RACH-less Inter-cell Mobility via Target Reference Signal Indexing
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Solution Overview
Problem
Current RACH-less handover operations for L1/2 inter-cell mobility in 5G networks face challenges in efficiently obtaining UL grants and accurately setting initial UL transmit power, leading to potential fallbacks to random access procedures and inefficient radio resource reservation.
Innovation Solution
The proposed solution involves the serving distributed unit informing the target distributed unit via a central unit about specific target reference signal indices for PDCCH transmission or PUSCH reception, allowing synchronized QCL information and delayed radio resource reservation until the cell change is triggered, thereby optimizing UL grants and reducing resource overbooking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If radio resources are reserved in advance for RACH-less handover, then handover preparation is simplified, but resource wastage occurs when handover is not triggered
Solution Approach 1:
The target gNB configures PDCCH monitoring parameters and prepares UL grants in advance during handover preparation phase, but actually activates these resources only when handover is triggered. This preliminary configuration enables fast handover execution while avoiding premature resource allocation that would cause wastage.
Solution Approach 2:
The system dynamically activates or deactivates PDCCH monitoring and UL grant resources based on handover trigger conditions. When handover is not triggered, the target gNB releases the configured resources; when triggered, the resources are activated immediately, optimizing resource utilization flexibility.
2Loss of time
If PDCCH is transmitted immediately upon handover trigger, then handover latency is reduced, but UL grant timing may not be optimized
Solution Approach 1:
The target gNB pre-configures PDCCH transmission parameters and UL grant settings before handover execution. When handover is triggered, the gNB can immediately transmit PDCCH using pre-prepared configurations, reducing latency while maintaining optimal timing through advance resource preparation.
Solution Approach 2:
The serving gNB provides feedback information including measurement results and handover decisions to the target gNB. This feedback mechanism enables the target gNB to optimize PDCCH transmission timing and UL grant allocation based on actual handover conditions while maintaining low latency.
3Reliability
If target gNB monitors PDCCH continuously, then PDCCH reception reliability is improved, but power consumption increases
Solution Approach 1:
Instead of continuous monitoring, the UE monitors PDCCH periodically based on configured parameters such as monitoring periodicity and activation conditions. The target gNB configures periodic PDCCH monitoring intervals that balance reliability requirements with power consumption constraints.
Solution Approach 2:
The PDCCH monitoring activity is dynamically adjusted based on handover state. When handover is triggered, monitoring is activated with optimized periodicity; when not triggered, monitoring is suspended or reduced to minimal levels, optimizing the balance between reliability and power consumption.
Data Source
AI summary
In this invention, when a serving distributed unit informs target distributed unit via a central unit about a target reference, it is proposed to use, signal index X/indices X1 . . . Xn for PDCCH transmissions or PUSCH receptions or a RACH-less handover:Send by a distributed unit of the serving cell towards a distributed unit of a target cell one of before, upon, or after transmission of a layer 1 serving cell change command to a user equipment, signaling comprising configuration information associated with the user equipment to perform a random access channel less handover of the user equipment to the target cell, wherein the configuration information informs the target cell about at least one target reference signal index that shall be used for at least one of at least one physical downlink control channel transmission or at least one physical uplink shared channel reception.