Multi-channel communication in a changing and disordered world
R. Sprik
WZI-UvA and TN-UTwente
Mobile phones, wireless internet and other wireless applications in modern telecommunication demand more and more bandwidth and reliability in the already crowded available frequency space. Furthermore, in a complex urban environment the signal is dispersed, distorted and continuously changing by reflection from buildings and cars.
Wave propagation in complex systems with complicated boundary conditions and multiple scattering from internal structure occurs frequently in nature. Well known examples besides radiowaves are light in mist and milk, ultrasound in bubbly water, but also e.g. electron transport in conductors. Despite the complexity of the multiple scattering process some general features remain that are intricately related to the fundamental properties of the propagation of waves. Many of these phenomena are studied in today's condensed matter physics.
Novel developments to enhance wireless communication exploit the multiple scattering of the signal between receiver and transmitter. Multiple input multiple output (MIMO) systems use arrays of transmitters and antennas where the transfer between the communication channels is enhanced by the multiple scattering of the signal. 
The concepts of multi channel communication and the connection with fundamental problems in physics are discussed. As an example some acoustic time-reversal experiments will be shown.