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Summary In this paper, we investigate the performance of a rate‐splitting multiple access (RSMA)‐based intelligent reflecting surface (IRS)‐assisted uplink hybrid satellite‐terrestrial network. We consider three different scenarios based on the channel phase knowledge at the IRS, namely, the ideal, partial, and blind cases. In the ideal case, the IRS has full knowledge of both the user‐to‐IRS and IRS‐to‐satellite channel phase information. In the partial case, the IRS has only the user‐to‐IRS channel phase information. Last, in the blind case, the IRS has no any knowledge of the phase information. We assume that the user‐to‐IRS channel follows Rician fading, and the IRS‐to‐satellite channel follows the shadowed Rician fading. The closed‐form tight outage probability expressions for all three scenarios are derived. The accuracy of the derivations is confirmed by simulation results. In addition, it is shown that the performance of the RSMA‐based system is superior to those of the conventional non‐orthogonal and orthogonal multiple access‐based systems with a small number of reflecting elements at high target rates. [ABSTRACT FROM AUTHOR]

Rate splitting multiple access (RSMA) is a powerful and upcoming multiple access technique that can serve as a promising technology for 5G and beyond applications. Due to the increase in the number of indoor communication devices, the internet of everything (IoE) demands higher bandwidth. Visible light communication (VLC) would be a viable solution for an indoor environment that offers high bandwidth, cost-free spectrum, and low power, and if employed with RSMA, the sum rate can be maximized. In this paper, we derive the closedform outage probability (OP) for the downlink RSMA-based VLC scheme over Rayleigh and Rician channels. We perform outage analyses for perfect as well as imperfect channel state information (CSI) and successive interference cancellation (SIC), respectively to study the system characteristics. Also, we show the superiority of RSMA over non-orthogonal multiple access (NOMA) for VLC-based system in terms of OP over Rayleigh and Rician channels. From the simulations, we show that the RSMA-based VLC system outperforms conventional NOMAbased VLC and the quality of services improves with the line of sight communication i.e., the Rician fading channel. [ABSTRACT FROM AUTHOR]

Massive multiple-input-multiple-output (M-MIMO) offers remarkable advantages in terms of spectral, energy, and hardware efficiency for future wireless systems. However, its performance relies on the accuracy of channel state information (CSI) available at the transceivers. This makes channel estimation pivotal in the context of M-MIMO systems. Prior research has focused on evaluating channel estimation methods under the assumption of spatially uncorrelated fading channel models. In this study, we evaluate the performance of the minimum-mean-square-error (MMSE) estimator in terms of the normalized mean square error (NMSE) in the uplink of M-MIMO systems over spatially correlated Rician fading. The NMSE allows for easy comparison of different M-MIMO configurations, serving as a relative performance indicator. Besides, it is an advantageous metric due to its normalization, scale invariance, and consistent performance indication across diverse scenarios. In the system model, we assume imperfections in channel estimation and that the random angles in the correlation model follow a Gaussian distribution. For this scenario, we derive an accurate closed-form expression for calculating the NMSE, which is validated via Monte-Carlo simulations. Our numerical results reveal that as the Rician K -factor decreases, approaching Rayleigh fading conditions, the NMSE improves. Additionally, spatial correlation and a reduction in the antenna array interelement spacing lead to a reduction in NMSE, further enhancing the overall system performance. [ABSTRACT FROM AUTHOR]

In this paper, we derive the maximum likelihood (ML) detector for downlink power domain non-orthogonal multiple access (PD-NOMA) in Rician fading channel, to enhance the detection performance of the previously proposed schemes. Then, we modify this ML detector to obtain the boundary based ML (BBML) detector which has much lower computational complexity compared to the original ML while it has the same error probability performance. This detector uses the full statistical channel state information (CSI), and for decision making, compares the received signal with the boundaries obtained based on ML criterion. The delay of this method is less than that of traditional successive interference cancellation (SIC). Analytic and simulation results show that the BBML detector is more efficient than SIC and also previously proposed multi-threshold detector (MTD), in downlink NOMA systems. [ABSTRACT FROM AUTHOR]

Neighbourhood area network (NAN) performance is analyzed with space shift keying (SSK) modulation and energy harvesting-based cooperative amplify-and-forward (AF) relaying. Wifi-enabled home appliances (HAs) can transfer the information to the utility control centre through the smart meter (SM) in the NAN. The HAs in NAN work on a power-saving mechanism, and they drastically increase the spectral efficiency. The Markov chain dynamically models the number of active HAs in the smart grid (SG) network. Moreover, simultaneous wireless information and power transfer combined with AF relaying-based SM helps overcome the rising demands of SG communication by providing an enhanced data rate, low latency, shorter coverage, widespread connectivity of the massive number of devices along with energy-efficiency. Mathematical expressions for average bit error probability are derived for NAN over mixed Saleh–Valenzuela and Rician fading channel based on the multi-user selection combination. The Monte Carlo simulation verifies the numerical results. The result illustrates that the SG NAN performance can be improved by combining SSK modulation with energy harvesting schemes. [ABSTRACT FROM AUTHOR]

In this paper, Drone-Assisted-Cooperation (DAC) for multi-cluster disaster scenarios have been considered, where the drone serves as an aerial relay among the ground users (GUs) belonging to each cluster. In particular, the probability-based statistical channel model is considered for assigning air-to-ground (A2G) links and Rayleigh channel distribution among GUs for multi-cluster DAC systems. In this proposal, we assume the probability-based statistical channel model among A2G links to be statistically independent of each other and dependent on the drone height and other surrounding environmental parameters. The system performance for the proposed scenario is evaluated using amplify-and-forward (AF) relaying at the drone and considering maximal ratio combining as a signal-combining approach at the destination.Two algorithms have also been developed in this study, one for modelling the A2G links and another for calculating the performance metrics of the proposal. The analytical framework has been developed for the proposed work and performance has been compared with the existing Rayleigh and Rician channel model. Furthermore, for a given drone height, the AF-noise component and variance of the AF-noise component have also been evaluated. However, the actual performance in the case of the proposed work comes over the existing state-of-the-art (Rayleigh and Rician fading distribution environment) in practical scenarios. [ABSTRACT FROM AUTHOR]

