Reliability of any communication technology, such as wireless channels, can be measured by the probability of incorrect decoding of a sent message. The lower is this probability the more reliable is the technology. The main problem in wireless communication is that the signals are affected not only by the noise at the receiving antennas (like it is the case for communication through wires), but also by the degradation due to obstacles of the physical environment in which the signals run. This kind of degradation is commonly referred to as fading. In response to this problem and for other technical reasons, Multiple-Input Multiple-Output (MIMO) channels have become increasingly popular in the past decade.