RACH-less Handover UL Grant Configuration for Failure Detection
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Solution Overview
Problem
Current mobile communication systems lack a method for detecting failures during RACH-less handovers and an effective procedure for terminals to recover from such failures, leading to prolonged handover interruption times.
Innovation Solution
The proposed solution involves configuring a UL grant resource for the terminal with a start time, expiration time, and maximum number of transmissions, allowing the terminal to quickly detect handover failures and perform a fallback procedure, such as a RACH procedure or RRC connection re-establishment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If RACH-less handover is implemented to minimize handover interruption time, then handover speed is improved, but failure detection capability deteriorates due to lack of specific detection methods
Solution Approach 1:
The base station pre-configures UL grant resources with explicit parameters (start time, expiration time, maximum number of transmissions) before handover. This preliminary configuration enables the terminal to autonomously detect handover failures by monitoring whether transmissions succeed within the configured parameters, without requiring additional detection signaling.
Solution Approach 2:
The terminal provides feedback to the base station about handover execution status by attempting transmissions using the pre-configured UL grant resources. If transmissions fail within the configured time and retry limits, the terminal reports handover failure, enabling the base station to detect and respond to handover issues.
2Speed
If UL grant resources are pre-configured for RACH-less handover, then handover execution speed is improved, but resource utilization efficiency deteriorates due to potential resource waste when handover fails
Solution Approach 1:
UL grant resources are pre-configured with predetermined parameters (start time, expiration time, maximum transmissions) that define their valid usage window. This allows rapid handover execution while ensuring resources are automatically invalidated if not used within the configured parameters, preventing indefinite resource occupation.
Solution Approach 2:
The base station configures specific parameters for UL grant resources including start time, expiration time, and maximum number of transmissions. These parameter changes create time-bound and retry-limited resource allocations that automatically expire or become reusable if handover fails, optimizing resource utilization while maintaining fast handover execution.
3Ease of operation
If maximum number of transmissions is configured for UL grant, then transmission control is improved, but complexity of managing transmission limits deteriorates
Solution Approach 1:
The terminal autonomously manages transmission attempts using the configured maximum number of transmissions parameter. The terminal itself counts retry attempts and stops transmissions when the limit is reached, without requiring complex base station control or additional signaling for each retry, simplifying overall system management.
Solution Approach 2:
The maximum number of transmissions is pre-configured in the UL grant parameters before handover execution. This preliminary configuration provides simple transmission control rules that the terminal follows automatically, avoiding complex real-time decision-making and reducing management complexity.
Data Source
AI summary
A method of a terminal for a RACH-less handover may comprise: receiving, from a source cell, information on a UL grant for UL transmission in a target cell, the information on the UL grant including a start time and an expiration time of the UL grant and/or a maximum number of transmissions according to the UL grant; performing transmission of an RRC reconfiguration complete message using resources indicated by the UL grant from the start time, until the expiration time or until the transmission is completed up to the maximum number of transmissions from the start time; and in response to the transmission of the RRC reconfiguration complete message not being successful until the expiration time or until the transmission is completed up to the maximum number of transmissions, performing a fallback procedure for the RACH-less handover.