Pattern division multiple access (PDMA) is a one type of multi-domain nonorthogonal multiple access (NOMA) that support massive connectivity and can improve spectral efficiency. The unique pattern is used by each user to map its transmitting data into a group of resource, which consist of frequency, code and spatial domain or combination of these resources. Power scaling and phase shifting are used to resolve ambiguity as consequence non uniform distribution of the received combined constellation. In this paper, we propose investigation on power scaling factor for each user in PDMA matrix to increase sum rate transmission and propose combine successive interference cancellation (SIC) based on diversity order and power scaling factor for each user. The simulation results confirm that the proper implement power scaling factor in pattern type 2 show best performance in Rician fading channels. [ABSTRACT FROM AUTHOR]

The practical applications within the domain of the fifth generation (5G) and the emerging beyond 5G network necessitate a high data transmission rate along with minimal achievable delay. With this objective in focus, the maximum capacity is extensively quantified through the utilization of the delay‐constrained effective capacity (EC) technique, which stands in contrast to Shannon's ergodic capacity. The current study is engaged in the analysis of EC within a delay‐limited wireless system operating in a double‐shadowed Rician (DSR) fading channel. Within this channel, only the Nakagami‐m distribution concept has been applied to both the dominant and secondary shadowing components of the proposed network model. A new exact closed‐form expression for EC within the DSR fading channel has been derived using the Fox‐H function. Furthermore, an analysis has been conducted for both high and low signal‐to‐noise ratios to provide further insights and explanations for the proposed model. It is worth noting that the results obtained from both simulation and analytical methods exhibit substantial similarity, revealing interdependence among various parameters present in the proposed model. Key Points: A closed‐form expression for effective capacity (EC) analysis is derived for a Double Shadowed Rician‐fading channel based on Nakagami‐m distribution only, utilizing the Fox‐H functionAdditionally, an investigation into the closed‐form EC expression at high signal‐to‐noise ratio (SNR) is undertaken. Furthermore, novel EC formulations are developed for communication systems operating in low‐SNR environmentsFinally, simulation results obtained from mathematical derivations are presented to validate the accuracy of the derived expressions [ABSTRACT FROM AUTHOR]

Recently, cell-free (CF) architectures, in which every user can potentially communicate with every base station, have received a lot of attention. This paper considers the uplink of fully and partially centralized CF networks where unmanned aerial vehicles serve as flying base stations (FBSs). A subset of FBSs participates in the reception of each user and a subset of users is received by each FBS. Deterministic equivalent expressions, exact asymptotically in the subset sizes and approximate for finite dimensions thereof, are derived for the spectral efficiency under Rician fading. Capitalizing on these expressions, the FBS deployment problem is investigated for different receiver architectures. The nonconvex deployment problem, tackled through a combination of gradient-based and Gibbs sampling algorithms, results in a superior performance with respect to a square grid deployment; this superiority extends to the minimum and aggregate spectral efficiency for both fully and partially centralized cell-free networks.

Smart hospitals are poised to greatly enhance life quality by offering persistent health monitoring capabilities. Remote healthcare and surgery, which are highly dependent on low latency, have seen a transformative improvement with the advent of 5G technology. This has facilitated a new breed of healthcare services, including monitoring and remote surgical procedures. The enhanced features of 5G, such as Enhanced Mobile Broadband (eMBB) and Ultra-Reliable Low Latency Communications (URLLC), have enabled the development of advanced healthcare systems. These systems reduce the need for direct patient contact in hospitals, which is especially pertinent as 5G becomes more widespread. This research presents novel hybrid detection algorithms, specifically QR decomposition with M-algorithm maximum likelihood-minimum mean square error (QRM-MLD-MMSE) and QRM-MLD-ZF (zero forcing), for use in Massive MIMO (M-MIMO) technology. These methods aim to decrease the latency in MIMO-based Non-Orthogonal Multiple Access (NOMA) waveforms while ensuring optimal bit error rate (BER) performance. We conducted simulations to evaluate parameters like BER and power spectral density (PSD) over Rician and Rayleigh channels using both the proposed hybrid and standard algorithms. The study concludes that our hybrid algorithms significantly enhance BER and PSD with lower complexity, marking a substantial improvement in 5G communication for smart healthcare applications. [ABSTRACT FROM AUTHOR]

In the wireless network, many physical conditions may arise where received signal power is shadowed by moving objects along the propagation paths, and further shadowing of the received signal may result from moving objects around the transmitters or receivers. This phenomenon is mathematically modelled in terms of the double (or dual) shadowing process brought about by fading channels where both dominant and scattered wave components fluctuate together. In this present study, the outcome aspects of dual-shadowed wireless fading channels are explored in accordance with outage analysis, channel capacity, and average bit error rate (ABER) for coherent as well as non-coherent modulation schemes. Here, the Rician envelope, which undergoes two shadowing effects, is assumed. The channel format described here is such that both dominant and scattered signals are impacted by the Nakagami m random variable (RV). As a model, the mathematical expressions are derived for channel capacity, outage analysis, and ABER for dual-shadowed Rician fading channels. The effects of different shadowing parameters are explored, and corresponding results are plotted. All the evaluative results are recognised by emulating the simulation results for various values of the fading parameters. [ABSTRACT FROM AUTHOR]

This paper investigates the reconfigurable intelligent surface (RIS)-aided uplink multicell massive multiple-input multiple-output (mMIMO) communication system with transceiver hardware impairments (THWIs), and the practical and feasible two-timescale scheme is used to design the phase shifts of the RIS. We consider the Rician channel model and use maximal-ratio combining (MRC) technology to process the received signal at the base stations (BS). The expression of the uplink achievable rate is derived and analyzed. Moreover, the genetic algorithm (GA) is used to optimize the phase shifts of the RIS to maximize the data rate. Finally, the accuracy of the derived results is verified. The simulation results show that appropriately increasing the number of RIS reflecting elements can compensate for the performance loss caused by inter-cell interference and THWIs and reduce the demand for BS antennas, which can significantly reduce the hardware costs at the BS. [ABSTRACT FROM AUTHOR]

