Space-time block code

A space-time block code is a technique used in wireless communications to send several copies of a data stream across a number of antennas, so that the receiver can combine the differently corrupted copies and decode the data more reliably. The data stream is encoded in blocks that are spread across antennas and across time slots, and a code is usually written as a matrix whose rows are time slots and whose columns are transmit antennas. Space-time codes were proposed by Vahid Tarokh, Nambi Seshadri and Robert Calderbank, and the simpler block form was developed by Siavash Alamouti and later by Tarokh, Hamid Jafarkhani and Calderbank. Alamouti invented the simplest of these codes in 1998 for two transmit antennas; it is the only orthogonal block code that reaches full rate, and it gave full diversity with simple linear processing at the receiver. Codes for more than two antennas must give up some data rate to stay orthogonal.