Service outage based power and rate allocation

This paper explores a spectrally efficient, variable rate transmission scheme under a service outage constraint for a block fading channel model. The service outage constraint is motivated by real time variable rate applications. In a service outage, the transmission code rate is below a given basic rate and may in fact be zero. Unlike an information outage in the capacity versus outage problem, asymptotically error free communication is maintained during a service outage. We solve the problem of maximizing the time average transmission code rate subject to the probability of service outage being sufficiently small. When the problem is feasible, the optimum power policy is shown to be a combination of water filling and channel inversion allocations. The optimum power allocation for delay limited capacity, capacity versus outage, and ergodic capacity are special cases of this optimum scheme. Numerical results for the Rayleigh fading channel are given.