Spectrally-Efficient Wireless Relaying Based on Superposition Coding

The wireless relay systems represent an important segment in the wireless communication systems. In a simple wireless relay scenario, a source node A
_S
needs to communicate to a destination A
_D
, with the help of a relay A
_R
. In this paper we introduce a new two-step relaying scheme based on superposition coding, SC-relaying. In step 1, A
_S
broadcasts a message, created by superposition coding, to A
_R
and A
_D
. After decoding the information from A
_S
, A
_R
relays a part of this message in step 2, by adapting the transmission rate with respect to the link quality towards A
_D
. The unique point of the proposed scheme is that the signal format in the two steps is chosen in a way that enables a simple combining at A
_D
. The numerical results show that the proposed scheme can bring a notable gain in spectral efficiency over the conventional multi-hop transmission with adaptive modulation, even in the case when the instantaneous SNR about all the links is not fully known at the source. In addition, the proposed scheme performs very closely to the scheme that is optimal in an information-theoretic sense.