Distributed video coding (DVC) is a new coding paradigm targeting applications with the need for low-complexity encoding at the cost of a higher decoding complexity. In the DVC architecture based on a feedback channel, the high decoding complexity is mainly due to the request-decode operation with repetitively fixed step size (induced by Slepian-Wolf decoding). In this paper, a parallel message-passing decoding algorithm for low density parity check (LDPC) syndrome is applied through Compute Unified Device Architecture (CUDA) based on General-Purpose Graphics Processing Unit (GPGPU). Furthermore, we propose an approach to reduce the number of requests dubbed as Ladder Request Step Size (LRSS) which leads to more speedup gain. Experimental results show that, through our work, significant speedup in decoding time is achieved with negligible loss in rate-distortion (RD) performance.