Search Results (194)

A software tool for realistic simulation of DDS output phase noise under non-ideal conditions is presented. Unlike approaches that rely solely on ideal clock scaling or require detailed device-specific characterization, the proposed method combines an ideal scaled contribution with an optional quantization floor and a compact phenomenological residual-noise model that captures output-stage limitations. The tool accepts sparse clock phase-noise data and DDS parameters, reconstructs the output spectrum, and exports ADIsimPLL-compatible models. Validation against AD9912 (50 MHz, 150 MHz) and AD9915 (123 MHz, 978 MHz) datasheet curves shows agreement within 2–3 dB for most offsets, with deviations up to 5 dB only at 10 Hz for the 978 MHz case. The approach enables phase-noise reconstruction from limited published data and supports hybrid DDS-driven PLL synthesizer studies. Full article

This paper proposes a AOA-assisted TDOA localization method based on an improved whale optimization algorithm (IWOA) combining TDOA and AOA for asynchronous wireless sensor networks (WSNs). A TDOA compensation scheme is first introduced to address network asynchrony. This scheme uses the communication timestamps between anchor nodes to estimate relative clock deviations and clock offsets. Then, a fusion algorithm using the compensated TDOA and AOA measurements enables high-precision localization with only two angle-measuring anchor nodes and a set of TDOA anchor nodes, reducing the number of required anchor nodes and improving deployment flexibility. Finally, the integration of IWOA enhances the optimization process, improving robustness. Simulations demonstrate that the proposed IWOA achieves superior robustness and accuracy under severe noise and adverse geometric conditions, significantly outperforming the Chan algorithm and other metaheuristic benchmarks. Meanwhile, the CWLS algorithm exhibits competitive performance in well-calibrated scenarios, revealing their complementary characteristics. The proposed method provides an effective solution for asynchronous WSNs, especially in challenging measurement environments. Full article

Adder neural networks remove multiplication from convolution, yet their direct L1-distance datapath still requires subtraction, absolute-value generation, and wide accumulation. We address this cost by mapping the online L1 operation to minimum selection and time-domain accumulation. The proposed accelerator processes a $3\times 3\times 16$ window for 16 output channels with 6-bit weights and activations. Each 6-bit minimum is divided into two 3-bit slices. A dual-mode digital-to-time converter (DM-DTC) encodes the most-significant slice in high-linearity (HL) mode and the least-significant slice in low-power (LP) mode. Readout is performed by a shared-clock time-to-digital converter (SC-TDC), in which one Gray-code time reference serves all paths while local latches preserve independent channel results. The training model reproduces code-dependent DTC nonlinearity, process–voltage–temperature variation, jitter, channel offset, TDC quantization, saturation, and scale mismatch. The architecture thereby combines significance-aware time encoding, channel-scalable readout, and hardware-aware adaptation. Post-layout simulations in 55 nm show that the 0.359 mm², 13.7 Kb design operates at 0.7–1.2 V and 5–30 MHz, consumes 0.025–0.324 mW, and achieves 43.2–94.3 TOPS/W. The normalized figure of merit is 6.01–13.09 POPS/W·bit². On CIFAR-10/ResNet-20, hardware errors reduce the baseline accuracy from 92.71% to 86.26%; error-aware training achieves 91.53%. Full article

Time synchronization plays a critical role in enabling coordinated control and accurate data fusion in the Industrial Internet of Things (IIoT). However, most existing time-triggered synchronization protocols rely on periodic information exchange, which leads to considerable communication and energy consumption, particularly in large-scale and resource-constrained deployments. To address these limitations, this study proposes an adaptive event-triggered time synchronization scheme that eliminates the need for periodic communication. Unlike conventional approaches that employ fixed or predefined time-varying thresholds, the proposed method constructs a fully distributed triggering mechanism based on both local clock evolution and synchronization discrepancies observed from neighboring nodes. The triggering threshold evolves automatically according to the network synchronization state and does not require additional coordination messages. Theoretical analysis shows that the logical clock skews asymptotically converge to a common value, while the logical clock offset disagreement is ultimately bounded within an explicitly characterized neighborhood. Simulation results demonstrate that the proposed scheme achieves a more effective balance between synchronization accuracy and communication overhead, while producing more evenly distributed triggering events than several representative event-triggered synchronization methods. Full article

