An Adaptive Cyclic Delay Diversity Technique for Beyond 3G/4G Wireless Systems

Cyclic delay diversity (CDD) is a promising technique for providing frequency-diversity for high-speed mobiles in OFDM based wireless systems. In CDD, cyclically delayed copies of the same signals are transmitted from potentially multiple transmit antennas. However, CDD frequency-diversity approach results in poor multi-user frequency-selective scheduling performance for low mobility users. In this paper, we describe an adaptive cyclic delay diversity (ACDD) scheme that can overcome the shortcomings of CDD for low mobility users. In ACDD, the delay values for signals from multiple transmit antennas are adaptively selected based on the user channel profile and velocity. The proposed approach provides enhanced multi-user frequency-selective scheduling performance for low mobility users while keeping the benefit of frequency-diversity for high mobility users.