Conditions Of Multipath Propagation Research Articles

Performance of the Direct Sequence Spread Spectrum Underwater Acoustic Communication System with Differential Detection in Strong Multipath Propagation Conditions

The underwater acoustic communication (UAC) operating in very shallow-water should ensure reliable transmission in conditions of strong multipath propagation, significantly disturbing the received signal. One of the techniques to achieve this goal is the direct sequence spread spectrum (DSSS) technique, which consists in binary phase shift keying (BPSK) according to a pseudo-random spreading sequence. This paper describes the DSSS data transmission tests in the simulation and experimental environment, using different types of pseudo-noise sequences: m-sequences and Kasami codes of the order 6 and 8. The transmitted signals are of different bandwidth and the detection at the receiver side was performed using two detection methods: non-differential and differential. The performed experiments allowed to draw important conclusions for the designing of a physical layer of the shallow-water UAC system. Both, m-sequences and Kasami codes allow to achieve a similar bit error rate, which at best was less than 10 −3. At the same time, the 6th order sequences are not long enough to achieve an acceptable BER under strong multipath conditions. In the case of transmission of wideband signals the differential detection algorithm allows to achieve a significantly better BER (less than 10 −2) than nondifferential one (BER not less than 10 −1). In the case of narrowband signals the simulation tests have shown that the non-differential algorithm gives a better BER, but experimental tests under conditions of strong multipath propagation did not confirm it. The differential algorithm allowed to achieve a BER less than 10 −2 in experimental tests, while the second algorithm allowed to obtain, at best, a BER less than 10 −1. In addition, two indicators have been proposed for a rough assessment which of the detection algorithms under current propagation conditions in the channel will allow to obtain a better BER.

Effectiveness of the Method of Adaptive Compensation of Active Interference in Conditions of Multipath Propagation

The effectiveness of the method of adaptive compensation of active interference in the spectral domain in case of multipath propagation of interference, caused by re-reflections from local objects and underlying surface, is evaluated. The possibility of compensation of interference in the conditions of its multipath propagation both in the main and in the compensatory receiving paths is established.

Theoretical Analysis of Adaptive Algorithm Modulation Scheme in 3D OFDM WiMAX System

The growth of wireless networking has contributed to the need for high-speed services and multimedia applications anywhere and at any time. OFDM WiMAX technology is now considered one of the most popular technologies capable of delivering faster implementation and lower cost than standard wired options for Broadband Wireless Connectivity in metropolitan areas. This paper proposes appropriate adaptive modulation to be used in wireless networks based on SISO and MIMO OFDM WiMAX, which allows the performance of the network to be improved in the case of non-line-of-sight communications that are typical in urban environments. The effects of several paths, signal attenuation, Doppler shift, and different mobility speeds on the performance of the system were investigated. Mathematical models analysis of adaptive modulation in SISO and MIMO systems is treated by using BER, SNR and noise components. Simulation results show that the adaptive algorithm would improve throughput. It can also be concluded that when processing signals in a receiving system under conditions of multi-path signal propagation, the use of adaptive algorithms has a positive effect on noise immunity.
 HIGHLIGHTS
 
 With the growing evolution of wireless communication technologies, there is still a need for higher data rates, increased system capacity, and improved service quality
 3D OFDM-MIMO WiMAX technology is now regarded as one of the most common solutions for Broadband Wireless Connectivity in Urban Areas, capable of offering faster implementation and lower costs than standard wired options
 Effective adaptive algorithm processing in 3D wireless networks based on SISO-OFDM and MIMO-OFDM WiMAX was proposed, enabling network performance to be enhanced in the case of non-LOS wireless communications, which are standard in urban conditions. On the performance of the system, signal attenuation, the effects of several paths, different mobility speeds and Doppler shift were studied
 The adaptive algorithm significantly reduces the probability of error and increases the throughput. It can be concluded that the use of adaptive spatio-temporal algorithms has a positive effect on noise immunity when processing signals in the receiving system under conditions of multipath signal propagation
 
