Effects Of Rayleigh Fading Research Articles

Channel Fading Effect Analysis on Diffusion Cooperation Strategies over Adaptive Networks

In this paper, we investigate the performance of the diffusion adaptation strategies for parameter estimation in wireless adaptive networks, where the nodes exchange information over noisy and fading wireless channels. This paper shows the differences between the effect of Rayleigh and Rician fading over wireless adaptive networks and proves that the Rician fading is a more practical model in such kinds of networks. Simulation results imply that the effect of Rayleigh fading is more degrading for the estimation process than Rician fading. Also, the simulation results show the performance of adapt then combine (ATC) diffusion algorithm is better than the combine then adapt (CTA) algorithm by merely considering noise in wireless channels. While the performance of CTA prevails ATC over the wireless adaptive network in the presence of noise plus channel fading.

Flying Height Optimization for Unmanned Aerial Vehicles in Cellular - Flying Adhoc Network

In Flying Adhoc NETwork (FANET), the communications between Unmanned Aerial Vehicles (UAV), UAVs to infrastructure, and UAVs to wireless sensors are crucial design factors. With strict energy constrain during flying operation, the allocation of power and resources, the flying strategy, and the medium access mechanism shall be effectively used. When employing cellular network as backhaul for UAVs, the flying height of UAVs not only affects the communication between UAVs and end users on the ground, but also determines the reception between infrastructure (base stations from the cellular network) to UAVs. In this paper, we optimize the flying height of UAVs for better reception from the cellular network by using stochastic geometry analysis to model the aggregated interference at the UAV side. The network system performance is also examined under the effect of fading-less channel and Rayleigh fading channel.This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium provided the original work is properly cited.

Positioning of a Wireless Relay Node for Useful Cooperative Communication

<span>Given the exorbitant amount of data transmitted and the increasing demand for data connectivity in the 21st century, it has become imperative to search for pro-active and sustainable solutions to the effectively alleviate the overwhelming burden imposed on wireless networks. In this study a Decode and Forward cooperative relay channel is analyzed, with the employment of Maximal Ratio Combining at the destination node as the method of offering diversity combining. The system framework used is based on a three-node relay channel with a source node, relay node and a destination node. A model for the wireless communications channel is formulated in order for simulation to be carried out to investigate the impact on performance of relaying on a node placed at the edge of cell. Firstly, an AWGN channel is used before the effect of Rayleigh fading is taken into consideration. Result shows that performance of cooperative relaying performance is always superior or similar to conventional relaying. Additionally, relaying is beneficial when the relay is placed closer to the receiver. </span>

Three‐dimensional sensor network connectivity considering border effects and channel randomness with application to underwater networks

Connectivity is an important measure that determines the quality of service of a network. The sensor networks that find applications in underwater, terrain and space communication requires the nodes to be three-dimensional (3D), and hence, 3D connectivity is a challenging issue to be addressed. Also, the networks are prone to fading and shadowing effects due to the barriers in the communication path. Hence, the analysis of deterministic connectivity is not valid as the range of connectivity is a randomly varying parameter in the presence of fading and shadowing. In this study, the authors provide an analysis of 3D connectivity under channel randomness considering the border effects, with application to the underwater networks, where the existence of network border is significant due to the presence of natural boundaries at bottom and surface of the ocean. The connectivity analysis in the presence of log-normal shadowing is performed, and closed-form expressions are derived. Also, the 3D connectivity under the combined effects of Rayleigh fading and log-normal shadowing is analysed, which can be approximated to the well-known K-distribution used to characterise underwater sensor networks. The analysis of the proposed work matches almost exactly with the simulation, and thus, the results are validated.

Evaluation of Macro Diversity Gain in Long Range ALOHA Networks

Macro reception diversity is a capability allowing a packet to be received by several base stations. In this letter, we propose a simple but accurate analytical model to estimate the macro diversity gain in pure and slotted ALOHA wireless networks. The proposed model takes into account Rayleigh fading, shadowing, and capture effect. We obtain simple closed-form formulas for the network packet loss rate. We find that systems with macro reception diversity can benefit from shadowing. With path loss exponent 4, packet loss rate constraint 10% and 8 dB shadowing, the capacity of pure ALOHA with macro diversity is at least 2 times as much as that in systems in which a device transmits only to the best base station.

