Modeling multiple antenna systems in realistic environments - a composite channel approach
Abstract: For evaluation of specific antenna arrangements in wireless communication systems we need physical channel models that take into account the directional domain. Here we propose a practical approach to wireless channel modeling in, particularly, mobile communication systems, by using an assumption that the channel can be divided into separate parts or regions that can be treated and modeled individually. The idea is that the antenna part of the channel is the part considered in the design of the user equipment and can be characterized by a single measurement of each design, while the propagation part of the channel can be characterized separately, independent of the user equipment, based on generic channel sounder measurements with, as far as possible, open areas around the transmitter and the receiver antennas. For more complex antenna environments we may imagine intermediate scattering regions of the channel model between the antenna parts and the propagation part, that perhaps can or cannot be handled separately, e.g., a mobile phone user body, an office desk, a vehicle etc. A first step in evaluating such a composite model approach is to verify the validity of link simulations were the mobile phone antennas together with the user can be handled as a super-antenna with its aggregate far-field pattern to be combined with a directional channel model in a classical way. This is presented in Paper IV and the method is in its extensible form referred to as the Composite Channel Method. It is found that this method, as we expected, work well for statistical performance evaluation of diversity or spatial multiplexing. An extension of the composite approach is outlined with an attempt to find a simple yet accurate directional scattering model for the user hand and body that still catch the proper influence of antenna efficiencies, fading statistics and correlation. Such an approach is tested and presented for a single antenna inside a car in Paper II. A full ray-tracing model as the one presented in Paper I and also used in Paper II can capture all important eects of a propagation environment also for multiple antennas systems to the price of high complexity of the geometrical model. In Paper III a first investigation of user influence on an indoor 2x2 MIMO link is performed based on a simple measurement setup and the diversity performance is evaluated. In Paper IV the first step of the composite channel approach is evaluated with respect to MIMO by channel measurements including user influence in static outdoor-to-indoor and indoor scenarios. The approach is verified for statistical properties such as antenna correlation and MIMO eigenvalue distributions. It is found that the presence of the user, apart from introducing hand and body absorption and mismatch that increases the path loss, also increases the correlation between the antenna elements and, thus, slightly decreases potential MIMO capacity.
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