Radar White Spaces

Regulation of secondary access to TV bands, the so-called TV White Spaces, are already in place in the United States and are expected to be finalized in the UK this year. Due to their attractive sub-Gigahertz frequency range TVWS offer important opportunities for applications which are range-limited, and this is currently being exploited for  example  for broadband wireless access to  "not-spots" and rural communities.  On the other hand  TVWS spectrum consists of  8 MHZ non-contiguous channels, and its availability varies greatly with location making it less suitable to support bandwidth-intensive applications like wireless distribution of HDTV and multimedia inside the homes. Moreover, in February 2012 the International Telecommunication Union (ITU) has brought forward a decision to clear a larger portion  of   Digital Terrestrial TV (DTT) broadcasting band for mobile services in Europe, Africa and part of the Middle East.  The release of this “Second Digital Dividend” is planned by 2015. Since TVWS spectrum are spatially unused portions of DTT spectrum, clearing more DTT spectrum for mobile broadband ma have an  impact on the availability of TVWS spectrum.

Radar bands are a good candidate for cognitive radio access because their operations is in many cases predictable in time and space and because they operate in large portion of spectrums “sweet-spot”, e.g. in the US over 1.7   GHz of spectrum from 225 MHz to 3.7 involves radar and radio navigation infrastructure. 

Especially, the S (2.7-3.4 GHz) and C (5.255-5.870) bands are attractive because these bands are close to  the ISM 2.4 GHz and 2.6 GHz 4G band for which both  WiFi and LTE  devices exist today that could be easily reused in radar bands, and this would reduce barriers to markets due to low-cost implementation and the economy of scale. The L (960-1215) MHz radar spectrum is of interest because, due to the lower frequency range, it can offer good coverag. It could be used   to support wireless connectivity for future M2M applications, such as smart grids and connectivity to vehicles.  

In addition to civilian radar bands, cognitive radio technology could also be used for sharing of the Military  radar spectrum.  In the UK the Ministry of Defence (MoD) is seeking to release and share spectrum to raise revenue and reduce £155 M/annum spectrum fee. A report by PA consultancy, which was commissioned by Ofcom has identified important opportunities for sharing of MoD spectrum using cognitive radio technology.

The 5150 MHz to 5350 MHz and 5470 MHz to 5725 MHz radar bands are already open to secondary access by IEEE 802.11 WLAN devices which use Dynamic Frequency Selection (DFS) to protect radars from harmful interference. However, secondary access to these bands somewhat “pre-dates” recent advance in cognitive radio technology. In particular it solely relies on the use of sensing-techniques, and do not incorporate the idea of using Gelocation databases, which is becoming the regulators’ preferred  method  for incumbent protection and white space detection. Furthermore, 802.11 operation in radar bands  is best-effort, as it could be interrupted upon detection of radar signals, and therefore do not satisfy QoS requirements.

Some recent papers that explore using Radar White Spaces