Product code and recurrent alternative decoding for wireless image transmission
Summary form only given. We have developed a novel channel coding scheme for image transmission over wireless channels. A key component of this scheme is the construction of the product code using a convolutional code and a recursive systematic code (RSC) in the horizontal and vertical directions, respectively. High performance transmission has been achieved through an innovative recurrent alternative decoding scheme based on constrained Viterbi decoding. We used RSC because of its systematic structure so that we did not need to transmit the original data portion of the RSC coding outcome since this portion can be obtained from the other direction of channel decoding. At the receiving end, the data will at first be decoded along the horizontal direction. After decoding, the position of a correctly decoded row will be assigned a positive sign and be preserved. When we decode along the vertical direction, the positive signs after horizontal decoding will be used as constraints in the Viterbi decoding algorithm to force the survival path's passing through these known positions of correctly decoded bits. The constrained Viterbi algorithm using known correct bits enables us to derive likely correct values for other bits. This reduces greatly possible paths along the trellis diagram even though some or the paths dropped may have smaller path cost due to channel noise corruption and would otherwise be preserved by the unconstrained Viterbi algorithm. Moreover, this also reduces significantly the comparisons between the branches and the received symbols. Similarly the use of the correctly localized columns are also preserved and used again to refine the next round of horizontal decoding. Such recurrent decoding will alternate between horizontal and vertical directions until all data is correctly decoded or until there is no more improvement in both directions. We investigated the performance of the proposed scheme for both BSC and GEC channels and report the results here.