Rician Fading Channels Research Articles

Massive Unsourced Random Access Over Rician Fading Channels: Design, Analysis, and Optimization

In this article, we investigate an unsourced random access scheme for massive machine-type communications (mMTC) in the sixth-generation (6G) wireless networks with sporadic data traffic. First, we establish a general framework for massive unsourced random access based on a two-layer signal coding, i.e., an outer code and an inner code. In particular, considering Rician fading in the scenario of mMTC, we design a novel codeword activity detection algorithm for the inner code of unsourced random access based on the distribution of received signals by exploiting the maximum-likelihood (ML) method. Then, we analyze the performance of the proposed codeword activity detection algorithm exploiting Fisher Information Matrix, which facilitates the derivative of the approximated distribution of the estimation error of the codeword activity vector when the number of base station (BS) antennas is sufficiently large. Furthermore, for the outer code, we propose an optimization algorithm to allocate the lengths of message bits and parity check bits, so as to strike a balance between the error probability and the complexity required for outer decoding. Finally, extensive simulation results validate the effectiveness of the proposed detection algorithm and the optimized length allocation scheme compared with an existing detection algorithm and a fixed-length allocation scheme.

Probality Density Function Analysis of Multipath Fading with Phase Error over Rayleigh and Rician Fading Channels in Equal Gain Diversity

Probality Density Function Analysis of Multipath Fading with Phase Error over Rayleigh and Rician Fading Channels in Equal Gain Diversity

Optimization of inter-fusion rule threshold for energy-efficient cluster-based cooperative spectrum sensing over Nakagami and Rician fading channels

ABSTRACT In cooperative spectrum sensing (CSS), in order to maximise the energy efficiency (EE) of cognitive radio (CR) users, users are divided into clusters. In this paper, the optimal inter-fusion rule threshold formula for different number of clusters and users is proposed for maximum EE in cluster-based CSS (CB-CSS). Different fusion rules are investigated for this purpose over Nakagami and Rician fading channel conditions. Simulations are conducted for different number of clusters and users using AND and OR intra-fusion rules and inter-fusion rule threshold is optimised in CB-CSS over the Nakagami-m fading channel and the Rician fading channel. The obtained mathematical expression for the inter-fusion rule threshold is verified by the results. It is investigated that when number of clusters are and number of users in a cluster are , OR-AND (, ) fusion rule achieves 2.46% more EE than AND-OR (, ) fusion rule in case of Nakagami fading channel and 5.06% more EE than AND-OR fusion rule in case of Rician fading channel. Further, EE with respect to number of users is compared between additive white gaussian noise (AWGN) channel and Nakagami and Rician fading channels.

On the Capacity-Achieving Input of Channels With Phase Quantization

Several information-theoretic studies on channels with output quantization have identified the capacity-achieving input distributions for different fading channels with 1-bit in-phase and quadrature (I/Q) output quantization. However, an exact characterization of the capacity-achieving input distribution for channels with multi-bit phase quantization has not been provided. In this paper, we consider four different channel models with multi-bit phase quantization at the output and identify the optimal input distribution for each channel model. We first consider a complex Gaussian channel with $b$-bit phase-quantized output and prove that the capacity-achieving distribution is a rotated $2^b$-phase shift keying (PSK). The analysis is then extended to multiple fading scenarios. We show that the optimality of rotated $2^b$-PSK continues to hold under noncoherent fast fading Rician channels with $b$-bit phase quantization when line-of-sight (LoS) is present. When channel state information (CSI) is available at the receiver, we identify $\frac{2\pi}{2^b}$-symmetry and constant amplitude as the necessary and sufficient conditions for the ergodic capacity-achieving input distribution; which a $2^b$-PSK satisfies. Finally, an optimum power control scheme is presented which achieves ergodic capacity when CSI is also available at the transmitter.

An Aggressive Cuckoo Search Algorithm for Optimum Power Allocation in a CDMA-Based Cellular Network.

