LTE: What does mean by relay node in lte network ?

Question

How RN works for lte Uu interface. Can someone please put some light on this topic ?

Answer 1

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.

The donor eNB (DeNB) is enhanced to provide S1 and X2 proxy functionality between the RN and other network nodes (other eNBs, MMEs and S-GWs). The S1 and X2 proxy functionality includes passing UE-dedicated S1 and X2 signalling messages as well as GTP data packets between the S1 and X2 interfaces associated with the RN and the S1 and X2 interfaces associated with other network nodes. Due to the proxy functionality, the DeNB appears as an MME (for S1-MME), an eNB (for X2) and an S-GW (for S1-U) to the RN.

Comments

The Relays just contain L1 and L2 of the eNodeB , not the complete LTE eNodeB stack.

-> Layer 3 (RRC) is terminated in Relay Node for the (Relay Node UE)   interface.
-> L1/L2 signaling (CQI, HARQ, etc) is performed between Relay Node and UE.
-> Relay Node has their own PCI (physical cell identity).
There are two different types of Relay's.

    Type-1 (Non-Transparency)
    Type-2 (Transparency)



Type-I relay will help the UE to access the eNodeB that are far from the coverage of the eNodeB. So the Type–I relay will transmit the common reference signal and the control information for the eNB and will help the eNodeB in extending the signals and service coverage area. Type-I Relay mainly perform IP packet forwarding in the (layer 3) and can make some contributions to the overall system capacity by enabling communication services and data transmissions for remote UE units.

Type-II Relay can help a local UE unit, which is located within the coverage of an eNB and has a direct communication link with the eNB, to improve its service quality and link capacity. So a Type-II RS does not transmit the common reference signal or the control information, and its main objective is to increase the overall system capacity by achieving multipath diversity and transmission gains for local UE unit
Increase the throughput

Answer 2

In the LTE Advanced Relaying function, an eNodeB can ‘relay’ data to a secondary eNodeB (called the
Relay Node RN) that is providing coverage to an area within the coverage of the base eNodeB. Using
this technology, the coverage can be extended close to the cell edge without the need for additional
backhaul links or infrastructure. The eNodeB will be able to relay a data stream across from it’s own
backhaul link across to the Relay Node and hence allow a UE to connect to the Relay Node. The Relay
Node will therefore be able to extend the coverage of the base eNodeB without the need for
additional backhaul infrastructure. The Relay Node will appear as a normal eNodeB to the UE and the
Relay Node will provide all Scheduling and HARQ functions.