Two-Step RACH Selection for Low-Latency 5G Random 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 a first message and a third message of the four-step RACH procedure are combined into one message, and the base station combines the second and fourth messages in response, with optional sounding reference signals, to reduce latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the four-step RACH procedure is used, then compatibility with LTE systems is maintained, but latency requirements of 5G/NR systems are not met
Solution Approach 1:
The patent segments the RACH procedure into two distinct modes: four-step RACH for LTE compatibility and two-step RACH for 5G low-latency requirements. The UE and base station can select between these segmented procedures based on system type and latency requirements, allowing each mode to be optimized independently for its specific use case.
Solution Approach 2:
The patent introduces dynamic selection capability where the UE can choose between four-step and two-step RACH procedures based on received RACH configuration information and determined system type. This dynamic adaptation allows the system to switch between procedures to meet different latency requirements while maintaining LTE compatibility when needed.
2Loss of time
If the two-step RACH procedure is used, then latency is reduced, but system complexity increases due to message combining and fallback mechanisms
Solution Approach 1:
The patent merges Message 1 and Message 3 of the four-step procedure into a single combined message transmitted in the two-step procedure. Similarly, the base station combines processing of Messages 2 and 4. This merging reduces the number of transmission rounds and setup time, directly addressing the latency reduction goal while the complexity is managed through standardized combining rules.
Solution Approach 2:
The patent implements preliminary configuration where the base station provides RACH configuration information to the UE before the actual RACH procedure begins. This preliminary action includes indicating whether two-step or four-step procedure should be used, allowing the UE to prepare appropriately and avoid unnecessary complexity during the actual access procedure.
Solution Approach 3:
The patent incorporates feedback mechanisms where the base station provides responses to UE transmissions, including indicators of whether the two-step procedure succeeded or if the UE should fallback to four-step procedure. This feedback loop manages complexity by providing clear decision criteria for procedure selection and switching based on actual system conditions.
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.