Multicast PDCP State Reconfiguration for HFN Ambiguity
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Solution Overview
Problem
In new radio (NR) Rel-17, the PDCP entity for multicast and broadcast services (MBS) faces challenges in setting initial values for PDCP sequence number (SN) and hyper frame number (HFN) due to mobility and RRC state transitions, leading to potential desynchronization and service discontinuity.
Innovation Solution
A method and apparatus for reconfiguring PDCP state variables and reporting status in scenarios requiring PDCP entity re-establishment, such as cell reselection or handover, by transmitting HFN ambiguity indications and using RRC messages to set reconfigured PDCP state variables, ensuring continuity and avoiding desynchronization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If PDCP entity is re-established due to cell reselection or handover, then mobility support is improved, but PDCP state variable desynchronization occurs
Solution Approach 1:
The patent implements feedback mechanisms where the UE reports HFN ambiguity indication to the network, and the network responds with reconfigured PDCP state variable values. This closed-loop feedback ensures that mobility operations (cell reselection, handover) can be performed while maintaining PDCP state synchronization between network and UE sides.
Solution Approach 2:
The patent applies preliminary action by having the network pre-configure PDCP state variable values before mobility events occur. The network provides reconfigured PDCP state variable values in advance through RRC messages, so that when cell reselection or handover occurs, the UE can immediately apply the correct initial values without desynchronization.
2Device complexity
If PDCP initial values are set to 0 for legacy unicast, then simplicity is improved, but service continuity deteriorates in multicast scenarios
Solution Approach 1:
The patent changes the PDCP initialization parameters from fixed zero values (legacy unicast approach) to dynamic network-provided values. The network configures specific PDCP state variable values including HFN and reference SN through RRC messages, allowing the system to maintain simplicity in initialization while ensuring service continuity through proper parameter selection for multicast scenarios.
3Measurement precision
If HFN is indicated by network to avoid desynchronization, then synchronization accuracy is improved, but signaling overhead increases
Solution Approach 1:
The patent applies partial action by having the network indicate only the necessary HFN information rather than complete PDCP state variables in all cases. The HFN ambiguity indication mechanism allows the UE to report only when ambiguity exists, and the network provides reconfigured values selectively, reducing signaling overhead while maintaining synchronization accuracy when needed.
Data Source
AI summary
Embodiments of the present application relate to a method and apparatus of supporting multicast and broadcast services. An exemplary UE may include: a transceiver; and a processor coupled to the transceiver, wherein the processor is configured to: transmit, via the transceiver, HFN ambiguity indication information to a RAN node, indicating that there is ambiguity in HFN of received PDCP data PDU associated with a multicast MRB in the UE; and perform a reconfiguration procedure of PDCP state variable of the multicast MRB in response to receiving information indicating a reconfigured PDCP state variable value for the multicast MRB.