Wireless Fading Channels Research Articles

Energy Minimization for IRS-Assisted SWIPT-MEC System.

With the rapid development of the internet of things (IoT) era, IoT devices may face limitations in battery capacity and computational capability. Simultaneous wireless information and power transfer (SWIPT) and mobile edge computing (MEC) have emerged as promising technologies to address these challenges. Due to wireless channel fading and susceptibility to obstacles, this paper introduces intelligent reflecting surfaces (IRS) to enhance the spectral and energy efficiency of wireless networks. We propose a system model for IRS-assisted uplink offloading computation, downlink offloading computation results, and simultaneous energy transfer. Considering constraints such as IRS phase shifts, latency, energy harvesting, and offloading transmit power, we jointly optimize the CPU frequency of IoT devices, offloading transmit power, local computation workload, power splitting (PS) ratio, and IRS phase shifts. This establishes a multi-variate coupled nonlinear problem aimed at minimizing IoT devices energy consumption. We design an effective alternating optimization (AO) iterative algorithm based on block coordinate descent, and utilize closed-form solutions, Dinkelbach-based Lagrange dual method, and semidefinite relaxation (SDR) method to minimize IoT devices energy consumption. Simulation results demonstrate that the proposed scheme achieves lower energy consumption compared to other resource allocation strategies.

A Novel Tight Closed-Form Capacity Analysis for Rician Fading Wireless Channel Using Small Limit Argument Approximation

A Novel Tight Closed-Form Capacity Analysis for Rician Fading Wireless Channel Using Small Limit Argument Approximation

Scoring Aided Federated Learning on Long-Tailed Data for Wireless IoMT Based Healthcare System.

In this article, we propose a novel federated learning (FL) framework for wireless Internet of Medical Things (IoMT) based healthcare systems, where multiple mobile clients and one edge server (ES) collaboratively train a shared model on long-tail data through wireless channels. However, the presence of long-tailed data in this system may introduce a biased global model which fails to handle the tail classes. Additionally, the occurrence of severe fading in wireless channels may prevent mobile clients from successfully uploading local models to the ES, thereby excluding them from participating in the model aggregation. These situations adversely affect the performance of FL. To overcome these challenges, we propose a novel scoring aided FL framework that uses a scoring-based sampling strategy to select mobile clients with more tailed data and better transmission conditions to upload their local models. Specifically, we leverage the logits to explore the data distribution among local clients and propose a logits based scoring client selection method to alleviate the impact of long-tailed data. Moreover, we address the impact of severe fading by incorporating the channel state information (CSI) and data rate of clients into the logits based scoring and proposing a novel logits and model upload rate based client selection method. Experimental results demonstrate the effectiveness of our proposed framework. In particular, compared to the conventional FedAvg, the proposed framework can achieve accuracy gains ranging from 4.44% to 28.36% on the CIFAR-10-LT dataset with an imbalance factor (IF) of 50.

Performance Analysis of BER and SNR Performance in High-QAM Modulations Using Advancements in MIMO Systems

Wireless communications is one of the most active areas of technology development of our time. This development is being driven primarily by the transformation of what has been largely a medium for supporting voice telephony into a medium for supporting other services, such as the transmission of video, images, text, and data. Today, the widely deployed network type is based on a centralized approach that requires a network point of access, commonly called the Access Point (AP), to serves as a gateway between the mobile device and the Internet. The obtained results demonstrate that spatial diversity along with the power of STBC significantly improves the error performance in frequency selective wireless fading channels. The BER level is depend on the modulation type, SNR value and channel behavior. Modulation schemes that we have used in this paper are 4-QAM, 8-QAM, 16-QAM and 64-QAM which further improved using forward error correction codes (FEC). A comparison is made between the diversity gains of MIMO systems in terms of BER for high QAM modulation scheme. This work presents, a simulation toll MATLAB R2023a used for model implemented using Nakagami channel to study the performance analysis of Bit Error rate (BER) V/S Signal to Noise ratio (SNR). Keywords: AWGN, BER, Fading Channel, MIMO System, Nakagami, OFDM, QAM Modulation, SNR, STBC etc.

