  This paper considers optimization of power and delay in a time-varying
wireless link using rateless codes. The link serves a sequence of
variable-length packets. Each packet is coded and transmitted over multiple
slots. Channel conditions can change from slot to slot and are unknown to the
transmitter. The amount of mutual information accumulated on each slot depends
on the random channel realization and the power used. The goal is to minimize
average service delay subject to an average power constraint. We formulate this
problem as a frame-based stochastic optimization problem and solve it via an
online algorithm. We show that the subproblem within each frame is a simple
integer program which can be effectively solved using a dynamic program. The
optimality of this online algorithm is proved using the frame-based Lyapunov
drift analysis.
