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

All Spirent Communications tests conducted in June measured audio quality between two MCPTT devices on an LTE network, Bantle said.

MCPTT-to-P25 voice calls are expected to utilize a gateway—likely ISSI—to support communications between LTE and LMR networks, with the MCPTT audio quality degraded to work with the lower-level P25 codec.

Although audio-quality tests have been conducted with LMR technology in the past, Bantle said he would like to conduct a new set of LMR tests with existing equipment to establish a baseline that public-safety officials could use to make an “apples-to-apples” comparison with MCPTT alternatives. Bantle also said he would like to conduct more audio-quality tests with MCPTT in different scenarios: off network, on network with the commercially available codec, and when used in a hybrid LMR-LTE environment.

In addition, Bantle said he would like to conduct tests that measure speech intelligibility, as well as traditional MOS scores.

There is increased skepticism within industry whether LTE will be able to deliver the kind of performance that public safety wants, because LTE devices typically transmit signals at much lower power levels and utilize internal antennas that significantly reduce effective off-network range. In addition, the 3GPP standards body has shifted its focus from the proximity-services standard that was designed to address public-safety off-network communications and is concentrating on vehicle-to-vehicle communications to support autonomous vehicles, according to multiple sources.