Wireless spectrum

Today, I was interviewed on the VoIP Users Conference. I was originally invited to talk about broadband access and netBlazr which I did at some length (and in some detail as it’s a technically savvy group).  But interestingly,  they also wanted to talk about spectrum issues.  Michael Graves, who signed me up for this session, had seen my paper “Valuing the white spaces above 3 GHz” and multiple questioners came back to spectrum issues, including TV white spaces, GSM and other mobile bands , 5 GHz and the prospects for unlicensed access to new bands.

netBlazr uses 5 GHz spectum that is already available and ideal for our purposes.  But we keep our eyes open for other potential bands, so here’s a summary of what’s in flux and how it might or might not be useful for netBlazr and others.

TV white spaces — This is spectrum that’s reserved for television as the primary service. However, not all channels are used in all locations and, with the advent of digital television, the number of channels in use has gone down.  In the US and the UK, this spectrum is becoming available on a “secondary use” basis for type-approved equipment, without licenses.  The way this works is: approved unlicensed radios include position sensing circuitry and, before transmitting, they check with a database of known primary users to determine which frequencies are available for secondary use at their current location.  There’s more in Wikipedia (of course).

The good news is TV white spaces are a widely noticed precedent which may eventually be applied in other bands. The bad news from netBlazr’s perspective, under current rules, there’s not much spectrum actually available in urban areas where we operate.  TV white spaces should be a boon to wireless ISPs in rural areas, but not for netBlazr.

Unlicensed GSM – this came up on the call, although I couldn’t add much.  Several EU jurisdictions now permit low-power (200 mW) unlicensed use for GSM1800 in previous unused frequencies at the edge of the GSM and the DECT-band, the so-called GSM/DECT Guard band. In the US, the only option I’m aware of it a slight overlap of GSM 900 channels with the US 900 MHz unlicensed ISM band (902-928 MHz).

5 GHz bands – these exist today and are key for netBlazr!  There are relatively large swaths of spectrum available at 5 GHz in many parts of the world.  In the US, we have up to 555 MHz of spectrum available in four bands under three slightly different sets of rules. Not all this spectrum is available everywhere, but 400+ MHz is typical in all major US cities. Wikipedia has a good list of the channels from a WiFi perspective.

For netBlazr’s purposes this spectrum is ideal.  We use a mesh of short range point-to-point links formed by radios with directional antennas.  Even the lowest power limits are fine for our short ranges and higher frequencies means directional antennas take less space.

On the call, we also talked about technical changes that will make the spectrum above 3 GHz more and more valuable over the next 10-20 years.  If you are interested, the technical details are in my essay Valuing the white spaces above 3 GHz.