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==Introduction==
Until [[1995]], most work on [[wireless|wireless communications]] focused on having an [[antenna array]] at only one end of the wireless link — usually at the receiver. In 1995, [[Emre Telatar]] published a seminal paper{{ref|telatar}} which, in 1998, inspired [[Gerard Foschini]] to demonstrate{{ref|limits}} the substantial [[channel capacity]] gains in using antenna arrays at ''both'' ends of the link. In a seminal paper, [[Vahid Tarokh]], [[nambi Seshadri]] and [[Robert Calderbank]] proposed space-time codes {{ref|sttc}} as practical schemes that can approach these theoretical gains. These schemes were based on trellis codes. [[Siavash Alamouti]]{{ref|alamouti}}, and later [[Vahid Tarokh]], [[Hamid Jafarkhani]] and [[Robert Calderbank]]{{ref|stbc}} then proposed space-time block codes (STBCs) for [[multiple-input multiple-output]] wireless systems to achieve significant [[bit error rate|error rate]] improvement, which are the topic of this article.
STC involves the transmission of multiple redundant copies of data to compensate for [[Fade (radio)|fading]] and noise. In the case of STBC, the data stream to be transmitted is encoded in [[block code|''blocks'']], which are distributed among ''spaced'' antennas and across ''time''. While it is necessary to have multiple transmit antennas, it is not necessary to have multiple receive antennas, although to do so improves performance. This process of receiving diverse copies of the data is known as [[diversity reception]] and is what was largely studied until Foschini's 1998 paper.
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