DMR, TETRA or P25: choosing a radio standard

Three digital radio standards come up in almost every professional radio conversation, and they are not competitors in the way the comparison implies. They were designed for different problems by different constituencies, and most organizations have a right answer that becomes obvious once the question is framed properly.

The short version

DMR

Digital Mobile Radio is an open ETSI standard, and the practical consequence of that is a broad and competitive equipment market. It uses two time slots within a 12.5 kHz channel, which effectively doubles capacity compared with an equivalent analogue channel, a real benefit when spectrum is assigned rather than chosen.

It comes in tiers. The distinction that matters commercially is between conventional operation, where users pick a channel, and Tier III trunking, where the system assigns channels automatically. Trunking becomes worthwhile when you have enough users that channel contention is a daily irritation rather than an occasional one.

DMR is where most commercial operations should start, and where most of them should finish. It is not a compromise standard; it is the standard that fits the requirement.

TETRA

Terrestrial Trunked Radio is also an ETSI standard, but it was designed from the outset for public safety and large-scale trunked operation. It offers very fast call setup, robust group calling, strong encryption, direct mode operation between handsets when infrastructure is unavailable, and the kind of resilience expected where a network failure is a public safety event.

It is correspondingly more expensive: in infrastructure, in terminals and in the expertise required to operate it. TETRA makes sense when an organization is running its own network at scale and the operational consequences of failure justify the investment. It rarely makes sense for a single site or a few dozen users, whatever the feature comparison suggests.

P25

Project 25 is a TIA standard developed for public safety in North America, with interoperability between agencies as a founding objective. Where P25 is mandated, it is mandated for good reasons and the question does not arise.

Outside that context the calculus is different. The installed base and the supply chain are concentrated in North America, which has implications for equipment availability, local support and spares in East Africa. If P25 is specified for an operation here, it is worth establishing early who will maintain it in five years and where replacement terminals will come from.

The question that decides it

Not 'which standard is best' but 'what is the failure mode we are buying against'.

• If the failure mode is inefficiency (teams not coordinating well, messages missed, phones used where radio would be faster) DMR addresses it at proportionate cost
• If the failure mode is a public safety event (a network outage during an emergency, agencies unable to coordinate) the case for TETRA or P25 is real
• If the failure mode is coverage across a wide or dispersed area rather than within a site, none of the three may be the answer

When none of them is the answer

Conventional land mobile radio requires infrastructure: repeaters, antennas, sites, power, and licensed spectrum. That is proportionate for a defined area. It becomes disproportionate when an operation is spread across a city or a region, because coverage cost rises with area while the benefit does not.

Broadband push-to-talk over cellular inverts that. It uses a mobile operator's existing network, so coverage is wherever the operator reaches, and the cost is a predictable per-user subscription rather than capital expenditure on infrastructure. It also removes the frequency assignment and the recurring spectrum licence.

The trade is dependence. You are relying on a public network that you do not control and that is shared with everybody else in a congestion event. For a guarding operation across a suburb that is an acceptable trade and often the right one. For an emergency service whose whole purpose is to function when public networks do not, it is not.

Moving from analogue without stopping work

Most organizations asking this question already have analogue radio, and the practical constraint is that the operation cannot pause while a new system is installed.

DMR handles this better than the alternatives because most DMR equipment can operate in analogue mode as well as digital. That allows a phased migration: repeaters and radios are replaced progressively, with mixed-mode operation covering the transition, rather than a single cutover on a Friday night. For a security operation running continuous shifts, that is often the difference between a feasible project and an unacceptable one.

It also allows a genuine pilot. Convert one site or one shift, run it alongside the existing system, and find out what the coverage design got wrong before committing the whole fleet, which is what the Kitisuru deployment did before it was extended.

Encryption and privacy across the standards

All three standards support encryption, and all three are frequently deployed without it because somebody assumed digital meant private. It does not. Digital modulation makes casual eavesdropping harder than analogue, but a determined listener with matching equipment is a different matter.

If your traffic includes cash movements, VIP schedules, incident locations or anything a criminal would find useful, encryption should be specified explicitly and its key management understood, including what happens when a radio is lost, which is the scenario that actually occurs.

What actually determines whether the system works

A point that gets lost in standards comparisons: the standard is not usually the reason a system fails. Coverage design is.

Repeater siting, antenna selection and height, power within licensed limits, and terrain between the units determine whether a radio works when someone needs it. A well-designed DMR system will outperform a badly designed TETRA system every time, and cost a fraction as much. Any conversation that reaches a standard before it reaches a site survey has started in the wrong place.

How to run the decision

• Establish the operating area and the terrain within it, on the ground rather than on a map
• Count users and estimate call volume honestly, including peak rather than average
• Define the failure mode you are protecting against, and what it costs when it happens
• Establish what local support and spares look like for each candidate over a five to ten year life
• Include spectrum licensing cost in the comparison, because it changes the answer between conventional radio and broadband push-to-talk

Do that, and the standard usually selects itself.

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