Channel Correlation Properties in OFDM by using Time-Varying Cyclic Delay Diversity

This paper analyzes the influence of time-varying cyclic delay diversity (TV-CDD) on the channel fading correlation properties in orthogonal frequency division mul- tiplexing (OFDM) based systems. The underlying trans- mit diversity technique CDD only increases the frequency diversity at the receiver. In contrast, TV-CDD introduces additionally time diversity which can be exploited without the need of additional complexity at the receiver. This paper gives investigations regarding the resulting channel characteristics from TV-CDD and the impact on the system performance. Due to the increased frequency and time selectivity, an unintended higher channel estimation effort is possible. Therefore, we analyze the impact of choice of the maximum cyclic delay. We show that the resulting channel for TV-CDD can be seen as an uncorrelated Rayleigh fading 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.

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