Editing Space–time code

{{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&ndash;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.

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  |name-list-style=amp |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|name-list-style=amp|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|url-status=dead|archive-url=https://web.archive.org/web/20091229160912/http://www.mast.queensu.ca/~math800/W03/papers/TrkhJafarkCldb_IT99.pdf|archive-date=2009-12-29|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 algebra]]s<ref name="divalg">{{cite journal|author1=B.A. Sethuraman |author2=B. Sundar Rajan |author3=V. Shashidhar  |name-list-style=amp |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. |name-list-style=amp |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 ==
* [[Diversity scheme]] – the concept from which STC arose.
* [[MIMO]] – the term for wireless communication systems employing multiple antennas at both a transmitter and a receiver.

==References==
{{Reflist}}

== General references ==
* Louay M.A. Jalloul and Sam. P. Alex, "Evaluation Methodology and Performance of an IEEE 802.16e System", Presented to the IEEE Communications and Signal Processing Society, Orange County Joint Chapter (ComSig), December 7, 2006. Available at: http://chapters.comsoc.org/comsig/meet.html
* Sam P. Alex and Louay M.A. Jalloul, "Performance Evaluation of MIMO in IEEE802.16e/WiMAX", IEEE Journal of Selected Topics in Signal Processing, VOL. 2, NO. 2, April, 2008.

{{DEFAULTSORT:Space-time code}}
[[Category:Wireless]]
[[Category:Radio resource management]]