Effects Of Multipath Fading Research Articles

Minimum Mean Square Error Receiver for Multipath Detection in Non-Orthogonal Multiple Access

Non-orthogonal multiple access (NOMA) is a promising technique for next-generation wireless communications. NOMA witnesses performance degradation due to multi access and multipath interferences in dispersive channel. Therefore, power domain cyclic spread multiple access (PDCSMA), a NOMA variant, has been presented recently to minimize the multipath fading effect. The performance of the PDCSMA is limited due to the noise enhancement during multipath detection. Therefore, this paper proposes a novel minimum mean square error (MMSE) based interference minimization technique for the PDCSMA. The proposed technique acts on received signal matched to each path to minimize multipath interference and the effective noise power due to channel dispersion. Unlike the decorrelator employed in the current PDCSMA, the proposed technique enhances the diversity while suppressing the noise enhancement, which is evident from simulation results.

Adaptive Spectrum Sensing in Cognitive Radio Employing Multitaper Method and Higher-Order STBC Techniques

The effects of the non-parametric multitaper method (MTM) and symmetrical higher-order space-time block-code (STBC) with full diversity techniques on the performance of spectrum sensing (SS) in cognitive radio (CR) systems are studied. The overall wireless link performance can be improved by using the STBC techniques to combat the multipath fading effects in wireless channels. The MTM is integrated with the STBC for spectrum estimation (SE), which will be termed multitaper spectrum estimation (MTSE)-STBC, and the given analysis of which is developed using the quadrature form approximation. Also, classical SE algorithms commonly focus on a fixed performance assessment method based on predefined false alarms or detection probabilities. Licensed users need to be protected against interference that opportunistic users might cause. An appropriate thresholding policy that varies concerning the designated values of false alarm and detection rates can achieve such protection. Utilization factors are instrumental in providing further protection for licensed users or occupied spectrum holes, and they need to be determined in advance and adopted in the detection policy. If utilization factors are not desirable, then a fine selection of appropriate threshold values will need to be decided as they have a major impact on the overall error probability performance. Using analytical and simulation methods, the assessment results revealed improved performance of the MTSE-STBC compared to other classical methods such as the Periodogram especially in the aspects of efficient transmission and less error probability. The proposed adaptive thresholding technique also proved useful in coping with different SE settings.

Optimum Weight Parameter of Weight Centroid Method for Indoor Positioning in Environment with Different Path Loss Exponent and Multipath Fading Effect

This paper proposes optimum weight parameter of weight centroid method for indoor positioning in environment with different path loss exponent and multipath fading effect. The indoor environment is defined as square with each side 10 m long. There is a transmitter installed in the center of each side. The distance error model is applied to calculate the distances between the location coordinates of user and the location coordinates of transmitters in environment with different path loss exponent and multipath fading. The total 100 location coordinates of user are estimated by using weight centroid method, varying weight parameter in the range of 1 to 10. The optimum weight parameter is defined as the case where mean of distance error of all positions is the least. The optimum weight parameter for environment with different path loss exponent and multipath fading effect is illustrated. The results show that the optimum weight parameter changes slightly with the path loss exponent and tends to change with the standard deviation of the multipath fading effect divided into 3 periods. The first period tends to increase slowly, the second period tends to increase rapidly, and the third period tends to fluctuate up and down. Moreover, the size of the indoor environment has very little impact on the optimum weight parameter. These results make it possible to select optimum weight parameter for case with path loss exponent and standard deviation of multipath fading effect that match or are close to the channel of indoor environment.

Performance analysis of massive MIMO using various transmit precoding schemes for a wireless network

SummaryAn evaluation of various transmit precoding schemes is proposed in this thesis on basis of spectral efficiency (SE) of massive MIMO (m‐MIMO) system in 2 GHz spectrum. The present generation of wireless networks must be rethought due to the rapidly rising user base, huge volume data transfer, wide coverage requirement, and exponential rise in data rate. 5G mobile network includes a multi‐fold increase in network capacity, energy conservation, decreased latency, higher coverage probability, and a seamless connection. m‐MIMO has provided good solution for enhancing the data rate with the coverage, overcoming the effects of multipath fading and has also increased diversity of the system. Massiveness of MIMO system along with 5G network is the key technology to address the issue of SE, throughput, improvement of QoS (quality of service), coverage probability, power delay profile, diversity simulation, energy efficiency, and improvement in bit error rate. Parameters such as SE, throughput, and coverage probability are important for any communication system, and their improvement can increase overall capacity of cellular network system and could meet the requirement of upcoming demand for mobile network. The research paper is focused on performance analysis of m‐MIMO with reference to the SE of various transmit precoding schemes. Simulation results show that SE provided by M‐MMSE (multi‐cell minimum mean‐squared error) technique of precoding ranks highest for the same number of antennas and pilot reuse factor as compared to other schemes.

