Non-P25 Digital Technology Hurts Interoperability Efforts
Wednesday, February 19, 2014 | Comments

A close examination shows that interoperability is broken into three areas as defined by the five lanes of the Safecom Interoperability Continuum: governance, standard operating procedures, training and exercises, usage and technology. Technology is last because for proper implementation, its selection must be carefully done only after governance is established and operational decisions, including interoperability, are made with regard to how that technology will be implemented and used. Technology’s purpose is to support an operation, not drive it.

Who are these “responders?” Beyond the usual three first responders of fire/rescue, EMS and law enforcement, the answer becomes incident driven. How often do you see a Department of Transportation (DOT) vehicle at the scene of a traffic collision? The current ice storms sweeping the East and South quickly add public works, transportation and utilities because all other responders can’t move until the roads are clear and safe for passage. Do the three first responders need to be able to communicate directly with these other supporting responders in these situations? The answer is a resounding yes.

From the governance perspective, local and state first responders in the U.S. include more than 70,000 fire/rescue agencies (the majority of them all-volunteer), 85,000 individual law enforcement agencies (often with overlapping jurisdictions), and EMS that includes a wide mix of paid, private (often under contract to governments) and volunteer organizations. Each of these generally budgets and operates independently.

These numbers presents a severe communications interoperability challenge, even under the best of conditions, with routine support from neighboring or overlapping jurisdictions being a daily occurrence. At the same time, the U.S. is rural in nature, having dense population centers, but with more than 50 percent of the actual landmass (particularly west of the Mississippi) being rural to very rural. Throw into that mix the added technology challenge that the U.S. operates in five major radio bands —VHF low, VHF high, UHF, 700 MHz and 800 MHz. Until the recent introduction of multiband radios (MBRs), users could communicate on at most two of those bands from a single radio with the great majority only having equipment operating in a single band. In spite of these challenges, billions of dollars in public investment generally directed toward improving interoperability has yielded significant improvements during the past 12 years. The fact that pubic safety is now allowing the introduction of incompatible digital technologies to the detriment of those gains has created significant concern among many.

Operationally, the U.S. almost always manages its incidents from the field, a basic tenet of the incident command system (ICS). This requires both wide-area communications for coordination of various responding agencies/units and involved dispatch centers, and on-scene unit-to-unit (off-infrastructure or direct-mode) communications, with responders rapidly switching between the two, preferably using only the channel selector switch on the top of a handset. This latter direct mode capability can present a real challenge in the digital environment, particularly for TDMA systems.

Operational requirements include not only interoperability between field units, but also the ability for those field units to interoperate on neighboring agencies’ infrastructure. During emergencies, it is wonderful to have backfill come in to support neighborhoods where stations are empty, but if the guest radios can’t operate on the host infrastructure, how can they be dispatched?

Project 25 (P25) technology was designed from the ground up to support the U.S. environment. While it works well in dense urban areas usually supported by large, trunked implementations, it also works well in rural environments for a small agency with its base (or standalone repeater) and 10 mobiles only needing a single 12.5- kilohertz channel for high-quality communications. For those not involved in spectrum management, even those single rural channels can be hard to find, especially in the overtaxed but most used VHF high band.

The widely fielded P25 Phase 1 is a single FDMA talk path per 12.5-kilohertz channel. More recently fielded P25 Phase 2 provides two TDMA talk paths per 12.5-kilohertz channel. Talk path in this discussion can be data or voice, or a combination of the two for TDMA. Importantly, P25 and TETRA equipment use highly tested and refined voice codecs (vocoder) specifically designed for the public-safety environment and not generally found in commercial-grade digital technologies. TDMA is excellent in congested areas, but not wide, rural expanses because of the significant hardened backhaul typically required between base station sites. TETRA and some other non-P25 digital technologies are regularly touted for inexpensive handsets, but handset savings have been found in studies to be quickly eaten up by the more intense interconnected infrastructure required to support those often lower powered (as compared with P25) TDMA handsets, as well as the ongoing operational expenses for backhaul between base stations for wide-area operations.

Many public-safety agencies require multisite wide-area coverage. P25 supports simulcast where a number of sites simultaneously carry the same coordinated signal on a single frequency. Most other digital technologies can’t support simulcast, instead using multicast where the same conversation must be carried on one of the two or four TDMA “slices” or a separate FDMA frequency across those multiple sites to cover the required footprint. Because those non-P25 digital technologies can’t overlap the same frequencies at nearby sites, this implementation can actually require significantly more spectrum to carry the same number of required wide-area talk paths.

However, from an interoperability perspective, probably the most important feature is high-powered handset on-scene simplex (direct mode) communications that is well supported by P25, with analog mode serving as the fallback common denominator for incident command operations in the U.S. All P25 receivers are inherently dual-mode analog and P25 digital; P25 receivers will automatically present whichever on-channel mode is heard to the radio’s speaker. High powered in this case refers to the typical U.S. 3- to 6-watt band-dependent handset that will reliably communicate in simplex mode around an incident scene, including in and out of buildings for applications such as fire ground operations.

Finally, those not intimately involved with the real world of emergency response want to add the “we can hook anything to anything” gateway solution to this mix of RF bands and incompatible technologies. From the seasoned communications unit leader’s (COML) perspective, those black boxes are called communications interoperability ending devices (IEDs). First there is the time required to set them up and/or properly engage and manage them; the emergent part of an incident is often over by then. They are also spectrum wasteful with one talk path per band per disparate technology; usually don’t pass all features and functions, such as unit ID and emergency trigger, between technologies; and importantly from an untrained user’s perspective, only provide coverage where the footprints of all interconnected systems overlap. Thus, gateways can be an indispensable solution when there is no alternative, but are almost always considered by COMLs to be the solution of last resort.

Given all of these concerns, coupled with a number of study cases where the introduction of non-P25 digital systems have been installed with significant negative impact on interoperability, the National Public Safety Telecommunications Council’s (NPSTC) Interoperability Committee is examining this issue in detail through its Emerging Digital Radio Technologies (EDRT) Working Group. The working group will release a white paper later this year, with the current findings being that the introduction of non-P25 digital technology almost always results in a significant reduction in interoperability. The solution is beginning to focus on the need for all handsets and all infrastructure to include 12.5-kilohertz analog, in addition to any other technology mode, to properly support interoperability.

For the counterpoint opinion on why non-P25 digital technologies don’t hurt interoperability efforts, click here.

John Powell has 43 years of first-hand interoperability experience including 32 years as a law enforcement first responder, was vice-chair of the Public Safety Wireless Advisory Committee (PSWAC) Interoperability Committee, chair of the FCC’s 700 MHz National Coordination Committee (NCC) Interoperability Subcommittee, principal subject matter expert author of the Safecom Interoperability Continuum, chair of the NPSTC Interoperability Committee, and is a life member and past president of the Association of Public-Safety Communications Officials (APCO) International.

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