Candidate Cell RACH for Faster L1/L2 Mobility Handover
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Solution Overview
Problem
Conventional wireless communication networks face challenges in mobility procedures, particularly at layer 3 (L3), which result in communication interruptions and increased latency due to the need for RRC connection establishment during handovers, while layer 1 (L1)/layer 2 (L2) mobility offers less flexibility in message transmission.
Innovation Solution
Implementing random access channel (RACH) transmission in candidate cells for L1/L2 mobility, allowing user equipment (UE) to identify and transmit PRACH messages to initiate L1/L2 mobility procedures based on synchronization signal blocks, enhancing flexibility and reducing signaling overhead.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If layer 3 (RRC) mobility procedure is used, then connection establishment is ensured, but communication interruption and latency increase
Solution Approach 1:
The mobility procedure is segmented into two independent parts: (1) L3 RRC connection establishment for reliability, and (2) L1/L2 random access channel transmission for fast handover initiation. This segmentation allows both reliability and speed to be achieved simultaneously by performing L1/L2 mobility procedures in parallel with L3 connection establishment.
Solution Approach 2:
The UE performs L1/L2 mobility procedures (transmitting PRACH messages, receiving handover commands) before the L3 RRC connection is fully established. This preliminary action enables the network to prepare resources and execute handover faster once the RRC connection is established, reducing overall latency.
2Speed
If layer 1/layer 2 mobility procedure is used, then handover speed is improved, but message transmission flexibility is reduced
Solution Approach 1:
The random access channel (RACH) is configured to serve multiple functions: (1) transmitting mobility control messages for L1/L2 handover, (2) maintaining compatibility with existing L3 RRC procedures, and (3) supporting both intra-frequency and inter-frequency scenarios. This multi-functionality provides flexibility while maintaining speed.
Solution Approach 2:
The RACH acts as an intermediary channel that bridges L1/L2 fast handover requirements with L3 connection management. It enables the UE to transmit mobility messages and receive handover commands at layer 1/2 speed while maintaining compatibility with layer 3 RRC procedures, thus providing both speed and flexibility.
3Adaptability or versatility
If conventional RACH configuration is used, then existing compatibility is maintained, but L1/L2 mobility initiation capability is insufficient
Solution Approach 1:
The network pre-configures the UE with RACH parameters and candidate cell information before mobility is needed. The UE stores this configuration and can immediately use it to transmit PRACH messages when mobility conditions arise, eliminating the need for complex real-time configuration and reducing operational complexity.
Solution Approach 2:
The UE autonomously determines when to transmit PRACH messages for L1/L2 mobility based on pre-configured criteria and network conditions. It automatically selects appropriate RACH occasions and transmits mobility initiation messages without requiring complex manual configuration or network intervention, simplifying the overall system operation.
Data Source
AI summary
This disclosure provides systems, methods and apparatus, including computer programs encoded on computer storage media for a user equipment (UE) to initiate a layer 1 or layer 2 mobility procedure. The UE receives a configuration of a random access channel (RACH) including RACH occasions for a candidate cell. The UE determines that a condition for a layer 1 or layer 2 mobility procedure to the candidate cell is satisfied. The UE transmits a physical RACH (PRACH) message to the candidate cell to initiate the layer 1 or layer 2 mobility procedure.