Telecommunication in a disordered environment with iterative time reversal

Abstract

Recent researches in the area of wave propagation in random media applied to telecommunications showed that, contrary to intuition, reverberation or scattering of waves in a disordered medium can actually help to increase the information transfer rate. The key element therein is the ability of a communication system to exploit independent channels of propagation. We present a method to transmit digital information through a highly scattering medium. It is based on iterations of a time-reversal process, and permits to focus short pulses, both spatially and temporally, from a base antenna to different users. This iterative technique is shown to be more efficient (lower inter-symbol interference and lower error rate) than classical time-reversal communication, while being computationally light and stable. Experiments are presented: digital information is conveyed from 15 transmitters to 15 receivers by ultrasonic waves propagating through a highly scattering slab. From a theoretical point of view, the iterative technique achieves the inverse filter of propagation in the subspace of non null singular values of the time reversal operator. We also investigate the influence of external additive noise, and show that the number of iterations can be optimized to give the lowest error rate.