TETRA Mission-Critical Radio Systems

Details

TETRA — Terrestrial Trunked Radio — is the ETSI standard written specifically for organisations whose communication cannot be allowed to stop. It is the technology behind emergency services, airports, metro systems, ports and large energy and chemical sites across Europe.

What the standard guarantees

Property	TETRA	Why it matters
Group call setup	Under 300 ms	The first word of a call is not lost
Carrier structure	4 slots per 25 kHz	Four conversations per carrier
Direct mode (DMO)	Standard	Radios talk without infrastructure
Fallback mode	Standard	A site keeps working without the core
Encryption	Air interface plus end-to-end	Confidentiality is designed in
Priority and pre-emption	Per user and per group	Emergency traffic displaces routine

The number worth dwelling on is 300 milliseconds. In an incident, users key up and speak immediately; a system that takes a second to allocate a channel loses the beginning of every transmission, which is exactly where the urgent information is.

Failure is designed for, not assumed away

TETRA degrades in defined stages rather than switching off:

1. Full operation — base stations connected to the core, national or regional roaming 2. Local site trunking — the link to the core is lost; the site continues serving its own users 3. Repeater mode — the site is reduced but still relays 4. Direct mode (DMO) — radios talk to each other with no infrastructure at all, at reduced range

Every stage is automatic. This staged degradation, more than any single feature, is why TETRA is specified for public safety. A commercial network has one failure mode: it works or it does not.

Where it is the right answer

Airports, metro and rail systems, ports, energy and utility operators, large oil, gas and chemical sites, disaster and emergency organisations, and municipal operations that coordinate with public agencies.

Where an outage would be an inconvenience rather than a hazard, DMR delivers the same coordination at a fraction of the infrastructure cost, and specifying TETRA is simply spending money that the operation does not require.

What a project involves

A TETRA system is infrastructure, and it is built as one:

Coverage objective defined by area and by in-building penetration requirement
RF planning and site selection, including redundancy of both sites and backhaul
Core network sizing, with redundancy proportional to the consequence of loss
Talkgroup, fleetmap and priority design — the part that outlives the hardware
Control room and dispatch integration, recording and incident logging
Terminals: handportable, mobile, and ATEX-certified where the site requires them
Frequency licensing through BTK
Commissioning, coverage verification measurement and documented handover

Enclosed volumes — tunnels, platforms, underground levels — are handled with dedicated indoor coverage rather than added transmit power.

Lifecycle

TETRA estates run for a decade or more, which makes the maintenance contract as significant as the purchase. TechnoRF covers firmware versions, core and base-station health, terminal repair and spares, fleetmap changes as the organisation restructures, coverage re-verification after construction, and licence administration.

Get in touch to discuss the coverage and resilience requirement for your site.

Frequently Asked Questions

What makes TETRA "mission critical" rather than just digital?

Three engineered properties. Call setup completes in under 300 milliseconds, so a group call is established before the speaker has finished drawing breath. Base stations fall back to local operation if the core network is lost, and radios fall back to direct mode if the base station is lost, so the system degrades in stages rather than failing. And air-interface plus end-to-end encryption is part of the standard, not an add-on.

TETRA or DMR — how is the choice made?

By what an outage costs. Where a communication failure means a delayed job, DMR is the economically correct answer and TETRA is over-specified. Where it means a risk to life or a halted public service — airports, metro, emergency response, major chemical plants — TETRA’s redundancy, call setup time and priority handling are what you are paying for. Headcount is a poor guide; consequence is the right one.

Can TETRA and DMR systems work together?

Yes, through gateways, and mixed estates are common: DMR inside a facility, TETRA for interoperability with public agencies, and a dispatch position that monitors both. Voice and basic group calls carry across reliably. Advanced data services, encryption and priority generally do not, so the gateway is planned as a voice bridge and not as a merge of two systems.

Does TETRA still make sense next to broadband?

For voice, yes. Broadband carries video and data that TETRA cannot, but it depends on a commercial mobile network that saturates precisely during a major incident. The common design today is TETRA for critical voice on infrastructure you control, with LTE or PoC alongside for video and data. See private LTE for how the two are combined.