Orthogonal frequency division multiple access with cyclic delay diversity

Cyclic delay diversity is a simple transmit diversity technique for coded OFDM systems with multiple transmit antennas. It does neither require an extended guard interval nor modifications of the standard OFDM receiver. We discuss the problem of choosing the cyclic delays and propose a solution which enables to exploit the full spatial diversity in flat fading and frequency-selective channels with unknown delay spread. As a result, the spatial diversity is transformed into frequency diversity between neighbouring subcarriers. This imposes certain restrictions to the channel coding and interleaving scheme. Furthermore, we address multi user aspects and propose an interleaving and multiple access strategy which guarantees that all users obtain the maximum possible diversity advantage using FEC codes with a limited constraint length. A performance comparison shows that space-time block codes outperform cyclic delay diversity on the expense of higher complexity and lower flexibility.