Uplink Latency Reduction via Shortened TTI in Unlicensed Spectrum
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Solution Overview
Problem
In wireless communication systems, particularly in unlicensed spectrum, there is a latency issue due to the delay between downlink and uplink transmissions, causing disruptions and delays in communication between user equipment (UE) and base stations, especially when the UE cannot send uplink transmissions during the same transmission opportunity (TxOp) if the grant is not received sufficiently early.
Innovation Solution
The solution involves determining whether to use a first or second timing configuration for communication in unlicensed radio frequency spectrum, where the second timing configuration has a shorter time difference between downlink and uplink communications, allowing for reduced latency by transmitting uplink messages during the same TxOp with a shortened transmission time interval (TTI) or fewer TTIs between the grant and the corresponding uplink message.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If a standard transmission time interval (TTI) is used for uplink transmissions in unlicensed spectrum, then the UE has sufficient time to process grants and prepare transmissions, but the latency increases causing the UE to wait for subsequent TxOp to transmit uplink messages
Solution Approach 1:
The patent changes the time parameter by introducing shortened TTI configurations specifically for uplink transmissions in unlicensed spectrum. The UE can be configured with multiple TTI lengths and select appropriate shortened TTIs for uplink messages, reducing the time between grant reception and uplink transmission while maintaining reliable communication through proper timing alignment.
Solution Approach 2:
The patent introduces dynamic TTI selection capability where the UE can adaptively choose between standard and shortened TTI configurations based on current communication conditions. The network can dynamically configure different TTI lengths for different uplink messages, allowing flexible adjustment of latency versus reliability trade-offs in real-time.
2Loss of time
If the number of TTIs between grant and corresponding uplink message is reduced, then the uplink transmission latency is reduced, but the processing time for the UE is insufficient
Solution Approach 1:
The patent changes the TTI duration parameter to create shortened TTI configurations that reduce the time between grant reception and uplink transmission. By defining specific shortened TTI lengths (e.g., 2ms, 4ms, or 7ms instead of standard 10ms), the patent achieves reduced latency while ensuring the UE has sufficient processing time within the shortened interval.
Solution Approach 2:
The patent segments the uplink transmission timeline into distinct shortened TTI intervals, allowing the UE to process grants and prepare transmissions within clearly defined, shorter time windows. This segmentation creates manageable processing intervals that reduce overall latency while maintaining adequate processing time for each segment.
3Productivity
If the UE waits for the next TxOp to send uplink transmission after receiving a grant, then the communication reliability is maintained, but the communication efficiency and productivity decrease
Solution Approach 1:
The patent enables the UE to perform preliminary uplink transmission actions within the same TxOp by using shortened TTIs. The UE can transmit uplink messages in response to grants received in the same TxOp, eliminating the need to wait for the next TxOp and improving communication efficiency while maintaining reliability through proper timing configuration.
Solution Approach 2:
The patent ensures continuous useful action by allowing uplink transmissions to occur without idle waiting periods between TxOps. By reducing the grant-to-uplink timing to fit within the same TxOp, the patent eliminates gaps in communication activity, maintaining continuous data flow and improving overall system productivity.
Data Source
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AI summary
Methods, systems, and devices for wireless communication are described. A user equipment (UE) may transmit uplink (UL) messages in unlicensed spectrum with a reduced UL timing delay. The UL timing delay may be reduced by using a shortened transmission time interval (TTI) (e.g., a TTI that is reduced in duration relative to other TTIs in the system or in a legacy system) or by reducing the number of TTIs between a grant and the corresponding UL message. The reduced UL timing delay may decrease the likelihood that the UE will wait for a subsequent transmit opportunity (TxOp) to transmit the UL message. In some cases, the reduced UL timing delay corresponds to a reduced hybrid automatic repeat request (HARQ) processing delay. In some cases, a time difference (e.g., measured in TTIs) between a measurement reference TTI a corresponding channel state information (CSI) report may also be reduced.