Terminal Device CSFB Fallback Frequency Determination
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Solution Overview
Problem
The current 4G wireless communications system does not support circuit-switched services, leading to frequent disconnections during mobile originating/terminating calls due to the need for circuit-switched fallback to 3G or 2G networks, which affects user communication experience.
Innovation Solution
A voice service processing method that allows terminal devices to determine an appropriate redirection frequency even without received frequency information, enabling them to access a network that supports voice services by using historical frequencies or frequencies obtained from other devices, thereby ensuring successful call handling and improving user experience.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If circuit switched fallback is used to enable voice service in 4G network, then voice service capability is improved, but call disconnection rate increases
Solution Approach 1:
The terminal device performs frequency scanning and network measurement in advance before the actual call fallback is needed. This preliminary action ensures that when CSFB is triggered, the terminal already has candidate frequency information available, reducing the time to find a suitable network and preventing call disconnections during the fallback process
Solution Approach 2:
The terminal device maintains a buffer of candidate frequency information from previous scans and measurements. This cushioning mechanism ensures that even if frequency information is not immediately available from network broadcasting, the terminal has pre-stored alternatives ready, preventing call failures during network switching
2Measurement precision
If terminal device waits for network-delivered frequency information before fallback, then network selection accuracy is improved, but fallback time increases
Solution Approach 1:
The terminal device performs frequency scanning and stores candidate frequency information in advance, before the actual fallback is needed. This preliminary action allows the terminal to immediately use pre-scan results when fallback is triggered, eliminating the waiting time for network-delivered frequency information while maintaining accurate network selection
Solution Approach 2:
The terminal device dynamically adjusts its frequency selection strategy by combining pre-scan results with real-time network measurements. This dynamic approach allows the terminal to quickly select from pre-identified candidate frequencies while still verifying current network conditions, achieving both speed and accuracy in the fallback process
3Reliability
If terminal device performs full frequency scan to find voice network, then network selection reliability is improved, but time consumption increases
Solution Approach 1:
The terminal device extracts and utilizes candidate frequency information from pre-scan results, separating this preliminary work from the critical fallback path. By taking out the frequency scanning activity and performing it in advance, the terminal maintains high network selection reliability through thorough scanning while avoiding time consumption during the actual fallback operation
Solution Approach 2:
The terminal device performs comprehensive frequency scanning and network measurements in advance, storing the results as candidate information. This preliminary action ensures that when fallback is needed, the terminal can quickly select from pre-validated candidate frequencies rather than performing a full scan during the time-critical fallback moment
Data Source
AI summary
A voice service processing method includes: sending, by a terminal device, a first message to a network device of a first network, where the first message requests a circuit switched fallback (CSFB) voice service; receiving, by the terminal device, a second message sent by the network device of the first network, where the second message instructs the terminal device to perform a network redirection; if the second message carries no frequency information, determining, by the terminal device, a redirection frequency, where the redirection frequency is a frequency supported by a second network; and sending, by the terminal device based on the redirection frequency, a connection request to a network device of the second network, to perform a circuit switched (CS) voice service.