What is Land Mobile Radio?

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- everything RF

Jun 18, 2019

A Land Mobile Radio (LMR) System is a public or private two-way wireless communication network commonly used by public safety organizations such as police, firefighters and emergency responders for critical communications. These systems are also used for industrial, transportation, utilities, security, logistics and military applications. 

A typical LMR system consists of handheld portable radios, vehicle mounted mobile radios, base stations and repeaters, and other supporting network infrastructure.

There are two types of land mobile radio systems: 

1.) Terrestrial Trunked Radio (TETRA) - It is the European standard for LMR systems, developed by European Telecommunications Standards Institute (ETSI) in 1995. This standard is designed for use by government agencies, emergency services, police forces, fire departments, paramedics, and emergency medical technicians for public safety networks. TETRA also has applications in the commercial market like transportation services, utilities, and logistics.

TETRA specifications:

  • 25 kHz channel bandwidth
  • 4-slot Time Division Multiple Access (TDMA)
  • π/4 Differential Quadrature Phase Shift Keying (DQPSK) modulation

2.) P25 (US) - Project 25 (P25) are the set of standards - developed by The Association of Public Safety Communications Officials (APCO) in October 1989 -  for the designing and manufacturing of interoperable digital two-way wireless communications products for public safety and first responders. These standards are open and user-driven. 

The goals of the standard include:

  • Interoperability among agencies
  • Interoperability among vendors
  • Spectral efficiency
  • Compatible with existing systems
  • Integrated voice and data services
  • Conventional, trunked and secure communications

P25 has two phases that are not compatible with each other, although Phase 2 radios can “fall back” to Phase 1 operation to maintain backward compatibility.

P25 Phase 1 specifications:

  • 12.5 kHz channel bandwidth
  • Frequency Domain Multiple Access (FDMA)
  • C4FM and CQPSK modulation

P25 Phase 2 specifications:

  • 12.5 kHz channel bandwidth
  • 2-slot Time Division Multiple Access (TDMA)
  • Harmonized Continuous Phase Modulation (H-CPM) modulation for subscribers
  • Harmonized Differential Quadrature Phase Shift Keying (H-DQPSK) modulation for fixed sites