Emergency Call Handling in Wireless Communication Systems
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Solution Overview
Problem
Emergency calls in wireless communication systems often experience delays due to unsuccessful attempts on the serving frequency or after redirection to another RAT or frequency, primarily because the network is unavailable, leading to high priority call delays.
Innovation Solution
A wireless communication device scans acceptable cells of any public land mobile network for the cell with the highest power and places the emergency call on that cell, increasing the chances of successful connection by expanding the number of available cells and reducing the likelihood of call drops due to dynamic RF conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the UE searches only suitable cells on which to place the emergency call, then the cell selection process is simple, but the emergency call may fail multiple times due to network unavailability, introducing delay
Solution Approach 1:
The patent segments the cell selection process into two distinct phases: first identifying acceptable cells (cells where emergency calls can be placed) and then selecting the best cell from those acceptable cells. This segmentation allows the UE to consider a broader set of cells for emergency call placement, increasing the likelihood of success while managing delay through structured search procedures.
Solution Approach 2:
The patent applies partial action by requiring that cells must be both acceptable and suitable before selection. This partial requirement (cells must satisfy multiple criteria) increases the reliability of emergency call placement by ensuring the selected cell can actually handle emergency calls, while the systematic approach prevents excessive searching that would cause delay.
2Reliability
If the UE redirects the emergency call to a different RAT or frequency after unsuccessful attempt, then the chance of successful connection increases, but the number of attempts increases, introducing delay
Solution Approach 1:
The patent performs preliminary action by having the UE identify and prepare a list of acceptable cells before attempting emergency call placement. This preliminary identification of suitable cells across different RATs and frequencies allows the UE to make informed redirection decisions quickly, increasing connection success while minimizing the time spent on multiple attempts.
Solution Approach 2:
The patent implements feedback mechanisms where the network provides information about acceptable cells and the UE uses this feedback to make intelligent redirection decisions. The UE receives feedback about cell suitability and uses this information to select the best cell for emergency call placement, reducing unnecessary attempts and minimizing delay.
3Reliability
If the UE switches to GSM mode to place emergency call, then location information can be used to locate the UE, but the UE may not be able to place the call if GSM is not available or network is unavailable
Solution Approach 1:
The patent applies universality by enabling the UE to operate in multiple modes (GSM and WCDMA) and select the appropriate mode for emergency call placement. The UE can switch between GSM and WCDMA based on availability and suitability, ensuring both location information availability and call placement flexibility. This multi-functional approach allows the UE to adapt to different network conditions while maintaining emergency call capability.
Data Source
AI summary
This disclosure describes techniques for efficiently handling emergency calls in a wireless communication system. The techniques are executed in a wireless communication device (WCD) that is interoperable between radio access technologies (RATs). For example, the WCD may support interoperability between the Global System for Mobile Communications (GSM) and the Universal Terrestrial Radio Access Network (UTRAN). Typically, the emergency call is redirected to another RAT or frequency following an unsuccessful emergency call. However, instead of searching only suitable cells on which to place the emergency call, a WCD that implements the described techniques searches acceptable cells of any public land mobile network and attempts to place the emergency call on the cell with the highest power. By placing the emergency call on the cell with the highest power, the techniques reduce delay in placing emergency calls by reducing the number of attempts required before successfully placing the emergency call.