UHF trunking: Promised land?

Private radio system users and commercial operators, pushed and prodded by consolidation and auctions, may view 450MHz-470MHz as the last bastion in which to operate. Manufacturers are keen to respond to new growth with new products.

The growth of specialized mobile radio (SMR) over the past 15 years largely derived from activity in the 800/900MHz bands, where trunking was allowed by the FCC and for which popular trunking protocols and equipment were created by major manufacturers such as Motorola, E.F. Johnson and Ericsson and supported by many smaller companies.

Over the past three years, most of 800/900MHz, through consolidation, buyouts and government auctions, now lies in the hands of a few large carriers, particularly enhanced SMRs (ESMRs). However, radio people are an entrepreneurial breed, and many service providers who handed over their frequencies are itching to reprise their former successes. Private industrial radio needs more airtime as well, but little spectrum is available above 800MHz.

The “refarming” process for the lower frequencies instigated by the FCC about five years ago created uncertainty. This, along with spectrum freezes above 800MHz and auctions in several bands, tied the hands of private and commercial licensees as well as manufacturers.

Refarming is over; it’s time to plant. Replacement of Part 90 rules to revise the Private Land Mobile Radio (PLMR) services went into effect in October 1997, with three particular effects: * All the former radio services have been consolidated into two pools, Public Safety and Industrial/Business, with frequency coordination competition for most of the latter. This reduces the types of service to four: conventional and trunked for each of the two pools. All other small radio service names are gone. * Narrowband standards have been adopted for channel spacing. * Trunking is now allowed in the 150MHz and 450MHz bands.

Private carriers and community repeater owners need the capacity trunking can provide. Trade associations have already noted that they don’t expect or want to see a “replay” with UHF of the 800MHz exclusivity created by the FCC. As Mark Crosby, president of the Industrial Telecommunications Association has said of 450MHz, “It’s all we have in the immediate future. Right now, for the short term of three to five years, we’ve got to look at this band.”

Back in the saddle again Dislocated SMR entrepreneurs now have the opportunity to set up multichannel trunked networks, as they did at 800MHz, by acquiring conventional UHF repeaters and converting to private carrier status. Analog SMRs, non-competition clauses not withstanding, can get back in business. They can again handle dispatch customers who cannot afford, and do not need, services as provided by large consolidator ESMRs.

The frequency coordination load since October has been heavy. Everyone is heading for the promised land-below 800MHz. As noted in this month’s editorial (see page 4), like the opening of the Old West, trunking may have effect of making incumbent conventional users identify with the Indians-urged to migrate or to sell out.

To continue the Old West analogy, UHF already has been “homesteaded” to some extent by “Sooners,” who, based on FCC staff opinions and a lack of specifically proscriptive regulation, built trunked systems in most major U.S. markets. Operators simply observed the old rule of “monitor before using.” What the FCC was busily trying to determine was already obvious to radio people: existing, affordable trunking equipment and no exclusivity-in short, plowable land. With the advent of the FCC’s Second Report and Order (SRO) on Part 88 last October, however, the territorial government arrived, and “Boomers,” not “Sooners,” are the order of the day.

No more ‘wide-open spaces’ The original separation for 450MHz-470MHz was 100kHz, which was reduced to 50kHz and then to 25kHz in 1967. In 1970, special low-power 12.5kHz offset channels were introduced. Refarming reduces separation for channels from 15kHz or 25kHz to 6.25kHz over the next seven years. Primary frequency licensees who do not change their systems are unaffected for the present and can replace system components with equally wideband equipment (although it is expected that everyone will migrate to narrowband over time). Manufacturers’ new applications for type-acceptance of affected radio devices must now comply with 12.5kHz for UHF, which will become 6.25kHz after the year 2005.

