For now, all White Spaces devices will use a geolocation database to avoid interfering with licensed spectrum users. The latest FCC Memorandum and Order on TV White Spaces says that it is still OK to have a device that uses spectrum sensing only (one that doesn’t consult a geolocation database for licensed spectrum users), but to get certified for sensing only, a device will have to satisfy the FCC’s Office of Engineering and Technology, then be approved by the Commissioners on a case-by-case basis.
So all the devices for the foreseeable future are going to use a geolocation database. But they will have spectrum-sensing capabilities too, in order to select the cleanest channel from the list of available channels provided by the database.
Fixed devices (access points) will normally have a wired Internet connection. Once a fixed device has figured out where it is, it can query the database over the Internet for a list of available channels. Then it can advertise itself on those channels.
Mobile devices (phones, laptops etc.) will normally have non-whitespace connections to the Internet too, for example Wi-Fi or cellular data. These devices can know where they are by GPS or some other location technology, and query the geolocation database over their non-whitespace connection. If a mobile device doesn’t have non-whitespace Internet connectivity, it can sit and wait until it senses a beacon from a fixed whitespace device, then query the geolocation database over the whitespace connection. There is a slight chance at this point that the mobile device is using a licensed frequency inside the licensee’s protected contour. This chance is mitigated because the contour includes a buffer zone, so a mobile device inside a protected contour should be beyond the range of any whitespace devices outside that contour. The interference will also be very brief, since when it gets the response from the database it will instantly switch to another channel.
Nine companies have proposed themselves as geolocation database providers. Here they are, linked to the proposals they filed with the FCC:
- Comsearch
- Google, Inc.
- Frequency Finder, Inc.
- KB Enterprises, LLC.
- Key Bridge Global, LLC.
- Neustar, Inc.
- Spectrum Bridge, Inc.
- Telcordia Technologies, Inc.
- WSdb, LLC.
Here’s an example of what a protected contour looks like. Here’s an example database. Note that this database is not accurate yet.
Actually, a geolocation database is overkill for most cases. The bulk of the information is just a reformatting of data the FCC already publishes online; it’s only 37 megabytes compressed. It could be kept in the phone since it doesn’t change much; it is updated weekly.
The proposed database will be useful for those rare events where the number of wireless microphones needed is so large that it won’t fit into the spectrum reserved for microphones, though in this case spectrum sensing would probably suffice. In other words, the geolocation database is a heavyweight solution to a lightweight problem.