  The design and experimental implementation of a waveform for high-accuracy
inter-node ranging in a coherent distributed antenna array is presented. Based
on a spectrally-sparse high-accuracy ranging waveform, the presented
multi-frequency waveform enables high-accuracy ranging between multiple nodes
in an array simultaneously, without interference. The waveform is based on a
unique time-frequency duplexing approach combining a stepped-frequency waveform
with different step cycles per node pair. The waveform also inherently includes
beneficial disambiguation properties. The ambiguity function of the waveform is
derived, and theoretical bounds on the ranging accuracy are obtained.
Measurements were conducted in software-defined radio-based nodes in a
three-element distributed array, demonstrating high-accuracy unambiguous
ranging between two slave nodes and one master node.
