Summary

Description

<p>Background. NASA missions undergo wide variation in communications link conditions. Over the course of months, the range changes dramatically from launch, to cruise, to say, Mars orbit, but link conditions change on much shorter time scales, as well. For example, a typical track of MRO tracked by the Deep-Space Network might start at antenna elevation 11°, rise to 72°, and then fall to 8° over a twelve hour period. Recent and near-future NASA missions have their data rates limited by dynamic effects such as weather (e.g., MRO Ka-band links), solar scintillation (e.g. Solar Probe), on-board interference (e.g., MRO CRISM interference), launch plumes, and other effects. A 2005 Mars Technology Program study reported that up to 50% more data can be returned on a typical Mars-lander to Mars-orbiter link when adaptive data rates are used on the link. Our task is to extend the concept of adaptive data rates to variable and adaptive coded modulation, in which the dynamic power and bandwidth resources can be much more effectively utilized. A 2010 study by ESA determined that in one practical scenario, a VCM system could more than double the total data volume returned. Our task is to make effective use of the CCSDS standard coded-modulations, thereby allowing us to operate close to the unconstrained capacity limit, regardless of link conditions. To do this, we will develop a physical-layer design that allows the transmitter to switch between coded modulations on a codeword-to-codeword basis, a mechanism to inform the receiver which coded modulation is being used, and the receiver tracking structures necessary to identify the coded-modulation and demodulate and decode the data appropriately.</p>