Adaptive RACH Procedure Selection for Low-Latency 5G Access
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Solution Overview
Problem
The four-step random access channel (RACH) procedure in LTE is not sufficient to meet the low latency requirements of 5G/NR wireless systems, necessitating a faster and more efficient RACH procedure.
Innovation Solution
A two-step RACH procedure is introduced, where the UE combines messages 1 and 3 of the four-step RACH into a single message and the base station combines messages 2 and 4, with the UE selecting the procedure based on RSRP thresholds and transmit power considerations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a four-step RACH procedure is used, then compatibility with LTE systems is maintained, but latency requirements of 5G/NR are not met
Solution Approach 1:
The patent combines messages 1 and 3 of the four-step RACH procedure into a single message 1, and combines messages 2 and 4 into a single message 2. This merging of multiple message exchanges into fewer combined messages directly reduces the RACH setup time while maintaining the essential functionality of the original four-step procedure, thereby resolving the contradiction between LTE compatibility and 5G latency requirements.
2Loss of time
If a two-step RACH procedure is implemented, then RACH setup time is reduced, but system complexity increases due to UE-based selection
Solution Approach 1:
The patent introduces RSRP thresholds as a parameter to guide UE's selection between two-step and four-step RACH procedures. By changing the decision criterion from a complex multi-factor evaluation to a simple threshold comparison based on RSRP measurements, the patent reduces device complexity while enabling adaptive procedure selection that optimizes RACH setup time based on channel conditions.
3Productivity
If message consolidation is performed, then RACH procedure efficiency is improved, but message reliability requirements become more stringent
Solution Approach 1:
The patent applies partial action by selectively consolidating messages based on RSRP thresholds and channel conditions. When conditions are favorable (high RSRP), the two-step consolidated procedure is used to maximize efficiency. When conditions are poor, the system can fall back to the more reliable four-step procedure, thereby balancing efficiency improvements with reliability requirements through conditional partial consolidation.
Data Source
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AI summary
The present disclosure describes a method, an apparatus, and a computer-readable medium for a random access channel (RACH) procedure at a user equipment. For example, the method may select a two-step RACH procedure or a four-step RACH procedure at the UE based at least on RACH configuration information received from a base station or the RACH configuration information at the UE. The example method may further include transmitting, from the UE, one or more messages associated with the two-step RACH procedure or the four-step RACH procedure based on the selection.