Frequency-selective Fading Channels Research Articles

Reduced-Complexity Intelligent Reflecting Surface Optimization for Single-Carrier Transmission in Frequency-Selective Fading Channel

Reduced-Complexity Intelligent Reflecting Surface Optimization for Single-Carrier Transmission in Frequency-Selective Fading Channel

Security in Spatially Correlated MIMO OSFBC OFDM Multicast System over Frequency Selective Fading Channel

The system performance can be improved significantly by employing orthogonal space-frequency block coding (OSFBC) and orthogonal frequency division multiplexing (OFDM) because in this combination the receiver suffers lesser complexity. Recently, the wireless systems are deploying by the increasing number of closely spaced antennas. So the assumption of in-dependency among the antenna brunches is not valid. Realizing the advantages of this combination of system and taking account the effect of antenna correlation, this work demonstrates the insight of secured wireless multicasting network consisting multiple antennas both in transmitter and receiver over spatially correlated frequency selective fading channels. The desired signals have been protected from eavesdropping by useful impact of antenna diversity and antenna correlation. The main contribution of this work is the development of mathematical models of the probability of non-zero secrecy multicast capacity (PNSMC) and the secure outage probability for multicasting (SOPM) to secure the system from eavesdropping. The analytical results are verified via Monte-Carlo simulation to ensure the validity of the developed mathematical model. Moreover, the numerical analysis gives a clear indication that security in OSFBC OFDM system with antenna diversity over spatially correlated frequency selective fading channel upgrades due to the effect of transmit antenna correlation and degrades due to receive antenna correlation. But the loss of this security can be significantly reduced employing antenna diversity with OSFBC-OFDM systems.

Channel Estimation in MIMO OFDM Systems with Tapped Delay Line Model

The continuous increase in the user demands fornew-generation communication systems, is making the wireless channel more complex and challenging for estimation, developing a simulation model for the channel,and evaluating the performance of different MIMO systems. In this work, a simulation model for multipath fading channels in wireless communication is performed. The model includes a selection of typical Tapped-Delay-Line channel models that can be implemented to reproduce the effects of representative channel distortion and interference. Based on the simulation results, the proposed method exhibits accurate channel estimation performance for frequency-selective fading channels. The proposed work employed LS, MMSE, and ML methods for channel estimation, using 16 and 32 pilots and fixed pilot locations in each frame. Results are obtained for 4x4, 8x8, 16x16, 16x8, and 16x4 MIMO systems and tapped delay line systems.

Matrix Reconstruction Algorithm-Assisted Multi-Carrier DCSK Scheme: An Effective Solution for Frequency-Selective Fading Channel

Matrix Reconstruction Algorithm-Assisted Multi-Carrier DCSK Scheme: An Effective Solution for Frequency-Selective Fading Channel

Massive MIMO-OFDM Transmission Without Cellular Networks Using Frequency - Selective Fading Channels

Abstract: For cell-free massive multi-input multi-output (CF-m-MIMO) across frequency-selective fading channels, this system introduces and determines the effectiveness of the orthogonal frequency-division multiplexing (OFDM)-based multi-carrier transmission. The CF-m-MIMO-OFDM system can accommodate a substantial user base and is flexible enough to offer a range of data rates for usage in a variety of contexts. With its scalability and flexibility, the CF-m-MIMO-OFDM transmission network can serve a large number of users at variable data rates. It is proposed to beamform in the frequency-domain conjugate, to choose a pilot, and to allocate resources differently for each user. User-specific resource allocation, pilot selection, and frequency-domain conjugate beamforming are all suggested. The CF-m-MIMO-OFDM system can support a large number of users and can offer varying data rates to accommodate a wide range of applications.

