Investigation on global positioning system signal scattering and propagation over the rough sea surface

This paper is devoted to the study of polarization properties, scattering properties and propagation properties of global positioning system （GPS） scattering signal over the rough sea surface. To investigate the polarization and the scattering properties, the scattering field and the bistatic scattering coefficient of modified Kirchhoff approximation using the tapered incident wave is derived in detail. In modeling the propagation properties of the GPS scattering signal in the evaporation duct, the initial field of parabolic equation traditionally computed by the antenna pattern using fast Fourier transform （FFT） is replaced by the GPS scattering field. And the propagation properties of the GPS scattering signal in the evaporation duct with different evaporation duct heights and elevation angles of GPS are discussed by the improved discrete mixed Fourier transform taking into account the sea surface roughness.

The Transmission Modes and Losses of the Poled Nano-crystal and Polymer Composite PbTiO_3 / PEK-c Thin-film Waveguides

Composite thin films of PbTiO3 nano-crystals and high transparency polymer polyetherketone （PEK-c） for application of non-linear optical devices were prepared by spin coating. The size of PbTiO3 nano-crystals was estimated to be 30-40 nm using a transmission electron microscope. The refractive index and the mode propagation losses at 633 nm were measured using the prism coupling technique and improved photographic technique respectively. They were found to be 1.6545 and 2.00 dB cm^-1 （fundamental mode）,respectively. Moreover, it is observed that this loss is increased at higher mode indices.

Cooperative communication technology based on relay antenna in high-speed train scenario

The user signal quality as well as the performance of transmission link experiences severe loss due to wireless channel fading and propagation loss in high-speed railway scenario.To improve the quality at the receiving end,spatial diversity was realized by means of cooperative communication technology based on the uncorrelated characteristics of the channels.The model of mobile communication system in high-speed railway was set up,and a cooperative scheme based on statistics was proposed.Mathematical analysis and simulation results show that the quality of the received signal and the performance of the transmission link are significantly improved using cooperative communication technology compared to that in non-cooperative communication mode.

The RCT Approach for Cell Coverage Prediction (Ⅱ): Experiment and Early Results

We study on the implementation flow of the radio computerized tomography (RCT) prediction method. A case in real cellular mobile radio (CMR) system together with the prediction results are also presented. As shown by the results, the RCT prediction method is marked for its convenience and rapidity, as well as its relative high precision even when the prediction procedure is highly simplified. Since it is developed according to the characteristics of wireless communication environments of our country and has concurrently merits from both statistical and deterministic prediction models, the RCT prediction method is in good agreement with engineering practices in cellular mobile communication in cities at home. Optimized by combining with other techniques, further improvement could be achieved in the stability and precision of the RCT prediction method which now serves as the core part of a software tool for commercial use in CMR system analysis and optimization.

The RCT Approach for Cell Coverage Prediction (Ⅰ) : Principles

A new method for the coverage prediction of Cellular Mobile Radio (CMR) system is developed and its basic principle is presented. Unlike the Statistical Prediction Model (SPM) that estimates propagation loss by empirical formulas or the Deterministic Prediction Model (DPM) that reckons propagation loss with analytical expressions, the Radio Computerized Tomography (RCT) method does not seek to express the propagation loss explicitly. The 2 D distribution of propagation loss factor is computed using CT technique, based on measured data collected through drive test under appropriate geometric constraint. The total propagation loss can be obtained by integral of propagation loss factor along the equivalent ray path. The advantages and limitations of the technique, as well as its implementation are discussed.

Broadband and lossless lithium niobate valley photonic crystal waveguide [Invited]

We investigate the influences of structure parameters and interface shapes on the bandwidth of the edge state of lithium niobate valley photonic crystals. By increasing the size difference of two air holes in the same unit cell, we find that the bandwidth of the lossless nontrivial edge state possesses a peak value of 0.0201(a/λ), which can be used to construct broadband valley photonic crystal waveguides. Mode field distributions verify that the waveguide is robust against sharp bends and exhibits chirality. When the unit cell is arranged in a bearded interface with the top and bottom components showing negative and positive valley Chern numbers, respectively, we find that the lithium niobate valley photonic crystal is more likely to exhibit a lossless edge state, which is difficult to be realized in valley waveguides with low refractive index materials. This work can provide guidance on the design of the high-performance topological waveguide.

Loss characteristics of helical-core fiber

A special optical fiber is investigated, which has a helical core in the cylindrical cladding. The beam propagation method （BPM） is used for analyzing the impacts of the geometric and physical parameters on the properties of mode losses of the helical-core fiber. The propagation loss is 0.32 dB/m for the fundamental mode and the propagation loss is 20.95 dB/m for the LPu mode in the wavelength range of 1050-1065 nm when the core diameter is 19 μm, the pitch of the core＇s helix is 2.66 mm, and the offset of the helix core from the center of the fiber axis is 31 μm. The core diameter of the single-mode helical-core fiber well exceeds that of the conventional large-mode-area fiber. The helical-core fiber can provide the effec- tive large-mode-area single-mode operation without coiling fiber or selecting excitation mode.