JPWO1996001545A1 - Mobile communication system using base station frequency correction method - Google Patents

Abstract

(57) [Abstract] A mobile communication system having a high-precision frequency base station device having a high-precision frequency oscillator, and a low-precision frequency base station device that is a base station device having a low-precision frequency oscillator and receives transmission waves from the high-precision frequency base station device at a transmission frequency with a predetermined frequency accuracy, and performs transmission and reception by controlling its own transmission and reception frequency to match the frequency accuracy of the received transmission waves. A mobile station device is provided that receives the transmission waves from the high-precision frequency base station device, controls a reference frequency that serves as a reference for its own transmission and reception frequency to match the frequency accuracy of the received transmission waves, and performs transmission and reception with the base station at a transmission and reception frequency based on the controlled reference frequency, and the low-precision frequency base station device may receive the transmission waves from the mobile station device that performs transmission and reception at a transmission and reception frequency based on the controlled reference frequency, controls the reference frequency that serves as a reference for its own transmission and reception frequency to match the frequency accuracy of the received transmission waves, and performs transmission and reception with the mobile station at a transmission and reception frequency based on the controlled reference frequency.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a frequency correction method for setting the transmission and reception frequencies of each base station with high accuracy in a mobile communication system in which multiple radio base stations each form a radio zone and mobile stations communicate with the base stations by moving within and between radio zones. Background Art In a mobile communication system, the accuracy of the transmission frequency from a base station must be high. This is because, for example, if the error in the transmission frequency of a base station is large, it will cause interference to other base stations and mobile stations communicating on adjacent frequencies, resulting in a deterioration in frequency utilization efficiency.

Furthermore, in digital mobile communication systems using phase modulation, if the frequency error between the mobile station and the base station exceeds a certain tolerance, demodulation may become impossible.

Therefore, in conventional mobile communication systems, base stations are equipped with oven-controlled frequency oscillators in their transceiver equipment to improve accuracy.

However, the oven-controlled, high-precision frequency oscillators used in base station transmitters and receivers are expensive and bulky, making it difficult to reduce the cost and size of base station transmitters and receivers.

On the other hand, in a mobile communication system, a mobile station moves through multiple radio zones and communicates by receiving radio signals from base stations in each radio zone. Therefore, it is necessary for the frequency accuracy of each base station to be high and consistent throughout the entire service area.

Therefore, in conventional mobile communication systems, base stations are equipped with high-precision reference frequency oscillators to ensure uniform frequency accuracy throughout the service area. Base stations do not have the ability to specifically correct their own reference frequencies; only mobile stations correct their own reference frequencies relative to their receiving frequencies.

In conventional mobile communication systems, when switching channels during a call while transitioning between zones, the mobile station must first adjust its own frequency to the new frequency before switching. This increases the time during which calls are unavailable. Another drawback is that the rate of missed calls increases when the mobile station is idle.

Furthermore, as mentioned above, each base station has a high-precision reference frequency oscillator, which makes it expensive, and the use of an oven-controlled reference frequency oscillator or the like increases the size of the equipment, which makes it difficult to select an installation location, etc., making it difficult to build a system. DISCLOSURE OF THE INVENTION Therefore, an object of the present invention is to provide a base station frequency correction method in a mobile communication system that can improve the precision of transmission and reception frequencies without using an expensive, voluminous high-precision frequency oscillator, and a mobile station apparatus and base station apparatus therefor.

Another object of the present invention is to provide a base station frequency correction method for a mobile communications system that improves service by inexpensively improving the frequency accuracy of each base station and eliminating problems that occur when a mobile station is in standby mode or when moving between radio zones.

According to one aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the transmission and reception frequency precision of which is not always uniform, and a mobile station that communicates through the plurality of base stations while moving within the plurality of radio zones, the mobile communications system comprising: a high-precision frequency base station device having a high-precision frequency oscillator; and a low-precision frequency base station device other than the high-precision frequency base station device, having a low-precision frequency oscillator, the low-precision frequency base station device receiving a transmission wave from the high-precision frequency base station device at a transmission frequency with a predetermined frequency precision, and controlling its own transmission and reception frequency to match the frequency precision of the received transmission wave for transmission and reception.

According to another aspect of the present invention, there is provided a base station device for each base station in a mobile communication system comprising multiple base stations forming multiple radio zones, each base station having a variable transmission and reception frequency accuracy, and a mobile station that moves within the multiple radio zones and communicates via the multiple base stations, the base station device comprising: receiving means for receiving transmission waves from other base stations at a transmission frequency with a predetermined frequency accuracy; frequency control means for controlling the transmission and reception frequency of the base station to match the frequency accuracy of the transmission wave received by the receiving means; and a transceiver for transmitting and receiving at the transmission and reception frequency controlled by the frequency control means.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the mobile station comprising: a high-precision frequency base station device having a high-precision frequency oscillator; a mobile station that receives transmission waves from the high-precision frequency base station device at a transmission frequency with a predetermined frequency accuracy, controls a reference frequency that serves as a basis for its own transmission and reception frequency to match the frequency accuracy of the received transmission waves, and transmits and receives signals to and from the base station at a transmission and reception frequency based on the controlled reference frequency; and a low-precision frequency base station device other than the high-precision frequency base station device having a low-precision frequency oscillator, that receives transmission waves from a mobile station that transmits and receives signals at a transmission and reception frequency based on the controlled reference frequency, controls a reference frequency that serves as a basis for its own transmission and reception frequency to match the frequency accuracy of the received transmission waves, and transmits and receives signals to and from the mobile station at a transmission and reception frequency based on the controlled transmission and reception frequency.

According to another aspect of the present invention, there is provided a mobile station device for a mobile station in a mobile communication system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the mobile station device comprising: means for receiving transmission waves from the base stations and determining whether the received transmission waves are of a high-precision frequency; means for controlling a reference frequency that serves as the basis for the transmission and reception frequencies of the mobile station to match the frequency accuracy of the transmission waves received by the receiving and determining means; and means for transmitting and receiving signals to and from the base stations at a transmission and reception frequency based on the reference frequency controlled by the controlling means.

