The Federal Communications Commission (FCC) has adopted a Report & Order amending its Part 90 technical rules to allow the use of Terrestrial Trunked Radio (TETRA) equipment and technology for private land mobile systems in the 450-470 MHz portion of the UHF band and in the 809-824/854-869 MHz Business/Industrial Land Transportation (B/ILT) band.
In its Order, the FCC described TETRA as “a spectrally efficient digital technology with potential to provide valuable benefits to land mobile radio users, such as higher security and lower latency than comparable technologies.” According to the FCC, allowing the use of TETRA in the 450-470 MHz and 809-824/854-869 MHz bands “will give private land mobile radio (PLMR) licensees additional equipment alternatives” and will benefit PLMR licensees in terms of equipment cost and capability.
The new rules governing the use of TETRA will go into effect 30 days after the FCC’s Order is published in the Federal Register (which has not yet occurred).
Background on TETRA
TETRA is a digital, trunked radio technology that uses Time Division Multiple Access (TDMA) with four channel slots in 25 kHz channel spacing. In its Order, the FCC noted, “By accommodating four voice paths in a 25 kHz channel, TETRA achieves 6.25 kHz per voice path efficiency, thus meeting, indeed exceeding, the 12.5 kHz per voice path ‘narrowbanding’ efficiency standard” applicable to the 450-512 MHz band effective January 1, 2013. The TETRA standard is used around the world (it was recently approved for use in Canada) and is supported by multiple manufacturers and vendors. Until now, the use of TETRA has been prohibited in the United States because TETRA exceeds the occupied bandwidth and emissions mask requirements of Part 90 of the FCC’s rules.
New Rules Permitting the Use of TETRA
The FCC has now amended its rules to permit the certification and use of TETRA equipment that does not meet the Part 90 occupied bandwidth limits and emissions masks, but only if the equipment meets the adjacent channel power (ACP) limit established for TETRA by the European Technical Standards Institute (ETSI). Specifically, the FCC’s amended rules will permit equipment to comply with the ACP limits in the TETRA standard for emissions close to the carrier, or up to 75 kHz offset from the carrier. However, for emissions more than 75 kHz from the carrier, the standard limit for all devices under Part 90 of the FCC’s rules will continue to apply.
The FCC has also determined that the use of TETRA will only be permitted in the 450-470 MHz portion of the UHF band and in those channels in the 809-824/854-869 MHz band that are not in the NPSPAC portion of the band. Because TETRA is a trunked technology and is not capable of monitoring a frequency before transmitting, the FCC determined that TETRA is not suitable for use on shared channels and may therefore be deployed only by licensees that are exempt from any monitoring requirements. The FCC also determined that TETRA should not be permitted in the NPSPAC portion of the 800 MHz band due to the closer spacing of NPSPAC channels (and thus greater susceptibility to adjacent channel interference) as well as concerns over interoperability with public safety systems.
Finally, the FCC addressed concerns expressed during the rulemaking proceeding that the potential deployment of TETRA in a low-elevation, high-density architecture could cause “near-far” interference to incumbent high-site systems. The FCC concluded that there is no need to supplement its existing rules for controlling near-far interference to specifically address a particular technology such as TETRA. However, the FCC also stated that it will consider further rule changes if TETRA systems should evolve to a high-density architecture that results in interference to public safety and other high-site systems.
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