  In this work, we investigate the minimum energy of transmitting correlated
sources over the Gaussian multiple-access channel (MAC). Compared to other
works on joint source-channel coding, we consider the general scenario where
the source and channel bandwidths are not naturally matched. In particular, we
proposed the use of hybrid digital-analog coding over to improve the
transmission energy efficiency. Different models of correlated sources are
studied. We first consider lossless transmission of binary sources over the
MAC. We then treat lossy transmission of Gaussian sources over the Gaussian
MAC, including CEO sources and multiterminal sources. In all cases, we show
that hybrid transmission achieves the best known energy efficiency.
