Polarization diversity in channel modeling for MIMO systems

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Tezin Türü: Yüksek Lisans

Tezin Yürütüldüğü Kurum: Orta Doğu Teknik Üniversitesi, Mühendislik Fakültesi, Elektrik ve Elektronik Mühendisliği Bölümü, Türkiye

Tezin Onay Tarihi: 2013

Öğrenci: BURAK SÖKER

Danışman: TEMEL ENGİN TUNCER

Özet:

In a multiple-input multiple-output (MIMO) system, inter-antenna distances can be made large and uncorrelated signals can be transmitted and received when there is sufficient space at the transmitter (TX) and receiver (RX). When the antennas are closely spaced, diversity advantage is lost and communication performance degrades. In this case, polarization diversity can be used in order to decrease the correlation and improve communication performance. A detailed channel model, which includes both cross polar discrimination (XPD) and correlation coefficient, is used in this study. Transmitter is assumed to have enough space and correlation is considered for the receiver only. Received signal correlation coefficients are generated from a realistic random 3-D model including antenna polarization orientations, XPD, azimuth and elevation angles of direction-of-arrival. In this study, channels with and without correlation are considered. Polarization diversity in a 2×2 MIMO communication system is investigated for Alamouti (AL) and spatial multiplexing (SM) transmission schemes considering both BER performance and channel capacity. In addition, effects of the number of antennas on SM BER and capacity are investigated for 3×3 and 4×4 MIMO systems. BER and capacity performance of single polarization and polarization diversity are compared for constant and distance dependent random channel parameters. The relative performance of single polarization and polarization diversity system depends significantly on the channel characteristics. It is shown that polarization diversity results better BER and capacity compared to single polarization especially when there is not enough space at the receiver. Therefore, polarization diversity can be used in MIMO systems with limited antenna space, in order to improve communication performance.