Non-coherent energy detectors are motivated for impulse radios with simple circuitry. A performance degradation arises from the threshold effect at low SNR. Here, the phase-locked loop (PLL) is applied to estimate the time-of-arrival (TOA) of received impulses. In the schemes, the impulses received are processed as the excitation signals in the sampled phased-locked loop. Furthermore, the principle of phase-locked frequency multiplier is introduced to improve the precision of TOA estimation, and an iterative algorithm is proposed to acquire the first arrival in multipath environment. The mean-square-error of the proposed TOA estimation is analyzed and verified by the simulations.
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