Telecommunications – Transmitter and receiver at separate stations – Plural transmitters or receivers
Patent
1996-03-06
1998-10-20
Pham, Chi H.
Telecommunications
Transmitter and receiver at separate stations
Plural transmitters or receivers
455517, 455502, H04B 700
Patent
active
058261974
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a frequency correction scheme for setting up transmission and reception frequencies of each base station at high precision, in a mobile communication system in which a plurality of radio base stations form respective radio zones, and a mobile station makes communications with the base stations while moving within the radio zones and among the radio zones.
BACKGROUND ART
In a mobile communication scheme, it is necessary for a precision of a transmission frequency from a base station to be a high precision. This is because, when an error of a transmission frequency of a base station has a large value for example, it is going to interfere with other base stations and mobile stations which make communications at neighboring frequencies, and as a result the frequency utilization efficiency is going to be deteriorated.
In addition, in a digital mobile communication scheme using phase modulation, there is also a case in which it becomes impossible to demodulate when a frequency error at a mobile station and a base station becomes greater than or equal to a certain tolerable value.
Consequently, in a base station of a conventional mobile communication scheme, a thermostatic chamber type frequency generator is provided in a transmission and reception device of a base station, so as to realize a high precision.
However, a high precision thermostatic chamber type frequency generator used in a transmission and reception device of a base station is expensive, as well as voluminous, and there is a problem that it is impossible to realize an economical and compact base station transmission and reception device.
On the other hand, in a mobile communication system, a mobile station moves through a plurality of radio zones and makes communication while receiving radio signals from a base station of each radio zone, so that it is necessary for a frequency precision of each base station to be a high precision and the same throughout an entire service area.
Consequently, in a conventional mobile communication system, a frequency precision of an entire service area is made uniform by providing a high precision reference frequency generator in a base station. In particular, no function for correcting a reference frequency of a base station is provided, and only a mobile station makes own station's reference frequency correction with respect to a reception frequency.
In such a conventional mobile communication system, at a time of channel switching during a zone transition while in communication, a switching operation is carried out at a mobile station side after own station's frequency is corrected to a frequency of a moving destination, so that a communication impossible time during a channel switching increases. Also, there is a drawback that a possibility for being absent upon arrival of a call increases in a case of waiting for receiving a call.
In addition, as described above, each base station is expensive as it has a high precision reference frequency generator, and a device size becomes large because of a use of a thermostatic chamber type reference frequency generator, etc., and in conjunction with that, there is a problem that a construction of a system becomes difficult as it becomes difficult to select a location to set up the device, etc.
DISCLOSURE OF THE INVENTION
Therefore, the present invention has an object to provide a base station frequency correction scheme in a mobile communication system and a mobile station device and a base station device for that purpose which are capable of setting transmission and reception frequencies in high precision, without using an expensive and voluminous high precision frequency generator.
Also, the present invention has another object to provide a base station frequency correction scheme in a mobile communication system in which it is made economical by setting a frequency precision of each base station in high precision inexpensively, while the inconvenience at times of waiting for receiving a call and radio zone transi
REFERENCES:
patent: 4509200 (1985-04-01), Luginbuhl et al.
patent: 4901368 (1990-02-01), Arnold et al.
patent: 5471648 (1995-11-01), Gourgue
patent: 5613193 (1997-03-01), Ishikawa et al.
Fujii Teruya
Hamada Katsunori
Kakinuma Kazuhiko
Nagata Kiyohito
Wakabayashi Tatsuaki
Arthur Gertrude
NTT Mobile Communications Network Inc.
Pham Chi H.
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