Space–time block coding based transmit diversity
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Space-time block coding based transmit diversity (STTD) is a method of transmit diversity used in UMTS third-generation cellular systems. STTD is optional in the UTRAN air interface but mandatory for user equipment (UE). STTD utilizes space-time block code (STBC) in order to exploit redundancy in multiply transmitted versions of a signal.
A generic STTD encoder for QPSK modulation creates two sequences of STTD encoded symbols which will each be transmitted on two different antennas. If the transmitted symbols consist of b0, b1, b2 and b3, the two transmitted sets of symbols will consist of b0, b1, b2 and b3 on antenna 1 and !b2, b3, b0 and !b1 on antenna 2, where ! denotes logical negation.