The capture effect is a frequently observed phenomenon in vehicular ad hoc networks (VANETs) communication. When conflicts arise during time slot access, failure to access does not necessarily occur; instead, successful access may still be achieved. The capture effect can enhance the likelihood of multiple access and improve communication efficiency. The security of VANETs communication is undoubtedly the primary concern. One crucial approach to enhance security involves the design of an efficient and reliable medium access control (MAC) protocol. Taking into account both aspects, we propose a novel framed slotted Aloha (FSA) MAC protocol model. Firstly, we derive the closed-form expression for the capture probability in the Rician fading channel in this paper. Subsequently, we analyze how the number of vehicles and time slots influence the success probability of vehicle access channels as well as examine the impact of the capture effect on this success probability. Then, under constraints regarding vehicle access channel success probability, we derive optimal values for slot numbers, access times, and transmission power while proposing a comprehensive implementation method to ensure high access channel success probabilities. We verify both theoretical derivations and proposed methods through simulation experiments. [ABSTRACT FROM AUTHOR]

This paper studies the performance of location-based beamforming with the presence of artificial noise (AN). Secure transmission can be achieved using the location information of the user. However, the shape of the beam depends on the number of antennas used. When the scale of the antenna array is not sufficiently large, it becomes difficult to differentiate the performance between the legitimate user and eavesdroppers nearby. In this paper, we leverage AN to minimize the area near the user with eavesdropping risk. The impact of AN is considered for both the legitimate user and the eavesdropper. Closed-form expressions are derived for the expectations of the signal to interference plus noise ratios (SINRs) and the bit error rates. Then, a secure beamforming scheme is proposed to ensure a minimum SINR requirement for the legitimate user and minimize the SINR of the eavesdropper. Numerical results show that, even with a small number of antennas, the proposed beamforming scheme can effectively degrade the performance of eavesdroppers near the legitimate user. [ABSTRACT FROM AUTHOR]

In multicell massive MIMO system, the maximum limit on area throughput can be achieved by improving spectral efficiency and cell density, as well as bandwidth. In order to evaluate the area throughput for such scenarios, the spectral efficiency (SE) that utilizes the linear zero forcing uplink combining scheme, can be modeled under the Rician fading channel and the BS in case of up-links, is responsible to estimate the channel. Different from existing work, the proposed model incorporates various estimators such as minimum mean square error (MMSE), element-wise minimum mean square error estimators under Rician fading. The multicell scenarios with uplink (UL) massive MIMO has been analyzed using the proposed model under different cases such as pilot reuse factor, coherence block length, different number of antennas, and different estimators. The simulation results and analysis are presented based on these parameters. It is found that the average summation of SE per cell can be improved by optimizing MMSE channel estimation using ZF UL combiner, installing multiple BS antennas, serving multiple number of UEs per cell, and using efficient pilot reuse factor. The MMSE and ZF uplink combining are found to be more suitable in improving SE as compared to MMSE-MR. For example, the uplink SE of MMSE channel estimator for pilot reuse factors, 1, 3, and 4, is calculated as 22.5 bit/s/Hz/cell, 22.3 bit/s/Hz/cell, and 21 bit/s/Hz/cell, respectively. The uplink SE for EW-MMSE channel estimator with pilot reuse factors, 1, 3, and 4, is calculated as 22.5 bit/s/Hz/cell, 22 bit/s/Hz/cell, and 22 bit/s/Hz/cell, respectively. For the uplink SE of LS channel estimators, it can be 17.9 bit/s/Hz/cell, 20.2 bit/s/Hz/cell, and 20 bit/s/Hz/cell with pilot reuse factors as f = 1, 3, and 4, respectively. So, for f = 3, the maximum calculated uplink SE for MMSE, EW-MMSE, and LS is 17.6 bit/s/Hz/cell, 17.8 bit/s/Hz/cell, and 13 bit/s/Hz/cell, respectively. It can be concluded that the improved performance is obtained by reducing the pilot contamination at a pilot reuse factor f = 3 with different values of SNR, coherence block length, number of UEs, and number of BS antennas. There is also trade-off between the pilot contamination mitigation and the larger SE. However, there is not much effect on coherence block as when it increases, then the SE increases as well. [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicles (UAVs), which enable both high flexibility and low cost, have been widely used in both military and civilian application scenarios. In this paper, we investigate a fixed-wing UAV relay system, where the fixed-wing UAV acts as a mobile relay with an elliptical trajectory between base station and ground users with broken communication links because of obstructions. Different time and power allocations are utilized to compute the outage probability among the Rician fading channel model. Due to the complexity of the formulated issue, we approximate the asymptotic solution using the first-order Maclaurin series convex optimization. Finally, we contrast the elliptical trajectory relay's outage probability performance with that of the circular trajectory relay and the fixed relay. In the meanwhile, we examine the impact of the elliptical trajectory's various long and short axis ratios on the outage probability of a relay system. The efficiency of the suggested elliptical trajectory relay method has been demonstrated in simulations. [ABSTRACT FROM AUTHOR]

Summary: In this paper, we have presented the outage probability analysis of multiple intelligent reflecting surface (IRS)‐assisted single‐input‐single‐output (SISO) system with switched diversity schemes. The switched diversity is simpler than the selection combining diversity technique, which can help in reducing the channel estimation overhead. There are two main types of switch diversity schemes, namely, switch and stay combining (SSC) and switch and examine combining (SEC). We consider a SISO wireless scenario in which a single transmitting antenna is sending its message to the receiving antenna with the aid of multiple IRS panels. This communication scenario will arise as a typical application of uplink scenario for future 6G wireless systems. The outage probability (OP) expressions for dual‐IRS‐panel‐aided SSC system and multiple‐IRS‐panel‐aided SEC system are analyzed, respectively, over Rician fading channels. We derive tight approximate OP expressions in closed form for a large number of IRS elements. Further, we derive a simple asymptotic OP for studying diversity order and coding gain. The OP performance with respect to each system parameter is thoroughly explored. Several numerical OP results are presented with corresponding simulated OP results to validate the accuracy of the presented analytical analysis. [ABSTRACT FROM AUTHOR]

