A filter algorithm for receiver tracking loops assisted by inertial information

In traditional satellite navigation receivers, the parameters of tracking loop such as loop bandwidth and integration time are usually set in the design of the receivers according to different scenarios. The signal tracking performance is limited in traditional receivers. In addition, when the tracking ability of weak signals is improved by extending the integration time, negative effect of residual frequency error becomes more and more serious with extension of the integration time. To solve these problems, this paper presents out research on receiver tracking algorithms and proposes an optimised tracking algorithm with inertial information. The receiver loop filter is designed based on Kalman filter, reducing the phase jitter caused by thermal noise in the weak signal environment and improving the signal tracking sensitivity. To confirm the feasibility of the proposed algorithm, simulation tests are conducted.

Generation and Measurement of Squeezed Vacuum States at Audio-Band Frequencies

Squeezed vacuum states at audio-band frequencies are important quantum resources for practical applications. We demonstrated the generation of squeezed vacuum states at the audio-band frequencies from a subthreshold optical parametric oscillator with a periodically poled KTiOPO4 crystal pumped by a homemade continuous wave single-frequency dual-wavelength laser. To detect squeezed vacuum states at audio-band frequencies, the influences of the local oscillator (LO) power, the common mode rejection ratio (CMRR) of balanced homodyne detectors, and the phase jitter between the LO and squeezed vacuum field on the measurement of squeezed vacuum states at audio-band frequencies were considered. By optimizing the LO power, improving the CMRR of photodetectors to 67 dB based on the design of differential fine-tuning circuit and adjustable bias voltage, and reducing the phase jitter between the LO and squeezed vacuum field to 1.7° with the help of the coherent locking technique, 6.1 ± 0.3 dB squeezed vacuum states at audio frequencies from 5 kHz to 20 kHz were generated. A 3.0 ± 0.3 dB phase squeezed vacuum state was obtained at the audio frequency of 3.5 kHz.

Improved Design of Bit Synchronization Clock Extraction in Digital Communication System

An improved method is proposed in this design to reduce the phase jitter after the synchronization or the random noise induced phase jitter in a bit synchronization clock extraction circuit. By using a newly added digital filter between the phase detector and the controller, the phase difference pulses from the phase detector are counted and processed, before being transmitted to the controller for adjusting the phase of the output clock. The design is completed by using FPGA chip and VHDL hardware description language and performs the simulation verification on Quartus II. The results show that the improved system performs the accurate extraction of bit synchronized clock, reduces the phase jitter problem, improves the system running efficiency and the ability of anti-interference, and guarantees the synchronization performance of the digital communication system.