Improved carrier tracking of space telemetry signals using cascaded phase locked loops

This paper describes a carrier aiding technique which employs cascaded phase-locked loops. This scheme can be useful when two unequal antennas are required to coherently demodulate the received signal, but due to an extremely weak signal-to-ratio (SNR) level and high Doppler rates, the smaller antenna is unable to lock on the carrier on its own. In order to determine the performance for a bank of (L-1) antennas when each one of them is aided by a single larger antenna, the joint pdf of the two cascaded phase error processes for these (L-1) pairs must be determined. These joint pdfs as well as the carrier loop SNRs of the aided antennas are derived based on Fokker-Planck techniques. The tracking and acquisition results are verified by simulation for the case L=2.