LTE Random Access Target TAG Identification via DCI Field
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Solution Overview
Problem
In LTE-Advanced systems, the current random access procedures face challenges in identifying the target Timing Advance Group (TAG) or cell, especially when cross-carrier scheduling is configured, leading to ambiguity in target UE identification and contention resolution, particularly in scenarios where the downlink physical control channel (PDCCH) of the secondary cell (SCell) experiences excessive interference.
Innovation Solution
The method involves modifying the DCI format to include a Target TAG/Cell Indicator Field (TIF/CIF) to explicitly identify the target TAG or cell, and configuring RACH resources to ensure unique identification and minimize contention, allowing the UE to correctly receive random access responses and perform scheduled uplink transmissions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If cross-carrier scheduling is configured for carrier aggregation, then the system can achieve better resource utilization and flexibility, but ambiguity arises in identifying the target TAG or cell for random access responses
Solution Approach 1:
The patent segments the identification process by introducing a specific field (CIF or TIF) within the RAR message structure that separately identifies the target TAG or cell. This segmentation allows the RAR message to carry both the random access response information and the target identification information independently, resolving the ambiguity caused by cross-carrier scheduling while maintaining system flexibility.
Solution Approach 2:
The patent introduces an intermediary identification field (CIF or TIF) as a mediator between the cross-carrier scheduling mechanism and the random access procedure. This intermediary field carries the target TAG or cell identification information, enabling the UE to correctly identify the target without being affected by the cross-carrier scheduling complexity.
2Productivity
If PDCCH orders are used to trigger random access procedures on SCell, then random access can be initiated, but excessive interference on SCell PDCCH prevents reliable reception
Solution Approach 1:
The patent extracts the random access triggering function from the interference-prone SCell PDCCH and relocates it to the PCell PDCCH. The PCell PDCCH sends the PDCCH order to trigger the random access procedure, while the SCell PDCCH focuses only on sending the RAR message with proper target identification. This extraction separates the triggering function from the interference source, improving reliability.
Solution Approach 2:
The patent changes the dimension of the problem by moving the PDCCH order transmission to a different carrier (PCell) than the one experiencing interference (SCell). This dimensional change in the communication path allows the random access triggering to occur reliably while still enabling SCell-based random access procedures.
3Reliability
If multiple timing advances are supported for uplink carrier aggregation, then uplink synchronization can be maintained across different cells, but the complexity of random access procedures increases
Solution Approach 1:
The patent segments the random access procedure into clearly defined steps with explicit target TAG identification. By introducing the CIF or TIF field in the RAR message, the procedure is divided into: (1) PDCCH order reception with target cell indication, (2) PRACH preamble transmission on indicated cell, (3) RAR reception with target TAG confirmation. This segmentation makes the complex multi-TA procedure more manageable and less error-prone.
Solution Approach 2:
The patent applies preliminary action by providing the UE with advance information about the target TAG or cell through the CIF or TIF field in the RAR message before the UE needs to apply the timing advance. This preliminary identification allows the UE to prepare the correct timing advance group in advance, reducing the complexity of real-time synchronization management.
Data Source
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AI summary
An eNodeB is configured to perform a method for a random access procedure in an LTE-Advanced system. The method includes receiving from a user equipment a random access preamble message on a physical random access channel (PRACH) on a first cell, the PRACH associated with a random access radio network temporary identifier (RA-RNTI). The method also includes transmitting to the user equipment a random access response (RAR) message on a second cell. At least one of the RAR message and the RA-RNTI includes information configured to allow the user equipment to identify a target Timing Advance Group (TAG) or cell associated with the RAR message.