Carrier phase estimation in real-time Global Navigation Satellite System (GNSS) receivers is usually performed by tracking loops due to their very low computational complexity. We show that a careful design of these loops allows them to operate properly in high-dynamics environments, that is, accelerations up to 40？g or more. Their phase and frequency discriminators and loop filter are derived considering the digital nature of the loop inputs. Based on these ideas, we propose a new loop structure named Unambiguous Frequency-Aided Phase-Locked Loop (UFA-PLL). In terms of tracking capacity and noise resistance UFA-PLL has the same advantages of frequently used coupled-loop schemes, but it is simpler to design and to implement. Moreover, it can keep phase lock in situations where other loops cannot. The loop design is completed selecting the correlation time and loop bandwidth that minimize the pull-out probability, without relying on typical rules of thumb. Optimal and efficient ways to smooth the phase estimates are also presented. Hence, high-quality phase measurements—usually exploited in offline and quasistatic applications—become practical for real-time and high-dynamics receivers. Experiments with fixed-point implementations of the proposed loops and actual radio signals are also shown. 1. Introduction A fundamental task of every Global Navigation Satellite System receiver is to synchronize with the visible satellite signals. Since Direct Sequence Spread Spectrum (DS-SS) signals are utilized, code and carrier synchronization is required, but a correlation stage is necessary to despread the signals before the synchronization algorithms can be applied. In real-time receivers the required economy of operations usually precludes the use of complex estimation schemes and tracking loops are preferred. Due to the correlation process these loops are necessarily discrete. The typical trade-off in tracking loop design is bandwidth versus dynamic performance: output noise increases with a larger loop bandwidth, while dynamic tracking error decreases with it [1]. Thus, the loop design becomes particularly challenging when the receivers are subject to high dynamics. To overcome this limitation other receiver structures have been proposed in [1], claiming tracking capability up to 150？g of acceleration, in contrast with the 5？g regularly assigned to tracking loops. However, the required computational burden is large since several simultaneous correlations and Fast Fourier Transform (FFT) computations are needed. In this paper we show a careful design of the
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