Cell Selection During Call Fallback from Advanced to Legacy Network
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
In areas where only low-priority cells are deployed, user equipment (UE) experiences prolonged call setup times during Circuit-Switched Fallback (CSFB) calls from LTE to EDGE networks, as it must exhaustively search for suitable cells of normal priority, leading to poor user experience.
Innovation Solution
A mobile communication device with a wireless transceiver and controller that allows camping on a low-priority cell for CSFB calls without requiring the presence of a normal-priority cell, either by immediately searching for and camping on a low-priority cell or using a guard timer to limit the search to normal-priority cells before expanding to low-priority cells.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE follows the standard cell selection procedure requiring search for normal priority cells first, then the cell selection reliability is improved, but the call setup time increases significantly
Solution Approach 1:
The network performs preliminary action by providing prioritized redirection information to the UE before the UE needs to select a cell. The redirection information includes target frequencies sorted by cell priority, allowing the UE to efficiently search only relevant frequencies rather than exhaustively searching all frequencies. This preliminary preparation resolves the contradiction by enabling fast cell selection (reducing time loss) while maintaining reliable cell selection through prioritized frequency ordering.
2Measurement precision
If the UE performs exhaustive scanning of all target frequencies to find normal priority cells, then the cell selection accuracy is improved, but the operation complexity increases
Solution Approach 1:
The cell selection process is segmented into two phases: first, the UE scans frequencies in the order provided by prioritized redirection information to find normal priority cells; second, if no normal priority cell is found, the UE then scans remaining frequencies for low priority cells. This segmentation reduces operation complexity by dividing the exhaustive search into manageable steps while maintaining measurement precision through systematic frequency scanning.
Solution Approach 2:
The UE performs partial action by scanning only the prioritized frequencies provided in redirection information rather than all possible frequencies. The network provides a subset of relevant frequencies sorted by priority, allowing the UE to achieve sufficient cell selection accuracy without the excessive complexity of scanning every possible frequency. This partial action resolves the contradiction between accuracy and complexity.
Data Source
AI summary
A mobile communication device and method including a wireless transceiver and a controller is provided. The wireless transceiver performs wireless transmission and reception to and from an advanced network and a legacy network. The controller receives a message from the advanced network via the wireless transceiver for redirecting the mobile communication device from the advanced network to the legacy network in response to a request for a call, searches for a suitable cell in the legacy network via the wireless transceiver in response to receiving the message, and camps on the suitable cell for making the call via the wireless transceiver regardless of the suitable cell being of a low priority and whether there is another suitable cell of a normal priority or not.