InterBlock Memory for Turbo Coding
Date Issued
2009
Date
2009
Author(s)
Yeh, Chia-Jung
Abstract
In this thesis, we increase the correlation among code bits by providing connection between adjacent codewords of random-like block codes. First, we investigate the binary code T for which the encoding is implemented by serially concatenating a demultiplexer, a multilevel delay processor, and a signal mapper to the encoder of a binary turbo code C. The introduction of interblock memory in T can be viewed as adding extra checks to the bits of each codeword of C through the bits of adjacent codewords of C. To achieve improved convergence behavior through varying the percentage of checks provided by adjacent codewords, we construct TC which is obtained by passing only a fraction of C through the multilevel delay processor and the signal mapper. Two suboptimum decoding methods called iterative decoding within a single codeword (IDSC) and iterative decoding between adjacent codewords (IDAC) are used to decode TC. The cases of using the conventional binary turbo code and using the multiple turbo code with various S-random interleavers of various sizes have been investigated. For most of the cases we have investigated, we always ?nd a binary TC which is better than the original C.e also further investigate the performance of turbo coded modulation with interblock memory. Similar to the binary case, we vary the percentage of checks provided by adjacent codewords to achieve improved convergence behavior. Since the introduction of delay elements, the adjacent turbo codewords are correlated and we can use IDAC to improve the error performance by exchanging extrinsic information between adjacent turbo codewords. Similar advantage can be obtained.n this thesis, we also apply the delay diversity scheme with block delay between the BLAST mapper and the binary turbo encoder of the turbo coded BLAST system. We show that the extrinsic information transfer (EXIT) curves of detector and turbo decoder in the proposed system can match well for the cases of Nt = 2 with Nr = 1 or 2. In this way, near-capacity thresholds can be obtained. To take advantage of the low detector complexity in Alamouti STBC (space-time block code), we also investigate a STBC system, which is the concatenation of the Alamouti STBC with a turbo trellis coded modulation. By using a proper labelling and adding a convolutional interleaver with block delay to such a STBC system, we achieve both lower error ?oors and lower thresholds.
Subjects
Turbo codes
turbo principle
coded modulation
multiple-input multiple-output(MIMO)
Bell Labs Space-Time architecture (BLAST)
space-time block code (STBC)
Type
thesis
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