NB-IoT Random Access Recovery via Cross-Carrier Uplink Grant
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In NB-IoT systems, terminal devices experience access failures due to missed detection of ACK messages during the random access process, particularly when uplink and downlink carriers are different, leading to retransmission failures and reduced access success rates.
Innovation Solution
A network device sends a contention resolution message and a first uplink grant message on a data transmission carrier to determine if the terminal device successfully resolves the contention problem, allowing for improved access success by ensuring proper message transmission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the base station retransmits msg4 on the PRB 2 when msg4 ACK is not received, then the base station attempts to ensure terminal device receives msg4, but the terminal device cannot receive the retransmitted msg4 because it is monitoring NPDCCH on PRB 3, leading to access failure
Solution Approach 1:
The patent introduces a new intermediary mechanism: the terminal device sends a confirmation message (containing its identity and uplink data) on the data transmission carrier PRB 3. This confirmation message serves as an intermediary indicator that allows the base station to indirectly verify whether the terminal device successfully received msg4, without requiring direct ACK detection on the uplink carrier PRB 2.
Solution Approach 2:
The patent implements a feedback mechanism where the terminal device provides explicit feedback about msg4 reception status by sending a confirmation message on PRB 3. The base station uses this feedback to determine whether to continue retransmission or proceed with normal communication, resolving the information asymmetry between base station and terminal device.
2Productivity
If the terminal device monitors NPDCCH on PRB 3 for msg5 transmission, then the terminal device can receive data on the configured carrier, but it cannot receive msg4 retransmission on PRB 2, causing contention resolution failure
Solution Approach 1:
The patent merges the contention resolution confirmation function with the existing data transmission process. The terminal device sends its confirmation message (which also serves as uplink data or can trigger uplink resource allocation) on the same data transmission carrier PRB 3 where it monitors for msg5. This eliminates the need for separate monitoring configurations and resolves the contradiction between data transmission efficiency and contention resolution reliability.
Solution Approach 2:
The confirmation message sent by the terminal device serves multiple functions: it confirms msg4 reception, provides uplink data (or requests uplink resources), and enables the base station to verify contention resolution status. This multi-functional approach allows the system to maintain high data transmission efficiency while ensuring reliable contention resolution.
3Measurement precision
If the base station uses uplink carrier PRB 2 for ACK detection, then it can verify terminal device response, but poor uplink signal or strong interference causes missed detection, leading to unnecessary retransmissions
Solution Approach 1:
The patent uses the confirmation message on PRB 3 as an intermediary indicator of successful msg4 reception. Instead of directly detecting ACK on the interference-prone uplink carrier PRB 2, the base station indirectly verifies reception through the terminal device's confirmation message sent on the data transmission carrier PRB 3, which typically has better signal conditions.
Data Source
AI summary
A network device sends a contention resolution message to a terminal device, and in instances when the network device determines that a target ACK sent by the terminal device is not received on an uplink carrier, the network device sends a first uplink grant message to the terminal device on a data transmission carrier. The terminal device may send a first message to the network device on the data transmission carrier based on the first uplink grant message. In this way, the network device can determine, based on the first message received on the data transmission carrier, whether the terminal device successfully resolves a contention problem, to avoid an access failure caused by missing detection of the target ACK, and improve an access success rate of the terminal device.