Abstract-This paper investigates the connection between the classical Sum-Product (SP) decoder for Low Density Parity Check (LDPC) codes and the recently proposed Gradient Projection (GP) decoding scheme presented in [1]. A graphical model for GP is exhibited based on which we derive an intermediate algorithm which establishes a bridge between graphical based algorithms (SP and variants) and an optimization based algorithm (GP). A more practical decoding algorithm with improved performance and reduced complexity is also proposed. A complexity analysis is provided and performance are studied through Monte-Carlo simulations
