HARQ Process for 5G Multicast Broadcast Service
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Solution Overview
Problem
In the 5G NR system, it is challenging for the gNB to correctly indicate to the UE whether downlink data transmission is an initial transmission or a retransmission, especially when the transmission mode is dynamically switched between point to multipoint (PTM) and point to point (PTP) modes during multicast broadcast service (MBS) data reception.
Innovation Solution
The method involves receiving downlink control information (DCI) on a physical downlink control channel (PDCCH) scrambled by a radio network temporary identifier (RNTI), where the NDI value determines if the data reception corresponds to an initial transmission or retransmission, by identifying the type of RNTI and using this information to differentiate between initial and retransmission data packets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the gNB dynamically switches transmission mode between PTM and PTP for MBS data transmission, then the system flexibility and adaptability are improved, but the complexity of correctly indicating initial transmission or retransmission to the UE increases
Solution Approach 1:
The patent introduces the RNTI type as an intermediary element to resolve the ambiguity in transmission mode indication. By checking whether the RNTI is of type 1 (PTM) or type 2 (PTP), the system can correctly identify transmission mode without relying solely on NDI toggling, thus resolving the complexity introduced by dynamic mode switching
Solution Approach 2:
The patent changes the parameter used for transmission mode indication from solely NDI value to a combination of RNTI type and NDI value. This parameter expansion allows the system to maintain clear indication of transmission mode even when dynamically switching between PTM and PTP modes
2Device complexity
If the gNB uses NDI field in DCI to indicate initial transmission or retransmission, then the HARQ process can be simplified, but the accuracy of indication becomes unreliable when transmission mode is dynamically changed
Solution Approach 1:
The RNTI type serves as a reliable intermediary indicator that remains consistent regardless of transmission mode changes. By combining RNTI type information with NDI value, the system achieves both simplified HARQ processing and reliable indication accuracy
Solution Approach 2:
The patent segments the indication mechanism into two independent parts: RNTI type identification and NDI value evaluation. This segmentation allows each component to perform its specific function reliably - RNTI type provides transmission mode context while NDI provides retransmission indication, together achieving high accuracy
3Reliability
If the UE performs HARQ processing for MBS data reception, then the data reliability is improved, but the processing complexity and challenges increase when transmission mode is dynamically switched
Solution Approach 1:
The RNTI type acts as a mediator that simplifies the UE's HARQ processing by providing clear transmission mode information. This allows the UE to correctly identify whether to perform soft combining or fresh decoding without adding processing complexity, thus maintaining high reliability
Solution Approach 2:
The patent changes the parameter set for HARQ decision-making from single NDI value to combined RNTI type and NDI value. This parameter change enables the UE to maintain simple and reliable HARQ processing even under dynamic transmission mode switching conditions
Data Source
AI summary
A method of HARQ process for MBS and a UE using the same method are provided. The method includes: receiving first DCI on a first PDCCH scrambled by a first RNTI, wherein the first DCI comprises a first NDI value and schedules a first downlink data reception corresponding to a HARQ process; receiving second DCI on a second PDCCH scrambled by a second RNTI, wherein the second DCI comprises a second NDI value and schedules a second downlink data reception corresponding to the HARQ process; identifying a first type of the first RNTI and a second type of the second RNTI; and determining, according to the first type and the second type, whether the first NDI value and the second NDI value are used for determining the second downlink data reception corresponds to an initial transmission or a retransmission of the first downlink data reception.