Inter-Technology Handoff Silence Reduction via MSC Indicator
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Solution Overview
Problem
Conventional wireless communication systems experience significant voice gaps during handoffs from packet-data wireless access networks to circuit wireless access networks, leading to communication disruptions and potential call drops due to the MSC/VLR's unawareness of inter-technology handoffs.
Innovation Solution
Incorporating a special indicator in handoff requests to the MSC/VLR to delay the handoff command until the new voice bearer path is established, reducing the voice gap by synchronizing the disconnection from the packet-data network with the connection to the circuit wireless access network.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If conventional handoff procedures are used without special indicators, then the handoff process is simple, but a large voice gap of 2000 milliseconds occurs during inter-technology handoff
Solution Approach 1:
The mobile device sends a handoff request message with a special indicator (setBit) before the actual handoff occurs. This preliminary indication allows the MSC/VLR to prepare the circuit-switched voice bearer path in advance, so that when the handoff is executed, the voice path is already ready, reducing the voice gap from 2000ms to 500ms.
Solution Approach 2:
A special indicator (setBit) is introduced as an intermediary element in the handoff request message. This bit acts as a signal to the MSC/VLR that an inter-technology handoff is being requested, triggering the MSC/VLR to initiate voice bearer path setup procedures. This intermediary mechanism enables coordination between packet-data and circuit-switched networks without complex signaling changes.
2Reliability
If the handoff is delayed until the new voice bearer path is established, then the voice gap is reduced, but the handoff coordination becomes more complex
Solution Approach 1:
The MSC/VLR receives feedback through the setBit indicator in the handoff request message, which informs it that an inter-technology handoff is needed. The MSC/VLR then coordinates the voice bearer path establishment and provides feedback by delaying the handoff command until the path is ready. This feedback mechanism ensures call continuity while maintaining relatively simple coordination through a single bit indicator.
3Speed
If the mobile device transitions quickly between networks, then the handoff speed is high, but communication silence occurs due to uncoordinated disconnection and connection
Solution Approach 1:
The MSC/VLR performs preliminary action by setting up the circuit-switched voice bearer path before the mobile device actually disconnects from the packet-data network. The handoff command is delayed until the voice path is established, ensuring that the connection is ready before disconnection occurs, thereby eliminating communication silence while maintaining fast handoff speed.
Data Source
AI summary
To perform an inter-technology handoff, an indicator in a service request message is received by a mobile switching center (MSC). The indicator is to indicate to the MSC that an inter-technology handoff from a packet-data wireless access network to a circuit wireless access network has been requested. The behavior of the MSC is modified in response to the indicator to reduce the communication silence during the inter-technology handoff.