Performance Of Wireless Systems Research Articles

Conditional GAN Empowered Channel Estimation and Pilot Design for Reconfigurable Intelligent Surfaces assisted Symbiotic Radio System

Reconfigurable intelligent surfaces (RISs) has been proven to be a promising technology to improve the performance of symbiotic radio (SR) systems. To take full advantage of RIS-assisted communications, it is crucial to obtain accurate channel state information for high-gain beamforming. However, the statistical distribution of the cascaded channels in a RIS-assisted SR system is complex, which gives rise to a huge challenge for channel estimation tasks. To address this issue, we propose a joint optimization method of channel estimation for the RIS-assisted SR system with pilot design based on deep learning (JPCGAN) in this paper. The proposed scheme uses a fully connected network for pilot design and develops a conditional generative adversarial network (cGAN) to predict the true channels. cGAN is especially helpful in trainning the network model properly and enhance the system’s robustness with an adaptive loss function. It can be obtained by simulation that compared with current methods, the JPCGAN scheme proposed in this paper can significantly improve the accuracy of channel estimation under low signal-to-noise radios.

Underwater optical wireless communication system performance improvement using convolutional neural networks

Many applications that could benefit from the underwater optical wireless communication technique face challenges in using this technology due to the substantial, varying attenuation that affects optical signal transmission through waterbodies. This research demonstrated that convolutional neural networks (CNNs) could readily address these problems. A modified CNN model was proposed to recover the original data of a non-return to zero on–off keying modulated signal transmitted optically through a tank full of Gulf seawater. A comparison between the proposed CNN model and a conventional fixed-threshold decoder (FTD) demonstrates the excellent performance of the proposed CNN model, which improved the bit error ratio (BER), signal-to-noise ratio (SNR), and effective channel length. The BER of the optical signals that are transmitted at powers of 24, 26, and 27 dBm and a bit rate of 10 Mbit/s at a distance of 3 m from the transmitter when FTD is used is 7.826 × 10−7, 5.049 × 10−8, and 8.38 × 10−10, respectively. When the CNN decoder is used at the same distance and powers, the BER is 6.23 × 10−14, 1.44 × 10−16, and 2.69 × 10−18, respectively. In conclusion, the BER decreased by about seven orders of magnitude, the effective channel length increased by four times, and the SNR decreased by about 20 dB. The simplicity of the proposed CNN decoder is independent of the prior knowledge of the channel conditions. Furthermore, the magnificent obtained results make the proposed CNN decoder an ideal substitute for ordinary underwater optical wireless communication decoders.

A Performance Analysis of Massive MIMO System using Antenna Selection Algorithms

A large number of transmitting components makes Massive Multiple-Input Multiple-Output (MIMO) one of the most hopeful solution for the 5G technology. However, a large antenna system boosts the hardware intricacy and cost of the system because of RF transceivers used at the base station for every antenna element. Hence, antenna selection is one of the most effective schemes to select a good subset of antennas with the finest channel circumstances and contribute maximum to the channel capacity. This paper presents Branch and Bound (BAB) algorithm for efficient antenna selection in Massive MIMO technology. The effectiveness of the simulated BAB algorithm is evaluated based on channel capacity and compared with the traditional state of arts such as fast antenna selection algorithm, Exhaustive Search, Fast antenna selection, CBF, CBW, Random antenna selection, etc. Sunflower Optimization-based antenna selection has been shown to provide improved results in terms of channel capacity when compared to the traditional Branch and Bound algorithm. The results indicate that the Sunflower Optimization technique is a promising alternative for antenna selection in Massive MIMO systems, especially in cases where a large number of antennas are present at the transmitter and receiver ends. The proposed solution provides significant improvements over the traditional methods, making it an attractive option for optimizing MIMO performance in future wireless communication systems.

Robust Transmission Design for RIS-Aided Wireless Communication With Both Imperfect CSI and Transceiver Hardware Impairments

Reconfigurable intelligent surface (RIS) has recently been regarded as a potential technique to enhance the performance of wireless communication systems by creating additional communication links. However, it is almost impossible to get the perfect channel state information (CSI) from the base station (BS) to the Internet of Things Devices (IoTDs) and the RIS-related channels. Furthermore, residual transceiver hardware impairments inevitably affect the performance of wireless communication systems. Hence, we study the robust design for an RIS-aided wireless communication system based on the imperfect CSI and hardware impairments. Minimizing the power consumption of BS is formulated by ensuring the minimum signal-to-interference-plus-noise ratio (SINR) demands of the IoTDs and the unit-modulus constraints of the RIS. Specifically, after approximating the nonconvex constraints by using the S-procedure and the successive convex approximation (SCA) methods, we adopt the block coordinate descent (BCD) technique to iteratively optimize one set of variables while keeping the other variables fixed in various channel uncertainty scenarios. Simulation results demonstrate that the influence of transceiver hardware impairments can be effectively decreased by deploying RIS even with channel uncertainty, which is more advantageous than increasing the number of BS’s antennas.