According to another aspect of the present invention, there is provided a base station device for each base station in a mobile communication system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmit and receive frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the base station device comprising: means for receiving a transmission wave from the mobile station and determining whether the received transmission wave is of a high-precision frequency; means for controlling a reference frequency that serves as a basis for the transmit and receive frequencies of the base station itself to match the frequency accuracy of the transmission wave received by the receiving and determining means; and means for transmitting and receiving signals to and from the mobile station at a transmit and receive frequency based on the reference frequency controlled by the controlling means.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the system comprising: a base station device for each base station that receives transmission waves from other base stations at a transmission frequency having a predetermined frequency accuracy and determines whether the received transmission waves are at a high-precision frequency based on frequency accuracy information contained in the transmission waves; a frequency control means that, when the receiving means determines that the received transmission waves are at a high-precision frequency, controls a reference frequency that serves as the basis for the transmission and reception frequency of the base station to match the frequency accuracy of the transmission waves received by the receiving means; and a transmission means that, after the frequency control means controls the base station's reference frequency to match the frequency accuracy of the transmission waves received by the receiving means, transmits transmission waves containing frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high, at a transmission frequency based on the reference frequency controlled by the frequency control means.

According to another aspect of the present invention, a mobile communications system is provided that includes a plurality of base stations that form a plurality of radio zones and whose transmit and receive frequency accuracy is not always uniform, and a mobile station that moves within the plurality of radio zones and communicates through the plurality of base stations. The base station equipment of each base station detects the presence or absence of transmission waves from other base stations, notifies a mobile station within the base station's radio zone of the transmission frequency of the detected transmission wave, and causes the mobile station to identify whether the detected transmission wave is a high-precision frequency and return the identification result. When the identification result returned from the mobile station indicates that the detected transmission wave is a high-precision frequency, the base station equipment controls the reference frequency that serves as the basis for the base station's transmit and receive frequency to match the frequency accuracy of the detected transmission wave. a frequency control means for controlling a reference frequency of the mobile station to match the frequency accuracy of the detected transmission wave; a transmission means for transmitting a transmission wave containing frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high, at a transmission frequency based on the reference frequency controlled by the frequency control means, after the frequency control means has controlled the reference frequency; a mobile station device for receiving a transmission wave at a transmission frequency notified by the receiving means of a base station currently serving the mobile station, and identifying whether the received transmission wave is a high-accuracy frequency based on the frequency accuracy information included in the transmission wave; and an identification result return means for returning the identification result obtained by the identification means to the base station currently serving the mobile station.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the transmission and reception frequency precision of which is not always uniform, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the system comprising: a base station device of each base station that detects the presence or absence of transmission waves from a mobile station communicating with another base station, and identifies whether the detected transmission waves are of a high-precision frequency based on frequency precision information contained in the detected transmission waves; and a frequency control device that, when the identification means identifies the detected transmission waves as of a high-precision frequency, adjusts the reference frequency that serves as the basis for the transmission and reception frequencies of the base station to match the frequency precision of the detected transmission waves.

According to another aspect of the present invention, there is provided a mobile communication method for a mobile communication system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracy, and a mobile station that communicates through the base stations while moving within the plurality of radio zones, the method comprising the steps of: transmitting a transmission wave at a transmission frequency with a predetermined frequency accuracy from a high-precision frequency base station device having a high-precision frequency oscillator; and receiving the transmission wave from the high-precision frequency base station device, in a low-precision frequency base station device having a low-precision frequency oscillator other than the high-precision frequency base station device, and adjusting its own transmission and reception frequency to match the frequency accuracy of the received transmission wave, thereby transmitting and receiving.

According to another aspect of the present invention, there is provided a mobile communication method for a mobile communication system including a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the method comprising the steps of: transmitting a transmission wave at a transmission frequency with a predetermined frequency accuracy from a high-precision frequency base station device having a high-precision frequency oscillator; receiving, in the mobile station device, the transmission wave from the high-precision frequency base station device, controlling a reference frequency that serves as a reference for the mobile station's transmission and reception frequency to match the frequency accuracy of the received transmission wave, and transmitting and receiving with the base station at a transmission and reception frequency based on the controlled reference frequency; and receiving, in the low-precision frequency base station device other than the high-precision frequency base station device, the transmission wave from a mobile station device that transmits and receives at a transmission and reception frequency based on the controlled reference frequency, controlling a reference frequency that serves as a reference for the mobile station's transmission and reception frequency to match the frequency accuracy of the received transmission wave, and transmitting and receiving with the mobile station at a transmission and reception frequency based on the controlled reference frequency.

According to another aspect of the present invention, there is provided a mobile communication method for a mobile communication system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmit and receive frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the method comprising the steps of: receiving, in the base station device of each base station, a transmission wave from another base station at a transmission frequency having a predetermined frequency accuracy and determining whether the received transmission wave is a high-precision frequency based on frequency accuracy information contained in the received transmission wave; when the received transmission wave is determined to be a high-precision frequency in the receiving and determining step, controlling, in the base station device of each base station, a reference frequency that serves as a basis for the transmission and receive frequency of the base station to match the frequency accuracy of the received transmission wave; and, after adjusting the base station's reference frequency to match the frequency accuracy of the received transmission wave in the controlling step, transmitting, in the base station device of each base station, a transmission wave including frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high, at a transmission frequency based on the reference frequency controlled in the controlling step.

