Factor graph based CRSC turbo code and iterative receiver design

Iterative receiver is poised to become the most prevalent receiver technology in near future. The paper explains the designing methodology of iterative receiver from graph theoretic approach. Modeling of well known turbo convolution code in factor graph framework with Sum-Product-Algorithm (SPA) has been discussed here. The model shows simpler representation of complex encoder trellis. Exchange of extrinsic information has been taken care of by SPA. The preset article attempts to show that various signal processing tasks in the receiver can be cast in a single graphical framework which is based on factor graph. Double-binary Circular Recursive Systematic Convolutional (CRSC) code as component encoder and bi-directional Soft Output Viterbi Algorithm (SOVA) as decoding algorithm have been selected for simulation of turbo code. This code has been adopted in DVB-RCS standard. Simulation results have been presented and the BER performance of the codec over AWGN channel has been evaluated in this paper.