Accelerated Federated Learning Over Wireless Fading Channels With Adaptive Stochastic Momentum

Accelerated Federated Learning Over Wireless Fading Channels With Adaptive Stochastic Momentum

Hybrid Precoding Design for Wireless Fading Channels

Precoding techniques are widely used to eliminate interference between multiple user signals in a wireless fading channel environment. The linear MMSE precoding technique, one of the most widely used techniques so far, has low computational complexity but has the disadvantage of relatively poor symbol error rate (SER) performance. The symbol-level precoding (SLP) technique, on which much research has been conducted recently, has excellent SER performance but has the disadvantage of being too computationally complex. In this paper, we propose a hybrid precoding technique that simultaneously applies SLP and MMSE precoding to appropriately adjust SER performance and computational complexity performance. If two different types of precoding techniques are applied simultaneously, interference may occur between signals to which different types of precoding are applied, which can significantly deteriorate SER performance. Therefore, in this paper, precoding is designed to prevent interference between the two signals using the null space of the channel matrices. Through computer simulation, the proposed scheme showed that its SER performance was superior to that of the linear MMSE scheme, and the computational complexity was much lower than that of the SLP scheme.

LoWait: Learning Optimal Waiting Time Threshold to Minimize Age of Information Over Wireless Fading Channels

LoWait: Learning Optimal Waiting Time Threshold to Minimize Age of Information Over Wireless Fading Channels

Performance Evaluation of a Linear Predictor Frequency Estimator for Mobile Flat Fading Wireless Channels

A well-known frequency estimation algorithm using the linear prediction method is analyzed for flat fading wireless channels. The estimator outputs are statistically analyzed and its jitter performances are compared with the non-fading case and the Cramer-Rao bound. We provide a closed form solution for the distribution and the variance of the frequency estimates under fading conditions by making valid assumptions. We also verify the theoretical model using simulations. Analysis shows that the variance of the estimates for flat fading channels reaches a threshold point and increasing the transmit power does not necessarily improve the performances any further.

Detection of Jamming Attacks for the Physical-Layer Authentication

This paper concerns the problem of defending against the jamming attack for the Physical-Layer Authentication (PLA). The problem is important due to the fact that jamming attacks can make the legitimate receiver reject a legitimate signal or accept an impersonating signal. In this paper, we propose two jamming detection schemes to defend against jamming attacks for the PLA. The first scheme is the Jamming-Attack Detection (JAD) scheme, which exploits the difference of noise variances between the handshaking and communication stages. The second scheme is the Composite Jamming-Attack Detection (CJAD) scheme, which exploits the difference of noise variances between Alice and Bob. Moreover, we provide the theoretical analysis of the proposed schemes over wireless fading channels and derive their closed-form expressions. We implement our schemes and conduct extensive performance comparisons. Our theoretical analysis and simulation results show that if security is the priority, the CJAD scheme is the best option. If we further consider the overhead, the JAD scheme is the best option under the strategy of jamming attacks and the CJAD scheme may be a better option under the strategy of enhanced jamming attacks, especially for the larger power of a jamming signal.

Diversity Techniques in Wireless Communication Systems: A Review

Fading can be considered as the major impairment of wireless communication channels. To overcome this problem, diversity techniques have been proposed. Diversity is a powerful communication technique that can be applied in time, frequency, and spatial domains in order to enhance communication system performance. The doctrine of diversity is based on the idea of deploying multiple antennas to transmit/receive multiple copies from the desired signals over independent paths to avoid simultaneous fading. In this paper a review of diversity techniques is done. An overview of differently proposed diversity techniques is made to highlight the problem statement in each of it and how the solutions are suggested and applied to conclude the best proposed ones to mitigate the problem of fading in wireless communication channels. The use of multiple antennas at both ends of the system and the principles of MIMO systems is also discussed in this article. Finally, the application of MIMO systems into 5G communication systems is reviewed.

