30.1.1 What is Relaying?
Relays are a key new feature of LTE-Advanced, introduced in Release 10 of the LTE specifications. These additional network nodes are designed to complement a macro-cellular network of regular eNodeBs with reduced cost, by expanding coverage or increasing capacity.
Early relays, in the form of repeaters, are already present in legacy radio interface technologies such as UMTS and Release 8 of LTE [1, 2]. Repeaters simply amplify the radio-frequency signal received from a macro base station. Compared to a base station, repeaters have a lower cost since they involve no baseband processing, backhaul network installation or subscription fee for access to the fixed public network. They are typically used to improve coverage in zones where the traffic is too light to justify the deployment of a base station, or where there is no easy backhaul network access, such as road segments in rural areas. Repeaters are also convenient for the provision of indoor coverage (e.g. in shopping malls). In the majority of cases, repeaters are deployed by network operators, but user-deployed low-power repeaters are also now available (e.g. to cover a shop or flat).
Although useful, repeaters exhibit two significant drawbacks:
- Since a repeater only amplifies the received signal, any received interference is also amplified. The signal quality in the zone ...