Cui Xiaozhun

Measurement technique of crosslink signal quality parameter for navigation satellite

Signal quality parameters represented electrical properties of the onboard equipment and have a major impact on the main task of crosslink. The traditional microwave signal quality assessment is to analyze the signal after down-converted and nonlinear distortion is introduced. To overcoming the fault of classical method, a technique using digital processing algorithm has been proposed. The crosslink signal is directly sampling by high speed sampler. Coherent receiving and demodulating are done base on soft defined technology, then the quality parameters can be analyzed such as phase consistence, phase error of IQ branch, eye pattern, correlation loss, etc. The actual signal evaluation results show that the accuracy of the proposed analytical method satisfy the crosslink signal quality parameter analysis.

Accurate delay measurement of BPSK modulator for time transfer

BPSK (binary phase shift keying) modulator is widely applied for time signal modulating in time transfer. The delay measurement precision of BPSK modulator is the key factor of the time transfer precision. A high accurate delay measurement of BPSK modulator is developed. Input signal and output signal of BPSK modulator are up-sampled in synchronization. After digital signal processing is done for the sampling data, the delay of BPSK modulator can be obtained. The absolute uncertainty with the proposed algorithm is less than 0.2ns with the sampling frequency 10 G Sa/s.

Analysis of automatic detection for unknown target

A research work is performed to analyze the automatic detection performance in a surveillance area by more than three sensors to detect the unknown non-active fixed or moving target or targets. In order to solve the detection ambiguity for the multiple target case caused by the deterministic and the stochastic reason, a self-defined evaluation parameter and several variables are defined and modeled mathematically in order to perform the deeper and detailed quantitative analysis to all the possible influence factors of the detection precision and reliability. The simulation results show that the defined parameter is an effective criterion for the unknown target detection.

Synchronization of carrier phase for GNSS signal assessment using variable step

Microwave direct sampling was adopted to avoid nonlinear distortion caused by down-convertor for signal quality evaluation of global navigation satellite system (GNSS). The sampling data number is too large for conversional carrier phase synchronization to realize. A carrier synchronization algorithm using variable step is presented to solve this problem. After the coarse initial phase of carrier has been evaluated using large step, the GNSS signal is stripped carrier and then the synchronization of PRN code was carried out. Finally, a fine phase evaluation of carrier was executed using small step. Simulation results show that the proposed algorithm is practicable and the accuracy of carrier phase synchronization is high. Select the appropriate step, the synchronization error can be less than 0.01 radians for the L-band carrier frequency.

Absolute Calibration of BOC Navigation Signal Transmission Channel

An absolute calibrate of BOC signal transmitting channel on navigation satellite based on software defined radio is addressed. At first, the BOC navigation signal and the pulse per second (PPS) generated by navigation time keeping system are sampled synchronously. After the sampling data of BOC signal is preprocessed, a serial-to-parallel transform is done for the intermediate frequency carried BOC signal data, the high rate data stream is converted into several low rate data streams. Parallel capture of code phase is done and the pesudocode starting point of each data stream can be gotten. With sampling data of PPS, the start points of the absolute delay can be decided. Integrating with the calibration delay of the preprocessing, time division processing, test cables and attenuator, the absolute delay of BOC navigation signal for transmitting channel is obtained. The simulated result indicates the precision of the calibrated algorithm is less than one sample period.

Delay calibration algorithm for BOC channel of RNSS using partial correlation

The delay caused by navigation signal transmission equipment of RNSS (Radio Navigation Satellite System) is a part of the whole link delay and must be subtracted in the application of positioning and timing. The absolute calibration of the transmission channel is affected the positioning and time transfer accuracy. The proposed delay measurement technique of BOC (Binary Offset Carrier) navigation signal transmission channel is based on digital signal processing. The BOC signal of navigation satellite and the 1PPS (1 Pulse Per Second) generated by navigation time keeping system are sampled in synchronization. The BOC signal data is processed using carrier-phase acquisition. The integral time is less than a period of the PRN (Pseudo-Random Noise) sequence. The start point of the PRN sequence is obtained and the absolute delay of BOC channel is calculated. The absolute uncertainty with the proposed algorithm is less than 0.2ns when the sampling frequency is 10 GSa/s.

Estimation technique for long-term performance of GNSS on-board clock based on monitoring information

In-orbit long-term performance of GNSS (Global Navigation Satellite System) clocks is being estimated with respect to the monitoring information of the phase comparisons between the main clock and the redundancy. In the satellite clock generator, the time-difference against each other for the onboard main clock and the redundancy is sampled continuously as monitoring information. The monitoring information is transmitted down to ground. The receiver on the sensor station demodulated the monitor information. Data processing is operated on the time-difference of on-board clocks and the long-term property of on-board clocks can be estimated. The proposed technique is considered to be simple, fast and need not require special time-frequency test equipment. Comparing to the ground measurements, a very good agreement can be obtained with the proposed technique.