Broadband wireless access and IP technologies - VBLAST detection algorithm

MIMO technology was proposed as early as 1908 to cope with wireless channel fading. In 1995, Bell Labs was the first to discover the great potential of MIMO system in channel capacity, and in 1996, Foshini of Bell Labs first proposed a space-time coding scheme, i.e., the diagonal-Bell Labs hierarchical space-time model, which can obtain very high spectrum utilization, but due to the complexity of its structure, it is difficult to be applied in practice, and is now rarely investigated. 1998, P.W. Wolniansky et al. gave a simple and practical space-time coding scheme on this basis, i.e., the vertical-Bell Labs layered space-time model. In 1998, P.W. Wolniansky et al. gave a simple and practical space-time coding scheme on this basis, i.e., Vertical Bell Labs Layered Space-Time (V-BLAST, Vertical Bell Labs Layered Space-Time) model, which can obtain very high spectrum utilisation and is easy to implement, and therefore has received wide attention once it was proposed. In this paper, we focus on airtime layered codes as well as the ZF detection algorithm and the MMSE detection algorithm in VBLAST systems and improve them to further enhance the performance of the two detection algorithms through sequential serial interference cancellation.

Broadband wireless access and IP technologies - VBLAST detection algorithm

MIMO technology was proposed as early as 1908 to cope with wireless channel fading. In 1995, Bell Labs was the first to discover the great potential of MIMO system in channel capacity, and in 1996, Foshini of Bell Labs first proposed a space-time coding scheme, i.e., the diagonal-Bell Labs hierarchical space-time model, which can obtain very high spectrum utilization, but due to the complexity of its structure, it is difficult to be applied in practice, and is now rarely investigated. 1998, P.W. Wolniansky et al. gave a simple and practical space-time coding scheme on this basis, i.e., the vertical-Bell Labs layered space-time model. In 1998, P.W. Wolniansky et al. gave a simple and practical space-time coding scheme on this basis, i.e., Vertical Bell Labs Layered Space-Time (V-BLAST, Vertical Bell Labs Layered Space-Time) model, which can obtain very high spectrum utilisation and is easy to implement, and therefore has received wide attention once it was proposed. In this paper, we focus on airtime layered codes as well as the ZF detection algorithm and the MMSE detection algorithm in VBLAST systems and improve them to further enhance the performance of the two detection algorithms through sequential serial interference cancellation.

Novel Energy Optimized LDPC Codes for Next-Generation MIMO OFDM Systems

With the increasing prevalence of internet services in our daily lives, there is a growing demand for spectrum, resulting in a shortage of available frequencies. This is primarily due to the recent surge in subscribers seeking faster and more dependable data rates. Researchers globally have suggested various solutions to combat the spectrum shortage, such as technology, modulation schemes, beamforming, intelligent reflective surfaces, and channel coding schemes. With respect to channel coding, multiple codes have been proposed to overcome challenging and uncertain channel conditions. The paper introduces a DWT-incorporated LDPC STBC system as a solution to meet the rigorous demands of 5G deployment and use cases. A comparative analysis of the proposed codes is conducted to assess their suitability for next-generation communication networks, considering SNR and BER. Results indicate that the suggested code performs optimally, achieving a BER of 10-4 at 7dB SNR for Rayleigh Faded wireless channel. Therefore, the suggested code is deemed the most suitable option for the deployment of 5G and beyond systems.

Least Square Estimation-Based Different Fast Fading Channel Models in MIMO-OFDM Systems

