Future wireless networks will be driven by various ubiquitous broadband services such as portable telephony, mobile Internet, Voice over IP, and IPTV. To accommodate a single cell"s large number of users, each running a different application on its mobile terminal, optimization of limited resources is critical. The transmission path from the base station to the mobile terminal is the downlink. In the downlink, feedback of mobile user"s condition to the base-station is essential for optimal allocation of limited resources, however, it is a system design challenge. Mobile user"s condition is comprised of its wireless channel condition, among multiple other such system metrics. This book explores optimal resource allocation, with partial knowledge of a mobile user"s condition at the base station. It shows the right feedback information is application dependent. The set of techniques explored improve the performance and bandwidth efficiency of future wireless systems. The work should be very useful to industry professionals in wireless networks, academicians - professors or graduate students; or anyone else with an interest in wireless communications.