Soft symbol estimation and forward scheme for cooperative relaying

Relay transmission technique can be utilized to increase coverage or enhance throughput for conventional cellular communication systems. There are two typical relaying schemes, Amplify-and-Forward (AF) and Decode-and-Forward (DF). This paper presents a new scheme named Soft symbol Estimation and Forward (SEF), which holds the advantages of both AF and DF, i.e. keeping soft information and obtaining decoding gain. This scheme has similar operations as DF except that the operations are performed in a soft-input-soft-output (SISO) fashion. The relay performs SISO decoding, SISO re-encoding and then the key point soft symbol estimation, which is derived based on Maximum Likelihood (ML) criteria. Simulation results prove that the proposed SEF scheme much outperforms both AF and DF.