Optimal Communication Channels in a Disordered World with Tamed Randomness

Multi-channel wireless systems have become a standard solution to address our information society's ever-increasing demand for more information transfer. The ultimate bound on the capacity such systems can achieve is the limited channel diversity in a given propagation medium, and countless proposals to reduce channel cross-talk by engineering software or hardware details of the signals and antenna arrays have been proposed. Here we demonstrate the physical shaping of the propagation medium itself to achieve optimal channel diversity. Using a reconfigurable metasurface placed inside a random environment, we tune the disorder and impose perfect orthogonality of wireless channels. We present experiments in the microwave domain in which we impose equal weights of the channel matrix eigenvalues for up to 4x4 systems, and almost equal weights in larger systems. We further describe one example of wireless image transmission in an office room in which we augmented the 3x3 system's number of effectively independent channels from 2 to the optimum of 3.