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We investigate the effect of radio-frequency interference (RFI) excision inestimating the cosmological \hi\ 21 cm power spectrum. Flagging ofRFI-contaminated channels results in a non-uniform sampling of the instrumentalbandpass response. Hence, the Fourier transformation (FT) of visibilities fromfrequency to delay domain contaminates the higher foreground-free delay modes,and separating the spectrally fluctuating \hi\ signal from spectrally smoothforegrounds becomes challenging. We have done a comparative analysis betweentwo algorithms, one-dimensional CLEAN and Least Square Spectral Analysis(LSSA), which have been used widely to solve this issue in the literature. Wetest these algorithms using the simulated SKA-1 low observations in thepresence of different RFI flagging scenarios. We find that in the presence ofrandom flagging of data, both algorithms perform well and can mitigate theforeground leakage issue. But, CLEAN fails to restrict the foreground leakagein the presence of periodic and periodic plus broadband RFI flagging and givesan extra bias to the estimated power spectrum. However, LSSA can restrict theforeground leakage for these RFI flagging scenarios and gives an unbiasedestimate of the \hi\ 21 cm power spectrum. We have also applied thesealgorithms to the upgraded GMRT observation and found that both CLEAN and LSSAgive consistent results in the presence of realistic random flagging scenariosfor this observed data set. This comparative analysis demonstrates theeffectiveness and robustness of these two algorithms in estimating the \hi\ 21cm power spectrum from the data set affected by different RFI scenarios.

A Comparative Analysis To Deal With Missing Spectral Information Caused By RFI In Cosmological HI 21CM Observations