Radio Terminal Fallback Signaling for Low-Load Random Access
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Solution Overview
Problem
The existing 2-step CBRA procedure in 5G NR systems faces challenges such as increased UE load, complexity, and battery consumption due to unclear fallback mechanisms to 4-step CBRA, and potential delays in random access procedures.
Innovation Solution
Implementing a method where the UE only attempts to receive a control message for the 4-step CBRA if a specific fallback notification is successfully decoded in the 2-step CBRA, and restarts the 2-step procedure upon failure, reducing unnecessary decoding efforts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE attempts to receive control messages for both 2-step CBRA and 4-step CBRA procedures, then the fallback mechanism is more robust, but the UE load and complexity increase
Solution Approach 1:
The network transmits a fallback notification in advance within the 2-step CBRA procedure, indicating whether fallback to 4-step CBRA is required. This allows the UE to prepare appropriately without needing to continuously monitor for both procedures, reducing complexity while maintaining reliability
Solution Approach 2:
The system dynamically switches between 2-step and 4-step CBRA procedures based on the fallback notification. The UE adapts its behavior by attempting to receive control messages only for the appropriate procedure, optimizing the balance between reliability and complexity based on current conditions
2Loss of time
If the UE continuously monitors for control messages in both procedures, then no random access delays occur, but battery consumption increases
Solution Approach 1:
The fallback notification is provided in advance, allowing the UE to determine the appropriate procedure before attempting random access. This prevents unnecessary monitoring and reduces battery consumption while ensuring timely access by avoiding delays from uncertain procedure selection
3Reliability
If the UE decodes all control messages regardless of procedure type, then message reception is more reliable, but unnecessary decoding efforts increase load
Solution Approach 1:
The fallback notification is decoded in advance to determine the appropriate procedure type. This preliminary action allows the UE to focus decoding efforts only on relevant control messages, maintaining reliability while reducing unnecessary decoding operations and simplifying the operational process
Data Source
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AI summary
A radio terminal (2) attempts to receive a second message of a 2-step random access procedure after transmitting a first message of the 2-step random access procedure. In response to successfully receiving the second message of the 2-step random access procedure and determining that the second message explicitly or implicitly indicates a fallback to a 4-step random access procedure, the radio terminal (2) further attempts to receive a control message that contains an uplink grant indicating uplink resources available for transmission of a third message of a 4-step random access procedure. This contributes to, for example, reducing the load on a radio terminal that supports a fallback from the 2-step random access procedure to the 4-step random access procedure.