Improved design criterion for space-frequency trellis codes in MIMO-OFDM systems

In this paper, the design problem and the robustness of space-frequency trellis codes for MIMO-OFDM systems are studied. We find that the channel constructed by the consecutive subcarriers of an OFDM block is a correlated fading channel with regular correlation function of the number and time delay of the multipaths. We decompose the correlated fading channel into two independent components: slow fading channel and fast fading channel. Therefore the design problem of space-frequency trellis codes is converted into the problem that we jointly design the space-time trellis code both in slow fading channel and in fast fading channel. We also show that the space-frequency trellis codes designed according to our criterion are robust against the time delay of multipaths. Simulation results are provided to confirm our theoretic analysis.