According to another aspect of the present invention, a mobile communication method for a mobile communication system including a plurality of base stations forming a plurality of radio zones, each of which has a variable transmission and reception frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, includes the steps of: detecting, in each base station's device, the presence or absence of a transmission wave from another base station and notifying a mobile station located within the base station's radio zone of the transmission frequency of the detected transmission wave; receiving, in the mobile station's device, a transmission wave based on the transmission frequency notified from the currently located base station in the detection and notification step, and identifying, based on frequency accuracy information included in the received transmission wave, whether the received transmission wave is a high-accuracy frequency; and, in the mobile station's device, determining whether the received transmission wave is a high-accuracy frequency. A mobile communication system is provided, comprising: a step of returning the identification result obtained in the step of transmitting and identifying to the currently serving base station; a step of, when the identification result returned from the mobile station in the returning step indicates that the detected transmission wave is of a high-precision frequency, controlling, in the base station equipment of each base station, a reference frequency that is the basis for the transmission and reception frequency of the base station to match the frequency accuracy of the detected transmission wave; and a step of, after adjusting the reference frequency in the controlling step to match the frequency accuracy of the detected transmission wave, transmitting, in the base station equipment of each base station, a transmission wave including frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high, at a transmission frequency based on the reference frequency controlled in the controlling step.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the system comprising: an identification step in the base station device of each base station detecting the presence or absence of transmission waves from a mobile station communicating with another base station and identifying whether the detected transmission waves are of a high-precision frequency based on frequency accuracy information contained in the detected transmission waves; and a step in the base station device of each base station, when it is identified in the detection and identification step that the detected transmission waves are of a high-precision frequency, adjusting the reference frequency that serves as the basis for the transmission and reception frequency of the base station to match the frequency accuracy of the detected transmission waves.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, wherein the plurality of base stations are in a predetermined order and have means for mutually notifying each other of information indicating the predetermined order; and wherein each base station receives transmission waves from other base stations, determines whether to perform frequency correction based on the predetermined order, and, if it determines to perform frequency correction, controls its own transmission and reception frequency to match the frequency accuracy of the received transmission waves, thereby transmitting and receiving.

According to another aspect of the present invention, there is provided a base station device for a mobile communication system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracy, and mobile stations that communicate through the plurality of base stations while moving within the plurality of radio zones, the plurality of base stations being in a predetermined order, and having means for communicating information indicating the predetermined order with each other. The base station device is characterized by having a receiving means for receiving transmission waves from other base stations, a frequency control means for determining whether to perform frequency correction based on the predetermined order, and, if a frequency correction is determined to be required, controlling the transmission and reception frequency of the base station to match the frequency accuracy of the transmission wave received by the receiving means, and a transceiver for transmitting and receiving at the transmission and reception frequency controlled by the frequency control means.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the system comprising: a mobile station device that receives a transmission wave from one of the plurality of base stations, controls a reference frequency that serves as a reference for the mobile station's transmission and reception frequency to match the frequency accuracy of the received transmission wave, and transmits and receives data to and from the base station at a transmission and reception frequency based on the controlled reference frequency; and a base station device that receives a transmission wave from the mobile station device that transmits and receives data at a transmission and reception frequency based on the controlled reference frequency, controls a reference frequency that serves as a reference for the mobile station's transmission and reception frequency to match the frequency accuracy of the received transmission wave, and transmits and receives data to and from the mobile station at a transmission and reception frequency based on the controlled transmission and reception frequency.

According to another aspect of the present invention, there is provided a base station device for each base station in a mobile communication system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the base station device comprising: means for receiving transmission waves from the mobile station and determining whether the received transmission waves are based on a reference frequency controlled for one of the plurality of base stations; means for controlling the reference frequency that serves as the basis for the transmission and reception frequencies of the base station to match the frequency accuracy of the transmission waves received by the receiving and determining means; and means for transmitting and receiving signals to and from the mobile station at a transmission and reception frequency based on the reference frequency controlled by the controlling means.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations. The system comprises: a receiving means for receiving transmission waves from other base stations and determining whether the received transmission waves are frequency-corrected based on frequency accuracy information contained in the transmission waves; a frequency control means for, when the receiving means determines that the received transmission waves are frequency-corrected, adjusting a reference frequency that serves as the basis for the transmission and reception frequencies of the base station to match the frequency accuracy of the transmission waves received by the receiving means; and a transmitting means for, after the frequency control means adjusts the reference frequency of the base station to match the frequency accuracy of the transmission waves received by the receiving means, transmitting transmission waves containing frequency accuracy information indicating that the transmission frequency has been frequency-corrected, at a transmission frequency based on the reference frequency controlled by the frequency control means.

According to another aspect of the present invention, a mobile communications system is provided that includes a plurality of base stations that form a plurality of radio zones and whose transmit and receive frequency accuracy is not always uniform, and a mobile station that communicates through the plurality of base stations while moving within the plurality of radio zones. The base station device of each base station detects the presence or absence of transmission waves from other base stations, notifies a mobile station within the base station's radio zone of the transmission frequency of the detected transmission wave, and causes the mobile station to identify whether the detected transmission wave has been frequency-corrected and return the identification result. When the identification result returned from the mobile station indicates that the detected transmission wave has been frequency-corrected, the system controls a reference frequency that serves as the basis for the base station's transmit and receive frequency to match the frequency accuracy of the detected transmission wave. a frequency control means for controlling a base station's own reference frequency to match the frequency accuracy of the detected transmission wave, and a transmitting means for transmitting a transmission wave at a transmission frequency based on the reference frequency controlled by the frequency control means, the transmission wave including frequency accuracy information indicating that the frequency accuracy of the transmission frequency has been frequency-corrected; a mobile station device for a mobile station receiving a transmission wave at a transmission frequency notified by the receiving means of a base station currently serving, and identifying whether the received transmission wave has been frequency-corrected based on the frequency accuracy information included in the received transmission wave; and an identifying result returning means for returning the identifying result obtained by the identifying means to the base station currently serving.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the system comprising: a base station device for each base station that detects the presence or absence of transmission waves from a mobile station communicating with another base station, and that identifies whether the detected transmission waves are frequency-corrected based on frequency precision information contained in the detected transmission waves; and a frequency control device that, when the identification means identifies the detected transmission waves as frequency-corrected, adjusts the reference frequency that serves as the basis for the base station's transmission and reception frequencies to match the frequency precision of the detected transmission waves.

