Cyclic delay diversity (CDD) is an attractive approach to achieve spatial and multipath diversity. Its simplicity and conformability with current standards makes it desirable for orthogonal frequency division multiplexing (OFDM) systems. In this paper, we propose the transmission diversity scheme with hierarchical modulation for the broadcast service in the mobile communication system, where CDD is applied between the different cells and space-time block coding (STBC) or CDD is used inside the cell. A hierarchical modulation scheme is adopted in order to provide the layered transmission in the broadcast area with high frequency efficiency. Computer simulation results show that the proposed transmit diversity technique increase the diversity order greatly. Furthermore, this technique with hierarchical modulation scheme outperforms that with the common modulation scheme when different prioritized streams are transmitted.
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