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Title:	Two-dimensional angle of arrival based beamforming approach for pilot contamination reduction in massive multiple-input multiple-output
Authors:	Ehab Ali Fitouri (P81099)
Supervisor:	Mahamod Ismail, Prof. Dr.
Keywords:	Universiti Kebangsaan Malaysia -- Dissertations Dissertations, Academic -- Malaysia Beamforming MIMO
Issue Date:	8-Feb-2019
Description:	Massive multiple-input multiple-output (M-MIMO) was recently introduced which has the potential to meet of the next generation wireless communication system capacity requirements by using a huge number of array antennas that have a benefit of beamforming gain. The beamforming is assisted with angles-of-arrival (AOA) information to separate between various users by exploiting the spatial diversity of the correlated channels or allowing spatial multiplexing by antenna weights adaptation based on the characteristics of the channels. However, since each user is assigned its own pilot sequences that are mutually orthogonal with other users within the same cell, they are non-orthogonal or are even the same with other pilot sequences in different cells, thus causing pilot contamination. These contaminated pilots affect downlink beamforming and results in interference that are directed toward the terminals that use similar pilot sequences. Most conventional inter-cell interference and pilot contamination mitigation techniques during the training phase are not suitable for M-MIMO due to the lack of coordination between pilot assignments and beam formed, which in consequence degrade system performance. The main objective of this research is to propose a two dimensional AOA (2D AOA) based beamforming approach for reducing pilot contamination in M-MIMO. Firstly, a multi-cell minimum mean square error (MMSE) estimator is developed based on the channel state information (CSI). The estimation simultaneously utilise 2D AOA information and statistical channel estimations to reduce the impact of pilot contamination by exploiting the uplink spatial properties of the propagated signals. Secondly, a new mathematical model for MMSE estimator is formulated and established while their performance is numerically evaluated in terms of estimation accuracy. Thirdly, efficient downlink beamforming (precoding) approaches are proposed based on the intended MMSE estimator. The performance of MMSE beamforming based on 2D AOA estimation methods; namely 2D Unitary Estimation of Signal Parameters via Rotational Invariance Techniques (2D UESPRIT), 2D Fourier Domain Line Search MUSIC (2D FDLSM), and 2D Propagator Method (2D PM)) are evaluated and compared in terms of achievable rate with deterministic MMSE and pilot contaminated system. Numerical results reveal that the achievable sum rate gains of 2D UESPRIT, 2D FDLSM, and 2D PM based beamforming are 97.6%, 92.4%, 86.3% of the desired deterministic performance, respectively, compared to pilot contaminated system, which achieved only 90% in its best case. Furthermore, the uplink achievable sum rate gains of 2D UESPRIT based MMSE estimator and conventional ESPRIT based MMSE estimator with respect to deterministic MMSE are 96.3% and 85.4%, respectively, compared to pilot contaminated system, which achieved only 90%. The findings from this research shows the feasibility of utilizing AOA based beamforming to reduce pilot contamination effect that is inherent in a larger order M-MIMO system for the Fifth Generation wireless transmissions.,Ph.D.
Pages:	125
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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