According to another aspect of the present invention, there is provided a mobile communications system comprising a plurality of base stations forming a plurality of radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that communicates through the plurality of base stations while moving within the plurality of radio zones, the plurality of base stations being in a predetermined order, and having means for mutually notifying each other of information indicating the predetermined order. The mobile communications system comprises the steps of: receiving, in the base station equipment of each base station, a transmission wave from another base station; and determining, in the base station equipment of each base station, whether or not to perform frequency correction based on the predetermined order; and, if a frequency correction is determined to be performed, adjusting the transmission and reception frequency of the base station to match the frequency accuracy of the received transmission wave, thereby transmitting and receiving.

According to another aspect of the present invention, there is provided a mobile communication method for a mobile communication system including a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the method comprising the steps of: receiving, in the mobile station device, a transmission wave from one of the plurality of base stations, adjusting a reference frequency that serves as a basis for the transmission and reception frequency of the mobile station to match the frequency accuracy of the received transmission wave, and transmitting and receiving signals to and from the base station at a transmission and reception frequency based on the adjusted reference frequency; and receiving, in the base station device of each base station, a transmission wave from a mobile station device that transmits and receives signals at a transmission and reception frequency based on the adjusted reference frequency, adjusting a reference frequency that serves as a basis for the transmission and reception frequency of the mobile station to match the frequency accuracy of the received transmission wave, and transmitting and receiving signals to and from the mobile station at a transmission and reception frequency based on the adjusted reference frequency.

According to another aspect of the present invention, there is provided a mobile communication method for a mobile communication system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmit and receive frequency accuracy, and a mobile station that moves within the plurality of radio zones and communicates via the plurality of base stations, the method comprising: a step of receiving, in the base station device of each base station, a transmission wave from another base station and determining whether the received transmission wave has been frequency-corrected based on frequency accuracy information contained in the received transmission wave; a step of controlling, in the base station device of each base station, a reference frequency that serves as the basis for the transmission and receive frequency of the base station to match the frequency accuracy of the received transmission wave when the received transmission wave is determined to be frequency-corrected in the receiving and determining step; and a step of transmitting, in the base station device of each base station, a transmission wave including frequency accuracy information indicating that the frequency accuracy of the transmission frequency has been frequency-corrected, at a transmission frequency based on the reference frequency controlled in the controlling step.

According to another aspect of the present invention, a mobile communication method for a mobile communication system including multiple base stations forming multiple radio zones, each with varying transmission and reception frequency accuracy, and a mobile station moving within the multiple radio zones and communicating via the multiple base stations, includes the steps of: detecting, in each base station's device, the presence or absence of a transmission wave from another base station and notifying a mobile station located within the base station's radio zone of the transmission frequency of the detected transmission wave; receiving, in the mobile station's device, a transmission wave based on the transmission frequency notified from the currently located base station in the detection and notification step, and identifying, based on frequency accuracy information included in the received transmission wave, whether the received transmission wave has been frequency-corrected; and, in the mobile station's device, determining whether the received transmission wave has been frequency-corrected. A mobile communication system is provided, comprising: a step of returning the identification result obtained in the identifying step to the base station currently serving the base station; a step of controlling, in the base station equipment of each base station, a reference frequency serving as a basis for the transmission and reception frequency of the base station to match the frequency accuracy of the detected transmission wave when the identification result returned from the mobile station in the returning step indicates that the detected transmission wave has been frequency-corrected; and a step of, after adjusting the reference frequency in the controlling step to match the frequency accuracy of the detected transmission wave, transmitting, in the base station equipment of each base station, a transmission wave including frequency accuracy information indicating that the frequency accuracy of the transmission frequency has been frequency-corrected, at a transmission frequency based on the reference frequency controlled in the controlling step.

According to another aspect of the present invention, there is provided a mobile communication system comprising a plurality of base stations forming a plurality of radio zones, the base stations having varying transmission and reception frequency accuracies, and a mobile station which moves within the plurality of radio zones and communicates via the plurality of base stations, the system comprising: a base station device of each base station detecting the presence or absence of a transmission wave from a mobile station currently communicating with another base station, and identifying whether the detected transmission wave has been frequency-corrected based on frequency accuracy information contained in the detected transmission wave; and a base station device of each base station, when it is determined that the detected transmission wave has been frequency-corrected, adjusting a reference frequency serving as a reference for the transmission and reception frequencies of the base station to match the frequency accuracy of the detected transmission wave.

FIG. 2 is a block diagram showing the configuration of a transmitter/receiver unit included in a low-precision frequency base station in the mobile communication system shown in FIG.

FIG. 3 is a schematic diagram showing the overall configuration of a mobile communication system according to a second embodiment of the present invention.

FIG. 4 is a block diagram showing the configuration of a transceiver unit included in a mobile station in the mobile communication system shown in FIG.

FIG. 5 is a block diagram showing the configuration of a transmitting and receiving unit included in the low-precision frequency base station in the mobile communication system shown in FIG.

FIG. 6 is a schematic diagram of a mobile communication system for explaining a frequency correction method of a base station in a mobile communication system according to a third embodiment of the present invention.

FIG. 7 shows an example of a notification information message format used in the mobile communication system shown in FIG.

FIG. 8 is a flowchart of the operation of the low-accuracy frequency base station in the mobile communication system shown in FIG. 6 when the broadcast information message format shown in FIG. 7 is used.

FIG. 9 shows another example of a notification information message format used in the mobile communication system shown in FIG.

FIG. 10 is a flowchart showing the operation of the low-precision frequency base station in the mobile communication system shown in FIG. 6 when using the broadcast information message format shown in FIG. 9.

FIG. 11 is a flowchart showing the operation of a low-precision frequency base station in the mobile communication system shown in FIG. 6 when using yet another reporting mode.