Circling the wagons Although UHF trunking is now “recognized and authorized” by the FCC, there are still several details hanging. The rules do allow trunking of existing and new channels, but they require potential system operators to obtain exclusivity for their intended service area. This is currently to be accomplished by securing written permission from all co-channel and adjacent channel licensees whose 39dBu service contours intersect a 70-mile radius from the proposed trunking station. If you have five channels, this means everyone else on those five channels, and the offsets to those five channels, in that radius. The consent agreements are to be submitted to the frequency coordinator and to the FCC with the license application.

Industry reaction to this rule has been, well, reactive. The requirement is difficult at best in congested metropolitan areas. Frequencies below 512MHz are mostly held by private users, whose decision to accept or reject interference may be uninformed. By definition, centralized trunking requires exclusive channels, and other users would have to be urged to convert their systems to trunking as well. Manufacturers, system operators, trade associations and communications attorneys alike have characterized the rule as “burdensome,” “unlikely,” “impractical” and some other terms I won’t repeat here. However, the industry has responded in a more positive fashion with several proposals to the FCC which may gain favor.

One proposal is to use interference-to-service contours instead of a radius to determine true co-channel and adjacent-channel licensees. Supported by AAR, AMTA, APCO, ITA, FIT, PCIA, UTC and Kenwood Communications, this method could determine actual interference potential, but would still require coverage studies. Operators might have to consider mergers, payoffs, frequency swaps, and relocation as solutions to head-to-head inference. An additional tool would be to do a search of dead licenses, verify abandonmentand request the FCC to cancel them, which takes about six months.

SBT, in a proposal supported in substance by PCIA, has recommended a developmental license for a fixed period (SBT, two years; PCIA, one year). Interference would be the responsibility of the developmental licensee. If no problems occur, the license converts to primary status.

SBT’s proposal in its Petition for Reconsideration is a similar plan to licensing for 43MHz paging, which can interfere with TV reception. Therefore, there is a precedent in the existing rules.

At presstime, industry sources indicated that the FCC has some sensitivity to modifying the current 70-mile rule, and may adopt a Memorandum Opinion and Order (MO&O), as early as the second quarter of 1998, using interference-to-service contours as the guide.

Smoky signals The wording of the refarming SRO also creates a technical vocabulary problem. The text of the refarming order partly discusses centralized trunking, but the codified concurrence rules just say “trunked operation,” They don’t specify centralized or decentralized.

Complicating this, in the past the FCC has issued a citation for operating a station authorized for conventional operation in a trunked mode above 512MHz.

Until the SRO, nothing in the FCC rules either prohibited or expressly permitted trunked operation below 800MHz. Informal bureau policy has been to disregard trunking below 512MHz, provided there is no interference. Operators of current and planned decentralized trunking systems (and coordinators) are left hanging by the wording as to whether a license for a trunked system requires concurrence from adjacent licensees regardless of system type-centralized or decentralized.

The Land Mobile Communications Council (LMCC) in trying to address this, has come up with a recommendation to make the actual technology irrelevant and to leave how the system is licensed up to the applicant. Systems would be coded, “YG” for a trunked and “IG” for a non-trunked or conventional system. The LMCC plan, currently undergoing a council advocacy vote, says from a frequency coordination standpoint, or from a commission spectrum management standpoint, “We don’t want to get into asking what kind of decentralized system you have; you license it the way you think that’s best.” An operator who has a decentralized system that monitors would not need clearance. If the system is decentralized with scan trunking in the unit, it could be licensed either as an IG or as a YG. The YG (trunked) license would still be liable to concurrence.

“Now, the flexibility is on the part of the industry,” said ITA’s Crosby, who is also an officer of the LMCC. “The industry can license however they want. So that if somebody had an LTR, that needs an exclusive YG, you license one channel as YG for the control channel, and all the other ones are IG. It doesn’t matter to us-we [frequency coordinators] don’t care. The coordinators don’t want to get into ‘Well, if you have this, then you’ve got to do that’ … The LMCC wants to give that to the commission-we don’t think that needs a rule change.”

