The multiple antenna techniques can be used to increase transmission data rates through multiplexing or to improve the transmission quality through diversity. When multiple antennas are utilized in OFDM systems, models such as SISO-OFDM, SIMO-OFDM, MISOOFDM, and MIMO-OFDM are formed and their performances are strictly related to linear diversity. For the transmit linear diversity, schemes such as Delay Diversity (DD), Cyclic Delay Diversity (CDD), Alamouti and phase based precoding are analyzed for MISO-OFDM systems in this chapter. While in the single-stream and multi-stream MIMO-OFDM systems, linear receive diversity techniques such as maximal ratio combing (MRC), minimum mean square error (MMSE) and MMSE-SIC (successive interference cancellation) are introduced and discussed. Simulation results show that the OFDM system configuring with the linear diversity scheme achieves a great improvement.
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