UE Handover Recovery Using Rejection Feedback
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Solution Overview
Problem
In LTE wireless communication systems, handover performance is hindered by delayed and failed handover procedures due to radio link failures, particularly when handover requests are rejected by target radio base stations due to lack of resources, leading to increased handover delay and user dissatisfaction.
Innovation Solution
The user equipment (UE) is informed of handover request rejections by the target radio base station, allowing it to select a recovery cell based on this information during radio link failure recovery, thereby reducing the likelihood of selecting resource-constrained cells and minimizing handover delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the UE selects a recovery cell based on standard procedures without handover rejection information, then the cell selection process is simple, but the handover delay increases and handover failure rate increases
Solution Approach 1:
The source eNB performs preliminary action by determining handover rejection information before the UE attempts recovery, and transmits this information to the UE in advance via RRC connection reestablishment message. This allows the UE to use the rejection information during cell selection without adding complex real-time processing, thereby reducing handover delay while maintaining manageable complexity.
Solution Approach 2:
The invention implements feedback by providing handover rejection information from the source eNB to the UE, enabling the UE to make informed cell selection decisions. The UE uses this feedback to avoid selecting target cells that have previously rejected handover requests, thus reducing handover failures and delays without significantly increasing system complexity.
2Reliability
If the UE attempts to recover to the originally selected target cell without rejection information, then the recovery procedure is straightforward, but the likelihood of selecting resource-constrained cells increases
Solution Approach 1:
The source eNB provides feedback information about handover rejections to the UE, enabling the UE to avoid selecting cells that have insufficient resources. This feedback mechanism improves handover success rate by preventing repeated attempts to resource-constrained cells while adding minimal complexity to the recovery procedure.
Solution Approach 2:
The UE autonomously uses the received handover rejection information to make intelligent cell selection decisions during recovery. By self-serving with this information, the UE can avoid resource-constrained cells without requiring complex network coordination, thereby improving reliability while keeping the procedure relatively simple.
3Reliability
If handover requests are transmitted without considering target cell resource availability, then the handover procedure is fast, but handover failures occur due to resource constraints
Solution Approach 1:
The source eNB performs preliminary assessment of target cell resource availability and determines handover rejection information before the UE initiates recovery. This preliminary action allows the network to proactively identify resource-constrained cells, improving handover success rate by guiding UE away from such cells without causing significant delay.
Solution Approach 2:
The invention implements feedback by transmitting handover rejection information from the source eNB to the UE, enabling the UE to make informed decisions about cell selection. This feedback improves handover reliability by preventing attempts to resource-constrained cells while minimizing the time penalty through efficient information transmission.
Data Source
AI summary
The present invention relates to methods and arrangements in a UE and a RBSin a wireless communications system, enabling an efficient handover of the user equipment. The method comprises transmitting (810) a message to the serving radio base station, the message indicating the need for a handover to a cell of a target radio base station. It also comprises observing (820) an indication that a handover request transmitted by the serving radio base station is rejected by the target radio base station, and selecting (830) a recovery cell based on the observed indication when detecting a radio link failure.