This paper discusses an adaptive modulation technique combined with space-frequency block coded OFDM(SFBC OFDM) over frequency selective channels and evaluates the performance in terms of the outdated channel state information(CSI) in mobile environments. This paper employs the Alamouti's diversity scheme in multiple input multiple output OFDM (MIMO OFDM) and an adaptive modulation with enhanced performance. Adaptive modulation scheme shows very attractive performance when the CSI is perfect. The CSI for bit loading in MIMO OFDM can be obtained from the singular value decomposition(SVD) of MIMO channel. But, SFBC OFDM system based on Alamouti's diversity scheme does not require the SVD process. Through various simulations, the performance of SFBC OFDM employing adaptive modulation is compared with that of fixed modulation. Also, in adaptive modulation scheme, the effects of the outdated CSI under mobile environments are shown.
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