Optimizing V2V communication in ITS: The benefits of silver-coated DSRC

The silver-coated DSRC of antennas are used for short-range communication between vehicles (V2V) in intelligent transportation systems (ITS), including DSRC (Dedicated Short-Range Communication). It has silver as a conducting material for the antennas and offers several benefits including higher data rates, increased range, and improved reliability for V2V communication. Using multiple antennas in a silver-coated DSRC provides spatial diversity, reducing the effects of multipath fading and interference. The radiation pattern can also be focused in a specific direction to increase the signal strength. The integration of artificial intelligence (AI) and autonomous drivers into ITS is becoming increasingly important, and V2V communication is a crucial aspect of these systems. The use of a silver-coated DSRC can provide a reliable and efficient solution for DSRC communication in V2V communication, which is essential for the success of ITS. The increased data rates, range, and reliability facilitate the exchange of information between autonomous vehicles, enabling them to make more informed decisions and operate more safely on roads.

Design analysis and performance enhancement of a 2-element MIMO skin-implantable antenna for IoT-based health monitoring devices.

Two two-element slotted patch multiple-input multiple-output (MIMO) antenna with coplanar waveguide (CPW) feed is proposed for deployment in implantable medical devices. Implantable devices are compact and demand high-gain antennae with unidirectional radiation patterns. Regarding compactness, the antenna has a size of 16 × 6×0.25 mm3 for the operating frequency of 2.45 GHz ISM band. Miniaturized antenna geometry is attained using the slots in the radiator and with the coplanar waveguide feed. An element MIMO configuration is used for establishing a reliable communication link. The two radiators maintain a connected ground topology with a minimum edge-to-edge spacing of 7.7 mm. Mutual coupling of -29 dB and operating frequency spectrum of 1300 MHz is attained at the center cut off frequency. Unidirectional power pattern and high gain of 2.3 dB is achieved. The proposed MIMO structure is suitable for mitigating multipath fading effect and realizing higher spectral efficiency in short range communication. The in-tissue measurement results for the scattering parameters and radiation characteristics are done by placing the antenna in a pork loin. Specific absorption rate (SAR) analysis is performed to confirm the user's safety from nearfield EM waves. Antenna has safe SAR value of 0.798 W/kg for 1-g of average tissue for the power of 1-mW. The low envelope correlation coefficient of 0.035 depicts the excellent diversity performance for MIMO operation.

A three‐dimensional wideband mmWave multiple‐input multiple‐output channel model for aerial reconfigurable intelligent surface‐assisted communication systems

SummaryThis paper presents a wideband millimeter wave (mmWave) channel model for aerial reconfigurable intelligent surface (ARIS) communications, in which the reconfigurable intelligent surface (RIS) is attached to an unmanned aerial vehicle (UAV) to enable intelligent signal reflections in the air. The model is established according to standard 3GPP channel models and considers important propagation factors, for example, large‐scale fading, small‐scale fading, and radiation pattern of reflection units (RUs). In addition, the model assumes three‐dimensional (3D) rotations of RIS and can capture its effects on channel characteristics. Based on the model, we propose a design method for RIS reflection phases. Statistics including channel amplitude, spatial, temporal, and frequency correlation functions (CFs), and space‐Doppler power spectral density (SD‐PSD) are obtained. The impacts of RU number, UAV height and speed, and RIS rotation on channel statistics are investigated. Results suggest that the designed reflection phases can effectively mitigate multipath fading and Doppler effect. Compared to the yaw angle of the UAV platform, channel characteristics are more sensitive to the roll and pitch angles.

Defected ground structure-based wideband circularly polarized 4-port MIMO antenna for future Wi-Fi 6E applications

A circularly-polarized (CP) wideband 4-port Multi-input multi-output (MIMO) antenna is proposed. The novel contribution of the proposed work lies in achieving CP through an L-shaped feedline and a carefully engineered orthogonally placed slotted ground plane geometry leading to a defected ground structure (DGS). A single-fed CP antenna structure is then converted to the 4-port MIMO antenna that achieves higher isolation due to polarization diversity. The MIMO antenna demonstrated an impedance bandwidth (IBW) spanning 65.01 % (from 3.81 GHz to 7.48 GHz), along with an axial ratio bandwidth (ARBW) of 20.10 % (from 5.47 GHz to 6.70 GHz). The 4-port CP MIMO antenna shows decent MIMO diversity performance. The measured results of the fabricated structure displayed good agreement with the simulated results. Antenna having both MIMO capability and circular polarization helps in reducing the multipath fading effect while increasing the latency. Thus, the proposed antenna having a wide overlapping Axial Ratio (AR) and Impedance Bandwidth (IBW) can be a very good choice for future devices using the Wireless Fidelity (Wi-Fi) 6E band.

