Reconfigurable intelligent surface (RIS) has been suggested as a promising solution to prevent wireless communication systems from transmission blockage. In this paper, the performance of reconfigurable intelligent surface in cooperative decode-and-forward relaying for hybrid radio frequency (RF)/free space optical (FSO) system is evaluated where parallel transmission of information occurs on the system downlink. In this network, the RF links in the system are assumed to follow Nakagami-m distributions while the FSO link is subjected to Gamma-Gamma distribution. Thus, the exact closed-form expressions of the system outage probability and average bit error rate are obtained to quantify the system performance. The accuracy of these expressions is justified by the Monte-Carlo simulations. Also, to get more physical insight from the derived outage probability expression, the asymptotic outage probability under the condition of higher signal-to-noise ratio (SNR) is provided. In addition, the results illustrate that the system and channel parameters significantly affect the performance of the concerned system. Furthermore, the results show that RIS-hybrid downlink system offers better performance than hybrid downlink system without RIS. Under the RIS system, the results demonstrate that RIS-hybrid downlink system outperforms RIS-FSO downlink system.
The integration of radar and communication has always been one of the cross-research hotspots in the field of radar and communication. In order to solve the problems of integration signal separation and the angle-distance coupling, this paper proposes a radar and communication integrated waveform based on random Orthogonal Frequency Division Multiplexing (OFDM) frequency offset modulation for Frequency Diversity Array (FDA). This waveform directly loads OFDM symbols to the elements of FDA, and each element carries a complete OFDM symbol with different information. Random frequency offsets are added between the elements to separate different signal of different elements, which can solve the problem of signal separation and form decoupled radar beam. After transmitting and receiving a series of the waveform, the transmission of communication data and the positioning of radar targets can be completed at the same time. The simulation results show that the waveform not only solves the problem of separating and uncoupling the integrated signal, but also improves the frequency band utilization rate and information transmission rate of the radar communication integrated system.
A new design of a 2×2-element subarray antenna based on an all-cavity resonator structure is presented in this article. A novel topology which employs only two resonators to lay out the subarray is proposed, and two X-band rectangular waveguide cavity resonators are utilized for the subarray physical implementation. The first resonator is a conventional half-guided resonator operating at the TE101 mode. The second resonator, which is an oversized TE102 resonator based, is modified in order to keep the TE101 mode to propagate within the bandwidth of interest and facilitate the connection with four radiating apertures. The developed coupling matrix approach is utilized to calculate the desirable frequency response, which is a standard 2nd order Chebyshev response with introducing filtering functionality to the realised gain response of the subarray. The simulation results obtained by two simulation softwares (CST and Ansoft HFSS) validate the calculation results. An extremely wide impedance bandwidth of 23% at center frequency 10 GHz when the reflection coefficient S11 = -10 dB is obtained. A very stable realised gain with less than 0.5 dBi variations over the bandwidth of interest (8.8-11.1 GHz) is obtained with a peak gain value of 13.1 dBi at 11 GHz. The radiation patterns have very low side lobe levels, particularly in the E-plane, due to the existence of small non-radiating area and maintaining small spacing between the radiating apertures. The proposed 2×2-element subarray has the advantages of wider bandwidth and low profile compared with our and other previous 2×2-element subarrays.
In this work, a novel all-textile washable metasurface antenna is designed for WBAN/WLAN and mid-band 5G applications. Metasurface antenna is obtained by implanting SRR (Split Ring Resonator) metamaterials that show left-hand characteristics to the patch plane. The metasurface arrays consisting of 4×1 and 4×2 SRRs are placed to both sides of a circular patch. The performance of the antenna is verified by a full-wave electromagnetic analysis tool. The results show that metamaterial arrays significantly increase gain and efficiency values of the circular patch antenna. Metasurface antenna consisting of 4×2 array of metamaterials increases the efficiency from 74% to 94.5% and the antenna gain from 6.81 dBi to 9.43 dBi. Performance of the antenna is observed on conformal surfaces, as well. An analysis is carried out to calculate the peak specific absorption rate on an arm phantom. Patterns of vertically bended antenna in ø=0° and 90° planes and low SAR values up to 30 dBm input power proved suitability of the metasurface antennas for on-body applications. The antennas are fabricated by using standard textile manufacturing techniques. It was confirmed by the measurement results that the metasurface formed by the linear SRR arrays increases the antenna gain. With its low cost, fabrication with standard off-the-shelf parts, high gain, and efficiency features, the proposed antenna can be used in wireless body area networks and 5G applications.