In the present scenario, with a rapidly growing demand for wireless data, it is time to improve the data rate for a wireless network. "NOMA-ARQ Network" known as "Non-Orthogonal Multiple Access—Automatic Repeat reQuest Network", is one of the solutions for achieving very low ultra-reliable low latency in network performance. The existing OMA systems require fixed time/frequency synchronization, which is very difficult to meet in practice. In this paper, we propose a comparison between OMA and NOMA. The overall system throughput is evaluated as a function of the number of information bits, channels used, and power. The throughput and outage probability are evaluated as a function of the number of information bits and various block lengths. The performance of the system is analysed in terms of reliability and throughput with the help of the type-1 ARQ protocol. While increasing the number of retransmissions, the reliability of the system gets boosted, thereby reducing the outage probability of reception of an error. Throughout the entire system, the performance of NOMA is found to be better than the OMA. [ABSTRACT FROM AUTHOR]

To meet the high-performance requirements of fifth-generation (5G) and sixth-generation (6G) wireless networks, in particular, ultra-reliable and low-latency communication (URLLC) is considered to be one of the most important communication scenarios in a wireless network. In this paper, we consider the effects of the Rician fading channel on the performance of cooperative device-to-device (D2D) communication with URLLC. For better performance, we maximize and examine the system's minimal rate of D2D communication. Due to the interference in D2D communication, the problem of maximizing the minimum rate becomes non-convex and difficult to solve. To solve this problem, a learning-to-optimize-based algorithm is proposed to find the optimal power allocation. The conventional branch and bound (BB) algorithm are used to learn the optimal pruning policy with supervised learning. Ensemble learning is used to train themultiple classifiers. To address the imbalanced problem, we used the supervised undersampling technique. Comparisons are made with the conventional BB algorithm and the heuristic algorithm. The outcome of the simulation demonstrates a notable performance improvement in power consumption. The proposed algorithm has significantly low computational complexity and runs faster as compared to the conventional BB algorithm and a heuristic algorithm. [ABSTRACT FROM AUTHOR]

A key component of cognitive radio technology is spectrum sensing, which finds and accesses unused frequency bands to efficiently use the underutilized spectrum. A potential method for spectrum sensing called cyclostationary feature detection (CFD) uses the cyclostationary characteristics of signals to distinguish between the signal and noise. Artificial neural networks (ANNs) have been suggested in recent years as a method for CFD based spectrum detection, which increases detection accuracy and decreases complexity. However, the variable signal to noise ratio (SNR) and noise variance have an impact on the effectiveness of ANNs for CFD-based spectrum sensing. The effectiveness of ANNs for CFD based spectrum sensing under different SNR and noise variance conditions is evaluated in this work for the determination of threshold value in a dynamic way. We look into how SNR and noise variance affect the precision of probability of detection (Pd) and system complexity. Out analysis show how well ANNs work for CFD based spectrum detection with dynamic threshold value in the presence of changing SNR and noise variation. The findings demonstrate that ANNs may still obtain high Pd values with low SNR and large noise variance while maintaining a modest level of system complexity. According to our research, for a variety of SNR and noise variance situations, ANNs may be a viable option for CFD based spectrum detection in cognitive radio (CR) networks. The proposed approach can significantly improve the detection accuracy and reduce the complexity of the system, thereby enhancing the overall performance of cognitive radio networks. Based on the proposed work, it is determined that MPSK modulation function well with additive white Gaussian noise (AWGN), Rayleigh, and Rician channels up to a lower SNR value of – 30 dB and MQAM supports a lower SNR value of up to – 20 dB. [ABSTRACT FROM AUTHOR]

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 P = 4 and number of users in a cluster are K = 6 , OR-AND ( n = 1 , r = P) fusion rule achieves 2.46% more EE than AND-OR ( n = K , r = 1) 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. [ABSTRACT FROM AUTHOR]

Correlation exists in all practical channels, and each channel's correlation level varies. Determining correlation matrices while estimating the channel and precoding is vital in providing spatial directivity to the signals. This paper considers the performance analysis of the downlink multi-cell multiuser Massive Multiple Input Multiple Output (mMIMO) system with user-specific correlation matrices for the Rician Fading channel. Using the Random Matrix Theory (RMT) results, the closed-form for the asymptotic analysis of ergodic downlink rate per user terminal (UT) is derived for the spatially correlated system with Regularized Zero-Forcing (RZF) scheme. A realistic multipath environment consisting of a dominant line-of-sight (LOS) path along the non-deterministic non-line-of-sight (NLOS) component with imperfect channel information and pilot contamination is considered for deriving the expression. The system is evaluated for the carrier frequency of 30 G H z in the mmWave range with different parameters using Monte Carlo simulations to validate the derived expression. The numerical results show that the derived expression for ergodic user rate provides a tight approximation for the large-dimensional system and accurate results for small values. As for the Rician Factor, κ = 0.5 , transmit power of 10 d B and training power of 6 d B , the average user rate obtained for M = 100 and K = 50 is 1.1233 bits/sec/Hz/User/cell for simulated value and 1.1243 bits/sec/Hz/User/cell for theoretical value. The proposed correlated multicellular mMIMO system is shifted from the mmWave range to s u b - 6 G H z to compare it with the existing system in (Sanguinetti et al. in IEEE Transactions on Communications 67:1939–1955, 2018). The derived results show the improvement in system throughput for the proposed system. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of spatially distributed reconfigurable intelligent surface (RIS)-aided non-orthogonal multiple access (NOMA) systems over Rician fading channels, where the spatial locations of multiple RISs are modeled by invoking the stochastic geometry. Accurate and asymptotic closed-form expressions in terms of the outage probability and ergodic rate are derived based on an optimal selection scheme. Accordingly, diversity orders are obtained to gain more insights on the considered network. It is revealed by simulations that the outage behaviour of distributed RIS-NOMA system outperforms that of RIS-aided orthogonal multiple access (OMA) and conventional multiple relays-aided NOMA counterparts, and the ergodic rate of distributed RIS-NOMA is superior to that of distributed RIS-OMA in the low signal-to-noise ratio region. Additionally, the performance enhancements through more densely deployed of RISs and/or more reflecting elements of RIS as well as the increased Rician factors are corroborated by the simulations. [ABSTRACT FROM AUTHOR]

