Strategies for Weather-Dependent Data Acquisition

Abstract

A strategy for data acquisition from a very distant spacecraft is presented, when the system performance can be severely degraded by the earth's weather due to the high microwave frequency being used. Two cases are considered, one in which there is a certain minimum data rate to be maintained and one in which there is not. The goal is to maximize expected data return, where we assume that there are always new data, or a backlog of old data, that can be sent if conditions are favorable. When there is no minimum rate to be maintained, the optimum strategy is typically the greedy strategy, which always transmits at that single rate which maximizes the expected data returned. If there is a minimum data rate which we strive to maintain even in adverse conditions, the optimum strategy transmits simultaneously at the minimum or base data rate and typically at a bonus data rate. We use a coding system designed for the bandwidthconstrained degraded broadcast channel. The optimum version of this system can, under realistic assumptions, save on the order of 5 dB over the conservative strategy of just transmitting at a single lower data rate.