Uplink Synchronization Maintenance in LTE Data Transmission
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Solution Overview
Problem
In LTE systems, when the Time Alignment Timer (TAT) expires, User Equipment (UE) is considered out-of-sync, leading to unnecessary downlink data retransmissions, wasting resources and causing signaling overhead and delay due to the need for random access procedures to regain synchronization.
Innovation Solution
A method where the UE determines if it still maintains uplink synchronization after TAT expiration by checking specific parameters, allowing it to send feedback or reserve resources only if these conditions are met, thereby avoiding unnecessary retransmissions and access procedures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the UE sends feedback after TAT expires, then the feedback can be sent timely, but the uplink synchronization may be lost causing transmission errors
Solution Approach 1:
The UE performs preliminary determination of whether uplink synchronization is maintained before sending feedback after TAT expiration. This preliminary check allows the UE to assess its synchronization status and make informed decisions about feedback transmission, preventing both premature feedback that could cause errors and delayed feedback that would increase latency.
Solution Approach 2:
The patent introduces dynamic decision-making where the UE adapts its feedback behavior based on real-time synchronization conditions. The UE dynamically determines whether to send feedback by evaluating parameters like timing advance values and synchronization state, allowing the system to flexibly respond to changing channel conditions rather than following a fixed protocol.
2Reliability
If the eNB requires random access procedure before sending downlink data, then uplink synchronization is ensured, but signaling overhead and delay increase
Solution Approach 1:
The patent extracts the synchronization verification step from the mandatory random access procedure. Instead of requiring full random access, the UE independently determines its synchronization status by checking parameters such as timing advance values and comparison with threshold values, separating the verification function from the complete access protocol.
Solution Approach 2:
The UE performs self-verification of its uplink synchronization status by autonomously evaluating its timing advance parameters and synchronization state without requiring external verification from the eNB. This self-service approach allows the UE to make informed decisions about feedback transmission based on its own measured conditions.
3Reliability
If the eNB retransmits downlink data multiple times, then the data delivery reliability is improved, but transmission resources are wasted
Solution Approach 1:
The patent enables feedback transmission from UE to eNB even after TAT expiration, provided the UE determines it maintains uplink synchronization. This feedback mechanism allows the eNB to receive acknowledgment or negative acknowledgment of downlink data, enabling efficient retransmission decisions without unnecessary repeated transmissions, thus conserving transmission resources while maintaining data delivery reliability.
Data Source
Figure 1a~1
Figure 1B~2
Figure 3~3A
AI summary
A method, an apparatus, a terminal, and a base station for data transmission are provided. The method includes: when downlink data is received after a TAT expires, determining whether a first preset parameter of a UE satisfies a first uplink synchronization maintenance condition; and when the first parameter of the UE satisfies the first uplink synchronization maintenance condition, sending, to a base station, a feedback corresponding to the downlink data; or when the first parameter of the UE does not satisfy the uplink synchronization maintenance condition, skipping sending, to the base station, a feedback corresponding to the downlink data, where the feedback is used to indicate whether the downlink data is received correctly, and the first synchronization maintenance condition is used to determine that the UE still maintains an uplink in-sync state after the TAT expires. The method, apparatus, terminal, and base station can reduce a waste of downlink data transmission resources between the base station and the UE.