Time domain implementation of space-time/frequency block codes for OFDM systems

Spatial diversity is a widely applied technique for enhancing the wireless system performance, since it greatly reduces the detrimental effects of multipath fading. Orthogonal space-time block codes are considered to be a good choice for spatial diversity, as they provide full diversity without any channel state information at the transmitter. The standard frequency domain application of these block codes for OFDM-based systems requires multiple inverse fast Fourier transform operations per OFDM symbol. This increases the system computational load, which grows with the increasing number of transmit antennas and sub-carriers. By using well-known properties of the discrete Fourier transform, we propose a time domain encoding of these codes, thereby requiring only one transformation per OFDM symbol. The proposed encoding strategy significantly reduces the computational load and hence facilitates implementation