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complexity but it may also be used for filling in coverage holes. In non-transparent relay the UE is aware
that it is communicating with the eNB via a RN. All of the data traffic and control signal transmission
between eNB and UE are forwarded along the same relay path. Although non-transparent relaying is
applicable for almost all cases, wherever the UE is, within the coverage of eNB or coverage holes, it may
not be an efficient way for all scenarios, because both the data and control signaling are conveyed
multiple times over the relay links and the access link of a relay path.
Depending on the relaying strategy, a relay may be part of the donor cell or it may control cells of its own.
In the case where the relay is part of the donor cell, the relay does not have a cell identity of its own. At
least part of the RRM is controlled by the eNodeB to which the donor cell belongs, while other parts of the
RRM may be located in the relay. In this case, a relay should preferably support LTE Rel-8 UEs, as well
as LTE Rel-10 UEs. Smart repeaters, Decode-and-Forward Relays and different types of L2 Relays are
examples of this type of relaying.
In the case where the relay is in control of cells of its own, the relay controls one or several cells and a
unique physical-layer cell identity is provided in each of the cells controlled by the relay. The same RRM
mechanisms are available and from a UE perspective there is no difference in accessing cells controlled
by a relay and cells controlled by a “normal” eNodeB. The cells controlled by the relay should also
support LTE Rel-8 UEs. Self-Backhauling (L3 Relay) uses this type of relaying.
The following describes the different types of relays have been defined in 3GPP 116 , but it should be noted
that not all types of relays have been adopted in the Rel-10 standards specifications:
A so called “Type 1” relay node is an in-band relaying node characterized by the following:
� It controls cells, each of which appears to a UE as a separate cell distinct from the donor cell
� Each cell shall have its own Physical Cell ID (defined in LTE Rel-8) and the relay node shall
transmit its own synchronization channels, reference symbols, etc.
� In the context of single-cell operation, the UE will receive scheduling information and HARQ
feedback directly from the relay node and send its control channels (SR/CQI/ACK) to the relay
node
� It appears as a Rel-8 eNodeB to Rel-8 UEs (i.e. it will be backwards compatible)
� To LTE-Advanced UEs, it should be possible for a Type 1 relay node to appear differently than a
Rel-8 eNodeB to allow for further performance enhancement
It can be understood from these characteristics that a Type 1 relay is a L3 relay.
A “Type 1a” and “Type 1b” relay nodes are Type 1 relays with the following exceptions:
� A Type 1a relay node operates out of band; that is the band for the Un and UU links are on
different bands
� A Type 1b relay nodes is a full duplex Type 1 relay node
A so-called “Type 2” relay node has also been proposed. A Type 2 relay is an in-band relay node
characterized by the following:
116 3GPP TR 36.814, Further advancements for E-UTRA physical layer aspects, 2010.
www.4gamericas.org February 2011 Page 57