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Mission Critical Voice Quality of Experience Access Time Measurement Methods



Jaden K. Pieper, Jesse M. Frey, Chelsea J. Greene, Zainab O. Soetan, Silas T. Thompson, Donald A. Bradshaw, Steven Voran


Access time generally describes the time associated with the establishment of a talk path upon user request to speak and has been identified as a key component of Quality of Experience (QoE) in communications. NIST’s Public Safety Communications Research (PSCR) division developed a method to measure and quantify the access time of any Push To Talk (PTT) communication system. This measurement method is a follow-on method to the Mouth-to-Ear (M2E) latency measurement system presented in Ref. [1]. In this paper, abroad definition of access time is created that is applicable across multiple PTT technologies. In this paper, a speech intelligibility-based access delay measurement system is introduced. This system measures the intelligibility of a target word based on when PTT was pushed within a pre-defined message. It relies only on speech going into and coming out of a voice communications system and PTT timing, so it functions as a fair platform to compare different technologies. Example measurements were performed across the following Land Mobile Radio (LMR) technologies: analog direct and conventional modes,and digital Project 25 (P25) direct and trunked (both phase 1 and phase 2) modes.
NIST Interagency/Internal Report (NISTIR) - 8275
Report Number


Access Delay, Access Time, Articulation Band Correlation Modified Rhyme Test (ABC- MRT), Audio, Communications, Delay, Device to Device (D2D), Direct Mode, Handset, Key Performance Indicator (KPI), Land Mobile Radio (LMR), Latency, Mission Critical Push To Talk (MCPTT), Mission Critical Voice (MCV), Modified Rhyme Test (MRT), Mouth-to-Ear (M2E), Project 25 (P25), Proximity Services (ProSe), Public Safety, Push To Talk (PTT), Quality of Experience (QoE), Quality of Service (QoS), Repeater, Root Mean Square Error (RMSE), Sidelink, Trunked Mode.


Pieper, J. , Frey, J. , Greene, C. , Soetan, Z. , Thompson, S. , Bradshaw, D. and Voran, S. (2019), Mission Critical Voice Quality of Experience Access Time Measurement Methods, NIST Interagency/Internal Report (NISTIR), National Institute of Standards and Technology, Gaithersburg, MD, [online], (Accessed July 19, 2024)


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Created October 15, 2019, Updated January 7, 2020