Opportunistic transmission for wireless data over fading channels under energy and delay constraints

Opportunistic communication techniques exploit the delay tolerance inherent in data services by designing channel dependent transmission strategies. The objective of this thesis is to find energy efficient transmission schemes under different delay constraints for a variety of communications scenarios where opportunism in transmission may be exploited.; In the first set of problems, we consider binary power control strategies for transferring a fixed size file over fading channels under constraints on both transmit energy and transmission delay. The goal is to maximize the probability of successfully transferring the entire file over a time-varying wireless channel modeled as a finite state Markov process. We consider two scenarios for the delay constraints: an average delay constraint and a strict delay constraint. The resulting optimal policies are shown to be a function of the channel state information (CSI), the residual battery energy at the transmitter and also the number of residual packets in the transmit buffer. It is observed that the probability of successful file transfer increases significantly when the CSI is exploited opportunistically.; In the second set of problems, we discuss the information theoretic limit of a block fading finite state Markov channel model under constraints on both the total battery energy and the communication delay. We derive the optimal power and rate control policies that maximize a lower bound on the expected sum of rates in the limit of large but finite energy. Our results also show that faster fading yields higher sum of rates in the delay constrained situations.; Taking into account the packet arrival statistics, in the third set of problems, we present a simplified scheduling scheme for packet transmission over a slow fading channel. We first derive the optimum minimum power transmission policy with constraints on both average delay and packet loss. The optimal policy requires a sophisticated table-look-up for implementation. In order to alleviate this problem, we design a simplified transmission policy and find that the minimum average power with the simplified scheme is very close to that achieved by the optimal policy.; The first three classes of problems above tackle opportunistic transmission in models where the opportunities in time are presented due to variations in fading channel states. In the last set of problems studied here, we characterize the opportunities presented for transmission explicitly in space due to mobility and changing mobile location, a situation reminiscent of Infostations. Using a random walk model to capture the movement of the mobile as well as the resulting channel in space, we derive optimal binary power control policies that maximize the utility of the mobile measured in bits per Joule.