LTE Advanced: 3GPP Solution for IMT-Advanced

9.7 Relay Enhancements

3GPP Release 11 is working on enhancing the relay functionality with moving relays. An example use case would be trains. High speed trains are currently deployed worldwide and providing the required services to the massive number of UEs that are moving with the train can be challenging. The carriages are well shielded with coated windows and therefore introduce a rather high penetration loss in the range of 20–30 dB. The high speed generates a Doppler frequency shift that causes frequency and channel estimation errors. Furthermore, the handover success rate of the connected UEs is lower compared to UEs moving with lower speed because of inaccurate or late neighbour cell measurements and excessive signalling; furthermore, frequent cell reselections drain UE batteries.

Mobile relays have gained attention recently as they are foreseen as a solution to combat issues that affect the UEs on board of the high speed trains [29], see Figure 9.26. A mobile relay is a base station/access point mounted in a moving vehicle that provides wireless connectivity service to end users inside the vehicle via an indoor antenna. The wireless backhauling connection to on-land network is provided via an outdoor antenna. The work item for mobile relays is beyond Release 11.

Figure 9.26 Mobile relay mounted on a train.

One potential enhancement is the capability to allow different ...