 GRAPHICAL ABSTRACT

ДВУХСТУПЕНЧАТЫЙ АЛГОРИТМ СОГЛАСОВАННОЙ ФИЛЬТРАЦИИ СИГНАЛОВ

Introduction. Introduction. To combat inter-symbol interference resulting from multipath signal propagation, spreading of the signal frequency spectrum, channel equalizing, OFDM-multiplexing with orthogonal frequency division of channels is used. To reduce the influence of non-linear signal distortions, methods of pre-distortion, diversity reception, as well as special algorithms for digital processing of the demodulator output signal are used. The effect of additive noise is reduced by using a filter matched to the signal. Objective. It is advisable to develop a matched filtering algorithm that allows one to simultaneously reduce the influence of additive noise, non-linear signal distortions and its multipath propagation on the correct message reception. The idea of selecting the orthogonality weight can also be used to achieve the goal. Result. To reduce the influence of non-linear distortions on the correct reception of a message under conditions of multipath signal propagation and additive interference, it is proposed to use two stages of signal processing. The first step is to minimize the noise dispersion caused by intersymbol interference and non-linear signal distortions. The specified dispersion is minimized by determining the orthogonality weight of the basis-functions that make up the signal. The second step is to use a classic matched filter. The proposed two-stage matched filtering algorithm makes it possible to simultaneously reduce the influence of non-linear distortions, intersymbol interference resulting from multipath propagation, and additive interference on the correct signal reception. Signals distorted and delayed in time relative to the main signal are proposed to be considered as additive interference.

Transmitting Image in 3D Wireless Channel using Adaptive Algorithm Processing with MMSE based on MIMO principles

With the growing evolution of wireless communication technologies, there is still a need for higher data rates, increased system capacity, and improved service quality. OFDM WiMAX technology is now regarded as one of the most common solutions for Broadband Wireless Connectivity in Urban Areas, capable of offering faster implementation and lower costs than standard wired options. This paper proposes effective adaptive algorithm processing with MMSE for use in wireless networks based on SISO and MIMO OFDM WiMAX, enabling network performance to be enhanced in the case of non-LOS wireless communications, which are standard in urban conditions. On the performance of the system, signal attenuation, the effects of several paths l, different mobility speeds and Doppler shift were studied. Combines the adaptive algorithm with MMSE, achieves improved joint channel estimation and signal detection which performs the technique effectively mobile. SNR, MSE and noise components are used to analyses mathematical models of adaptive modulation for transmitting images in SISO and MIMO systems. Simulation results show that the adaptive algorithm with MMSE would improve throughput. For example, when SNR equal 15 dB, the probability of MSE for BPSK based on MIMO principle is equal to 0.0016 with adaptive algorithm. Also, for the same value of SNR, the probability of MSE for BPSK based on MIMO principle is equal to 0.164 without adaptive algorithm. It can also be concluded that when processing signals in a receiving system under conditions of multi-path signal propagation, the use of adaptive algorithms with MMSE has a positive effect on noise immunity.

НАПРАВЛЕННЫЕ И ПОЛЯРИЗАЦИОННЫЕ СВОЙСТВА МИКРОПОЛОСКОВОЙ РЕКОНФИГУРИРУЕМОЙ АНТЕННЫ, ПЕРЕСТРАИВАЕМОЙ ПО ЧАСТОТЕ И ПОЛЯРИЗАЦИИ

A reconfigurable antenna is an antenna with parameters that can be varied according to therequirements of a particular situation. Under variable parameters we can understand the operatingfrequency range, radiation pattern, polarization, as well as various combinations of these parameters.In this paper, we propose the design of a reconfigurable microstrip antenna with tunablefrequency and polarization, and investigate its radiation pattern and polarisation properties. Theantenna has compact dimensions and can be used in wireless communication systems operating inthe 2–7 GHz range. 5 pin diodes are included into the antenna design to change the resonant frequencyand polarization of the antenna by turning the diodes on and off. The simulation of theproposed antenna was performed in the FEKO program and the main parameters of the antennawere obtained. The analysis of the simulation results showed that for the lower part of the studiedfrequency range (2.05, 2.45 and 3.7 GHz), the polarization is linear. When operating in the highersub-range (5.4, 5.6 and 5.75 GHz), the antenna is circularly polarized, and the direction of thepolarisation vector rotation depends on the connection of the diodes. This ability to switch polarizationto orthogonal at the same frequency allows to perform efficient signal reception in the conditionsof multipath propagation.