Design and evaluation of space‐time coded multiple input multiple output‐orthogonal frequency division multiplexing physical layer

SummaryTwo fundamental aspects of wireless communication, which make it challenging and interesting, are fading and interference. Multiple input multiple output (MIMO) and orthogonal frequency division multiplexing (OFDM) techniques when utilized together effectively combat fading and interference thereby achieving the requirement of high data rate and high performance. In this paper, a 2 × 1 MIMO‐OFDM baseband model of the physical layer according to IEEE 802.16.1 standard employing 256 subcarriers capable of transmitting 192 Mbps in a 21‐MHz bandwidth frequency selective fading channel is designed. All essential blocks of the communication system like channel coding, modulation, time synchronization, frequency synchronization, channel estimation, residual carrier frequency offset (CFO) estimation, and channel decoding are covered at the algorithm level. A two‐step time synchronization method is used in this work to avoid any ambiguity in frame detection. A long preamble, consisting of three short preambles, is designed to aid in time synchronization, frequency synchronization, and channel estimation. To evaluate the performance of the proposed design, simulations were carried out in MATLAB‐SIMULINK.

Complementary Coded Identical Code Cyclic Shift Multiple Access Under Asynchronous Frequency-Selective Fading Channels

A complementary coded code-division multiple-access (CC-CDMA) system is built on the direct sequence (DS) spread spectrum technique, which can suppress multipath interferences and multiple-access interferences due to the ideal correlation property of complementary codes (CCs). However, the DS spread spectrum technique will cause poor bandwidth efficiency; the CC-CDMA system suffers from serious interferences due to the ideal correlation of CCs may not be reconstructed at the receiver after passing through asynchronous frequency selective fading channels. In this paper, we propose a complementary coded identical code cyclic shift multiple access (CC-ICCSMA) system under asynchronous frequency selective fading channels, which allows multiple data streams to transmit in parallel by sharing one spreading code for improving the bandwidth efficiency. Considering the impact of interferences, we propose an ICCS matched filterbank to tackle the interferences, which can decode the data under all paths and achieve a high multipath diversity gain. Simulation results show that the proposed CC-ICCSMA system can achieve higher bandwidth efficiency than that of traditional CC-CDMA and can outperform the traditional DS-CDMA schemes in terms of bit-error rates and transmission rates.

A Novel Kernel Algorithm for Finite Impulse Response Channel Identification


 
 
 
 Over the last few years, kernel adaptive filters have gained in importance as the kernel trick started to be used in classic linear adaptive filters in order to address various regression and time-series prediction issues in nonlinear environments.In this paper, we study a recursive method for identifying finite impulse response (FIR) nonlinear systems based on binary-value observation systems. We also apply the kernel trick to the recursive projection (RP) algorithm, yielding a novel recursive algorithm based on a positive definite kernel. For purposes, our approach is compared with the recursive projection (RP) algorithm in the process of identifying the parameters of two channels, with the first of them being a frequency-selective fading channel, called a broadband radio access network (BRAN B) channel, and the other being a a theoretical frequency-selective channel, known as the Macchi channel. Monte Carlo simulation results are presented to show the performance of the proposed algorithm.
 
 
 

A use-case efficient DFrFT-based index modulated-OFDM system in the presence of CFO

Index modulated orthogonal frequency division multiplexing (OFDM-IM) only utilizes partial resources to transmit signals according to use case requirement, it leads to higher energy efficiency and spectral efficiency than the classical OFDM. However, in the presence of inter-carrier interference (ICI) due to carrier frequency offset (CFO), the performance of index modulated OFDM system severely deteriorates. To mitigate this issue, a novel discrete fractional Fourier transform (DFrFT) based OFDM-IM scheme over Rayleigh frequency selective fading channel is proposed in this paper. The optimum DFrFT angle (αopt) for this new scheme at various CFO values has been calculated theoretically. Incorporating these estimated αopt, the proposed system achieves a gain of 8 dB over conventional FFT-based OFDM-IM at bit error rate (BER) = 10−3 in a high normalized CFO (ϵ) environment (ϵ=0.2). The system model is also verified for different user applications, i.e., high data rate and low data rate applications. Simulation and analytical results show that the proposed model has a robust and superior performance compared to the conventional FFT-based OFDM-IM, DFrFT-based OFDM, and classical OFDM. Moreover, the proposed DFrFT-OFDM-IM model achieves all these superiorities with the same complexity as the conventional FFT-based OFDM-IM system.

