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This means that the voice coding technology, known as a vocoder, must operate with as few bits as possible. LMR systems work with narrow channel bandwidths and high transmission power that requires low data rates to support high spectral efficiency. Unfortunately, LMR and LTE devices are not directly interoperable since their networks have been designed and built to different technical standards. The emergence of hybrid LMR-LTE networks means that both LMR (mobile radios) and LTE devices (smartphones) will need to interoperate. However, given the need for LTE’s flexibility and data capabilities, it is likely that hybrid LMR-LTE networks featuring both technologies will proliferate. Consequently, it is unlikely in the near term that cellular LTE networks will replace LMR for voice communication in Mission Critical PTT applications. Unlike LMR, LTE networks are dependent on an infrastructure of cellular towers and were primarily developed for phone and business communications where coverage, reliability and resistance to noise or other harsh environmental factors were secondary considerations.

Recently, there have been efforts to interconnect LMR systems to cellular LTE networks in order to increase communication flexibility and add support for high data rate applications. “direct mode”) without the need of infrastructure. Land mobile radios provide outstanding range, reliability and direct user-to-user communications (i.e. LMR is designed specifically to provide MCPTT service in demanding environments such as public safety, manufacturing, transportation and energy industries. Land Mobile Radio (LMR) systems such as APCO Project 25 and Digital Mobile Radio (DMR) have a long and successful track record providing Mission Critical Push-To-Talk (MCPTT) voice services.

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