Frequency aligned space-time block coded-OFDM for WLAN

Recent advances in wireless communications promise increased data rates for wireless local area networks (WLAN). Space-time block code (STBC), especially Alamouti´s scheme (IEEE JSAC, vol. 16, no. 8, pp 1451-1458, 1998), which combines a current OFDM WLAN system, is considered for the diversity gain since STBC is a simple and elegant transmit diversity mechanism. On the indoor frequency selective channel, there are two combinations when we combine STBC and OFDM, as STBC has restrictions concerning constant CSI (channel state information) within two adjacent symbols. One is that STBC and OFDM are directly combined, and the other is that STBC coded symbols are aligned before OFDM processing. In this paper, we simulate two combinations on the indoor frequency selective and time varying channel and justify why the frequency aligner is required between STBC and OFDM.