Abstract
The eLoran system is an international standardized positioning, navigation, and timing service system, which can complement global navigation satellite systems to cope with navigation and timing warfare. The eLoran receiver measures time-of-arrival (TOA) through cycle identification, which is key in determining timing and positioning accuracy. However, noise and skywave interference can cause cycle identification errors, resulting in TOA-measurement errors that are integral multiples of 10 μs. Therefore, this article proposes a cycle identification method in the joint time–frequency domain. Based on the spectrum-division method to determine the cycle identification range, the time–domain peak-to-peak ratio and waveform matching are used for accurate cycle identification. The performance of the method is analyzed via simulation. When the signal-to-noise ratio (SNR) ≥ 0 dB and skywave-to-groundwave ratio (SGR) ≤ 23 dB, the success rate of cycle identification is 100%; when SNR ≥ −13 dB and SGR ≤ 23 dB, the success rate exceeds 75%. To verify its practicability, the method was implemented in the eLoran receiver and tested at three test sites within 1000 km using actual signals emitted by an eLoran system. The results show that the method has a high identification probability and can be used in modern eLoran receivers to improve TOA-measurement accuracy.
Highlights
With continuous improvements in informatization, positioning, navigation, and timing (PNT) systems have become indispensable for social development and modern national defense infrastructure, reflecting a country’s international status and comprehensive strength [1,2,3]
When a global navigation satellite systems (GNSS) signal is unavailable, the enhanced long-range navigation (eLoran) system can be used as a backup, which reduces the risk caused by relying on GNSS; this allows for coping with timing warfare and navigation
After adding noise to the signal, the signal-to-noise ratio (SNR) of groundwave was −5 the amplitude ratio of the skywave to the groundwave was skywave-to-groundwave ratio (SGR) = 10 dB; the time-delay dB; the amplitude ratio of the skywave to the groundwave was SGR = 10 dB; the timedifference between the skywave and the groundwave was ∆T = 62.5 μs; and the sampling delay difference between the skywave and the groundwave was ∆ = 62.5 μs; and the rate of the simulation process signal was f s = 2 MHz
Summary
With continuous improvements in informatization, positioning, navigation, and timing (PNT) systems have become indispensable for social development and modern national defense infrastructure, reflecting a country’s international status and comprehensive strength [1,2,3]. The enhanced long-range navigation (eLoran) system evolved from the Loran-C system It is an internationally standardized medium and a long-range land-based radio system [7,8]. It can satisfy the requirements of PNT applications in most fields in terms of accuracy, reliability, and continuity. It can provide a time service better than 100 ns and a position service of 20 m after differential correction [7,9]. When a GNSS signal is unavailable, the eLoran system can be used as a backup, which reduces the risk caused by relying on GNSS; this allows for coping with timing warfare and navigation
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