Shadow Fading Research Articles

3D Boundary Modeling and Handover Analysis of Aerial Users in Heterogeneous Networks

Aerial user equipments (AUEs) levitating in the air are growingly used in various applications for the agility, but leads to link fluctuation and deterioration of handover (HO) performance, which is marked in heterogeneous networks (HetNets). However, existing HO models have not investigated HO performance of cellular-connected unmanned aerial vehicles (UAVs) under the influence of shadow fading at different altitudes. This paper proposes a 3D boundary model derived by trigger conditions to analyze HO performance of aerial users considering the shadow fading effect in two-tier HetNets, where the 3D HO trigger boundary and handover failure (HF) boundary are both in the form of a hemispherical shell with typical small base station (SBS) as center, composed of the point sets corresponding to the above HO events, which are derived by the Received Signal Strength (RSS) ratio of target SBS to source macro base station (MBS). Especially, the calculation of HO events probabilities under trigger conditions are transformed to the relationship between time-to-trigger (TTT) and during time inside 3D boundary by exploring the positional relationship between straight line and hemispherical shell boundaries. Thus, the compact expressions of HO probability, HF probability and PP probability are obtained to quantify the effect of 3D mobility and HO parameters in various deployment of HetNets. Theoretical results show that HF and PP probability dramatically drop by 68.5% and 47.1% when <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$H=20$</tex-math></inline-formula> m comparing to scenario of terrestrial users and HetNets deployment should be considered when choosing appropriate HO parameters.

Channel measurement and characterisation for 5G multi‐scenarios at 26 and 38 GHz

AbstractMillimetre‐wave (mmWave) frequencies play a vital role in fifth‐generation (5G) wireless systems and beyond due to the vast available bandwidth of several GHz. This paper presents channel characteristics and their channel models for mmWave based on extensive channel measurements at 26 and 38 GHz conducted in 5G scenarios, such as the rooftop, the high‐speed railway, and the Industrial Internet of Things scenarios. The channel sounder receiver (Rx) uses an omnidirectional or phased array antenna to meet the requirements of channel measurement, such as recording absolute delay and obtaining 3‐dimensional angular information. We use the classical close‐in model and floating‐intercept model to model path loss. Meanwhile, channel statistics in the delay domain are derived from the measured power delay profiles. Note that the different scenarios are measured with the same channel sounder, making the measurement results of different scenarios comparable. It is shown that the shadow fading parameter σ is 0.7 dB as fewer large scatterers exist in the rooftop scenario. Moreover, due to the significant dependence of delay spread on the geometric relationship between the transmitter (Tx), Rx, and surrounding environment, the statistical data in the delay domain varies significantly in different scenarios. The channel characteristics and models will guide future air‐interface, beamforming, and transceiver designs for 5G and beyond.

Evaluation of 60 GHz Wireless Connectivity for an Automated Warehouse Suitable for Industry 4.0

The fourth industrial revolution focuses on the digitization and automation of supply chains resulting in a significant transformation of methods for goods production and delivery systems. To enable this, automated warehousing is demanding unprecedented vehicle-to-vehicle and vehicle-to-infrastructure communication rates and reliability. The 60 GHz frequency band can deliver multi-gigabit/second data rates to satisfy the increasing demands of network connectivity by smart warehouses. In this paper, we aim to investigate the network connectivity in the 60 GHz millimeter-wave band inside an automated warehouse. A key hindrance to robust and high-speed network connectivity, especially, at mmWave frequencies stems from numerous non-line-of-sight (nLOS) paths in the transmission medium due to various interacting objects such as metal shelves and storage boxes. The continual change in the warehouse storage configuration significantly affects the multipath reflected components and shadow fading effects, thus adding complexity to establishing stable, yet fast, network coverage. In this study, network connectivity in an automated warehouse is analyzed at 60 GHz using Network Simulator-3 (NS-3) channel simulations. We examine a simple warehouse model with several metallic shelves and storage materials of standard proportions. Our investigation indicates that the indoor warehouse network performance relies on the line-of-sight and nLOS propagation paths, the existence of reflective materials, and the autonomous material handling agents present around the access point (AP). In addition, we discuss the network performance under varied conditions including the AP height and storage materials on the warehouse shelves. We also analyze the network performance in each aisle of the warehouse in addition to its SINR heatmap to understand the 60 GHz network connectivity.

