Cross-Carrier PRACH Triggering Using DCI for Low-Latency Mobility
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Solution Overview
Problem
Current wireless communications systems face challenges in efficiently triggering physical random access channel (PRACH) transmissions due to reliance on higher layer signaling with high latency or physical downlink control channels that do not support cross-carrier triggering, particularly during cell changes requiring timing adjustments.
Innovation Solution
Implementing downlink control information (DCI) for cross-carrier PRACH triggering, allowing UE to transmit PRACH in a candidate cell, reducing latency and enabling layer 1 and layer 2 based mobility.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If higher layer signaling is used for PRACH triggering, then the system maintains simplicity in control channel design, but the triggering latency becomes excessively high
Solution Approach 1:
The patent introduces DCI as an intermediary mechanism that bridges the gap between higher layer signaling and physical layer PRACH transmission. The DCI format 1_0 with specific field configurations acts as a mediator that carries PRACH triggering information efficiently without requiring complex dedicated control channels, thus reducing latency while maintaining relatively simple system structure
Solution Approach 2:
The patent changes the parameter configuration of existing DCI format 1_0 by selectively enabling or disabling specific fields (such as frequency domain resource assignment, time domain resource assignment, and hopping parameters) depending on the PRACH triggering scenario. This allows the same DCI structure to serve multiple functions without increasing overall system complexity
2Loss of time
If physical downlink control channel is used for PRACH triggering, then the triggering speed improves, but cross-carrier triggering capability is lost
Solution Approach 1:
The patent makes DCI format 1_0 a universal control message that can trigger PRACH on both serving cell and candidate cell carriers. By configuring the DCI to include carrier indication fields and making the frequency domain resource assignment field optional, the same DCI structure can adapt to different carrier scenarios, providing cross-carrier triggering capability while maintaining fast physical layer triggering speed
3Productivity
If cross-carrier PRACH triggering is implemented, then mobility efficiency improves, but the complexity of cell configuration and management increases
Solution Approach 1:
The patent performs preliminary configuration of candidate cells and their associated PRACH resources before mobility events occur. The network pre-configures the UE with a list of candidate cells and their parameters, so that when PRACH triggering is needed, the UE can immediately use the pre-configured information without complex real-time configuration exchanges, thus improving mobility efficiency while managing complexity through advance preparation
Data Source
AI summary
Certain aspects of the present disclosure provide a method of wireless communication by a user equipment (UE), generally including receiving signaling configuring the UE with a set of candidate cells, receiving, from a serving cell, downlink control information (DCI) indicating one candidate cell of the set of candidate cells as a target cell for transmitting a physical random access channel (PRACH), and transmitting the PRACH in the target cell.