Trunking at 800MHz began in the 1970s. A computer-dependent system to use spectrum more efficiently, trunking takes advantage of the recurrent idleness of transmitters. A pool of channels is shared among a large group of users who are automatically switched to an inactive channel. In a five-channel trunking system, with each channel loaded 50%, channels can be accessed 88% of the time. In a 20-channel system, with 50% loading, acccess is virtually constant.

Trunking 101 Trunking falls into two basic types: centralized and decentralized trunking.

*Centralized trunking – There are two classes of centralized trunking. One uses a dedicated data command channel as a control channel, which all inactive units monitor, leaving the remaining channels (four, in a five-channel set) open for communications. Base station repeaters are governed by a microprocessor, the system central controller.

In the other class, logic-trunked radio (LTR), control data is sent out on the frequency that is the next available channel. Units assigned to the home channel use their home frequency. If it is busy, subaudible digital signals switch a user’s fleet to any available channel. Each repeater contains a logic module responsible for signaling on its own channel, and the module in each repeater shares information with all other logic modules through a coaxial data bus.

* Decentralized trunking – Centralized trunking is thought by some to be impractical for VHF and UHF because of a lack of exclusive channels in those bands. Decentralized trunking monitors or scans Scan-based trunking protocols will work on non-exclusive channels. Prior to the completion of refarming, many users wanted spectrum efficiency and features of 800MHz trunking, but the FCC prohibited the use of 800MHz-type centralized interconnected base stations and switches in VHF and UHF systems. Protocols were created to go around this limitation by putting the trunking functions into VHF and UHF mobile and portable units. The protocols incorporated dispatch trunking capability using standard VHF or UHF repeaters. With these scan-based systems, channel assignment is determined by the logic in the mobile, not by a controller at the repeater site. Because scan-based trunking is not “centralized,” FCC frequency coordination requirements were not considered to apply.

UHF trunking advantages over 800MHz trunking include adequate coverage with more range than 800MHz. Repeaters for VHF and UHF cost less than comparable 800MHz systems. Mobiles and portables are also generally less expensive. Private carrier licensees that convert conventional 450MHz repeaters to trunked operation can load more customers with existing equipment.

The advantages of any trunked system include automatic clear channel selection; privacy; channel exclusivity; and selective calling.

Networking and technology Digital technology has led to the development of networks of multiple trunked systems to provide wide-area coverage with features such as connectivity, roaming and network management. Digital networking can be accomplished through multisite controllers, from companies such as Ericsson.

Site controllers for multiprotocol trunking and networking, from companies such as SmartLink, circumvent problems with proprietary formats and allow analog systems to compete with ESMRs. Multiprotocol systems enable frequency crossbanding, call hand-off, and management of customer access and use.

Transcrypt International/E.F. Johnson introduced its LTR-Net distributed trunking technology and its 2000VX repeater in 1997 as a basis for networking systems. The LTR-Net trunking protocol allows over-the-air compatibility with existing LTR subscriber units. Kenwood Systems Group released a 100W UHF repeater in 1997, compatible with KSG controllers, for trunked and conventional systems for UHF.

A networking protocol introduced in 1997 by Trident Micro Systems is also pushing the movement to UHF trunking. The Passport NTS trunking protocol, backward-compatible with LTR, supports wide-area networking, roaming between networked sites, selective calling and telephone interconnect.

Trident’s protocol permits crossbanding among 220MHz, 450MHz and 900MHz. Protocol-equipped radios use direct frequency assignment to determine operating frequency. Trident announced free licenses to qualified manufacturers, and in a joint announcement at AMTEX in November, 1997, five manufacturers (Kenwood Communications; Ritron, Standard Communications and SEA), lined up to support the protocol. All the companies are manufacturing equipment that supports Passport or a hybrid of Passport, LTR and conventional UHF.

Additionally there several new releases of UHF trunking portables and mobiles from companies such as Midland USA and Uniden.

Numerous exhibitors will have UHF-trunking-related system and user equipment at IWCE, April 22-24. The product guide on page 34 lists equipment introductions in the exhibit hall.