  Detection and mitigation of radio frequency interference (RFI) is the first
and also the key step for data processing in radio observations, especially for
ongoing low frequency radio experiments towards the detection of the cosmic
dawn and epoch of reionization (EoR). In this paper we demonstrate the
technique and efficiency of RFI identification and mitigation for the 21
Centimeter Array (21CMA), a radio interferometer dedicated to the statistical
measurement of EoR. For terrestrial, man-made RFI, we concentrate mainly on a
statistical approach by identifying and then excising non-Gaussian signatures,
in the sense that the extremely weak cosmic signal is actually buried under
thermal and therefore Gaussian noise. We also introduce the so-called
visibility correlation coefficient instead of conventional visibility, which
allows a further suppression of rapidly time-varying RFI. Finally, we briefly
discuss removals of the sky RFI, the leakage of sidelobes from off-field strong
radio sources with time-invariant power and a featureless spectrum. It turns
out that state of the art technique should allow us to detect and mitigate RFI
to a satisfactory level in present low frequency interferometer observations
such as those acquired with the 21CMA, and the accuracy and efficiency can be
greatly improved with the employment of low-cost, high-speed computing
facilities for data acquisition and processing.
