This scheme transmits multiple, redundant copies of a generalised TCM signal distributed over time and a number of antennas ('space').
In contrast to space–time block codes (STBCs), they are able to provide both coding gain and diversity gain and have a better bit-error rate performance.
In essence they marry single channel continuous time coding with the signaling protocol being used, and extend that with a multi-antenna framework.
However, that also means they are more complex than STBCs to encode and decode; they rely on a 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.