Existing target sorting methods suffer severe performance degradation or even failure under inherent severe spectrum overlap, homogeneous protocol parameters, and scarce single-source points in Synchronous Non-Orthogonal Frequency Hopping (SNOFH) scenarios. To address this challenge, this paper proposes a passive sorting framework for SNOFH UAV swarm signals based on multi-station relative hopping time difference. The proposed framework constructs a spatial-location-driven sorting feature system, designs a kernel joint distribution adaptation module to eliminate inter-station measurement discrepancies, and develops a multi-scale wavelet-based method to achieve sub-sampling level hopping time extraction, reducing the dependence on prior FH parameters and hardware radio frequency fingerprints. Experimental comparisons between the proposed and reference sorting methods are conducted on a simulated SNOFH dataset to validate the performance of the proposed sorting framework. The experimental results show that the proposed method achieves the highest sorting accuracy of 98%, outperforming adopted baselines in most SNOFH cases. The proposed method exhibits favorable robustness with noise interference, clock-synchronization error, carrier-frequency offset and multipath influence. It is a suitable choice for UAV swarm sorting under regular and slow-varying UAV formations. Full article

The current use of artificial light during the natural dark phase has acquired contaminant dimensions, known as “light pollution”. It is well known that exposure to dim light at night (dLAN) during the postnatal period severely impairs the immune system and related organs, but few reports have demonstrated the effects of dLAN during the fetal period. This study, therefore, examines whether exposure to dim light at night during two critical developmental windows (i.e., prenatal and postnatal periods) leads to long-lasting dysregulation of circadian, behavioral, and immune organization, as well as spleen immune responses, in early adulthood. To address this question, these outcomes were assessed using two defined sampling time points. To answer this question, we exposed two groups of C57BL/6J male mice to dim night light during the gestational and postnatal periods and compared them with control groups that were exposed to light–dark conditions (12 h each, LD). Parametric and non-parametric activity/rest values were analyzed with circular statistics. Compared to their controls, we found differences in alpha, onset, offset, M10, and L5 start time in dLAN groups. We also assessed the transcript levels of clock genes and inflammatory mediators in spleen tissue and found a dampening of daily variation in mRNA expression in both experimental groups. Finally, we used an ovalbumin (OVA) allergy challenge to test the B-cell response in the spleen and found a significantly higher cell recruitment to the spleen and more anti-OVA IgE. Together, these results clearly show that dLAN, at two ZT sampling points, affects peripheral molecular clocks and responses in the spleen, and that these effects are independent of the life stage at which exposure to dim light at night occurs. Full article

As the modulation rate in high-speed optical communication systems continues to increase and modulation formats become increasingly complex, conventional electrical-domain sampling techniques, limited by the “electronic bottleneck,” are unable to meet the time-domain analysis requirements of optical vector signals with bandwidths exceeding 100 GHz. In this paper, a system based on linear optical sampling (LOS) is implemented for time-domain analysis of high-speed polarization-division-multiplexed (PDM) optical vector signals. An unbalanced input method is proposed to ensure the integrity of the sampling clock when the power of the signal under test is zero; a resampling method combined with soft integration is proposed to replace the conventional peak detection method, improving the accuracy of sampling point position and amplitude information extraction; and an adaptive frequency offset estimation algorithm is proposed to compensate for the continuously varying frequency offset caused by the use of low-repetition-rate sampling pulses. We constructed a signal acquisition system for optical vector signal measurement based on LOS. Using the above methods, the eye diagrams and constellation diagrams of 50 Gbaud PDM-QPSK (quadrature phase-shift keying), PDM-16QAM (quadrature amplitude modulation), and PDM-32QAM signals are successfully measured, and related parameters, including error vector magnitude (EVM) and signal-to-noise ratio (SNR), are calculated. The experimental results show that the proposed system achieves quasi-real-time measurement of 500 Gbps optical vector signals, and the measured performance parameters are on the same order of magnitude as those obtained from a commercial high-speed oscilloscope. Full article