Multi-Connectivity for URLLC and Coexistence With eMBB in Time-Varying and Frequency-Selective Fading Channels

Multi-connectivity enables a 5G cellular system to meet the challenging reliability requirements of downlink ultra-reliable low-latency communication (URLLC) data traffic. In it, multiple base stations (BSs) transmit to the URLLC user by pre-empting time-frequency resources assigned to enhanced mobile broadband (eMBB) users. We derive insightful expressions for achievability, which is the probability that the URLLC user’s block error rate (BLER) requirement is met by multi-connectivity. We do so for both joint transmission (JT) and orthogonal transmission (OT) modes of URLLC for the general case in which the transmissions occur over frequency-selective channels. We then propose a low-complexity algorithm to jointly select the set of cooperating BSs and their modulation and coding schemes (MCSs) to minimize the eMBB throughput loss. For time-varying channels with feedback delays, we present an alternate stochastic reliability requirement for URLLC traffic. The MCS selected on the basis of this requirement has a markedly higher probability of meeting the BLER target over the grid of URLLC user locations. Our results highlight the different trade-offs between URLLC achievability, eMBB throughput loss, and channel state information feedback overhead of OT and JT. They bring out the significant impact of feedback delays even at moderate Doppler spreads.

Indexed-channel estimation under frequency and time-selective fading channels in high-mobility systems

<p><span lang="EN-US">Index modulation (IM) techniques have been employed in different communication systems to improve bandwidth efficiency by carrying additional information bits. In high-mobility communication systems and under both time-selective and frequency-selective fading channels with Doppler spread, channel variations can be tracked by employing pilot-aided channel estimation with minimum mean-squared error estimation. However, inserting pilot symbols among information symbols reduces the system's spectral efficiency in pilot-aided channel estimation schemes. We propose pilot-aided channel estimation with zero-pilot symbols and an energy detection scheme to tackle this issue. Part of the information bit-stream is conveyed by the indices of zero-pilot symbols leading to an increase in the system's spectral efficiency. We used an energy detector at the receiver to detect the transmitted zero-pilot symbols. This paper examines the impacts of diversity order on the zero-pilot symbol detection error probability and the mean-squared of error estimation. The impacts of pilot symbols number and the zero-pilot symbol number on the mean-squared error of the minimum mean-squared error (MMSE) estimator and the system error performance are also investigated in this paper.</span></p>

Design and Simulation of MIMO Systems over Rayleigh Fading Channel and Using Near-Maximum-Likelihood Detection

While coding is the main element for the success of the MIMO system implementation, the communication channel is the main component that ascertains this. This paper describes the design and simulation of a 2x2, 4x4, and 8x8 MIMO system which is used exclusively in 5G mobile systems. The detection performed in such a system is near-maximum-likelihood detection. The noise added at the front end of the receiver is additive white Gaussian noise with zero mean and variance which depends upon the signal-to-noise ratio (SNR) while the signal is transmitted over a frequency-selective Rayleigh fading channel. The MIMO system operates at a much higher level of complexity to exploit the channel space-time resources. Orthogonal space-time block codes are used at the transmitter. An Image is transmitted and the received image is compared with the transmitted image and BER is calculated. This is done for varying SNRs. The whole project is performed over a front-end application where the various parameters are populated and run. This makes the simulation extremely easy for the 2x2 or 4x4 or 8x8 MIMO application with varying channel parameters. The modulation scheme used in this work is BPSK.

Tutorial for Space-Time ICI Parallel Cancellation Techniques for OFDM Systems

Orthogonal frequency division multiplexing (OFDM) expects the subcarriers to be orthogonal. However, the factors, such as residual carrier frequency, offset time variations due to Doppler shift or phase noise leads to a loss in the orthogonality between subcarriers and results in inter-carrier interference (ICI). Further developing the parallel cancellation (PC) scheme to mitigate the ICI of OFDM systems, the authors expand this OFDM symbol-based PC scheme into a space-time (ST) coded system. This simple space-time parallel cancellation (STPC) scheme is a technique that combines the useful properties of ST and PC schemes together. Computer simulations indicate that OFDM systems using the STPC scheme outperform the regular PC and ST systems in slow and fast frequency selective fading channels, specifically at a high signal-noise ratio (SNR). Furthermore, the error floor of the STPC-OFDM system is significantly lower than that of the regular ST systems without increasing computational load.

