The FCC has announced that come September it will decide on one of the more controversial plans regarding use of the radio spectrum, TV white space. The outcome of this long-contested issue could have a major impact on dozens of wireless markets including competitive cellular service, hot spots, fixed mobile convergence, and mobile unified communications.
White space describes the idea of allowing unlicensed or “lightly licensed” operation in part of the spectrum allocated for broadcast television. The proposal is being promoted by the Wireless Innovation Alliance, an industry association backed by Google, Microsoft, Motorola, Dell, and others. Parts of that proposal are being challenged by TV broadcasters and manufacturers of other wireless products including microphones and theatre hearing devices, who claim that white space operation would interfere with their products or services.
These initiatives are most interesting because they deal with two of the fundamental issues in regulation: how actively should the government be involved in shaping a competitive marketplace and does the current policy of auctioning radio spectrum into perpetuity really foster the best interests of society. However, this issue does provide the FCC with a unique opportunity to make a real long-term contribution to the development of wireless technologies.
What’s “White Space”
The definition of “white space” has been a moving target throughout this debate. In all cases it has to do with some use of the broadcast television band that currently runs from 54 MHz to 806 MHz. The band is non-continuous as other services like FM radio are interspersed among the TV channels. The upper portion of that, 698 – 806 MHz was auctioned off earlier this year as part of the plan to migrate to digital over-the-air broadcast TV, so the spectrum available to white space initiatives will be 54 MHz to 698 MHz (current TV channels 2 through 51). Those sub-700 MHz channels are greatly prized given their lower loss and excellent building penetration characteristics.
The original idea white space idea was to send unlicensed transmissions on the guard bands between adjacent TV channels; guard bands are vacant slots of radio spectrum used to limit interference between channels. Those guardbands are roughly 1 MHz wide and scattered across the 54 – 698 MHz band.
Along the way, the white space idea morphed into a plan to use whole TV channels that were not being used to carry broadcast programs; the Wireless Innovation Alliance claims that in many US markets, as much as 75% of the TV airwaves are unused. A single 6 MHz TV channel could carry a simplex transmission rate of around 15 Mbps though 5 M to 10 Mbps would be more realistic. With 49 channels defined (channels 2 to 51) a 75% vacancy rate would leave as much as 216 MHz of available 700 MHz spectrum in those markets. To estimate the monetary value of that resource, the FCC raised $19.6 billion auctioning roughly 60 MHz of spectrum in the 700 MHz band in March of this year.
The Two Applications for White Space
The important thing to note about the white space debate, is that it really about two separate issues: fixed-location wireless access and personal-portable white space devices. Fixed-location wireless access covers WiMAX-like point-to-multipoint radio access systems based on the developing IEEE 802.22 standard to provide Internet access in underserved rural areas. The amazing thing about this version of white space plan is that the broadcasters seem to have no problem with it whatever. The interference-avoidance solution being proposed for 802.22 would use a database that identified TV broadcasters operating in each area. As the base stations would be known and all of the client devices are slaved to a base station, the interference issues can be effectively managed.
According to Carl R. Stevenson, President of WK3C Wireless LLC and Chairman of the IEEE 802.22 Committee in a post to wireless blogger Steve Stroh, “I am happy to report that the broadcast community is supportive of what we're doing in 802.22 and they have, from the very beginning, been actively participating in the development of the standard in a most cooperative and constructive way”. Hmmm, I thought the broadcasters were opposed to white space plans.
Developments on the personal-portable front are far more contentious and the technical issues are clearly more challenging. There could be thousands of personal-portable devices scattered around the countryside, all of which would be capable of transmitting in licensed TV bands. If any of those devices went haywire, it could impact TV transmissions or other TV band devices operating in that area. For example, Shure manufactures wireless microphones that operate on TV channels 7-13 (i.e. 174-216 MHz) and channels 14-69 (470-806 MHz). How are you going to locate and squelch the offending device, particularly if it is portable and operates on an unpredictable schedule?
The original interference avoidance plan proposed for personal-portable white space devices was based on frequency sensing and avoidance. However, such a system would have to be capable of sensing signals at very low levels given the fact that they might be operating indoors and receiving a weak signal from a distant TV transmitter. In a series of FCC-sponsored tests, the prototype devices failed to operate effectively. In a recent test conducted at FedEx Field during a Washington Redskins’ game, and none of the prototype white space boxes worked perfectly. The wireless devices the teams use also operate on TV channels.
The proponents are now proposing a solution based on frequency sensing in combination with a database (akin to the 802.22 model), plus a requirement for other devices to transmit a beacon signal that would make them easier to detect. However, the distributed nature of the network will probably call for some fail-safe procedure to find and squelch bad-behaving clients.
White Space- The FCC’s Opportunity of a Lifetime
While there are technical problems to be addressed, white space represents an opportunity that’s too good to pass up. However, the FCC should be looking beyond simple interference issues. Non-interfering operation must be a sine qua non for white space devices, but that’s not setting the bar high enough. New white space regulations will make a multi-billion dollar resource available to profit making enterprises at essentially no cost. The government should be looking for a lot more in return.
To really foster the public good, the FCC should mandate that anyone benefitting from this government-provided freebie must incorporate some new wireless technology in their solution. The price of admission to this game should be a significant R&D investment in wireless technology. There are plenty of great ideas floating around in the wireless space, so let’s use the white space as the incubator to test them out. That list would include software defined radio, cognitive radio, fixed-mobile convergence, mobile ad hoc networks, as well as a gaggle of Layer 1 enhancements.
Unlike the idiotic Muni-WiFi fiasco where government agencies thought they should compete with private enterprise, encouraging investment is an important role for government. Licenses and frequency auctions have left us with an entrenched, close-minded oligopoly in wireless, and white space gives us the opportunity to change the basic calculus. Making white space the technology incubator for wireless could spur the biggest advance in since that other government-sponsored initiative, the Internet.