Implementation of 23 Gbps optical wireless link for 750 km inter-aircraft communications

Optical device research and development is crucial for the implementation of miniaturized wireless optical transmission systems that are capable of transmitting large amounts of data at fast speeds. This work presents the design and evaluation of an optical link for the inter-aircraft interconnects. At the transmitter, the vertically cavity surface emission laser (VCSEL) is used to generate a directly modulated non-return to zero (NRZ) signal. In the receiver, direct detection and Gaussian low-pass filtering are used. The system’s performance is evaluated and compared with and without the use of filtration at the detector. BER, sensitivities, and data transmission capability are used to evaluate the performance of optical wireless systems using optisystem software. The range and data rate are enhanced 9-fold and 4-fold, respectively, in comparison to earlier schemes. The results presented show a transmission range of 750 km at a 23 Gbps data rate with a BER of 10−29.

Aperture-averaged scintillation for a weak underwater turbulence-affected Gaussian beam using the OTOPS model.

The calculation of optical system performance for laser beam propagation in optical turbulence, such as bit error rate (BER), signal-to-noise ratio, and probability of fade, requires the knowledge of scintillation. In this paper, we show the analytical expressions of the aperture-averaged scintillation using a new recently introduced power spectrum of the refractive index fluctuations for underwater turbulence, the oceanic turbulence optical power spectrum (OTOPS). In addition, we use this main result to investigate the impact of weak oceanic turbulence on free-space optical system performance for a propagating Gaussian beam wave. Similar to the atmospheric turbulence case, results show that aperture averaging can reduce the mean BER and the probability of fade several orders of magnitude if the receiver aperture is chosen with a diameter larger than the Fresnel zone, L/k. Being valid for weak turbulence regime in any natural waters, results present the variations of irradiance fluctuations and the performance of underwater optical wireless communication systems depending on the practical values of average temperature and average salinity concentration that can be encountered in any world's waters.

Wireless Communication System Performance in M2M Nakagami-m Fading Channel

In this paper, we investigate a wireless mobile communication system with a cooperative network operating over a mobile-to-mobile (M2M) fading channel in the presence of co-channel interference. Since there is no direct line of sight between the source (S) and the destination (D) due to various obstacles, the signal transmission takes place by using a relay (R). We modeled and represented the desired signal and co-channel interference by using the Nakagami-m fading distribution from the source (S) to the relay (R), as well as from the relay (R) to the destination (D). As the popularity of M2M communication has increased in 5G cellular networks, the performance analysis of the proposed system is of great importance. We derived closed-form expressions for the probability density function (PDF) and cumulative distribution function (CDF) of the signal-to-interference ratio (SIR) at the input of the destination station. Based on the cumulative distribution function (CDF), we also evaluated the outage probability (Pout) of the proposed communication system. In addition, we derived a closed-form approximate expression for the level crossing rate (LCR) by using the Laplace approximation formula for the three-fold integral. Validity of the derived theoretical results we approved by Monte Carlo simulations.

Minimizing Age-of-Information in HARQ-CC Aided NOMA Systems

In this paper, we investigate the timeliness performance of a downlink wireless communication system with non-orthogonal multiple access (NOMA). The timeliness of the system is characterized by Age of Information (AoI). To efficiently utilize the time-frequency resource and achieve a tradeoff between timeliness and reliability, we propose an adaptive transmission policy under hybrid automatic repeat request with chase combining (HARQ-CC) aided NOMA systems. In particular, the BS can adaptively adjust the power allocation and decide whether to transmit old or new packets to users in the NOMA system, based on the current AoI status and the positive/negative acknowledgement (ACK/NACK) feedback signal. We first analyze the BLER under such adaptive systems, and then formulate an AoI minimization problem based on the derived BLER. By transforming the objective function to a Markov Decision Process (MDP) problem, an optimal policy is obtained to minimize the average AoI of the system. Considering the high complexity of the MDP, we further divise an alternative near-optimal policy based on Lyapunov Drift function. Furthermore, we consider the fairness of users and propose a greedy policy to minimize the maximal expected AoI of users. Based on extensive simulations, it has been found that NOMA can outperform OMA on both an overall and a user-level basis when operating with adaptive retransmission and power allocation strategies.