High-precision time synchronization among high-dynamic platforms is an important foundation for distributed detection, cooperative sensing, and networked operation of high-speed mobile platforms. In high-dynamic two-way microwave links, rapid variations in propagation geometry, Doppler-related frequency offsets, and link-quality fluctuations can break the approximate symmetry between uplink and downlink propagation. Although geometric and motion compensation can remove the dominant propagation-asymmetry term, residual asymmetric errors caused by propagation modeling errors, compensation mismatch, and link degradation may still remain and couple into clock-offset estimation, thereby reducing synchronization stability and accuracy. To address this problem, this paper proposes a modeling and joint estimation method for residual asymmetric errors in high-dynamic two-way microwave links. The post-compensation residual error is modeled as a recursively estimable dynamic state, and its rate of change is introduced to characterize the short-term evolution of the residual term. Meanwhile, a four-timestamp and frequency-offset joint observation model is constructed, in which frequency-offset information is used as an observation-level auxiliary constraint to enhance local separability among the clock offset, frequency offset, and residual link state. On this basis, a link-state-information-assisted IMM-IEKF is adopted to realize online joint estimation of clock parameters and link residual errors. Under the equivalent stochastic-error simulation setting, the proposed method effectively suppresses post-compensation residual asymmetric errors and achieves sub-nanosecond synchronization accuracy under strong-dynamic and degraded-link conditions. Full article

High-precision satellite clock offset prediction is a core prerequisite for the BeiDou-3 Global Navigation Satellite System to achieve precise single-point positioning and timing. However, because of space radiation and the physical aging of the clock itself, the operational state of onboard atomic clocks exhibits a high degree of physical heterogeneity and time-varying drift characteristics. Traditional physical models struggle to capture complex nonlinear residuals, while existing deep learning methods often face boundary discontinuities caused by baseline separation when handling long-sequence forecasts. Furthermore, channel crosstalk in multivariate prediction and insufficient sensitivity to dynamic multiscale features limit the robustness of long-term predictions. To address these issues, this paper proposes a clock offset prediction architecture that integrates physically motivated statistical constraints with dynamic adaptive feature learning. Extensive experiments conducted using real BDS-3 precise clock difference products provided by Wuhan University demonstrate that the proposed method effectively mitigates the performance degradation often observed in existing models on heterogeneous satellites during the evaluated period. In the 24-h extrapolation task, the architecture achieved an average root-mean-square error as low as 0.507 ns, significantly improving prediction accuracy. It outperformed mainstream physical models and advanced deep learning baseline algorithms, providing a promising framework with good interpretability for high-precision clock error forecasting under dynamic space weather conditions. Full article

Frequency synthesis is an important aspect of an atomic clock. It is also imperative that the synthesized frequency exhibits good short term stability or, in other words, exhibits good phase noise. Conventionally single-PLL-system-based approaches have been made for realizing the frequency synthesizers required for hydrogen maser atomic clocks. In this article, a novel approach involving a master–slave-based phase-locked loop (MSPLL) method is presented for frequency synthesis in a hydrogen maser atomic clock. The novelty of this paper lies in the fact that the way two phase-locked loops are coupled to obtain advantage in improving the master oscillator’s stability to match maser physics subsystem stability and at the same time achieving lower jitter by the design. The design involves the usage of a master and a slave phase-locked loop with coupled custom designed direct digital synthesizers for ensuring that the hydrogen maser’s frequency stability is transferred to the master oscillator. The slave PLL (SPLL) generates a low jitter clock for the master PLL (MPLL), thereby guaranteeing reliable tracking of the input reference of 10 MHz, obtained by down-converting the maser physics subsystem frequency of ∼1.4 GHz. A novel mathematical model was derived for the proposed MSPLL design which aids in determination of the settling time of phase, which in turn, leads to the investigation of jitter variance in time domain. A detailed study and analysis of the settling time, phase noise in frequency domain, phase jitter in time domain. and stability performance is presented. The results were validated by the experimental data. The realized frequency synthesizer deduced a settling time of phase that can be adjusted between 689 $\mathsf{\mu }$s to 811 $\mathsf{\mu }$s. The synthesized frequency’s phase noise is ≤−114 dBc/Hz at 1 Hz offset, and it was observed that this design induces a very low phase noise to the output signal with respect to the physics subsystem. The achieved short-term stability of the output signal at 1 s is approximately (7.66 × ${10}^{-12}$) ${\tau }^{-1/2}$, which is very close to the physics subsystem stability. In terms of stability degradation factor, the proposed MSPLL design exhibits an excellent short-term stability that is one order better than that of the existing methods. Full article

