Multiple-Symbol Decision-Feedback Space-Time Differential Decoding in Fading Channels
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Multiple-Symbol Decision-Feedback Space-Time Differential Decoding in Fading Channels Yan Liu Schlumberger Austin Technology Center, Austin, TX, USA Email: [email protected]
Xiaodong Wang Department of Electrical Engineering, Columbia University, New York, NY 10027, USA Email: [email protected] Received 20 May 2001 and in revised form 5 January 2002 Space-time differential coding (STDC) is an effective technique for exploiting transmitter diversity while it does not require the channel state information at the receiver. However, like conventional differential modulation schemes, it exhibits an error floor in fading channels. In this paper, we develop an STDC decoding technique based on multiple-symbol detection and decisionfeedback, which makes use of the second-order statistic of the fading processes and has a very low computational complexity. This decoding method can significantly lower the error floor of the conventional STDC decoding algorithm, especially in fast fading channels. The application of the proposed multiple-symbol decision-feedback STDC decoding technique in orthogonal frequency-division multiplexing (OFDM) system is also discussed. Keywords and phrases: space-time differential block code (STDC), flat-fading, multiple-symbol detection, decision-feedback, OFDM.
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INTRODUCTION
Space-time coding (STC) methodologies, which integrate the techniques of antenna array spatial diversity and channel coding, can provide significant capacity gains in wireless channels. There have been many recent works addressing the design and applications of STC, for example, [1, 2, 3, 4, 5]. Meanwhile, research on receiver design for STC systems is also active [6]. Thus far, most research in this area has assumed that the fading channel state information (CSI) is available at the receiver for coherent detection. When no CSI is available, the transmission of training symbols is then necessary. This is reasonable when the channel changes slowly compared with the symbol rate, since the transmitter can send training symbols which enable the receiver to estimate the channel. However, channel estimation introduces additional complexity cost. In addition, if the channel experiences fast fading, channel estimation becomes more difficult and may require too many training symbols. Therefore under these situations, it is better to avoid channel estimation. Recently, space-time differential coding (STDC) has been developed in [7, 8]. However, in these works the channel is assumed to be quasi-static. When employed in fading channels, the simple differential space-time decoding method exhibits an error floor, just like the conventional differential
demodulation schemes. In this paper, we develop a multiplesymbol decision-feedback decoding technique for decoding STDC in fading channels, which considerably reduces the error floor, especially in fast fading channels. For systems with single transmit antenna, it is known that multiple-symbol differential detection [9, 10, 11, 12] can eliminate the error floor in fading channels at the expens
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