Performance Of Wireless Systems Research Articles

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.

On the Performance of Multihop THz Wireless System Over Mixed Channel Fading With Shadowing and Antenna Misalignment

The existing relay-assisted terahertz (THz) wireless system is limited to dual-hop transmission with pointing errors and short-term fading without considering the shadowing effect. This paper analyzes the performance of a multihop-assisted backhaul communication mixed with an access link under the shadowed fading with antenna misalignment errors. We derive novel probability density and distribution functions of the signal-to-noise ratio (SNR) of the multihop link employing channel-assisted (CA) and fixed-gain (FG) amplify-and-forward (AF) relaying for each hop by considering independent but not identically distributed (i.ni.d) <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\alpha $ </tex-math></inline-formula> - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula> fading channel with pointing errors. We present analytical expressions for the outage probability and average bit-error-rate (ABER) and develop asymptotic analysis in high SNR regime to derive the diversity order for both CA-multihop and FG-multihop backhaul links. We use the derived results of the multihop systems to analyze the statistical performance of the integrated backhaul-access relaying for both uplink and downlink transmission considering the generalized- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K$ </tex-math></inline-formula> shadowed fading model in the access link. We also present exact and asymptotic expressions of the outage probability for the considered mixed system. We perform computer simulations to provide design and deployment aspects of employing multiple relays to enhance THz wireless transmissions.

High-Speed Trains Access Connectivity Through RIS-Assisted FSO Communications

Free-space optic (FSO) is a promising solution to provide broadband Internet access for high-speed trains (HSTs). Besides, reconfigurable intelligent surfaces (RIS) are considered as hardware technology to improve performance of optical wireless communication systems. In this paper, we propose a RIS-assisted FSO system to provide access connectivity for HTSs, as an upgrade for the existing direct and relay-assisted FSO access setups. Our motivation is mainly based on well-proven results indicating that a RIS-assisted optical wireless system, with a large enough number of RIS elements, outperforms a relay-assisted one thanks to its programmable structure. We firstly compute the statistical expressions of the considered RIS-assisted FSO channels under weak and moderate-to-strong fading conditions. Then, the network's average signal-to-noise ratio and outage probability are formulated based on the assumed fading conditions, and for two fixed- and dynamic-oriented RIS coverage scenarios. Our results reveal that the proposed access network offers up to around 44% higher data rates and 240% wider coverage area for each FSO base station (FSO-BS) compared to those of the relay-assisted one. The increase of coverage area, on average, reduces 67% the number of required FSO-BSs for a given distance, which results in fewer handover processes compared to the alternative setups. Finally, the results are verified through Monte-Carlo simulations.

Robust Online CSI Estimation in a Complex Environment

Channel state information (CSI) estimation is one of the key techniques for improving the performance of wireless communication systems. Meanwhile, the fifth generation wireless communication systems require higher accuracy and lower latency for CSI estimation. In this paper, the methods of noise modeling and online learning are combined to improve the accuracy and reduce the latency. The complex noise environment (considering noise and interference together) is modeled as a specific mixture of Gaussian (MoG) distribution because of its widely approximation capability to any continuous distribution. The MoG CSI estimation (MoG-CE) model and expectation maximization (EM) algorithm are introduced as one of the baseline methods. Further, the parameters of the model can be updated in real time based on the prior knowledge of historical information. Therefore, the online MoG CSI estimation (O-MoG-CE) model and online MoG dynamic CSI estimation (O-MoG-D-CE) model are proposed for time-invariant and time-varying CSI estimations, respectively. The above models can not only self-adapt to various complex communication scenarios robustly but also achieve online and dynamic CSI estimation to improve the accuracy and reduce the latency significantly. In addition, the proposed models can be formulated as standard maximum a posteriori estimations and efficient online expectation maximization (OEM) algorithms are applied for the estimations in a pure machine learning fashion. Comparing with baseline methods, the simulation results demonstrate the superiority of the proposed methods in terms of the accuracy, latency and computation consumption.

