07.19.2006 08:00 AM
Originally featured on BroadcastEngineering.com
How much is enough?
The FCC late last month approved a measurement procedure to allow Unlicensed National Information Infrastructure (UNII) devices to operate in the 5GHz band, sharing bands used by the federal government for radar.
Specifically, the action requires UNII devices operating in the 5.25GHz to 5.35GHz and 5.47GHZ to 5.725 GHz bands to use Dynamic Frequency Selection (DFS) to avoid interfering with the radar.
Association for Maximum Service Television president David Donovan casts a wary eye on these developments. According to Donovan, proponents of allowing unlicensed devices into the broadcast spectrum point to UNII device protections like DFS to argue that WiFi and other unlicensed devices can operate in broadcast band without causing harmful interference.
In general, the issue is important because unlicensed devices could negate or diminish the effectiveness of broadcasters seeking to retain their over-the-air audience at a time when they and consumers have spent billions of dollars to upgrade their equipment for DTV.
According to Donovan and MSTV vice president of policy and technology Bruce Franca, it is a mistake to compare the UNII device experience with what will unfold if unlicensed devices are allowed into the broadcast band.
According to the pair, the two situations are different on a number of fronts:
- Broadcast signals are 4 million times less powerful than radar systems.
- Radar send and receive sites are almost always collocated so it’s relatively easy for UNII devices to detect where interference would occur and shut off.
- In the broadcast environment, DTV receivers are spread across a broad area and it’s impossible for an unlicensed device to detect their locations.
- Radar systems are designed to be jammed, so they are much more tolerant of interference from unlicensed devices than broadcast systems.
Donovan fears the adoption of procedures to measure UNII interference will give those pushing for unlicensed devices in the broadcast band more leverage in Congress. The Senate Commerce committee has recommended the full body pass sweeping communications legislation, which includes a provision to allow unlicensed devices into the broadcast band.
The commission action to allow unlicensed devices into the 5GHz band should go a long way to satiating the demand for spectrum for unlicensed use, such as WiFi. The vote cleared the way to 255MHz of spectrum, bringing the total to 700MHz available for unlicensed devices. “How much are we going to give these guys?” Donovan asked.