In cellular wireless communication systems, channel estimation (CE) plays a pivotal role as a crucial technique applied in orthogonal frequency division multiplexing (OFDM) modulation. CE utilizes a variety of methods, including decision-directed channel estimation, pilot-assisted channel estimation (PACE), and blind channel estimation. Among these options, PACE is widely favored for its remarkable stability and consistent superior performance. The idea of massive multiple-input multiple-output (MIMO) shows tremendous potential for the future of wireless communications. However, existing massive MIMO systems face challenges with their high computational complexity and intricate spatial structures, preventing efficient utilization of channel and sparsity features in these multiantenna systems. In communication channels, the signal received is often influenced by the characteristics of the channel and noise present at the receiver. To address this issue, an efficient dataset is utilized, employing the least square (LS) algorithm for minimization. OFDM is a commonly and widely used modulation method in communication systems utilized to specifically combat resonance fading in wireless channels. In wireless communication systems employing OFDM-MIMO, frequency selectivity and time-varying attributes due to multipath channels cause Intercarrier Interference (ICI) among symbols. Channel estimation is a vital aspect for mitigating the effects of fading channels. This investigation focuses on the application of a method examined in the study, which involves a block-type pilot symbol-assisted estimation technique for Rayleigh and Rician fading channel models. The research assesses the performance of the least square (LS) channel estimators in fast-fading channel models while employing various symbol mapping techniques focusing on bit error rate, throughput, and mean square error. The results indicate that the LS estimator exhibits excellent performance in Rayleigh and AWGN channels within the pedestrian A (PedA) model for both uplink and downlink scenarios. It outperforms the PedA model without channel estimation.

Generalized Tag-Based Physical-Layer Authentication Under Frequency Selective Fading Channels

Physical Layer Authentication (PLA) in wireless systems has drawn much attention because it can provide information-theoretic security. However, the performance of the prior PLA schemes significantly declines under a frequency selective fading channel and the theoretical analysis of a PLA scheme becomes extremely challenging under a frequency selective fading channel as compared to that under a frequency flat fading channel. This paper addresses the problem of authenticating transmitters at the physical layer under a frequency selective fading channel. We propose two tag-based PLA schemes under a frequency selective fading channel. The first scheme is the Generalized Tag-based PLA (GT-PLA) scheme, where the negative effect caused by a frequency selective fading channel is compensated for. If the channel reciprocity holds, we will propose the second scheme to further improve the performance of the GT-PLA scheme, named the Adaptive Generalized Tag-based PLA (AGT-PLA) scheme. We provide the theoretical analysis of both proposed schemes over wireless fading channels in terms of robustness, security, and compatibility, and derive their closed-form expressions. Moreover, we implement the proposed schemes and conduct extensive performance comparisons. Our experimental results demonstrate that the GT-PLA scheme achieves higher robustness over the prior PLA schemes while the AGT-PLA scheme can further improve the performance of the GT-PLA scheme in terms of robustness, security, and compatibility.

Outdoor THz fading modeling by means of gaussian and gamma mixture distributions

Terahertz (THz) band offers a vast amount of bandwidth and is envisioned to become a key enabler for a number of next generation wireless applications. In this direction, appropriate channel models, encapsulating the large and small-scale fading phenomena, need to be developed for both indoor and outdoor communications environments. The THz large-scale fading characteristics have been extensively investigated for both indoor and outdoor scenarios. The study of indoor THz small-scale fading has recently gained the momentum, while the small-scale fading of outdoor THz wireless channels has not yet been investigated. Motivated by this, this contribution introduces Gaussian mixture (GM) distribution as a suitable small-scale fading model for outdoor THz wireless links. In more detail, multiple outdoor THz wireless measurements recorded at different transceiver separation distance are fed to an expectation-maximization fitting algorithm, which returns the parameters of the GM probability density function. The fitting accuracy of the analytical GMs is evaluated in terms of the Kolmogorov-Smirnov, Kullback-Leibler (KL) and root-mean-square-error (RMSE) tests. The results reveal that as the number of mixtures increases the resulting analytical GMs perform a better fit to the empirical distributions. In addition, the KL and RMSE metrics indicate that the increase of mixtures beyond a particular number result to no significant improvement of the fitting accuracy. Finally, following the same approach as in the case of GM, we examine the suitability of mixture Gamma to capture the small-scale fading characteristics of the outdoor THz channels.