Joint Impact of Phase Error, Transceiver Hardware Impairments, and Mobile Interferers on RIS-Aided Wireless System Over κ-μ Fading Channels

Reconfigurable intelligent surface (RIS) has recently emerged as a promising technology that can potentially benefit the existing wireless communication technologies in addition to being able to fulfill the more stringent requirements of beyond- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5^{th}$ </tex-math></inline-formula> generation/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$6^{th}$ </tex-math></inline-formula> generation wireless networks. Motivated by the numerous benefits of RIS technology for improving the performance of wireless communication systems, in this letter, a RIS-aided wireless system is considered in which the destination node is surrounded by the mobile co-channel interferers (CCIs). Each mobile CCI follows the random waypoint (RWP) mobility pattern within a circular region centered around the destination node. Source-destination, source-RIS, RIS-destination, and each interferer-destination links follow the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\kappa - \mu $ </tex-math></inline-formula> distribution. Additionally, a more realistic system model is considered that also incorporates the impact of transceiver (transmitter as well as receiver) hardware distortions. The system’s performance is evaluated by deriving novel closed-form expressions for the coverage probability (CP) and ergodic capacity (EC) based on the cumulative distribution function and probability density function (PDF) of the received signal-to-interference-plus-distortion-plus-noise ratio (SIDNR).

A Wideband Dual-Polarized Ring-Loaded Cross Bowtie Antenna for Wireless Capsule Endoscopes: Design and Link Analysis

This work presents a novel on- body wideband dual-polarized antenna to stabilize and enhance the link performance of wireless capsule endoscopy systems. By introducing a cross-bowtie structure with a planar compact feed method, the antenna achieves a dual-polarized performance with high port-to-port isolation. A loaded ring with additional stubs is also implemented to further enhance the bandwidth and provide a flat in-band performance from 381 to 990 MHz. The proposed antenna is measured with both homogeneous phantom and ex vivo test to validate the impedance matching performance. To validate the effectiveness of the proposed on- body antenna on the communication link, a capsule helical antenna with omnidirectional radiation pattern is designed and measured. Finally, comprehensive link studies are conducted considering the varied capsule orientations and locations, with a peak <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\vert S_{21}\vert $ </tex-math></inline-formula> value of–25.5 dB at the 60 mm implant depth and an acceptable link loss due to the capsule position error. The proposed on- body antenna can be regarded as a good candidate for a practical capsule endoscopy system due to its stable and enhanced transmission performance when compared with its counterparts.

Analysis of RIS-Assisted FSO Systems Over F Turbulence Channel With Pointing Errors and Imperfect CSI

Reconfigurable intelligent surface (RIS) is an enabling solution to enhance the wireless communication system performance by smartly tunning the signal reflection via a large number of reconfigurable passive elements. In this letter, we present the performance analysis of RIS-assisted FSO communication systems over Fisher-Snedecor <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mathcal {F}$ </tex-math></inline-formula> distribution channel considering imperfect channel state information (CSI) and pointing errors under two types of detection schemes. The probability density function (PDF) and cumulative distribution function (CDF) of signal-to-noise ratio (SNR) are deduced in terms of multivariable Fox’s H function. Utilizing these results, the novel expressions for outage probability, average BER and ergodic capacity are derived. All presented results are verified by Monte Carlo simulations.

Performance Analysis Antenna Diversity Technique with Wavelet Transform Using Array Gain for Millimeter Wave Communication System

Utilizing antenna diversity techniques has become a well-known approach to improve the performance of wireless communication systems. Multiple antenna arrays with half-length spacing, such as a uniform linear array (ULA), have been taken into consideration. Since 60 GHz is an unlicensed frequency band and ideal for local propagation, it is where the technology is being used. The transmitter and receiver both accomplish QAM modulation and demodulation. The performance in terms of bit error rate (BER) was tested in MATLAB simulation software for all antenna diversity scenarios: the single input and single output (SISO) DWT, multiple input and single output (MISO) DWT, single input and multiple output (SIMO) DWT, and multiple input and multiple output (MIMO) DWT. The MIMO DWT was shown to be the best of them. The performance of MIMO OFDM using various wavelets was also simulated, and the performance of the Haar wavelet transform was 2 dB better than that of the other wavelet transform. Compared to simulation results, the analytical results showed good agreement with little discrepancy.

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.