Intelligent Reflecting Surface Aided Wireless Information Surveillance

This paper investigates a new concept of employing intelligent reflecting surface (IRS) to enhance the monitoring performance of wireless information surveillance system, where a full-duplex legitimate monitor is employed to eavesdrop the suspicious transmission from a transmitter to a receiver with the help of an IRS. Under this setup, we consider three IRS deployment strategies, where the IRS is placed near the suspicious transmitter, the suspicious receiver and the legitimate monitor, respectively. First, the monitoring rate achievable by the IRS-aided surveillance system under each deployment strategy is analyzed, which reveals that deploying the IRS near the suspicions transmitter achieves the maximum rate with an asymptotically large number of IRS reflecting elements. Next, efficient algorithms are proposed to maximize the monitoring rate by jointly optimizing the receive and jamming beamforming vectors at the legitimate monitor and the reflection coefficients at the IRS. In particular, a performance upper bound is obtained via properly characterizing the upper and lower bounds of the jamming signal power and using semidefinite relaxation (SDR), while low-complexity algorithms based on the penalty dual decomposition (PDD) framework are also presented to achieve near-optimal performance. Finally, numerical results are presented to validate our analysis as well as the effectiveness of the proposed algorithms, and useful insights are drawn.

A Power-Frequency Joint Optimization Frequency Hopping Strategy for Covert Communication

The security of wireless communication has been a paramount concern. In this letter, we propose a novel power-frequency joint allocation strategy (PFJAS), which can achieve high anti-jamming capability and covert performance for wireless communication systems. Specifically, a joint transmit power and frequency optimization problem is formulated to maximize the detection error probability at the warden, under constraints of transmission reliability and frequency selection uniformity. Then, the formulated optimization problem is solved by utilizing an alternating algorithm, where the power allocation and frequency selection (PAFS) algorithm based on Block Coordinate Descent (BCD) is iteratively performed until satisfying the performance requirement. Numerical results show our proposed PFJAS can achieve high anti-jamming capability and covert performance by exploiting the background noise in the environment.

A survey on reconfigurable intelligent surfaces: Wireless communication perspective

AbstractUsing reconfigurable intelligent surfaces (RISs) to improve the coverage and the data rate of future wireless networks is a viable option. These surfaces are constituted of a significant number of passive and nearly passive components that interact with incident signals in a smart way, such as by reflecting them, to increase the wireless system's performance as a result of which the notion of a smart radio environment comes to fruition. In this survey, a study review of RIS‐assisted wireless communication is supplied starting with the principles of RIS which include the hardware architecture, the control mechanisms, and the discussions of previously held views about the channel model and pathloss; then the performance analysis considering different performance parameters, analytical approaches and metrics are presented to describe the RIS‐assisted wireless network performance improvements. Despite its enormous promise, RIS confronts new hurdles in integrating into wireless networks efficiently due to its passive nature. Consequently, the channel estimation for, both full and nearly passive RIS and the RIS deployments are compared under various wireless communication models and for single and multi‐users. Lastly, the challenges and potential future study areas for the RIS aided wireless communication systems are proposed.

Development and Validation of Testing System for Automated Millimeter-Wave Phased Array Multibeam Near-Field Measurement

To ensure millimeter-wave (mmWave) radio system performance, multiple beam-steered radiation patterns of phased arrays are required to be measured in conventional antenna measurement ranges. This is typically done by sequentially measuring the radiation pattern of phased array under test (AUT) with the AUT mechanically rotating in a far-field setup for each steered beam in a beam-lock mode. However, the conventional pattern measurement procedure for mmWave phased arrays with multiple beams is time-consuming and costly due to the repetitive mechanical rotation and the use of far-field anechoic chamber. The problem becomes even more pronounced for mmWave phased arrays with large-scale antenna configuration due to many more beam states and more directive beam patterns. To address this issue, this paper proposes a novel near-field multi-beam measurement system for mmWave phased arrays, which offers unique advantages in terms of short measurement time, support for full automation, no need for mechanical rotation, compact measurement setup and low system cost. For the pattern with its beam steered to any given direction can be reconstructed based on the AUT element patterns retrieved from a few sparse measurement samples. In this work, the principle and effectiveness of the proposed measurement system have been firstly validated by electromagnetic simulations with CST Studio Suite. Besides, a practical system prototype has been built and experimentally validated where the near-field reconstructed multi-beam patterns are shown to match well with the far-field target patterns in terms of beam direction, beam gain, and pattern similarity percentage.

