomes law, the FCC will be mandated to auction off large chunks of spectrum, thereby raising an estimated $25 billion, of which $15 billion goes to the Treasury; $7 billion to build a national public safety network; and $1.75 billion to compensate TV stations for giving up the spectrum they own but no longer use thanks to the transition from analog to digital TV.
The FCC did get it’s wrist slapped, however, in my opinion for not allowing AT&T and Verizon to turn the last auction into something resembling a 19th century land grab by the railroads. This time around they are explicitly entitled to bid on reclaimed chunks of spectrum. The newly aggregated public safety bands won’t be a freebie, either; they’ll “be developed by cellphone companies that would agree to give first priority to public safety transmissions during an emergency.” Hopefully they’ll be given a lot of priority.
There is one major plus to the pending auction other than money. According to the Times article, “The legislation also provides for the creation of bands of unlicensed airwaves, so-called white space, around each segment of auctioned spectrum for use in building large Wi-Fi networks in urban areas and for use by cellphone companies in temporarily easing crowding on their networks.” Assuming that the devil isn’t in the details, this could open a whole new chapter in wireless development.
Dynamic Spectrum Access
The most promising solution to spectrum congestion is cognitive radio networking. Cognitive networks move intelligence to the edge of the networks, enabling different transmitters to dynamically change their frequency or modulation in order to avoid interfering with other stations sharing the same portion of the spectrum. Cognitive radios need to be able to sense and respond to the presence of other signals in their intended operating bands, using advanced software radio techniques – known as dynamic spectrum access – to minimize interference.
Spectrum management can be achieved one of two ways: by reference to a central database or by dynamically responding to other signals. Spectrum Bridge has developed a database approach to frequency reuse for the TV white spaces, an approach which the FCC recently approved. Under Part 15 of the FCC rules if you want to use an unlicensed TV band device (TVBD) on these frequencies, you must first check Spectrum Bridge’s database for a list of authorized channels at your location and input the exact location of your device into their database before proceeding.
While the database approach is very helpful, it’s a static solution to the problem. The Shared Spectrum Company (SSC) was recently granted four patents that cover the basics of dynamic spectrum access: determining spectrum availability within a network; monitoring and detecting channel occupancy; detecting and classifying signals within a channel; and implementing an efficient method for reusing spectrum while mitigating interference. SSC has developed DSA-enabled cognitive radios that can operate in the TV white spaces without causing interference to other devices, thereby greatly increasing spectral efficiency and improving quality of service over what has been impossible to date.
xG Technology Inc. claims to have built “the world’s first carrier-grade cognitive radio cellular network” in Fort Lauderdale, FL. The company’s xMax network automatically reallocates mobile units to different frequencies in order to minimize interference and optimize network utilization. While xG’s network technology is still in the trial stage, it’s passed some preliminary military testing and looks to be getting ready for prime time.
Whether it’s xG’s cognitive radio network or someone else’s, dynamic spectrum access—made possible by cognitive radio technologies—is a potential game changer that could enable billions of humans—not to mention the billions of machine-to-machine (M2M) devices now starting to come online—to ‘share the air’ without fear of bringing networks to their knees.
