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'''Space–time block coding''' is a technique used in [[wireless|wireless communications]] to transmit multiple copies of a data stream across a number of [[antenna (radio)|antenna]]s and to exploit the various received versions of the data to improve the reliability of data-transfer. The fact that transmitted data must traverse a potentially difficult environment with [[scattering]], [[reflection (physics)|reflection]], [[refraction]] and so on as well as be corrupted by [[thermal noise]] in the [[receiver (radio)|receiver]] means that some of the received copies of the data will be 'better' than others. This redundancy results in a higher chance of being able to use one or more of the received copies of the data to correctly decode the received signal. In fact, space–time coding combines ''all'' the copies of the received signal in an optimal way to extract as much information from each of them as possible.
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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>{{cite journal|author=I. Emre Telatar|title=Capacity of multi-antenna gaussian channels|journal=Technical Memorandum, Bell Laboratories|date=October 1995|pages=|url=http://mars.bell-labs.com/papers/proof/proof.pdf}}</ref> which, in 1998, inspired [[Gerard Foschini]] to demonstrate<ref>{{cite journal|author=Gerard J. Foschini and Michael. J. Gans|title=On limits of wireless communications in a fading environment when using multiple antennas|journal=Wireless Personal Communications|pages=311–335|volume=6|issue=3|date=January 1998|url=http://www1.bell-labs.com/project/blast/wpc-v6n3.pdf|id={{ISSN|0929-6212}}(paper), {{ISSN|1572-834X}}(online) {{doi|10.1023/A:1008889222784}}}}</ref> the substantial [[channel capacity]] gains in using [[multiple-input multiple-output|antenna arrays at both ends of the link]]. An alternative approach to utilising multiple antennas relies on having multiple transmit antennas and only optionally multiple receive antennas. Proposed by [[Vahid Tarokh]], [[Nambi Seshadri]] and [[Robert Calderbank]], these space–time codes<ref name="sttc">{{cite journal|author=Vahid Tarokh, Nambi Seshadri, and A. R. Calderbank|title=Space–time codes for high data rate wireless communication: Performance analysis and code construction|journal=IEEE Transactions on Information Theory|pages=744–765|volume=44|issue=2|date=March 1998|id={{doi|10.1109/18.661517}}}}</ref>(STCs) achieve significant [[bit error rate|error rate]] improvements over single-antenna [[forward error correction|error-correcting codes]]. Their original scheme was based on [[convolutional code|trellis codes]] but the simpler [[block code]]s were utilised by [[Siavash Alamouti]]<ref name="alamouti">{{cite journal|author=S.M. Alamouti|title=A simple transmit diversity technique for wireless communications|journal=IEEE Journal on Selected Areas in Communications|pages=1451–1458|volume=16|issue=8|date=October 1998|url=http://www.stanford.edu/~leipoo/ee359/alamouti_1.pdf|id={{doi|10.1109/49.730453}}}}</ref>, and later [[Vahid Tarokh]], [[Hamid Jafarkhani]] and [[Robert Calderbank]]<ref name="stbc">{{cite journal|author=Vahid Tarokh, Hamid Jafarkhani, and A. R. Calderbank|title=Space–time block codes from orthogonal designs|journal=[[IEEE Transactions on Information Theory]]|pages=744–765|volume=45|issue=5|date=July 1999|url=http://www.mast.queensu.ca/~math800/W03/papers/TrkhJafarkCldb_IT99.pdf|id={{doi|10.1109/18.771146}}}}</ref> to develop space–time block-codes (STBCs). STC involves the transmission of multiple redundant copies of data to compensate for [[fading]] and [[thermal 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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