arXiv subjects

Phichai Youplao

Publications and source records attributed to Phichai Youplao.

4 recordsLinked to original sources

arXiv2026

Continuous Intra-Symbol Phase Noise Tracking for THz OFDM via Polynomial Reconstruction

Terahertz (THz) communication systems for sixth-generation (6G) networks are severely impaired by Wiener phase noise (WPN), whose innovation variance at sub-THz carriers is substantially larger than in millimeter-wave 5G systems. Conventional common-phase-error (CPE) compensation applies a single phase rotation per OFDM symbol and becomes inadequate when the phase trajectory varies significantly within the symbol duration. This letter proposes continuous phase trajectory reconstruction (CPTR), a closed-form intra-symbol phase noise tracking method that reconstructs the sample-level phase trajectory from pilot observations via least-squares polynomial fitting with $\mathcal{O}(N_p+N)$ complexity. We characterize the polynomial approximation error under WPN and derive the Cramér--Rao bound (CRB) for polynomial phase coefficient estimation, showing that CPTR is minimum-variance unbiased within the polynomial surrogate model. Simulations at 300~GHz with \textit{N}~=~1024 and 16-QAM show that CPTR remains within 0.2~dB of the CRB across SNR~=~10--45~dB while achieving significantly lower complexity than Kalman-based tracking and substantial BER gains over CPE, linear interpolation, and cubic spline methods.

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arXiv2026

Innovation-Domain Decision-Directed Phase Tracking for Wiener Phase Noise in Fast Rayleigh Fading

This letter proposes an innovation-domain decision-directed phase tracking (ID-DDPT) architecture for coherent detection over Rayleigh fading channels with temporally correlated phase evolution and Wiener phase noise. By reformulating phase tracking into the innovation domain, replacing the unbounded cumulative phase with its stationary increments, the proposed method converts a non-stationary estimation problem into a stable low-complexity filtering problem. A closed-form expression for the steady-state residual phase error variance is derived under the locked-regime assumption, along with an analytical optimal smoothing factor. Modeling the residual phase distortion as an effective signal-to-noise ratio (SNR) attenuation yields a tractable bit error rate (BER) approximation for BPSK over Rayleigh fading. A first-order error-propagation analysis further characterizes the impact of decision errors and provides insight into the onset of cycle slips. Simulation results demonstrate that ID-DDPT outperforms DBPSK and a complexity-equivalent scalar Kalman tracker (SKT), achieving near-coherent performance with $\mathcal{O}(1)$ per-symbol complexity and minimal pilot overhead.

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arXiv2026

Noise-Robust Frequency Estimation via Overlapped Sampling-Intervals Zero-Crossing Fitting

The trade-off between noise averaging and temporal resolution fundamentally limits conventional zero-crossing frequency estimators under dynamic and noisy conditions. This paper presents an overlapped sampling-intervals zero-crossing fitting method (OS-ZFM), which introduces a structured overlapping regression framework that decouples noise averaging from temporal update rate. The method adopts a deterministic closed-form formulation, enabling a unified bias-variance analysis to characterize the statistical behavior of the estimator and clarify the role of structured data reuse. Numerical results under intensity and background noise at a signal-to-noise ratio (SNR) of 10 dB show that OS-ZFM reduces median estimation error by more than 60\% compared to conventional zero-crossing fitting methods at the same temporal resolution. It further achieves up to 90\% reduction relative to basic zero-crossing detection and consistently yields lower estimation errors than Hilbert-transform-based estimators. Experimental validation utilizing impact-induced transient motion measured by laser Doppler interferometry demonstrates that OS-ZFM reconstructs smooth and physically consistent trajectories with improved temporal fidelity. Owing to its low computational complexity and deterministic formulation, the proposed method enables accurate real-time frequency and acceleration tracking in resource-constrained measurement systems.

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arXiv2024

An Optical Method for Evaluating the Mechanical Properties of Wires Under Impact Tensile Load

The dynamic properties of materials utilized in architecture or engineering applications can significantly affect their performance under dynamic or impact loading conditions. To evaluate such behavior, force transducers are commonly employed in testing. However, the calibration of force transducers is typically limited to static conditions and relies solely on gravitational forces exerted on standard masses. Thus, assessing the uncertainty in force measurements using force transducers during dynamic loading conditions remains a challenging task, presenting a significant obstacle in accurately characterizing the dynamic behavior of materials. In this work, an optical technique to evaluate the mechanical properties of wires subjected to impact tensile loads is presented. The wire under test is subjected to an impact tensile load by applying the inertial force of a rigid mass, which is supported by utilizing an aerostatic linear bearing with sufficiently small friction. The inertial force applied to the wire can be determined by multiplying the mass of the rigid mass by its acceleration, where the acceleration can be measured employing a Michelson type optical interferometer. The performance of the proposed method is demonstrated through experiments and analysis of the dynamic characteristics of a tungsten wire under impact tensile loading conditions.

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