This paper proposes an aggressive cuckoo search algorithm for optimum power allocation in a CDMA-based cellular network. To make the cuckoo search algorithm aggressive, adaptive parameters are used to vary the step size and probability of discovery. Furthermore, the Lévy flight is replaced with the Beta distribution to further improve the performance of the algorithm. To prove that the proposed algorithm is superior, the algorithm is tested on 23 benchmark test functions and its results are compared with those of 10 other standard optimization algorithms and 4 other advanced optimization algorithms. The performance of the proposed algorithm is proved via the statistical analysis of the results using the Wilcoxon rank-sum test. The proposed algorithm is then utilized in determining the optimal uplink power for multiple users in a CDMA-based cellular network in three different scenarios through Rician fading channels. The resultant allocated power should ensure that each mobile station meets its predetermined signal-to-interference-and-noise ratio while utilizing the least amount of power.

Reconfigurable Intelligent Surface aided Indoor and Outdoor User Distribution in Heterogeneous Network

Millimeter wave communication suffers from static blockages such as trees, buildings and so on. Reconfigurable Intelligent Surfaces (RISs) has been adapted to solve this blockage problem and enable the urban environment user to choose mmW enabled small cells as their source transmitter or to choose macro cells in case of non-line of sight exists. RIS is a promising network technology to improve the quality of service parameters such as spectral efficiency and energy efficiency by artificially reconfiguring the propagation environment of electromagnetic waves. An indoor user can be connected with mmW band if the line of sight (LOS) link exists. Otherwise, the system utilizes RIS transmission model to have reliable and low-latency communication. It reflects the capability of RISs to enable enhanced communications in challenging environments. An optimization problem is formulated to maximize the sum data rate of an indoor user by phase shift optimization at the RIS. The outage probability of the proposed scheme is analyzed under Rician fading channel. The proposed RIS enabled method targets to enhance the overall performance in terms of average spectral efficiency and achievable data rate in the presence of blockages and system imperfections. The data rate is increased by three fold times than that of the transmission without RIS. The utility of this framework is discussed for both indoor and outdoor environments.

Spatially Correlated Reconfigurable Intelligent Surfaces-Aided Cell-Free Massive MIMO Systems

Reconfigurable intelligent surfaces (RISs) and cell-free (CF) massive multiple-input multiple-output (MIMO) are two promising technologies for realizing beyond-fifth generation (5G) networks. In this paper, we study the uplink spectral efficiency (SE) of a practical spatially correlated RISs-aided CF massive MIMO system over Rician fading channels. Specifically, we derive the closed-form expression for characterizing the uplink SE of the system, which shows that increasing the number of RIS elements can improve the system performance. Moreover, the results unveil that the spatial correlation of RIS has a significant impact on the system while leading to the best performance gain at a half wavelength spacing. Finally, the accuracy of our analytical results are verified by Monte-Carlo simulations.

RIS-Aided Wireless Communications: Extra Degrees of Freedom via Rotation and Location Optimization

We consider the extra degree of freedom offered by the rotation of the reconfigurable intelligent surface (RIS) plane and investigate its potential in improving the performance of RIS-assisted wireless communication systems. By considering radiation pattern modeling at all involved nodes, we first derive the composite channel gain and present a closed-form upper bound for the system ergodic capacity over cascade Rician fading channels. Then, we reconstruct the composite channel gain by taking the rotations at the RIS plane, transmit antenna, and receive antenna into account, and extract the optimal rotation angles after investigating their impacts on the capacity. Moreover, we present a location-dependent expression of the ergodic capacity and investigate the RIS deployment strategy, i.e. the joint rotation adjustment and location selection. Finally, simulation results verify the accuracy of the theoretical analyses and deployment strategy. Although the RIS location has a big impact on the performance, our results showcase that the RIS rotation plays a more important role. In other words, we can obtain a considerable improvement by properly rotating the RIS rather than moving it over a wide area. For instance, we can achieve more than 200% performance improvement through rotating the RIS by 42.14°, while an 150% improvement is obtained by shifting the RIS over 400 meters.