5G Channel Estimation Based on Whale Optimization Algorithm

This paper presents a novel approach, based on the whale optimization algorithm (WOA), for channel estimation in wireless communication systems. The proposed method provides a means to accurately estimate the wireless channel, while not requiring the statistical characteristics of the channel. This method uses the WOA to search for the best channel statistical characteristics toward the ultimate goal of having the smallest bit error rate (BER). The proposed approach is aimed at enhancing the efficiency of pilot-based OFDM systems under frequency-selective fading channels used in the performance testing of 5G New Radio gNodeB. In terms of BER and mean square error (MSE), the performance of the proposed WOA-based channel estimation algorithm is evaluated and compared with the conventional least square (LS) and minimum mean square error (MMSE) algorithms. The simulation results demonstrate that the proposed algorithm provides highly competitive performance over the MMSE algorithm and significantly outperforms the LS algorithm in a variety of system configurations. Since the requirement on prior channel statistics information makes the MMSE algorithm impractical or extremely complex, the proposed WOA-based channel estimation algorithm should be a suitable and promising candidate for dealing with channel estimation problems. The simulation framework is implemented in MATLAB and available upon request.

Generalized Tag-Based Physical-Layer Authentication Under Frequency Selective Fading Channels

Physical Layer Authentication (PLA) in wireless systems has drawn much attention because it can provide information-theoretic security. However, the performance of the prior PLA schemes significantly declines under a frequency selective fading channel and the theoretical analysis of a PLA scheme becomes extremely challenging under a frequency selective fading channel as compared to that under a frequency flat fading channel. This paper addresses the problem of authenticating transmitters at the physical layer under a frequency selective fading channel. We propose two tag-based PLA schemes under a frequency selective fading channel. The first scheme is the Generalized Tag-based PLA (GT-PLA) scheme, where the negative effect caused by a frequency selective fading channel is compensated for. If the channel reciprocity holds, we will propose the second scheme to further improve the performance of the GT-PLA scheme, named the Adaptive Generalized Tag-based PLA (AGT-PLA) scheme. We provide the theoretical analysis of both proposed schemes over wireless fading channels in terms of robustness, security, and compatibility, and derive their closed-form expressions. Moreover, we implement the proposed schemes and conduct extensive performance comparisons. Our experimental results demonstrate that the GT-PLA scheme achieves higher robustness over the prior PLA schemes while the AGT-PLA scheme can further improve the performance of the GT-PLA scheme in terms of robustness, security, and compatibility.

In-phase and quadrature filter shape index modulation

This paper proposes a novel modulation scheme called “In Phase and Quadrature-Filter Shape Index Modulation” (IQ-FSIM). It aims to enhance the spectral/energy efficiencies (SE/EE) while generalizing several existing modulations and index modulation (IM) domains. In this system, the bitstream is divided into three sub-streams. The first is mapped using amplitude–phase modulation, and the other two are mapped separately to an index of a filter shape at the in-phase and quadrature components. IQ-FSIM in SISO mode enhances the SE by 2log _2 N (double FSIM gain), thanks to the independent indexation of N different filter shapes on each component changing at the symbol rate. A low-complexity matched filter-based detector that reaches the optimal joint ML performance is proposed. The theoretical lower bounds for the probability of filter index error and the symbol/bit error rate (SER/BER) are derived and validated. The computational complexity of the proposed IQ-FSIM transceiver is estimated and compared to its predecessor FSIM, where it is shown that IQ-FSIM provides up to 93.7% complexity reduction compared to FSIM along with different advantages. In addition, the results reveal that both IQ-FSIM and its special case FSIM, even with non-optimal filter shapes, outperform the equivalent schemes with/without IM of the same SE in AWGN, flat, and frequency-selective fading channels.

