Telecommunications – Radiotelephone system – Zoned or cellular telephone system
Reexamination Certificate
1999-12-10
2002-02-05
Chang, Vivian (Department: 2682)
Telecommunications
Radiotelephone system
Zoned or cellular telephone system
C455S436000, C455S439000
Reexamination Certificate
active
06345186
ABSTRACT:
BACKGROUND
The present invention relates to an arrangement for providing mobile stations in (or outside) a cellular communication system with radio coverage when they are in a mobile vehicle. The invention also relates to a base station providing mobile stations in a mobile vehicle with radio coverage, to a cellular communication system in which radio coverage is provided for mobile stations in a mobile vehicle and to a method of providing radio communication for mobile stations in a mobile vehicle.
The user of a mobile station who is inside a mobile vehicle such as for example a train or similar will notice that the radio coverage sometimes is poor or even non-existent. This is a problem since when travelling it may be impossible to make or to receive any calls at certain parts of the track, ongoing calls may be dropped and the quality may also be varying. If, for example, a part of the track lacks radio coverage, such as for example in a tunnel, then the inside of the vehicle, e.g. the train, will experience the same lack of coverage and all ongoing calls will be dropped. It will of course also be impossible to make or receive any calls.
There are several problems associated with the provision of radio coverage to mobile stations in a mobile vehicle. Often such a mobile vehicle comprises a metal structure, inside which the mobile stations are located. The radio frequent signal, uplink (towards the base station) as well as downlink (from the base station to the mobile stations) will therefore be attenuated which has as a consequence that a mobile station will have to transmit on a higher power level than would have been necessary for example in free air. This means that the available talk/standby time will be decreased which is clearly disadvantageous. Furthermore the call will have a lower signal strength. This means that a call has a higher probability of being dropped close to the cell border. Another problem associated with mobile stations in a mobile vehicle is that all mobile stations in a specific network will be handed over to the next cell at about the same location which produces a high load on the network as such. The individual calls also run a certain risk of being dropped during a handover. Another problem is that all the cells that the mobile vehicle passes have to be dimensioned for the mobile vehicle, or rather the mobile stations that may be travelling with it, even though the cell otherwise might be sparsely populated or hardly populated at all which as such leads to a poor and unsatisfactory usage of equipment.
Numerous attempts have been done to find a satisfactory solution to these problems. Various solutions are for example based on the use of various kind of repeaters in order to enhance the radio coverage inside the train from the surrounding cell it passes through. It is common to all such known solutions that they make use of the existing cellular network and they can not make the radio environment inside the mobile vehicle any better than it is outside the mobile vehicle, and, if a part of the track lacks coverage, the situation will be the same inside the mobile vehicle.
U.S. Pat. No. 5,519,761 relates to an airborne radio telecommunication system. According to this document an aircraft can be provided with a repeater, as discussed above, but in a particular embodiment the repeater can be replaced by an airborne base station. The airborne base station has capability of registering telephones at the aircraft and the airborne base station then registers the telephone in the ground based system. Thus, once a telephone has been registered in the airborne base station, the airborne base station searches for the strongest pilot signal from a ground base station and registers with it therefore, also here the existing communications system is used, an airborne base station substantially only being used for temporary registration purposes.
SUMMARY
What is needed is therefore an arrangement that efficiently can provide a mobile station with radio coverage when the mobile station is inside a mobile vehicle, particularly a mobile vehicle comprising a metal structure, in a satisfactory manner, particularly without requiring the mobile station transmitting using a particularly high power level and with a satisfactory or high strength and carrier to interference ratio. An arrangement is also needed through which the dropping of calls due to the mobile vehicle having a poor radio coverage can be reduced or avoided. Particularly a base station is needed trough which the above mentioned objects can be achieved. Still further a cellular communication system is needed through which the above mentioned objects are fulfilled and through which the load on the network can be appropriately dimensioned without taking into consideration temporary situations such as for example a mobile vehicle passing which considerably changes the circumstances in the network as far as load etc. is concerned. Furthermore a communication system is needed through which the equipment in the system can be efficiently used and through which the load is not unduly high, i.e. for example because of a number of mobile stations having to perform a handover at substantially the same time at substantially the same place. Particularly an arrangement and a system respectively is needed through which the risk of calls being dropped due to poor radio coverage or due to handover is reduced.
A method of providing a mobile station with the radio coverage when the mobile station is within the mobile vehicle is also needed through which the above mentioned objects are accomplished.
Therefore an arrangement for providing mobile stations, of a cellular communication system, in a mobile vehicle with radio coverage, said mobile vehicle being mobile within or outside the cellular radio network which comprises a number of fixed radio base stations and a number of switching arrangements. The arrangement comprises a mobile base station arranged within the mobile vehicle which serves at least one cell provided in said mobile vehicle, internal antenna means arranged within the mobile vehicle for providing communication with the mobile stations in the mobile vehicle, external communication means for providing communication between the mobile vehicle and the core network (the fixed part of the network) and, when the mobile base station is (or intends to become) stationary within a fixed cell, at least for a given time period, it is docked with said fixed cell such that handovers are allowed between the mobile base station cell and the said stationary cell. Particularly handovers are not allowed when the mobile cells served by the mobile base station(s) are not within coverage of and stationary etc. within a fixed cell. Thus the inventive concept comprises the provision of one or more mobile cells within the mobile vehicle. Through using an appropriate internal antenna arrangement, the entire mobile vehicle will have an excellent radio environment. Such an antenna arrangement is advantageously so arranged that the distance between any mobile station within the mobile vehicle and the antenna arrangement is as short as possible leading to the requirements as to required power level are low which both results in low power consumption in the respective mobile stations and it also has as a result that only a little radio frequency energy is radiated into surrounding cells. The mobile cell(s) within the mobile vehicle will therefore not be noticed by the cells through which it travels. Particularly handovers between a mobile cell served by the mobile base station and a fixed cell are allowed when the mobile vehicle is detected or indicates that it will becomes stationary in a fixed cell in addition to when it actually is stationary within a fixed cell. Even more particularly, a neighbouring relationship is established between a mobile cell and a fixed cell when the mobile cell intends to stop in a fixed cell, according to which neighbouring relationship handovers are allowed between the mobile and the fixed cells respectively.
Kopp Nina
Östrup Peter
Schultz Johan
Burns Doane Swecker & Mathis L.L.P.
Chang Vivian
Nguyen Duc
Telefonaktiebolaget LM Ericsson (publ)
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