Fundamental Relationships for Deriving QoE in Systems

In the context of subjective user studies conducted to derive relationships between influence factors and QoE, user diversity leads to distributions of user scores for test conditions. Such models are commonly exploited by service/network providers to derive various QoE metrics in their system, such as expected QoE, or the percentage of users rating above a certain threshold. The question arises as to how to combine a) user rating distributions obtained from subjective studies, and b) system performance condition distributions, so as to obtain the actual observed QoE distribution in the system? Moreover, how can various QoE metrics of interest in the system be derived? We prove a fundamental relationship showing that the expected system QoE is equal to the expected Mean Opinion Score (MOS) in the system. While subjective user studies commonly report only QoS-to-MOS mapping functions, we show that to derive additional QoE metrics in the system, it is necessary to use corresponding QoS-to-QoE metric mapping functions (beyond only QoS-to-MOS) as derived from user rating distributions in subjective studies. The results of the paper provide important insights for deriving QoE metrics from a systems perspective.