Power reduction on QPSK modulation codings for geopositioning application using LEO satellites

Minimum transmission power using transponders in low earth orbit satellite is a major requirement for the new geo-positioning system, known as Geolocal. It utilises a repeater in space and ground-based precise geodetic reference bases. We discuss and compare two digital codings on the QPSK (quadrature phase shift keying) modulation: concatenated Reed-Solomon/Convolutional Coding and concatenated BCH (Bose-Chaudhuri-Hocquenghem) with LDPC (Low Density Parity Code). We show that the latter brings 8 dB power gain on the whole two-way ground to satellite link allowing a reduction in the power requirements on the small platforms carrying the transponders.