Fallback Carrier Load Management for Reduced CSFB Latency
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Solution Overview
Problem
The existing circuit switched fallback (CSFB) process for wireless communication devices (WCDs) is inefficient due to the time-consuming scanning of CDMA carriers, which can take up to 480 milliseconds, and is further hindered by carriers with high load, leading to unnecessary delays in call setup.
Innovation Solution
A method that directs WCDs to scan the least-loaded carriers of the fallback network, determined by the first network in collaboration with the second network, to avoid wasting time on carriers unlikely to be assigned due to high load, thereby reducing latency in fallback communication setups.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If WCDs scan all CDMA carriers to find coverage, then coverage detection reliability is improved, but call setup time increases significantly
Solution Approach 1:
The network performs preliminary actions by determining and providing the list of least-loaded carriers to the WCD before the WCD begins scanning. This allows the WCD to skip scanning high-load carriers and directly scan only the recommended carriers, reducing scan time while maintaining coverage detection reliability.
Solution Approach 2:
Instead of treating all carriers uniformly, the system applies local quality by identifying and recommending specific carriers with lower load. The WCD scans only these locally optimized carriers rather than all carriers, reducing overall scan time while maintaining reliable coverage detection.
2Reliability
If WCDs scan high-load carriers, then coverage detection completeness is improved, but productivity decreases due to unnecessary delays
Solution Approach 1:
The system extracts and excludes high-load carriers from the scanning list, providing only the least-loaded carriers to the WCD. This removes the harmful element (high-load carriers causing delays) while maintaining coverage detection completeness through the remaining recommended carriers.
Solution Approach 2:
Instead of scanning all carriers (excessive action), the WCD scans only a partial subset of carriers that are least-loaded and recommended by the network. This partial action is sufficient for coverage detection while significantly improving call setup efficiency.
3Loss of information
If the network provides a comprehensive list of all carriers, then information completeness is improved, but device complexity increases due to inefficient scanning
Solution Approach 1:
The network performs preliminary analysis to determine and provide only the least-loaded carriers in the list, rather than all carriers. This preliminary filtering reduces the information the WCD needs to process, simplifying the scanning process while maintaining necessary carrier information completeness.
Solution Approach 2:
The carrier list is segmented into least-loaded carriers and high-load carriers. The network provides only the relevant segment (least-loaded carriers) to the WCD, reducing information overhead and simplifying the WCD's scanning process while maintaining coverage detection effectiveness.
Data Source
AI summary
A method and system to help manage latency in setup of fallback communications, such as circuit switched fallback calls for instance, by taking into account the load on various fallback carriers. When a first network is serving a device and engages in a process to facilitate setup of a communication for the device to be served by a second, fallback network, the first network will work with the second network to determine which local carriers of the second network are least loaded, and the first network will then direct the WCD to scan those determined least-loaded carriers in particular. This process may thus help to avoid having the WCD spend time scanning local carriers of the second network that the second network is unlikely to assign in any event due to loading.