FIG. 12 is a schematic diagram of a mobile communication system for explaining a base station frequency correction method in a mobile communication system according to a fourth embodiment of the present invention.

FIG. 13 is a diagram showing an example of a broadcast information message format used in the mobile communication system shown in FIG.

FIG. 14 is a diagram showing an example of an operator specific information message format used in the mobile communication system shown in FIG.

FIG. 15 is a sequence flowchart of the operation in the mobile communication system shown in FIG. 12 when the broadcast information message format shown in FIG. 13 and the operator specific information message format shown in FIG. 14 are used.

FIG. 16 is a schematic diagram of a mobile communication system for explaining a base station frequency correction method in a mobile communication system according to a fifth embodiment of the present invention.

FIG. 17 shows an example of the structure of an uplink communication channel used in the mobile communication system shown in FIG.

18 is a schematic diagram of a mobile communication system for explaining a base station frequency correction method in a mobile communication system according to a sixth embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION First, a first embodiment of the present invention will be described with reference to FIGS.

Figure 1 shows the overall configuration of a mobile communication system according to a first embodiment of the present invention. The mobile communication system shown in Figure 1 comprises a first radio zone 11 including a first base station 1 and a mobile station 3, and a second radio zone 12 including a second base station 5. First base station 1 and mobile station 3 communicate at frequency f0 via antenna 1a and antenna 3a.

In the mobile communications system of this first embodiment, only some of the base stations constituting each radio zone are equipped with high-precision frequency oscillators, while the remaining base stations are equipped with low-cost, compact frequency oscillators instead, while employing the base station equipment configuration described below. As a result, high-precision transmission and reception frequencies can be achieved for these remaining base stations even with only low-cost, compact frequency oscillators.

For this purpose, in Figure 1, the first base station 1 is provided with a high-precision frequency oscillator 1b. On the other hand, the second base station 5, as one of the other base station devices mentioned above, has a base station configuration with a transceiver unit as shown in Figure 2, and the frequency oscillator of this second base station 5 is not particularly high-precision, but is low-cost and compact.

Here, the transceiver section of the second base station 5, which does not have a high-precision frequency oscillator, is composed of, as shown in FIG. 2, a duplexer 21 connected to the antenna 5a and separating the transmit frequency from the receive frequency, a switch 23 connected to the duplexer 21, a transmitter 25 connected to one contact of the switch 23, a receive circuit 27 connected to the other contact of the switch 23, a frequency reference circuit 29 connected to the receive circuit 27, a receiver 22 connected to the duplexer 21, and a frequency synthesizer 24 connected to the receiver 22 and the transmitter 25.

Prior to initiating communication with a mobile station, the second base station 5 having a transceiver unit configured as described above switches switch 23 to the receiving circuit 27 side to correct its own transmitting and receiving frequency. This allows the second base station 5 to receive a transmission signal from the first base station 1 having the high-precision frequency oscillator 1b via antenna 5a, and inputs this received signal to the receiving circuit 27 via the branching filter 21 and switch 23. Whether or not this received signal is from the first base station 1 having the high-precision frequency oscillator 1b can be determined by frequency or demodulated data, among other methods.

The receiver circuit 27 receives the received signal from the first base station 1 and controls the frequency of the frequency reference circuit 29 to have a frequency accuracy comparable to that of the received signal, using, for example, the technology disclosed in Japanese Patent Laid-Open Publication No. 63-281526.

In this way, the frequency of frequency reference circuit 29 is controlled to be approximately the same as the frequency precision of the high-precision frequency oscillator 1b, which is the frequency precision of the received signal. When a call is initiated, the reference signal output from frequency reference circuit 29 is supplied to frequency synthesizer 24, which then supplies local signals for transmission and reception to transmitter 25 and receiver 22, respectively, thereby initiating transmission and reception.

As described above, according to this first embodiment, each base station receives a transmission frequency from another base station having a high-precision frequency oscillator and autonomously controls its own transmission and reception frequency to have the same accuracy as the received frequency. This allows each base station to transmit and receive at a high-precision frequency without having to provide a high-precision frequency oscillator for each base station, thereby enabling more economical and compact base stations in a mobile communications system.

Next, a second embodiment of the present invention will be described with reference to FIGS.

Figure 3 shows the overall configuration of a mobile communication system according to a second embodiment of the present invention. The mobile communication system shown in Figure 3 comprises a first wireless zone 11 including a first base station 1 and a mobile station 3A, and a second wireless zone 12 including a second base station 5A and a mobile station 3A that has moved from the first wireless zone 11. In the first wireless zone 11, the first base station 1 and the mobile station 3A communicate via antennas 1a and 3a. When the mobile station 3A moves to the second wireless zone 12, the mobile station 3A and the second base station 5A communicate via antennas 3a and 5a.

In the mobile communications system of this second embodiment, only some of the base stations constituting each radio zone are equipped with high-precision frequency oscillators, while the remaining base stations are equipped with low-cost, compact frequency oscillators instead of high-precision frequency oscillators. Meanwhile, the mobile station and these other base stations employ the mobile station and base station configurations described below, respectively. This allows these other base stations to achieve high-precision transmission and reception frequencies even with only low-cost, compact frequency oscillators.

For this reason, in FIG. 3, the first base station 1 is provided with a high-precision frequency oscillator 1b. A base station having such a high-precision frequency oscillator 1b will hereinafter be referred to as a high-precision frequency base station. Meanwhile, the second base station 5A, as one of the aforementioned other base station devices, has a base station device configuration having a transceiver unit as described below. The frequency oscillator of this second base station 5A is not particularly high-precision, but is low-cost and compact. A base station having such a low-precision frequency oscillator will hereinafter be referred to as a low-precision frequency base station. Furthermore, the frequency oscillator provided in the mobile station 3A is also naturally low-cost and compact. As will be described later, the mobile station 3A controls the reference frequency that serves as the basis for its own transmission and reception frequencies so that it is approximately the same as the transmission frequency of a high-precision frequency base station such as the first base station device 1. When the mobile station 3A thus controlled communicates with a second base station device 5A, which is one of the other base stations, the reference frequency that serves as the basis for the transmission and reception frequencies of the second base station device 5A is controlled so that it is approximately the same as the transmission frequency of the mobile station 3A, thereby accurately controlling the transmission and reception frequencies of the second base station device 5A.

