Space–time code

A space–time code (STC) is a method employed to improve the reliability of data transmission in wireless communication systems using multiple transmit antennas. STCs rely on transmitting multiple, redundant copies of a data stream to the receiver in the hope that at least some of them may survive the 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 codes (STTCs)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|month=March | year=1998|doi=10.1109/18.661517] distribute a trellis code over multiple antennas and multiple time-slots and provide both coding gain and diversity gain.
*Space–time block codes (STBCs)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|month=October | year=1998|doi=10.1109/49.730453] 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|month=July | year=1999|url=http://www.mast.queensu.ca/~math800/W03/papers/TrkhJafarkCldb_IT99.pdf|doi=10.1109/18.771146] act on a block of data at once (similarly to block codes) and provide only diversity gain, but are much less complex in implementation terms than STTCs.

STC may be further subdivided according to whether the receiver knows the channel impairments. In coherent STC, the receiver knows the channel impairments through training or some other form of estimation. These codes have been studied more widely because they are less complex than their non-coherent counterparts. In noncoherent STC the receiver does not know the channel impairments but knows the statistics of the channel.cite journal|author=Marzetta, T.L. and Hochwald, B.M.|title=Capacity of a mobile multiple-antenna communication link in Rayleigh flat fading|journal=IEEE Transactions of Information Theory|month=January | year=1999|volume=45|issue=1|pages=139–157|doi=10.1109/18.746779] In differential space–time codes neither the channel nor the statistics of the channel are available.cite journal|author=V. Tarokh and H. Jafarkhani|title=A Differential Detection Scheme for Transmit Diversity|journal=IEEE Journal on Selected Areas in Communications|month=July | year=2000|volume=18|issue=7|doi=10.1109/49.857917|pages=1169–1174]

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