Noor M. Khan

A Critical Analysis of Research Potential, Challenges, and Future Directives in Industrial Wireless Sensor Networks

In recent years, industrial wireless sensor networks (IWSNs) have emerged as an important research theme with applications spanning a wide range of industries including automation, monitoring, process control, feedback systems, and automotive. Wide scope of IWSNs applications ranging from small production units, large oil and gas industries to nuclear fission control, enables a fast-paced research in this field. Though IWSNs offer advantages of low cost, flexibility, scalability, self-healing, easy deployment, and reformation, yet they pose certain limitations on available potential and introduce challenges on multiple fronts due to their susceptibility to highly complex and uncertain industrial environments. In this paper, a detailed discussion on design objectives, challenges, and solutions, for IWSNs, are presented. A careful evaluation of industrial systems, deadlines, and possible hazards in industrial atmosphere are discussed. This paper also presents a thorough review of the existing standards and industrial protocols and gives a critical evaluation of potential of these standards and protocols along with a detailed discussion on available hardware platforms, specific industrial energy harvesting techniques and their capabilities. This paper lists main service providers for IWSNs solutions and gives insight of future trends and research gaps in the field of IWSNs.

Modeling and Characterization of MIMO Mobile-to-Mobile Communication Channels Using Elliptical Scattering Geometry

In this paper, we develop a two-dimensional (2-D) elliptical geometrical scattering model for multiple-input multiple-output (MIMO) mobile-to-mobile (M2M) communication channels. The elliptical geometry is supposed to be an appropriate approach to model streets and canyons in M2M communication environment. We assume that both mobile stations (MSs) are located at the centers of ellipses and are surrounded by uniformly distributed scatterers present on the elliptical loci. The equal spacing between two consecutive scatterers on the elliptical loci forces the angle-of-arrival (AoA) or angle-of-departure (AoD) distribution at either of the MSs to be non-isotropic. We provide an empirical model for such a non-isotropic AoA and compare its results with the numerical curves of the elliptical geometry which results in excellent agreement. Utilizing the non-isotropic AoA and the proposed geometrical model, we derive closed-form expressions for the marginal and joint correlation function of the channel coefficients. We provide various plots to analyze the correlation among the diffused components of M2M MIMO communication link. Furthermore, a comparison of the correlation curves obtained from the mathematical expression of the proposed model is carried out with the existing results in the literature. In order to validate the proposed model, the elliptical geometrical shape is transformed into circular one. The resulting comparative analysis verifies that the circular geometrical models are the special cases of our proposed model.

3-D Spatial Spread Quantifiers for Multipath Fading Wireless Channels

This letter proposes a novel generalized method to quantify the angular dispersion of radiated energy in realistic 3-D space. Based on the first three coefficients of the 2-D Fourier transform, simple mathematical expressions are derived to independently or jointly quantify the angular dispersion of energy in a reduced 2-D or realistic 3-D space, respectively. The proposed quantifiers include mean direction of arrival, circular variance, true standard deviation, angular spreads, angular constriction, and direction of maximum fading. The proposed quantifiers are helpful in establishing an appropriate mechanism to measure the angular dispersion in 3-D space. These quantifiers provide results in radians with true physical meaning unlike their counterparts in the literature. Moreover, an analysis on the impact of distribution truncation/distortion on the degree of accuracy in measuring the angular dispersion is presented which signifies the importance of true angular spread quantification. The proposed quantifiers can thus be considered as an appropriate goodness-of-fit criterion in the characterization of spatial statistics of multipath fading channels.

Adaptive Power-Control Based Energy-Efficient Routing in Wireless Sensor Networks

Efficient utilization of energy is a hot topic of research in the field of wireless sensor networks. Limited battery resource at a sensor node coupled with the hostile multi-path fading propagation environment makes the task of the network to provide reliable data services with an enhanced lifetime, challenging. In order to achieve this goal, a number of efforts have been made by the researchers; one such key strategy is an energy-aware routing embedded with transmission power control mechanism. In this strategy, every sensor node in a network transmits at a lowest possible power level to maintain on one hand reliable wireless links with other neighboring nodes and saves the energy on the other. In this paper, we propose a novel routing technique embedded with transmission power control for wireless sensor networks while considering a realistic radio fading environment. The proposed strategy considers channel fading in the propagation environment and mitigate it through transmission power control mechanism. The main aim of the proposed protocol, APCEER, is to reduce the communication interference among sensor nodes, establish energy-efficient routes from source to sink and thus, to save energy of each and every sensor node in the network. This results in an overall increase of network lifetime, transmission throughput, energy saving and reduce communication interference and collision. Simulation and experimental results show that the proposed scheme outperforms the existing energy-aware routing strategies that are not equipped with a power control mechanism. The proposed protocol thus utilizes in urban applications of wireless sensor networks that need ultra efficient utilization of energy by power-constrained nodes operating in severe fading conditions.

