18 novembre 2009

UK, radio cognitiva per gli "spazi bianchi"

Anche il regolatore britannico OFCOM si occupa, come l'americana FCC, della questione "whitespaces", le finestre di frequenza UHF lasciate libere dalla riorganizzazione dello spettro televisivo del digitale terrestre. L'authority propone una pubblica consultazione sull'uso di tecnologie di radio cognitiva per una gestione automatica dell'offerta di servizi di accesso Internet wireless a larga banda che dovrà andare a occupare questi "spazi bianchi". In Gran Bretagna si pensa soprattutto alla copertura Internet di aree rurali scarsamente infrastrutturate. A differenza di quanto accade per sistemi come WiMax, Wi-Fi o Bluetooth, che operano, con o senza licenza, su frequenze predeterminate, i futuri dispositivi wireless per i whitespace utilizzeranno le stesse frequenze della televisione e non è pensabile quindi venderne modelli con canali preimpostati, né consentire agli utenti di sintonizzare i loro apparati. La possibile soluzione è una intelligenza di bordo che permetta al dispositivo di verificare da solo la disponibilità di frequenze libere.
Secondo OFCOM questa intelligenza dovrebbe funzionare sul principio della geolocalizzazione. Il dispositivo calcola (per esempio col GPS) la sua posizione geografica e consulta un database aggiornato con le frequenze televisive occupate in quella zona. Una volta identificati i canali liberi decide quali utilizzare.
Oggi il regolatore bandisce una consultazione su questo tipo di approccio, per studiarne la fattibilità. Potete scaricare il documento da questa pagina, da dove ho estratto anche il seguente Executive Summary. A febbraio 2010, a termini di presentazione scaduti, il regolatore avvierà l'iter decisionale.
Digital Dividend: Geolocation for Cognitive Access


1.1 Since its launch in 2005, our Digital Dividend Review (DDR) has considered how to make the spectrum freed up by digital switchover (DSO) available for new uses. This includes the capacity available within the spectrum that will be retained to carry the six digital terrestrial television (DTT) multiplexes after DSO. This is known as interleaved spectrum because not all this spectrum in any particular location will be used for DTT and so is available for other services on a shared (or interleaved) basis.

1.2 In our statement of 13 December 2007 on our approach to awarding the digital dividend, we considered the use of interleaved spectrum by licence-exempt cognitive applications (i.e. those exempted from the need to be licensed under the Wireless Telegraphy Act 2006 ). We concluded that we should allow cognitive access as long as we were satisfied that it would not cause harmful interference to licensed uses, including DTT and programme-making and special events (PMSE). This could potentially bring substantial benefits to citizens and consumers in the form of new devices and services.

1.3 We published a consultation on proposed parameters for licence-exempt cognitive devices using interleaved spectrum on 16 February 2009. In a subsequent statement published on 1 July 2009 we concluded that cognitive devices should either sense the presence of other signals or make use of a geolocation database to determine which spectrum was unused in the vicinity. In that statement we provisionally concluded on the parameters needed for sensing but noted that further discussion would be needed as to how a geolocation database might operate. This discussion document is intended to stimulate and inform such discussion.

Cognitive access to interleaved spectrum

1.4 Much previous work has assumed that cognitive devices would sense the use of spectrum by monitoring for licensed transmissions and only transmitting if they found none in a particular frequency range. Recent studies have shown however that the signal levels they would need to sense down to, in order to be certain of not causing harmful interference, are extremely low and so alternative approaches are now being considered.

1.5 The most promising alternative to sensing (also known as detection) appears to be geolocation, where cognitive devices measure their location and make use of a geolocation database to determine which frequencies they can use at their current location. They are prohibited from transmitting until they have successfully determined from the database which frequencies, if any, they are able to transmit on in their location. In this case parameters such as locational accuracy and frequency of database enquiry are important.

1.6 This discussion document focuses on geolocation and the mechanisms likely to be needed for it to work. It is intended as input to the thinking that is taking place around the world on geolocation rather than as a statement of clear regulatory intent. As such, it is hoped that it will further discussion and speed the development of possible geolocation solutions. It does not seek to change in any way the decisions on general cognitive access and sensing set out in our July 2009 statement.

Key geolocation issues

1.7 We see five key issues to be addressed in developing a geolocation approach.

1.8 The information to be provided by the device to the database(s). We suggest that this be flexible with the device allowed to select from providing only its location through to providing location, locational accuracy, device type and preferences as to the amount of information that it receives. As the device provides additional information the database can tailor its response, in some cases allowing higher power levels. We note that this may require standardisation work around the protocols to be used.

1.9 The information returned from the database(s) to the device. We suggest that this should be a list of frequencies and power levels for each geographical pixel or location. Alternatively, if the device has moved to a different country, the database might return the address that the device now needs to send its enquiry to.

1.10 The frequency of update of the database(s) and hence the periodicity with which devices will need to re-consult. Because some licensed uses of relevant frequencies might require access at short notice - for example some PMSE users - we suggest that devices be required to recheck the database at least every two hours.

1.11 The modelling algorithms and device parameters to be used to populate the database(s). We make some detailed suggestions as to propagation algorithms, assumed device sensitivity and methodology that would enable the database to derive the list of frequencies that could be available for cognitive devices from the information provided about licensed use.

1.12 The maintenance of the database(s). We note that someone will need to develop and host the database and that costs will be incurred. We seek views as to who should be responsible for the database and on what terms, where the costs might fall and what role it would be appropriate for regulators to play.

Next steps

1.13 This discussion invites responses by 9 February 2010. We will consider any responses we receive and then decide on what to do next.

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