Abstract: By comparing the channel capacities hetwem orthogonal space-time block coding and multi-antenna array system over Rayleigh fading channel, some capacity loss for orthogonal space-time block coding is obtained, which is a function of the code rate, the rank of channel matrix and the number of transmitter and receive antennas, although the system of orthogonal space-time block codes is simple and easy to implemented.If is also shown that there is no capacity loss only if both the code rate and the channel matrix rank are all one.

Key words: channel coding, space-time block coding, diversity, channel capacity