Combining Receiver Damaged by Beaulieu-Xie Fading and Rician Co-Channel Interference with a Purpose of Machine Learning QoS Level Prediction

In this paper, a wireless system is considered impacted by Beaulieu-Xie (BX) fading and Rician co-channel interference (CCI). A selection diversity combining technique is used to combat multi-path fading and CCI effects. The expression for the level crossing rate (LCR) is formulated for the receiver with more input branches, and the corresponding curves that have dependence on the signal-to-interference ratio (SIR) are drawn. On the basis of the presented graphs, we quantify the amount of LCR affected by the presence of fading and interference. Additionally, we propose a classification-based predictive model which leverages the previously calculated LCR value as one of inputs among other variables (number of users, base station, the day of the week) with the aim of Quality of Service (QoS) level prediction.

PILOT: High-Precision Indoor Localization for Autonomous Drones

In many scenarios, unmanned aerial vehicles (UAVs), aka drones, need to have the capability of autonomous flight to carry out their missions successfully. In order to fly autonomously, drones need to know their location constantly. Then, based on their current position and the final destination, navigation commands will be generated and drones will be guided to their destination. Localization can be easily carried out in outdoor environments using GPS signals and drone inertial measurement units (IMUs). However, such an approach is not feasible in indoor environments or GPS-denied areas. In this paper, we propose a localization scheme for drones called PILOT (High-Precision Indoor Localization for Autonomous Drones), which is specifically designed for indoor environments. PILOT relies on ultrasonic acoustic signals to estimate the target drone's location. To obtain a precise final estimation of the drone's location, PILOT deploys a three-stage localization scheme. The first two stages provide robustness against the multi-path fading effect of indoor environments and mitigate the ranging error. Then, in the third stage, PILOT deploys a simple yet effective technique to reduce the localization error induced by the relative geometry between transmitters and receivers, which significantly reduces the height estimation error. The performance of PILOT was assessed in different scenarios, and the results indicate that it achieves centimeter-level accuracy for three-dimensional drone localization.

Development of real-time monitoring BLE-LoRa positioning system based on RSSI for non-line-of-sight condition

Indoor positioning has become popular in this decade and is used to locate users or objects in indoor environments. This is because global positioning system (GPS) is not efficient for indoor use due to the multipath fading effect. This research is about development bluetooth low energy (BLE) indoor positioning system with the aid of long range (LoRa) network and guideline on selection of the BLE beacons. Next, positioning systems are developed consisting of BLE beacons, a transceiver of hybrid BLE-LoRa module, a LoRa receiver and Raspberry Pi as real-time monitoring. The received signal strength indicator (RSSI) and BLE Mac address from BLE beacons received via LoRa network are analyzed using the positioning algorithm designed in MATLAB. The positioning algorithm incorporates distance estimation, filter implementation and trilateration technique. The estimated location is analyzed with the root mean square error (RMSE) and cumulative distribution function (CDF). According to the results, implementing the filter reduces the positioning accuracy error, achieving 90% accuracy of positioning error less than 1.20 meters for the whole testbed. Finally, the algorithm is embedded into Raspberry Pi to view the location via desktop.

An IEEE Standard for Industrial Wireless Performance Evaluation

Adoption of wireless systems for use in industrial scenarios is increasing, although slowly, in process control and discrete manufacturing. In particular, factories must make the leap towards wireless networks as a central form of communications to enable certain capabilities out-lined by Industry 4.0. Acceptance of wireless as a principal communications mode is slowed by the fact that it is indeed less reliable and less deterministic than its wired counterparts. The industrial wireless medium is susceptible to interference and multi-path fading effects, and their impacts are exacerbated by the mission critical nature of the attached sensing and control applications. Adoption of wireless networks can be made more acceptable if the uncertainty of the wireless medium is better understood and wireless devices are designed to accommodate such uncertainty. This can be achieved through analysis of the RF environment beyond its propagation characteristics and the standardized evaluation of wireless network performance prior to deployment. This article describes the ongoing approach taken by the IEEE P1451.5p working group for the standardization of industrial wireless network performance evaluation. A strategy for modeling channel degradation factors (aggressors) and perspectives on profiling the model for replication of different radio environment scenarios are presented.