This paper proposes a novel approach based on the copula models for estimating Millimeter-Wave channel parameters with Rician fading in a correlated MIMO system. Even though the use of these waves faces numerous challenges, having an accurate estimation of their parameters would be a crucial notion for the improved performance of this channel. Since the considered system in this paper is a MIMO system with nearby transmitter antennas, the components of the received signals are correlated. However, a general model is not available for this kind of correlation. By taking into account the correlation, this model enables a precise Joint Probability Density Function (JPDF) by employing copula models for the received signals in the antennas. We also obtain more precise channel parameter estimates using this density function. The multi-path fading parameters in a MIMO system and the correlation coefficients between the transmitter and receiver antennas are both presented in this paper. Some simulations are employed to assess the validity and reliability of estimating Millimeter-Wave channel parameters in a MIMO system. [ABSTRACT FROM AUTHOR]

In this paper, we consider a downlink non-orthogonal multiple access (NOMA) network assisted by two reconfigurable intelligent surfaces (RISs) over Rician fading channels, in which each user communicates with the base station by the virtue of a RIS to enhance the reliability of the received signal. To evaluate the system performance of our proposed RIS-NOMA network, we first derive the exact and asymptotic expressions for the outage probability and ergodic rate of two users. Then, we derive the exact and asymptotic upper bound expressions for the ergodic rate of the nearby user. Based on asymptotic analytical results, the diversity orders for the outage probability and the high signal-to-noise ratio (SNR) slopes for the ergodic rate of the two users are obtained in the high SNR regime. Moreover, we derive the system throughputs of the proposed RIS-NOMA network in delay-limited and delay-tolerant transmission modes. Numerical results confirm our analysis and demonstrate that: 1) The outage probability and ergodic rate of RIS-NOMA networks are superior to that of RIS-assisted orthogonal multiple access (OMA) networks; 2) The RIS-NOMA networks have ability to achieve a larger system throughput compared to RIS-OMA networks; and 3) The system performance of RIS-NOMA networks can be significantly improved as the number of reflecting elements and Rician factor increases. [ABSTRACT FROM AUTHOR]

Energy efficiency (EE) is the main target of wireless communication nowadays. In this paper, we investigate hybrid precoding (HP) and massive multiple-input multiple-output (MIMO) systems for a high-altitude platform (HAP). The HAP is an emerging solution operating in the stratosphere at an amplitude of up to 20–40 km to provide communication facilities that can achieve the best features of both terrestrial and satellite systems. The existing hybrid beamforming solution on a HAP requires a large number of high-resolution phase shifters (PSs) to realize analog beamforming and radio frequency (RF) chains associated with each antenna and achieve better performance. This leads to enormous power consumption, high costs, and high hardware complexity. To address such issues, one possible solution that has to be tweaked is to minimize the number of PSs and RFs or reduce their power consumption. This study proposes an HP sub-connected low-resolution bit PSs to address these challenges while lowering overall power consumption and achieving EE. To significantly reduce the RF chain in a massive MIMO system, HP is a suitable solution. This study further examined adaptive cross-entropy (ACE), a machine learning-based optimization that optimizes the achievable sum rate and energy efficiency in the Rician fading channel for HAP massive MIMO systems. ACE randomly generates several candidate solutions according to the probability distribution (PD) of the elements in HP. According to their sum rate, it adaptively weights these candidates' HP and improves the PD in HP systems by minimizing the cross-entropy. Furthermore, this work suggests energy consumption analysis performance evaluation to unveil the fact that the proposed technique based on a sub-connected low-bit PS architecture can achieve near-optimum EE and sum rates compared with the previously reported methods. [ABSTRACT FROM AUTHOR]

This paper adopts an unmanned aerial vehicle (UAV) relay to forward data from a source sensor to a remote base station (BS). To ensure reliable data transmission, our objective is to minimize the average outage probability along the three-dimensional (3D) UAV trajectory under the UAV mobility and source/relay power allocation constraints. The UAV mobility causes the time-varying Rician fading channel, thus the outage probability function considers both the distance-based large-scale fading and a time-varying Rician factor. To tackle our formulated non-convex problem, we approximate the outage probability by its first-order asymptotic form, based on which we propose a block coordinate descent (BCD) iteration algorithm by alternatively solving the 3D UAV trajectory and power allocation subproblems. The successive convex optimization (SCO) method is applied to deal with the 3D UAV trajectory subproblem. To reveal the advantage by designing the 3D UAV trajectory, we also consider joint optimization of the two-dimensional (2D) UAV trajectory and power allocation to minimize the average outage probability. Extensive simulations verify the accuracy of the approximate outage probability, and the results show that considering the time-varying Rician fading channel, the 3D UAV trajectory helps to obtain a lower link outage probability than the 2D UAV trajectory. [ABSTRACT FROM AUTHOR]

