Pathfinding Pulsar Observations with the CVN Incorporating the FAST

The importance of Very Long Baseline Interferometry(VLBI)for pulsar research is becoming increasingly prominent and receiving more and more attention.We present the pathfinding pulsar observation results with the Chinese VLBI Network(CVN)incorporating the Five-hundred-meter Aperture Spherical radio Telescope(FAST).On MJD 60045(11th April 2023),PSRs B0919+06 and B1133+16 were observed with the phase-referencing mode in the L-band using four radio telescopes(FAST,TianMa,Haoping,and Nanshan)and correlated with the pulsar binning mode of the distributed FX-style software correlator in Shanghai.After further data processing with the NRAO Astronomical Image Processing System(AIPS),we detected these two pulsars and fitted their current positions with accuracy at the milliarcsecond level.By comparison,our results show significantly better agreement with predicted values based on historical VLBI observations than those with previous timing observations,as pulsar astrometry with the VLBI provides a more direct and model-independent method for accurately obtaining related parameters.

Multiplexing modulation design optimization and quality evaluation of BDS-3 PPP service signal

The Precise Point Positioning(PPP)service of BeiDou-3 Navigation Satellite System(BDS-3)is implemented on its Geostationary Earth Orbit(GEO)satellites.However,its signal design is limited by the actual power of satellite and other conditions.Furthermore,the design needs to fully consider the compatibility of diferent service phases.Starting from the actual state of the BDS-3 GEO satellite,this paper studies the multiplexing modulation of the BDS PPP service signal that is based on the Asymmetric Constant Envelope Binary Ofset Carrier(ACE-BOC)technique and proposes several feasible schemes for this signal.Comparison and optimization of these techniques are made from the aspects of transmission efciency,multiplexing efciency,and service forward compatibility.Based on the Type-III ACE-BOC multiplexing modulation technique,phase rotation and intermodulation reconstruction techniques are proposed to suppress the intermodulation interference issue.Finally,a signal based on improved ACE-BOC multiplexing is designed.The quality of the proposed signal was continuously monitored and tested using large-diameter antennas.The evaluation results show that the power spectrum deviation of the signal is 0.228 dB,the correlation loss is 0.110 dB,the S-curve slope deviation is 1.558%on average,the average length diference between the positive/negative chip and the ideal chip is only 0.0006 ns,and the coherence between the carrier and the pseudo code is 0.082°.All quality indicators are satisfactory,indicating that the proposed signal multiplexing modulation technique is an ideal solution that meets all the requirements of the design constraints,and can achieve efcient information broadcasting and forward compatibility of the BDS PPP service.