IRS-Assisted OTFS System: Design and Analysis

Intelligent reflecting surface (IRS) is a recent technology garnering lots of attention amongst the wireless communication research community due to its ability to improve the channel conditions extravagantly. The main feature of IRS technology is its capability to tune the phases of the reflecting elements to trigger a cohesive amalgamation of various multipath. IRS can easily co-exist with almost all technologies, thereby offering flexibility to the designers to come up with attractive systems. Further, orthogonal time frequency space (OTFS) is a recent 2D modulation technique that can mitigate the drawbacks of the traditional orthogonal frequency division multiplexing (OFDM) for fifth generation (5G) and beyond networks, especially in high Doppler wireless environments like vehicle-to-everything (V2X) and millimeter wave (mmWave) communications. This paper presents the system architecture of the IRS-assisted OTFS scheme in the delay-Doppler (DD) domain, including the modulation, demodulation, and detection methods. The selection of the reflection coefficients play the most vital role in the IRS-OTFS system, like any IRS system. IRS reflection optimization cannot perfectly line up all multipath with the same phase in the frequency-selective channels. We adopt an IRS phase optimization method where only the strongest delay-Doppler path is phase-aligned, while the paths with lesser strengths will be out of phase with the direct path. This reconfigurability of IRS elements enhances the OTFS modulation scheme, thereby significantly mitigating the multipath fading effects in high Doppler channels. Additionally, we propose a channel estimation for the IRS-OTFS system where both data and pilots are embedded in the same OTFS frame with minimal guard-band overhead. The paper presents extensive simulation results on the error-rate performance of the proposed system over Rayleigh and Rician fading channels. The effects of the number of IRS elements, the phase selections, and the channel estimation method on the system's performance are investigated. The comprehensive simulation study demonstrates that by exploiting the features of both OTFS and IRS, the proposed approach can provide impressive performance in high Doppler environments.

REST and EDA architectures in IoT actuation

While most Internet of Things (IoT) solutions involve sensing, some of them also introduce actuation mechanisms. Specifically, devices interact with assets in the environment and transmit sensor readouts to applications that perform analytics. These applications typically reside on the network core and, in turn, process the readouts that trigger the transmission of actuation commands to the device. One important issue in these schemes is the nature of the communication channels. Most devices are wireless and therefore they are affected by the effects of signal multipath fading that results in application loss. More importantly, these impairments may cause actuation commands to be lost or to be critically delayed. In this context, several standard mechanisms have been proposed for the transmission of traffic from the application to the devices. They fall under two main architectural categories: (1) Representational State Transfer (REST) and (2) Event Driven Architecture (EDA). In this paper, we analyze two protocols associated with each of these two architectures by comparing them in order to assess their efficiency in IoT actuation solutions. This analysis leads to the development of a mathematical model that drives an algorithm that enables the dynamic selection of the right technology based on network impairments.

Laboratory Analysis on the Performance of 5G NSA Communication in a Suburban Scenario

The propagation of information by electromagnetic waves suffers different types of interference, according to the characteristics of the environment. The 5G system relies on adaptive modulation and coding techniques to better suit the channel and maximize effective data exchange between the user equipment and the network. Practical studies on the behaviour of the system under different environmental conditions, subject to attenuation processes such as fading, are important to understand and improve the 5G efficiency. This work has analysed the effect of the MCS (Modulation and Coding Scheme) variation on throughput for channel degraded by the multipath fading effect in a mobile communication. The analysis was carried out showing that the decision algorithms in terms of MCS switching to maintain adequate data rates according to the requirement (QoS) is an important factor. Considering both 64 QAM and 256 QAM, the throughput degradation effect was more evident in higher-order modulations due to the higher probability of bit error in the symbol constellation. This study can be a key for understanding and developing robust MCS switcher for 5G and beyond communications.