Asymptotic Capacity Analysis of Large-Scale MIMO AF Relay Networks in a Composite Fading Environment

Large-scale multiple-input–multiple-output (MIMO) networks, together with relay technology, have received considerable attention due to their remarkable capacity potential. Nevertheless, the majority of recent research studies on the asymptotic capacity of large-scale MIMO amplify-and-forward (AF) relay networks are limited to a fundamental assumption of small-scale fading, where the effect of large-scale fading, including shadow fading and path loss, is ignored. Motivated by this observation, in this paper, we present an extended model for the asymptotic capacity analysis in a composite fading environment, where Rayleigh fading, shadow fading, and path loss effect are incorporated altogether. Moreover, a realistic relay distribution is considered for real-world application of our capacity analysis. The proposed model consists of one source and one destination that are both equipped with $M$ antennas, which communicate through $K$ relays, each having $N$ antennas. We first employ random matrix theory to derive the empirical cumulative distribution of the channel covariance matrix and analyze the asymptotic capacity per source–destination antenna pair as both $M$ and $NK$ tend to infinity, but their ratio remains as a constant. We then consider the asymptotic capacity under two asymptotic cases for a finite and an infinite number of relays, respectively. It is shown through both theoretical analysis and Monte Carlo simulations that increasing the shadowing standard deviation can improve asymptotic capacity, whereas increasing the path loss exponent would lead to a capacity reduction. Our simulation results also reveal the effects of the relay distribution, as well as the source and relay transmission powers, on the asymptotic capacity.

An Analytical Study on Eavesdropping Attacks in Wireless Nets of Things

The security of Internet of Things (IoT) has received extensive attention recently. This paper presents a novel analytical model to investigate the eavesdropping attacks in Wireless Net of Things (WNoT). Our model considers various channel conditions, including thepath loss, theshadow fading effect, andRayleigh fading effect. Besides, we also consider the eavesdroppers in WNoT equipped with either omnidirectional antennas or directional antennas. Extensive simulation results show that our model is accurate and effective to model the eavesdropping attacks in WNoT. Besides, our results also indicate that the probability of eavesdropping attacks heavily depends on the shadow fading effect, the path loss effect, Rayleigh fading effect, and the antenna models. In particular, we find that the shadow fading effect is beneficial to the eavesdropping attacks while both the path loss effect and Rayleigh fading effect are detrimental. Besides, using directional antennas at eavesdroppers can also increase the eavesdropping probability. Our results offer some useful implications on designing antieavesdropping schemes in WNoT.

Level Crossing Rate of Macrodiversity System in the Presence of Multipath Fading and Shadowing

Macrodiversity system including macrodiversity SC receiver and two microdiversity SC receivers is consid- ered in this paper. Received signal experiences, simultane- ously, both, long term fading and short term fading. Microdiversity SC receivers reduce Rayleigh fading effects on system performance and macrodiversity SC receivers mitigate Gamma shadowing effects on system performance. Closed form expressions for level crossing rate of microdi- versity SC receivers output signals envelopes are calcu- lated. This expression is used for evaluation of level crossing rate of macrodiversity SC receiver output signal envelope. Numerical expressions are illustrated to show the influence of Gamma shadowing severity on level crossing rate.

Generalised trade‐off model for energy‐efficient WSN synchronisation

A mathematical framework to obtain a generalised energy-efficient trade-off model for generic wireless sensor networks (WSNs) while attaining sensing node synchronisation at a given network-wide estimation error threshold is presented. The model outputs both a theoretical optimal solution as well as a set of sub-optimal solutions to cater for real-world WSN designs. The robustness of the proposed framework is examined with an example in which randomly deployed sensors are affected by path-loss and uncorrelated Rayleigh fading effects.

Performance Evaluation of a New Secured Coded Hybrid Spread Spectrum System under Effect of Different Channels Types

In this paper, the performance of a new secured coded DS/FFH/TH hybrid spread spectrum system is evaluated. The evaluation is performed using four different spreading codes, which are long sequence, PN sequence, gold sequence, and chaotic sequence. The evaluation is performed under the effect of AWGN, Rayleigh fading, and frequency selective fading channels. The results show that the system presents a superior improvement in the performance especially in the severe fading conditions.

Network coding for relaying networks over double‐link rayleigh fading channels using priority in decoding

AbstractNowadays, wireless networks are employed for many applications, but they face some problems such as power source limitation and collision due to common media. These problems decrease the network throughput and increase the power consumption. Fading is another important characteristic of wireless channels, which degrades the network performance. On the contrary, network coding is a useful method that can be applied to increase throughput. We extend the network coding model from two nodes with one relay to four nodes with the same relay over Rayleigh fading channels. Each side of the relay consists of two neighbouring nodes, which relaying nodes are not needed between them. In this paper, we propose a new method that uses priority property for decoding so that high or low priority for a node means that the node will XOR received data from relay node and its own data or data received from its neighbour, respectively. Also, decoding procedure includes two stages in which one of the neighbour nodes in each side has high priority and the other one has low priority. Then, network performance and the effects of Rayleigh fading on network coding over double‐link channels are studied under power‐constant and channel‐inversion schemes. By solving optimisation problems called Double‐Link Network Coding Constant Power and Double‐Link Network Coding Channel Inversion, we obtain optimum network throughput. The results show that the proposed method increases network throughput and decreases power consumption by reducing number of time slots in comparison with the simple method. Copyright © 2013 John Wiley & Sons, Ltd.