Low-Altitude UAV Air-to-Ground Multilink Channel Modeling and Analysis at 2.4 and 5.9 GHz

Due to low cost and high operability, unmanned aerial vehicle(UAV) becomes a key component in future intelligent transportation system(ITS) for various use cases. Air-to-ground(A2G) communication is a fundamental technology for integration of UAV in the ITS, where accurate analysis and modeling of UAV A2G wireless channel are of great importance for communication algorithm development. In this paper, we present a comprehensive analysis and modeling of low altitude UAV A2G channel at 2.4 and 5.9 GHz based on multi-link channel measurement campaign. Based on the measured data, the value of path loss as a function of the elevation angle and distance is proposed. Further, the shadow fading(SF) is analyzed for different frequency bands and the spatial correlation is evaluated. Particularly, it is found that the influence of UAV altitude on shadowing is significant and should be considered when developing A2G communication system.

Closed-Form Analysis of the α-Beaulieu-Xie Shadowed Fading Channel

The presented research proposes the α-modification of the Beaulieu-Xie shadowed fading channel for wireless communications. For the assumed model the closed-form analytical description of the basic statistical characteristics is carried out (i.e., probability density function, cumulative distribution function, and their asymptotics). The derived statistical description is exemplified on the problems of the average bit error rate and ergodic capacity calculation, for which the exact analytic and high signal-to-noise ratio asymptotic expressions are derived. The performed extensive numerical analysis demonstrates high correspondence with the analytical work and helps to study the dependence of the channel nonlinearity effects on the bit error probability.

Performance Optimization of Multipair Massive MIMO Polarized Relay Systems

In this paper, we analyze the challenges faced by multipair massive Multiple-input-multiple-output (MIMO) relay channels in 5G wireless communication systems, where high path loss and severe shadow fading between different user nodes can cause poor channel quality. To overcome these limitations, we propose a polarization selection scheme for antenna arrays combining multipair massive MIMO relay and beamforming to improve MIMO relay channel quality. Specifically, our main goal is to exploit the potential of polarization diversity to maintain and improve the link quality while maintaining the compact size of the MIMO antenna array. To achieve this goal, we introduce a dynamic weighted particle swarm optimization algorithm with contraction factor (CF-DWPSO) to select the polarization direction. In addition, we employ distributed beamforming to effectively suppress or eliminate inter-pair interference. The performance of the simulation analysis shows that CF-DWPSO combined with beamforming provides significant performance improvement of the multipair massive MIMO polarized relay channels, which further indicates that it is of great necessity for improving the performance of this system to optimize the polarization selection by combining beamforming techniques.

Extremely Accurate, Generic and Tractable Exponential Bounds for the Gaussian Q Function With Applications in Communication Systems

In this letter, we apply the Fejer’s Rule of interpolatory integration in a modified manner to obtain a very generic, tractable and extremely accurate approximation for the Gaussian <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> function. We further show the utility of the proposed approximation by simplifying the error performance metrics like average symbol error probability (ASEP) of popular digital modulation techniques over a very useful κ-μ shadowed fading channel. This eliminates the need of mathematical softwares which require very high processing power (a constraint at the receiver side) yielding simplified and cost effective receiver’s design. In addition, an insight on the asymptotic ASEP (and diversity order thereof) is also highlighted in this letter.

Machine-Learning-Based Combined Path Loss and Shadowing Model in LoRaWAN for Energy Efficiency Enhancement

Many practical Internet of Things (IoT) applications require deploying End Nodes (ENs) in hard-to-access places where replacing batteries is difficult or impossible. As a result, the ENs demand high energy efficiency. Long Range Wide Area Network (LoRaWAN) is an IoT protocol that aims to achieve low energy consumption. However, the energy consumption in LoRaWAN is related to transmission power, which can be set mainly based on path loss and shadow fading modeling and link budget analysis. Hence, appropriately setting this transmission power parameter saves energy and guarantees reliable communication links. Traditional path loss and shadow fading modeling and transmission power setting do not consider the variations caused by different environmental effects. In this work, we show via real-life data analysis that path loss and shadow fading depend on environmental variables. We propose Machine Learning models to calculate the empirical path loss and shadow fading, which is used to set the transmission power to save ENs’ energy. Our models include the effects of distance, frequency, temperature, relative humidity, barometric pressure, particulate matter, and Signal to Noise Ratio. Specifically, the models are based on Multiple Linear Regression, Support Vector Regression, Random Forests, and Artificial Neural Networks, exhibiting a Root Mean Square Error (RMSE) up to 1.566 dB and R up to 0.94. For energy saving, the developed models serve to set the transmission power and Spreading Factor based on the Adaptative Data Rate (ADR) algorithm principles, which reduces the link margin saving energy up to 43% compared with the traditional ADR protocol.