A sparse channel estimation approach based on doubly spread underwater acoustic (UWA) channels is widely used to detect coherent acoustic orthogonal frequency division multiplexing (OFDM) signals. A new time-domain channel estimation (CE) technique for OFDM based UWA communication with Rician fading is used to exploit the channel sparsity. First, to improve the estimation accuracy in high noise conditions, we have exploited the channel sparsity to generate a closed-form equation for the termination condition. Then, in low-level noise instances, the additional criterion to balance estimation accuracy and computing costs has been established. By incorporating these two requirements within the orthogonal-matching-pursuit (OMP) structure, an adaptive-OMP (AOMP) algorithm has been proposed. The AOMP and maximum a posteriori probability (MAP) techniques are combined to provide a computationally efficient, and a new AOMP-MAP scheme for estimating the sparse complex channel path gain has been proposed. Further, The minimum variance unbiased estimator is used to improve the proposed CE technique. Exploiting the experimental channel data, computer simulations reveal that the proposed CE technique obtains the outstanding outcomes. [ABSTRACT FROM AUTHOR]

This paper consider a Drone Assisted Network Coded Cooperation (DA-NCC) scenario for Line of Sight (LoS) channel environments. For analysing the performance of DA-NCC, Decode-and-Forward (DF) protocol is used at the drone and Selection Combining (SC) is performed at the destination node. An analytical closed-form formulation of the outage probability is devised and proven through simulations to assess network performance of the DA-NCC system. In order to have a better understanding of deterministic networks, a discussion on capacity and a comparison of alternative rectangular designs for deterministic networks are also presented. Insightful results on the relation among drone height, DNC-noise and network geometry may play an important role during the performance analysis of the DA-NCC system. Using closed-form expressions of performance measures, system designers can quickly examine the effects of various parameters on the DA-NCC network's performance. [ABSTRACT FROM AUTHOR]

In this work, we investigate a prediction-sensing based cooperative energy harvesting cognitive radio network (EH-CRN) over a Rician fading environment. Incorporating a prediction based sensing mechanism provides enhanced protection to the quality-of-service (QoS) of the primary user (PU) subsequently leading to an improved spectrum efficiency. The complex channel model in analysing the performance of the prediction-sensing based EH-CRN is taken to be as Rician considering the envisioned higher frequency communication systems. An optimal sensing time is also evaluated whereat the secondary network throughput is the maximum. The system behaviour is analysed in terms of two standard performance indices viz., outage probability (OP) and the symbol error rate (SER). The exact analytical expression for both the OP and SER in a Rician fading channel environment is obtained. The impact of Rician fading factor, signal-to-noise ratio (SNR), number of cooperative cognitive radio nodes, data rate parameter and prediction error on the detection probability, harvested energy, normalized throughput, OP and SER is analysed and discussed. The SER for different digital modulation techniques are also obtained. Monte Carlo simulations verify the correctness of the analytical modelling of the system. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surface (RIS) has been envisioned as one of the promising solutions for enhancing signal transmissions in high-speed communications (HSC). In this paper, we present a time-varying channel model with distance-dependent Rician factors for the RIS-assisted HSC. Our model not only contains Rayleigh components and Doppler shift (DS) terms but also distance-dependent Rician factors, for characterizing time-varying features. In particular, we show that when the vehicle is far from the base station and the RIS, the channel contains only Rayleigh fading. However, when they are close enough, the channel can be considered as a light-of-sight channel. Based on the proposed model, it is proven that using RIS phase shift optimization, the DS of the cascaded links can be aligned with the DS of the direct link; and if the direct link is blocked, the DS can be removed entirely. Furthermore, we derive the closed-form expressions for the ergodic spectral efficiency and the outage probability of the proposed system. Besides, it is observed that the deployment strategy also affects the system performance. Simulation results validate all analyses. [ABSTRACT FROM AUTHOR]

This paper derives the asymptotic distribution of the normalized $k$ -th maximum order statistics of a sequence of non-central chi-square random variables with non-identical non-centrality parameters. We demonstrate the utility of these results in characterizing the signal-to-noise ratio in three different applications in wireless communication systems where the statistics of the $k$ -th maximum channel power over Rician fading links are of interest. Furthermore, we derive simple expressions for the asymptotic outage probability, average throughput, achievable throughput, and average bit error probability. The proposed results are validated via extensive Monte Carlo simulations. [ABSTRACT FROM AUTHOR]

Reconfigurable intelligent surface (RIS) can be employed in a cell-free system to create favorable propagation conditions from base stations (BSs) to users via configurable elements. However, prior works on RIS-aided cell-free system designs mainly rely on the instantaneous channel state information (CSI), which may incur substantial overhead due to extremely high dimensions of estimated channels. To mitigate this issue, a low-complexity algorithm via the two-timescale transmission protocol is proposed in this paper, where the joint beamforming at BSs and RISs is facilitated via alternating optimization framework to maximize the average weighted sum-rate. Specifically, the passive beamformers at RISs are optimized through the statistical CSI, and the transmit beamformers at BSs are based on the instantaneous CSI of effective channels. In this manner, a closed-form expression for the achievable weighted sum-rate is derived, which enables the evaluation of the impact of key parameters on system performance. To gain more insights, a special case without line-of-sight (LoS) components is further investigated, where a power gain on the order of $\mathcal {O}(M)$ is achieved, with $M$ being the BS antennas number. Numerical results validate the tightness of our derived analytical expression and show the fast convergence of the proposed algorithm. Findings illustrate that the performance of the proposed algorithm with two-timescale CSI is comparable to that with instantaneous CSI in low or moderate SNR regime. The impact of key system parameters such as the number of RIS elements, CSI settings and Rician factor is also evaluated. Moreover, the remarkable advantages from the adoption of the cell-free paradigm and the deployment of RISs are demonstrated intuitively. [ABSTRACT FROM AUTHOR]

We consider a full duplex (FD) massive multiple-input multiple-output (mMIMO) cell-free (CF) system, where a large number of multi-antenna FD access points (APs) jointly serve multiple FD user equipments (UEs). The APs transmit precoded downlink pilots for the UEs to estimate the effective downlink channel. For this system, we derive closed-form uplink and downlink spectral efficiency (SE) expressions by considering i) radio-frequency (RF) impairments at the APs and UEs; ii) dynamic resolution analog-to-digital converter/digital-to-analog converter (ADC/DAC) architecture at the APs and low-resolution ADC/DACs at the UEs; and iii) spatially-correlated Rician channels. We then maximize the non-convex global energy efficiency metric by using the block minorization-maximization technique, which decomposes the main optimization into multiple convex surrogate sub-problems. We analytically show that the SE gain obtained with downlink training is limited for practical CF systems with RF and ADC/DAC impairments, Rician channel and pilot contamination. We also extensively investigate the impact of FD interferences on the downlink training gain. [ABSTRACT FROM AUTHOR]

