Fading Severity Research Articles

Performance Analysis for Reconfigurable Intelligent Surface-aided Communication Systems with Energy Harvesting under Imperfect Nakagami-m Channel Information

Reconfigurable intelligent surface (RIS) can serve as a passive relay to maintain communication between a transceiver in severe scenarios of no direct link between them. In addition, harvesting energy from radio frequency (RF) signals can meliorate significantly energy efficiency. In this research, we propose RIS-aided communication systems with energy harvesting (RISwEH) which combine both RIS and RF energy harvesting to improve energy efficiency as well as communication reliability. To evaluate realistically and quickly the performance of the RISwEH, we propose the explicit formulas of the system throughput and the outage probability under the realistic scenario of Nakagami-m fading and imperfect channel state information (CSI). Moreover, we propose an optimization algorithm relied upon a Golden section search to attain the optimum value of the time splitting factor of energy harvester to obtain the best system performance. Various results corroborate the theoretical derivations, confirm the efficacy of the proposed optimization algorithm, and illustrate the influence of innumerable system settings on the system performance. Particularly, the imperfect CSI deteriorates considerably the system performance. Nonetheless, the performance of the RISwEH can be enhanced by accreting the quantity of the elements of the RIS as well as with the lower fading severity. Furthermore, the time splitting factor also impacts dramatically the outage performance of the RISwEH and its optimal value mitigates significantly the outage probability.

Characterization of the coding gain for M-PSK with conjoint signals under correlated Nakagami-m fading channels

In the paper, a comprehensive analysis is presented on the conjoint coding gain achieved in arbitrarily correlated M-ary phase-shift keying (M-PSK) signals in a spatial diversity system. The system operates over Nakagami-m fading channels and is affected by additive white Gaussian noise (AWGN). The proposed signal synthesizer primarily induces an even phase shift in the output signals. To enhance the coding gain, an orthogonal transformation matrix is introduced, which effectively preserves energy and operates independently of the channel correlation matrix, making it blind to signal information measurements. The main objective is to generate additional copies of conjoint signals from the received signals, simulating the scenario as if there were more antennas deployed. To evaluate the system’s performance in terms of symbol error rate (SER), an analytical framework is developed and its accuracy is validated through Monte-Carlo simulations. Moreover, extensive tests are conducted to explore the impact of different antenna configurations and fading severity levels. The fading severity, denoted as ’m’, is varied in the experiments, considering values of 0.5, 1, 3, and 7. Additionally, the measurements incorporate varying antenna spacing values relative to the signal carrier wavelength, specifically 0.1, 0.2, and 0.5. The results obtained from the experiments demonstrate that the coding gains achieved depend on the value of ’m’, with higher gains observed for lower ’m’ values. However, as ’m’ increases, the coding gains become negligible.

Average bit error probability performance of intelligent reflecting surface‐aided wireless communications over Hoyt fading

SummaryIn this article, the performance of a wireless communication system with an intelligent reflecting surface (IRS) panel installed between the transmitter and receiver is studied. The channel is considered to be the Hoyt faded and additive white Gaussian noise. Closed‐form expressions for average bit error probability (ABEP) for both coherent Gray‐coded rectangular quadrature amplitude modulation and non‐coherent modulation schemes are presented. We apply the moment‐generating function‐based method for the derivation. In addition, asymptotic ABEP expressions are also obtained. Using asymptotic ABEP expressions, we obtained diversity order which is a function of the number of IRS elements. The effect of the number of IRS elements and fading parameters on the ABEP is studied. The ABEP performance improves with an increase in the number of reflecting elements but degrades with an increase in the fading severity. The accuracy of each analytical ABEP expression is verified by the simulation of the system considered herewith.

Outage probability and error rate analysis of full duplex relay in asymmetric fading channels

SummaryFull duplex (FD) technique has evolved as a viable solution to address the spectrum scarce issue. It has gained research interest for its potential to double the wireless link capacity and enhance spectral efficiency (SE). In this paper, the end‐to‐end performance of an amplify‐and‐forward full duplex relay(FDR) in asymmetric Rayleigh–Rician fading channels is explored, unlike the other works that assume symmetric fading conditions in both the links. The asymmetric or mixed fading channels properly model the realistic communication scenarios like satellite/terrestrial wireless communication systems. In this work, we consider that the source‐relay link experiences Rayleigh fading and the relay‐destination link experiences Rician fading. The novel exact and lower bound closed form analytical expressions for outage probability (OP) and bit error rate (BER) for the considered FD system are derived. Moreover, the effect of severity of fading and the amount of residual self‐interference (RSI) on the performance of FDR are also studied. In addition, MC simulations are carried out to validate the results. It is observed that the performance metrics, OP and BER, are highly dependent on the severity of fading and the amount of RSI. Furthermore, it is found that typically at the SNR of 10 dB, an improvement of approximately 27.6% in OP is obtained. Also, our work offers appreciable SNR gain, for example, for a BER of 10−2, an SNR improvement of around 11 dB is achieved. These findings have been compared with the mixed Rayleigh–Rician fading channel conditions considering only half duplex(HD) mode. These parameter metrics are helpful in analyzing the performance of FD in various communication scenarios such as LoS/NLoS conditions and hence pave the way for more realistic FDR.