For this reason, the mobile station 3A has a transceiver unit as shown in FIG. 4, which is composed of a branching filter 31 connected to the antenna 3a and separating the transmit frequency from the receive frequency, a transmitter 32 and a receiver 33 connected to the branching filter 31, a frequency reference circuit 34 that generates a reference frequency, a frequency synthesizer 35 that receives a reference signal from the frequency reference circuit 34 and supplies a transmit local signal and a receive local signal to the transmitter 32 and the receiver 33, respectively, thereby causing the transmitter 32 and the receiver 33 to perform transmit and receive operations, a first control variable buffer 37 and a second control variable buffer 38 that store, as a control variable, the difference between the transmit frequency from the first base station 1, which is a high-precision frequency base station, and the reference frequency of the mobile station 3A, and a control unit 36 that controls the overall operation.

As shown in FIG. 5, the transmitter/receiver section of the second base station 5A, which does not have a high-precision frequency oscillator, is composed of a branching filter 51 connected to the antenna 5a and separating the transmit frequency from the receive frequency, a transmitter 52 and a receiver 53 connected to the branching filter 51, a frequency reference circuit 54 that generates a reference frequency, a frequency synthesizer 55 that receives a reference signal from the frequency reference circuit 54 and supplies a transmit local signal and a receive local signal to the transmitter 52 and the receiver 53, respectively, thereby causing the transmitter 52 and the receiver 53 to perform transmit and receive operations, a control variable buffer 57 that stores the difference between the transmit frequency from the mobile station 3A and the reference frequency of the second base station 5A as a control variable, and a control unit 56 that controls the overall operation.

In the mobile communications system consisting of the base stations and mobile stations configured as described above, first base station 1 transmits and receives using a high-precision frequency generated by high-precision frequency oscillator 1b, while mobile station 3A and second base station 5A generate reference frequencies that serve as the basis for transmission and reception frequencies using frequency reference circuits 34 and 54, respectively, and supply these reference frequency signals to frequency synthesizers 35 and 55, which in turn enable transmitters 32 and 52 and receivers 33 and 53 to perform transmission and reception operations. However, the reference frequencies output from frequency reference circuits 34 and 54 may differ from the high-precision frequency from first base station 1.

Incidentally, when the wireless transmission method is, for example, a digital phase modulation system, it is necessary to keep the error between the mobile station's receiving frequency and the base station's transmitting frequency within a certain tolerance. Therefore, when mobile station 3A communicates with first base station 1, mobile station 3A must control its own reference frequency so that the accuracy of the transmission frequency from first base station 1 is approximately the same.

More specifically, when mobile station 3A receives a transmission signal from first base station 1, it uses first control variable buffer 37 to control the reference frequency of its own frequency reference circuit 34 so that the reference frequency has the same accuracy as the transmission frequency of first base station 1, and also stores the control variable stored in first control variable buffer 37 in second control variable buffer 38. Note that a method for controlling the reference frequency of mobile station 3A so that the reference frequency has the same accuracy as the transmission frequency of first base station 1 can utilize, for example, the technology disclosed in Japanese Patent Application Laid-Open No. 63-281526.

After storing the control amounts in the control amount buffers 37 and 38, the mobile station 3A controls the reference frequency via the frequency reference circuit 34 based on the stored control amounts, particularly the control amount stored in the second control amount buffer 38.

The first base station 1 transmits data containing information indicating that the first base station 1 is a high-precision frequency base station equipped with a high-precision frequency oscillator 1b. Therefore, a mobile station 3A receiving data from the first base station 1 can identify from the received data that the other base station is a high-precision frequency base station equipped with a high-precision frequency oscillator 1b, i.e., the first base station 1.

As described above, when a mobile station 3A, which communicates with a first base station 1 and has its own reference frequency controlled to the same degree of accuracy as the transmission frequency of the first base station 1, moves from the first wireless zone 11 to the second wireless zone 12 as shown by the arrow in FIG. 3 and communicates with a second base station 5A in this second wireless zone 12, the transmission and reception frequency of the second base station 5A may differ from that of the mobile station 3A, and in fact often does. Assuming that these are different, the mobile station 3A stores the control variables in the first control variable buffer 37 and the second control variable buffer 38 as described above. Using one of the control variable buffers 37, 38, the first control variable buffer 37, the mobile station 3A controls its reference frequency to be approximately the same as the transmission frequency of the second base station 5A, thereby detecting the transmission frequency of the second base station 5A and becoming able to communicate with the second base station 5A.

In this way, after the mobile station 3A is able to communicate with the second base station 5A, the mobile station 3A controls the frequency reference circuit 34 using the control variable stored in the second control variable buffer 38. As a result, the transmission frequency of the mobile station 3A becomes approximately as accurate as that of the first base station 1, which is a high-precision base station.

After the transmission frequency of mobile station 3A becomes approximately the same as the accuracy of the first base station 1, the second base station 5A, which is a low-accuracy base station, uses the control variable buffer 54 to control the reference frequency that serves as the basis for the transmission and reception frequencies of this second base station 5A so that the accuracy of the transmission frequency of mobile station 3A becomes approximately the same as the frequency accuracy of the first base station 1, which is a high-accuracy base station, and the control variable at this time is stored in the control variable buffer 54.

The mobile station 3A is configured to transmit data to the second base station 5A including information indicating that the mobile station 3A has communicated with the first base station 1, which is a high-precision frequency base station, and the second base station 5A is configured to determine, based on the data received from the mobile station 3A, that the mobile station 3A has communicated with the first base station 1, which is a high-precision frequency base station.