LSTM projected layer neural network-based signal estimation and channel state estimator for OFDM wireless communication systems

<abstract><p>Advanced wireless communication technologies, such as 5G, are faced with significant challenges in accurately estimating the transmitted signal and characterizing the channel. One of the major obstacles is the interference caused by the delay spread, which results from receiving multiple signal copies through different paths. To mitigate this issue, the orthogonal frequency division modulation (OFDM) technique is often employed. Efficient signal detection and optimal channel estimation are crucial for enhancing the performance of multi-carrier wireless communication systems. To this end, this paper proposes a Long Short Term Memory-Projected Layer (LSTM-PL) deep neural network(DNN) based channel estimator to detect received OFDM signal. The results show that the LSTM-PL algorithm outperforms traditional methods such as Least Squares(LS), Minimum Mean Square Error (MMSE) and other LSTM deep learning channel estimation methods like Long Short Term Memory(LSTM)-DNN and Bidirectional-LSTM(Bi-LSTM)-DNN, as evidenced by Symbol-Error Rate (SER) outcomes.</p></abstract>

MIMO-OFDM Techniques for Wireless Communication System: Performance Evaluation Review

The use of multiple antennas in wireless communication systems has resulted in multiple channels that facilitate the speed of data transfer and improved channel capacity. This technique that basically involves multiple input and multiple output (MIMO) antennas helps to improve system performance by reducing bit error rate (BER) while increasing signal to noise ratio (SNR). Also, the use of orthogonal frequency division multiplexing (OFDM) has helped in mitigating inter-symbol interference (ISI). A combination of MIMO and OFDM produces the MIMO-OFDM scheme. This paper reviewed the performance of BER in MIMO-OFDM system considering various digital modulation techniques. An empirical review of previous studies on MIMO-OFDM system regarding BER performance evaluation was carried out. The study demonstrated the performance of digital modulation schemes in OFDM system with respect the Quadrature Amplitude Modulation (QAM). The results of the simulation based on MATLAB code revealed that lower order modulation yielded better BER performance than higher order. Furthermore,MIMO-OFDM system was modeled in MATLAB/Simulink and simulated to show that the use of multiple antennas at the transmitter and receiver helps in improving the performance of wireless communication system by reducing BER while increasing SNRconsidering two multipath channels – Rayleigh and Rician.

Visible-light wireless communication system performance signature improvement for high bit rate transmission system

Abstract This paper deals with the visible-light communication (VLC) network system improvement for high bit rate transmission system. The previous model use the visualizer analyzer for the estimate of bit error rate in which the maxi. Q factor is reached to 2.51. The previous study is used free space channel over along length of 200 km by the optical wireless communication (OWC) channel with available data rates of 4 Gb/s. This presented model has a transmission rate of 10 Gb/s which has a maximum Q factor of 6.34 at the same operating parameters by using CW laser as an optical source and Mach–Zehnder modulator with two cascades optical wireless communication (OWC) channel.

Implementation of 10 Gbps optical wireless link for 200 km inter-aircraft optical communications

Abstract The enhancements related to optical devices are highly required for high-speed compact wireless optical transmission systems. This paper focuses on development and analysis of the communication system for inter-aircraft applications. The vertical cavity surface emitting laser (VCSEL) is employed at the transmitter for generating directly modulated non-return to zero (NRZ) signal. Direct detection along with Gaussian low pass filtering is employed in the receiver. The performance of the system is examined as well as compared with and without application of filtering at the receiver. The performance of optical wireless system is analyzed in terms of BER, eye-pattern, sensitivity, SNR, and Q-factor. The data rate is enhanced by 4-fold and transmission distance is improved by 250% in comparison with earlier inter-satellite links.

