Session
Swifty Session 2
Location
Utah State University, Logan, UT
Abstract
Low Earth Orbit satellites impart a Doppler shift on transmitted signals. This Doppler shift imposes challenges on the receiver design. Optimum band-edge filters can measure the Doppler offset, and frequency-locked loops (FLLs) containing them can correct the Doppler offset. However, optimum band-edge filters require knowledge of the structure of the signal of interest in order to compute the filter coefficients. Prefilter delay-multiply elements can be used to generate a Doppler tone that can be placed in an FLL, but this technique also requires knowledge of the signal structure and is not well suited for frequency shift keyed signals. It is possible to construct a modified band-edge FLL which can track and correct both phase-shift keyed (PSK) and frequency-shift keyed (FSK) signals. The design is further improved by varying the loop bandwidth between acquisition and tracking, which prevents the FLL from unintentionally distorting the frequency-corrected signal in the main receiver. This paper presents and demonstrates this signal-agnostic Doppler correction technique and compares its performance to optimum band edge filters and prefilter delay-multiply techniques. Results are shown for signals with multiple modulation types and modulation rates.
SSC23-S2-15 Presentation
Signal-Agnostic Technique for Satellite Doppler Correction
Utah State University, Logan, UT
Low Earth Orbit satellites impart a Doppler shift on transmitted signals. This Doppler shift imposes challenges on the receiver design. Optimum band-edge filters can measure the Doppler offset, and frequency-locked loops (FLLs) containing them can correct the Doppler offset. However, optimum band-edge filters require knowledge of the structure of the signal of interest in order to compute the filter coefficients. Prefilter delay-multiply elements can be used to generate a Doppler tone that can be placed in an FLL, but this technique also requires knowledge of the signal structure and is not well suited for frequency shift keyed signals. It is possible to construct a modified band-edge FLL which can track and correct both phase-shift keyed (PSK) and frequency-shift keyed (FSK) signals. The design is further improved by varying the loop bandwidth between acquisition and tracking, which prevents the FLL from unintentionally distorting the frequency-corrected signal in the main receiver. This paper presents and demonstrates this signal-agnostic Doppler correction technique and compares its performance to optimum band edge filters and prefilter delay-multiply techniques. Results are shown for signals with multiple modulation types and modulation rates.
