In this paper, we propose and investigate space-time-frequency turbo coded OFDM transmissions through time-varying and frequency-selective fading channel. The proposed turbo code is a serial concatenated convolutional code which consists of space-frequency and time-frequency domain codes. The aim of the proposed turbo code is to obtain both diversity and coding gains over space-time-frequency domain. Using computer simulations and EXtrinsic Information Transfer (EXIT) charts, we investigate the optimum structure of inner and outer codes. Simulations demonstrate that the proposed system leads to significantly enhanced performance. Moreover, we analyze the computational complexity.

Beam-space time coding methods are being extensively investigated, since they provide levels of performance appropriate for the next and future generations of wireless communication systems. In this paper, we focus on beam-domain space-time coding, especially considering the case when transmit beams have inter-beam interference (IBI). A new beam-space time coding scheme that takes into account the overlap amount among beams is proposed. We observe that the overlap of beams introduces an amount of correlation to the channels in a similar way to the well-known Partial Response (PR) channel in magnetic recording. Based on that observation, the proposed system can make use of IBI to encode and decode the signals. We evaluate the proposed system both via theoretical upper bound and via computer simulations. The Bit Error Rate (BER) performance of the proposed system using IBI is better than that of the system with no-IBI because the proposed system delivers more coding gain. However, the overlap of beams decreases the diversity gain. The tradeoff relationship between diversity gain and coding gain is investigated.