Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Patent
1997-04-24
1999-11-30
Bost, Dwayne D.
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
45441, 45440, 45442, H04Q 722, H04Q 730, H04Q 738
Patent
active
059958359
DESCRIPTION:
BRIEF SUMMARY
The present invention relates in general to a method of transferring a call set up with a mobile station in a digital cellular radio network from one cell to another. Such a transfer is generally referred to as a "handover". More particularly, the invention relates to a safe handover method for use in a transport network for handing over a call set up with a mobile station from a current channel associated with a current base station to a following channel associated with a following base station. The method is implemented along a mobile station path which is associated in deterministic manner with successive base stations in a radio network for communicating with mobile stations. In addition, the network is "synchronized", which means that the base stations in the network are synchronized with one another ignoring a substantially zero propagation time difference. The unit time intervals for conveying data in the transmit and receive channels for two arbitrary base stations of the radio network coincide.
In a cellular digital network of the GSM (global system for mobile communication) network, the handover of a call from a current channel to a following channel appears as a critical stage in call management. Such a handover can give rise to two types of momentary break in the call, referred to as a "synchronization" break and as a "power" break. A momentary synchronization break, which typically lasts for about 20 ms in GMS, stems from synchronization of the mobile station. The mobile station is synchronized in time and in frequency on the current channel prior to handover and it needs to resynchronize onto the following channel after handover. During the time required by the mobile station to achieve new synchronization, the call is momentarily interrupted. A power break is the result of the fact that when the mobile station is changing cells, it is located at maximum acceptable distances both from the current base station and from the following base station. In a notional zone at the boundary between two cells, the power of data received by the mobile station in said zone from each of the base stations concerned, i.e. the current station and the following station, is therefore at a minimum level. Radio propagation phenomena can thus cause the mobile station to cease receiving call data momentarily.
The prior art provides for remedying the causes of call synchronization breaks by providing a synchronized network in which the current and following channels concerned with a handover of a particular call are identical. In GSM, this identity of current and following channels gives rise to the same time interval and the same frequency. However, it provides no way of mitigating "power" breaks in a call that is set up.
A main object of the invention is to provide a safe method of channel-to-channel handover for a call set up with a mobile station in a radio network, that provides an effective remedy against power breaks in a call.
To this end, the invention provides a method of safely handing over a call set up between a mobile station using a current channel associated with a current base station to a following channel associated with a following base station along a path in a transport network for said mobile station, which path is associated in deterministic manner with successive base stations in a radio network for communication with mobile stations, the method being characterized in that said current and following channels are identical, and in that it comprises the following cyclical steps: said established call in said following channel as transmitted in said current channel by said mobile station; which said UP data is received by the current base station in said current channel and by the following base station in said following channel; call over said current and following channels respectively from said current base station and said following base station, as soon as said propagation time difference is less than a first predetermined threshold; and channel, and validating said call in the following c
REFERENCES:
patent: 5101501 (1992-03-01), Gilhousen
patent: 5260943 (1993-11-01), Comroe et al.
patent: 5327575 (1994-07-01), Menich et al.
patent: 5513380 (1996-04-01), Ivanov et al.
patent: 5648955 (1997-07-01), Jensen et al.
patent: 5711003 (1998-01-01), Dupuy
patent: 5812539 (1998-09-01), Dent
patent: 5924033 (1999-07-01), Carlsson et al.
de Seze Fabrice
Kumar Vinod
ALCATEL N.V.
Bost Dwayne D.
Gantt Alan
LandOfFree
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