Wavelet transform performs frequency transform with different time window widths to enable accurate time-frequency analysis for sensing. Time and frequency sampling of scalogram are not uniform to eliminate redundancy. One method achieves fine time sampling with fewer operations, but the frequency direction sampling is not uniform or fine, and sidelobes are high. To address these problems, this study proposes a simple wavelet transform with fine time and frequency sampling. The proposed method consists of phase multiplication and signal addition. Frequency transform of any time window width is possible by changing the additive width of the signal. Furthermore, by adding the results, wavelet transform using a triangular window that lowers sidelobes is realized using a small number of complex multiplication operations. When the proposed method is applied to a chirp waveform, the frequency transition of the signal could be finely confirmed.
With the increasing demand for network services, the power consumption of equipment has been steadily rising each year, especially in the access network domain. Passive Optical Networks (PON) traditionally operate on the principle of ensuring service provision to the farthest user. Consequently, performance tends to be excessive for short to medium distances, leading to surplus power consumption. In this study, we address the issue of reducing power consumption in access networks by tackling surplus power. Our approach involves utilizing three different types of Reed-Solomon (RS) decoders to apply appropriate forward error correction (FEC) redundancy based on transmission distance, aiming to lower power consumption of RS decoders in optical network units (ONUs). Subsequently, we evaluated the power saving of FEC decoding in a 10G-class PON and report over 48% average power saving compared to the conventional homogeneous FEC-based network.
This paper investigates the impact of nonlinear optical effects on Time-Domain Single Carrier Index Modulation (TDSC-IM) optical signals in Wavelength Division Multiplexing-Passive Optical Network (WDM-PON) systems that use standard single-mode fibers. Simulations indicate that TDSC-IM optical signals with high peak-to-average power ratio (PAPR) can maintain sufficient signal-to-noise ratios (SNRs) in C-band transmission in optical delivery networks with standard single mode fibers, while O-band transmission suffers larger nonlinear effects. This paper demonstrates that the degradation in the SNRs of the 25 GBaud quaternary phase shift keying (QPSK) based TDSC-IM optical signals can be less than 1dB for 8 wavelength channel WDM-PON systems with 50GHz spacing.
This paper presents a new concept of designing circularly polarized folded reflectarray (CPFRA) antennas. By applying the dual-reflector shaping technique to the CPFRA antennas, the reflection-phase distributions of the two reflecting surfaces comprising the CPFRA antennas are modified to realize low profile, high aperture efficiency, and arbitrary aperture-field distribution simultaneously. Numerical simulations based on the geometrical optics show that the aperture efficiency can be improved up to around 100% by realizing uniform aperture-field distribution and reducing the spillover. Designs of CPFRA antennas with low sidelobe levels are also presented.
Polarimetric synthetic aperture radar (PolSAR) image exhibits a high degree of spatial information. However, the PolSAR image is subjected to speckle noise, which degrades the information quality. A speckle correction filter is proposed in this paper based on spatial polarimetric coherence. Evidence of polarimetric coherence between spatial neighboring pixels is presented. It shows that polarimetric coherence is highly correlated with neighboring pixels. Based on these characteristics, a speckle correction filter is proposed by calculating the polarimetric coherency level on a selected neighboring pixel. A correction is applied to the pixel which has a low polarimetric coherence level. A generalized three-step adaptive filter is proposed, including neighbor selection, coherency criterion, and incoherent correction. The influence of the filter on scattering mechanisms is compared by using eigenvalue-based decomposition. Qualitatively, the result shows the proposed correction filter removes the outliers in the low entropy region. Quantitively the filter can suppress the speckle noise and its variance up to 19.08%.
To build a stable wireless communication system in an indoor environment, it is necessary to perform highly accurate simulations of radio wave propagation characteristics. The ITU-R Recommendation P series, especially ITU-R P.1238, lists estimation models for propagation loss in indoor environments under various conditions. However, there are a few cases in which propagation loss has been measured at various frequencies in the same building and under the same conditions. In these cases, necessary parameters may not be described, meaning that simulation cannot be easily performed. In this paper, we measure the radio wave propagation characteristics on the same floor and across floors for the 922MHz to 28GHz frequency band, which is often used in office spaces. We then apply a path loss model to each frequency and calculate the coefficient of office environment (N) and inter-floor attenuation (Lf(n)).