Voice Synchronization During Cellular to WLAN Handoff
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Solution Overview
Problem
Existing wireless communication systems face challenges in maintaining voice call quality during handoffs between cellular networks and WLANs, as differences in transmission delays can result in noticeable artifacts like 'pop' sounds or missing voice segments.
Innovation Solution
A method and system that temporarily maintain connections with both networks, compare voice data delays, and adjust timing to synchronize voice streams before completing the handoff, using a handoff synchronizer to ensure seamless transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voice calls are handed off between cellular network and WLAN, then network coverage and service continuity are improved, but voice call quality deteriorates due to transmission delay differences causing artifacts like pop sounds and missing voice segments
Solution Approach 1:
The system establishes a connecting call through the target WLAN network before breaking the existing cellular network connection. During this preliminary phase, the system measures transmission delays on both networks and adjusts packet timing to synchronize voice streams, preventing quality artifacts before the handoff completes
Solution Approach 2:
The system uses an IP gateway and call control equipment as intermediaries to coordinate the handoff process. These intermediaries manage the temporary dual-connection state, measure transmission delays, and synchronize voice packets between the cellular and WLAN networks to ensure seamless transition without quality degradation
2Reliability
If connections with both networks are temporarily maintained during handoff, then voice stream synchronization is improved, but device complexity and processing requirements increase
Solution Approach 1:
The system divides the handoff process into distinct functional segments: connection establishment, transmission delay measurement, voice packet timing adjustment, and connection switching. This segmentation allows complex operations to be managed in discrete, manageable steps with dedicated processing for each function
3Speed
If transmission delay differences between networks are not compensated, then handoff speed is improved, but voice call quality deteriorates due to timing mismatches and artifacts
Solution Approach 1:
The system dynamically adjusts the timing parameter of voice packets based on measured transmission delay differences between networks. By changing the timing parameter of packets sent over the WLAN connection relative to cellular packets, the system synchronizes voice streams and eliminates artifacts while maintaining fast handoff
Data Source
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AI summary
A method, mobile electronic device and system for synchronizing hand-off of a voice media session between a WAN/cellular network and a WLAN network. When a hand-off occurs, the connection with both networks is temporarily maintained and the voice data on both connections compared to determine differences in the delays experienced over both connections. The timing of one or both voice streams is adjusted to synchronize the voice streams, and then the handoff is completed.