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 a posteriori (APP) detectors. A simplified serial concatenation system is 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 is also 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 are shown to perform as well as the more complicated parallel concatenation systems, offering substantial gains over uncoded systems. Additionally, the effect of precoding is investigated. Simulation results comparing the parallel and serial concatenation systems are also presented.