Turbo Decoding for PR4: Parallel Versus Serial Concatenation

Recent work on the application of turbo decoding techniques to partial response class 4 (PR4) channels has focused on parallel concatenation systems that require three APP detectors. A simplified serial concatenation system will be presented that uses as its outer code a single convolutional code and as its inner code the partial response channel. An extension of this serial concatenation system will also be presented that combines a second code with the channel, forming a more powerful inner code. Both proposed systems require only two APP detectors, offering significant savings in complexity and computation time. These serial concatenation systems will be shown to perform as well as the more complicated parallel concatenation systems, offering substantial gains over uncoded systems. Additionally, the effect of precoding will be investigated. Simulation results comparing the parallel and serial concatenation systems will be presented.