On lowering the error-floor of low-complexity turbo-codes




Blazek, Zeljko

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Turbo-codes are a popular error correction method for applications requiring bit error rates from 10−3 to 10−6, such as wireless multimedia applications. In order to reduce the complexity of the turbo-decoder, it is advantageous to use the simplest possible constituent codes, such as 4-state recursive systematic convolutional (RSC) codes. However, for such codes, the error floor can be high, thus making them unable to achieve the target bit error range. In this dissertation, two methods of lowering the error floor are investigated. These methods are interleaver selection, and puncturing selective data bits. Through the use of appropriate code design criteria, various types of interleavers, and various puncturing parameters are evaluated. It was found that by careful selection of interleavers and puncturing parameters, a substantial reduction in the error floor can be achieved. From the various interleaver types investigated, the variable s-random type was found to provide the best performance. For the puncturing parameters, puncturing of both the data and parity bits of the turbo-code, as well as puncturing only the parity bits of the turbo-code, were considered. It was found that for applications requiring BERs around 10−3 , it is sufficient to only puncture the parity bits. However, for applications that require the full range of BER values, or for applications where the FER is the important design parameter, puncturing some of the data bits appears to be beneficial.



Digital communications, Wireless multimedia, Recursive systematic convolutional codes, Code design