This paper covers the use of oscilloscopes in near-field, pre-compliance radiating tests. Using commercial low-cost planar magnetic probes, a procedure is presented to use the time-domain waveforms to address emitted radiation patterns. In spite of its lower sensitivity in relation to spectrum analyzers, a comparison between both instruments is presented, with the inferior response of the oscilloscope compensated by means of off-the-shelf broadband amplifiers. Complete system calibration is described and performed, relating the voltage measurements in a transmission-line structure to field amplitudes provided by a full-wave simulation. Two different typical devices are tested using the procedure here developed: a direct current motor, driven by a square wave, and a microprocessor board. Results show the potential use of the almost omnipresent instrument in sophisticated field evaluations, enabling its use in situations where spectrum analyzers are not available.
For the principle that intermittent sampling and repeater jamming (ISRJ) is obtained by discontinuous sampling of radar signal in time domain, a novel random redundancy (RR) waveform based on multiple input multiple output (MIMO) radar and multi-carrier phase code (MCPC) radar signal is proposed, namely RR-MCPC signal. From the point of waveform design, chaotic sequences are used to encode each chip in time domain for the signal with a multi-carrier phase code multiphase coding structure. Moreover, some chips are randomly arranged with equal amount of redundant coding in time-frequency domain. In MIMO radar, the subcarriers of radar signal are divided into multiple channels for transmission, and then the received signal is processed in each channel. Ensure that the intermittent sampling, whether in time domain or frequency domain, will sample redundant information in a channel. So it cannot match the matched filter. Therefore, the RR processing makes the signal have the characteristics of anti-ISRJ, which can availably restrain the interference of ISRJ false target. The results show that the signal-jamming ratio (SJR) improvement factor of RR-MCPC signal after pulse compression is optimized by 2.47-2.69 dB compared with the multi-carrier phase code signal under the typical parameters expressed in this paper.
This paper proposes the design and implementation of a circular triangle fractal antenna for portable ultra-wideband (UWB) communication applications with band rejection at WLAN band. The presented antenna is made with iterative generation of a circular triangle shaped elements arranged in circular fashion with self-similarity and periodicity property with coplanar waveguide feed. The overall dimensions of the antenna are 28× 27 x 1.6 mm3. The fractal resonating plane and ground plane dimensions of the proposed antenna are optimized to obtain a resonance bandwidth of 2.39-12.28 GHz which corresponds to fractional bandwidth of 134.8% with notch band from 5.45 to 6.27 GHz to mitigate the problem of interference from WLAN. The peak gain detected is 11.16 dBi. The proposed prototype was fabricated on a 1.6 mm thick FR4 material with the relative permittivity of 4.4, and the sample was tested. The experimental results are in close agreement with the simulated ones. The time domain analysis indicates that the proposed antenna is not dispersive. The antenna radiates in a virtually omnidirectional pattern. Due to these merits, this proposed antenna can be used in UWB applications.
To enhance transmission performance, a novel three-coil wireless power transfer system is proposed in this work. Unlike the traditional system in which three coils are resonant, the coils in the proposed system are hybrid resonant. According to theoretical calculation, it is found that output power is dependent on resonant frequency of the transmitting coil and the relay coil once the receiving coil is set to resonate at the operating frequency. Simulation work is conducted. Under various distance between transmitting coil and relay coil, resonant frequency of the two coils at which the output power is maximized is obtained. Compared with the traditional resonant system, the simulation result shows that output power of the proposed hybrid resonant system is higher especially at smaller distance. For further validation, experiments have been carried out which verify that better performance can be realized with the proposed hybrid resonant system.
A compression algorithm for the T-matrix scattering solution from multiple objects and incident fields is derived and examined which we call the Compressed T-Matrix Algorithm (CTMA). The CTMA is derived by applying the SVD and Woodbury matrix-inverse identity to compress the original T-matrix system of equations and simultaneously compress the matrix of right-hand side incident field vectors. This is suited for scattering problems with many incident directions. We quantify the compression rates for different collections of dielectric spheres and draw comparisons to the Characteristic Basis Function Method (CBFM) with which the CTMA shares many structural similarities.
