Optimizing handover performance in LTE networks containing relays

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Master's thesis
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[9] + 79
The purpose of relays in Long Term Evolution (LTE) networks is to provide coverage extension and higher bitrates for cell edge users. Similar to any other new nodes in the network, relays bring new challenges. One of these challenges concerns mobility. More specifically, back and forth data transmission between the Donor Evolved NodeB (DeNB) and the Relay (RN) during the handover can occur. For the services that are sensitive to packet loss, receiving all the packets at the destination is crucial. In cellular networks when the User Equipment (UE) detaches from the old cell and attaches to the new cell, it faces a short disruption. In the disruption time when the UE is not connected to anywhere, packets can be easily lost. To avoid the consequences of these packet losses, the data forwarding concept was developed and the lost packets in handover were identified and forwarded to the destination. The forwarded packets would be transmitted to the UE as it becomes attached to the new cell. In the networks using the relays all the packets should still transfer via the DeNB. If the UE is connected to the RN and is handed over to a new cell, the unacknowledged packets between the RN and the UE which are still in the RN buffer should be transmitted back to the DeNB and onwards to the target afterwards. Furthermore, the ongoing packets in S1 interface are transmitted through the old path until the path switch occurs. This data transfer from the DeNB to the RN and again back to the DeNB increases the latency and occupies the resources in the Un interface. In this thesis work the problem of back and forth forwarding is studied. Different solutions to overcome this challenge are proposed and simulations are performed to evaluate the proposals. The evaluated approaches showed up to considerable performance enhancement compared to the previous solutions.
Hämäläinen, Jyri
Thesis advisor
Susitaival, Riikka
LTE, handover, relay, data forwarding
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