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The zero field splitting (ZFS) quantifies the energy difference for the ground electron spin-triplet of a nitrogen-vacancy center in the absence of external fields. The values of the ZFS play a key role in determining the Larmor precession of the Bloch sphere and the Rabi oscillation of a spin system. The ZFS is generally detected using coherent spin manipulation by sweeping microwaves (MWs) at frequencies close to resonance with the ZFS. In this letter, we report our experimental observations of the red-shift effect on the ZFS as a function of the MW power for two different thermal environments of a sample. We find an asymptotic property of the red shifts of the ZFS. Given the identical initial thermal equilibrium states of the sample, the differences in the raw values of the ZFS between the two cases randomly vary from 47 kHz to 1505 kHz over the entire experimental range. According to the asymptotic approximation, the differences are reduced to 29-166 kHz with a standard deviation of 49 kHz, suggesting a significant elimination of the red-shift effect. To the best of our knowledge, no other study has addressed the quantification and elimination of the red shift-effect of the MW field dependence using the asymptotic approximation.

Owing to the ubiquity of cellular communication signals, positioning with the fifth generation (5G) signal has emerged as a promising solution in global navigation satellite system-denied areas. Unfortunately, although the widely employed antenna arrays in 5G remote radio units (RRUs) facilitate the measurement of the direction of arrival (DOA), DOA-based positioning performance is severely degraded by array errors. This paper proposes an in-situ calibration framework with a user terminal transmitting 5G reference signals at several known positions in the actual operating environment and the accessible RRUs estimating their array errors from these reference signals. Further, since sub-6GHz small-cell RRUs deployed for indoor coverage generally have small-aperture antenna arrays, while 5G signals have plentiful bandwidth resources, this work segregates the multipath components via super-resolution delay estimation based on the maximum likelihood criteria. This differs significantly from existing in-situ calibration works which resolve multipaths in the spatial domain. The superiority of the proposed method is first verified by numerical simulations. We then demonstrate via field test with commercial 5G equipment that, a reduction of 46.7% for 1-${\sigma}$ DOA estimation error can be achieved by in-situ calibration using the proposed method., Comment: 14 pages, 11 figures, accepted by IEEE Transactions on Microwave Theory and Techniques

Channel-state-information-based localization in 5G networks has been a promising way to obtain highly accurate positions compared to previous communication networks. However, there is no unified and effective platform to support the research on 5G localization algorithms. This paper releases a link-level simulator for 5G localization, which can depict realistic physical behaviors of the 5G positioning signal transmission. Specifically, we first develop a simulation architecture considering more elaborate parameter configuration and physical-layer processing. The architecture supports the link modeling at sub-6GHz and millimeter-wave (mmWave) frequency bands. Subsequently, the critical physical-layer components that determine the localization performance are designed and integrated. In particular, a lightweight new-radio channel model and hardware impairment functions that significantly limit the parameter estimation accuracy are developed. Finally, we present three application cases to evaluate the simulator, i.e. two-dimensional mobile terminal localization, mmWave beam sweeping, and beamforming-based angle estimation. The numerical results in the application cases present the performance diversity of localization algorithms in various impairment conditions.

In ground-based extensive air shower experiments, the direction and energy are reconstructed by measuring the relative arrival time of secondary particles, and the energy they deposit. The measurement precision of the arrival time is crucial for determination of the angular resolution. For this purpose, we need to obtain a precise relative time offset for each detector, and to apply the calibration process. The time offset is associated with the photomultiplier tube, cable, relevant electronic circuits, etc. In view of the transit time through long cables being heavily dependent on the ambient temperature, a real-time calibration method for the cable transit time is investigated in this paper. Even with a poor-resolution time-to-digital converter, this method can achieve high precision. This has been successfully demonstrated with the Front-End-Electronic board used in the Daya Bay neutrino experiment.