WTRU Handover Timer for Radio Link Failure Recovery
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Solution Overview
Problem
Long Term Evolution (LTE) wireless communication systems lack robust procedures for managing radio link interruptions and failures during handover processes, which can lead to connectivity issues due to factors like user equipment mobility and external interference.
Innovation Solution
Implementing a timer/counter scheme in wireless transmit/receive units (WTRU) to manage handover processes and radio link failures consistently, allowing for detection of interruptions and re-establishment of communications links through configured procedures, including the use of dedicated or random preambles for handover completion verification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If hard handover is used in LTE systems, then handover speed and system capacity are improved, but radio link failure risk increases during handover
Solution Approach 1:
The patent applies preliminary action by starting a handover timer immediately when the handover command is sent to the UE. This timer is configured in advance with an expected handover time value, allowing the system to proactively monitor whether the handover completes within the anticipated time frame, thereby detecting failures early before they propagate
Solution Approach 2:
The patent implements feedback mechanisms through multiple timers (handover timer, radio link failure timer, reestablishment timer) that continuously monitor the handover process and provide feedback signals. When timers expire or specific conditions are met, the system receives feedback about handover status and automatically triggers appropriate recovery procedures, creating a closed-loop control system that enhances reliability
2Reliability
If soft handover is used in CDMA systems, then radio link reliability is improved, but handover speed and system capacity are reduced
Solution Approach 1:
The patent applies dynamics by making the handover procedure adaptive through configurable timer values and multiple operational modes. The handover timer and other parameters can be dynamically adjusted based on network conditions, UE capabilities, and handover scenarios, allowing the system to optimize between speed and reliability depending on the situation rather than being fixed in one approach
3Device complexity
If handover procedure is simplified in LTE, then device complexity is reduced, but radio link failure management capability is weakened
Solution Approach 1:
The patent implements self-service by enabling the UE to autonomously detect handover failures through local timer monitoring and automatically initiate radio link failure recovery procedures without requiring complex network-side intervention. The UE independently manages the handover timer, detects expirations, and triggers reestablishment procedures, reducing the need for complex coordinated control while maintaining robust failure management
Data Source
AI summary
A wireless transmit/receive unit (WTRU) (152) in a wireless communications system includes a transceiver (153) for transmitting and receiving data from a plurality of base stations (154, 156, 357) and a controller (151) communicatively coupled to the transceiver (153) and configured to adjust an operation mode of the transceiver (153). In the WTRU (152), adjusting comprises configuring the transceiver (153) to begin a radio link handover procedure responsive to receiving a handover (HO) command from a first of the plurality of base stations (154, 156, 357) over a first communications link, specifying a first time, and reconfiguring the transceiver (153) to begin a radio link interruption procedure responsive to an expiry of the first time prior to completion of the radio link handover procedure. In the WTRU (152), the radio link interruption procedure first attempts to re-establish the first communications link.