Tech Talk: 3GPP Makes Major Progress with MCPTT

March 17, 2016
Third Generation Partnership Project (3GPP) Plenary meetings.
Third Generation Partnership Project (3GPP) Plenary meetings.

By Dean Prochaska, FirstNet Director of Standards

This post is the second blog in a "Tech Talk" series on FirstNet’s standards development activities.  It focuses on the results from 3GPP Plenary meetings that were conducted last week in Gothenburg, Sweden.  The Middle Class Tax Relief and Job Creation Act of 2012, Section 6206(c)(7), directs FirstNet, in consultation with the Director of NIST, the FCC, and the Public Safety Advisory Committee (PSAC), to represent the interests of public safety users of the nationwide public safety broadband network (NPSBN) in the development of interoperability standards.

I’m writing this blog post from an empty meeting room in Gothenburg, Sweden, where the weeklong 3rd Generation Partnership Project (3GPP) Plenary meetings have just wrapped up. As you may recall from my last blog post published on February 10th, it discussed how FirstNet’s NPSBN will be based upon the wireless Long Term Evolution (LTE) technology standards created by the global 3GPP standards development organization.

In it, I discussed some of the major features that were completed in 3GPP Release 12, including basic service enablers for Mission Critical Push to Talk over LTE (MCPTT).  More importantly, I mentioned that we were nearing the completion of 3GPP Release 13, which contains the technical specifications for MCPTT.

The FirstNet standards development team has been working diligently within the 3GPP technical committees supporting the creation of standards based upon communications requirements of Public Safety for MCPTT since January of 2014. This has been a huge undertaking by the FirstNet standards team and the global 3GPP members.  I am pleased to report that, just a few hours ago, we completed the 3GPP Release 13 standards for MCPTT during our Plenary meetings this week here in Sweden.

To give you an idea of the scope and size of the 3GPP Plenary sessions held this week, they consisted of the primary Technical Specification Groups (TSGs) which include:

  • The Radio Access Network (RAN) TSG Plenary – which had about 115 organizations and almost 300 people registered for the meeting;
  • The Core Network and Terminals (CT) TSG Plenary - which had about 60 organizations and about 125 people registered for the meeting and finally;
  • The Service and System Aspects (SA) TSG Plenary – which had about 85 organizations and 170 people registered for the meeting.

In addition, each of these Plenary TSGs have many subordinate Working Groups that report to them (RAN has 5, CT has 5, and SA has 6), with all of their work getting formal approval at their associated Plenary level.

As you can imagine with a group the size of 3GPP, working on a consensus-based approach can provide for some tense moments, and this was certainly the case for completing Release 13 MCPTT this past week.  Leading up to this meeting, all of the major elements of Release 13 MCPTT were completed about 4 weeks ago, except for the selection of a speech vocoder, which is a critical component that converts analog voice into a digital stream of data.

For the last year or so, two primary vocoders have been evaluated for consideration and use for the MCPTT service.  The first option was the Adaptive Multi-Rate Wideband (AMR-WB) speech vocoder which is the current mandated vocoder for commercial Voice over LTE (VoLTE) service.  It has been widely used in wireless devices for numerous years and is presently installed in hundreds of millions of LTE mobile devices today.  The second option proposed for MCPTT was a new speech vocoder called Enhanced Voice Services (EVS), which has not yet been widely deployed.

The Public Safety community has stressed the importance of vocoder selection for many years based upon their experiences with the transition from analog to digital land mobile radio systems. 

Based upon this background, some of the key vocoder factors that we focused on within the 3GPP technical committees were:

  1. It needs to be a proven vocoder - what this effectively means is that it has been successfully integrated into many, many devices and has been widely deployed in the field by network operators.  The Public Safety community cannot afford to deploy a vocoder that may fail during emergency situations based on the relative maturity of the vocoder;
  2. The speech being transmitted and received must be intelligible, especially when voice communications are being used in the loud background noise environments frequently experienced by first responders during emergency situations;
  3. It must perform at least as well or better than what the existing Public Safety Land Mobile Radio (LMR) speech vocoders are capable of today, in similar operating conditions such as poor RF environments;
  4. The vocoder selected should not be cost prohibitive;  and
  5. A single mandatory vocoder to best ensure interoperability among and across agencies, cities, counties, states, nations, etc.

Over the last year, in support of our 3GPP standards development for MCPTT, a research team at the Public Safety Communications Research (PSCR) program conducted testing to evaluate the two vocoders under consideration for MCPTT (in addition to several other vocoders outside of the 3GPP realm).  This testing identified multiple audio vocoders for LTE that can deliver speech intelligibility that meets or exceeds minimum acceptable mission-critical requirements in the wide range of noise environments that fire fighters and other first responders encounter.

These tests also confirmed that the speech intelligibility of audio vocoders clearly depends on the data rate available for transmission of voice signals.  This testing was performed under the presumption of ideal RF conditions; however, we all know that most wireless systems do not always operate in such RF environments.  Hence the next step of the project was to re-evaluate the vocoders under imperfect RF channel conditions, again with the loud background noise environments.

Based on the results of the testing, along with the aforementioned key vocoder factors, FirstNet and other foreign government public safety representatives that are planning on deploying LTE based public safety networks agreed that the AMR-WB vocoder should be selected as the single mandatory vocoder for 3GPP MCPTT in Release 13. AMR-WB has been deployed in many devices around the world, and thus commercial operators have already dealt with issues associated with integrating this vocoder into the handsets.  Additionally, the selection of a single mandatory vocoder will promise interoperability across handsets.

During the course of standardizing MCPTT for Release 13, the EVS vocoder was proposed as the mandatory vocoder, whereas the Public Safety proponents in 3GPP proposed AMR-WB as the mandatory vocoder. As mentioned above, 3GPP is a consensus-based organization. In order to finally resolve the stalemate, and in order to complete the MCPTT standards for Release 13, a compromise was achieved and finalized this past week in Sweden. AMR-WB will be the sole mandatory vocoder for MCPTT in Release 13. Additionally, if an operator so chooses, the EVS vocoder in Super Wide Band (SWB) mode can be optionally included along with the AMR-WB vocoder.

FirstNet is very pleased with this outcome, and in our next blog about our standards development activities, we plan to go into more detail about some of the features contained in Release 13 for public safety.



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