Excluding DMR the other three digital standards are widely used for public safety organisations across the globe, some preferred in a specific region. While replacing the FM analog are capable of transferring data as well voice implementing text messaging and encryption. Below are being compared each standards looking at carrier, backward compatibility, security: 

Standard DMR TETRA TETRAPOL P25 (APCO)
Analog fallback

Time Division Multiple Access  ✓
Frequency Division Multiple Access

 ✗
End-to-end encryption

DMR stands for Digital Mobile Radio, standard defined by ETSI through TS 102 361 parts 1-4 used mostly for commercial clients is a limited standard using AMBE+2 vocoder a proprietary standard achieving 12,5 kHz equivalent bandwidth through 2 slots TDMA. DMR is designed in three tiers:

  • Tier I - conventional standard for non-infrastructure use only (no repeaters) through low power commercial applications using a maximum of 0,5 watt RF power. PMR446 radios are one of the widely used applications, important remark is license-free in European PMR band ranking 446,000 - 446,200 MHz, simplex repeaters  / gateways applications such as parrots are permitted.
  • Tier II - licensed conventional radio systems, mobile and handheld operated devices providing advanced voice featured and integrated IP data services for high power communications. Potential applications are private organizations which requires a geographical coverage through low cost infrastructure and backward compatibility with the traditional analog FM networks.
  • Tier III - covers trunking operation supporting voice and short messaging handling as well as data service including support for IPv4 and IPv6. 

TETRA known as Terrestrial Truncked Radio is a ETSI trunked radio standard. first version being published in 1995 specially designed to be used by governmental agencies, public safety networks, rail transport, transport services, military. TETRA uses TDMA with four channels (slots) on one carrier and 25 kHz channel spacing. TETRA mobile stations communicate in trunk-mode operation (TMO) using switching and management infrastructure or in direct-mode operation (DMO) where network coverage is not available. DMO includes the possibility to one or more TETRA terminals as relays (DMO gateway from DMO to TMO or DMO repeater from DMO to DMO).

Full-duplex direct connection to other TETRA users or the PSTN is possible, for protection against eavesdropping, air interface and end-to-end encryption is available, authentication and registration of terminals is supported by the TETRA network infrastructure. 

The standard chunk of Lorem Ipsum used since the 1500s is reproduced below for those interested. Sections 1.10.32 and 1.10.33 from "de Finibus Bonorum et Malorum" by Cicero are also reproduced in their exact original form, accompanied by English versions from the 1914 translation by H. Rackham.