  Recently, the way people consume video content has been undergoing a dramatic
change. Plain TV sets, that have been the center of home entertainment for a
long time, are losing grounds to Hybrid TV's, PC's, game consoles, and, more
recently, mobile devices such as tablets and smartphones. The new predominant
paradigm is: watch what I want, when I want, and where I want.
  The challenges of this shift are manifold. On the one hand, broadcast
technologies such as DVB-T/C/S need to be extended or replaced by mechanisms
supporting asynchronous viewing, such as IPTV and video streaming over
best-effort networks, while remaining scalable to millions of users. On the
other hand, the dramatic increase of wireless data traffic begins to stretch
the capabilities of the existing wireless infrastructure to its limits.
Finally, there is a challenge to video streaming technologies to cope with a
high heterogeneity of end-user devices and dynamically changing network
conditions, in particular in wireless and mobile networks.
  In the present work, our goal is to design an efficient system that supports
a high number of unicast streaming sessions in a dense wireless access network.
We address this goal by jointly considering the two problems of wireless
transmission scheduling and video quality adaptation, using techniques inspired
by the robustness and simplicity of Proportional-Integral-Derivative (PID)
controllers. We show that the control-theoretic approach allows to efficiently
utilize available wireless resources, providing high Quality of Experience
(QoE) to a large number of users.