Enabling OTFS-TSMA for Smart Railways mMTC Over LEO Satellite: A Differential Doppler Shift Perspective

Recently, grant-free orthogonal time–frequency space-based tandem spreading multiple access (OTFS-TSMA) is proposed for machine-type communications (mMTCs) in smart railways environmental sensing. To achieve massive connections with scarce radio resources, OTFS-TSMA combines the advantages of OTFS and TSMA. It shows high connectivity and reliability under time–frequency-selective fading channels. Meanwhile, smart railways require over-horizon and all-weather environmental sensing based on mMTC, and the implementation of both would cost a lot in terrestrial networks. With the development of low-Earth orbit (LEO) satellites, enabling smart railways mMTC over LEO satellite is a potential diagram. However, in this scenario, due to the larger transmission delay and Doppler frequency shift, the time–frequency resource requirements of the OTFS modulation-based system increase significantly and are difficult to meet. To this end, OTFS-TSMA based on differential Doppler shift is proposed in this article. Specifically, in this article, the satellite-to-ground communication system model consisting of three sections is introduced, and the Doppler shift and differential Doppler shift characteristics of access points (APs) are investigated. Next, it is proven that designing OTFS-based multiple access schemes over the LEO satellite based on differential Doppler shift is not only resource-friendly but also has the advantages of service continuity and controllable multiuser interference. Then, the transceiver of differential-Doppler-shift-based OTFS-TSMA and its improved designs are proposed. Finally, the simulation results demonstrate that the proposed transceiver realizes high resource efficiency, collision resolution capability, and reliability for smart railways mMTC over the LEO satellite.

Ordered Block Detector for Single-Carrier Generalized Spatial Modulation in Frequency-Selective Fading Channels

In this letter, we present a detection algorithm for single-carrier generalized spatial modulation in frequency-selective fading channels. We extend the ordered-block minimum mean square error (OB-MMSE) detector, originally conceived for flat fading channels, to frequency-selective fading channels by exploiting the format of unique word-based single-carrier block transmission and incorporating decision feedback. Moreover, a frequency-domain prefilter is used to ameliorate error propagation and simplify the operation of OB-MMSE detector. Simulation results show the efficacy of the proposed algorithm.

Performance analysis of FBMC/OQAM systems in frequency-selective channels

Filter bank multicarrier (FBMC) systems based on offset QAM modulation (FBMC/OQAM) represent an interesting alternative to the widely used OFDM scheme for machine type communications or cognitive radio. In this paper the performance of FBMC/OQAM systems exploiting a single-tap receiver in frequency-selective Rayleigh fading channels, is analyzed. In particular, the SER and the asymptotic SER (i.e., for a large number of subcarriers) for any prototype filter, is derived. Moreover, a simple closed-form approximate expression of the asymptotic SER is obtained by taking into account, for each active subcarrier, only intersymbol interference terms due to the considered subcarrier and the adjacent subacarriers, and intercarrier interference terms due to the adjacent subcarriers. The numerical results show that the obtained SER expression can predict the actual performance of the system while the asymptotic SER expression provides a useful upper-bound. Moreover, the curves obtained by exploiting the derived simple closed-form approximate expression can be used to predict the asymptotic upper-bound when the considered prototype filter is adopted.

Enhanced diversity scheme for orthogonal frequency division multiplexing systems over doubly selective fading channels

AbstractFrequency‐time selective fading degrades the performance of communication systems, but it also provides an opportunity to collect multipath diversity and Doppler diversity. In this paper, an oversampled grouped‐linear‐constellation‐precoding (GLCP) scheme is proposed for orthogonal frequency division multiplexing (OFDM) systems to extract the diversity inherent in doubly selective fading channels. In the proposed scheme, GLCP is employed to precode the information symbols of OFDM at the transmitter, and the precoded OFDM symbols are oversampled in the time domain at the receiver. A full‐groups maximum likelihood (ML) decoder and a successive group decoder to decode the oversampled OFDM symbols with diversity gains are developed. The successive group decoder combines the group ML decoding algorithm with a block‐decision‐feedback‐equalization (BDFE) algorithm. The proposed scheme can take advantage of both the GLCP scheme and the oversampling scheme to achieve multipath diversity gains and Doppler diversity gains in doubly selective fading channels. Simulation results show that the proposed scheme can significantly improve the performance of OFDM systems in the frequency selective fading channel and the doubly selective fading channel in terms of bit error ratio, indicating that the diversity gains can be greatly enhanced by the proposed scheme in doubly selective fading channels.