LTE-advanced relaying for outdoor range extension

Future cellular wireless networks based on MIMO-OFDM enable high data rates in outdoor scenarios. Limitations in coverage, especially at cell-edge, might be overcome by transmission over relays, which is therefore widely discussed for LTE-advanced networks. Here, a multi-hop relay node is placed at the cell-edge or in a coverage hole in order to compensate for the penetration path loss caused by buildings. Relay nodes can be deployed in two modes, either as amplify and forward or as decode and forward relay. The later system may benefit from independent link adaptation which is a key concept especially under fading conditions in outdoor broadband wireless. This paper reports on first multi-hop relaying field trials in the LTE downlink. These field trials were carried out in a single-cell, single sector urban outdoor environment within the Berlin LTE-advanced testbed. Results show that outdoor relaying is a key concept to deliver high data rates to the cell edge. Furthermore, results show that rates above 60 Mbps are achievable and outdoor relaying yields for a 300 m range extension. In addition, results show that multi-hop relaying provides cell-edge users with a minimum data rate of at least 20 Mbps which is mandatory, especially if QoS constraints have to be met.