The performance of wireless data transmission to mobile vehicles is improved if channel state information is available at the transmitter but movement of vehicles causes outdating of channel estimates. The concept of a predictor antenna has recently been proposed, where an antenna is placed in front of other antennas on the roof of the vehicle to sense the radio environment in advance. This can comparatively provide an order-of-magnitude improvement in channel prediction performance. A potential problem with this idea is that closely placed antennas will experience mutual electromagnetic couplings. These may reduce the efficiency of the predictor antenna concept if they are not taken into account. In this paper, we discuss about how to treat the forgoing issue and eventually evaluate a promising candidate on measured channels. We argue that only open-circuit voltage method would be realistic for the present application. The usefulness of the proposed decoupling method is demonstrated on field measurements obtained in downtown Dresden, Germany. We also partly address the sensitivity of the open-circuit decoupling method to the accuracy of the utilized network parameters.

A simple radiation efficiency metric is introduced to include the effects of non-ideal source/receiver impedances. The features of this parameter are highlighted and its compact formula is derived. The notion of mean matching efficiency is established. Simulations prove that this matching efficiency is quite useful in a quick estimation of diversity performance of multi-port antennas in rich isotropic multipath environments.

Accuracy limitation in evaluation of diversity gains based on cumulative distribution function curves is highlighted. New devised closed-form formulas are provided for Selection Combining and Maximum Ratio Combining diversity schemes rendering diversity gain as a function of correlation and radiation efficiencies. Accuracy of these formulas is studied and verified by numerical simulations. These formulas take a central role for the cases when engineers are limited to a finite number of measured voltage samples at different ports to provide them with accurate calculation of ergodic diversity gain. This letter also reveals dependency of different diversity gains upon total embedded efficiencies of branches and underscores the significance of identical efficiencies of two-element terminals for their optimum performance in multipath environments.

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Using predictor antenna systems for modern wireless moving relays and base stations on top of vehicles such as buses, trains etc. proves to be a reliable approach for collecting channel state information to such fast moving nodes. Recently, it has been shown that coupling between different ports of a multiport antenna system used as a part of a predictor system can reduce the prediction performance. In this study, by integrating position and velocity vectors in the channel covariance matrix as seen at the antenna ports in a rich multipath environment, the authors quantify the impact of antenna coupling on prediction performance. Moreover, practically these predictor systems are designed for a certain target velocity. They further quantify the adverse effect of velocities, different from the target velocity, on prediction performance. In case open-circuit decoupling is necessary, the sensitivity of the predictor antenna system performance with respect to the accuracy of the input network parameters is disclosed.