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Capital Currents: 5 GHz Unlicensed Devices

Wed, 09/11/2013 - 6:40pm
Jeffrey Krauss, President of Telecommunications and Technology Policy

The 2013 Cable Show was held in Washington and was well attended by FCC staffers. The industry continuously pleaded with the FCC to move quickly to make more unlicensed spectrum available at 5 GHz. The FCC has a proceeding underway, but the situation is very complicated.

The FCC regulates the 5725-5850 MHz “WiFi” band under Section 15.247 of the FCC Rules. But much of the current interest deals with the bands known as Unlicensed National Information Infrastructure (“U-NII”) regulated under Section 15.407. And an important part of the FCC proceeding deals with two bands in the 5 GHz range that are not currently allocated for either WiFi or U-NII use.

The FCC uses this band classification scheme: band 1 is 5150-5250 MHz; band 2A is 5250-5350 MHz; band 2B is 5350- 5470 MHz (this would be a new allocation for unlicensed use); band 2C is 5470-5725 MHz; band 3 is 5725-5825 MHz (with a proposal to extend this to 5850 MHz); and band 4 is 5850-5925 MHz (this would also be a new allocation for unlicensed use).

The big dispute in this proceeding deals with interference.

There are incumbent licensed systems in these bands, and, the incumbent users are objecting to any technical changes that might increase interference. It’s mainly the Federal Government systems that are at risk.

There has already been interference. In early 2009, the Federal Aviation Administration (FAA) reported interference to their Terminal Doppler Weather Radar (TDWR) that operates within the 5600-5650 MHz band (in band 2C). FCC rules require that devices operating in band 2C use Dynamic Frequency Selection (“DFS”) to listen before transmitting, in order to detect nearby radars and avoid their frequencies. Most of the interference cases were due to devices designed to operate as WiFi devices in band 3, without DFS, that were illegally modified to operate in band 2C. New rules will require manufacturers to design products that cannot be modified to operate illegally. But in some cases, even devices with DFS did not detect the radar transmissions.

DFS is the FCC’s primary tool for accomplishing frequency sharing in these bands. In order to work, the precise characteristics of the incumbent licensed systems must be known, and programmed into the unlicensed devices. DFS is already required for devices in bands 2A and 2C. But new specifications may well be needed, both for detection of TDWR radars, and for other licensed systems in bands 2B and 4.

Band 1 is used by the Globalstar satellite network. To protect this system against interference, the FCC rules currently limit band 1 unlicensed devices to only 50 milliwatts of output power, and they must be used indoors only. The FCC is now proposing to eliminate the indoor-only requirement, and allow 250 milliwatts of power, the same as in the adjacent band 2A. Not surprisingly, Globalstar is opposed.

Band 2B (5350-5470 MHz) is proposed but not currently available for unlicensed use. But it has a wide variety of incumbent users. The primary user is the Defense Department, for groundbased, shipborne, and airborne radars. NASA uses this band to track rockets, missiles, satellites, launch vehicles, and other targets. Synthetic aperture radar (SAR) systems on satellites in this band perform observations and measurements of surface topography, soil moisture, and sea surface height. DoD and Department of Homeland Security both use this band for the control of unmanned aircraft systems—drones.

Broadcast and media entities use weather radars operating in the 5350-5470 MHz band. Whew.

Nonetheless, the FCC suggests that unlicensed devices could operate in this band with the same technical requirements, including DFS, as bands 2A and 2C. But making DFS work, with so many different incumbent systems to detect, will be a challenge.

FCC proposes to modify the band 3 technical rules such as power density and antenna gain to conform them to the 5GHz WiFi rules. That should be simple and accomplished quickly.

Most challenging is band 4, 5850-5925 MHz. In 1999, the FCC allocated that band for the Intelligent Transportation Systems (ITS) radio service. The technology is now approaching deployment.

According to the FCC, this technology supports vehicle-to-vehicle (V2V) and vehicle-to- infrastructure (V2I) communications that can save lives by warning drivers of an impending dangerous condition or event in time to take corrective or evasive actions. The US Department of Transportation (DoT) believes that this technology could help prevent the majority of types of crashes that typically occur in the real world, such as crashes at intersections or while changing lanes. Indeed, by the end of 2013, DoT is expected to decide whether to require ITS transmitters and receivers as a safety feature in all new cars.

The auto industry and DoT have opposed use of band 4 for unlicensed devices, based on the interference likelihood. Qualcomm already makes chip sets for the ITS radios being used in test beds and pilot programs, but also has a strong interest in unlicensed devices. Qualcomm has proposed a compromise that would allow unlicensed devices to use a portion of band 4.

In spite of cable industry pleas, it will be several years before all the interference studies are done and new technical rules are adopted. Stay tuned.

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