The basic climatic characteristic of the tropical areas is abundant precipitation throughout the year. For such precipitation the radio signal (RF) power of these areas gets diminished in communicating any signaling information from a sender to a receiver i.e. rain fading occurs in these areas. Rain fading is one of the major causes which decline the characteristics of radio system in tropical areas. To reduce excessive rain fading various fade reduction techniques such as diversification techniques, adaptive power control technique and adaptive waveform technique have been used. Frequency diversification technique is an effective technique for diminishing rain fading. In this work in order to diminish rain fading a suggested model has been implemented. Frequency diversification improvement factor is accepted to heighten the performance of this suggested model. Besides, by adopting an experimental data sheet a comparison of this suggested model with a number of various existing rain attenuation predicted models has been depicted for validation of the suggested model. The experiment was performed by accepting two mm-Wave connectors acting on two frequencies of 26 GHz and 38 GHz, respectively, for observing which model renders better result in the tropical region with respect of various distances, frequencies, and elevation angles.
This paper studies the optimal design of a double-sided linear flux switching permanent magnet motor (DLFSPM) to improve the average thrust generated by motor operation and reduce the fluctuation range of thrust applying the Response surface methodology (RSM) and Particle Swarm Optimization (PSO). An analytical mathematical model of the electromagnetic thrust force of the DLFSPMs is developed. The functional model of the optimization parameters and objectives based on the RSM is constructed. The finite element analysis (FEA) is used to carry out numerical experiments on the geometric structure design variables. PSO is applied to an optimization tool for optimizing the DLFSPMs' mover structure parameters. Finally, the FEA comparison and analysis of the optimization results with the initial results reveal a significant improvement in the electromagnetic characteristics of the DLFSPMs. The feasibility and effectiveness of the optimization method are verified by the FEA results.
Carr-Purcell-Meiboom-Gill (CPMG) is generally used as the measurement sequence of unilateral NMR (UMR) sensors, and the NMR signals collected by the sequence are composed of a series of echo signals. In the traditional CPMG measurement signal, each echo peak value is first taken and then denoised, which would lead to the inaccuracy of the peak point taken, resulting in deviation. To ensure the measurement result more accurate, this paper proposes to employ wavelet technology to denoise the echo signal first, and then take the peak point to analyze the data. Firstly, a simplified model of the spin-echo signal without the influence of gradient magnetic field was established, and white noise was applied to a certain extent. Then, Signal to Noise Ratio (SNR) and Root Mean Square Error (RMSE) were used as evaluation indexes. The denoising effects under different wavelet bases and thresholds were compared. Finally, the Matlab simulation result showed that wavelet analysis had a good effect on the denoising of unilateral NMR spin echo signal.
The study of outer-rotor coreless bearingless permanent magnet synchronous generator (ORC-BPMSG) is intended to pave the way for the future of high-speed flywheel energy storage systems. A multi-objective parameter optimization method is proposed for the outer-rotor coreless bearingless permanent magnet synchronous generator with the aim of improving the fundamental wave content of the generator's output voltage, reducing harmonics and optimizing the suspension force at the same time. Firstly, the basic parameters and operating principle of the generator are described. Then, the response surface (RS) method is used to obtain the objective functions for the total harmonics distortion (THD), the mean value of the suspension force and the suspension force pulsation. The optimal optimizations of the ORC-BPMSG are selected by establishing the pareto solution set through the improved multi-objective particle swarm optimization (MOPSO) algorithm. Finally, the optimal ORC-BPMSG prototype is fabricated, and the performance of the prototype is verified. The experiments show that the optimized generator output voltage has fewer harmonics and operates reliably.
We study TE-wave propagation in a hollow waveguide with a graded transition from a lossy right-handed material (RHM) filling the left-hand half of the waveguide to the impedance-matched lossy left-handed material (LHM) filling the right-hand half of the waveguide. The transition between the two media is graded along the direction perpendicular to the boundary between the two materials (chosen to be the z-direction), and the permittivity ε(ω, z) and permeability μ(ω, z) are chosen to vary according to hyperbolic tangent functions along the z-direction. We obtain exact analytical solutions to Maxwell's equations for lossy media, and the solutions for the field components confirm the expected properties of RHM-LHM structures. Thereafter, a numerical study of the wave propagation over an impedance-matched graded RHM-LHM interface is performed, using COMSOL software. The numerical study shows an excellent agreement between the numerical simulations and analytical results. Compared to other solution methods, the present approach has the advantage of being able to model more realistic smooth transitions between different materials. However, in the limiting case, it includes correct results for abrupt transitions as well. In the present approach we also introduce the interface width as an additional degree of freedom that can be used in the design of practical RHM-LHM interfaces.