Multi-Antenna Assisted Spectrum Sensing for Cognitive Radio in Nakagami-M Fading Channel

CR (Cognitive Radio) is a key technology that enables the limited and inefficiently used frequency bands to be used more effectively with an opportunistic approach. Communication performance and continuity in cognitive radio networks are highly dependent on whether the spectrum sensing function is performed correctly or not. Spectrum sensing is a critical issue of cognitive radio technology because of the shadowing, fading, and time-varying natures of wireless channels. To sense the limited or unused frequency bands, different methods for spectrum sensing have been proposed. Here, improved energy detection is used for this work. Energy detection is a spectrum sensing technique based on measuring the received signal energy and deciding the presence or absence of the primary user by comparing the received energy level with a threshold. Fading channels shows that the speed of the SU increases, the energy detection performance decreases in deterioration in detection probability

Effects of Jamming Attacks on Wireless Networked Control Systems Under Disturbance

Jamming attacks on wireless networked control systems are investigated for the scenarios where the system dynamics face exogenous disturbance. In particular, the control input packets are assumed to be transmitted from a controller to a remotely located linear plant over an insecure wireless communication channel that is subject to jamming attacks. The time-varying likelihood of transmission failures on this channel depends on the power of the jamming interference signal emitted by an attacker. We show that jamming attacks can prevent stability when the system faces disturbance, even if the attacked system without disturbance is stable. We also show that stability under jamming and disturbance can be achieved if the average jamming interference power is restricted in a certain way that we characterize in this article. We illustrate our results on an example networked control system with a fading wireless channel, where the outage probability is affected by jamming attacks.

New Preamble Sequence for WiMAX System with Improved Synchronization Accuracy

Worldwide Interoperability for Microwave Access (WiMAX) trusts Multiple Input Multiple Output-Orthogonal Frequency Division Multiplexing (MIMO-OFDM) combination for the deployment of physical layer functions and for connecting the medium access control to the wireless media. Even though Orthogonal Frequency Division Multiplexing (OFDM) facilitates reliable digital broadband transmission in the fading wireless channels, the presence of synchronization errors in the form of Carrier Frequency Offset (CFO) and Time Offset (TO) adversely affect the performance of OFDM based physical layers. The objective of this work is to improve the accuracy of the frequency and the time offset estimation in the WiMAX physical layer. A method to enhance the synchronization accuracy by fine-tuning the merit factor of the preamble sequence is suggested in this paper. Also, a new preamble with improved synchronization accuracy is proposed for the WiMAX system. The performance of the proposed preamble is evaluated in a Rayleigh fading channel and the results of simulations show that the Mean Square Error (MSE) in offset estimation is significantly reduced and it outperforms the standard WiMAX preamble.

Hybrid Physical-Layer Authentication

Physical-Layer Authentication (PLA) attracts a lot of research interests because of its significant advantages over upper-layer authentication mechanisms: high security and low complexity. The PLA schemes can be categorized into passive and active schemes. In this paper, we extensively leverage the advantages of both the active and passive schemes as a reference scheme, named as the Direct Hybrid (DH) scheme. Although the DH scheme improves the authentication performance of the prior PLA schemes, it has limitations, e.g., high communication overhead. Then, we further propose two hybrid PLA schemes to overcome the limitations of the DH scheme. The first proposed scheme further uses the advantage of the Challenge-Response Authentication Mechanism (CRAM) scheme, named as the CR-based Hybrid (CRH) scheme. Although both DH and CRH schemes significantly improve the authentication performance of the prior PLA schemes, they do not address one significant limitation of the active scheme, i.e., to set the power allocation of a tag empirically. Thus, based on the CRH scheme, we further propose the Adaptive CR-Based Hybrid (ACRH) scheme to adaptively set the parameter instead of the empirical setting. Moreover, we provide the theoretical analysis of the proposed schemes over wireless fading channels and derive their closed-form expressions in terms of the Probability of Detection (PD), Probability of False Alarm (PFA), and optimal threshold, respectively. At last, we discuss the advantages and disadvantages of the proposed schemes and give some useful suggestions for seeking a better tradeoff. Our experimental results show that, in comparison with the active scheme, the DH scheme has better robustness, and the CRH scheme has better both robustness and compatibility but it sacrifices the security. The ARCH scheme achieves a better tradeoff than the remaining schemes.