Performance Analysis of a Prediction-Sensing Based Cooperative Energy Harvesting CRN Over Rician Fading Channels

Performance Analysis of a Prediction-Sensing Based Cooperative Energy Harvesting CRN Over Rician Fading Channels

A Modified Geometry-Based MIMO Channel Model for Tunnel Scattering Communication Environments

In this study, a modified non-stationary geometry-based scattering model for tunnel vehicle-to-vehicle (V2V) multiple-input multiple-output Ricean fading channels is presented. The proposed channel introduces non-line-of-sight three-dimensional multi-bounced scattering propagation paths under an assumption of equivalent scattering points to depict the tunnel environments, in which the scatterers are randomly distributed on the semi-cylindrical tunnel wall (i.e., cable racks, jetfans, road signs, lighting facilities). Furthermore, the time-varying channel statistics (i.e., the space and frequency correlation functions) resulting from the relative movement between the mobile transmitter and mobile receiver are analyzed. Finally, numerical results show that the space correlations of the proposed model significantly decrease when the multi-bounced scattering rays are taken into account; moreover, when the velocity and the antenna angle γR increase, the correlations decrease therewith, which exhibits good agreement with the existing V2V scattering channel models and measured data in a real tunnel environment, demonstrating the rationality of the underlying channel model.

Multiple reconfigurable intelligent surfaces assisted downlink NOMA system

SummaryPaper has considered multiple reconfigurable intelligent surfaces (RISs) assisted downlink non‐orthogonal multiple accesses (NOMA) system, referred to as MR‐NOMA. Multiple RISs create a line‐of‐sight (LOS) channel between BS and users to improve network coverage, especially in high frequencies and severe path attenuation scenarios. In MR‐NOMA, all RISs are in series and activated simultaneously; therefore, multiplicative beamforming gain from the inter‐RIS channels is achieved. Bit error probability (BEP) under the Rician fading channel is derived and compared with simulation results. It is observed that BEP performance depends on the number of passive reflecting elements, Rician factor, and positions of RISs panels in the MR‐NOMA.

Weighted Sum-Rate of Intelligent Reflecting Surface Aided Multiuser Downlink Transmission With Statistical CSI

Intelligent reflecting surface (IRS) is a newly emerged technology that can increase the energy and spectral efficiency of wireless communication systems. This paper considers an IRS-aided multi-user multiple-input single-output (MISO) communication system, and presents a detailed analysis and optimization framework for the weighted sum-rate (WSR) of the downlink transmission over Rician fading channels. Unlike most of the prior works where the active beamformer at the base station (BS) and passive beamformer at the IRS are jointly designed based on the instantaneous channel state information (CSI), this paper proposes a low-complexity transmission protocol where the IRS passive beamforming and BS power allocation coefficient vector are optimized in the large timescale based on the statistical CSI, and the BS transmit beamforming is designed in the small timescale based on only the instantaneous CSI of the effective BS-user channels. Therefore, the channel training overhead in each channel coherence interval under our proposed protocol is independent of the number of IRS reflecting elements, which is in sharp contrast to most of the prior works. By considering maximum-ratio transmit beamforming at the BS, we derive a lower bound of the ergodic WSR in closed-form. Then, we propose an efficient algorithm to jointly optimize the IRS passive beamforming and BS power allocation coefficient vector for maximizing the ergodic WSR lower bound. Numerical results validate the tightness of our derived WSR bound and show that the proposed scheme outperforms various existing schemes in terms of complexity or capacity performance.

Completion time minimization for multi-antenna UAV-enabled data collection in uncorrelated Rician fading

In 5G, the unmanned aerial vehicle (UAV) is regarded as an essential way to support energy-saving, reliable, and low-cost data collection in wireless sensor networks. However, UAV-based data collection inevitably suffers from more significant data collection delays due to the UAV movement time in large application scenarios. In this paper, we consider a UAV-enabled wireless sensor network under the uncorrelated Rician fading channel, where a multi-antenna UAV is dispatched to collect data from ground sensor nodes (SNs). The objective is to minimize the mission completion time, including UAV flight and data collection time, by jointly optimizing UAV trajectory, UAV-SN transmission scheduling, and trajectory-based time allocation under the constraints of UAV speed, outage probability, data size, and transmission power. To solve this nonconvex problem, we decompose it into two subproblems: 1) trajectory optimization and 2) UAV-SN transmission scheduling and trajectory-based time allocation optimization. In the trajectory optimization, we first rewrite the outage probability constraint into the communication distance constraint and propose a Spiral-based method to find the shortest trajectory covering all SNs. Then, we propose a scheduling initialization algorithm and employ alternating optimization to solve the UAV-SN transmission scheduling and trajectory-based time allocation optimization. Finally, numerical results show that the proposed algorithm outperforms the benchmark and typical algorithms in terms of the mission completion time through a large number of experiments.

