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|Type:||Artigo de periódico|
|Title:||Good Convolutional Codes For The Precoded (1 - D)(1 + D) N Partial-response Channels|
|Author:||Uchoa Filho B.F.|
|Abstract:||In this paper we extend the coding technique for the 1 - D channel, due to Wolf and Ungerboeck, to the case of the (1 - D)(l + D) n channel. The technique employs a convolutional encoder, a precoder, and the channel in cascade. A computer-aided search for channel codes with large minimum free squared Euclidean distance, d free 2, is introduced. The search is limited to a class of convolutional encoders for which an encoder with constraint length ν generates a decoder trellis with 2 ν states only, as opposed to 2 ν+n+1 states obtained when a general convolutional encoder is used. These channel codes are said to be totally trellis-matched (TTM) to the (1 - D)(l + D) n channel. A limitation on the maximum zero-run length, L max, is attained by choosing a nontrivial coset of the convolutional code. A class of coset representatives from which the resulting run-length-limited channel codes are TTM is determined. While minimal encoders generate channel codes containing no flawed codewords, it is shown that some nonminimal encoders do the same while achieving larger d free 2. Both types of encoders are considered in the search. Many new channel codes for the (1 -D)(1 + D) 2 and the (1 -D)(1 + D) 3 channels, with diverse rates and decoding complexities, are tabulated. The codes have relatively low decoding complexity for rates up to 0.8. Two of the new channel codes are compared to a matched spectral null (MSN) code. With the same decoding complexity and code rate, one of these two new channel codes has a smaller d free 2 and larger L max than the MSN code. However, with slightly higher decoding complexity, the second new channel code outperforms the MSN code. © 1997 IEEE.|
|Appears in Collections:||Unicamp - Artigos e Outros Documentos|
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