Characterization of 3D Elliptical Spatial Channel Model for MIMO Mobile-to-Mobile Communication Environment

In this paper, we develop three dimensional (3D) elliptical cylindrical geometrical channel model for multiple-input–multiple-output mobile-to-mobile communication environments. It is assumed that both the mobile nodes are surrounded by uniformly distributed infinite number of scatterers sprinkled over the surfaces of an elliptical-based cylindrical shapes. The mobile nodes are located at the centers of the bottom surfaces of elliptical cylinders and both the mobile nodes are equipped with low-elevated multiple antenna arrays. The proposed model is designed for urban areas, where mostly the mobile subscribers reside and are on the move. This model takes into account the effect of multiple antenna array attributes, roadside infrastructure, the dimensions of the propagation medium, transmit–receiver distance and the velocity of mobile nodes. Using the proposed channel model, expressions for the joint and marginal cross correlation functions are derived for non-isotropic scattering environments. The derived expression are simulated for various parameters to verify their effect on the antenna correlations. The obtained correlation graph is compared with measured data that confirms a close agreement with it. Finally, by changing various parameters of the proposed channel model, some existing 2D and 3D channel models are deduced.

Geometrical Modeling of Scattering Environment for Highways in Umbrella Cell Based MIMO Communication Systems

In this paper, we develop a three-dimensional (3D) eccentricity-based cylindrical geometrical channel model for nonisotropic multiple-input-multiple-output (MIMO) communication systems under umbrella macrocellular environment. We use elliptic cylindrical geometry to model the scattering phenomenon in streets, canyons and highways. The scattering objects like, high-rise building, trees and vegetation that lie along the roadside premises are modeled by the height of an elliptical cylinder. The proposed channel model targets fast moving vehicles on the highways in an umbrella-cell of cellular communication networks. We assume that both ends of the communication link are equipped with multiple antenna arrays, where, mobile-station antenna height is lower than base-station antenna. Utilizing the proposed MIMO communication channel model, we obtain closed-form expressions for the space–time correlation function among the MIMO antenna elements. The obtained theoretical expressions are plotted and analyzed for different values of channel parameters. Finally, we compare the proposed model with the existing models in the literature and prove that our model can be deduced to the existing two-dimensional and 3D channel models.

Low Complexity Linear Channel Estimation for MIMO Communication Systems

Channel estimation is employed to get the current knowledge of channel states for an optimum detection in fading environments. In this paper, a new recursive multiple input multiple output (MIMO) channel estimation is proposed which is based on the recursive least square solution. The proposed recursive algorithm utilizes short training sequence on one hand and requires low computational complexity on the other hand. The algorithm is evaluated on a MIMO communication system through simulations. It is realized that the proposed algorithm provides fast convergence as compared to recursive least square (RLS) and robust variable forgetting factor RLS (RVFF-RLS) adaptive algorithms while utilizing lesser computational cost and provides independency on forgetting factor.

Elliptical channel model employing propagation of signals in 3D space

Geometrically-based stochastic channel modeling approach has been a hot area of research for the last two decades to model the surrounding physical scattering environment around the mobile station (MS) in cellular mobile communication systems. The mobile users moving in vehicles on the high ways, in streets and canyons are more critical to model their surrounding environments. In order to model such scattering environment, we extend the earlier proposed two-dimensional (2D) elliptical geometric channel model for macrocellular communication systems by introducing elevation of the base station (BS). We consider that MS is placed at the middle of the ellipse and surrounded by uniformly distributed scatterers on the boundary region of the ellipse. Furthermore, we also consider elevation of the BS that is installed in scattering-free region. Taking these assumptions into account, we derive a simple mathematical expression for the probability distribution functions (PDFs) of angle-of-arrival. The elliptical geometry is such that it has adjustable dimensions and can model the streets and highways in a better way according to their widths.