The BeiDou-3 (BDS-3) Precise Point Positioning service (PPP-B2b) can realize decimeter-level positioning by broadcasting satellite orbit, clock offset, and code bias corrections via GEO satellites, enabling PPP without reliance on ground communication networks. However, the current PPP-B2b service only provides corrections for BDS-3 and GPS satellites, which limits the number of available satellites and may affect positioning performance in challenging environments. To further enhance the positioning performance, we propose to incorporate Galileo observation into the PPP-B2b positioning. A PPP model integrating PPP-B2b service and broadcast ephemeris was established. First, the accuracy of the Galileo broadcast ephemeris was evaluated using precise orbit and clock products as references. The results show that the mean signal-in-space range error (SISRE) standard deviation of Galileo broadcast ephemeris is 0.30, which is only a little worse than that of GPS from PPP-B2b service. Then, the positioning experiments were conducted under different elevation cutoff angles. The experiments were conducted using data from 94 reference stations in China over a 7-day period. The results demonstrate that the inclusion of Galileo satellites significantly increases the number of visible satellites and improves satellite geometry. Compared with the BDS-3/GPS dual-system PPP solution, the BDS-3/GPS/Galileo triple-system PPP solution reduces the horizontal convergence time by approximately 13.70–16.67% and the vertical convergence time by about 18.75–20.00% under cutoff angles from 7° to 30° based on the 68th percentile statistics. The 95th percentile results further confirm the advantage of the triple-system solution under a more stringent statistical criterion. Where convergence is achieved, the triple-system solution reduces the horizontal convergence time by approximately 6.0–7.3% and the vertical convergence time by about 15.3–26.0%. Moreover, the triple-system solution exhibits a smaller re-convergence jump under abnormal observation conditions. In addition, under high elevation cutoff conditions, the introduction of Galileo satellites effectively improves PPP availability, thereby enhancing the continuity and robustness of PPP. These results indicate that incorporating Galileo observation within the PPP-B2b framework can effectively improve PPP performance and provide a simple and practical approach for high-precision real-time positioning. Full article

In global navigation satellite systems (GNSS), the system time reference is maintained by the ground control segment and kept traceable to UTC, enabling inter-system compatibility and interoperability. Advances in onboard atomic-clock stability and inter-satellite time transfer accuracy make it feasible for a constellation to autonomously realize a space-based time reference, with periodic traceability updates and steering via satellite–ground links to enhance resilient time maintenance. BeiDou-3 (BDS-3) carries high-performance onboard hydrogen masers and Ka-band inter-satellite links (ISL) for time transfer, providing stable frequency sources and high-precision time transfer capability for establishing a space-based time reference. Using in-orbit BDS-3 clock offset data, we propose a space-based autonomous timekeeping approach that combines high-precision ISL synchronization with timekeeping by a small ensemble of hydrogen masers, together with a space–ground cooperative strategy with BeiDou time (BDT). The approach first performs constellation-wide synchronization using ISL, then selects a timekeeping ensemble based on in-orbit clock performance to generate a space-based ensemble atomic timescale, denoted TA(SPACE); when satellite–ground links are available, TA(SPACE) is steered to BDT to maintain consistency with the ground time reference. Based on this space-based time reference, satellite clock offsets are predicted to generate clock-parameter products. Experiments show that, in the autonomous mode, the time offset between TA(SPACE) and BDT is kept within 25.06 ± 41.47 ns over 90 days, whereas in the space–ground cooperative mode, satellite–ground steering stabilizes the offset within 10 ns. The proposed approach provides a practical solution for constellation time maintenance under disruptions such as anomalous ground injection, improving the resilience and reliability of GNSS services. Full article

