Uplink Timing Advance Control for Carrier Aggregation
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Solution Overview
Problem
In LTE-A systems, maintaining uplink time alignment across multiple serving cells with different propagation properties is challenging due to varying timing advance values, leading to potential desynchronization and interference issues.
Innovation Solution
A user equipment (UE) receives timing advance commands (TACs) for multiple serving cells and determines whether to transmit uplink data based on a threshold difference between these TACs, ensuring that the first serving cell always performs uplink transmission regardless of the timing difference, while adjusting or dropping transmissions through other cells to maintain alignment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If carrier aggregation is used to improve uplink data transmission capacity, then data transmission efficiency is improved, but uplink time alignment becomes difficult to maintain due to different propagation delays
Solution Approach 1:
The patent segments the timing advance management by designating one serving cell as a reference cell and others as non-reference cells. Each cell type has different timing advance application rules, allowing the system to maintain time alignment across aggregated carriers while enabling flexible uplink transmission on multiple cells.
Solution Approach 2:
The patent changes the timing advance parameter application based on cell type. For reference cells, timing advance is adjusted based on propagation delay measurements, while for non-reference cells, timing advance is derived from the reference cell's timing advance plus an offset. This parameter differentiation resolves the time alignment issue while maintaining multi-cell transmission capability.
2Reliability
If timing advance values are adjusted for each serving cell to maintain alignment, then uplink time alignment is improved, but transmission timing coordination becomes complex
Solution Approach 1:
The patent merges the timing advance control of non-reference cells with the reference cell by deriving non-reference cell timing advance from the reference cell's timing advance plus an offset. This reduces the number of independent timing advance adjustments needed, simplifying coordination while maintaining alignment across all serving cells.
Solution Approach 2:
The reference cell acts as an intermediary for timing advance management. Instead of independently managing timing advance for each cell, the system uses the reference cell's timing advance as a baseline and applies offsets for other cells, reducing overall system complexity.
3Productivity
If uplink transmission is performed on all serving cells simultaneously, then data transmission rate is improved, but interference between cells increases due to timing differences
Solution Approach 1:
The patent applies different transmission characteristics to different cell types. Reference cells use dynamically adjusted timing advance based on propagation delay, while non-reference cells use derived timing advance with offsets. This local differentiation allows simultaneous transmission on multiple cells while minimizing timing misalignment and resulting interference.
Data Source
AI summary
Disclosed are a method and an apparatus for transmitting uplink data by means of multiple serving cells. A method for a terminal for transmitting uplink data by means of multiple serving cells may comprise the steps of: the terminal receiving a first timing advance command (TAC) for a first serving cell and a second TAC for a second serving cell; and determining whether the terminal transmits uplink data by means of the second serving cell on the basis of whether the timing difference is below the threshold value, wherein the timing difference is acquired on the basis of the first TAC and the second TAC, and the first serving cell can be a cell configured so that an uplink can be always transmitted regardless of the timing difference.