A Survey on QoE-oriented Wireless Resources Scheduling <s> C. Utility-based Optimization <s> Network protocols in layered architectures have historically been obtained on an ad hoc basis, and many of the recent cross-layer designs are also conducted through piecemeal approaches. Network protocol stacks may instead be holistically analyzed and systematically designed as distributed solutions to some global optimization problems. This paper presents a survey of the recent efforts towards a systematic understanding of layering as optimization decomposition, where the overall communication network is modeled by a generalized network utility maximization problem, each layer corresponds to a decomposed subproblem, and the interfaces among layers are quantified as functions of the optimization variables coordinating the subproblems. There can be many alternative decompositions, leading to a choice of different layering architectures. This paper surveys the current status of horizontal decomposition into distributed computation, and vertical decomposition into functional modules such as congestion control, routing, scheduling, random access, power control, and channel coding. Key messages and methods arising from many recent works are summarized, and open issues discussed. Through case studies, it is illustrated how layering as Optimization Decomposition provides a common language to think about modularization in the face of complex, networked interactions, a unifying, top-down approach to design protocol stacks, and a mathematical theory of network architectures <s> BIB001 </s> A Survey on QoE-oriented Wireless Resources Scheduling <s> C. Utility-based Optimization <s> Utility functions, describing the value of a good or a resource from an end user's point of view, are widely used as an important ingredient for all sorts of microeconomic models. In the context of resource allocation in communication networks, a logarithmic version of utility usually serves as the standard example due to its simplicity and mathematical tractability. In this paper we argue that indeed there are much more (and better) reasons to consider logarithmic utilities as really paradigmatic, at least when it comes to characterizing user experience with specific telecommunication services. We justify this claim with the help of recent results from Quality of Experience (QoE) research, and demonstrate that, especially for Voice-over-IP and mobile broadband scenarios, there is increasing evidence that user experience and satisfaction follows logarithmic laws. Finally, we go even one step further and put these results into the broader context of the Weber-Fechner Law, a key principle in psychophysics describing the general relationship between the magnitude of a physical stimulus and its perceived intensity within the human sensory system. <s> BIB002
The concept of utility functions emerged from microeconomics theory and formalizes the relationship between the service performance and the user perceived experience and satisfaction BIB002 . More specifically, the following utility function U : X → R relates the set X of all resources a user could possibly have to real numbers, such that U (x) < U (y) implies that the user prefers y over x, with x, y ∈ X. The utility-based scheduling optimization may then be regarded as a maximization of the users' aggregated sum of utilities through Network Utility Maximization (NUM) methods and mechanisms BIB001 . In mathematical terms, using NUM to allocate network resources (e.g., transmission power, transmission rate, etc.) corresponds to perform the following maximization: where U i corresponds to the utility function of the i th user (therefore x i stands for the resources allocated for this user) and X max denotes the bounds of the available resources.