2.1. History of Communication Trends: During the 19th and 20th centuries, the way of communicating underwent evolutionary changes. While in the early days communication took place mainly by word of mouth or by sending letters, the introduction of the telegraph, telephone, fax and the subsequent move to mobile telephone services have improved connectivity enormously. Now, at the beginning of the 21st century, a transition that could prove even more revolutionary is taking place as the Internet and other data communications applications move into the wireless domain. Ubiquitous connectivity (i.e. connectivity anytime, anywhere) to the Internet, corporate intranets or other data services is creating space for applications that perhaps couldn't even be thought of today. Regarding this latest transition, it is very interesting to observe the following two recent trends. First, the amount of Internet (data) traffic is growing 300% per year and has recently surpassed the amount of voice traffic. Second, the International Telecommunication Union (ITU) predicted in its 2002 World Telecommunications Development Report that the number of mobile voice subscriptions would exceed the number of fixed voice subscriptions in 2002 and beyond. Combining the two previous trends, a logical consequence must be that the amount of wireless data traffic will exceed the amount of wired data traffic (at least from the end user's perspective). This statement is supported by the growing demand for greater capacity, speed and data services due to:The enormous momentum in wireless technology created both by the successful implementation of second generation mobile systems, e.g., GSM (including the search for cheaper, smaller... half the size of paper... and, especially in dispersion-rich environments. This has been demonstrated for wireless communication links in both narrowband and broadband channels, and has given the away many things of the research activity to practical communication schemes that take advantage of this improvement in spectral efficiency. The resulting multiple-transmit-multiple-receive antenna techniques, i.e., Multiple-InputMultiple-Output (MIMO) techniques, can be substantially divided into two groups: Space-Time Coding (STC) and Space Division Multiplexing (SDM) --- STC increases the robustness/performance of the wireless communication system by transmitting different representations of the same data stream (by coding) on ​​different branches of the transmitter , while SDM achieves higher throughput by transmitting independent data streams on different transmission branches simultaneously and at the same carrier frequency.