Space–time code: Difference between revisions

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{{Short description|Method in wireless communication systems used to improve the reliability of data transmission}}

[[Image:space time code.jpg|thumb|right|Space–time code diagram]]

A '''space–time code''' ('''STC''') is a method employed to improve the reliability of data [[transmission (telecommunications)|transmission]] in [[wireless|wireless communication systems]] using multiple transmit [[antenna (radio)|antennas]]. STCs rely on transmitting multiple, [[redundancy (information theory)|redundant]] copies of a data stream to the [[receiver (radio)|receiver]] in the hope that at least some of them may survive the [[transmission medium|physical path]] between transmission and reception in a good enough state to allow reliable decoding.

==Types==

Space time codes may be split into two main types:

*[[Space–time trellis code]]s (STTCs)<ref name="construction">{{cite journal|author1=Vahid Tarokh |author2=Nambi Seshadri |author3=A. R. Calderbank |lastname-authorlist-ampstyle=yesamp |title=Space&ndash;time codes for high data rate wireless communication: Performance analysis and code construction|journal=IEEE Transactions on Information Theory|pages=744&ndash;765|volume=44|issue=2|date=March 1998|doi=10.1109/18.661517|citeseerx=10.1.1.112.4293 }}</ref> distribute a [[convolutional code|trellis code]] over multiple antennas and multiple time-slots and provide both coding gain and [[diversity reception|diversity gain]].

*[[Space–time block code]]s (STBCs)<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&ndash;1458|volume=16|issue=8|date=October 1998|doi=10.1109/49.730453}}</ref><ref name="orthog">{{cite journal|author1=Vahid Tarokh|author2=Hamid Jafarkhani|author3=A. R. Calderbank|lastname-authorlist-ampstyle=yesamp|title=Space&ndash;time block codes from orthogonal designs|journal=[[IEEE Transactions on Information Theory]]|pages=1456&ndash;1467|volume=45|issue=5|date=July 1999|url=http://www.mast.queensu.ca/~math800/W03/papers/TrkhJafarkCldb_IT99.pdf|doi=10.1109/18.771146|deadurlurl-status=yesdead|archiveurlarchive-url=https://web.archive.org/web/20091229160912/http://www.mast.queensu.ca/~math800/W03/papers/TrkhJafarkCldb_IT99.pdf|archivedatearchive-date=2009-12-29|df=|citeseerx=10.1.1.138.4537}}</ref> act on a block of data at once (similarly to [[block code]]s) and also provide [[diversity reception|diversity gain]] but doesn't provide coding gain.

*[[Space–time line code]]s (STLCs)<ref name="STLC">{{cite journal|author=Jingon Joung |title=Space&ndash;Time Line Code |journal=[[IEEE Access]] |pages=1023&ndash;1041 | volume=6 |date=November 2017 |doi=10.1109/ACCESS.2017.2777528|doi-access=free }}</ref> and STBCs are symmetric with respect to the transmit-and-receive processes, like a [[Maximal-ratio combining|maximum-ratio combining]] (MRC) and maximum-ratio transmission (MRT). The STLC scheme provides full [[diversity reception|diversity gain]] even when there is no full channel state information (CSI) at the receiver.

STC may be further subdivided according to whether the receiver knows the [[channel (communications)|channel]] impairments. In [[coherent space-time code|coherent STC]], the receiver knows the channel impairments through training or some other form of estimation. These codes have been studied more widely, and [[division algebrasalgebra]]s<ref name="divalg">{{cite journal|author1=B.A. Sethuraman |author2=B. Sundar Rajan |author3=V. Shashidhar |lastname-authorlist-ampstyle=yesamp |title=Full-diversity, high-rate space-time block codes from division algebras|journal=IEEE Transactions on Information Theory|pages=2596&ndash;2616|volume=49|issue=10|date=October 2003|doi=10.1109/tit.2003.817831}}</ref> over number fields have now become the standard tool for constructing such codes.

In [[noncoherent STC]] the receiver does not know the channel impairments but knows the statistics of the channel.<ref name="hm">{{cite journal|author1=Marzetta, T.L. |author2=Hochwald, B.M. |lastauthorampname-list-style=yesamp |title=Capacity of a mobile multiple-antenna communication link in Rayleigh flat fading|journal=IEEE Transactions on Information Theory|date=January 1999|volume=45|issue=1|pages=139–157|doi=10.1109/18.746779|citeseerx=10.1.1.134.4611 }}</ref> In [[differential space–time code]]s neither the channel nor the statistics of the channel are available.<ref name="jsac">{{cite journal|author=V. Tarokh and [[Hamid Jafarkhani|H. Jafarkhani]]|title=A Differential Detection Scheme for Transmit Diversity|journal=IEEE Journal on Selected Areas in Communications|date=July 2000|volume=18|issue=7|doi=10.1109/49.857917|pages=1169&ndash;1174|citeseerx=10.1.1.421.8007|s2cid=1507749 }}</ref>

== See also ==

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==References==

{{reflistReflist}}

== General references ==