2020/3

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Atmospheric Refractivity Estimation from Radar Sea Clutter Using Novel Hybrid Model of Genetic Algorithm and Artificial Neural Networks
(Společnost pro radioelektronické inženýrství, 2020-09) Tepecik, Cemil; Navruz, Isa; Altinoz, O. Tolga
This paper is focused on solving the inversion problem of refractivity from clutter (RFC) technique. A novel hybrid model is developed that can estimate the atmospheric refractivity (M profile) with a high accuracy, for surface based duct case, which is most effective non¬standard propagation condition on radar observation. The model uses propagation factor curve in horizontal axis, whose characteristics is determined by M profile for esti¬mation. The model is based on artificial neural network, which includes a dynamic training data approach, and a problem adapted genetic algorithm. Dynamic training data set application is a nonstandard approach in neural network applications, in which every obtained result are dynamically added to data set during the estimation pro¬cess, for a better estimation. Firstly, neural network and genetic algorithm have been adapted to the characteristics of inversion problem separately. Then, the mentioned two methods have been harmonized and run together. Ulti-mately, the final algorithm has evolved into a complex adapted hybrid model, which is easily applicable to clutter data obtained by any real radar from the real environment. The results show that the proposed model presents consid¬erably effective solution to refractivity estimation problem.
Design of OAM Beam Directional Modulation Signal in Communication and Guidance Integration
(Společnost pro radioelektronické inženýrství, 2020-09) Zhu, Changju; Song, Maozhong; Dang, Xiaoyu
An orbital angular momentum directional modulation (OAM-DM) signal is proposed for communication and guidance integration. This signal is transmitted by a uniform circular antenna array (UCA). We divide the array into odd and even antenna groups. Each group is excited by differential coded digital modulation waveform to send different signal constellations in different directions. In order to improve the performance of angle estimation, we have designed specific phase shift sequences to obtain the different OAM modes. Mode detection can eliminate multiple value ambiguity of elevation and azimuth angles. The single antenna receiver can demodulate the OAM-DM signal to communicate, detect OAM modes and estimate angles in different directions. Finally, we assess the effectiveness of the proposed approach via numerical simulation.
A Compact Circular Loop Inspired Frequency and Bandwidth Reconfigurable Antenna for 4G, 5G, and X- Band Applications
(Společnost pro radioelektronické inženýrství, 2020-09) Rasool, Maryam; Khan, Aabia; Bhatti, Farooq; Ijaz, Bilal; Iftikhar, Adnan
This paper presents a printed patch antenna design to achieve frequency and bandwidth reconfigurability. Two RF PIN diodes are simultaneously operated to achieve the multi-reconfigurability operation. The patch is inspired from a circular loop design. The basic structure of loop is altered, and PIN diodes are integrated into the patch. The antenna operates in dual band configuration at 3.42 and 8.02 GHz in the diodes ‘OFF’ state, whereas the antenna switches to triple band operation at 2.21, 4.85, and 10.19 GHz in the diodes ‘ON’ state. Moreover, the antenna also exhibits an increased bandwidth from 7.54 to 12 GHz in the diodes ‘ON’ state, as compared to a narrow bandwidth from 7.71 to 8.48 GHz in the diodes ‘OFF’ state. The proposed antenna structure is implemented and fabricated using FR4 epoxy substrate of relative permittivity 4.4, and thickness 1.6 mm. Implemented design exhibits measured gains of 3.06 dBi, 2.81 dBi, and 2.92 dBi at 2.21, 4.85, and 10.19 GHz in the PIN diodes ‘ON’ state, respectively, while in the PIN diodes ‘OFF’ state, at 3.42 GHz the gain is 3.03 dBi and at 8.02 GHz the gain is 3.37 dBi. Overall, simulation results agree well with the measured results.
Machine Intelligence Technique for Blockage Effects in Next-Generation Heterogeneous Networks
(Společnost pro radioelektronické inženýrství, 2020-09) Amalorpava Mary Rajee, Samuel; Merline, Arulraj
Millimeter wave (mmWave) links such as 28 GHz and 60 GHz propose high data rates and capacity needed in 5G Heterogeneous network (Hetnet) real-time system. The key factors in network planning of Hetnet are the locations and links of base stations, and their coverage, transmitted power, antenna angle, orientation etc. How-ever, large-scale blockages like static buildings, human etc. affect the performance of urban Hetnets especially at mmWave frequencies. A mathematical framework to model dynamic blockages is adapted and their impact on cellular network performance is analyzed. A machine learning approach based on Q-learning with Epsilon-Greedy algo¬rithm is proposed to solve the blockage problem in such complex networks. The proposed results are evident and show the positive effect of increasing the base station den¬sity linearly with the blockage density to maintain the net¬work connectivity. The performance of the proposed Epsi¬lon-Greedy algorithm is compared with Epsilon-Soft algo-rithm. The performances of above said mmWave links are compared in terms of their coverage probability and throughput. The results show that an Epsilon-Greedy algo¬rithm outperforms an Epsilon-Soft algorithm.
A Covert Communication System Using Non-Zero Mean Normal Distributions
(Společnost pro radioelektronické inženýrství, 2020-09) Xu, Zhijiang; Lu, Weidang; Gong, Yi; Hua, Jingyu; Jin, Wenbing
A covert communication system is proposed in this study, in which a~ non-zero mean Gaussian sequence is used as a~ random carrier and its mean is modulated by a~ covert binary bit. The aperiodic transmitted signal exhibits the same statistical characteristics as the ambient noise to confuse an~ eavesdropper. The received signal is multiplied with the pseudo-random sequence synchronized with the transmitter to recover these positive and negative mean Gaussian sequence. The sample mean estimator and hard decision are used to determine the covert message, and accordingly, theoretical bit error rate in additive white Gaussian noise channel is also derived. Simulation results are very consistent with the theoretical derivation. The proposed system works in the physical layer with the advantages of simple structure, strong concealment, good BER performance and very suitable for low-cost, resource-limited and low-rate transmission devices.

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