NAS Function Reconnection Procedure for LTE Mobile Stations
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Solution Overview
Problem
The LTE-AS function in mobile communication systems can only perform reconnection procedures for radio base stations with a 'UE Context', leading to issues where incoming signals are not received by mobile stations due to unestablished RRC connections, and a specific reconnection procedure using the NAS function has not been established.
Innovation Solution
A mobile communication method that utilizes both a first protocol function for processing between the mobile station and the radio base station and a second protocol function (NAS) for upper-level processing between the mobile station and the switching center, including steps for transmitting reconnection requests and service requests when the first connection becomes idle, ensuring proper reconnection and signal delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the LTE-AS function transmits an RRC Connection Reestablishment Request to a radio base station not having the UE Context, then the reconnection procedure is initiated, but the connection is changed to idle state without waiting for T311 timer expiration, causing the S1 connection to remain active while the RRC connection is released
Solution Approach 1:
The patent applies preliminary action by having the NAS function proactively detect when the RRC connection transitions to idle state and initiate a service request to the MME before the S1 connection is actually needed. This提前 action ensures that the S1 connection is reestablished in advance, preventing the scenario where incoming signals cannot be delivered due to the mismatch between active S1 connection and released RRC connection.
Solution Approach 2:
The patent implements feedback by establishing a monitoring mechanism where the NAS function continuously monitors the RRC connection state and provides feedback to trigger appropriate actions. When the RRC connection is detected to be in idle state, the NAS function sends a service request to the MME, creating a feedback loop that ensures the S1 connection status matches the RRC connection status, thereby enabling reliable incoming signal delivery.
2Adaptability or versatility
If the RRC connection is released while the S1 connection is maintained, then the mobile station can move to a different radio base station, but the switching center cannot properly deliver incoming signals to the mobile station
Solution Approach 1:
The patent uses feedback by having the NAS function monitor RRC connection state and communicate with the MME to ensure S1 connection status reflects the actual RRC connection status. This feedback mechanism ensures that when the RRC connection is released, the S1 connection is also properly managed, enabling the MME to correctly route incoming signals to the appropriate radio base station while maintaining mobile station mobility.
Solution Approach 2:
The NAS function acts as an intermediary between the RRC layer and the NAS layer, mediating the connection state information between the radio access network and the core network. This intermediary role ensures that the MME has accurate information about the mobile station's connection status, enabling proper signal routing while supporting mobility.
3Reliability
If a specific reconnection procedure using the NAS function is implemented, then the defect of the LTE-AS function is resolved, but additional protocol processing steps are added to the communication system
Solution Approach 1:
The patent applies universality by having the NAS function, which already exists in the mobile station for other purposes, take on the additional responsibility of monitoring RRC connection state and managing S1 connection reestablishment. This multi-functionality approach resolves the connection reliability issue without requiring a completely new separate mechanism, thereby limiting the increase in overall system complexity.
Solution Approach 2:
The patent implements self-service by enabling the NAS function to autonomously detect RRC connection state changes and initiate appropriate service requests to the MME without requiring external intervention or complex centralized control. This self-service capability resolves the connection issue through a relatively simple autonomous mechanism, minimizing the added complexity.
Data Source
AI summary
A mobile communication method according to the present invention includes the steps of: transmitting, from an LTE-AS function to an EMM function, a reconnection request, when the LTE-AS function detects that an RRC connection is chanted to an idle state; and transmitting, at the EMM function, a service request, when the EMM function receives the reconnection request and detects that the LTE-AS function is in a coverage area.