Mission-Critical PTT Set for LTE Release 13, Release 12 Freeze Likely in 2015
Tuesday, September 02, 2014 | Comments

Work is underway on mission-critical voice for the Long Term Evolution (LTE) standard in Release 13, set for finalization in the third quarter of 2016. In addition, the freeze for LTE Release 12, which includes several public-safety features, could be delayed to the first quarter of 2015, according to industry sources.

The functional freeze date is when the standard is considered finalized and no further changes or functions can be added to that release. LTE Release 12, also called LTE Advanced, includes proximity services (ProSe) or direct mode communications and group communications or push to talk (PTT).

Release 12 was expected to be complete in December but it might slip to quarter one 2015, sources said. The delay likely won’t have a large impact on public-safety broadband efforts, said European and U.S. officials.

“Any delays to standardization, whilst they are a concern, are unlikely to have a significant impact to most countries,” said Phil Kidner, TETRA + Critical Communications Association CEO. “A notable exception is the United Kingdom, which does not currently own its own network and is looking to replace its current arrangements when its existing contracts expire.

“Most European public-safety users are very happy with their existing networks and are looking to enhance them rather than replace them. One of the first countries to implement a nationwide TETRA network is now updating that network for critical communications and purchasing broadband services from public providers. This model is being followed by other countries.”

The First Responder Network Authority (FirstNet) is the U.S. organization working to build a nationwide LTE network for public-safety and critical infrastructure industries. “We understand that [3GPP officials] are working toward a December target date but may need additional time,” said FirstNet spokesman Ryan Oremland. “We should know more next month but don’t expect it to have a substantive impact on FirstNet’s work if Release 12 should move to the next meeting cycle.”

Mission-critical PTT (MCPTT) requirements definition is ongoing in Release 13, and architecture work is just started, according to a presentation by Balazs Bertenyi, chairman of Third Generation Partnership Project (3GPP) Technical Specification Group (TSG) Service and System Aspects (SA) at the 3GPP Critical Communications Workshop 26 – 27 August.

The MCPTT feature emulates functions provided by professional mobile radio (PMR)/LMR systems. The feature is mainly for group call support, but private one-to-one calls will be supported too. MCPTT will work in both on-network and off-network scenarios, but not all functions will be available when a device operates off-network. It is designed to support mission-critical use, but the feature can be deployed in non-mission-critical scenarios.

MCPTT will include regular group calls, broadcast group calls where no response is expected by the initiating user, groups calls based on priorities such as emergency group call that could pre-empt other calls in progress, and private one-to-one calls.

Both of the Release 12 critical communications features will be further developed in Release 13.

In Release 12, basic discovery and communications functionality specific to proximity services (ProSe) and D2D were added. Release 13 will add the following pieces of functionality:

• Restricted ProSe direct discovery for non-public safety use;

• ProSe direct discovery for public-safety use;

• Support for model B ProSe direct discovery for all use cases (i.e. open and restricted);

• ProSe user equipment (UE)-network relays for public-safety use;

• ProSe UE-UE relays for public-safety use;

• ProSe direct communications one-to-one for public-safety use.

Basic group communications was specified in Release 12 with building blocks for communications to a group of end user devices for the design of the applications layer functionality.

Release 13 will add the following pieces of functionality for group communications:

• Group communications between group members via the network.

• Group communications between group members via the network and a ProSe UE-to-network relay.

• Relationship between a group and members using ProSe group communications — notably, interaction between group communication and ProSe UE-UE or UE-network relays.

• Support for evolved Multimedia Broadcast Multimedia Service (eMBMS) single cell broadcast areas, for networks where this deployment scenario is needed.

Another public-safety feature to be included in Release 13 is called Isolated E-UTRAN operation for Public Safety (IOPS). This would be resilience in case of a loss of backhaul for critical communications. The feature supports locally routed communications in E-UTRAN for nomadic eNodeBs or base stations operating without backhaul connectivity or regulator eNodeBs experiencing temporary loss of backhaul connectivity.

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