Uplink Time Alignment via Combined MAC PDU for LTE-Advanced
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Solution Overview
Problem
The LTE-Advanced system lacks clear specifications for determining which cell (PCell or SCell) to receive a timing advance command during uplink time alignment, and efficiently updating uplink timing for multiple component carriers, as it requires multiple MAC control elements in separate PDUs, which is inefficient.
Innovation Solution
A method where a communication device in a wireless communication system is configured with a primary cell and secondary cells, transmitting a random access preamble on an activated secondary cell and receiving a random access response including a timing advance command on the primary or another secondary cell, and incorporating multiple timing advance commands in a single MAC PDU with indices to specify which command applies to which component carrier.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple timing advance commands are sent in separate MAC PDUs, then each cell can receive its timing advance command, but the system efficiency deteriorates due to multiple transmissions
Solution Approach 1:
The patent combines multiple timing advance commands for different cells into a single MAC PDU. The MAC control element includes a bitmap indicating which cells have received timing advance commands, allowing the eNodeB to send multiple commands in one transmission rather than requiring separate MAC PDUs for each cell.
Solution Approach 2:
The MAC control element is designed to serve multiple cells simultaneously. By including a bitmap field that indicates timing advance command status for each cell, the single MAC PDU can perform the function of multiple separate timing advance command transmissions, improving system efficiency while ensuring reliable delivery to all configured cells.
2Reliability
If the UE monitors all component carriers for timing advance commands, then uplink time alignment is maintained, but the device complexity increases
Solution Approach 1:
The patent applies different monitoring strategies for different cells based on their activation state. The UE monitors timing advance commands for activated secondary cells through the random access procedure, while the primary cell timing is maintained through existing mechanisms. This differentiated approach reduces unnecessary monitoring complexity for deactivated cells while maintaining reliable time alignment for active cells.
Data Source
AI summary
A method of handling uplink time alignment for a communication device in a wireless communication system is disclosed. The method comprises being configured a primary cell and at least a secondary cell by a network of the wireless communication system, transmitting a random access preamble of a random access procedure on the secondary cell when one of the at least a secondary cell is activated, and receiving a random access response including a timing advance command for the secondary cell on the primary cell, the secondary cell, or another one of the at least a secondary cells.