SRVCC Handover Command Message Handling in LTE-UTRAN Inter-RAT Transition
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Solution Overview
Problem
Existing systems face challenges in determining and performing Single Radio Voice Call Continuity (SRVCC) handovers between LTE and UTRAN networks, particularly due to the lack of SRVCC-related information elements in handover command messages, which can lead to invalid handover attempts and disruptions in voice call continuity.
Innovation Solution
The system and method for determining SRVCC handovers involve receiving handover command messages with or without SRVCC-related information elements, using a circuit-switched RAB from the 'RAB information for setup' element to perform SRVCC handovers, and discarding invalid messages to prevent handover initiation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the LTE network sends a Handover to UTRAN Command Message without SRVCC related information elements, then the message format is simpler and easier to process, but the wireless device cannot correctly identify SRVCC handover procedures leading to handover failures
Solution Approach 1:
The patent introduces a new information element called 'RAB info to replace' as an intermediary element in the handover command message. This element enables the wireless device to identify which packet-switched bearer should be replaced by the circuit-switched RAB, thereby correctly identifying SRVCC handover procedures without complicating the overall message structure. The intermediary element bridges the gap between simple message format and reliable handover execution.
2Reliability
If the handover command message includes SRVCC related information elements, then the wireless device can correctly identify and execute SRVCC handovers, but the message becomes more complex and requires additional processing
Solution Approach 1:
The patent segments the handover command message into distinct information elements, with the 'RAB info to replace' element specifically dedicated to SRVCC identification. This segmentation allows the message to include necessary SRVCC information while maintaining a structured and organized format that facilitates easier processing. The segmentation principle enables the system to handle complex information requirements without proportionally increasing overall message complexity.
3Reliability
If the wireless device discards handover command messages without SRVCC information elements, then invalid handover attempts are prevented, but legitimate SRVCC handovers may be missed
Solution Approach 1:
The patent implements preliminary action by including the 'RAB info to replace' information element in the handover command message before the handover execution. This preliminary inclusion of SRVCC identification information ensures that wireless devices can correctly identify SRVCC handover procedures in advance, preventing both invalid handover attempts and missed legitimate SRVCC handovers. The preliminary action resolves the contradiction by providing necessary information upfront.
Data Source
AI summary
The techniques introduced herein provide a system and method for determining whether an inter-RAT handover is an SRVCC handover, and for performing the subsequent SRVCC handover. The techniques include receiving a handover command message that does not include SRVCC related information elements, for example “RAB info to replace,” but continuing with an SRVCC handover using a circuit-switched RAB provided in the information for setup. The techniques also include receiving a handover command message that does include SRVCC related information elements and performing the SRVCC handover by an alternative method.