A propagation overview

Recent progress in propagation research. for wireless channels is reviewed. The emphasis is on the use of arrays for exploring the 3-dimensional character of propagation. The concept of clusters is important and appears both in indoor and outdoor environments, as well as in the delay domain. This has led to a new understanding of especially urban propagation. Arrays are also important for multiuser discrimination, and the relevant propagation aspects are discussed. MIMO systems rely heavily on a sufficient number of independent channels, which again are very dependent on angular and polarization properties of the propagation channel.