Power efficient transmission policies for multimedia traffic over wireless channels
scheduling; delay; power control; fading channels
The current and future wireless systems need to support a multitude of services with a wide range of data rates and reliability requirements. The limited battery resource at a mobile terminal coupled with the hostile multipath fading channel makes the problem of providing reliable high data rate services challenging. In this thesis we develop a new framework for the design of power efficient transmission mechanisms that support multimedia traffic having different delay constraints. First, we present optimal design techniques that substantially reduce the transmission power (exceeding 60% in certain cases) for small increases in average communication delays for a single user scenario thereby providing another avenue for mobile devices to save on battery power. The power minimizing schedulers adapt the transmission rate and power based on the queue and channel state. We also construct a variable rate modulation scheme to show the benefits of the proposed formulation in a practical system. Power optimal schedulers with absolute packet delay constraints are also studied and their performance is evaluated via simulations. Second, we design power efficient schedulers that satisfy average delay bounds for multiple users in a broadcast channel. Optimal schedulers that jointly allocate rate and power to the different users based on the different buffer and channel conditions are presented in code-division multiple access (CDMA) and time-division multiple access (TDMA) regimes used commonly in current cellular standards. We show that joint scheduling gains over non-cooperative single user schedulers are largest when the users belong to different delay classes. We also show the superiority of CDMA over TDMA in terms of a larger set of achievable delays and at consistently lower powers. Near optimal low complexity schedulers are introduced in which computational complexity increases gracefully with increasing number of users. We also compute achievable power regions under average delay constraints in a multiple access channel with global and local queue state information. Finally, we develop a framework for designing power limited delay bounded transmission schemes that minimize the outage probability in fading channels with feedback. We explicitly construct schemes that quantitatively demonstrates the outage reduction with increasing delays and amounts of feedback information.
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- ECE Publications