Channel characteristics analysis of millimetre‐wave bands in Hyperloop scenarios based on ray‐tracing

AbstractA reliable train‐to‐ground wireless communication system is proposed for the foundation of the safe operation of Hyperloop. The wireless channel characteristics of Hyperloops at millimetre‐wave (mmWave) bands are analysed based on the ray‐tracing method. Considering the reflection paths and line of sight path, the channel transfer function expression is derived for each multipath and then the channel impulse response is obtained. On this basis, the investigation and analysis of the large‐scale and small‐scale channel characteristics, including the path loss, shadow fading, delay spread, and angular spread of 4 different mmWave frequency carriers, that is, 28/38/45/60 GHz, are conducted. Simulation results show that the path loss increases as the frequency increases while the time delay spread and angular spread almost keep unchanged. The relevant research results will contribute to the design of future Hyperloop wireless communication systems.

Sub-6 GHz to mmWave for 5G-Advanced and Beyond: Channel Measurements, Characteristics and Impact on System Performance

In the 5G-Advanced and beyond systems, multi-frequency cooperative networking will become an inevitable development trend. However, the channels have not been fully investigated at multi-frequency bands and in multi-scenarios by using the same channel sounder, especially for the sub-6 GHz to millimeter-wave (mmWave) bands. In this paper, we carry out channel measurements at four frequency bands (3.3, 6.5, 15, and 28 GHz) in two scenarios including Urban Micro (UMi) and Outdoor-to-Indoor (O2I) with the same channel sounder. The channel characteristics are extracted and modeled, including path loss (PL), shadow fading, frequency dependence of cluster features, root mean square (RMS) delay spread (DS), Ricean K-factor, and the correlation properties. We mainly focus on the analysis of large-scale parameters and more consideration of the link budget coverage problem. We present the frequency dependence model of the channel characteristics. Among them, in the non-line-of-sight (NLoS) condition, it is found that except for theoretical value brought by higher frequency, additional path loss increment will be generated. Based on these channel characteristics, the impact on performance of the wireless system is analyzed including cell coverage radius, data rate and bit error rate (BER). The results can give an insight into the spectrum selection and optimization in 5G-Advanced and beyond multi-frequency communication systems.

Probabilistic stability of power control systems with Nakagami-m fading channels

ABSTRACT This paper analyses the probabilistic stability of power control systems under Nakagami-m fading channels caused by multi-path propagation. First, the Nakagami-m fading model is utilised to capture the feature of shadowed fading channels. The Foschini–Miljanic algorithm is utilised to achieve the desired quality-of-service, and a stability condition is given for the power control system. Then, the probability of the system being stable is obtained for power control systems. Afterwards, the monotonicity of the probability with respect to the communication distance is revealed, which sheds light on the node configuration. Furthermore, it is shown that Nakagami-m fading links can model the channel gains better than Rayleigh fading links by adjusting the shape parameter. Finally, an example is given to illustrate the effectiveness of the theoretical results.

Radio Channel Measurements and Characterization in Substation Scenarios for Power Grid Internet of Things

Wireless communication technologies play a key role to support the implementation of power grid Internet of Things (PIoT). An in-depth knowledge of the radio channel is vital to the application of wireless communication technologies in PIoT. This paper investigates the radio channel measurements and characterization for PIoT substation scenarios. A novel channel sounder is designed for achieving omnidirectional measurements and phased array antennas based directional measurements, and a directional multipath components extraction algorithm is proposed. The channel sounding system is verified and is used to perform a series of 3.35 GHz omnidirectional and directional channel measurements in four substation scenarios, involving a 10 kV switch room, a 110 kV GIS room, a semi-indoor 110 kV substation and an outdoor 220 kV substation. Based on the measured channel impulse responses data, both large-scale and small-scale fading characteristics of substation channels are extracted and analyzed. Empirical models of path loss, shadow fading, Ricean K-factor and root-mean-square (RMS) delay spread are proposed. In addition, results of RMS angle spread of departure and RMS angle spread of arrival are presented. These results will provide useful reference for the deployment and optimization of wireless communication networks in PIoT substation scenarios.