We consider a cell-free massive multiple-input multiple-output (MIMO) system with multi-antenna access points and user equipments (UEs) over Weichselberger Rician fading channels with random phase-shifts. More specifically, we investigate the uplink spectral efficiency (SE) for two pragmatic processing schemes: 1) the fully centralized processing scheme with global minimum mean square error (MMSE) or maximum ratio (MR) combining; 2) the large-scale fading decoding (LSFD) scheme with local MMSE or MR combining. To improve the system SE performance, we propose a practical uplink precoding scheme based on only the eigenbasis of the UE-side correlation matrices. Moreover, we derive novel closed-form SE expressions for characterizing the LSFD scheme with the MR combining. Numerical results validate the accuracy of our derived expressions and show that the proposed precoding scheme can significantly improve the SE performance compared with the scenario without any precoding scheme. [ABSTRACT FROM AUTHOR]

Unmanned aerial vehicles (UAVs) are foreseen to constitute promising airborne communication devices as a benefit of their superior channel quality. But UAV-to-ground (U2G) communications are vulnerable to eavesdropping. Hence, we conceive a sophisticated physical layer security solution for improving the secrecy rate of multi-antenna aided U2G systems. Explicitly, the secrecy rate of the U2G MIMO wiretap channels is derived by using random matrix theory. The resultant explicit expression is then applied in the joint optimization of the MIMO transceiver and the UAV location relying on an alternating optimization technique. Our numerical results show that the joint transceiver and location optimization conceived facilitates secure communications even in the challenging scenario, where the legitimate channel of confidential information is inferior to the eavesdropping channel. [ABSTRACT FROM AUTHOR]

The paper studies a reconfigurable intelligent surface (RIS)-assisted multi-user uplink massive multiple-input multiple-output (MIMO) system with imperfect hardware. At the RIS, the paper considers phase noise, while at the base station, the paper takes into consideration the radio frequency impairments and low-resolution analog-to-digital converters. The paper derives approximate expressions for the ergodic achievable rate in closed forms under Rician fading channels. For the cases of infinite numbers of antennas and infinite numbers of reflecting elements, asymptotic data rates are derived to provide new design insights. The derived power scaling laws indicate that while guaranteeing a required system performance, the transmit power of the users can be scaled down at most by the factor $\frac{1}{M}$ when $M$ goes infinite, or by the factor $\frac{1}{MN}$ when $M$ and $N$ go infinite, where $M$ is the number of antennas and $N$ is the number of the reflecting units. Furthermore, an optimization algorithm is proposed based on the genetic algorithm to solve the phase shift optimization problem with the aim of maximizing the sum rate of the system. Additionally, the optimization problem with discrete phase shifts is considered. Finally, numerical results are provided to validate the correctness of the analytical results. [ABSTRACT FROM AUTHOR]

In this letter, we propose a novel scheme for symbol timing offset (STO) estimation by using a convolutional neural network (CNN)-deep neural network (DNN) model (CDM) architecture for the orthogonal frequency division multiplexing (OFDM) system over different fading channel models. The proposed scheme estimates STO in the presence of carrier frequency offset (CFO) and without prior knowledge of the channel, modulation format, and transmitted OFDM signal parameters. The CDM architecture achieves better estimation accuracy gain compared to that of statistical-based and pilot-assisted CNN-based methods. Finally, the proposed CDM is validated over a radio frequency testbed, and the desired constellation diagram is obtained. [ABSTRACT FROM AUTHOR]

Summary: Paper 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. [ABSTRACT FROM AUTHOR]

Future non-terrestrial networks aim to achieve a throughput of Terabits/s. Therefore, free-space optical (FSO) communications have been adopted as a candidate solution due to their ability to achieve an extremely high data rate. Nonetheless, FSO communications are sensitive to the adverse effects of beam scintillation, beam-wander-induced pointing errors, free-space loss, and weather conditions. Space-air-ground (SAG) FSO transmission and hybrid single-hop (SH) FSO/radio frequency (RF) transmission are promising solutions to improve the performance of FSO links and can be integrated into a satellite communication (Satcom) system. In this work, we carry out a thorough capacity analysis of the resulting integrated SAG-FSO/SH-FSO/RF Satcom system, where Gamma-Gamma and Rician distributions are used to characterize FSO and RF links, respectively. The exact analytical expressions are derived and validated by Monte-Carlo simulations. We also obtain asymptotic expressions for the ergodic capacity in the high signal-to-noise ratio region. The numerical results highlight the significant potential of the integrated SAG-FSO/SH-FSO/RF Satcom system over existing solutions. We also show that the integrated Satcom system with intensity modulation and direct detection can achieve a capacity gain over that with a heterodyne detection technique over all satellite zenith angles. [ABSTRACT FROM AUTHOR]

UAVs can be used as aerial relays to provide communication services in remote uncovered areas or dense environments with occasional high capacity demands. However, due to the low power of Internet-of-Things (IoT) devices, UAV-based IoT applications, such as precision agriculture and environment monitoring, may experience high shadowing or equipment failure, which degrades the communications’ quality between IoT devices and their gateways. To tackle this issue, we consider the long range (LoRa) communication technology. Specifically, we investigate the performance of LoRA-enabled aerial communications, where a LoRa gateway communicates with a distant IoT device through the assistance of an amplify-and-forward (AF) aerial relay. Under the assumption of shadowed Rician fading channels, we characterize at first the end-to-end LoRa communication link. Then, we derive an exact symbol error rate expression for the underlying system model. Finally, numerical results are presented to corroborate the efficacy of our derived expressions and provide valuable insights into the error performance of LoRa-enabled aerial networks. [ABSTRACT FROM AUTHOR]

