The Relay Node supports the eNB functionality meaning it terminates the radio protocols of the E-UTRA radio interface, and the S1 and X2 interfaces. In addition to the eNB functionality, the RN also supports a subset of the UE functionality, e.g. physical layer, layer-2, RRC, and NAS functionality, in order to wirelessly connect to the DeNB.
With respect to the relay node’s usage of spectrum, its operation can be divided into inband and outband types. For both inband and outband relaying, it is possible to operate the eNB-to-relay link on the same carrier frequency as eNB-to-UE links. 3GPP Release 8, UEs can connect to the donor cell in both cases.
At least "Type 1" and “Type 1a” RNs are supported by LTE-Advanced. A "Type 1" RN is an inband RN characterized, A Type 1a relay node is characterized by the same set of features as the Type 1 relay node, except “Type 1a” operates outband.