A Graph Convolution Network Based Adaptive Cooperative Spectrum Sensing in Cognitive Radio Network

The hidden node problem is one of the most challenging issue in Cooperative Spectrum Sensing (CSS). The system models adopted by the existing Deep Learning-based spectrum sensing methods have not focused on modeling the hidden node scenario in cognitive radio networks. Further, these methods are unable to adapt to the dynamic channel conditions in the wireless environment since they have not considered the effect of fading environment. Motivated from these limitations, we propose GCN-CSS, a novel Graph Convolution Network (GCN) based cooperative spectrum sensing methodology which adapts to the dynamic changes in the Cognitive Radio Network. To the best of the author's knowledge, this is the first work to apply GCN for solving CSS problem. We have considered a practical system model which handles the dynamic channel condition i.e. SUs with multiple antennas experiencing different fading models with different fading severity. We have also catered the scenario of imperfect reporting channel between the SUs and the fusion centre along with the imperfect sensing channel to prove the robustness of the proposed model. With sufficient simulations, the superiority of the proposed methodology is proven in different dynamic scenarios of the wireless environment.

On the Secrecy Analysis of Dual-Hop SWIPT-Based Multi-Source Underlay Cognitive Radio Networks

This paper investigates the intercept probability (IP) performance for a dual-hop multi-secondary user (SU) underlay cognitive-radio networks. Whereby, the relay R is self-powered by harvesting energy from secondary sources using the time switching variant (TS) of simultaneous wireless information and power transfer (SWIPT) protocol. Single-antenna SUs are transmitting data to multi-antennas end-user D, performing maximal-ratio combining (MRC) diversity technique, through R in presence of (i) a primary network composed of a primary transmitter <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(\mathrm {PU_{t}})$ </tex-math></inline-formula> and receiver <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$(\mathrm {PU_{r}})$ </tex-math></inline-formula> pair, and (ii) a passive eavesdropper at each hop (i.e., E1 and E2), attempting to overhear the communication. Moreover, we suppose that the second eavesdropper has multiple antennas and employs the MRC technique, that the relay employs the Decode-and-Forward relaying protocol, that the two hops are subject to the Rayleigh fading model, and that the channel state information is fully known at both D and E2. Because of the underlying strategy, the SUs are constantly modifying their transmit powers to prevent interference with primary users. A closed-form expression of the IP is obtained by taking into consideration the correlation between the secrecy capacities for both hops. The impact of other essential factors on IP, such as the transmit power of sources, the fading severity parameter, and the maximum tolerable interference power (MTIP), is also investigated. Specifically, we want to know if the energy harvester (i.e., relay) might improve the security of such a system even more for low MTIP or transmit power of SUs. Monte Carlo simulations verify all of the obtained results, and valuable insights into the secrecy of the considered system are achieved.

PERFORMANCE ANALYSIS OF GMSK-BASED COOPERATIVE COMMUNICATION IN WIRELESS SENSOR NETWORKS

An efficacious energy model based on Gaussian minimum shift keying (GMSK) for cooperative communication is proposed in this paper. The influence of the rate at which data are transmitted, distance, severity of fading, and quantity of participating nodes on the energy expended for communication by the proposed model is investigated through simulations. The influence of the rate at which data are transmitted and the quantity of participating nodes on the energy expended in circuitry is also studied. Through the simulations, it is apparent that the energy consumed by the circuit dominates the energy consumed for transmission for all of the transmission data rates, path loss exponents, bit error rates, and transmission distances considered.

