A roadmap on QoE metrics and models

5G communications are expected to adopt a user-centric service provisioning approach, transforming the current Quality of Service (QoS) networking paradigm to a Quality of Experience (QoE) platform. Towards this direction, the design of QoE quantification methods is a vast necessity, prior to the design of QoE-driven service/network management techniques and the proposal of QoE-aware customer experience management and charging policies. Contributing to this effort, in this paper we provide a comprehensive overview and inventory of the currently available QoE estimation approaches and models. More specifically, we discuss the relation between QoS and QoE, the major QoE influence factors, the QoE evaluation end estimation process, and the dominant objective QoE estimation models.