Enhancing measured MIMO capacity by adapting the locations of the antenna elements

We show that the multiple-input, multiple-output (MIMO) capacity of measured, indoor flat-fading channels may be improved by adaptively changing the locations of the antenna elements. Moving the antenna elements is a way to provide spatial diversity to a MIMO link without decreasing the number of parallel data streams. First, we demonstrate that significant variations in equal-power capacity are possible using measured data from finely sampled virtual arrays at both ends of a MIMO link. Second, using steepest descent and a simulated path-type channel derived from measured data, we adapt the element locations. In line-of-sight (LOS) and obstructed-line-of-sight (OLOS) examples, the local maximum capacity is reached within 5 and 10 iterations, respectively. The improvements relative to the equally spaced arrays are approximately 22% and 19%, respectively.