Random Access Msg3 Retransmission Timer Management in Unlicensed 5G
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Solution Overview
Problem
In 5G wireless systems operating in unlicensed spectrum, listen before talk (LBT) failures lead to reduced transmission opportunities for random access messages, causing inefficiencies in contention resolution and increased latency, as existing timer management strategies are not optimal for both user equipment (UE) and network resource allocation.
Innovation Solution
Implementing a retransmission timer (msg3RetxTimer) that starts upon LBT failure for initial msg3 transmission opportunities, allowing the UE to determine if a retransmission grant is received before expiry, and adjusting the contention resolution timer behavior in conjunction with the retransmission timer to optimize resource selection and reduce latency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a retransmission timer is started upon LBT failure for initial msg3 transmission opportunities, then the UE can determine whether a retransmission grant is received before expiry, but the RA procedure latency increases due to additional timer management and potential retransmission waiting time
Solution Approach 1:
The patent implements dynamic timer management where the retransmission timer (msg3RetxTimer) is conditionally started based on LBT failure detection, and its duration is adjusted based on whether a retransmission grant is received. The timer is stopped when a retransmission grant is received, allowing flexible adaptation to channel conditions and reducing unnecessary waiting time when retransmission is available.
Solution Approach 2:
The patent starts the retransmission timer in advance upon detecting LBT failure, before the actual retransmission attempt. This preliminary timer setup allows the UE to proactively manage the retransmission process and determine contention resolution success/failure timing, rather than waiting passively for the procedure to complete.
2Productivity
If the UE waits for retransmission grant before attempting msg3 retransmission, then network resource allocation is optimized, but UE power consumption increases due to extended monitoring and timer management
Solution Approach 1:
The patent implements a feedback mechanism where the UE monitors for retransmission grants from the network during the timer period. The network provides feedback through downlink control information indicating whether retransmission resources are available, allowing the UE to adapt its transmission strategy and power consumption accordingly.
Solution Approach 2:
The UE autonomously manages its own retransmission process by starting and monitoring the retransmission timer, detecting LBT failures, and determining contention resolution outcomes without requiring continuous network control. This self-service approach reduces unnecessary network-UE signaling and optimizes overall system efficiency.
3Productivity
If contention resolution timer behavior is adjusted in conjunction with retransmission timer, then overall procedure efficiency is improved, but device complexity increases due to coordinated timer management
Solution Approach 1:
The patent merges the management of the retransmission timer (msg3RetxTimer) with the contention resolution timer behavior. When a retransmission grant is received, both timers are coordinated and stopped together, and the contention resolution procedure is restarted. This combined approach simplifies overall timer management by linking related timing functions.
Solution Approach 2:
The retransmission timer serves multiple functions: it monitors for retransmission grants, determines contention resolution timing, and coordinates with the contention resolution timer. This multi-functional design reduces the need for separate specialized timers and simplifies the overall system architecture.
Data Source
AI summary
Systems, methods, apparatuses, and computer program products for random access procedures, for example when operating in unlicensed band, are provided. One method may include starting a retransmission timer when LBT failure is detected at a UE for one or more initial msg3 transmission opportunities. The method may also include determining whether a retransmission grant is received before expiry of the retransmission timer.