RACH-Less L1/L2 Mobility Handover for Low-Latency Cell Switching
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Solution Overview
Problem
Handover latency and user plane interruption time are increased due to the need for contention-based random access channel procedures in cellular networks, particularly in 5G wireless communication systems.
Innovation Solution
Prioritize RACH-less Layer 1/Layer 2 triggered mobility (LTM) handovers by identifying suitable target cells with matching timing advance or zero timing advance, allowing for contention-free handovers, thereby reducing handover latency and user plane interruption time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If contention-based random access channel procedures are used for handover, then handover reliability is improved, but handover latency and user plane interruption time increase
Solution Approach 1:
The patent extracts and removes the random access channel (RACH) procedure from the handover process by implementing RACH-less handover. This eliminates the contention-based access steps that cause latency while maintaining handover reliability through alternative mechanisms such as dedicated resources and pre-synchronized timing advance values.
Solution Approach 2:
The patent applies preliminary action by pre-configuring timing advance (TA) values and dedicated resources for target cells before handover occurs. The serving base station receives RACH-less handover configurations and TA information in advance, allowing the UE to perform seamless handover without contention-based random access procedures.
2Reliability
If contention-based random access channel procedures are used for handover, then channel access reliability is improved, but user plane interruption time increases
Solution Approach 1:
The patent removes the contention-based RACH procedure from the handover process, eliminating the source of user plane interruption. By using RACH-less handover with pre-configured dedicated resources, the user plane can maintain continuity without the delays associated with random access channel contention.
Solution Approach 2:
The patent enables continuous user plane action during handover by establishing dedicated resources and pre-synchronized timing advance values before the handover occurs. This allows the user plane data flow to continue uninterrupted while the control plane performs the handover signaling.
3Speed
If RACH-less Layer 1/Layer 2 triggered mobility handovers are prioritized, then handover speed is improved, but device complexity increases
Solution Approach 1:
The patent implements a universal handover mechanism that can operate in both RACH-based and RACH-less modes depending on configuration. The base station and UE are designed to support multiple handover types, allowing the system to select the optimal mode (RACH-less for speed, RACH-based for reliability) based on current conditions, thereby managing complexity through flexibility.
Data Source
AI summary
In general, the current subject matter relates to prioritizing random access channel layer-less (RACH-less) layer 1/layer 2 triggered mobility (LTM). In some implementations, prioritizing RACH-less LTM can include receiving, at a serving distributed unit (DU) of a base station from a centralized unit control plane of the base station, information indicative of a RACH-less handover configuration for a plurality of LTM target cells of the base station or timing advance information for each of the plurality of LTM target cells; identifying, at the serving DU and based on the received information, at least one of the target cells for which RACH-less handover of service for a user equipment (UE) can be performed; and selecting, at the serving DU, one of the at least one identified target cells for handover of service for the UE from the serving DU, and triggering the handover of the service to the selected target cell.