Hybrid Random Access Procedure for Unlicensed Spectrum
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Solution Overview
Problem
Current LTE and NR radio access procedures, such as the 4-step RACH, experience high latency due to Listen Before Talk (LBT) failures in unlicensed spectrum, while the proposed 2-step RACH reduces latency but faces issues with resource allocation and collision probability, especially during simultaneous UE access.
Innovation Solution
Implementing a hybrid random access procedure that allows base stations to configure devices to use either a 4-step or 2-step RACH procedure based on specific conditions, such as RRC connection re-establishment or traffic class, to control collision probability and resource allocation, thereby ensuring fair coexistence in unlicensed spectrum.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If 4-step RACH procedure is used, then collision probability is reduced, but latency increases due to LBT failures
Solution Approach 1:
The patent implements a dynamic random access mechanism where the base station can switch between 4-step and 2-step RACH procedures based on real-time channel conditions and LBT success rates. This dynamic adaptation allows the system to optimize between collision reduction (4-step) and latency reduction (2-step) depending on current spectrum availability, resolving the contradiction between reliability and time loss.
Solution Approach 2:
The patent changes the procedural parameter of random access by supporting multiple modes (4-step and 2-step RACH) and dynamically selecting between them. The base station configures different RACH parameters including procedure type, resource allocation, and LBT requirements based on channel conditions, allowing the system to adapt the access procedure to minimize both collisions and latency under different operating conditions.
2Loss of time
If 2-step RACH procedure is used, then latency is reduced, but collision probability increases during simultaneous UE access
Solution Approach 1:
The patent employs dynamic selection between 2-step and 4-step RACH based on channel conditions. When LBT success rate is high and channel conditions are good, the system uses 2-step RACH to minimize latency. When simultaneous access attempts are detected or channel conditions deteriorate, the system switches to 4-step RACH to reduce collision probability, thus dynamically balancing latency and collision trade-offs.
Solution Approach 2:
The patent implements feedback mechanisms where the base station monitors LBT success rates, collision indicators, and channel conditions, then uses this feedback to dynamically adjust the random access procedure configuration. The base station can send RACH configuration messages to UEs based on observed collision patterns and channel state, allowing the system to adaptively reduce collisions while maintaining low latency when possible.
3Productivity
If hybrid RACH procedure is implemented, then resource allocation is optimized, but device complexity increases
Solution Approach 1:
The patent implements a universal random access framework that supports both 4-step and 2-step RACH procedures through a single hybrid configuration mechanism. The base station maintains a unified configuration structure that can accommodate multiple RACH modes, resource allocations, and parameter sets, allowing the same system to serve different service types (e.g., URLLC, eMBB, mMTC) with appropriate RACH procedures without requiring separate dedicated configurations for each mode.
Data Source
AI summary
A method comprises configuring, by a base station, a device with a first mode of performing random access procedure. The method includes configuring the device with a second mode of performing random access procedure. The device is configured to access either the first mode of performing random access procedure or the second mode of performing random access procedure. The method also includes configuring an availability of the second mode of performing random access procedure.