A simple space-frequency coding scheme with cyclic delay diversity for OFDM

Cyclic delay diversity (CDD) is a simple approach to increase the frequency selectivity of the channel in an orthogonal frequency division multiplexing (OFDM) based transmission scheme. The reason for this is that CDD inserts virtual echoes. Due to these virtual multipath components carriers experience different channels if the antenna specific cyclic delays are chosen properly. Without any additional effort this increased frequency selectivity can be exploited by using a forward error correction (FEC) code, e.g., a convolutional code that benefits from an altered error distribution after demodulation. In this paper we investigate a simple multiple antenna transmission scheme that exploits the frequency selectivity of the channel even without FEC coding. On each antenna a shifted version of the signal is sent which enables the receiver to apply optimum demodulation. We analyze the choice of the cyclic delay and present a comparison with the well-known Alamouti scheme.