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White spaces exploitation at the TV band

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03/02/2012

Imagen: http://www.tvtechnology.com/Over the last years there was a rising interest in cognitive-radio-based systems which take advantage of TV white spaces. The benefits of working at these frequencies are well known: provided that the signal propagation conditions are better as the frequency is reduced, this technology would be suitable, for instance, to improve the communication quality in scenarios such as rural areas or inside heavy masonry buildings. Furthermore, these systems are not so sensitive to the presence of obstacles between emitter and receiver.

The fact that these systems do not require license is an unquestionable advantage. Nevertheless, they need specific tools to avoid interferences among users. Apart from this, another technological challenge that arises is the geographical variability of white spaces. This means that roaming problems are possible whether a user is moving between countries or even inside certain nations, Spain for example.

As usual, one of the keys of commercial success is the standardization. Accordingly, the 802.11, also known as “Wireless Regional Area Network” (WRAN) was the first-approved standard. The system employs a base station which covers an area of radius spanning from 30 Km (typical) to 100 Km. It is designed to provide a throughput of 1.5 Mbps in the downstream and 384 Kbps in the upstream in densely forested areas. On the other hand, the 802.11af standard (not published yet) comes from an early idea of Microsoft and Google, who were interested in an enhanced WiFi-like protocol by using the TV white spaces (also known as WiFi 2.0 or White-Fi). To achieve that, a Wifi-like access point is needed (previously adapted to work at the UHF band). This standard will provide more speed and coverage than the conventional WiFi, apart from supporting quality of service guarantees in a more easy way. Both standards are grounded on the better performance of the TV white spaces. This means that some services, which will be unfeasible if based in higher frequencies, are also possible.

It is not clear that there will be a competition between these two standards. The 802.22 seems more appropriate to last-mile services, whereas the 802.11af appears better suited to shorter-range personal applications. On the other hand, it is likely that the first standard with commercial application will be the 802.11af mainly for two reasons: it is backed by the Wifi Alliance and also due to the low equipment costs. The slow evolution of the 802.22 (the first draft was written in 2004) gets the impression that this technology is not profitable yet, although the results would be very interesting.
Gradiant, which is plenty aware of the technological potential of these standards, follow their evolution very closely. Also, it has developed its own white spaces database and holds a lot of experience in radiocommunication systems.