Effect of terahertz-wave phase noise and millimeter-wave multipath fading on Beyond 5G wireless system

Effect of terahertz-wave phase noise and millimeter-wave multipath fading on Beyond 5G wireless system

A Deep Learning-Based Robust Automatic Modulation Classification Scheme for Next-Generation Networks

Due to stochastic wireless environment, the process of modulation classification has become a challenging task. Because of its powerful feature extraction ability and promising performance over the conventional schemes, deep learning (DL) models are employed to automatic modulation classification (AMC) problems. Most of the conventional models proposed are tested for the limited set of modulation schemes transmitted over additive white Gaussian noise (AWGN) channels without considering the effect of multipath fading and Doppler shift. The next-generation networks use adaptive and higher-order quadrature amplitude modulation (QAM) schemes for higher spectral efficiency. The classification accuracy of conventional DL-based AMC schemes drastically reduces, when different order QAM modulation schemes are accommodated. In this work, different scaling factors are selected for the generation of [Formula: see text]-QAM frames. The combination of scaling factors, which maximize the classification accuracy is chosen. A convolutional neural network (CNN) with six stages is employed for AMC. The simulation results show that the classification accuracy of proposed scheme is higher than the conventional DL-based schemes under various signal-to-noise ratio (SNR) conditions. The proposed scheme shows at least 4% improvement in classification accuracy over the other DL-based schemes.

Modeling and Analysis of MIMO Multipath Channels With Aerial Intelligent Reflecting Surface

Recently, intelligent reflecting surface (IRS) has become a research focus for its capability of controlling the radio propagation environments. Compared to the conventional terrestrial IRS, aerial IRS (AIRS) exploiting unmanned aerial vehicle (UAV)/high-altitude platform (HAP) can provide better deployment flexibility. To this end, a three-dimensional (3D) one-cylinder model is first developed for AIRS-assisted multiple-input multiple-output (MIMO) narrowband channels. In order to change the wireless channel with AIRS and create a favorable propagation environment, we propose a novel method of designing the phase-shifts for the IRS elements. Based on the model, channel impulse response (CIR), space-time correlation function, and channel capacity are derived and thoroughly investigated. A key observation in this paper is that multipath and Doppler effects in radio propagation environments can be effectively mitigated via adjusting the phase-shifts of IRS. More specifically, for the special propagation environments in the absence of any scatterers, it is found that the effects of multipath fading can be completely eliminated by IRSs. While for the general propagation environments with multiple scatterers, a small number of IRS elements can also significantly reduce the Doppler spread and the deep fades of the channels. Based on the numerical investigation of channel correlations, it is shown that channel non-stationarity is not introduced into the time domain when the phase shift of IRS is linear related to the time. Moreover, the channel capacity can also be improved by the proposed methods. Finally, the model with non-ideal IRSs is considered and it is found that using non-ideal IRSs results in poor performances compared with using ideal IRSs. These conclusions will provide a fundamental support for developing intelligent and controllable propagation environments of the future sixth-generation (6G) wireless networks.

Reducing cyclic prefix overhead based on symbol repetition in NB-IoT-based maritime communication

With the increasing maritime activities, a great demand of wide-area maritime digital data services is needed. Therefore, Narrowband Internet of Things (NB-IoT) that can provide wide coverage has been expected as an application for maritime communication networks (MCNS). In this paper, we aim to enhance the spectral efficiency in NB-IoT by reducing the cyclic prefix (CP) overhead in random access signal without causing interference. The key point of the proposed scheme is the symbols transmitted for multiple times repeatedly in NB-IoT. Specifically, all CP are removed and multi-path fading effect is eliminated by using a repeated symbol to cover the disturbed symbol to construct a circular convolution structure of the channel with the same effect as adding CP. In addition, a single-tap equalization is still appropriate. To validate the effectiveness of the proposed scheme, simulation results are carried out with respect to the bit error ratio (BER).

Lifetime Enhancement of Cooperative Wireless Ad-Hoc Networks using Optimal Power Allocation and Relay Selection Scheme

Cooperative Communication (CC) has greatly reduced the effect of multipath fading, thereby improving the quality of transmitted signals in wireless ad-hoc networks. However, existing works on CC suffers from degradation of network lifetime due to inaccurate selection of the optimal relay terminal. This results in frequent battery recharging due to high energy consumed and battery depletion. Hence, in this paper, lifetime enhancement of cooperative wireless ad-hoc networks is carried out using allocated optimal power and relay selection scheme to ensure an optimal selection of the best relay by balancing and conserving the energy consumption of the nodes. Transmit power optimization problems were formulated for Amplify-and-Forward (AF) and Decode-and-Forward (DF) relaying strategies to obtain the optimal power allocations required to transmit the information. The proposed scheme named Energy-Aware Relay Selection (EARS) was simulated in MATLAB software environment and average network lifetime performance evaluation was performed. The result obtained shows that the proposed EARS improves the network performance by 10.06% and 3.56% for AF and DF relaying strategies, respectively over the existing power-aware relay selection schemes.