Evaluation of the Use of Low Precision Floating-Point Arithmetic for Applications in Radio Astronomy

Abstract

Conventionally, the front-end Digital Signal Processing (DSP) for applications in radio astronomy employed low-precision fixed-point arithmetic. However, the next-generation large-scale projects for radio astronomy such as the Square Kilometre Array (SKA), Atacama Large Millimeter/sub-millimeter Array (ALMA) upgrade and the proposed next-generation Very Large Array (ngVLA) have ambitious science goals that require higher sensitivities that in turn require high-precision arithmetic implementations. Also, the increasing strength, bandwidth and number of sources of Radio Frequency Interference (RFI) exacerbate the need for high-precision arithmetic. These factors lead to higher cost and power and longer design cycles for the DSP systems in radio astronomy. Meanwhile, hardware manufacturers are offering native support for low-precision floating-point number formats such as float16 and bfloat16 and variants of those. In addition to those, ‘posits’, a new number representation has been introduced by John Gustafson and is claiming to offer better accuracy compared to float16 under certain conditions. With these compact data formats, it is expected that signal processing systems to consume lower power and resources. For typical radio astronomical observations, the achievable sensitivity is determined by the ability to suppress RFI and the accuracy of delay correction. In the following, these two ‘qualitative’ aspects are studied for the front-end DSP modules of the SKA correlator and beamformer where the coefficients are represented with float16, bfloat16, variants of those formats and posit16 and compared against the current fixed-point representation.