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Abstract
ABSTRACT
Massive Multiple Input Multiple Output (MIMO) is one of the major technologies used in 5G. This thesis focuses on the beamforming design problem for the downlink Massive MIMO system. A Weighted Minimum Mean Square Error (WMMSE)-based solution is suggested, to work out the optimization issue of receive and transmit beamforming vectors, wherever the link between the system utility maximization issue and the weighted sum error Mean Square Error (MSE) minimization issue has been utilized to convert the non-convex constrained optimization issue into an equivalent convex issue. After that, the receive and transmit beamforming vectors are calculated using Block Coordinate Descent (BCD) procedure. However, the beamforming optimization issue has been solvedwith considering the practical antenna array gain in the channel model and optimum weights calculations. So, the design of the array geometry and its configuration is of the most major problem in the optimization problem solution. Therefore, for first time different array geometries have been proposed to reduce mutual coupling impact on array gain variation among array elements. These different arrays are 2 Dimensions (2D)likeCircular Array (CA), Uniform Planar Array (UPA), Uniform Planar Circular Array (UPCA), and Centric Planar Circular Array (CPCA), or 3 Dimensions (3D)likeConical Array (CoA) and Conformal Array (CfA). Such arrays are suggested to be implemented at BS and after that the steering vector for array geometry is derived. In addition, the diversity parameters Envelope Correlation Coefficient (ECC) and Diversity Gain (DG) have been simulated through Computer Simulation Technology-Microwave Studio (CST-MWS) for each proposed antenna array geometry. Furthermore, after selection of the appropriated geometrythe beamforming optimization problem is solved using a practical massive MIMO. Secondly, for more improvement on intra-cell interference between the users, another practical antenna array element has been designed and studied. This antenna array element is a curl antenna where this antenna is a circularly polarized one. Therefore, finally, the possibility of dividing the users’ part of them receives vertically and others connect horizontally with the Base Station (BS) is designed to increase the system capacity. Thirdly, all the previous studies are based on a known antenna array element. Therefor our final contribution is to design a low-profile, Circular Polarized (CP), and large gain antenna element with MIMO capability in the millimeter Wave (mmW) frequency band. Initially, a rectangular slot is inserted on the Half Circle Truncation (HCT) patch antenna toraise the bandwidth. The antenna behavior is improved regarding to gain, the matching of impedance and bandwidths of Axial Ratio (AR) by truncated the patch antenna with HCT.
Finally, the suggested 2×2 MIMO antenna has been designed with 16 ×16×0.508〖mm〗^3 overall structure size.