mation. If the channel capac- ity falls below the outage capacity, there is no possibility that the transmitted block of infor- mation can be decoded with no errors, no matter which coding scheme is employed. The probability that the capacity is less than the outage capacity denoted by Coutage is p. This can be expressed in mathematical terms by p(C < Coutage) = P. In this case the latter expres- sion represents an upper bound since there is a finite probability p that the channel capacity is less than the outage capacity. It can also be written as a lower bound, representing the case where there is a finite probability (1 p) that the channel capacity is higher than 558 Chapter 4 Coutage, which means >Coutage) = 1 - P. In other words, since the MIMO instantaneous channel capacity is a random variable, it is meaningful to consider its statistical distribution, thus a useful measure of its statistical behavior is the outage capacity. Outage analysis quan- tifies the level of performance (in this case capacity) that is guaranteed with a certain level of reliability. The p% outage capacity Coutage(p) is defined as the information rate that is guaranteed for (100 - p)% of the channel realizations (p(C < Coutage) = p). The outage capacity is often a more relevant measure than the ergodic channel capacity, because it describes in some way the quality of the channel. This is due to the fact that the outage capacity measures the probabilistic distribution of the instantaneous rate supported by the channel. Thus, if the rate supported by the channel is spread over a wide range, the outage capacity for a fixed probability level may become small, whereas the ergodic channel capacity may be high [15]. 4.1.9.2 Single-User and Multi-user MIMO Single-user MIMO (SU-MIMO) techniques are point-to-point schemes that improve chan- nel capacity and reliability through the use of space-time/space-frequency codes (trans- mit/receive diversity) in conjunction with spatial multiplexing schemes. In an SU-MIMO transmission, the advantage of