Delay Calibration in Software-Defined Radios for High-Accuracy Microwave Ranging

Localization is an important aspect in a number of sensing applications, including distributed antenna arrays where inter-node range accuracy on the order of lambda/15 is required to support distributed beamforming. For microwave frequencies, this leads to range accuracies of cm or mm. When ranging is implemented in commercial hardware such as software-defined radios, the additional delays incurred within the system must be accurately characterized to ensure that delays proportional to lambda/15 are accounted for. In this paper, we implement a calibration approach that uses internal crosstalk between channels in a commercial software-defined radio to determine systematic latencies. Using linear-frequency modulated pulses, we demonstrate the ability to estimate hardware-induced ranging errors with a standard deviation of 6.245 mm using 10 linear-frequency modulated pulses with a time-bandwidth product of 850 at various carrier frequencies. When used for distributed antenna arrays, this delay estimation error supports distributed beamforming at frequencies up to 3.2 GHz.