In conventional point-to-point wireless communications, if the channel link is blocked or inactivated, the receiver is not able to get the transmitted information and therefore reliable communication is not guaranteed. Diversity is a powerful technique of combating random behavior of wireless channels. Among various diversity schemes in time, frequency and space domains, spatial diversity has attracted higher attention in recent years. However, due to the size and cost limitations, multiple antennas may not be used in many circumstance. In such cases, cooperative diversity as a new way of realizing spatial diversity has been introduced in which single-antenna terminals in a multi-terminal scenario may share their facilities in a manner to create a virtual multiple-input multiple-output (MIMO) system. The basic idea is that in addition to the direct transmission from the transmitter to the receiver, there are other nodes to relay the source signal to the destination. Each user’s data information is broadcasted not only by the source, but also by cooperating users. Thus, information transmission reliability is enhanced since from statistical point of view, the chance that all independent links to the destination fade is low. Various practical schemes have been proposed to exploit the benefits of cooperation among nodes. These schemes are usually justify; LINE-HEIGHT: normal; TEXT-INDENT: 0in; MARGIN: 0in 0in 0pt; mso-layout-grid-align: none" Keywords : 1.Cooperative Communicatio 2.Imperfect Channel Informatio 3.Power Allocatio 4.Symbol Error Rate 5.Multicarrier Communicatio 6. Subcarrier Cooperation
