'''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 [[convolutional code|trellis (or convolutional) code]] 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 so doing.
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, being based on [[convolutional code|trellis codes]], 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.
