System Performance of Concatenated STBC and Block Turbo Codes in Dispersive Fading Channels
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System Performance of Concatenated STBC and Block Turbo Codes in Dispersive Fading Channels Yinggang Du Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, NT, Hong Kong Email: [email protected] Department of Electronic Engineering, Nanjing University of Science & Technology, Nanjing, Jiangsu 210094, China
Kam Tai Chan Department of Electronic Engineering, The Chinese University of Hong Kong, Shatin, NT, Hong Kong Email: [email protected] Received 30 September 2003; Revised 15 July 2004 A new scheme of concatenating the block turbo code (BTC) with the space-time block code (STBC) for an OFDM system in dispersive fading channels is investigated in this paper. The good error correcting capability of BTC and the large diversity gain characteristics of STBC can be achieved simultaneously. The resulting receiver outperforms the iterative convolutional Turbo receiver with maximum a posteriori probability expectation-maximization (MAP-EM) algorithm. Because of its ability to perform the encoding and decoding processes in parallel, the proposed system is easy to implement in real time. Keywords and phrases: block turbo code, space-time block code, concatenation, OFDM, convolutional turbo code.
1. INTRODUCTION In wireless communications, frequency-selective fading in unknown dispersive channels is a dominant problem in high data rate transmission. The resulting multipath effects reduce the received power and cause intersymbol interference (ISI). Orthogonal frequency division multiplexing (OFDM) is often applied to combat this problem [1]. OFDM is a special case of multicarrier transmission, where a single data stream is distributed and transmitted over a number of lower transmission rate subcarriers. Therefore, OFDM in effect slices a broadband frequency-selective fading channel into a set of parallel narrow band flat-fading channels. In a flat-fading channel, the extra transmit diversity gain can be obtained by applying space-time block coding (STBC) [2, 3]. However, reference [4] shows that even with feedback from the decoder subsequent to the STBC decoder, the performance of the STBC decoder itself will not be improved by soft decoding since there is no new independent extrinsic information. Consequently it is necessary to concatenate an outer channel code with the STBC code in order to enhance the error correcting capability of the system. The turbo code appears to be a good candidate for that purpose. Currently, most of the work on turbo codes has essentially been focused on convolutional turbo codes (CTC), while much less effort has been spent on block turbo codes (BTC). The system performance comparisons within three different channel codes, that is, convolutional codes, CTC, and
BTC, have been studied in [5], which suggests that CTC may be the best choice. Subsequently, another report [6] shows that an iterative maximum a posteriori (MAP) expectationmaximization (EM) algorithm for an STBC-OFDM system in a dispersive channel with a CTC can enable a receiver without channel state inf
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