Shadow Fading Research Articles

Connectivity Analysis of Cognitive Radio Ad-hoc Networks with Shadow Fading

In this paper, we analyze the connectivity of cognitive radio ad-hoc networks in a log-normal shadow fading environment. Considering secondary user and primary user’s locations and primary user’s active state are randomly distributed according to a homogeneous Poisson process and taking into account the spectrum sensing efficiency of secondary user, we derive mathematical models to investigate the connectivity of cognitive radio ad-hoc networks in three aspects and compare with the connectivity of ad-hoc networks. First, from the viewpoint of a secondary user, we study the communication probability of that secondary user. Second, we examine the possibility that two secondary users can establish a direct communication link between them. Finally, we extend to the case of finding the probability that two arbitrary secondary users can communicate via multi-hop path. We verify the correctness of our analytical approach by comparing with simulations. The numerical results show that in cognitive radio ad-hoc networks, high fading variance helps to remarkably improve connectivity behavior in the same condition of secondary user’s density and primary user’s average active rate. Furthermore, the impact of shadowing on wireless connection probability dominates that of primary user’s average active rate. Finally, the spectrum sensing efficiency of secondary user significantly impacts the connectivity features. The analysis in this paper provides an efficient way for system designers to characterize and optimize the connectivity of cognitive radio ad-hoc networks in practical wireless environment.

Exact Performance Analysis of AF Based Hybrid Satellite-Terrestrial Relay Network with Co-Channel Interference

This paper considers the effect of co-channel interference on hybrid satellite-terrestrial relay network. In particular, we investigate the problem of amplify-and-forward (AF) relaying in hybrid satellite-terrestrial link, where the relay is interfered by multiple co-channel interferers. The direct link between satellite and terrestrial destination is not available due to masking by surroundings. The destination node can only receive signals from satellite with the assistance of a relay node situated at ground. The satellite-relay link is assumed to follow the shadowed Rice fading, while the channels of interferer-relay and relay-destination links experience Nakagami-m fading. For the considered AF relaying scheme, we first derive the analytical expression for the moment generating function (MGF) of the output signal-to-interference- plus-noise ratio (SINR). Then, we use the obtained MGF to derive the average symbol error rate (SER) of the considered scenario for M-ary phase shift keying (M-PSK) constellation under these generalized fading channels.

Analysis of UWB communication over IEEE 802.15.3a channel by superseding lognormal shadowing by Mixture of Gamma distributions

In this paper, we calculate the bit error rate (BER) of the ultra-wide band (UWB) wireless communication system over IEEE 802.15.3a channel model by superseding the lognormal (LN) shadow fading distribution to the Mixture of Gamma (MG) distributions. In general, shadow fading is the effect of random fluctuation of received signal power around the mean path loss and it is modeled as LN distribution. In this work, we approximate the LN shadow fading distribution to the MG distributions, because of intractable, indefinite mathematical expression of the characteristic function (CF) and moment generating function (MGF) of the LN distribution, which are required to evaluate BER of the UWB communication system. To estimate the approximate MG distributions parameters, we use rth moment algorithm with least square non-linear curve fitting criteria. This work employs the L-fingers RAKE receiver which is needed to collect the total energy at the receiver in the UWB system. The results show that 5-MG distributions is the good fit for LN shadow fading distribution of the UWB communication system. The proposed analytical BER is closely matched to the simulated BER for all the four IEEE 802.15.3a channel models. It verifies the accuracy of the approximation considered in this BER analysis.