Performance Analysis of Dual-Hop AF Cognitive Relay Networks with Best Selection and Interference Constraints

In this paper, a dual-hop underlay cognitive relay network (CRN) with a best-relay selection (BRS) scheme under spectrum-sharing constraints from the primary user (PU) is investigated. The system model in this work consists of one PU, one secondary user (SU) and a few SU relays. Both users exchange the information using a half-duplex mode through amplify-and-forward (AF) SU relays. Moreover, all channels are modelled using the Nakagami-m fading model. In this work, the outage probabilities (OPs) are derived for the proposed system model under several scenarios to investigate the network performance under interference power constraint Ip at the PU receiver. In addition, the impacts of the number of relays and the channel fading severity parameters are investigated as well. Furthermore, the system performance is investigated for several PU locations. The various numerical results are verified using a Monte Carlo simulation. Overall, the obtained results show that several factors such as the number of relays, channel fading severity parameters and PU location have a major impact on the outage performance of the SU. The simulation and analytical results are perfectly matched, confirming the accuracy of the analytical derivations.

Secrecy Outage Analysis of Relay-User Pairing for Secure Hybrid Satellite-Terrestrial Networks

In this paper, we study the physical-layer security of a hybrid satellite-terrestrial network composed of a satellite, multiple terrestrial decode-and-forward (DF) relays and users in the presence of a terrestrial eavesdropper who attempts to tap legitimate information from both satellite and relays. We consider two different scenarios: I) the channel state information (CSI) of wiretap links is known, and II) the CSI of wiretap links is unknown. Accordingly, optimal and suboptimal relay-user pairing schemes are proposed for the aforementioned two scenarios, respectively. Specifically, a relay-user pair maximizing the secrecy rate is chosen as the optimal one to participate in the transmission, where all links’ CSI is used to perform relay-user pairing. However, suboptimal relay-user pairing scheme is designed only relying on the main links’ CSI without requiring wiretap links’ CSI, where a relay-user pair with the maximal transmission rate of main link is selected. Also, closed-form expressions of secrecy outage probability with both integer and rational fading severity parameter are derived in the case of satellite links undergo Shadowed-Rician fading and terrestrial links subject to Rayleigh fading. Furthermore, asymptotic secrecy outage probability analysis is conducted in the high signal-to-noise ratio region. Numerical results reveal that relay-user pairing is beneficial to further improve physical-layer security of the hybrid satellite-terrestrial network.

Mixed FSO/RF Based Multiple HAPs Assisted Multiuser Multiantenna Terrestrial Communication

In this work, a mixed free-space optics (FSO)/radio-frequency (RF) based multiple serial high altitude platforms (HAPs) assisted multiuser multiantenna terrestrial communication system is considered. For the considered multi-hop system, earth station to HAP and HAP to HAP links are assumed as FSO links, and HAP to terrestrial mobile users (MUs) link is assumed as RF link. At the FSO detector both the heterodyne detection and intensity modulation direct detection techniques are considered. Atmospheric turbulence of the ES to HAP FSO link is modeled with Gamma-Gamma fading along with the pointing error impairments. As HAP situates in the stratosphere, negligible atmospheric turbulence exists at HAP altitude (20 km), hence, only pointing error is considered for the inter HAP links. Further, the HAP consists of multiantenna array to provide high data-rates to the terrestrial users via RF links, considered to be Nakagami-m distributed. The intermediate HAPs perform selective decode-and-forward relaying and opportunistic user scheduling is performed for the best user selection. For the performance analysis, analytical expression of overall outage probability is obtained and the impact of various selection parameters like pointing error, FSO detection type, MU selection, number of antennas, and RF fading severity are observed on the outage performance. Asymptotic outage probability is also derived to obtain the diversity order of the considered communication system. Further, considering various modulation schemes, a generalized average bit-error-rate expression is derived and the impact of pointing error, FSO detection type, MU selection, number of antennas, and RF fading severity are observed on its performance. Finally, derived results are validated through Monte-Carlo simulations.

Capacity of Backscatter Communication Under Arbitrary Fading Dependence

We analyze the impact of arbitrary dependence between the forward and backward links in backscatter communication systems. Specifically, we quantify the effect of positive and negative dependence between these fading links on channel capacity by using Copula theory. The benefits of this approach are highlighted over the classical framework of linear dependence based on Pearson’s correlation coefficient, which is also analyzed. Results show that for a fixed transmit power budget, capacity grows with positive dependence as well as with fading severity in the low signal-to-noise ratio (SNR) regime. Conversely, fading dependence becomes immaterial in the high SNR regime.