Power Allocation for Amplify-and-Forward Relaying with Correlated Shadowing

Power allocation is a key technique to exploit the benefits of cooperative relaying. In this paper, we investigate the effect of shadowing on the power allocation of amplify-and-forward cooperative relaying systems. Considering the joint effects of path loss, correlated shadowing and flat Rayleigh fading, the approximate outage probability at high signal-to-noise ratio (SNR) is first derived. Then we solve the power allocation problem by minimizing the approximate outage probability subject to a total power constraint. It is shown by the analytical results that the correlation coefficients and the standard deviations of shadowing have significant impacts on the power allocation. The simulation results show that the proposed power allocation scheme yields about 2 dB SNR gain compared to the equal power allocation in the high SNR regime.

Relay Placement for Amplify-and-Forward Relay Channels with Correlated Shadowing

In this letter, we investigate the optimal relay placement problem for the amplify-and-forward relay channels. Considering the joint effects of path loss, correlated shadowing, and flat Rayleigh fading, we first derive the approximate outage probability in the high signal-to-noise ratio (SNR) regime. Then, the optimal relay placement problem is formulated to minimize the derived approximate outage probability. It is shown by the analytical results that the correlation coefficients and the standard deviations of shadowing have significant impacts on the optimal relay placement. Somewhat surprisingly, we show that the optimal relay position may not be on the line connecting the source and the destination for certain scenarios.

Cross-Layer Performance Analysis of CSMA/iCA Based Wireless Local Area Network

Carrier sense multiple access with improvised collision avoidance (CSMA/iCA) has recently been proposed as an enhancement to CSMA/CA. It has been reported to be superior than the legacy counterpart in terms of throughput efficiency, packet transmission delay and quantitative fairness index. Nevertheless, the superiority has been shown assuming ideal network conditions: error-free physical layer (L1) and saturated (always non empty) queue at medium access control layer (L2). These strict assumptions, however, do not accurately hold in the real-world Wireless Local Area Networks since the wireless medium is generally error-prone and the arrival of the packets at L2 queue is generally bursty resulting in non-saturated queue occupancy. Thus, the reported performance, especially throughput, in such typical L1/L2 settings is not complete to understand the performance benefit that CSMA/iCA offers under the realistic network settings. In this paper, we relax the aforesaid ideal assumptions and present a cross-layer (L1/L2) performance analysis. Our cross-layer analytical model considers the effect of Rayleigh fading induced bit errors in L1 and non-saturated queue occupancy due to Poisson packet arrival at L2 queue. By virtue of the validated numerical results, we show that the CSMA/iCA consistently retains its throughput gain over CSMA/CA for the non-ideal wireless settings as well.

Analysis of Optimal Weighted Cooperative Spectrum Sensing with Multiple Antenna Elements

This paper investigates the use of cooperative spectrum sensing (CSS) to detect primary user (PU) signals during spectrum sharing between the PU and the secondary user (SU). In particular, we employ a variant of CSS (which achieves space diversity), called weighted gain combining CSS (W-CSS), which has the potential to achieve increased diversity gain and enhance detection performance. In a typical W-CSS system, the SU needs to obtain the PU signal power information in order to set the proper weight value. However, as it is hard for the SU to ascertain whether the PU is present or absent, this is difficult to obtain. To address this problem, a PU signal power estimation algorithm is introduced. In addition, we also analyze the statistics of the estimator and derive the detection probability of the W-CSS when the PU signal power estimation algorithm is applied. The analysis and related simulation results reveal that the detection probability of the proposed W-CSS under time-variant Rayleigh fading asymptotically approaches the detection probability in an additive white Gaussian noise channel as the number of antennas is increased. This also follows results from our Monte Carlo simulations, showing that multiple antenna elements could suppress the effect of Rayleigh fading. In short, the accuracy of the estimation algorithm is affected by channel variation (especially in the case of fast Rayleigh fading). Hence, to address this problem, we employ multiple antenna elements with a square-law combining energy detector in the W-CSS. key words: cognitive radio, cooperative spectrum sensing, NeymanPearson theorem, multiple antenna elements