Energy Efficient Power Allocation for Distributed Antenna System over Shadowed Nakagami Fading Channel

In this paper, the energy efficiency (EE) of downlink distributed antenna system (DAS) with multiple receive antennas is investigated over composite fading channel that takes the path loss, shadow fading and Nak- agami-m fading into account. Our aim is to maximize EE which is defined as the ratio of the transmission rate to the total consumed power under the constraints of maximum transmit power of each remote antenna. According to the definition of EE and using the upper bound of average EE, the optimized objective function is provided. Based on this, utilizing Karush-Kuhn-Tucker (KKT) conditions and math- ematical derivation, a suboptimal energy efficient power allocation (PA) scheme is developed, and closed-form PA coefficients are obtained. The developed scheme has the EE performance close to the existing optimal scheme. Moreover, it has relatively lower complexity than the existing scheme because only the statistic channel infor- mation and less iteration are required. Besides, it includes the scheme in composite Rayleigh channel as a special case. Simulation results show the effectiveness of the devel- oped scheme.

On Critical Density for Coverage and Connectivity in Directional Sensor Network over Stochastic Channels Using Continuum Percolation

Sensing coverage, which is one of vital issues in the design of wireless sensor networks (WSNs), can usually interact with other performance metrics such as network connectivity and energy consumption. Whatever the metrics, the fundamental problem is to know at least how many sensor nodes are needed to maintain both sensing coverage and network connectivity. In this paper, we propose a Percolation Model on Novel Gilbert Graph (PM-NGG) to obtain the critical density at which the network can become fully covered and connected considering the similarity between the occurrence of percolation and the formation of a covered and connected network. The PM-NGG is based on directional sensor network where sensors are assigned a determined sensing direction with angular intervals varying from 0 to 2 π. Furthermore, we define the sensing and communication model in directional sensor network in presence of channel randomness including deterministic path attenuation, shadow fading, and multipath fading. Besides, we discuss the coverage and connectivity together as a whole under the proposed model. It is worth mentioning that the theoretical analysis and simulation results of the relationship between critical density and transmitting power give insights into the design of directional sensor network in practice.

Generation of 2D correlated random shadowing based on the deterministic MR-FDPF model

In modern mobile telecommunications, shadow fading has to be modeled by a two-dimensional (2D) correlated random variable since shadow fading may present both cross-correlation and spatial correlation due to the presence of similar obstacles during the propagation. In this paper, 2D correlated random shadowing is generated based on the multi-resolution frequency domain ParFlow (MR-FDPF) model. The MR-FDPF model is a 2D deterministic radio propagation model, so a 2D deterministic shadowing can be firstly extracted from it. Then, a 2D correlated random shadowing can be generated by considering the extracted 2D deterministic shadowing to be a realization of it. Moreover, based on the generated 2D correlated random shadowing, a complete 2D semi-deterministic path loss model can be proposed. The proposed methodology of this paper can be implemented into system-level simulators where it will be very useful due to its ability to generate realistic shadow fading.

Level Crossing Rate of Macro-diversity System with Two Micro-diversity SC Receivers over Correlated Gamma Shadowed α–µ Multipath Fading Channels

ABSTRACTIn this article, macro-diversity structure with macro-diversity selection combining (SC) receiver and two micro-diversity SC receivers operating over correlated shadowed multipath fading channel are analysed. Received signal is subjected simultaneously to α–µ short-term fading and gamma long-term fading (shadowing) resulting in system performance degradation. Macro-diversity SC receiver aims to reduce gamma shadowing effect while micro-diversity SC receivers aim to mitigate α–μ small-scale multipath fading effects. Useful infinite series expressions for the second-order statistical measure such as level crossing rate (LCR) of macro-diversity SC receiver output signal is efficiently derived. Numerical results are presented to examine the influence of various gamma shadowing and α–µ multipath fading parameters on LCR of the proposed system.

Sum-Rate Analysis for 3D MIMO with ZF Receivers in Ricean/Lognormal Fading Channels

In this paper, we investigate the performance evaluation of three dimensional (3D) multiple-input multiple-output (MIMO) systems with an adjustable base station (BS) antenna tilt angle and zero-forcing (ZF) receivers in Ricean/Lognormal fading channels. In particular, we take the lognormal shadow fading, 3D antenna gain with antenna tilt angle and path-loss into account. First, we derive a closed-form lower bound on the sum rate, then we obtain the optimal BS antenna tilt angle based on the derived lower bound, and finally we present linear approximations for the sum rate in high and low-SNR regimes, respectively. Based on our analytical results, we gain valuable insights into the impact of key system parameters, such as the BS antenna tilt angle, the Ricean K-factor and the radius of cell, on the sum rate performance of 3D MIMO with ZF receivers.

