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November 2007 | Volume 10/ Number 11
Packet Voice over Wireless

It’s as Plain as Black and WhiteSpace

The Internet is a vibrant, free market environment where companies compete to deliver innovative services to consumers, and where consumers benefit from increasing choices and vigorous price competition. The market for consumer Internet access in the U.S. on the other hand is not as competitive.

In America, most homes are limited to two main broadband options: DSL or cable, and for each home there is usually only one supplier option for each of these. This lack of competition is a concern to consumers, government and the Internet services industry. It is a concern to consumers because of lack of choice. It is a concern to companies providing services over the Internet because the Internet Access providers have the power to discriminate against their traffic. It is a concern to government because universal broadband access is becoming a requirement for international competitiveness.

We are all aware of the national debate over how the ground-rules for broadband Internet access should be changed (or not changed) in order to prevent the USA from slipping further behind the rest of the developed world in broadband adoption, speed and price. Most people agree that increased competition would help. One vector of this debate is how to develop wireless as a competitor to DSL, cable and fiber optic.

The primary advantage of fixed wireless compared to wired technologies is that it is cheaper to deploy, especially in thinly-populated areas. Its primary disadvantage is that while it can offer speeds comparable to DSL it isn’t remotely as fast as fiber, so it is not a complete solution for the new media-intensive applications that are currently the biggest and fastest-growing users of Internet bandwidth.

WiFi has been hugely successful as a local area network medium, but it has had mixed success as a substitute for DSL and cable. Wouldn’t it be nice if there was a wireless technology that had all the advantages that made WiFi so successful, but none of the limitations that make it unsuitable as a broadband access technology? In fact, there are currently two main candidates to fulfill this role: 802.16 (WiMAX) and 802.22 (WhiteSpace). WiMAX is further along in its life, and it has evolved to be both a fixed and a mobile technology. 802.22 for now has no aspirations to mobility, but it has a feature that makes it a better candidate for fixed broadband access than WiMAX: the spectrum that it uses is better and, like WiFi spectrum, it is unlicensed. This spectrum lies between 54 MHz and 863 MHz. This spectrum has great propagation characteristics. It can travel over tens of kilometers and pass through walls. This means that 802.22 systems can have wider coverage areas than WiMAX, and use indoor antennas.

There is a serious technical challenge though. This is the same spectrum used by VHF and UHF television. Television stations do need licenses to use this spectrum, and of course it would not fly for their transmissions to be interfered with by 802.22 systems. On the other hand, this spectrum is a valuable national resource, and studies have found that much of it is unused most of the time. The idea of 802.22 is to keep track of what parts of the local spectrum are being used by TV stations, and avoid those frequencies. This is where 802.22 gets its colloquial name: it uses the “white spaces” between active television channels.

The technology that 802.22 employs to keep track of which frequencies are okay to use is called “cognitive radio”. Cognitive radio is complicated and compute-intensive. An 802.22 base station (BS) keeps track of all the transmitters in its environment, including TV stations, wireless microphones, other 802.22 base stations, and all the 802.22 customer premises equipment (CPE). The CPEs are only allowed to transmit when the BS tells them to. The BS gets this information from the CPEs which sense radio activity and report it back to the BS. This is called Distributed Sensing. 802.22 must also provide for multiple BSs to operate close together without interfering with each other.

So the technical challenges are significant. As of this writing the FCC was still deliberating whether to move ahead with opening up the white space to unlicensed operation. IT

Michael Stanford has been an entrepreneur and strategist in Voice-over-IP for over a decade. His strengths are technical depth, business analytic skills and the ability to communicate clearly. In his current consulting practice, Michael specializes in VoIP wireless networks, both WiFi and WiMAX. Internet Telephony Magazine recognized him as one of “The Top 100 Voices of IP Communications” and VoIP News named him one of “The 50 Most Influential People in VoIP”.

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