PS-to-CS Handover for VoIP Call Continuity in Wireless Networks
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Solution Overview
Problem
There is a need to maintain call continuity in wireless communication as users roam between different wireless networks with varying radio access technologies, such as W-CDMA and GSM, especially for voice calls initiated through Voice-over-Internet Protocol (VoIP) in High-Speed Packet Access (HSPA) networks.
Innovation Solution
The solution involves performing packet-switched to circuit-switched (PS-to-CS) and circuit-switched to packet-switched (CS-to-PS) handovers, where user equipment (UE) establishes a circuit-switched call while a VoIP call is pending, switches the data path, and then hands over the call to another cell, either within the W-CDMA network or to a GSM network, to ensure continuous voice communication.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a UE maintains a VoIP call in a W-CDMA network and roams to a GSM cell that does not support VoIP, then the UE can continue to access the network, but the voice call continuity is lost because the target cell cannot support the same service
Solution Approach 1:
The patent introduces a circuit-switched call as an intermediary mechanism to bridge the gap between packet-switched VoIP and circuit-switched voice services. When the UE detects that the target cell does not support VoIP, it establishes a CS call through the core network, which acts as a mediator to maintain voice continuity across different network domains and access technologies.
Solution Approach 2:
The patent changes the service domain parameter from packet-switched (PS) to circuit-switched (CS) when roaming to a non-VoIP-capable cell. This parameter change allows the UE to switch from VoIP to circuit-switched voice service, maintaining call continuity by adapting to the target cell's capabilities while preserving the ongoing voice communication.
2Reliability
If the UE switches from packet-switched VoIP to circuit-switched voice call during handover, then call continuity is maintained in non-VoIP cells, but the data path and service domain must be changed
Solution Approach 1:
The patent performs preliminary actions by establishing the circuit-switched call before terminating the packet-switched VoIP call. The UE or network sets up the CS call while the PS call is still active, switches the data path in advance, and only then terminates the PS call. This preliminary action ensures call continuity without service interruption despite the complexity of data path switching.
3Adaptability or versatility
If the UE registers with the network for both PS and CS domains, then the UE can receive calls in either domain, but the registration and signaling overhead increases
Solution Approach 1:
The patent implements dynamic domain registration where the UE adjusts its registration status based on the current cell's capabilities. The UE checks whether the serving cell supports VoIP and accordingly registers for PS domain only, CS domain only, or both domains. This dynamic approach reduces unnecessary registration overhead while maintaining the ability to receive calls in the appropriate domain.
Data Source
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AI summary
Techniques for performing handover in order to maintain call continuity for a user equipment (UE) are described. The UE may communicate with a first cell in a radio access network (RAN) for a packet-switched (PS) call, e.g., for Voice-over-Internet Protocol (VoIP) via High-Speed Packet Access (HSPA) in W-CDMA. The UE may send measurement reports to the RAN and may receive trigger from the RAN. The UE may establish a circuit-switched (CS) call with the first cell while the PS call is pending at the first cell. The PS call and the CS call may be for a voice call, and the UE may switch data path for the voice call from the PS call to the CS call and then terminate the PS call. The UE may then perform handover of the CS call from the first cell to a second cell, which may not support VoIP.