Improved Distributed Cooperative Spectrum Sensing (DCSS) For Cognitive Radio Adhoc Network

Cooperation among cognitive radios for spectrum sensing is deemed essential for environments with deep shadows. In this paper, we study cooperative spectrum sensing for cognitive radio ad hoc networks where there is no fusion center to aggregate the information from various secondary users. We propose a novel consensus-inspired cooperative sensing scheme based on linear iterations that is fully distributed and low-cost. In addition, the trade-offs on the number of consensus iterations are explored for scenarios with different shadow fading characteristics. Furthermore, we model Insistent Spectrum Sensing Data Falsification (ISSDF) attack aimed at consensus-based iterative schemes and show its destructive effect on the cooperation performance which accordingly results in reduced spectrum efficiency and increased interference with primary users. We propose a trust management scheme to mitigate these attacks and evaluate the performance improvement through extensive Monte Carlo simulations for large-scale cognitive radio ad hoc networks in TV white space. Our proposed trust management reduces the harm of a set of collusive ISSDF attackers up to two orders of magnitude in terms of missed-detection and false alarm error rates. Moreover, in a hostile environment, integration of trust management into cooperative schemes considerably relaxes the sensitivity requirements on the cognitive radio devices.

Exploiting Coexistence Between UMTS and LTE for Greener Cellular Networks with Particle Swarm Optimization

Switching base stations (BSs) off is considered an effective method for improving energy efficiency. This switch-off approach is a system-level approach that can be applied to an area covered by multiple cells, even if those cells use different radio access technologies. This study focuses on exploiting the coexistence of universal mobile telecommunications system and long-term evolution to achieve a balance between network performance (meeting the demands for high data rates at peak traffic hours) and energy efficiency based on traffic load variations while guaranteeing maximum coverage for the region. Particle swarm optimization has been adopted to maximize the cells' coverage area during a switch-off session with constraints for the transmission power of the BS (Ptx), the total antenna gain (G), the signal-to-interference-plus-noise ratio, and shadow fading (?). Moreover, the modulation and coding scheme and data rate are considered in this study. The results show that daily energy savings of up to 27.86 % can be achieved while guaranteeing cell coverage.

Intelligent cooperation management among solar powered base stations towards a green cellular network in a country with an equatorial climate

Energy efficiency in cellular networks is a growing concern for cellular operators with regard to maintaining profitability and reducing their overall environmental impact. Because evolved node Bs (eNBs) for long-term evolution wireless cellular networks are deployed to accommodate peak traffic, they are underutilized most of the time, especially under low-traffic conditions. Hence, switching eNBs on and off in accordance with traffic pattern variations is considered to be an effective method of improving energy efficiency in cellular networks. However, two main concerns of network operators when applying this technique are coverage issues and securing radio service for an entire area in response to the increased size of some cells to provide coverage for cell areas that are switched off. This study focuses on the parameters that affect coverage in order to find a balance between cellular network energy consumption and the area of cell coverage. To achieve this goal, particle swarm optimization, a bio-inspired computational method, has been adopted in this study to maximize the cell coverage area under the constraints of the transmission power of the eNB $$(P_{tx})$$(Ptx), the total antenna gain (G), the bandwidth (BW), the signal-to-interference-plus-noise ratio (SINR), and shadow fading $$(\sigma )$$(�). In addition, the study investigated potential for gains in operational expenditures by operating eNB on solar energy. The optimum criteria, including economic, technical and environmental feasibility parameters, were analyzed using the HOMER.