Performance Analysis and Optimization of NOMA-Based Cell-Free Massive MIMO for IoT

This article investigates the performance of nonorthogonal multiple access (NOMA)-based cell-free massive multiple-input–multiple-output (mMIMO) for the Internet of Things (IoT) considering spatially correlated Rician fading channels. The exact closed form of downlink spectral efficiency (SE) and energy efficiency expressions is derived with three estimators and the maximum ratio transmission by taking the impacts of imperfect successive interference cancellation and pilot contamination into account. Subsequently, the performance of a local-MMSE precoder with the three aforementioned estimators is analyzed. Then, a large-scale fading-based user pairing scheme is proposed to further analyze the system SE. Besides, we formulate the optimum power control design as a max–min problem and a computational efficient suboptimal algorithm is proposed based on the successive convex approximation. Furthermore, our results reveal that the magnitude of the spatial correlation negligibly effects the SE in spatially correlated Rician fading channels. Then, numerical results confirm the positive effect of the proposed power control scheme. Also, our results further illustrate that NOMA-based cell-free mMIMO for IoT provides significant performance gain compared with its counterpart deploying conventional orthogonal multiple-access schemes.

Achievable Rate and Energy Efficiency Analysis of Multiuser Relay-Aided Massive MIMO Downlink

In this article, the achievable sum rate and the energy efficiency (EE) are investigated for a multiuser relay-aided massive multiple-input–multiple-output (MIMO) downlink. Low-resolution digital-to-analog converters (DACs) are equipped at both the base station (BS) and the relay station (RS), and the amplify-and-forward protocol is adopted at the RS. Under the Rician fading channel, closed-form approximate expressions for the achievable sum rate are derived with perfect and imperfect channel state information. A more general power law is extracted to save transmit power without reducing the achievable sum rate, and a local optimal power allocation scheme is proposed to improve the channel capacity of active users. Then, the tradeoff between the achievable sum rate and the EE is discussed. The numerical results show that, due to the quantization noise, the transmit power has a limited increase in the achievable rate. In addition, it is more valuable to improve the DAC quantization bit at the RS when the number of BS antennas is larger than that of RS antennas. In addition, under strong line-of-sight channels or high pilot transmit power conditions, the channel estimation accuracy is higher, and the best tradeoff between the achievable sum rate and the EE can be obtained when the DAC quantization bit is 4.

Performance analysis of RIS aided NOMA networks with hardware impairments

Reconfigurable intelligent surface (RIS) has stimulated their potential applications for improving the performance of wireless communication networks. In this paper, the performance of RIS aided non-orthogonal multiple access (NOMA) networks with hardware impairments over Rician fading channels is investigated. More specifically, the exact and asymptotic expressions of outage probability for a pair of users, that is, the nearby user n and distant user m are derived, where the imperfect successive interference cancellation (ipSIC) and perfect SIC (pSIC) are taken into consideration. According to the approximate analyses, the diversity orders of user n with ipSIC/pSIC and user m are obtained in the high signal-to-noise radio regime. It indicates that the diversity orders are in connection with reflecting elements and Rician factors except the channel ordering. The impact of these parameters on outage behaviors of RIS-NOMA networks is also analysed. In addition, the system throughput of RIS-NOMA networks with ipSIC/pSIC is surveyed in detail. Monte Carlo simulations are present to verify the correctness of theoretical analyses that: (1) The outage probability of user n with pSIC is superior to that of orthogonal user, while the outage probability of user m is inferior to that of orthogonal user and (2) as the number of reflecting elements and Rician factors increases, the outage behaviors of RIS-NOMA networks are enhanced carefully.

On the spectral efficiency of cell‐free massive MIMO system in irregular 5G mobile networks

SummarySpectral efficiency (SE) is one of the eminent requirements in 5G mobile networks. Cell‐free (CF) massive MIMO is deemed a key technology to provide substantial SE in 5G compared with the cellular and small cell approaches. Most of the prior studies have been focusing on the access points (APs) uniform distribution to assess the SE performance. However, 5G networks are typically dense, irregularly distributed, and mostly constrained by channel impairments. Therefore, considering a uniform distribution of APs is unrealistic. This paper considers a practical network distribution by taking into account the irregular and adaptive APs distribution based on the Poisson point process approach and over the Rician fading channels. Therein, the downlink (DL) SE of CF massive MIMO system is accurately investigated bearing in mind the AP's irregular distribution and fast channel variation for both perfect and imperfect channel state information (CSI) cases. The simulation results have shown that the DL SE of the CF massive MIMO system is considerably affected when considering the irregular deployment of APs compared with the uniform distribution, especially when the phase noise effect is tense. The SE gain performance is reduced by 37.9% in the DL transmissions, compared with the uniform model. Besides, the results have proven that the DL SE gain is remarkably improved when the APs are largely distributed within the network. However, the gained DL SE is affected when increasing the user's density and length of the uplink training period.

