Voice Quality Experience Evaluation: MOS Laboratory Test and Spectrum Analysis of Failures in VoLTE Calls

In recent years, Voice over IP (VoIP) call feature has become increasingly accessible to customers due to advancements in internet services and the emergence of voice call applications. However, identifying the variables that impact Voice over Long-Term Evolution (VoLTE) performance, particularly in quantifying end-user experience in the field and the effects of radio conditions and IP impairments on voice quality as measured by the Mean Opinion Score (MOS), presents challenges for carriers. MOS is a widely used metric for evaluating voice quality, and there is a significant commitment from both mobile device manufacturers and carriers to ensure superior voice quality during voice calls. To this end, MOS experiments are performed to evaluate the reliability of VoLTE calls, which is currently the best approach for measuring voice quality. In this study, we present MOS experimentation results in laboratory environments to homologate 146 different smartphone models. As results, we highlight the challenges associated with MOS testing in VoLTE calls under controlled conditions and discuss the primary issues found and how they were addressed. These experimental analyses offer substantial opportunities for enhancing the design and operation of audio quality during VoLTE calls and detail potentially improvements for 5GVoNR calls.