  A new communication scheme for Gaussian parallel relay networks based on
superposition coding and partial decoding at the relays is presented. Some
specific examples are proposed in which two codebook layers are superimposed.
The first level codebook is constructed with symbols from a binary or ternary
alphabet while the second level codebook is composed of codewords chosen with
Gaussian symbols. The new communication scheme is a generalization of
decode-and-forward, amplify-and-forward, and bursty-amplify-and-forward. The
asymptotic low SNR regime is studied using achievable rates and minimum
energy-per-bit as performance metrics. It is shown that the new scheme
outperforms all previously known schemes for some channels and parameter
ranges.
