Using “predictor antennas” for long-range prediction of fast fading for moving relays

Channel state information at transmitters is important for advanced transmission schemes. However, feedback and transmission control delays of multiple milliseconds in LTE systems result in severe outdating of this information at vehicular velocities. Channel prediction based on extrapolation of the short-term fading is inadequate in LTE systems at vehicular velocities and high carrier frequencies. We here propose and evaluate a simple scheme which may extend the prediction horizon when used on vehicles: Use an additional antenna, a “predictor antenna”, placed in front of the transmission antennas in the direction of travel. This is of particular interest for use with moving relays: Local access points placed on e.g. buses or trams. A measurement-based study for 20 MHz downlink channels at 2.68 GHz is reported here for both line-of-sight and non-line-of-sight conditions.