Radio Protocols for LTE and LTE-Advanced

Chapter 13

Relay

Relay is the technology that relays radio transmissions between the eNB and the UE in a wireless manner. It is regarded as one of the key technologies introduced in LTE Release 10, and is realized by an additional network node called the Relay Node (RN) located between the eNB and the UE. By using the Relay Node, operators can improve cell coverage and throughput in various types of locations with relatively low CAPital EXpenditure (CAPEX) and OPerating EXpenditure (OPEX).

13.1 Deployment Scenarios

Deploying an eNB in every location is not cost effective and sometimes not easy, in that it requires fixed and wired backhaul. During the study of relay technology, various scenarios were identified where relay deployment was deemed much more useful than normal eNB deployment [1]. The identified scenarios are summarized below:

• Coverage extension: An RN can be deployed at a cell edge to extend the coverage of the eNB. A typical deployment would be at a cell edge in a rural area where the population is sparse.
• Dead spot mitigation: An RN can be deployed in a dead spot to remove a coverage hole from the cell. A coverage hole is usually caused by physical obstructions such as buildings, tunnels, and so on.
• Throughput enhancement: An RN can be deployed in a hot spot or indoor area to increase the throughput in that particular area.
• Temporary coverage: An RN can be deployed in an area hosting special events (e.g., sports games, music concerts) or experiencing natural disasters ...