The rapid development of 6G wireless networks requires ultra-high data rates that traditional microwave frequencies cannot support. Photonics-assisted terahertz (THz) technologies offer a promising solution by combining high-capacity optical fibers with wideband wireless transmission. However, as bandwidth expands, sampling frequency offset (SFO) becomes a critical issue that degrades signal quality in single-carrier systems. This paper evaluates the performance of two main compensation methods within a photonics-assisted THz system operating at 320 GHz. We compare the Gardner clock recovery algorithm and the Digital Interpolation Compensation Algorithm (DICA) across various modulation formats and offset levels. Our findings indicate that the Gardner algorithm is effective for low-order modulation when the SFO is below 100 ppm, but its performance fails outside this range. Conversely, the DICA provides robust compensation up to 1000 ppm regardless of the modulation format, provided that the exact offset value is known. Without proper compensation, the system BER increases significantly as the SFO grows. These results demonstrate the complementary nature of these two algorithms and provide a practical guide for selecting compensation strategies in future high-speed THz communication links. Full article

This paper presents a novel dual-mode memristor-based ring oscillator designed for energy-efficient, wireless biomedical signal conditioning systems. The proposed architecture leverages a compact DTMOS memristor emulator, consisting of only two transistors and one capacitor, to replace the conventional NMOS pull-down devices in a three-stage PMOS ring oscillator. This integration enables two distinct operating modes within a single compact core: a fixed-frequency mode for stable clock generation and carrier synthesis, and a programmable chirp mode for frequency-modulated signal generation. The fixed-frequency mode achieves continuous tuning from 3.142 GHz to 4.017 GHz via varactor control, with an ultra-low power consumption of only 111 µW at 4.017 GHz. The chirp mode generates linear frequency sweeps starting from 0.8 GHz, with the sweep range independently controllable through the state capacitor value and the pulse width of the control signal (SW_Chirp). Designed in a standard 0.18 µm CMOS process, the oscillator exhibits a low phase noise of −87.82 dBc/Hz at a 1 MHz offset for the three-stage configuration, improving to −94.3 dBc/Hz for the five-stage design. The overall frequency coverage spans 0.8–4.017 GHz, representing a 133.6% fractional range. The calculated figure of merit (FoM) is −169.45 dBc/Hz. Experimental validation using a discrete CD4007 prototype confirms the oscillation principle, while comprehensive simulations demonstrate robust performance across process corners and temperature variations. With its zero-static-power memristor core, wide tunability, and dual-mode reconfigurability, the proposed oscillator is ideally suited for multi-standard wireless biomedical applications, including implantable telemetry, neural stimulation, ultra-wideband (UWB) transmitters, and non-contact vital sign monitoring. Full article

Time synchronization is a fundamental requirement for the reliable operation of Control and Data Acquisition Systems (CODASs) in large-scale fusion experiments such as the Divertor Tokamak Test (DTT). Distributed diagnostics, sensors, and control subsystems must share a unified time reference to guarantee deterministic data acquisition and stable plasma control. This paper presents the FPGA-based implementation and evaluation of a synchronization system that combines the IEEE 1588 Precision Time Protocol (PTP) with Pulse Per Second (PPS) generation. The proposed platform is built on Zynq UltraScale+ Kria KR260 System-on-Modules (SOMs) running a customized PetaLinux distribution with LinuxPTP utilities. Hardware timestamping is enabled through the integrated Timestamping Unit (TSU) in the Gigabit Ethernet MAC, while a hardware logic module generates PPS signals from the synchronized PTP clock. Experimental validation demonstrates nanosecond-level synchronization with an RMS timing accuracy of approximately 8.5 ns. A detailed analysis of PPS offset, network path delay, and servo adjustments confirms stability of the timing system. The proposed design offers a low-cost, flexible, fully customizable and controllable solution for distributed diagnostic and control systems in fusion facilities. Full article