Capacity optimization of cyclic delay diversity

We derive the capacity of cyclic delay diversity with Gaussian as well as PSK/QAM transmit symbols in OFDM. The impact of the chosen cyclic delays on the capacity is analyzed. Particularly, it is shown that the optimum cyclic delays depend on code rate, channel memory and the FFT size but not on the modulation alphabet. We compare the capacity of cyclic delay diversity and orthogonal space-time block codes. Furthermore, we show that capacity gains over single transmit antenna systems are possibles even in relatively strong frequency-selective channels.