MCPTT Begins Rollout without Full Compliance

Answering a call to enhance the quality and possibilities of critical communications, the Third Generation Partnership Project (3GPP) has added key features toward that end in recent releases. To support both military communications (MilCom) and public safety radios, for example, 3GPP Release 12 featured proximity services. Release 13 added support for mission-critical push-to-talk (MCPTT), among other features, in 2016. Release 14 introduced mission-critical data and video features, while Release 15 added further support for mission-critical communications.

The goal of the Release 13 MCPTT—and push-to-talk capabilities in general—is to better satisfy the needs of public-safety communications. Emergency responders need reliable communications that are readily available with little latency. Individual calls, from one user to another, must be supported as well as group calls. These and other features are now evident as MCPTT solutions begin emerging in the market.

AT&T, for example, recently unveiled its Enhanced Push-to-Talk (EPTT) services and continues to partner on carrier-integrated products. Among the features of these solutions, which are based on the 3GPP MCPTT standards, are push-to-talk data over 4G LTE. The carrier promises to provide enhanced situational awareness, emergency calling, and priority treatment while maintaining interoperability with legacy two-way radios such as APCO P25. With the push of a button, a user can supposedly make a group call to as many as 250 team members.

Targeting wireless carriers like AT&T, Motorola Solutions offers PTT 9.0. It promises features that comply with the 3GPP MCPTT standard, such as emergency calling and remote monitoring. Users also can take advantage of location-enabled talkgroups.

These are just two examples of the multiple rollouts that are occurring. Despite the impressive capabilities they provide, however, none of these solutions fully comply with the standard. One challenge is the 3GPP standard’s stringent latency requirements. However, a bigger issue hampering MCPTT solutions is the proximity services (ProSe) feature, which was also included in Release 13.

The goal of ProSe is to support direct-mode communications between devices in instances when Long Term Evolution (LTE) network infrastructure is not available. With chipset vendors failing to support ProSe, however, this effort is hampered. It is believed that they are waiting for the demand for ProSe chipsets to make it worth the investment of adding this feature to their solutions. Yet another concern is the communication range offered by ProSe service. An LTE device, transmitting at 0.25 W with an internal antenna, will never match the range and power provided by a land mobile radio with an external antenna transmitting with at least 12X that power.

While this issue is most often cited as an obstacle to full compliance with MCPTT, other network challenges also have been mentioned. Such issues will impact new public safety standards, such as FirstNet in the U.S., which is slated to leverage MCPTT to replace LMR push to talk. While some point to fifth-generation (5G) cellular as a potential solution, the purpose of LMR is to provide services off or beyond cellular networks. Such an approach is designed to overcome issues like in-building and rural coverage gaps, which generally afflict consumer networks. Although MCPTT for LTE was added to enhance communications, the public safety industry will only know more when ProSe devices are available for testing.

For more information on how Keysight supports the ongoing developments in LMR testing, click here.

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