Approximate Outage Probability and Capacity for <inline-formula> <tex-math notation="TeX">$\kappa$</tex-math></inline-formula>- <inline-formula> <tex-math notation="TeX">$\mu$</tex-math></inline-formula> Shadowed Fading

Recently, a generalization of $\kappa$ - $\mu$ fading and Rician shadowed fading, i.e, $\kappa$ - $\mu$ shadowed fading has been proposed. In this work, we derive approximate expressions for outage probability and channel capacity when the signal of interest and interferers both experience $\kappa$ - $\mu$ shadowed fading with arbitrary parameters. The expressions are expressed in terms of well known hypergeometric function, which can be easily evaluated numerically. Finally, simulation results are provided which shows that our approximation is fairly tight.

Channel Characteristics in High-Speed Railway: A Survey of Channel Propagation Properties

In this article, we give an overview of recent research on propagation properties in high-speed railways (HSRs). The channel fading in HSRs is a big challenge for wireless access. It is essential to understand the channel-fading behavior before the system design. The novel results of propagation and channel models are presented. The details of channel characteristics, such as path loss, shadow fading, and Ricean K- factor, are discussed in each scenario. A comprehensive picture of propagation and channel-modeling research in railways is shown.

Characterization of Quasi-Stationarity Regions for Vehicle-to-Vehicle Radio Channels

We analyze the nonwide-sense-stationarity (non-WSS) of vehicle-to-vehicle (V2V) radio channels using three metrics: 1) the correlation matrix distance (CMD); 2) the wideband spectral divergence (SD); and 3) the shadow fading correlation. The analysis is based on measurements carried out at 5.3 GHz using a ${\mathbf 30} \times {\mathbf 4}$ MIMO system in suburban, urban, and underground parking areas. Several factors such as the existence of a line-of-sight (LOS), the speed of cars, and the antenna array size and configuration are considered in the analysis of non-WSS. It is found that quasi-stationarity region ranges from 3 to 80 m in different V2V scenarios, and is strongly affected by the above factors. Based on the comparison of the equivalent quasi-stationarity region size estimated by the three metrics, it is suggested to use SD and shadowing correlation metrics for systems with small electrical array apertures and to use CMD metric only for arrays with large electrical apertures.

Improving the Performance of Multi-Hop Wireless Networks by Selective Transmission Power Control

In a multi-hop wireless network, connectivity is determined by the link that is established by the receiving signal strength computed by subtracting the path loss from the transmission power. Two path loss models are commonly used in research, namely two-ray ground and shadow fading, which determine the receiving signal strength and affect the link quality. Link quality is one of the key factors that affect network performance. In general, network performance improves with better link quality in a wireless network. In this study, we measure the network connectivity and performance in a shadow fading path loss model, and our observation shows that both are severely degraded in this path loss model. To improve network performance, we propose power control schemes utilizing link quality to identify the set of nodes required to adjust the transmission power in order to improve the network throughput in both homogeneous and heterogeneous multi-hop wireless networks. Numerical studies to evaluate the proposed schemes are presented and compared.

Finite series representation of Rician shadowed channel with integral fading parameter and the associated exact performance analysis

With the deployment of small cells and device to device communications in future heterogeneous networks, in many situations we would encounter mobile radio channels with partly blocked line of sight component, which are well modeled by the Rician shadowed (RS) fading channel. In this paper, by the usage of Kummer transformation, a simplified representation of the RS fading channel with integral fading parameter is given. It is a finite series representation involving only exponential function and low order polynomials. This allows engineers not only the closed-form expressions for exact performance analysis over RS fading channel, but also the insights on the system design tactics.

