IEEE 802.22

The IEEE 802.22 WG is a project for developping wireless regional area networks (WRAN). This working group has been created after the FCC proposition to allow the use of TV vacant bands by license-exempt devices.

1. WRAN

WRAN aim at bringing broadband access in rural and remote areas. The 802.22 WG takes advantage of better propagation characteristics at VHF and low-UHF and of the unused TV channels that exist in these sparsely populated areas. It can be seen as an extension of the existing standard (WiFi, WiMax) to large areas with small density of population:

The IEEE 802.22 future standard is designed to work into the UHF bands. These bands are also used by other systems:

• TV: ATSC and NTSC in the US. DVB in Europe
• Wireless microphones

The IEEE 802.22 is a standard based on cognitive radio, and more precisely on opportunist radio. Before initiating a communication, the user terminal has to scan the UHF bands to determine the free ones, send back the information to the base station so that a common channel can be found.

For more information, check this presentation: WRAN system concept (ppt). It has been done at the IEEE 802.22 WG meeting of November 2004.

We focus here the sensing part of the IEEE 802.22 standard since it is the only part of the standard that is based on cognitive staff.

Note that an important issue is that the regulator allows the use of UHF bands by secondary user. In Europe, the different countries regulators are therefore set up a working group about this question: TG4. This group is also in charge of the regulation of the numerical dividend.

2. Sensing in IEEE 802.22

The sensing system has to be able to detect TV (DTV, NTSC, DVB-T and wireless microphones) at various signal power levels to avoid interference. These sensing requirements are the following ones: (see Spectrum sensing requirements).

• DTV/ATSC (numerical TV) : -116dBm (6MHz)
• NTSC (analogic TV) : -94dBm (6MHz)
• Wireless Microphone : -107dBm (200kHz)

2.1. TV signals

The main interest is the detection of DTV/ATSC signals since NTSC (or analog TV) broadcasting should be stopped in a few years - the so-called numerical dividend. Detection signals at level close to -116dBm can be converted in terms of signal to noise ratio as detection signal with a SNR minor to -10dB [1]. This detection problem is hence a challenging one !

Several algorithms have been proposed to detecte DVB signals at these SNR. The algorithm proposed by the IEEE 802.22 WG can be found here and another one here. ATSC signal detection algorithm is also available here.

2.2. Microphones signals

Wireless microphones can use either (depending on the manufacturer) analog modulation (FM), or digital modulation. In general, linear modulation of QPSK symbols. A detection algorithm, which also works for detecting DVB signals can be found here.

3. See also

• Official website of IEEE 802.22 WG

References:

[1] C. Cordeiro, K. Challapali, D. Birru, and N. Sai Shankar, IEEE 802.22: an introduction to the first wireless standard based on cognitive radios, Journal of Communications, vol. 1, no. 1, pp. 38–47, 2006.