The effects of Rayleigh distributed multipath fading on carrier recovery performance

Multipath fading as encountered in the portable radio communications environment produces rapid and large carrier phase changes coincident with rapid fades. Any phase-locked loop (PLL) used for carrier recovery must accurately track these phase changes. This experiment studies the effects of PLL parameters on carrier recovery performance in the presence of noise-free multipath fading by use of a hardware fading simulator and a typical analog carrier recovery circuit. The Doppler spread, PLL damping factor, and PLL 3dB loop bandwidth were individually and jointly varied to determine their relationships to loop phase error performance. The key parameter affecting the loop phase error behavior is the ratio of the 3dB loop bandwidth to the Doppler spread, not their individual values. Important relationships between this ratio and performance measures of the carrier recovery loop were also found.