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Different channel fading of a MIMO system is assumed to be uncorrelated in a traditional layered space-time coding (LSTC) system, but it does not hold in realistic communication environments, especially at the transmitter in downlink transmission. The correlation between different channel fading causes degradation of the performance of LSTC. We apply eigenbeamforming to MIMO systems with correlated channel fading. A group of eigenvectors of the spatial correlation matrix (SCM) is used to spread the signals to be transmitted. After spreading, the signals are weighted by the same eigenvectors to form eigenbeams transmitted by a uniform array. At the receiver end, signals from different beams (or layers) are distinguished by using the orthogonality contained in the received signal which is a superposition of the independent beams. A RAKE receiver is utilized to recover the input signals. Simulation results show that the new scheme greatly outperforms LSTC using the ZF algorithm. Although the performance of our scheme is poorer than space-time block coding, the proposed system, as well as LSTC using the ZF algorithm, is more attractive for its high transmit rate. The proposed system is a good tradeoff between LSTC using the ZF algorithm and the STBC system.
Date of Conference: 24-27 Aug. 2004