Investigation of the LoRa Transceiver in Conditions of Multipath Propagation of Radio Signals

Kucherov D. Investigation of the LoRa Transceiver in Conditions of Multipath Propagation of Radio Signals / Dmytro Kucherov, , Andrei Berezkin, Volodymyr Nakonechnyi, Olha Sushchenko, Ihor Ogirko, Olha Ogirko, Ruslan Skrynkovsky // Advances in Science, Technology and Engineering Systems Journal. - 2021. - Vol. 6. - No. 1. - С. 1106-1111.

Моделирование навигационного сигнала ГЛОНАСС в условиях многолучевого распространения

Моделирование навигационного сигнала ГЛОНАСС в условиях многолучевого распространения

ИСПОЛЬЗОВАНИЕ РАЗВЕТВЛЕННОГО БИСПЕКТРАЛЬНО-ОРГАНИЗОВАННОГО КОДА В НЕСТАЦИОНАРНЫХ КАНАЛАХ СВЯЗИ С ЗАМИРАНИЯМИ

One of the main problems in modern wireless telecommunication systems and networks is the transmission and reception of signals in a multipath environment. Due to the nonideal impulse response of the communication channel, the frequency selective fading of the transmitted signal occurs. Diffraction and interference effects create a complex non-stationary structure of the electromagnetic field, which varies greatly in space and time. The method of branched BIS is organized - redundant coding, which allows you to receive and recognize a signal in a digital communication system in the presence of additive Gaussian noise, multipath propagation of radio waves, fading, random signal delays, as well as random changes in Doppler frequency shift. The advantages of the bispectral signal processing method include the ability to identify and evaluate the phase relationships of the spectral components in the observation, high noise immunity with respect to additive Gaussian noise and invariance to random signal time delays. The proposed method is based on solving the problem of multi-alternative detection and distinguishing of known triple signals against the background of interference according to test statistics – estimating the amplitude bispectrum by comparing the corresponding peak values of bi-amplitudes at the output of the matched bispectral filter. Since the bi-amplitude serves as a measure of the contribution of the frequency-phase dependences specified in a polyharmonic signal, the reception rule is to choose a triplet as the solution of a bispectrically organized signal, whose frequency dependencies are most similar to the frequency dependencies in the adopted oscillation. The aim of the work is to substantiate the advantages of using a branched bispectrically-organized code in digital radio communication systems in conditions of fading and multipath propagation of radio waves in comparison with the known redundant code. The results of computer statistical modeling of communication systems with the proposed coding method and the known one show a lower probability of symbol error for branched bispectrically-organized redundant coding under conditions of multipath radio propagation channels within the considered Rice and Rayleigh fade models. Computer simulations performed to show that the proposed method of branched bispectrically-organized redundant coding improves noise immunity in the propagation of radio waves in a channel with additive white Gaussian noise and also in a multipath radio link with fast and slow fading compared to the known frequency-redundant system-prototype.

Algorithm for received signal in multipath propagation conditions

This article discusses the received signal reception algorithm under conditions of multipath propagation of radio waves. As well as an analytical expression of the effectiveness of this algorithm is derived from the point of view of SNR.