Channel Modeling for UAV-to-Ground Communications With Posture Variation and Fuselage Scattering Effect

Unmanned aerial vehicle (UAV)-to-ground (U2G) channel models play a pivotal role in reliable communications between UAV and ground terminal. This paper proposes a three-dimensional (3D) non-stationary hybrid model including large-scale and small-scale fading for U2G multiple-input-multiple-output (MIMO) channels. Distinctive channel characteristics under U2G scenarios, i.e., 3D trajectory and posture of UAV, fuselage scattering effect (FSE), and posture variation fading (PVF) are incorporated into the proposed model. The channel parameters, i.e., path loss (PL), shadow fading (SF), path delay, and path angle, are generated incorporating machine learning (ML) and ray tracing (RT) techniques to capture the structure-related characteristics. In order to guarantee the physical continuity of channel parameters such as Doppler phase and path power, the time evolution methods of inter- and intra- stationary intervals are proposed. Key statistical properties, including temporal auto-correction function (ACF), power delay profile (PDP), level crossing rate (LCR), average fading duration (AFD), and stationary interval (SI), are analyzed with the impact of the change of fuselage and posture variation. It is demonstrated that both posture variation and fuselage scattering have crucial effects on channel characteristics. The validity and practicability of the proposed model are verified by comparing the simulation results with the measured ones.

Measurement‐based omnidirectional millimetre‐wave and sub‐THz propagation analysis in a large cubicle office environment

AbstractFor 5G beyond and/or 6G mobile services, a new spectrum at frequencies above 100 GHz has received great attention lately. To characterise the similarities and the differences between frequencies below 100 GHz and above 100 GHz, this paper provides analyses of multi‐frequency propagation characteristics based on wideband measurements at 28, 38, 71, 82, and 159 GHz, with an emphasis on the sub‐THz (i.e. the 159 GHz) propagation characteristics. All the frequency measurements were conducted in the same cubicle office room environment by locating the transmitter and the receiver at the same positions. The measurement results show that the path loss and the shadow fading characteristics do not exhibit significant differences depending on the frequency range from 28 to 159 GHz. However, the delay spread shows a generally decreasing trend as the frequency increases. Additionally, angular domain analyses were conducted with the 159 GHz measurements.

Impact of Antenna Design, Electromagnetic Propagation, and RF Frequency on the Performance of Wireless Communication Systems in Urban Environments

The design and optimization of antennas, electromagnetic propagation, radio frequency (RF), and channel characterization are vital to the performance of the system in the rapidly developing area of wireless communication. Antennas are electronic components that transform electrical currents into electromagnetic waves and vice versa. They are critical to the operation of any wireless network and their design and optimization are therefore of paramount importance. The goal of this research was to find out how different factors, like antenna type, electromagnetic environment, RF, and channel characteristics, affect the efficiency of a wireless network. Multipath fading of 8 dB, shadow fading of 3 dB, and path loss of 100 dB were used in the study with a microstrip antenna in a suburban propagation scenario at an RF frequency of 5 GHz. Antenna design, electromagnetic propagation scenario, radio frequency (RF), and channel characteristics were all shown to have an impact on the wireless communication system performance. The performance metrics of the wireless sensor network were almost, but not quite, those that were hoped for in a real-world setting. Several avenues for future study are suggested, and the results have important implications for the design and optimization of wireless communication systems.

Secrecy Performance of α−κ−μ Shadowed Fading Channel

In this paper, the physical layer security aspects of a wireless framework over α − κ − μ shadowed (AKMS) fading channel are examined by acquiring closed-form novel expressions of average secrecy capacity, secure outage probability (SOP), and strictly positive secrecy capacity. The lower bound of SOP is derived along with the asymptotic expression of SOP at the high signal-to-noise ratio regime in order to achieve secrecy diversity gain. Capitalizing on these expressions, the consequences due to the simultaneous occurrence of fading and shadowing are quantified. Finally, Monte-Carlo simulations are demonstrated to assess the correctness of the expressions.