An Improved Digital Automatic Gain Control Method for DAB Receivers

Abstract Digital Audio Broadcasting (DAB) is designed for reliable reception up to vehicle speed of 120 km/h. The high vehicle speed reception requires fast Automatic Gain Control (AGC) to compensate the Rayleigh fading effects in wireless environment. But fast AGC will also incorrectly amplify DAB's null symbol and the following phase reference symbol to cause synchronization problem. Traditional DAB receivers use an 'agc_hold' signal to hold the AGC voltage to avoid the incorrect amplification during the null symbol. But this method requires one extra pin on both the RF tuner and the baseband decoder chips of the DAB receiver. Also it requires good time alignment between the 'agc_hold' signal and the actual null symbol, which brings the complexity to the receiver design. In this paper we proposed an improved AGC method which does not require the 'agc_hold' signal, while still keeps the null symbol quite clear. The new AGC method can be digitally implemented and integrated into the baseband decoder. Comparing to the traditional AGC method, the proposed method reduces the pin numbers of both the RF tuner and the baseband decoder chips. Also it reduces the communications between the RF tuner and the baseband decoder, thus simplifies the receiver design.

BICM-ID with 3-Dimensional BPSK and Signal Space Diversity over Rayleigh Channel

A BICM-ID system with 3-dimensional rotated BPSK constellation and signal space diversity (SSD) is proposed to combat the effect of Rayleigh fading. A new criterion based on mutual information is proposed to find the optimal rotation matrix, and the labeling that fits well with the outer code is presented. Simulation results show that at BER of 10-5 over a Rayleigh fading channel, with the code length of 192,000bits and the iteration number of 100, the performance of the proposed system is only about 0.8dB from the Gaussian-input Shannon limit and exceeds the limit constrained by the traditional QPSK input without rotation or SSD, at the spectrum efficiency of 1bit/s/Hz.

Modelling and simulation of Rayleigh fading, path loss, and shadowing fading for wireless mobile networks

In this paper, we first derive two explicit mathematical expressions of bit error rates (BERs) with Rayleigh fading for differential phase shift keying (DPSK) and quadrature amplitude modulation (QAM), and establish corresponding simulation models to realize the effect of Rayleigh fading. Next, we propose a mathematical expression to define the effect of shadowing fading and an approach to computing it. Then, we optimize the effect of path loss through adapting the value of the path loss exponent to different environments. Finally, using a packet-oriented simulation tool, OPtimized Network Engineering Tool (OPNET), we realize the effects of Rayleigh fading and shadowing fading, optimize the effect of path loss, and investigate the integrated impact of these effects on the performance of wireless mobile networks including wireless local area networks (WLANs) and mobile ad hoc networks (MANETs). Simulation results not only coincide with the experimental results in present literature, but also show that these effects exert a non-negligible impact on the performance of wireless mobile networks. Accordingly, our new models and approaches make the present over-optimistic simulation results more accurate and reasonable.

EVALUATION OF OPTIMAL TRANSMIT POWER IN WIRELESS SENSOR NETWORKS IN PRESENCE OF RAYLEIGH FADING

Design of an energy efficient wireless sensor network (WSN) has emerged as an important research area. Minimizing energy consumption is the primary objective for WSN. WSN is usually characterized by tiny size, low cost and low transmission power. So optimization of transmission power is of great importance. Optimal transmit power not only achieves better network lifetime but also reduces inter-node interference significantly. In this paper we carry out simulation studies to investigate the effects of Rayleigh fading on the performance of WSN and optimal transmit power in presence of Rayleigh fading is derived. The effects of bit rate and Rayleigh fading on optimal transmit power are investigated under several network conditions. In this paper the network performance is estimated in terms of a quality of service (QoS) constraint given by the maximum tolerable bit error rate (BER). The derived optimal transmit power maintains a minimum BER constraint. The impact of fading on critical bit rate i.e., the bit rate below which a desired BER can not be achieved with any amount of transmit power is also studied.

Downlink Cooperative Transmission by Superposition Modulation: Performance Analysis and Power Allocation Strategy

In this paper, we proposed 2 new downlink cooperative transmission strategies based on superposition modulations: Scheme (a), QPSK superimposed modulation and scheme (b), orthogonal 4-PAM superimposed modulation. In both schemes, Rayleigh fading and path loss effect are introduced into channel model. We analyzed the symbol error rate (SER) performances and derived their theoretical expressions. The analytical SER expression of scheme (b) is achieved. Furthermore, we investigated the optimal power allocation problem through both analytical and numerical approach. Finally, the derived analytical expressions were verified by simulation results. Our proposed superposition scheme (b) can outperform the classical downlink cooperative scheme by 2 dB, and the performance advantage of Scheme (a) achieves by 5 dB.