Field trials of DVB-T sensing for TV White Spaces

The use of TV White Space spectrum on a secondary, unlicensed basis has been of great interest in academia, industry and regulatory bodies worldwide. Proposed applications have included residential data transfer and content streaming, and rural broadband. In the US, the FCC has published rules for unlicenced devices in the TV bands, while in the UK, Ofcom has released statements on the subject. Central to these regulatory requirements is the constraint that all unlicenced devices must operate as secondary users and cause no interference to primary users. We study autonomous spectrum sensing as a means of avoiding interference. Using this technique, a device uses its own receiver to decide if a particular channel is available or not by listening from transmissions from primary users. A particular challenge is the well-known ‘hidden node’ problem in which a device is shielded from a transmitter but not a receiver that would suffer from interference. To guarantee protection to primary users under these circumstances requires very low sensing thresholds and the FCC (−115 dBm) and Ofcom (−120 dBm) have both proposed levels that are below the noise floor.