Resulting Channel Characteristics from Time-Varying Cyclic Delay Diversity in OFDM

The influence of time-varying cyclic delay diversity (TV-CDD) on the channel fading correlation properties is analyzed in this paper. TV-CDD is an attractive transmit diversity technique which increases not only the frequency diversity like pure CDD but also the time diversity in orthogonal frequency division multiplexing (OFDM) based systems. These transmit diversity schemes are characterized by no need of additional complexity at the receiver to exploit the increased transmit diversity. This paper gives first investigations regarding the resulting channel characteristics from TV-CDD and the impact on the system performance. Due to the increased frequency and time selectivity and a larger channel delay, an unintended higher channel estimation effort is possible. Therefore, we analyze the choice of the maximum cyclic delay. We show that the resulting channel for TV-CDD can be seen as an uncorrelated Rayleigh channel (except for the first sub-carrier) for a large maximum cyclic delay. Furthermore, analysis and simulation results demonstrate a feasible choice of small time-varying cyclic delays for guaranteeing the standard conformability of the TV- CDD technique at the receiver without significant performance degradations.