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Mission Critical Voice QoE Mouth-to-Ear Latency Measurement Methods



Jesse Frey, Jaden Pieper, Silas Thompson


Mouth-to-ear (M2E) latency describes the time it takes speech input in a voice communication transmit device to be output from a receiving device, and has been identified as a key component of quality of experience (QoE) in communications. NIST's PSCR division developed a method to measure and quantify the M2E latency of any communications system transmitting audio, with specific emphasis on push to talk (PTT) devices. This measurement method is the first step in establishing QoE key performance indicators (KPI) for mission critical voice (MCV) and a measurement system to quantify these QoE KPIs. Additional measurement methods will be established and published in the near future. The measurement system provides a fair platform for the comparisons of M2E latency across radio communications technologies. Both single and two location measurement systems were developed. The single location measurement system is a simpler setup ideal for measurements performed in a single, controlled setting. The two location system allows for the measurement of M2E latency between devices in two distinct locations and adds the capability to see potential effects of distance and signal propagation on the latency a user experiences. Example measurements of the M2E latency of VHF and UHF land mobile radios (LMR) operating in both direct mode and in trunked mode were performed. These tests demonstrated that both the single and two location tests return consistent measurement results.
NIST Interagency/Internal Report (NISTIR) - 8206
Report Number


Audio, Communications, Delay, Direct Mode, Handset, Key Performance Indicator (KPI), Land Mobile Radio (LMR), Latency, Mission Critical Push To Talk (MCPTT), Mission Critical Voice (MCV), Mouth-to-ear (M2E), Project 25 (P25), Public Safety, Push To Talk (PTT), Quality of Experience (QoE), Quality of Service (QoS), Repeater, Trunked Mode, Ultra High Frequency (UHF), Very High Frequency (VHF).


Frey, J. , Pieper, J. and Thompson, S. (2018), Mission Critical Voice QoE Mouth-to-Ear Latency Measurement Methods, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed May 28, 2024)


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Created February 28, 2018, Updated October 12, 2021