Abstract
Frequency-locked detector (FLD) has been widely utilized in tracking loops of Global Positioning System (GPS) receivers to indicate their locking status. The relation between FLD and lock status has been seldom discussed. The traditional PLL experience is not suitable for FLL. In this paper, the threshold setting criteria for frequency-locked detector in the GPS receiver has been proposed by analyzing statistical characteristic of FLD output. The approximate probability distribution of frequency-locked detector is theoretically derived by using a statistical approach, which reveals the relationship between probabilities of frequency-locked detector and the carrier-to-noise ratio (C/N0) of the received GPS signal. The relationship among mean-time-to-lose-lock (MTLL), detection threshold and lock probability related to C/N0 can be further discovered by utilizing this probability. Therefore, a theoretical basis for threshold setting criteria in frequency locked loops for GPS receivers is provided based on mean-time-to-lose-lock analysis.
Highlights
In the Global Positioning System (GPS) receiver, the lock detector is usually used to indicate the signal tracking status by comparing with a threshold
The GPS receiver mainly relies on phase locked loop (PLL) and delay locked loop (DLL) to track signal and frequency locked loop (FLL) is a transition part to bridge acquisition and PLL + DLL
The results show that the theoretical thresholds fit well with Frequency-locked detector (FLD) outputs of real signals, which provide a solid support for FLD threshold
Summary
In the Global Positioning System (GPS) receiver, the lock detector is usually used to indicate the signal tracking status by comparing with a threshold. In high performance GPS receivers, such as high dynamic and high sensitivity receivers, the FLL has been widely used when the carrier phase could not be tracked by PLL or aids PLL to track signal [3,4] It indicates the significance of analyzing frequency-locked detector. By neglecting absolute phase error and permitting relative phase rotation of the received signal and the local carrier replica, an FLL can, typically, acquire and track signals that are at higher frequency offsets than a PLL. Our main purpose is to analyze the statistical performance of FLD by mean-time-to-lose-lock approaches, and make comparison with PLD, which has been studied by Jin et al [14]
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