High-Accuracy Unambiguous Localization Using Spectrally Sparse Code-Modulated Signals

Open-loop coherent distributed antenna arrays require that the localization error between the nodes is λ/15 or less to achieve 90% coherent gain with high probability, leading to ranging accuracies on the order of cm for beamforming at microwave frequencies. We present a ranging system using two code-modulated tones generated on separate transceivers in software-defined radio for unambiguous high-accuracy localization of nodes in distributed antenna arrays. The best peak-to-sidelobe level was -0.89 dB with the code-modulated waveform compared to -0.11 dB for a standard two-tone waveform, each with a frequency separation of 10 MHz. This increased suppression, though minimal in a traditional radar detection sense, is significant for cooperative ranging between nodes in a distributed array. The code-modulated two-tone waveform achieved a range accuracy below 3 cm in a wireless ranging setup.