Throughput Optimization in Adaptive Transmit Antenna Selection Systems With Limited Feedback

We investigate the performance of a downlink wireless system with a multiantenna base station under the effect of limited channel feedback. In order to inactivate transmit antennas with poor channel quality and, thus, reduce the feedback overhead, a channel gain threshold-based multiantenna selection (CGT-MAS) scheme is proposed without optimization (NOCGT-MAS) and the corresponding single-antenna scheme (NOCGT-SAS) is considered as a baseline. Considering that the number of selected antennas affects both data transmission rate and the feedback overhead, an effective throughput defined as the difference between the data transmission rate and feedback rate is employed for evaluating the system performance. We conduct an effective throughput analysis for both the NOCGT-SAS and NOCGT-MAS schemes and show that an optimal channel gain threshold exists to maximize the effective throughput of the proposed NOCGT-MAS scheme. As a consequence, we propose the optimal instantaneous CGT-MAS algorithm (OICGT-MAS) to maximize the instantaneous effective throughput. Besides, we derive a closed-form expression of an average effective throughput for the CGT-MAS scheme and propose an optimal average channel gain threshold-based multiantenna selection algorithm (OACGT-MAS) for maximizing the derived average effective throughput. Numerical results demonstrate that the effective throughput of the proposed NOCGT-MAS is substantially better than that of conventional NOCGT-SAS. Moreover, although the OICGT-MAS scheme has a slight advantage over OACGT-MAS in terms of the effective throughput, it has a much higher computational complexity than the latter method.

Optical wireless communication system performance in natural water turbulence of any strength.

The recently introduced power spectrum model for natural water turbulence, i.e., that at any average temperature, average salinity, and stratification [J. Opt. Soc. Am. A37, 1614 (2020)JOAOD61084-752910.1364/JOSAA.399150], is extended from weak to moderate-to-strong regimes with the help of the spatial filtering approach. Based on the extended spectrum, the expressions for the scintillation index (SI) are obtained, and based on its signal-to-noise ratio and bit error rate of the underwater wireless optical communication (UWOC) system with the on-off-keying modulation and gamma-gamma irradiance distribution model, the analysis is performed. The obtained results are compared with those derived from the widely used Nikishov and Nikishov spectrum. It is shown that the natural water turbulence results in the SI for plane (spherical) waves attaining higher maxima values at shorter propagation distances, about 20 m (40 m) with respect to 30 m (50 m) of Nikishovs turbulence. Therefore, it predicts a stronger degradation of the UWOC system performance in weak and moderate turbulence regimes.

Quan-Transformer Based Channel Feedback for RIS-Aided Wireless Communication Systems

Reconfigurable intelligent surface (RIS) has become one of the key technologies for future 6G communications due to its characteristics of an intelligent and controllable wireless environment. In the frequency division duplex mode, the user equipment feeds back the downlink channel state information (CSI) to the base station through the feedback link, to obtain potential gains for the RIS-aided wireless communication system. A large number of RIS reflection elements greatly increase the feedback link cost of the system. In this letter, Quan-Transformer, a sample network framework for CSI compression and reconstruction, is proposed based on Transformer network. The proposed framework can not only compress CSI effectively but also recover CSI with high precision, which improves the performance of the RIS-aided wireless communication system. According to the experimental results, compared with the CsiNet scheme, the achievable sum-rate and normalized mean squared error of the proposed scheme are increased by 6.57% and 3.32%, respectively.

Performance Analysis of I/Q Imbalance With Hardware Impairments Over Hyper Fox’s H-Fading Channels

Impairments baseband model in-phase and quadrature-phase Imbalance (IQI) and Residual hardware impairments (RHI) are two key factors degrading the performance of wireless communication systems (WCSs), particularly when high-frequency bands are employed, as in 5G systems and beyond. The impact of either IQI or RHI on the performance of various WCSs has been investigated exclusively in a separate way. To fill this gap, in this paper, the joint effect of both IQI and RHI on the performance of a WCS subject to Hyper Fox’s H-fading (HFHF) channel, is investigated. Such a fading model generalizes most, if not all, of well-known fading and turbulence models. To this end, closed-form expressions for the outage probability (OP), Average channel capacity (ACC) under constant power with optimum rate adaptation (ORA) policy, and average symbol error probability (ASEP) for both coherent and non-coherent modulation schemes are derived. Specifically, all the analytical expressions are derived for three different scenarios: (i) ideal Tx and Rx impaired, (ii) Tx impaired and ideal Rx, and (iii) both Tx and Rx are impaired. Further, asymptotic expressions for OP, ACC under ORA policy, and ASEP are obtained, based on which, insightful discussions on the IQI and RHI impacts are made. <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha -\mu $ </tex-math></inline-formula> and Málaga <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {M}$ </tex-math></inline-formula> turbulence with pointing error distribution models have been considered as particular cases of the HFHF distribution. The analytical derivations, endorsed by simulation results, demonstrate that the RF impairments’ effects should be seriously taken into account in the design of next-generation wireless technologies.