Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1996-10-21
2001-01-16
Eisenzopf, Reinhard J. (Department: 2745)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S444000, C455S449000
Reexamination Certificate
active
06175735
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a mobile radio communications system, a base station and a controller for such a mobile radio communications system, and also to a method of handing over a call.
2. Description of Related Art
Contemporary cellular mobile radio communications systems are generally formed by a plurality of base stations, in which each base station can be linked to a given number of subscriber stations (=mobile stations) whose locations may change inside a certain geographical area. Such a geographical area will be referenced radio coverage area or radio cell in the following. The radio coverage areas of individual base stations in the mobile radio communications system may then be so large that they cover radio coverage areas of other base stations. As a result, the respective geographical areas of radio cells of different sizes may be covered several times. Depending on the size of the geographical area, the radio cells or radio coverage areas may then be combined to individual hierarchical cell layers. Once a mobile subscriber station moves away from the radio coverage area of a base station with which it is just having a telephone call, care has to be taken that the call to the mobile subscriber station is taken over by another radio cell, i.e. by another base station. The occurrence of such a change of radio cells may be detected, for example, by measurements of the signal field strength, the signal-to-noise ratio, the bit error rate, the distance between base station and mobile subscriber station, and so on. If such a situation is detected, a call handover or handoff may be necessary.
EP 526 436 A1 proposes a method of call handover for a mobile radio communications system with various cell layers. A criterion for a call handover is used the speed of the relevant mobile subscriber station.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a mobile radio communications system of the type defined in the opening paragraph, in which improved use of the individual radio coverage areas is possible.
This object is achieved with a mobile radio communications system of the type defined in the opening paragraph, in that the mobile radio communications system comprises means for handing over a call between a base station and a mobile station in dependence on the dwell time of the mobile station in a radio coverage area and/or in dependence on the duration of the call.
It is possible for a call to be handed over from the coverage area of a base station to the coverage area of the further base station without considerable additional expenditure, in that the dwell time or the duration of the call of a mobile station can be simply determined, for example, by a counter, without the necessity of having a costly detection of, for example, the speed of the mobile station. All the radio cells i.e. all the radio coverage areas of the mobile radio communications system are then identified by their respective cell layers and can thus be assigned to a specific cell hierarchy. Consequently, the call is released, i.e. the call handover is triggered in dependence on the type of cell, that is to say, in accordance with the respective hierarchy of the cell of origin, and the dwell time of a call in the coverage area of the respective destination cell, and while the identification of the destination cells of the respective cell layers is taken into consideration. In addition, in dependence on the type of cell, that is to say, in accordance with the respective hierarchy of the cell of origin and the duration of a call from a mobile station to the base station of the cell of origin, and while the identification of the destination cells of the respective cell layers is taken into consideration, a call can be handed over to the further base stations which also cover the radio coverage area. By taking the call duration in a cell of origin into consideration, the call handover can be suppressed in dependence on the type of the respective cell if also further means in the system can be used to remove the reason why a call is triggered. On the whole, by taking the dwell time and/or the call duration into consideration, a call is thus handed over fast, the destination cells are selected reliably and individual radio coverage areas are used with maximum efficiency.
An effective control of the call handover is ensured when the mobile station is connected to the base station of a higher-order cell layer, that is, a macro cell or umbrella cell, in that the mobile radio communications system has at least two layers of a cell hierarchy, and in that means are provided for handing over a call which exists between a base station and a mobile station in dependence on the dwell time of the mobile station in a radio coverage area, if a call is handed down to a radio station of a lower-order layer of the cell hierarchy.
The control of the call handover in dependence on the dwell time may then be effected in that the means for handing over a call which exists between a base station and a mobile station in dependence on the duration of the call are provided if the duration of the call exceeds a predefinable first value.
Accordingly, an effective control of the call handover is ensured when the mobile station is connected to the base station of a lower-order cell layer, i.e. micro cell or macro cell, in that the mobile radio communications system has at least two layers of a cell hierarchy, and in that the means for handing over a call which exists between a base station and a mobile station in dependence on the duration of the call are provided if a call is handed up to a radio station of a higher-order layer of the cell hierarchy.
The control of a call handover in dependence on the duration of the call may in that case be effected in such a way that the means for handing over a call which exists between a base station and a mobile station in dependence on the duration of the call are provided if the duration of the call falls short of a predefinable first value.
A highly reliable control of the call handover is effected in that the mobile radio communications system comprises further means for handing over a call in dependence on predefinable criterions, more particularly, criterions with respect to layer, distance and/or quality.
For an effective implementation of the handing over of a call, it is advantageous that the mobile radio communications system comprises means for identifying an assignment of the base stations of the mobile radio communications system to at least two hierarchical layers.
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
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Appiah Charles N.
Eisenzopf Reinhard J.
Lucent Technologies - Inc.
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