Research on a Coherent Dedispersion Algorithm for Pulsar Baseband Data

Abstract

When the pulsar signal propagates in the interstellar medium(ISM), the high frequency and low frequency components of the signal reach the radio telescope with a certain delay. Therefore, the pulsar signal will appear energy dispersion, which will broaden the pulse profile, decrease the signal to noise ratio(SNR), and even lead to the disappearance of the pulse signal. In this paper, we analyze the sampling, polarization and arrangement of baseband data based on the coherent dedispersion algorithm for the problem of pulsar baseband data dedispersion. We systematically study the coherent dedispersion data processing procedure and test the pulse profile changes under different FFT block sizes. An optimal selection strategy of FFT block sizes is proposed for reducing the operation time and obtaining a better pulse profile. We propose two methods, one is the generation of ISM transfer function, the other is the pulsar period and phase prediction method at a certain time, and discuss integral and folding strategies. We test the algorithm based on the baseband data of CASPSR and Medusa terminals observed by Parkes 64m radio telescope, and analyze the reading and processing methods of baseband data of different terminals. The experimental results show that the pulse profile with SNR greater than 200 is obtained, which verifies the effectiveness of the algorithm.

The RFI Fast Mitigation Algorithm Based on Block LMS Filter

“…In this experiment, only one polarization data (pol1) was used. After undergoing dispersion removal, folding, integration, and other operations, the original pulsar profile was obtained (Zhang et al 2023), as shown in Figure 4. After adding interference to the original astronomical signal, the resulting signal pol1 + v 1 undergoes dispersion, folding, integration, and other operations to generate a pulsar profile image containing RFI, as shown in Figure 5.…”

PSRDP: A Parallel Processing Method for Pulsar Baseband Data

“…To restore the original characteristics of pulsar signals, it is necessary to perform dedispersion, where coherent dedispersion involves filtering the observed signal through the inverse of the transfer function of the ISM. In theory, coherent dedispersion can completely eliminate the dispersion effects caused by the ISM in the signal (Zhang et al 2023a).…”

“…The period of pulsars is very stable, but the locations of observatories, pulse dispersion, orbit parameters of the solar system (Romer delay, Shapiro delay and Einstein delay) and binary systems can affect the times-of-arrival of pulses, which in turn affects the folding period of pulsar data (Pennucci 2015). In order to accurately fold the pulse profile and the phase of a certain timestamp, it is necessary to predict the folding period and the phase of the pulsar at that timestamp (Zhang et al 2023a).…”

Research on Ultra-wide Bandwidth Low-frequency Signal Channelization for Xinjiang 110 m Radio Telescope

“…The specific process is diagrammed in Figure 8. The pulsar baseband data are processed in blocks to improve the processing efficiency, and the time domain data are converted to the frequency domain by FFT to perform coherent dedispersion (Zhang et al 2023b) using information such as center frequency, bandwidth, and dispersion measure (DM). After that, the center frequency, bandwidth, and DM of the newly generated UBPB data are set and the dispersion is added to the dispersive data (the inverse of coherent dispersion), which are converted to the time domain by IFFT and finally stored as baseband data.…”