A study on relaying soft information with error prone relays

Cooperative communication is an effective way of achieving spatial diversity when it is impossible to employ multiple antennas. Recently, a new relaying technique, so called Soft Decode and Forward, has been proposed, which aims to combine the benefits of conventional relaying techniques, i.e. "Decode and Forward" and "Amplify and Forward", and to mitigate the shortcomings of those conventional methods. We study the error performance of two cooperative scenarios employing soft-DF. We propose a novel approach to estimate the bit-error probability and the equivalent channel SNR for relaying techniques of consideration in the paper that employ the BCJR-algorithm for decoding. We also consider the mutual information loss due to applying different encoders at the relay.