VoLTE Call Reliability via UE NAS Registration Blocking
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Solution Overview
Problem
Voice over LTE (VoLTE) and Video over LTE (ViLTE) calls experience high dropout rates due to Radio Link Failure (RLF), leading to financial consequences for carriers as they result in poor network performance and key performance indicator (KPI) degradation, especially in areas with poor LTE coverage.
Innovation Solution
Implementing a method where User Equipment (UE) prioritizes LTE frequencies during cell re-establishment procedures by using a timer (T311) to limit scanning of non-LTE frequencies, blocking NAS registration on other RATs during a timer duration, and extending the RRC re-establishment timer to ensure successful LTE connection re-establishment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If UE scans non-LTE frequencies during cell re-establishment, then adaptability to different networks is improved, but VoLTE call reliability deteriorates due to dropped calls
Solution Approach 1:
The system performs preliminary actions by starting the T311 timer immediately upon detecting RLF, which pre-establishes a time-bound constraint that prevents subsequent NAS registration on non-LTE RATs. This preliminary timing mechanism ensures LTE frequency prioritization is automatically enforced during the critical re-establishment window, resolving the contradiction by pre-committing to LTE before the UE can switch to non-LTE networks
Solution Approach 2:
The T311 timer acts as an intermediary mechanism that mediates between the UE's need to adapt to available networks and the requirement to maintain VoLTE calls. The timer indirectly controls frequency scanning behavior by blocking NAS registration on non-LTE RATs during its duration, thus preventing direct conflict between network adaptability and call reliability
2Speed
If UE performs NAS registration on other RATs during re-establishment, then connection recovery speed is improved, but LTE connectivity is lost causing call dropout
Solution Approach 1:
The system applies preliminary anti-action by proactively blocking NAS registration on non-LTE RATs through the T311 timer mechanism. This preemptive block prevents the UE from registering on alternative RATs that would otherwise provide faster connection recovery but would cause LTE connectivity loss and call dropout. The anti-action is built into the timer's expiration logic
3Reliability
If RRC re-establishment timer is extended, then LTE connection re-establishment reliability is improved, but call setup time increases
Solution Approach 1:
The system changes the time parameter of the RRC re-establishment timer (T311) from its default value to an extended value specifically for VoLTE calls. This parameter modification increases the maximum duration the UE can attempt LTE re-establishment, improving reliability by allowing more time for LTE network response while maintaining the same timer mechanism, thus accepting controlled time loss for critical voice services
Data Source
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AI summary
A method for improving reliability of Voice over LTE (VoLTE)/ Video over LTE (ViLTE) calls includes detecting, by a User Equipment (UE) camped on a first Radio Access Technology (RAT), a problem with a radio connection on the first RAT at a first time. After detecting the problem with the radio connection, the UE blocks Non-Access Stratum (NAS) registration on a second RAT in a time period between the first time and a second time later than the first time. The second RAT is different than the first RAT.