Range-Independent TDOA Localization Using Stepwise Accuracy Enhancement Under Speed Uncertainty

This study proposes a stepwise accuracy enhancement (SAE) method for jointly estimating signal propagation speed, near-field position, and far-field direction-of-arrival (DOA) without requiring prior source range knowledge. Time difference of arrival (TDOA) methods excel at near-field localization but are limited in the far field by the thresholding effect. The modified polar representation (MPR) framework mitigates this limitation by unifying near and far field localization. However, previous MPR-based studies assumed known propagation speed, often impractical. SAE overcomes this by treating propagation speed as an unknown parameter to be concurrently estimated with source location. SAE formulates this joint estimation as a quadratically constrained quadratic optimization (QCQP) problem, then mitigates the parameter estimation bias by minimizing the impact of TDOA measurement errors. Simulations validate the effectiveness of SAE for joint estimation irrespective of source range, achieving the Cramer-Rao lower bound (CRLB) in small noise.