To see the latest iteration of white space device rules in the US (and one page for the UK), I found this from the IETF:

http://www.ietf.org/proceedings/81/slides/paws-1.pdf

and then this last minute update:

http://smartenergyuniverse.com/standards-loop-technology/752-fcc-releases-revised-tv-white-space-tvws-rules

One important change has been that the original requirement for spectrum sensing, down to -116 dBm, has been made optional. The major tool now used is instead the TVWS database. Probably a good move. Attemtping to detect such weak signal reliably proved difficult, and the effect of white space device transmissions in other channels (not just the adjacent channels) was also an issue.

You might be interested in this initial test of white space devices, from 2007:

http://hraunfoss.fcc.gov/edocs_public/attachmatch/DOC-275666A1.pdf

Cognitive Radios(CRs) are seen as the solution to the current low usage of the radio spectrum. It is the key technology that will enable flexible, efficient and reliable spectrum use by adapting the radio’s operating characteristics to the real-time conditions of the environment. CRs have the potential to utilize the large amount of unused spectrum in an intelligent way while not interfering with other incumbent devices in frequency bands already licensed for specific uses. CRs are enabled by the rapid and significant advancements in radio technologies (e.g. ,software-defined radios, frequency agility, power control, etc.), and can be characterized by the utilization of disruptive techniques such as wide-band spectrum sensing, real-time spectrum allocation and acquisition, and real-time measurement dissemination

I think that the main movements are currently among regulators, standardisation bodies related with spectrum regulation, TV operators and a few companies. The research advances in cognitive radio, but not necessarily in 802.22...

While 802.11 was so successful, we use to think that a new standard is going to be followed by millions of papers :-)

Actually, 802.11 came to live in well known conditions -almost- by choosing the ISM bands for operation. 802.22 supposes a very important change of paradigm: operators using licensed bands the have paid for are expected to accept that other are going to use their bands intelligently for the sake of efficiency. Operators have obvious ressistance to these technologies. I suspect that the movements explained above by Albert Manfredi from signal recognition to database queries not only have a technical explanation, but also a tactical one: the TV operator has influence on the content of databases, but no influence at all in signal detection! For the latter, it must trust others' technology ...?

You can check this book: http://wireless.ictp.it/tvws/book/ It has a chapter on TVWS standards.

A very good and recent paper on the advances of cognitive radio is:

Advances in cognitive radio networks, Beibei & Liu, IEEE Journal of Selected Topics in Signal Processing, vol. 5, num.1, feb 2011, pp. 5-23

http://dx.doi.org/10.1109/JSTSP.2010.2093210

I certainly agree with Javier Simó. The most important goal in this instance has to be to protect the licensed users of the band. So the geo-location database is the more fool-proof way of achieving that goal. But of course, any unlicensed user would also want to know if another unlicensed user is already using that channel, so spectrum sensing, even if not all the way down to -116 dBm, is still a useful feature.

I think there is a technically important difference between TVWS usage and 802.11 (WiFi). In typical WiFi, the strongest signals in a given channel are usually the only ones to worry about. WiFi is short range, so even if a very weak signal is present in that frequency channel, another user can get on that channel without worry about co-channel interference in the local area. Whereas in TVWS, the licensed signal can easily be much weaker than any close-by unlicensed interferer.

So with WiFi, the strong interfering signals are the main concern. In TVWS, the weakest interfering signals are the main concern.

Cognitive Radios are very intensive research topic you can get a good idea by seeing this paper titled "A Study of Recent Trends in Cognitive Radio Communications and Networks for Licence free Connectivity" from proceeding at IJERT.

In 2004 IEEE 802.22 initiated the first standardization worldwide effort for air interface based on CR for the use of TVWS.

Recent advancement in detection are

1. Statistical based sensing:-

Y. Zeng and Y. C. Liang, “Spectrum-sensing algorithms for cognitive radio based on statistical covariances,” IEEE Trans

2. Filter-Based Sensing

Y. Zeng and Y. C. Liang, “Spectrum-sensing algorithms for cognitive radio based on statistical covariances,” IEEE Trans

3. Fast Sensing

H. Li, C. Li, and H. Dai, “Quickest spectrum sensing in cognitive radio,” in Proc. 42nd Annu. Conf. Inf. Sci. Syst

4. Learning/Reasoning-Based Sensing:

U. Berthold, F. Fu, M. van der Schaar, and F. Jondral, “Detection of spectral resources in cognitive radios using reinforcement learning,” in Proc. 3rd IEEE Symp. New Frontiers in Dynamic Spectrum Access Netw. (DySPAN)

Recent advancement in primary protection is available in:

http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=5199373

for the combine recent advances you can also follow

https://www.cs.cmu.edu/~prs/NSF_CRN_Report_Final.pdf

An opportunistic operation model for mobile cellular networks:

Ádám Horváth, "Applying Opportunistic Spectrum Access in Mobile Cellular Networks," Infocommunications Journal, ISSN: 2061-2079, Volume 5, Number 2, 5 oldal (36-40), 2013.

Cognitive radio techniques are used for increasing the radio frequency utilization, which are allowing for new emergency and military communication services. US FCC considers these techniques in unlicensed UHF TV bands and VHF. In addition, regulatory domain, Ofcom in the United Kingdom, has already considered the use of CR technologies. The industry stake holders have also participated in international standards activities prevailing the deployment of cognitive radio techniques for next generation radio and dynamic spectrum access and coexistence. To handle user detection and protection, the system should have policy database that should determine what actions are acceptable in what circumstances. This database may dynamically configure changes in policy. Initial synchronicity standards also provided the systems of measuring interference and mitigating interference using manual management.

You can refer the following link please.

http://staff.utar.edu.my/gohhg/research/files2/IEEE%20Standards%20Supporting%20Cognitive%20Radio%20and%20Networks,%20Dynamic%20Spectrum%20Access,%20and%20Coexistence.pdf

http://amanuel-wran.blogspot.com/