CS Fallback Signaling via Intermediary MSC for MT Call Setup
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Solution Overview
Problem
The Location Area/Tracking Area (LA/TA) mismatch problem occurs during circuit switched (CS) Fallback in mobile telecommunications networks, causing mobile terminated calls to be lost when a user equipment (UE) transitions from a SAE/LTE network to a GSM or UMTS network, as the existing CS Fallback procedures fail to coordinate GSM and SAE/LTE cells effectively.
Innovation Solution
An enhanced eNodeB node and method that receive a paging message identifying suitable location areas, determine the current location of the UE, and establish a signaling connection between the UE and the initial mobile switching center (MSC) via a second MSC, which interfaces with a base station controller or radio network controller managing the target 2G/3G cell, allowing the mobile terminated call to be established.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the existing CS Fallback procedures are used for MT calls, then the call setup process is simple, but the call is lost when the UE has moved to a new location area not covered by the initially indicated suitable location areas
Solution Approach 1:
The patent introduces a second MSC as an intermediary node to resolve the LA/TA mismatch problem. When the UE is in a location area not covered by the initially indicated suitable location areas, the second MSC acts as a mediator to establish the signaling connection between the UE and the initial MSC, enabling the MT call to be successfully set up without losing the call.
2Reliability
If the enhanced eNodeB determines the current location of the UE and establishes a signaling connection via a second MSC, then the MT call is prevented from being lost, but the procedure complexity increases
Solution Approach 1:
The enhanced eNodeB performs preliminary actions by determining the current location of the UE before the MT call setup procedure begins. This preliminary location determination allows the enhanced eNodeB to identify the appropriate target 2G/3G cell and establish the necessary signaling connection via the second MSC in advance, ensuring the MT call can be successfully established even when the UE is in a location area not covered by the initially indicated suitable location areas.
3Adaptability or versatility
If the enhanced eNodeB identifies a target 2G/3G cell in a location area associated with the current location of the UE, then the signaling connection can be established, but the coordination between GSM and SAE/LTE cells becomes more complex
Solution Approach 1:
The patent implements dynamic adaptability by allowing the enhanced eNodeB to identify a target 2G/3G cell in a location area associated with the current location of the UE, even when this location area is not covered by the initially indicated suitable location areas. This dynamic approach enables the system to adapt to the UE's current location and establish the necessary signaling connection via the second MSC, thereby expanding the coverage area while managing the coordination complexity through predefined procedures.
Data Source
AI summary
In order to prevent a mobile terminated (MT) call to a user equipment (UE) from being lost by addressing a Location Area/Tracking Area (LA/TA) mismatch problem that could occur during a circuit switched (CS) Fallback, the method comprises the steps of: receiving a paging message from a mobility management entity, MME, where the paging message identifies suitable location areas, the paging message is sent because a first mobile switching center, MSC1, received a MT call request for the UE; determining that there are no 2G/3G cells belonging to the suitable location areas based on a current location of the UE; identifying a target 2G/3G cell in a location area associated with the current location of the UE but not part of the 2G/3G cells belonging to the suitable location areas; and enabling a signaling connection to be established between the UE and the first MSC1 via a second mobile switching center, MSC2, where the second MSC2 interfaces with a base station controller, BSC2, or a radio network controller, RNC2, that manages the target 2G/3G cell, where the signaling connection allows the MT call to be established with the UE.