Report Details Results of Mission-Critical Voice over LTE Speech Intelligibility Tests
Thursday, January 04, 2018 | Comments

A new report summarizes the results of speech intelligibility tests on five speech codec operating modes that might be chosen to provide mission-critical voice services to public-safety users over a Long Term Evolution (LTE)-based radio access network (RAN).

The National Telecommunications and Information Administration (NTIA) report details the results of an investigation of speech intelligibility in different radio environments recently completed by the Institute for Telecommunication Sciences (ITS) audio quality research team on behalf of the Department of Homeland (DHS) Science and Technology Directorate (S&T).

ITS performed two distinct but related speech intelligibility tests on five speech codec operating modes that might provide mission-critical voice services to users on the First Responder Network Authority (FirstNet) or other public-safety LTE networks. The tests followed the MRT paradigm — the American National Standards Institute (ANSI)-standardized method for measuring intelligibility — to measure intelligibility under 120 different conditions of simulated network degradation and background noise applied at various levels emulating a variety of field conditions that might be encountered by first responders.

The reported test results will enable those who design RANs and radio access augmentation strategies to make decisions based on speech intelligibility. This is key for public-safety stakeholders because speech intelligibility directly affects first responder operations.

First responders must send and receive speech messages with high intelligibly to protect lives and property. Network congestion, weak in-building coverage and the limits of outdoor coverage can all cause reductions in speech intelligibility. The report is part of a decades-long portfolio of research into the relationship between radio link conditions, as defined by quantifiable engineering parameters, and the perceived quality of the transmission, the user quality of experience.

The testing methods and results are fully documented in NTIA Technical Report 18-529, Intelligibility Robustness of Five Speech Codec Modes in Frame-Erasure and Background-Noise Environments, published Dec. 28.

The latest report follows ITS work in 2015 that helped identify which digital speech and audio technologies are best suited for mission-critical voice communications over a 4G wireless network.

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