Finite Block Length Analysis of RIS-Assisted UAV-Based Multiuser IoT Communication System With Non-Linear EH

Reconfigurable intelligent surface (RIS) has emerged as an important transmission technology for numerous applications in Internet of Things (IoT) systems. Thus, in this paper, we investigate the application of RIS in energy harvesting (EH) based unmanned aerial vehicle (UAV) communication network with finite block length (BL) codes, where a rotary wing type flying UAV communicates with the multiple single antenna IoT users with the aid of multiple RISs mounted on several skyscraper buildings. To transmit the signal to a particular IoT user, the UAV selects an RIS on the basis of either UAV-RIS (i.e., partial) or UAV-RIS-IoT (i.e., full) channel state information (CSI) and then transmits the signal through the selected RIS along with the direct link transmission. In particular, we derive (i) the expression for probability of RIS selection, (ii) the statistical distribution of instantaneously received information signal-to-noise ratio (SNR) at the IoT user. Based on the derived statistics, we analyze the performance of the considered system under finite BL codes in terms of the average outage probability, average block error rate (ABLER) and goodput averaged over entire flying duration. Moreover, the BLER performance with finite BL codes is also compared with the infinite BL codes scenario. Additionally, we also investigate the impact of various channel and system parameters like imperfect CSI, number of RISs and the number of reflecting elements at each RIS, location of IoT users, variable altitude of the UAV, and the severity of channel fading of UAV-RIS link on the system performance. Furthermore, we have obtained the optimum UAV location in each time slot which minimizes the ABLER per time slot over all the users in the network. The analytical results are corroborated with Monte Carlo simulations.

CSIN-assisted AF dual-hop relaying communication systems over imperfect Nagakami-[formula omitted] fading channels: Exact error performance

Relaying-based communication techniques are promising for current and future wireless systems. Amplify-and-forward (AF) relaying is more attractive due to the low cost and simplicity in its relay implementation. As compared to other AF schemes, the channel-state-information (CSI)-and-noise (CSIN)-assisted one is optimal and practically recommended. However, up to this moment, the exact symbol error rate (SER) performance of CSIN-assisted AF dual-hop relaying systems has been analytically derived only for Rayleigh fading environments, while for other more generic fading models, including Nakagami-m, it has been computed either approximately or via long-running time computer simulations. Thus, in this paper, we consider a CSIN-assisted AF dual-hop relaying system with independent and non-identical Nakagami-m fading channels and derive a new expression for its exact SER performance under the effect of imperfect channel estimation. The derived expression includes infinite series that can truncate quickly using a few terms, requires short computational time as compare to simulation, shows perfect matching with the simulation results, and offers remarkable accuracy enhancement over its approximate peer derived in literature. In addition, it helps in demonstrating some useful insights into the system’s realistic error performance considering different system and fading severity conditions. For example, results show that the system’s exact SER performance is dominated by the worse fading hop, does not change when the system’s two fading hops exchange their fading conditions, and improves faster with the per symbol average SNR when the fading severity conditions are better.

Performance evaluation of multiuser Internet of Things wireless‐powered relaying networks with transceiver hardware imperfections over Nakagami‐m fading channels

SummaryWe investigate the performance of multiuser Internet of Things (IoT) relay networks in the presence of transceiver hardware impairments. In particular, IoT users communicate with a destination via a simultaneous wireless information and power transfer (SWIPT) amplify‐and‐forward relay. We exploit both time‐switching (TS) and power‐splitting (PS) protocols at the SWIPT‐aided relay terminal. Specifically, we derive the exact outage probability (OP) expressions for both TS and PS schemes under transceiver hardware imperfections over Nakagami‐m fading channels. In addition, we derive the asymptotic OP expressions for both TS and PS schemes in the high signal‐to‐noise ratio regime. From which, the diversity order of can be achieved, where denotes the fading severity parameter for the channel between IoT users and relay. Furthermore, we present a tight upper bound for the ergodic capacity (EC) under both TS and PS schemes with transceiver hardware impairments over Nakagami‐m fading channels. Moreover, our results demonstrate the impact of number of IoT users, fading severity parameters, TS factor, PS factor, and energy conversion efficiency, on the system performance. We also validate our analytical findings via numerical and simulation results.

Capacity Estimation for a DS-CDMA System in Nakagami-m Fading

Ιn this paper, a novel closed-form expression of the Shannon average channel capacity per user for direct- sequence code-division multiple access (DS-CDMA) systems, operating in Nakagami-m fading, with optimum RAKE reception, is obtained. Numerical results are also presented to illustrate the proposed mathematical analysis and to point out the effect of the fading severity on the user’s average channel capacity.

