L2 Triggered Contention-Free Random Access for 5G Cell Switching

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Current wireless mobile communication systems face challenges in minimizing service interruption and latency during cell switch operations, particularly when transitioning between cells in 5G networks.

Innovation Solution

The method involves enabling contention-free random access for cell switch operations in conjunction with Layer 2 (L2) downlink messages, specifically using a second random access procedure that includes a preamble index field, a SSB field, a PRACH mask field, and a supplementary uplink related field, to ensure seamless and interruption-free cell switching.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If L3 measurements and RRC signalling triggered Reconfiguration with Synch are used for serving cell change, then complete L2 (and L1) resets are performed, but this results in more latency, more overhead and more interruption time

Engineering Contradiction:

Improveserving cell change completenessVSAvoidinterruption time

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The patent segments the random access procedure into two types: contention-based random access (CBRA) and contention-free random access (CFRA). By introducing CFRA as a separate, dedicated procedure for serving cell change, the system avoids the overhead and latency of complete L2/L1 resets while maintaining reliability. The CFRA procedure is triggered by a specific MAC CE command that directly initiates random access without full reconfiguration.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The patent implements preliminary action by pre-configuring uplink resources and random access parameters before the serving cell change occurs. The MAC CE command includes pre-configured information such as SSB index, PRACH mask index, and uplink grant, allowing the UE to immediately perform random access without waiting for full RRC reconfiguration. This reduces interruption time while ensuring reliable cell switching.

Inventive Principle:

Principle #10Preliminary action

2Reliability

If L3 measurements and RRC signalling triggered Reconfiguration with Synch are used for serving cell change, then complete L2 (and L1) resets are performed, but this involves more overhead

Engineering Contradiction:

Improveserving cell change completenessVSAvoidsignaling overhead

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The patent extracts the essential elements needed for serving cell change from the complete RRC reconfiguration procedure. Instead of performing full L2/L1 resets with extensive signaling, the system uses a streamlined MAC CE-based approach that extracts only the necessary components: SSB index, PRACH mask index, uplink grant, and timing advance. This reduces signaling overhead while maintaining the reliability of serving cell change.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

Inventive Principle:

Principle #10Preliminary action

3Loss of time

If contention-free random access is implemented for cell switch, then service interruption is reduced, but specific random access parameters must be pre-configured

Engineering Contradiction:

Improveservice interruptionVSAvoidparameter configuration

Core Design Contradiction:

Loss of timeVSDevice complexity

Solution Approach 1:

The patent makes the MAC CE command multi-functional by enabling it to serve both as a serving cell change trigger and as a carrier for transmitting random access parameters. The same MAC CE structure is used to indicate cell change and to convey CFRA parameters (SSB index, PRACH mask index, uplink grant), eliminating the need for separate configuration messages and reducing overall signaling overhead.

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent introduces a dedicated MAC CE command as an intermediary between the gNB and UE for coordinating serving cell change. This MAC CE acts as a mediator that carries all necessary information (SSB index, PRACH mask index, uplink grant, timing advance) in a standardized format, simplifying the interaction and reducing the complexity of parameter configuration compared to ad-hoc signaling approaches.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS20250133453A1Method and apparatus for performing random access in mobile wireless communication system

Publication Date: 2025.04.24 BLACKPIN INC

AI summary

A method for random access is provided. The method provides means to trigger either contention based random access or contention free random access in a specific cell based on medium access control message. The medium access control message is designed to achieve high speed processing. With this method, layer-1/layer-2 triggered mobility is performed with less interruption.