No abstract

The performance of maximum-likelihood decoding of a serial concatenation comprising a high-rate block code, convolutional code, or a turbo code, a uniform interleaver, and a partial response channel with additive white Gaussian noise will be addressed. The effect of a channel precoder on the system performance is also considered. Bit-and word-error rate estimates based upon properties of the average Euclidean distance spectrum of the coded partial response channel are derived. The estimates are compared to computer simulation results, and implications for system design are discussed.

The partial response channel can be viewed as a rate-1 encoder in which the output alphabet differs from the input alphabet. In serially concatenated coding schemes, the partial response channel can serve as the inner encoder. Recent work on the application of turbo decoding techniques to partial response channels has focused on using a parallel concatenation of convolutional encoders as the outer code and the partial response channel as the inner code. This system requires three a posteriori probability (APP) detectors-one matched to the channel and two matched to the constituent encoders. A simplified system will be presented that uses as its outer code a single convolutional code and as its inner code the partial response channel. The simplified system requires only two APP detectors, offering significant savings in complexity and computation time. This single convolutional code system will be shown to perform as well as the more complicated system, offering substantial gains over uncoded systems. Simulation results for three magnetic recording channel models will be presented: a partial response channel with additive white Gaussian noise, an equalized Lorentzian channel model, and a media noise model called the microtrack model. Since the use of an outer Reed-Solomon code is anticipated in an actual system, the burst-error statistics are investigated. System performance with various interleaver designs and precoders is also investigated. Index Terms-Concatenated coding, iterative methods, partial response signaling, turbo codes. I. INTRODUCTION T URBO codes were introduced by Berrou et al. [1] in 1993 as two or more parallel concatenated convolutional codes (PCCC's) connected with an interleaver and decoded using an iterative technique. These codes are capable of operating near Shannon capacity on an additive white Gaussian noise (AWGN) channel. The term "turbo decoding" has subsequently come to refer to this iterative decoding process. Therefore, in this paper, Paper approved by S. S. Pietrobon, the Editor for Coding Theory and Techniques of the IEEE Communications Society.

No abstract