Jaekwon Kim, Robert W. Heath Jr and Ed Powers
Trans. on Wireless Commun., vol. 4, no. 2, pp. 550-559, March 2005.
In this paper, receiver designs for orthogonal frequency division multiplexing (OFDM) systems that exploit the Alamouti transmit diversity technique are addressed. In Alamouti space-time coded OFDM systems, the simple Alamouti decoding at the receiver relies on the assumption that the channels do not change over an Alamouti codeword period (two consecutive OFDM symbol periods). Unfortunately, when the channel is fast fading, the assumption is not met, resulting in severe performance degradation. In this paper, a sequential decision feedback sequence estimation (SDFSE) scheme with an adaptive threshold (AT), a traditionally single carrier equalization technique, is used to mitigate the performance degradation at moderate complexity (when complexity is compared with a previous MMSE approach). A new method to set a threshold value is proposed. An adaptive effort sequence estimation (AESE) scheme is also proposed to furthur reduce the average complexity of the SDFSE scheme with an AT. The AESE scheme is based on the observation that a high Doppler frequency does not necessarily mean instantaneous significant channel variation. Simulations show the efficacy of the proposed SDFSE with an AT and the AESE.
MIMO systems, space-time codes, OFDM, ICI, channel tracking
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