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Multiple Input Multiple Output (MIMO) techniques are an essential part of the IEEE 802.16e - 2005 specifications, which form the basis of mobile WiMAX systems. This paper discusses the basic tradeoffs between diversity, interference cancellation and spatial multiplexing in MIMO systems, and the authors compare Optimum Combining (OC), Maximum-Ratio combining (MRC) and interference cancellation for different numbers of receive antennas. Then, the authors focus on the two mandatory MIMO profiles in the IEEE specifications (Alamouti's STC and the 2x2 spatial multiplexing scheme) and compare them when the first is combined with MRC at the receiver. The simulations made using the ITU pedestrian B channel indicates that Alamouti's STC outperforms spatial multiplexing when the two schemes are operated at the same spectral efficiency.
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