In this letter, we investigate the ergodic capacity of the Relay-Reconfigurable Intelligent Surface (Relay-RIS) system exploiting the three-dimensional channel model, which is different from existing works ignoring antenna height. Specifically, we propose a novel three-dimensional statistical channel for the Relay-RIS system. The upper bound expressions of the ergodic capacity are deduced in diverse propagation environments. Meanwhile, the impact of channel condition and deployment location on the capacity improvement is quantified, and the minimum number of reflecting elements to achieve a given rate threshold is obtained. Simulation results verify the effectiveness of the Relay-RIS system and the three-dimensional deployment strategy. [ABSTRACT FROM AUTHOR]

Non-orthogonal multiple access (NOMA) is considered by the 3GPP as a potential technology for beyond 5G wireless networks to support massive connectivity with robust reliability. However, the massive increase in connected users critically leads to data security problems owing to the high possibility of eavesdropping. In this paper, uplink secure NOMA (sNOMA) schemes based on chaotic physical layer security (PLS) are proposed to achieve two-fold secrecy of integrated channel coding and secret key approaches. Different code-domain and power-domain techniques are employed for sNOMA designs over realistic fading channel environments. Equal power allocation strategy is used for the transmitted chaotic signals in code-domain sNOMA (CD-sNOMA), whereas dynamic power control is employed in power-domain sNOMA (PD-sNOMA) and the hybrid code-power-domain sNOMA (CPD-sNOMA) approaches. The former design adopts joint maximum Likelihood (ML) signal detection while the later scenarios utilize integrated receiver designs based on successive interference cancellation (SIC) and ML techniques. For the proposed sNOMA schemes, power control algorithms are presented to optimize the system performance over constrained total received power and target error rate. Numerical results validate the effectiveness of sNOMA designs compared with the benchmark systems under the worst-case secrecy of unauthorized receiver with complete knowledge of the transmission scheme and associated channel. Valuable tradeoffs are demonstrated between the achieved error rate, connectivity, security gap, and complexity. Moreover, the utilized chaotic signals offer robust and cost-effective PLS solutions with a huge key-space to combat the most powerful brute-force eavesdropping attacks.

Massive multiple-input multiple-output base stations use multiple spatial diversity branches, which are often assumed to be uncorrelated in theoretical work. Correlated branches are seldom considered since they are mathematically less tractable. For correlated Rician fading, only the first- and second-order moments have been explored. To describe propagation environments more accurately, full distribution functions are needed. This manuscript provides distribution functions for the maximum ratio combining effective channel, a quadratic form of a random complex normal channel vector. Its mean vector and covariance matrix are based on a plane wave model incorporating array geometry, antenna element pattern, power angular spectra and power delay profiles. Closed-form approximations of the distribution functions are presented, to allow the fast evaluation of many real-world scenarios. The statistical framework is used to show that low-directivity antenna elements provide better performance in angular constricted Rician fading with off-axis incidence than high-directivity elements. Moreover, two base station array layouts are compared, showing that a half-circle array illuminates a cell more evenly than a uniform linear array. With the full distribution functions available, performance can be compared over the full range of received powers and not only based on the average signal-to-noise ratio.

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. [ABSTRACT FROM AUTHOR]

We consider multiple unmanned aerial vehicles (UAVs) serving a density of ground terminals (GTs) as base stations. The objective is to minimize the outage probability of GT-to-UAV transmissions. Optimal placement of UAVs under different UAV altitude constraints and GT densities is studied. A practical variant of the Rician fading model, which has been developed by Azari et al. (2018) specifically for UAV systems, is used to model the communication channels. First, the structure of optimal deployments is determined when the common altitude constraint is large. For a wide class of GT densities, it is shown that all UAVs should be placed to the same location in an optimal deployment. A design implication is that one can use a single multi-antenna UAV as opposed to multiple single-antenna UAVs without loss of optimality. Next, using a random deployment argument, a general upper bound on the optimal outage probability is found for any density of GTs and any number of UAVs. Further, for any arbitrary user density, centralized and distributed numerical algorithms are designed using particle swarm optimization and modified gradient descent algorithms, respectively. Simulations show that our distributed algorithm provides almost optimal results even with considerably reduced communication and sensing ranges at the UAVs. [ABSTRACT FROM AUTHOR]

We investigate a multi-pair full-duplex (FD) two-way communication system assisted by a reconfigurable intelligent surface (RIS), where each user-pair exchanges information via RIS. Unlike most existing works related to FD systems with RIS, we take into account an inevitable electromagnetic interference (EMI) and also consider a practical Rician channel between RIS and users, and spatial correlation owing to size constraint at the RIS. In addition we consider low-cost hardware at RIS and users resulting in impairments. We first derive an approximate expression for the achievable sum-rate of the system. We then optimize RIS phases to achieve the optimum sum-rate using particle swarm optimization (PSO) algorithm. We, through the simulation results, show the optimality of PSO algorithm and the impact of EMI and hardware impairments on the sum-rate. [ABSTRACT FROM AUTHOR]

The operation of point-to-point communication assisted with reconfigurable intelligent surface, where the multi-hop channels between the source and the destination are subject to Rician fading but are not necessarily independent, is investigated. Considering binary phase-shift keying signaling for the data transmission and optimal maximum-likelihood detection at the receiver, a system performance evaluation is conducted in terms of reliability and capacity. For such, the distributions of the magnitude of the product of the complex channel gains are first obtained for both, the case when the channel gains are independent and the case when they are correlated. Subsequently, expressions of the system’s error rate and the upper-bounds on the average capacity are obtained for the said correlated and uncorrelated channel cases. Numerical results corroborating the analysis are also presented. In particular, it is revealed that correlation between the channels has negligible effect on the error rate when the fading is Rayleigh distributed, and that an increase in the value of the Rician parameter pertaining to the channel between the receiver pair has reduced impact on the reduction of the error rate, which provides practical guidelines for system deployments with high reliability. [ABSTRACT FROM AUTHOR]