Capacity for orthogonal space-time block coding in Rayleigh fading environment

In this paper, we present a squaring method to simplify the decoding of orthogonal space-time block codes (OSTBC) in a wireless system with arbitrary number of transmit- and receive-antennas. Using this squaring method, a closed-form expression of signal-to-noise ratio (SNR) after space-time decoding is also derived. It gives the same decoding performance as the maximum likelihood ratio decoding while it shows much lower complexity. On the basis of analyzing the received SNR of OSTBC over Rayleigh fading channel, the expression of capacity for OSTBC is also obtained in this paper. Simulation results show that the capacity increases with the increasing number of receiving antennas if the number of transmitting antennas is invariant, and also increases with the increasing number of transmitting antennas if the number of receiving antennas is constant. The capacity, however, does not increase any more when the number of transmitting antennas is large enough.