RRC Handover Preparation for Category 0 UE in LTE
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Solution Overview
Problem
In 3GPP LTE networks, category 0 user equipment experiences handover failures and radio link failures when transferred to legacy base stations that do not support the new RRC protocol, leading to unnecessary signaling and reduced battery life due to non-compatibility issues.
Innovation Solution
A new branch of the handover preparation information message is introduced in the RRC protocol specifically for category 0 UEs, allowing the source network node to interpret handover failures as non-support by the target node, thereby avoiding further handover attempts to incompatible legacy eNBs and releasing the UE to idle mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If handover preparation is performed using legacy RRC protocol messages, then compatibility with legacy eNBs is maintained, but handover failures occur for category 0 UEs due to protocol non-compatibility
Solution Approach 1:
The handover preparation information message is segmented into two distinct branches: a legacy branch for compatibility with existing eNBs and a new branch specifically for category 0 UEs. This segmentation allows the system to maintain backward compatibility while simultaneously supporting the new UE category without interference
Solution Approach 2:
The solution adds a new dimension to the handover preparation message structure by introducing an additional branch rather than modifying the existing legacy structure. This dimensional addition allows category 0 specific information to be transmitted without disrupting legacy protocol operations
2Productivity
If the source eNB attempts handover to a legacy target eNB that does not support category 0 UEs, then handover preparation is initiated, but the handover fails causing radio link failure and unnecessary signaling
Solution Approach 1:
The solution performs preliminary action by including category 0 capability indication in the handover preparation request message before the actual handover execution. This allows the target eNB to pre-assess compatibility and reject incompatible handovers early, preventing subsequent handover failures and the energy-consuming re-establishment procedures
Solution Approach 2:
The system implements feedback mechanism where the target eNB's response to the handover preparation request (success or failure) provides information back to the source eNB. The source eNB uses this feedback to interpret target eNB capability and avoid future handover attempts to incompatible nodes, thereby preventing unnecessary energy consumption
3Reliability
If the source eNB interprets handover preparation failure as target eNB non-support for category 0 UEs, then further handover attempts to incompatible nodes are avoided, but this requires enhanced interpretation logic
Solution Approach 1:
The solution uses message structure changes (analogous to color changes) by introducing distinct branches in the handover preparation information message. The presence or absence of the new branch clearly indicates category 0 support capability, providing an intuitive and easily interpretable signal to the target eNB without requiring complex interpretation logic
Data Source
AI summary
A method in a first network node for handover preparation of a user equipment of a first category in a wireless communications network. The handover preparation is performed between a first cell served by the first network node and a second cell served by a second network node comprised in the wireless communications network. The first network node sends (301) to the second network node a message comprising information indicating a request for preparation of a handover of the user equipment. The request is specific for user equipment of the first category.The first network node receives (302) from the second network node a message indicating failure to prepare the handover.The first network node interprets (303) the message indicating failure to prepare the handover as an indication that the second network node does not support any user equipment of the first category.