Initial MCPTT tests deliver ‘significantly better’ audio quality than LMR, according to Spirent

Mission-critical push-to-talk (MCPTT) services will not be introduced commercially until late this year, but early tests of multiple vendors’ offerings exhibited “significantly better” audio-quality scores than land-mobile-radio (LMR) systems, according an official from Spirent Communications, which conducted the tests.

Spirent Communications conducted the audio-quality tests during the June MCPTT plugtests event conducted by ETSI at Texas A&M University, where more than 30 vendors demonstrated interoperability at a 92% success rate, according to ETSI. The Spirent Communications audio-quality tests were not formally part of the ETSI event, but many vendors still participated in the audio-quality tests, which yielded encouraging results, according to Kurt Bantle, senior solutions architect for Spirent.

“We can’t discuss individual [results for specific vendors],” Bantle said during an interview with IWCE’s Urgent Communications. “But, for the most part, the audio quality, from a MOS [mean opinion score] perspective, across MCPTT is really good—it was almost surprisingly good. For the first time ever running audio-quality test cases [for MCPTT], I was really impressed with all of the participants.”

Audio-quality MOS scores range from 0 to 5, with 5 reflecting the best audio quality. Citing a non-disclosure agreement (NDA) associated with the ETSI event, Bantle declined to provide exact figures but said that the MCPTT MOS scores were “in the upper range of what MOS scores typically are” and “significantly better” than MOS scores associated with LMR technology.

Spirent Communications’ MCPTT tests support anecdotal evidence provided by numerous users of push-to-talk-over-cellular (PoC) technologies, which use broadband connections to leverage greater bandwidth and higher-level codecs to support voice communications. However, PoC technologies traditionally have been proprietary, while MCPTT is a 3GPP open standard that is designed to foster interoperability.

A veteran of voice-over-LTE (VoLTE) audio-quality tests, Bantle said that the ETSI plugtests in June provided an ideal opportunity to gauge the audio quality and compatibility of MCPTT offerings from many different vendors.

“When I saw that the MCPTT plugtest was going on, I asked, ‘Is anyone actually testing what the audio sounds like?’” he said. “It’s great to get the protocol down, but—from years of VoLTE testing—I know that you can have 100% perfect protocol and the codecs are not in sync.”

Bantle said that the Spirent Communications’ tests demonstrated that MCPTT can deliver high-quality voice communications, even when multiple vendors were used to deliver the audio.

 “We had a really good mix—we had single-source participation, and we had multi-source participation,” Bantle said. “We definitely got to see a really good cross section of different clients, different servers and different devices. It was good to see that broad [portfolio] of devices testing their audio quality.

“The MOS scores were definitely in the upper end of that range. They were all good. There was not a really wide variance between the different players—they were really all pretty consistent. We definitely had some [vendors] who were better than others, but all of them were significantly better than LMR numbers.”