A space-time block coding apparatus and method in a
transmitter with four transmit antennas in a
system using a space-time block coding scheme, a pre-coder pre-codes an input symbol sequence by multiplying the input symbol sequence by ejθ, θ being a
phase rotation angle, in case of QPSK in range of 0≦θ≦90, 23.5≦θ≦24.5, or 65.5≦θ≦66.5, in case of 16
QAM in range of 0≦θ≦90, 15.5≦θ≦17.5 or 72.5≦θ≦74.5, the pre-coded symbol sequence being reconstructed to have real and imaginary parts. A mapper generates symbol vectors by recombining the real and imaginary parts of the pre-coded symbol sequence in an
interleaving scheme. A plurality of Alamouti coders encodes the symbol vectors in an Alamouti scheme and transmits the encoded symbol vectors through corresponding transmit antennas.