Investigating the Combination of Deep Learning for Channel Estimation and Power Optimization in a Non-Orthogonal Multiple Access System.

In a non-orthogonal multiple access (NOMA) system, the successive interference cancellation (SIC) procedure is typically employed at the receiver side, where several user’s signals are decoded in a subsequent manner. Fading channels may disperse the transmitted signal and originate dependencies among its samples, which may affect the channel estimation procedure and consequently affect the SIC process and signal detection accuracy. In this work, the impact of Deep Neural Network (DNN) in explicitly estimating the channel coefficients for each user in NOMA cell is investigated in both Rayleigh and Rician fading channels. The proposed approach integrates the Long Short-Term Memory (LSTM) network into the NOMA system where this LSTM network is utilized to predict the channel coefficients. DNN is trained using different channel statistics and then utilized to predict the desired channel parameters that will be exploited by the receiver to retrieve the original data. Furthermore, this work examines how the channel estimation based on Deep Learning (DL) and power optimization scheme are jointly utilized for multiuser (MU) recognition in downlink Power Domain Non-Orthogonal Multiple Access (PD-NOMA) system. Power factors are optimized with a view to maximize the sum rate of the users on the basis of entire power transmitted and Quality of service (QoS) constraints. An investigation for the optimization problem is given where Lagrange function and Karush–Kuhn–Tucker (KKT) optimality conditions are applied to deduce the optimum power coefficients. Simulation results for different metrics, such as bit error rate (BER), sum rate, outage probability and individual user capacity, have proved the superiority of the proposed DL-based channel estimation over conventional NOMA approach. Additionally, the performance of optimized power scheme and fixed power scheme are evaluated when DL-based channel estimation is implemented.

On the Performance of Cooperative Relaying Systems with NOMA in κ − μ Fading Environment

Nonorthogonal multiple access (NOMA) is considered to be a promising solution for the fifth generation (5G) wireless networks. The performance of the 5G wireless networks in terms of outage probability, achievable rate, and other important network performance metrics can be remarkably improved by the integration of NOMA with cooperative relaying transmission technique. In this paper, we investigate the performance of the cooperative relaying system integrated with NOMA in terms of outage probability and achievable rate over κ − μ fading channels. Analytical expressions for the outage probability and the achievable rate are obtained for the system mentioned above. Moreover, corresponding expressions for Rician and Rayleigh fading channels are also presented in this paper as special cases of κ − μ fading channels. Some numerical examples are presented here for illustration purposes. The analytical results obtained in this paper are all validated via simulation.

Моделирование каналов связи с многолучевым распространением сигналов процедурами помехоустойчивого кодирования в рамках стандарта LTE

A scheme of orthogonal frequency division multiplexing technologies with a cyclic prefix was used, using the fast Fourier transform algorithm and amplifiers on the transmitter side and a normalizer on the receiver side. By adjusting the gains of the transmitting and receiving sides, the circuit practically makes it possible to reduce situations when inter-symbol interference (ISI) is affected to situations where it does not exist. The proposed model is modeled using Simulink based on MATLAB. The scheme was investigated for the bit error rate (BER) using the additive white Gaussian noise (AWGN) channel and the multipath Rice fading channel operating under the influence of ISI and different parameters for the channel were investigated, where cases of signal delay similar to the EPA standards (Extended Pedestrian A model) were considered. Data transmission in the system includes a Relay channel and AWGN with different values of signal-to-noise ratio (SNR, dB) and different values of Gain, dbGain amplifier. Result: A graph of data transmission performance in a multipath channel with fading with respect to BER and SNR (BER ≈ 0 with values of SNR –21dB) was obtained. The effect of intersymbol interference on the receiver side is also considered by analyzing eye diagrams. The research data can be used in the design of radio engineering devices for data transmission over a wireless network.