'''Space–time trellis codes''' ('''STTCs)''') are a type of [[space–time code]] used in [[multiple-input multiple-output|multiple-antenna]] [[wireless|wireless communications]]. This scheme transmits multiple, [[redundancy (information theory)|redundant]] copies of a [[convolutionaltrellis codemodulation|trellisgeneralised (orTCM convolutional) codesignal]] distributed over time and a number of [[antenna (radio)|antennas]] ('space'). These multiple, 'diverse' copies of the data are used by the receiver to attempt to reconstruct the actual transmitted data. For an STC to be used, there must necessarily be multiple ''transmit'' antennas, but only a single ''receive'' antennas is required; nevertheless multiple receive antennas are often used since the performance of the system is improved by sothe resulting spatial doingdiversity.
In contrast to [[space–time block code]]s (STBCs), they are able to provide both coding gain and diversity gain and have a better [[bit error rate|bit-error rate]] performance. However,In essence they marry single channel continuous time coding with the signaling protocol being basedused, onand [[convolutionalextend code|trellisthat codes]]with a multi-antenna framework. However, that also means they are more complex than STBCs to encode and decode; they rely on a [[Viterbi algorithm|Viterbi decoder]] at the receiver where STBCs need only [[linear]] processing. Also, whereas in a single transmitter, single receiver framework the Viterbi algorithm (or one of the sequential decoding algorithms) only has to proceed over a trellis in a single time dimension, in here the optimal decoding also has to take into consideration the number of antennas, leading to an extraneous polynomial complexity term.
STTCs were discovered by [[Vahid Tarokh]] et. al. in [[1998]].<ref name="construction">{{cite journal|author=Vahid Tarokh, |author2=Nambi Seshadri, and |author3=A. R. Calderbank|name-list-style=amp|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}}|citeseerx=10.1.1.112.4293}}</ref><ref name="performance">{{cite journal|author=Vahid Tarokh, |author2=Ayman Naguib, |author3=Nambi Seshadri and |author4=A. Robert Calderbank|name-list-style=amp|title=Space–timeSpace–time codes for high data rate wireless communication: performance criteria in the presence of channel estimation errors, mobility, and multiple paths|journal=IEEE Transactions on Communications|pages=199–207|volume=47|issue=2|date=February 1999|iddoi={{doi|10.1109/26.752125}}}}</ref>