Performance Analysis of RIS-Assisted FSO Communications over Fisher–Snedecor F Turbulence Channels

The Fisher–Snedecor (F-S) F distribution has recently been introduced as a tractable turbulence-induced (TI) fading model that fits well with the experimental data. This paper provides a performance evaluation of a free-space optical (FSO) re-configurable intelligent surface (RIS)-assisted communications (ACs) link over the F-S F TI fading channels, assuming the intensity modulation–direct detection (IM–DD) technique. In particular, novel and closed-form (C-F) analytical expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the end-to-end signal-to-noise ratio (SNR) in terms of Gaussian hyper-geometric functions are efficiently derived. Capitalizing on the obtained results, novel C-F analytical expressions for the moment generating function (MMGF), outage probability (OP), average bit error rate (BER) and ergodic channel capacity (Cγ) of the FSO RIS-ACs system over the F-S F TI fading channels are provided and numerically evaluated under the various TI fading severity conditions. Furthermore, the second-order (S-O) statistical expressions for the level crossing rate (LCR) and average fade duration (AFD) are obtained and thoroughly examined for various FSO RIS-ACs system model parameters.

Examination of the fifth-generation vehicular simultaneous wireless information and power transfer cooperative non-orthogonal multiple access network in military scenarios considering time-varying and imperfect channel state information conditions

In a defense scenario, the communicating nodes are mobile and, due to this, the fading channel links become time selective in nature. Non-orthogonal multiple access (NOMA) is a promising technique in modern wireless communication systems, and it is employed in a variety of defense ad hoc wireless communication scenarios where nodes are mobile and it is difficult to estimate the channel coefficients perfectly. NOMA contributes to increased spectral efficiency (SE), firstly by enabling fifth-generation new radio deployment in the 3.5 GHz frequency range, and secondly by employing a simultaneous wireless information and power transfer (SWIPT) time switching and power splitting-based cooperative NOMA (C-NOMA) network where simple radio frequency circuitry is used for energy harvesting. NOMA together with the selective decode-and-forward (S-DF) protocol will increase the SE and energy efficiency simultaneously. The outage probability performance is evaluated for various values of the fading severity parameter and node velocity forming the channel error. It is significant to note that digital S-DF-based SWIPT C-NOMA performs much better than an analog amplify-and-forward-based C-NOMA SWIPT system.

New look on relay selection strategies for full-duplex multiple-relay NOMA over Nakagami-m fading channels

By removing the orthogonal use of radio-resources, non-orthogonal multiple access (NOMA) has been introduced to improve the spectral efficiency of fifth generation (5G) and beyond networks. This paper studies the system performance in a dual-hop multi-relay NOMA using decode-and-forward (DF) scheme over Nakagami-m fading channels. A group of NOMA users is considered, i.e. the near and far users which are decided by how strong these related channels are. Specifically, we obtain a closed-form expression of the outage probability of the near/far NOMA users when the several relay selection schemes are adopted for selecting the best among M intermediate relays. As main finding, this paper introduces three strategies including two-stage relay selection, max-min and power allocation based relay selection schemes. As main benefit, the NOMA users are considered to employ selection combining technique in order to improve signal transmissions for an increased reliability in the context of massive connections in 5G wireless communications. By conducting numerical simulations, we evaluate the impact of the number of intermediate relays, the NOMA power allocation factor, and the Nakagami-m fading severity parameter on the outage performance of the NOMA users. Finally, the outage probability along with throughout in delay-limited transmission mode are provided via numerical results and the necessary comparisons are provided.

New Results and Applications about the Level Crossing Rate of SC Receiver output Signal in the Presence of Gamma Shadowing and k-μ or Rician Multipath Fading

In this paper,the wireless communication system with dual SC receiver operating over shadowed multipath fading channel is considered. The multipath fadingis k-μor Rician.The received signal experiences the short term fading which is resulting in SC receiver envelope variation and Gamma long term fading resulting in SC receiver envelope power variation. The closed form expressions for joint probability density functions of SC receiver output signal envelope and their first derivative of SC receiver output signal envelope are calculated for both, k-μand Rician fading. These expressions are used for evaluation of average level crossing rate of SC receiver output signal envelopes. The numerical expressions are plotted to show the effect of Rician fading severity parameter and Gamma shadowing severity parameter on the average level crossing rate of SC receiver output signal envelope.

Performance analysis of L-MRC receiver with estimation error over Beaulieu-Xie fading channels

A smart receiver is used in advanced wireless communication to trim down the fading and shadowing effects. Performance of such receivers depends on the accuracy of the channels estimation. This paper derived general expression of average bit error rate (BER) and outage probability for L branch Maximum Ratio Combining (L-MRC) receiver over Beaulieu-Xie (BX) fading channels with Imperfect Channel Estimation (ICE). The BX fading model characterizes dominant multiple specular components with some diffuse power. The probability density function (PDF) of output signal to noise ratio is evaluated for L-MRC receiver with channel estimation error over the BX model. The expression of average BER is formulated for binary coherent and non-coherent modulation and the outage probability of the system. The impacts of severity of fading and error estimation on the system performance are analyzed by using the numerical evaluation of the finding expressions.