NCC POLICY DIRECTS PUBLIC SAFETY TOWARD MORE ROBUST SYSTEMS

“Historically, the NCC has expressed concerns about the out-of-band emissions from the CMRS portion of the 700 MHz band,” said Glen Nash, immediate past pres. of Assn. of Public Safety Communications Officials and chmn. of NCC’s technology subcommittee. Because FCC has said that for now it’s not interested in tightening out-of-band emission limits of commercial mobile radio service (CMRS) operators, NCC was asked to examine increasing design level of public safety systems “in order to survive in the higher noise environment potentially to come from the CMRS portion of this band,” Nash said. Policy statement adopted by NCC steering committee, which outlines scenarios in which public safety operators could raise their signal levels to mitigate interference, appeared designed to head off similar kinds of problems that these users faced at 800 MHz.

Recommendation adopted by steering committee was designed to be statement of NCC rather than advisory to FCC for rulemaking, Nash said. NCC agreed that: (1) Design criterion for public safety coverage should be 40 dBm throughout particular jurisdiction, not to extend that level more than 3 miles outside of that jurisdiction. (2) Public safety users could design systems for signal levels below that point, but they would be more susceptible to interference. (3) System designers should be advised to opt for minimum signal level of 50 dBm in areas where interference could be expected from out-of-band emissions from commercial wireless operators. Under all 3 scenarios, NCC said interference into adjacent jurisdictions should be avoided by using directional antennas, antenna down tilt, power reduction. FCC has allocated 24 MHz of spectrum at 700 MHz for public safety operations, which will be made available when band is vacated by broadcasters as part of DTV transition.

While steering committee had been asked to consider whether there should be national standard for design of public safety radio systems involving more robust signal levels, Nash said it became clear there wasn’t support for such a standard. “There are many applications in which a particular user may have a need to design to a lesser standard,” he said. Nonetheless, Nash said standard was needed to provide baseline for public safety users to design system, using numbers that would be recognized by other users that could provide protection accordingly.

Several public safety officials expressed concerns about costs and siting challenges of redesigning systems with stronger signal levels. Robert Schlieman, project manager for N.Y. State Office for Technology, said his office had done computer analysis of what would be required to take systems to 50 dBm level in 3 different counties with different topographies. “It more than doubles the number of sites that are required,” he said. “Frankly, that’s not an acceptable change as a general rule.”

Doubling transmission sites could pose particular problem in rural areas, particularly in western part of country, said David Buchanan of San Bernardino County, Cal. “Frankly, for us in the West, even if you could come up with the money to double the sites you can’t come up with the sites themselves because of all the environmental restrictions,” he said. Much of land that would be available for siting is either owned by Bureau of Land Management or is protected wilderness area, making approval of new towers even more difficult, he said. Buchanan said dense number of users packed into spectrum available for public safety had been likened to environmental pollution. “I would still urge the NCC to reconsider that our spectrum can’t be polluted with a lot of out-of-band noise. It’s just killing the rest of us and we won’t be able to put systems together and that’s going to be a shame,” he said.

“The very cause of the issue we are dealing with here is interference -- real in 800 MHz and potential in 700 MHz -- from CMRS-type systems,” said Wayne LeLand, representing Motorola and Telecommunications Industry Assn. (TIA). He said TIA continued to stand by its White Paper that said that unless there was some limitation on out-of-band emissions of CMRS operators, “there is going to be interference,” he said. “In our view, the only way of doing that is somehow to limit the potential interference from CMRS carriers and perhaps if the FCC is unwilling to do that, you have to write your congressman.”

Acknowledgment that FCC wasn’t likely to limit out-of- band emissions of CMRS operators to reduce interference stems from order Commission issued in July. Among other things, order turned down TIA proposal for limitation on signal strength of commercial transmissions while recognizing that some commercial stations in 777-792 MHz and nearby public safety base station receivers could require certain mitigation measures. But FCC said it was interested in exploring ways to provide for more-robust public safety signals and interference mitigation measures that were tailored to specific circumstances rather than categorical limits. Part of original Nextel reconfiguration proposal to eliminate public safety interference at 800 MHz recommended that base-to-mobile signal strength for public safety operators be increased to 53 dBm in cases where interference is problem from nearby CMRS systems.

Still, cost concerns in increasing signal strength were raised repeatedly at NCC meeting. Representative of Houston Police Dept. said city had spent $183 million on designing its communications system with 40 dBm contour. Cost of redesigning to 50 dBm would be hard to imagine, he said. “Unless we can come up with very deep pockets that we can tap financially, you are putting these types of systems out of the reach of cities,” he said. Nash said that was point of policy statement recommending that systems be designed for 40 dBm, with suggestion of 50 dBm in areas where CMRS interference could pose potential problem. “You are going to have to make a decision there as to what you actually design for,” Nash said. “If you choose to design for 30 dBm, it will be ‘buyer beware.'”