A frequency offset estimator and its method used in gfsk demodulator

Abstract

The invention discloses a frequency offset estimator used in a GFSK demodulator and a method thereof. In the frequency offset estimator, the signal obtained by the digital differential phase detector is first transmitted to the feedback frequency offset estimator with fast convergence characteristics of frequency offset estimation, and an average value calculator is used to calculate the initial frequency offset of the signal shift, and feed back to the front-end digital down-conversion module to complete the initial frequency offset recovery, and then use the median selector and Kalman filter to periodically estimate the frequency drift value, when the accumulated frequency drift value reaches the adjustment threshold, the estimated The value is fed forward to the adjustable threshold decider to change its decision threshold. The invention has fast convergence speed at the initial receiving stage and frequency drift tracking function in the receiving process, and the structure has the characteristics of low power consumption while reducing the frequency deviation estimation time.

Description

technical field [0001] The present invention relates to a frequency offset estimation circuit for wireless communication, in particular to a frequency offset estimator used in a GFSK demodulator and a frequency offset estimation method thereof. Background technique [0002] As a modulation method suitable for low-rate short-distance wireless communication, GFSK (Gaussian Frequency Shift Keying) has the characteristics of simple modem structure, strong anti-interference ability, and low power consumption, so it is one of the most suitable modulation methods for IoT devices one. And GFSK, as a modulation signal with frequency modulation as the modulation mode, effectively estimates and tracks the frequency offset, which plays a key role in improving the performance of the entire demodulator. [0003] The traditional GFSK frequency offset estimation scheme adopts the feedback method, uses the data information before and after the decision device to estimate the frequency offse...

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Problems solved by technology

[0003] The traditional GFSK frequency offset estimation scheme adopts the feedback method, uses the data information before and after the decision device to estimate the frequency offset, and then feeds back to the digital frequency synthesizer used to control the digital down-conversion, thereby eliminating the frequency offset and frequency drift tracking function, literature Ye Zhang, Jan Henning Mueller, Bastian Mohr, and Stefan Heinen, "A Low-Power Low-Complexity Multi-Standard Digital Receiver for JointClock Recovery and Carrier Frequency Offset Calibration", IEEE TCASI: Regular Papers, vol :61, pp.3478-3486, 2014, Issue: 12 uses the data before and after the decision device to estimate the frequency offset. After each estimation is completed, the estimated value is fed back to the previous digital frequency synthesizer. The adjustment of the output frequency of the frequency synthesizer is completed in the form of a table. This scheme has two main disadvantages. The first is that the feedback loop is long, and it cannot achieve real-time frequency offset recovery in the presence of frequency drift, which in turn affects system demodulation. The second is that the same circuit structure is used for the initial frequency offset estimation and subsequent frequency drift tracking, and the design of low power consumption is not considered.

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