As described above, according to this second embodiment, a mobile station receives a transmission frequency from a high-precision frequency base station and controls the reference frequency that serves as the basis for its own transmission and reception frequencies so that the frequency accuracy is similar to that of the received transmission frequency. If the mobile station attempting to communicate has already communicated with a high-precision frequency base station, the low-precision frequency base station controls the reference frequency that serves as the basis for its own transmission and reception frequencies so that the accuracy is similar to that of the mobile station's transmission frequency. Therefore, a low-precision frequency base station other than a high-precision frequency base station can control its own frequency via the mobile station to an accuracy similar to that of the transmission and reception frequency of the high-precision frequency base station without providing a high-precision frequency oscillator, thereby enabling more economical and compact base stations in a mobile communications system.

Next, a third embodiment of the present invention will be described with reference to FIGS.

Figure 6 shows the overall configuration of a mobile communications system according to a third embodiment of the present invention. In Figure 6, 61a, 61b, and 61c are base stations that do not have a high-precision reference frequency oscillator and that receive, demodulate, and perform frequency correction on the transmission frequency of base station 61e (described later) and that share the same service area. 63 is a mobile station that can operate in radio zones A, B, and C. 61e is a base station that has a high-precision reference frequency oscillator. A, B, C, and E are the radio zones of base stations 61a, 61b, 61c, and 61e, respectively. f1, f2, f3, and f4 are the frequencies of the transmission waves of base stations 61a, 61b, 61c, and 61e, respectively. f5 is the frequency of unwanted foreign waves in the same frequency band as frequencies f1 to f3.

Base station 61a receives and demodulates the transmission waves of frequencies f2, f4, and f5. Based on the demodulated signal content, it recognizes that frequency f2 is an uncorrected base station transmission wave of the same system, frequency f4 is a base station transmission wave with a high-precision reference frequency oscillator, and frequency f5 is an unanalyzable external wave, and then corrects its own reference frequency to frequency f4.

Base station 61b also receives and demodulates and analyzes the transmitted waves of frequencies f1, f3, and f5, and recognizes that frequency f1 has already been corrected, and then corrects its own reference frequency to this frequency f1.

Furthermore, base station 61c similarly receives and demodulates and analyzes the transmitted waves of frequencies f2 and f5, thereby recognizing that frequency f2 has already been corrected, and then corrects its own reference frequency for this frequency f2.

As a result, wireless zones A, B, and C achieve uniform frequency accuracy without erroneous frequency correction due to unwanted external waves f5, and establish frequency accuracy with the same high absolute precision as wireless zone E. Mobile station 63 can smoothly transition between wireless zones A, B, and C during standby or during a call in a short time without having to adjust the reference frequency to the corresponding base station frequency each time the wireless zone is changed.

Here, if mobile station 63 has the function and right to be present in base station 61e, smooth zone transitions during standby or during a call can be made to wireless zone E in a short time, as described above.

Furthermore, when building the service areas of wireless zones A, B, and C, base stations can be manufactured inexpensively, and their compact size makes it easier to secure installation locations.

In this third embodiment, the following specific examples are possible methods for a low-precision frequency base station to autonomously select a base station for frequency correction.

As a first example, it is possible to use a broadcast information message format such as that shown in Figure 7. In this case, the operation of the low-accuracy frequency base station 61a in Figure 6 proceeds as follows, following the flowchart in Figure 8.

After starting the frequency correction operation (S0), the base station 61a measures the electric field level of the surrounding downstream frequency band (S1), determines whether downstream radio waves are present (S2), and recognizes the presence of f2 and f4 from the obtained reception levels. It then receives and demodulates the broadcast information of each of these f2 and f4 radio waves and analyzes their contents (S3).

If the surrounding radio zones A and E are PDC (Personal Digital Cellular Telecommunication System) systems (compliant with the RCR (Research and Development Center for Radio Systems) STANDARD (RCR STD-27)), base station 61e and base station 61b each specify whether their own transmission frequencies are high-precision or low-precision by specifying a "high-precision transmission wave/low-precision transmission wave bit" in the newly defined "extended information element" in the control channel broadcast information as shown in Figure 7. This allows base station 61a to recognize that f4 is a radio wave transmitted from high-precision frequency base station 61e. For example, setting this "high-precision transmission wave/low-precision transmission wave bit" to 1 indicates high precision. Note that in Figure 7, the parentheses indicate the contents of each information element, and the shaded areas indicate newly defined parts.

Therefore, the base station 61a determines whether the "high-precision transmission wave/low-precision transmission wave bit" of each broadcast information is 1 (S4), and corrects its own reference frequency based on the frequency determined to be high-precision (S5).

Using this method, base station 61a performs frequency correction and achieves frequency accuracy equivalent to that of base station 61e. The "high-precision transmission wave/low-precision transmission wave bit" in the broadcast information for its own transmission wave is then set to high-precision transmission wave.

Next, as a second specific example, it is possible to use a broadcast information message format such as that shown in Figure 9. In this case, the operation of the low-accuracy frequency base station 61a in Figure 6 proceeds as follows, following the flowchart in Figure 10.

After starting the frequency correction operation (S10), base station 61a measures the electric field level of the surrounding downlink frequency bands (S11), determines whether downlink radio waves are present (S12), and recognizes the presence of f2 and f4 from the obtained reception levels. It then receives and demodulates the broadcast information for each of these f2 and f4 radio waves and analyzes their contents (S13).

If the surrounding radio zones A and E use the PDC system (compliant with RCR STD-27), as shown in Figure 9, the operator can distinguish between high-precision frequency base stations and low-precision frequency base stations during system operation by using the "intra-group network number" within the "network number" defined in the broadcast information. This allows base station 61a to recognize that f4 is a radio wave transmitted from high-precision frequency base station 61e.

For example, "internal network numbers" 0 to 7 are used for high-precision frequency base stations, and 8 to 15 are used for low-precision frequency base stations. Note that in FIG. 9, the parentheses indicate the content of each information element.

