Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1998-08-13
2001-06-12
Trost, William G. (Department: 2746)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S437000, C455S439000, C455S442000, C455S438000
Reexamination Certificate
active
06246876
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to inter-exchange hand-offs, and more particularly, to a method for synchronizing a group switch change within an anchor exchange with a mobile telephone traffic channel change during an inter-exchange hand-off.
2. Description of Related Art
Inter-exchange hand-offs involve the passing off of mobile telephone call connections from one mobile switching center to another mobile switching center. Within a hand-off operation, three types of mobile switching center exchanges may be present. An anchor exchange is the mobile switching center with which a call was originated. A serving exchange is the mobile switching center presently serving a call, and a target exchange is a mobile switching center to which a call is being handed off. A serving exchange and a target exchange may also comprise the anchor exchange. A hand-off from a serving exchange to the anchor exchange is known as a hand-off back, while a hand-off from the serving exchange to a non-anchor exchange is referred to as a hand-off to third.
One type of inter-exchange hand-off protocol is the ANSI 41 network protocol. In an ANSI 41 network, when a digital-to-digital or analog-to-digital hand-off is carried out, the problem of speech muting will appear. This problem arises due to the time delay required (about 400 milliseconds) for a mobile telephone to leave a present voice channel (digital or analog) and lock on to a new digital voice channel in the target cell of the target exchange. If the change of voice channels is not synchronized properly with the change of the group switch in the anchor exchange for the call, severe distortion will occur that adversely affects the speech and data quality during the hand-off. This problem is much less severe in analog-to-analog inter-exchange hand-offs because the speech muting delays of locking to an analog voice channel are insignificant. At present, no way exist to synchronize the group switch change of the anchor exchange with the mobile phone inter-exchange hand-off of voice channels. Some method for overcoming this problem is greatly desired.
SUMMARY OF THE INVENTION
The present invention comprises a method and apparatus for the synchronization of inter-exchange hand-offs within a cellular telecommunications system. The method and system enables synchronization of the change of a mobile station from a traffic channel served by a serving exchange to a traffic channel served by a target exchange with the switching of the traffic path for the call at the anchor exchange from the serving exchange to the target exchange.
When a mobile station switches from a traffic channel supported by a serving exchange to a traffic channel supported by a target exchange, the mobile station transmits an indicator message to the serving exchange to identify that the change of channels has occurred. In response to the indicator message, the serving exchange transmits a synchronization message to the anchor exchange for the call. In response to the synchronization message, the anchor exchange switches the group switch residing within the anchor exchange from the traffic path to the server exchange to the traffic path at the target exchange. This completes the inter-exchange handoff.
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Jenkens & Gilchrist P.C.
Milord Marceau
Telefonaktiebolaget L M Ericsson (publ)
Trost William G.
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