Accurate Carrier Frequency Offset Estimation Using Modulation Phase Cancellation for PCM/FM Telemetry Signals

Carrier frequency offset (CFO) estimation is a fundamental task in pulse code modulation/frequency modulation telemetry. In addition to its conventional role in frequency correction for data symbol detection, CFO inherently carries Doppler information associated with target motion, making it potentially useful for assisting radial velocity measurement. However, existing CFO estimators are mainly designed for data detection, and their estimation accuracy is often limited. To enable precise velocity measurement, this article proposes a high-precision CFO estimation method based on modulation phase cancellation. Unlike conventional statistics-based approaches, the proposed method constructs the modulation phase by performing symbol detection and premodulation filter estimation. This allows effective cancellation of the modulation phase induced by transmitted data symbols, thereby producing a single-tone CFO signal. Furthermore, a recursive least squares (RLSs) based framework is developed to estimate the response of the premodulation filter, where a suitable filter order is determined by minimizing the designed residual phase error. Finally, the performance of the proposed method is validated using both numerical simulations and experimental data. The results demonstrate that the proposed method substantially improves CFO estimation accuracy and achieves performance closer to the modified Cramer-Rao bound.