Multi-Receiver Fast LTE Return from CSFB Voice Calls
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Solution Overview
Problem
The existing CSFB procedure for switching between LTE and legacy networks is slow, leading to long re-camp times and poor user experience due to the need to search for LTE cells after voice call release, especially when legacy networks do not provide LTE cell information in RRC connection release messages.
Innovation Solution
A wireless device with multiple receivers processes voice calls on legacy networks using one receiver while simultaneously searching for the strongest suitable LTE cell using another receiver, allowing for fast return to LTE after the voice call is released by camping on the strongest suitable LTE cell found during the call.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If the UE performs a normal cell search procedure after voice call release in CSFB mode, then the UE can find a suitable LTE cell, but the re-camp time increases dramatically (up to 20 seconds)
Solution Approach 1:
The UE performs cell search and identifies suitable LTE cells in advance during the voice call while connected to the legacy network. The second receiver continuously monitors LTE frequencies and stores information about suitable cells before the voice call releases, so when the call ends, the UE can immediately camp on a pre-identified LTE cell without performing a full cell search procedure.
Solution Approach 2:
The cell search activity continues uninterrupted during the voice call by using the second receiver to monitor LTE cells simultaneously while the first receiver handles the voice call on the legacy network. This continuous monitoring ensures that when the voice call releases, the UE already has up-to-date information about suitable LTE cells, eliminating the need for a post-release cell search.
2Productivity
If the UE uses a single receiver for both voice call processing and cell search, then the device complexity is reduced, but the cell search cannot occur simultaneously with voice call processing
Solution Approach 1:
The second receiver is configured to perform multiple functions: during the voice call, it searches for and monitors LTE cells; after the voice call releases, it can be quickly switched to assist in the camp-on process. This multi-functionality allows the receiver to serve both voice call support and cell search purposes without requiring entirely separate hardware components.
Solution Approach 2:
The receiver resources are segmented into two independent paths: the first receiver dedicated to voice call processing on the legacy network, and the second receiver dedicated to LTE cell search and monitoring. This segmentation allows both operations to proceed simultaneously without interference, resolving the conflict between voice call handling and cell search activities.
3Reliability
If the UE searches for LTE cells after voice call release, then it can return to LTE network, but the user experience deteriorates due to service interruption
Solution Approach 1:
The UE prepares the list of suitable LTE cells in advance during the voice call, so when the call releases, the transition back to LTE is immediate. This preliminary identification of target cells ensures that the UE can resume LTE services instantly after voice call release, providing a seamless user experience without noticeable service interruption.
Data Source
AI summary
Methods and apparatuses to use multiple receivers of a wireless communication device for fast return to a first network from a second network after termination of a Circuit Switched Fallback (CSFB) voice call is disclosed. A first receiver of the wireless communication device is used to process the CSFB voice call on the second network, while a second receiver of the wireless communication device is used to determine a strongest suitable cell available on the first network, while the voice call is active. A strongest suitable cell is instantly available to the wireless communication device after the CSFB voice call ends. In some embodiments, the first network is an LTE network, and the second network is a legacy network.