Craig Johnston / 11.01.2006 12:00AM
DoD Uplinks Moving to 2 GHz BAS Band
The Department of Defense is moving from its 1.8 GHz Space Ground System spectrum in a chain reaction to free up 1.7 GHz spectrum for an advanced wireless device spectrum auction.
Broadcasters are concerned about the FCC's authorizing the DoD uplink spectrum shift because they fear it will interfere with TV stations using the 2 GHz band for electronic newsgathering. They point to the fact that the DoD uplinks are tasked with tracking and transmitting to non-geosynchronous satellites, which range from horizon to horizon.
They have also voiced concern with the 1-10 kW transmitting power authorized for the uplinks, and the amount of side lobe radiation that could be generated from those high-powered transmissions.
Because ENG receive-only antennas are usually located on the tallest natural or man-made structures available to allow live-shots from almost anywhere in the broadcast market, these sites will be particularly susceptible to such side lobe radiation, broadcasters say.
The Society of Broadcast Engineers, National Association of Broadcasters and Association of Maximum Service Television have all filed objections with the commission, claiming the uplinks were incompatible with ENG operations in the same band. To date their objections have been denied.
TV Technology spoke both on and off the record with broadcast organizations about DoD's uplink spectrum move, then put some of those organizations' questions to the DoD.
The unknown timeline was one element that worried broadcasters, to which a DoD representative replied that the [2 GHz] capability "will be added beginning approximately 2010 at a yet to be determined location."
From previous front and back-door conversations broadcasters have had with DoD, they expect Vandenberg Air Force Base in California to be the first uplink to be changed.
Broadcasters suspected that a delaying factor in DoD's decision to transition from 1.8 GHz to 2 GHz operations was the lack of 2 GHz capability in current satellites. When asked if current satellites were, in fact, agile enough to handle 2 GHz, DoD representatives said that the department "has programmed and budgeted for the transition to the 2GHz band. DoD still plans to utilize the spectrum currently authorized for satellite operations in the band 1755-1850 MHz. This was established via a DoD policy memo that mandated a dual-band capability for future satellites. Those systems already on orbit or awaiting launch will be dependent on access to the 1755-1850 MHz frequency band for decades."
That DoD plans to use both its 1.8 GHz band spectrum and the 2 GHz band struck Dane Erickson, chairman of SBEs' FCC Liaison Committee as inconsistent.
"If those uplinks are staying there, then what's the problem with the displaced government microwave links that are getting moved to 1.8 gigs?" he asked. "If they're saying that these uplinks are going to continue at 1.8 gigs, then this is just a spectrum grab for additional bandwidth, and it's not because the uplinks have to be vacated out of 1.8 gigs to make room for the fixed point-to-point links that are being bumped out of 1.7 gigs."
Asked what measures DoD will take to on the uplinks to reduce side lobe radiation to the levels that will meet the FCC's noise threshold degradation requirements, the DoD said that its satellite transmissions "are designed to meet the antenna radiation suppression standards established by National Telecommunications and Information Administration [NTIA] as the President's primary advisor for federal use of spectrum. Within the existing budgetary and programmatic constraints, the department is investigating the best method for effectively sharing spectrum with the incumbent Broadcast Auxiliary Services [BAS] given the importance of both communities."
CLEARLY SPELLED OUT
Ericksen said he's unfamiliar with NTIA's radiation suppression standards, but noted that the FCC's standards are clearly spelled out. Normally when a new microwave user comes into a band, it is required to demonstrate it will not interfere with incumbent services in that spectrum. EIA/TIA Telecommunications System Bulletin 10-F, "Interference Criteria for Microwave Systems" allows up to a 1 dB degradation of a protected receiver's threshold.
There are methods to reduce side lobe leakage from uplinks, like installing "pie plate" shrouds around the edge of dishes. Erickson doubts there is room for such shrouds within the existing radomes, the hemispherical covers surrounding the top of the uplinks.
"However, if DoD can meet that 1 dB threshold, there will be no problem for TV's 2 GHz operation," he said.
The FCC has ruled that the military will have to coordinate with incumbent users of the band during the spectrum move.
"The development of a spectrum-sharing criteria between DoD and existing users at 2 GHz will require the Department to share information about its operations," the DoD representative said, regarding the move. "Specifically, the earth station transmit characteristics will be the foundation for creating an equitable sharing environment. Coordination will be different for each site and based upon transmit power, antenna elevations, local topography, and the BAS environment."
Broadcasters have pointed out that the horizon-to-horizon tracking of satellites by DoD uplinks will require real-time frequency coordination, and that the relative difference in transmitting power between DoD uplinks and ENG operators means only broadcasters will experience interference.
It should be noted that in making their arguments, broadcast organizations have been careful not to suggest their ENG live shots are more important than mission-critical military transmissions to the satellites. But they pointed to the critical role such ENG operations play in alerting the public during manmade or natural disasters.