METHOD OF CODING INFORMATION DISTRIBUTED BY WIRELESS COMMUNICATION LINES UNDER CONDITIONS OF INTERFERENCE

The subject matter of the paper is the processes of analysis and evaluation of the effectiveness of information coding methods in wireless systems. The aim is to improve noise immunity of information messages under conditions of powerful electromagnetic interference, with the help of complex signal-code constructions. The objective is to develop a method for noise-immune encoding in a wireless information transmission system, providing increase in information transmission rate. The methods used: Simulation and digital signal coding. The following results have been obtained: A method for encoding information transmitted via wireless communication lines in presence of interference. For signal coding, it is proposed to use Gaussian monocycle with time-dependent position-pulse modulation (PPM). It is shown that for organization of independent channels within a single frequency band, it is practical to use a system of orthogonal codes. Pulses of the useful information signal accumulated in a receiver correlator provide significantly increase in signal-to-noise ratio, allowing transmission of information over a wide frequency range well below the noise level. As a result of encoding information in wireless information transmission systems with the help of ultra-short pulse signals, the effectiveness of the proposed method is a quantitatively and qualitatively evaluated. Conclusion. Using Pulse Position Modulation coding in wireless information transmission systems allows transmitting large volumes of information with high transmission rate and high noise immunity of the communication channel as well as protecting the channel from message interception. Ability to work with low radiating power and high signal capacity to penetrate various obstacles ensure fulfilment of electromagnetic compatibility requirements as well as stable communication in conditions of multipath radio wave propagation. A possibility that powerful electromagnetic disturbances accompanying a lightning discharge may have catastrophic impact on the information transmission channel is also eliminated.

Fluctuations of the peak pressure level of man-made impulsive sound signals propagating in the ocean

The theory of wave propagation and fluctuations in random media has been broadly studied; however the works studying the influence of a changing underwater acoustic environment on the spatial decay and fluctuations of the peak pressure in broadband and impulsive signals are limited. Using a method based on the formulation developed by Dyer and Makris to estimate intensity fluctuations of sound signals in the ocean in conditions of saturated multipath propagation, this paper presents an approach to model peak pressure fluctuations of transient signals propagating underwater. In contrast to the formulation of Dyer and Makris, the approach presented in this work applies extreme value theory using the properties of the peak pressure as a maximum value taken from a Rayleigh distributed amplitude. The location and scale parameters obtained from the best fit to a Gumbel distribution are used to estimate the probability of the peak pressure level staying below a certain threshold. The theory was applied to measurements of signals from an airgun array and offshore impact pile driving, resulting in good agreement in both cases.

Computation of the key parameters of radio signals propagating through a perturbed ionosphere in the land-satellite channel

An analysis of the key parameters of HF/UHF radio signals was carried out for land-satellite radio channels, which determine the effects of fading in a perturbed ionosphere. Using the parameters of the perturbed plasma, the effects of the absorption and phase fluctuations of radio signals are analyzed for a channel with fading. For the evaluation of the effect of scattering of a radio signal by ionospheric inhomogeneities in an approximation of small-scale scintillations, expressions for the root-mean-square (RMS) magnitude of signal intensity and phase scintillations are presented. Scintillation index σI2 that corresponds to variations in a signal under the conditions of multipath propagation with fading is investigated by using experimental data. It is shown that roughly ∼10% of inhomogeneities of the electron concentration in the F region of the ionosphere, perturbed during a magnetic storm, yield strong quickly fading radio signals in the VHF/UHF range with significant fluctuations (up to 1%) in the intensity of the signal and phase fluctuations (up to hundreds of radians). The calculated magnitudes of the scintillation index are in good agreement with experimentally observed data.

Frequency domain multi‐user receivers for IEEE 802.15.4a short‐range communication network

ABSTRACTIn this letter, we propose frequency domain receivers for an IEEE 802.15.4a short‐range communication network: the uplink case is taken into account, considering a scenario where several devices communicate with a coordinator node. The channel model has been also derived according to the IEEE 802.15.4a recommendations. Results show that the proposed approach can be beneficial in short‐range systems under severe conditions of multipath propagation and interference. An interesting novelty of the proposed approach is that both single‐user and multi‐user FD receivers based on the minimum mean square error criterion can be derived by exploiting the zero padding technique which is intrinsic in the symbol structure of the standard. Copyright © 2012 John Wiley & Sons, Ltd.

Noise immunity of the wireless communications scheme based on ultrawideband chaotic radio pulses in multipath channels

The problem of determining the noise immunity of wireless data transmission based on ultrawide-band (UWB) chaotic radio pulses in the multipath channel with white noise is substantiated. The results have been calculated via numerical simulation using the multipath channel models describing UWB signal propagation in rooms of different classes at distances as long as several tens of meters. The direct chaotic communications method is shown to have the noise immunity high enough to employ this scheme in practical wireless applications where information is transmitted under severe conditions of multipath propagation. In this case, the ultimate data transfer rates are found to 25 Mb/s.

