Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-08-13
2001-08-28
Hunter, Daniel (Department: 2684)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S422100, C455S011100, C455S007000, C455S443000
Reexamination Certificate
active
06282425
ABSTRACT:
This application is the national phase of international application PCT/F197/00757 filed Dec. 4, 1997 which designated the U.S.
BACKGROUND OF THE INVENTION
This invention relates to a cellular radio system and particularly to efficient utilization of its capacity.
In prior art cellular radio system base stations are arranged in such a way that the geographical areas they cover usually overlap to some extent. Therefore mobile stations located in the border areas of the coverage areas of the base stations usually can select among several alternative base stations the one offering the best audibility. For practical reasons, however, the aim is to arrange adjacent base stations in such a way that their overlapping coverage area is as small as possible. This allows a geographical area of a maximum size to be covered with a minimum number of base stations.
The overlapping coverage area of adjacent base stations being as small as possible has, however, caused problems. For instance, in the border areas of the base station coverage areas there can be shadow regions where the audibility of the system is poor. A further problem is that the traffic capacity of one of the two adjacent base stations can be fully reserved, while the other can still have plenty of free traffic capacity available. In this case a mobile station trying to contact the fully reserved base station is not able to establish a telecommunication connection, unless it happens to be located in the overlapping (as small as possible) coverage area of the base stations where both base stations are audible. In order to enable the traffic load to be more efficiently divided between the base stations, it would therefore be advantageous that the overlapping coverage area of adjacent base stations would be as large as possible, whereby as many mobile stations as possible could select the base station among a plural number of base stations audible at the point concerned. This would, however, significantly increase the price of the system because more base stations would need to be built within an area of a specific size.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above mentioned problem and to provide a cellular radio system with a better audibility within the border areas between the base station coverage areas, which allows the overlapping coverage areas of adjacent base stations to be made larger, without causing a significant increase in the price of the system and which allows more efficient utilization of the traffic capacity available to the system. This object is achieved with a cellular radio system of the invention, said system including base stations which comprise transceiver means and antenna means for creating a radio connection to mobile stations located within their radio coverage area and an antenna means, which is operationally connected to at least a first and a second base station and which comprises means for further transmitting over the radio path signals received at least from the first and the second base station and, correspondingly, means for feeding signals received over the radio path to at least the first and the second base station. The cellular radio system of the invention is characterized in that, in order to adjust the load on said base stations, the system includes a control means for making said common antenna means to further transmit, at mutually different power levels, over the radio path the signals fed by the first and the second base station.
The invention is based on the idea that when a common antenna means is arranged for the base stations, in addition to separate antennas of their own, and when the common antenna means is equipped in such a way that both the base stations can use it at the same time for communicating with mobile stations located within the area, then the audibility of the system is significantly improved, because any shadow areas can then be eliminated more efficiently than before, without causing the need to increase the number of base stations. In a system like this the load on the base stations can be adjusted via the control unit in such a way that the control unit makes the antenna means to further transmit, at mutually different power levels, the signals received from the first and the second base station. This allows stepless adjustment of the base station coverage areas, allowing at the same time the load on the radio cells maintained by adjacent base stations to be adjusted optimally.
Thus the most significant advantages the invention provides are that it improves audibility within the border areas of the base station coverage areas, without significant additional costs, and at the same time it allows stepless levelling of the traffic load on adjacent base stations, performed by adjusting their coverage area, because a larger overlapping base station coverage area will include more mobile stations that can use either one of the adjacent base stations for their connections. In addition, due to larger base station coverage areas the number of handovers is reduced and they can be performed more smoothly than before, because at the moment of the handover the mobile station has already moved deep into the coverage area of the “new” base station, whereby the audibility between the new base station and the mobile station is better from the very beginning (after handover).
In a preferred embodiment of a cellular radio system of the invention the control means of the system can, e.g. on the basis of the prevailing traffic situation, connect the antenna means for the use of both the first and the second base station simultaneously or, alternatively, only for the first or the second base station. This embodiment of the invention allows more efficient utilization of the traffic capacity available. In other words, if for instance the traffic capacity of the first base station is fully reserved at a particular moment, but the second base station at the same time still has plenty of free traffic capacity, the control unit can bring the common antenna means to a state where it is only available to the second base station. This reduces the coverage area of the first base station and causes some of the mobile stations located within the overlapping coverage area of the first and the second base station to perform handover to the area of the second base station, which naturally releases traffic capacity at the first base station.
In the above mentioned embodiment the control unit is preferably arranged to control the antenna means so that it will maintain the traffic load between the base stations as even as possible. The common antenna means is thus made unavailable to one of the base stations already long before the traffic capacity of the base station concerned is fully in use.
The control means controlling the common antenna element can be the base station controller of one of the base stations. Alternatively, said control means can consist of an independent control unit arranged in connection with the common antenna means, said control unit controlling the common antenna means only on the basis of the data transmitted by the first and the second base station. Due to this it is possible not to burden the higher levels of the system, such as the base station controller or the mobile services switching centre, with the control of the common antenna means.
Preferred embodiments of the cellular radio system of the invention are described in the attached dependent claims
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patent: 0 566 551 (1993-10-01), None
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patent: 96/38014 (1996-11-01), None
Hunter Daniel
Nokia Telecommunications Oy
Pillsbury & Winthrop LLP
Zewdu Meless
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