Accurate Asymptotic Characterization of α-κ-μ Shadowed Fading Channel With Application to Secure URLLC

In this paper, we propose a novel characterization method of α-κ-μ shadowed fading channel. For both the single α-κ-μ shadowed random variable (RV) and the sum of independent identically distributed α-κ-μ shadowed RVs, we accurately derive asymptotic closed-form expressions of their probability density functions (PDFs), cumulative distribution functions (CDFs), and moment-generating functions (MGFs) in this method. Moreover, we analyze the secure ultra-reliable and low latency communications (URLLC) in terms of average information leakage (AIL) in the massive multiple-input multiple-output (MIMO) system based on the proposed method. Numerical results of the proposed theory analysis are supported by Monte-Carlo simulations to validate the accuracy of the derivation.

Performance analysis of improved path loss models for millimeter-wave wireless network channels at 28 GHz and 38 GHz.

The importance of the path loss in millimeter wave channel propagation cannot be taken for granted in terms of deployment, design, performance assessment, and planning. The path loss helps to determine the network's geographic coverage. Although many path loss models, including statistical and empirical models based on measurement and linear regression, have been proposed by various researchers, high fidelity is required to determine the performance of the wireless network's channel. This research validates the improved version of the well-known close in (CI) and floating intercept (FI) path loss models at frequency bands of 28 and 38 GHz. The measurement surroundings comprised of an enclosed passageway with vertical-horizontal (V-H) and vertical-vertical (V-V) antenna polarizations. One of the key findings of this study is that the enhanced versions of these models typically perform better in terms of consistency than the standard models thereby justifying their high accuracy level. The improved versions of the CI and the FI models demonstrate a significant improvement for various antenna polarizations. The mean prediction error (MPE) and standard deviation error (SDE) also show how precisely and accurately the improved models predict the path loss. Additionally, the improved models provide the reasonable responsiveness and uniformity of the parameters with the change in the antenna polarization and lower the shadow fading's standard deviation in LOS as well as NLOS situations. The results confirm that the modified versions of CI and FI models predict path loss better in an enclosed environment for 5G networks.

Measurements and Modeling of Large-Scale Channel Characteristics in Subway Tunnels at 1.8 and 5.8 GHz

Radio propagation characteristics in subway tunnels are significant for designing reliable wireless communications. To obtain large-scale channel characteristics, extensive propagation measurements are conducted in a straight subway tunnel at 1.8 and 5.8 GHz, respectively. Based on the measurements, some typical large-scale channel parameters are extracted and modeled, such as path loss, shadow fading, and channel correlation. The path loss exponents are found to be 2.83 and 2.55 at 1.8 and 5.8 GHz, respectively, with shadow fading standard deviation of 1.58 and 2.58 dB. Shadow fading decorrelation distance is 8.71 m for 1.8 GHz and 11.65 m for 5.8 GHz, respectively. Moreover, cross-correlation coefficient of shadow fading in two dual-link scenarios is around 0.1, which shows that there is fairly low cross-correlation in a subway tunnel. The results in this letter are useful for link budget, handover scheme design, and network planning of subway communication system.

Channel Characterization and Ray-Tracing Assisted Stochastic Modeling for Urban Vehicle-to-Infrastructure Terahertz Communications

To support intelligent vehicular services, vehicular ad-hoc networks (VANET) require high-speed communications from vehicles to infrastructure (V2I). To meet such demands, the Terahertz (THz) band, with abundant spectrum resources, is envisioned as a promising solution. However, a premise problem is channel modeling for THz V2I communications. In this paper, ray-tracing (RT) techniques are utilized to analyze the V2I channel in an urban scenario at 300 GHz. Channel statistics, including path loss, shadow fading, etc, are thoroughly characterized. The parameters of multi-path components (MPCs) and similarity of MPCs existing on identical streets are analyzed and modeled. Furthermore, the birth and death processes of MPCs are carefully characterized and modeled. A new criterion, namely, the virtual transmitter position scheme, is proposed to determine the birth and death of MPCs and the evolution of MPCs during their lifetime. Based on this, a ray-tracing assisted stochastic channel model (RTA-SCM), is proposed, which combines the RT technique and stochastic processes. The effectiveness and accuracy of RTA-SCM are validated by comparing it against RT data and geometry-based stochastic models. The proposed model can be utilized in time-varying THz V2I communications.