Physical layer secrecy of a cognitive radio with spatially correlated Alamouti OSTBC system

In this paper, an underlay spectrum-sharing system with Alamouti orthogonal space–time block coding (OSTBC) is considered to analyze and evaluate the physical layer security (PLS) performance of the cognitive radio system under a practical scenario with spatially correlated transmit antennas. It is assumed that there exists a passive eavesdropper and the cognitive channel and the wiretap channel follow Rayleigh fading distribution. To investigate and study the PLS performance of the cognitive system, first closed-form expressions are derived for three PLS metrics, namely: the probability of strictly-positive secrecy capacity (PSPSC), the secrecy outage probability (SOP), and the average secrecy capacity (ASC). Then numerical results obtained from the derived closed-form expressions are presented and validated by the computer simulations, to study the effects of spatial correlation on the PLS performance of the considered cognitive radio system under different parameters. It is shown that increasing the SNR of the cognitive system (Alice-to-Bob) channel yields an improvement in the PLS of the cognitive system. Moreover, a smaller value of the eavesdropping (Alice-to-Eve) channel SNR always leads to a better PLS for the cognitive system. It is also observed that the spatial correlation related to Alice-to-Bob channel degrades the PLS, and the spatial correlation related to Alice-to-Eve channel has less impact on the PLS performance.

Simulation of Vehicular Network Use in Emergency Situations and Security Applications on a Pakistan Highway

VANETs (vehicular ad hoc networks), which are revolutionary techniques to enhance road safety, can be used to broadcast information about dangerous traffic conditions or accidents. However, distributing important information for driver safety and well-being has strict time and reliability requirements. This is because messages must be received by all cars involved in a potentially dangerous scenario for proper precautions to be taken to avoid the problem from materializing or intensifying. Because of the deterioration in conventional wireless communication system performance, ensuring that such requirements are met is a serious concern. To validate the concept before the actual installation of such systems and their absorption into the vehicle sector, it is therefore critical to employ simulation methodologies that are both reliable and thorough. This piece consists of large-scale, realistic security simulation research of an emergency situation based on actual road traffic data acquired on a Pakistan route. The study’s findings are detailed in the following paragraphs. Aspects such as the incorporation of fixed communication units along a stretch of roadway and the performance of the vehicular network notifying all vehicles engaged in the various accident scenarios modeled on the same stretch of highway were evaluated. Both of these characteristics were designed to increase safety and security applications. After doing the investigation, it was observed that when fixed communication units are incorporated into the network infrastructure, there is a shorter delay in receiving the accident notification. This was the conclusion made after reviewing the findings. Drivers of vehicles located closer to the accident site will be able to respond in a timely and safe manner as a result of this improvement in network performance, and drivers security of vehicles located further away will have the option of exiting the highway to avoid potential congestion caused by increased road traffic.

On the Position Optimization of IRS

The intelligent reflecting surface (IRS) technology is emerged as an enabling technology for beyond fifth-generation systems and Internet of Things networks in which the signal propagation is reconfigured to enhance wireless system performance. IRS consists of many passive elements and each reflecting the incident signal with a certain phase shift to collectively achieve the required beamforming. The IRS is to be a low profile and lightweight setting with a conformal geometry; hence, its position can be easily engineered to achieve certain performance enhancements. In the current literature, however, the flexibility in the IRS position is often overlooked since it is considered as a given fixture. We argue that optimizing the IRS position provides a new degree of freedom in the network design and enables extra performance gain. In this article, we analytically characterize the optimal IRS’s position to maximize the achievable system rate. We then obtain the optimal IRS positions for different IRS settings with fixed height and variable height and consider both cost-efficient equal phase shift IRS, and nonequal phase shift IRS that enables sophisticated beamforming. We further incorporate antenna directivity in our analysis and investigate its effect on the optimal IRS position in each case. Simulation results show that the provided optimal position yields higher performance than settings with random IRS locations. Our results provide significant practical insights on the network coverage design using the IRS.

CSVAG: Optimizing Vertical Handoff Using Hybrid Cuckoo Search and Genetic Algorithm-Based Approaches

One of the primary challenges that wireless technology in the present generation is facing is always best connected (ABC) service. This is possible only when the wireless overlay networks follow a cooperative and coordinated process. Vertical handoff is one such process. Concerning this process, the main challenge is to develop algorithms that take care of optimal connection management with proper resource utilization for uninterrupted mobility. In this paper, we develop a new hybrid cuckoo search (CS) and genetic algorithm (GA) that maximizes the performance of heterogeneous wireless systems in terms of minimizing latency, handover failure probability, and enhancing the throughput. We focus on an optimized simulation framework to demonstrate the advantage of our hybrid model. It can be discerned from the simulation analysis that the proposed hybrid technique increases throughput by 17% and 8% compared to the cuckoo search and genetic algorithms applied individually. The performance of the proposed scheme is promising for applications wherein the handoff mechanisms have to be optimized to control frequent handoffs to further reduce the power consumption of user equipment.