Analyses of Relay Nodes Deployment in 4G Wireless Mobile Multihop Relay Networks

In 4G cellular networks: LTE/LTE-Advanced and the mobile WiMAX network, some key impact factors: white Gaussian noise, wireless interference, shadow fading, etc., degrade signal transmission quality and reduce wireless service coverage significantly. The degradations can be improved by deploying more eNBs or BSs, but the expensive eNB/BS extremely increases network cost. The specifications of LTE-Advanced and IEEE 802.16j thus propose a relay-based scheme, namely mobile multihop relay (MMR) networks, to cooperate with the existing cellular network while not obviously increasing the relay station (RS) deployment cost. Various types of RSs: Fixed RS, Nomadic RS and Mobile RS, can be adopted in MMR networks. To efficiently deploy different types of RSs becomes a critical issue. Thus, this paper first analyzes the impact factors: transmission quality, deployment price, service coverage and RS overlap index, and then models the cost-effective issue of the RS deployment as an optimization problem. The paper proposes an adaptive cost-based RS deployment (ACRD) approach to form a cost function in terms of all impact factors, and then solves the optimization problem by determining the RS deployment with the least network cost as the solution. Numerical results demonstrate that ACRD outperforms the compared approaches in network cost, transmission quality, RS deployment price, service coverage, and RS overlap index. Additionally, ACRD deploys more RSs on the areas with high-density populations and thus increases transmission quality and guarantees the quality of service (QoS). Finally, the worst case running time of ACRD is analyzed, which requires $$ T(n) = O(I \cdot P) $$T(n)=O(I·P).

On the delay reduction of wireless ad hoc networks with directional antennas

It is shown that the throughput capacity of wireless ad hoc networks using omni-directional antennas (OMN networks) is significantly decreased with the increased number of nodes. One major reason lies in the interference caused by using omni-directional antennas, which just broadcast radio signal in all directions. Thus, a communication with multiple short-ranged hops is suggested in such networks to avoid interference and improve the throughput. However, the multi-hop transmission can also significantly increase the end-to-end delay.In this paper, we investigate the throughput improvement and the delay reduction by using directional antennas in wireless ad hoc networks. We call such wireless ad hoc networks using directional antennas as DIR networks. In particular, we investigate the effective transmission range of directional antennas with consideration of various channel conditions, such as the large scale path loss and the shadow fading effect. We have found that directional antennas can significantly increase the transmission range compared with omni-directional antennas even under the same channel condition. Besides, we derive the throughput and the delay of a DIR network by constructing a routing scheme and a time-division multi-access (TDMA) scheme. We have found that using directional antennas not only can increase the throughput capacity but also can decrease the delay by reducing the number of hops.

Large-Scale Fading Characteristics of Indoor Channel at 45-GHz Band

The channel measurement and modeling of large- scale fading characteristics of 45-GHz band in three typical indoor environments are investigated. An automatic measurement system owning a sufficient dynamic range is designed to overcome the prominent attenuation in 45-GHz band. After conducting extensive measurements, large-scale fading characteristics including path-loss exponent, cross-polarization discrimination ratio, and standard deviation of shadow fading are obtained and compared in different scenario setups. Goodness-of-fit test is applied to validate whether the assumed log-normal distribution can describe the shadow fading characteristics.

A New Approach for Coverage Analysis of Multihop Cooperative Networks Subject to Lognormal-Rice Fading

A strip-shaped sensor network is considered, where randomly placed nodes communicate cooperatively by forming an opportunistic large array (OLA). The transmission from a group of cooperating nodes to another group of nodes is modeled with a quasi-stationary Markov chain, where the transmission channel is assumed to experience lognormal shadowing and Rice fading. The distribution of received power at a node is calculated as a three-step process, which includes finding the distribution of random distance between nodes in addition to other channel impairments, that is, fading and shadowing. It is shown that, in the presence of all three channel impairments, the received power at a node follows a lognormal distribution. This approximation uses a series of steps that involves techniques such as moment matching and moment generating function (MGF). Using the underlying Markov chain properties, the one-hop success probability of the network is derived. The system performance and coverage range of the network are quantified as a function of various network parameters and node topologies. The theoretical results are validated by performing computer simulations.