Modeling of MIMO Radio Channels for Mobile-to-Mobile and Umbrella Cell Based Cellular Communication Systems.
Mobile-to-mobile (M2M) and fixed-to-mobile (F2M) communication technology has shown astonishing intrusion in battle-fields, cellular and vehicular networks, intelligent transportation systems and internet of things. Mobile nodes involved in these infrastructures demand a high data rate connectivity over radio fading links.
This dissertation concentrates on the geometrical modeling of the spatial characteristics of two-dimensional (2D) and three-dimensional (3D) radio fading channel for multiple-input-multiple-output (MIMO) M2M and MIMO F2M communication scenarios. Closed-form expressions for the joint and marginal space-time correlation functions among MIMO antenna array elements and probability density function (PDF) of angle-of-arrival (AoA) of the multipaths in nonisotropic environments are presented.
Initially, the emphasis has been on the 2D propagation scenario; where, mobile subscribers are equipped with low elevated multiple antenna array structures and they intend to communicate on the move without any base station (BS). These mobile subscribers usually reside on structured-bounded highways or in the “long and narrow” streets and canyons; where, the distribution of scattering objects along the roadside regions are non-isotropic in nature. It is observed that elliptical geometry is an appropriate shape, which correlates more accurately the layout of such propagation environments than the circular shape. In the proposed model, it is assumed that the mobile stations reside at the centers of two different ellipses and the scatterers are distributed uniformly along the boundaries of the ellipses. The ellipses are independently rotatable along the horizontal plane corresponding to the direction of mobile stations. The lengths of major and minor axes and the eccentricities of the ellipses are assumed to be dependant on the physical measurement of the propagation environments. Using the proposed geometrical model, the closed-form expression of PDF of AoA/AoD is obtained for non-isotropic scattering environments. Based on this AoA/AoD, mathematical expression of joint and marginal PDFs of space-time correlations among the MIMO antenna elements are derived. The 2D eccentricity based channel model is then extended to 3D elliptical-based cylindrical channel model to accommodate the high-rise structures present along the roadside premises of highways, streets or canyons. In this model, the scattering objects are assumed to be placed on the surfaces of the elliptical-based cylinders around both transmitter and receiver nodes. The horizontal dimension of the physical propagation medium is modeled by eccentricity and height of the scatterers are modeled by the height of cylinders. Mobile stations are placed at the centers of the cylinders equipped with multiple antenna arrays. The dimension of cylinders are independently adjustable and rotatable according to the physical dimension of the propagation medium and the direction of motion of MS’s. Here again the mathematical expressions for correlations among MIMO M2M links are formulated and the obtained theoretical results are simulated and compared with the measured data. In the last part of thesis, a 3D elliptical based geometrical channel model is proposed to model umbrella-cell in a cellular communication environment, which provides trustworthy communication links for speedy vehicles on the highways. In the proposed model, mobile subscriber is assumed to be located at the center of the elliptical cylinder equipped with low-rise antenna array and the scatterers are assumed to be uniformly distributed on the surface of the cylinder; whereas, the BS is on the top of high-rise tower with multiple antenna structure and is assumed to be scatter-free. Using the proposed model an expression for space-time correlation among antenna elements is derived.