An LDPC Coded Adaptive Decode-and-Forward Scheme Based on the EESM Model

User Cooperation is a promising technology to obtain diversity gain at terminals. According to the traditional decode-and-forward scheme, relay node help to transmit source node´s information with fixed number of modulation symbols all the time. It is not optimal in view of spectral efficiency, especially when the channel state is good. This paper introduces the adaptive DF scheme based on the minus exponential effective-SNR mapping (EESM) model. The optimal number to relay is predicted accurately. Furthermore, adaptive modulation is supported. The reliability requirement is satisfied, and the radio resource is saved for transmitting new information. Theoretical analysis and simulation results indicate that the adaptive DF scheme improves the spectral efficiency significantly.