Random Access Preamble Detection on Unlicensed Carriers
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Solution Overview
Problem
In conventional LTE systems, multiple User Equipments (UEs) cannot simultaneously send preamble signals when using an unlicensed carrier due to the listen before talk (LBT) mechanism, as they detect the carrier as busy and refrain from transmitting.
Innovation Solution
The proposed solution involves a terminal receiving an RRC configuration message to detect preamble signals or indication information when the carrier is busy, allowing it to send a second preamble signal on the same carrier, and utilizing a licensed carrier for random access responses to improve success rates, along with adding a time offset to the RAR time window and prolonging the contention resolution timer based on LBT detection and message forwarding times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If multiple UEs perform LBT on the same unlicensed carrier before sending preambles, then each UE can detect carrier availability, but multiple UEs cannot simultaneously send preamble signals when the carrier is detected as busy
Solution Approach 1:
The patent segments the random access procedure into two distinct paths: a first random access procedure for UEs that detect the carrier as idle (can send preambles immediately), and a second random access procedure for UEs that detect the carrier as busy (must wait and retry). This segmentation allows simultaneous access attempts while managing collision scenarios separately, resolving the contradiction between reliability and simultaneous transmission capability.
2Ease of operation
If a UE waits for the carrier to be idle before sending a preamble, then collision is avoided, but access delay increases and simultaneous access is prevented
Solution Approach 1:
The patent applies preliminary action by having UEs perform LBT (Listen Before Talk) before transmitting preambles. UEs that detect the carrier as idle can immediately proceed with preamble transmission, while those detecting busy status are directed to a second procedure with extended timing. This preliminary detection and classification reduces overall access delay by allowing immediate access for clear carriers while managing busy carrier scenarios separately.
3Productivity
If the RAR time window is kept short, then response efficiency is maintained, but UEs may fail to receive RAR messages when carrier conditions are unfavorable
Solution Approach 1:
The patent applies dynamics by making the RAR time window duration adaptive rather than fixed. For the first random access procedure (idle carrier detection), a shorter RAR window is used to maintain response efficiency. For the second procedure (busy carrier detection), the RAR window is extended to account for additional LBT detection time and potential message forwarding delays, ensuring reliable RAR reception under varying carrier conditions.
4Reliability
If LBT detection time and message forwarding time are accounted for in timing adjustments, then RAR reception reliability is improved, but system complexity increases
Solution Approach 1:
The patent applies feedback by having the network measure and determine the message forwarding time based on actual LBT detection and message transmission performance. This measured feedback is then used to adjust the RAR time window duration and timing parameters for the second random access procedure. This feedback-based approach improves RAR reception reliability while managing complexity through empirical measurement rather than complex theoretical calculations.
Data Source
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AI summary
Embodiments of this application relate to the communications field, and provide a random access method and an apparatus, to resolve a problem that a plurality of UEs cannot simultaneously send preamble signals during random access. The method includes: performing, by a terminal, listen before talk LBT on a first carrier; detecting, by the terminal, a first signal on the first carrier if the terminal determines, through the LBT, that the first carrier is in a busy state, where the first carrier includes an unlicensed carrier, the first signal includes a first preamble signal or indication information, and the indication information is used to indicate that the first carrier is used to send the first preamble signal; and if the terminal detects the first preamble signal or the indication information, sending, by the terminal, a second preamble signal to a base station on the first carrier to attempt to access the base station. The embodiments of this application are applied to a random access process.