Statistical characteristics of an ensemble of ultrawideband communications channels under the conditions of multipath signal propagation in rooms

The estimates of data rates in the ultrawideband direct chaotic scheme of data transmission in rooms, which can be achieved at a specified level of error probability under the conditions of multipath signal propagation in wireless communications networks, are presented. The estimates have been obtained via direct numerical simulation of energy reception of chaotic signals at the output of communications channels. The channel impulse responses were formed according to the statistical model developed by the IEEE 802.15 working group for indoor applications. In the approximation of a dominant reverberation interference (multipath propagation), the portion of channels making it possible to transmit data with rates from 10 to 50 Mb/s and the practically important error probability (Pb ∼ 10−5−10−4) is determined for the chaotic signal bandwidths Δf = 500 and 2000 MHz. It have been first revealed that, in the given ensemble of channels, the small portion of channels (5–20%) with high levels of error probability Pb substantially affects the dependence of the error probability averaged over the given type of channels (\( \bar P_b \) (R)) on the transmission rate. It has been demonstrated that quantity \( \bar P_b \) (R) is the practically important characteristic of noise immunity for the significant portion (∼80–95%) of channels of the given type.

Method of frequency-time localization of complex signals under a priori uncertainty conditions

An efficient method of frequency-time localization of the energy of complex unknown-shape signals is developed on the basis of solving an optimization problem with the objective function in the form of the l2 norm. The method is based on estimating the mutual-correlation level of the complex amplitude-phase distributions recovered with different resolutions in the analyzed frequency-time domain. Under conditions of single-and multipath propagation of waves, the values of the signal-localization effectiveness are compared on the basis of simulation modeling results.

Power efficient Viterbi decoder based on pre-computation technique for portable digital multimedia broadcasting receiver

Digital multimedia broadcasting (DMB) is a reliable multi-service system for mobile and portable receivers. DMB system allows interference-free reception under the conditions of multipath propagation and transmission errors using coded orthogonal frequency division multiplexing modulation (COFDM) and unequal error protection (UEP) scheme. For error correction of portable DMB receivers, punctured convolutional code and viterbi decoder is developed but it needs lots of computations for real-time operation. So, it is desired to design a high speed and low-power hardware scheme for viterbi decoder. This paper proposes a combined add-compare-select (ACS) and path metric normalization (PMN) unit using pre-computation technique for DMB system. The proposed PMN unit reduces the critical path by applying fixed value selection algorithm using the comparison tree properties. We also propose an ACS structure using the decomposition and pre-computation technique for reducing the complexity of the adder, comparator and multiplexer. Simulation results shows that area, gate delay and power consumption are reduced about 3.78%, 23.80%, and 12.22%, respectively.

Division of a Multifrequency Multipath Field by Regularization Methods

Within the framework of the quadratic and non-quadratic regularization theory based on lp norms, we analyze the problem of spatial localization of the power of coherent-signal sources using minimum a priori information on shapes of wideband signals and their frequency-temporal domains of existence, as well as statistical characteristics of disturbances. A numerical experiment using a circular antenna array proves the efficiency of the algorithms proposed for digital reconstruction of the angular energy distribution under conditions of multipath propagation.

ADAPTIVE SIGNAL PROCESSING IN ANTENNA ARRAYS WITH ALLOWANCE FOR THE RANK OF THE IMPULSE-RESPONSE MATRIX OF A MULTIPATH CHANNEL

We consider adaptive spatial signal processing in antenna arrays under conditions of multipath propagation. It is shown that estimation of the elements of the matrix of multichannel impulse response (MCIR) in the receiving channels of antenna arrays is not sufficient for performing such a processing, and we should also determine the MCIR-matrix rank, which is equal to the minimum number of adaptive spatial channels for reception of a multipath signal. We propose a threshold method for estimating the rank of the MCIR matrix on the basis of the statistical properties of maximum-likelihood estimation of the elements of this matrix and a priori information on the properties of internal noise in the receiving channels of the system. The weight vectors of the beamformer processor ensuring adaptive spatial signal processing are estimated.