Opportunistic packet scheduling with imperfect channel knowledge

We consider transmission control (rate and power) strategies for transferring a fixed size file (finite number of packets) over fading channels under constraints on both transmit energy and average transmission delay. The goal is to maximize the probability of successfully transferring the entire file over a time-varying wireless channel modelled as a finite state Markov process. We investigate the performance degradation caused by the imperfect (delayed or erratic) channel knowledge. The resulting optimal policies are shown to be a function of the available channel state information (CSI), the residual battery energy as well as 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. However. when counting the power expenditure over the pilot for channel estimation, the transmitter chooses to use pilot only if there is sufficient energy left for packet transfer, otherwise, a channel independent policy is deployed instead.