Handover Protocol Selection via Implicit RRC Indicators
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Solution Overview
Problem
User equipment (UE) faces challenges in communicating with a second base station during handover, particularly when unaware of the connected core network, making seamless handover management difficult.
Innovation Solution
A communication device and method that involves receiving a radio resource control (RRC) message to connect to a second cell, transmitting an RRC response, and exchanging Evolved Packet System (EPS) Non Access Stratum (NAS) messages with the Evolved Packet Core (EPC) network using specific protocols based on the RRC message content, such as EPS or 5G protocols, to facilitate handover without explicit core network type indication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the UE performs handover to a second BS without knowing which core network the second BS is connected to, then the handover can be executed, but the UE cannot determine which NAS protocol to use for communication with the core network
Solution Approach 1:
The network side performs preliminary actions by including protocol identification information (such as PDU Session ID or EPS bearer ID) in the handover command message before the UE executes the handover. This allows the UE to determine the appropriate NAS protocol in advance, avoiding communication failures after handover execution.
Solution Approach 2:
The handover command message acts as an intermediary carrier that transports protocol identification information from the network side to the UE. This intermediary mechanism enables the UE to infer the core network type without direct indication, resolving the information gap during handover.
2Reliability
If the RRC message includes explicit core network type indication, then the UE can determine the correct NAS protocol, but the signaling overhead increases
Solution Approach 1:
The invention makes existing RRC message fields (such as PDU Session ID or EPS bearer ID) serve multiple functions: their original function for session management and an additional function as implicit indicators of core network type. This eliminates the need for separate explicit indication fields, maintaining message structure simplicity while ensuring reliable protocol selection.
Solution Approach 2:
The invention changes the interpretation logic of existing message parameters rather than adding new parameters. By interpreting the presence or type of certain IDs (PDU Session ID vs. EPS bearer ID) as implicit core network type indicators, the system achieves reliable protocol determination without increasing signaling overhead or message complexity.
Data Source
AI summary
A communication device for handling a handover is configured to execute the instructions of: communicating with a base station (BS) via a first cell; receiving a radio resource control (RRC) message configuring the communication device to connect to a second cell, from the first cell; connecting to the second cell according to the RRC message, and transmitting a RRC response message for responding to the RRC message to the second cell; and exchanging a plurality of Evolved Packet System (EPS) Non Access Stratum (NAS) messages with an Evolved Packet Core (EPC) network according to an EPS NAS protocol via the second cell, when the RRC message does not include a Protocol Data Unit (PDU) Session Identity (ID), includes an EPS bearer ID or includes a handover type of a “5GStoEPS”.