Cognitive Radio for WMANs

 
Cognitive Radio for WMANs
As discussed in Section 4.5, a WMAN will cover an area much larger than a WLAN does. The radius
of a WMAN can reach several kilometers. The most widely referred standard for WMANs is IEEE
802.16, also often called as WiMAX standard, or broadband wireless access (BWA) technology.
Different from WLAN technologies, WMANs usually support mobile terminals. For instance, the
IEEE 802.16e standard can support a terminal moving at a vehicular speed. Like WLANs, a WMAN
can also use cognitive radio to make it possible to underlay/overlay in those spectra that have been
already occupied by incumbent users.
It is to be noted that WiMAX is flexible in its channel sizes and can use the 6 MHz width of the
underused TV channels. For a WiMAX system using a bandwidth below 900 MHz, its coverage can
be three times larger than that in 2.4 GHz, reducing the number of base stations required well below
3G’s requirements, making mobile WiMAX clouds an even stronger proposition against cellular, both
in licensed and unlicensed modes.
It is very interesting to note that, many technologies could use TV spectra, though the WiMAX
community is keen to claim it for its own. In March 2004, when the IEEE 802.225 group was set
up, the 802.16 Working Group was angered when its proposal that the cognitive radio work should
be under its auspices, rather than in a separate group, was defeated. However, this has not halted its
supporters, led by Intel, in their quest to turn the 802.22 efforts to their advantage.
The story behind the conflict between the IEEE 802.16 and the IEEE 802.22 groups highlights
the importance of cognitive radio technology and its applications in either WMANs or WRANs (also
called “Wi-TV ” technology) operating in underused VHF/UHF TV bands.
The IEEE 802.22 working group insisted at the time the group began work that Wi-TV would
work with existing IEEE 802 architectures, serving as a “regional area network” complementing both
the Wi-Fi LAN and the WiMAX MAN. The IEEE 802.22 group also pointed out that WiMAX is not
suitable for TV spectrum because it does not include cognitive radio functions.
On the other hand, IEEE 802.16 group denounced that claim, noting that WiMAX does in fact
have a provision for cognitive radios (IEEE 802.16h) to avoid interference with other WiMAX devices
at higher frequencies, and that it could easily be adapted for UHF frequencies.
In December 2004, the IEEE 802.22 group accused the 802.16 group of overstepping its scope
and developing its cognitive radios for “coexistence with primary users,” not just WiMAX users, and
asked the WiMAX committee to reaffirm the limits of its scope. The WiMAX group declined and
received support from another IEEE task group, 802.19, which saw no reason why both groups could
not work on the problem separately.
The company that controls cognitive radio technology really will have its hand on the rudder
of the creation of next-generation communications, and the commercial vendors behind the shadowy
IEEE task groups know that.
As another development, very recently (according to a report written on February 28, 2005),
telecom agencies in India and Canada are working together on a cognitive radio-based broadband
wireless technology: The networks will operate in the 5 GHz spectrum (or possibly the licensed
Multichannel Multipoint Distribution Service (MMDS) bands) and transmit as far as one to two
kilometers. The base station would use as many as 48 antenna beams. The system would use cognitive
radio technology to identify interference and poor links and then change its own signal transmission
to improve the weak links. Ultimately, the agencies hope to develop this as a low-costs system that
can be used in underdeveloped regions or areas with aging telecom infrastructure.
It is interesting to see that an Indian government body is involved in such a research project which
appears to be primarily targeted at unlicensed bands, given that India only very recently de-licensed
the 2.4 GHz band for Wi-Fi. The 5.1 GHz band is still only available for unlicensed use indoors.