LTE Advanced: 3GPP Solution for IMT-Advanced

9.3 Physical Layer

When relay standardization work started, 3GPP collected first requirements with relevant simulation assumptions in [1]. Subsequently the physical layer functionality was specified in [4]. This functionality will be explained in the rest of this chapter.

9.3.1 Inband and Outband Relays

There are different options how to share the capacity between access link and backhaul link. The relay node needs to operate on four different unidirectional links: Both uplink and downlink with both UE and donor eNodeB. The inband relay uses the same frequency band for the access and the backhaul link while the outband relay uses different frequencies. The access and the backhaul links are separated in the time domain in case of inband relays. The difference between inband and outband relays is illustrated in Figure 9.3.

Figure 9.3 Principles of inband and outband relays.

The frequency usage is shown in Figure 9.4. In case of inband relays, both backhaul and access link share the same frequency while outband relays use different frequencies for these links. Inband relays are more efficient from the spectrum usage point of view because both access and backhaul links are sharing the same spectrum. On the other hand, outband relays provide more capacity since the backhaul link does not eat from the access link capacity, at the expense of requiring more spectrum.

Figure 9.4 Frequency ...