The base station 61a then determines whether the "intra-group network number" in each broadcast information is any of 0 to 7 (S14), and corrects its own reference frequency based on the frequency determined to be highly accurate (S15).

Using this method, base station 61a performs frequency correction and achieves frequency accuracy equivalent to that of base station 61e. Base station 61a then sets the "intra-group network number" in the broadcast information of its own transmission waves to one of 0 to 7, indicating high accuracy.

Next, as a third specific example, a mobile communications system operator may operate the system by separating the transmission frequency bands for high-precision frequency base stations and low-precision frequency base stations. For example, frequency bands f1 and f4 are used for high-precision frequency base stations, and frequency bands f2 and f3 are used for low-precision frequency base stations. Each base station stores this frequency band division as operational information in advance. In this case, the operation of the low-precision frequency base station 61a in FIG. 6 proceeds as follows, following the flowchart in FIG. 11.

After starting the frequency correction operation (S20), the base station 61a measures the downlink field level of the frequency bands f1 and f4, which are used by high-precision frequency base stations (S21), determines whether high-precision downlink radio waves are present (S22), and recognizes the presence of f4 from the obtained reception level. If there are multiple high-precision frequencies (S23 Yes), the base station 61a selects the radio wave with the highest reception level (S24). The base station 61a then corrects its own reference frequency based on the obtained high-precision frequencies (S25).

Using this method, base station 61a performs frequency correction and achieves frequency accuracy equivalent to that of base station 61e. Base station 61a then transmits its own transmission signals using a frequency in the frequency band for high-precision frequency base stations, e.g., f1.

Next, a fourth embodiment of the present invention will be described with reference to FIGS.

Figure 12 shows the overall configuration of a mobile communications system according to a fourth embodiment of the present invention. In Figure 12, 61a and 62b denote base stations without high-precision reference frequency oscillators, 61e denotes a base station with a high-precision reference frequency oscillator, 63a and 63b denote mobile stations located in radio zones A and B, respectively, A, B, and E denote the radio zones of base stations 61a, 61b, and 61e, respectively, f1-1 and f1-2 denote the frequencies of the transmitted and received waves of base station 61a, f2 denotes the frequency of the transmitted and received waves of base station 61b, f4 denotes the frequency of the transmitted waves of base station 61e, and f5 denotes the frequency of unwanted foreign waves in the same frequency band as frequencies f1-1, f1-2, f2, and f4.

Base station 61a measures the electric field level around its own station and detects the presence of transmitted or received waves of frequencies f2, f4, and f5 in the vicinity. Base station 61a then instructs mobile station 63a, which is present in its own station's radio zone A, to analyze frequencies f2, f4, and f5.

Mobile station 63a receives and demodulates each frequency in accordance with this instruction, analyzes the content of the demodulated signal, and determines that frequency f2 is an uncorrected base station transmission wave from the same system, frequency f4 is a base station transmission wave with a high-precision reference frequency oscillator, and frequency f5 is an unanalyzable foreign wave. Mobile station 63a then notifies base station 61a of the analysis results.

As a result, the base station 61a corrects its own reference frequency for this frequency f4 and transmits a signal including the corrected frequency.

Similarly, base station 61b instructs mobile station 63b to analyze frequencies f1-1 and f5, and recognizes from the analysis results of mobile station 63b that frequency f1-1 has already been corrected, and then corrects the reference frequency of its own station for frequency f1-1.

As a result, base stations 61a and 61b do not have the ability to demodulate base station transmission waves, and wireless zones A and B achieve uniform frequency accuracy without erroneous frequency correction due to unwanted external waves f5, and establish high frequency accuracy with absolute accuracy equivalent to that of wireless zone E. Mobile stations 63a and 63b can smoothly transition between zones in standby or during a call in wireless zones A and B in a short time without having to perform reference frequency correction to the corresponding base station frequency each time they transition between wireless zones.

If mobile stations 63a and 63b have the capability and right to be within the coverage area of base station 61e, smooth zone transitions during standby or during a call can be made to radio zone E in a short time, as described above.

Furthermore, when establishing the service areas of wireless zones A and B, base stations can be manufactured inexpensively, and their compact size makes it easier to secure installation locations. It also makes it easier to establish a continuous service area with wireless zone E.

In this fourth embodiment, the following specific examples are possible for the low-precision frequency base station to select a base station to be subjected to frequency correction.

That is, it is possible to use a broadcast information message format as shown in FIG. 13 and an operator specific information message format as shown in FIG. 14.

In the broadcast information message format of Figure 13, when the radio zone is PDC (compliant with RCR STD-27), as in the first specific example of the third embodiment, each base station specifies whether its transmission frequency is high-precision or low-precision by specifying a "high-precision transmission wave/low-precision transmission wave bit" within a newly defined "extended information element" in the broadcast information of the control channel. Also, a new information element called "signal content analysis frequency" is defined in the broadcast information so that the base station can request the mobile station to analyze the broadcast information. Meanwhile, in the operator-specific information message format of Figure 14, a new message called "signal content analysis result report" is defined as operator-specific information so that the mobile station can report the results of the broadcast information analysis to the base station. Note that in Figures 13 and 14, the parentheses indicate the content of each information element, and the shaded areas indicate newly defined portions.

In this case, the operations of the low-accuracy frequency base station 61a, the high-accuracy frequency base station 61e, and the mobile station 63a in FIG. 12 proceed as follows, following the sequence flowchart in FIG. 15.

First, base station 61e is transmitting on f4 (S30). At this point, base station 61a measures the downstream field level in the vicinity (S31) and recognizes the presence of f4 from the obtained reception level (S32).

Therefore, the base station 61a starts transmitting on f1-1 to form wireless zone A (S33), and the mobile station 63a recognizes wireless zone A by receiving f1-1 and enters the zone (S34). Next, the base station 61a notifies the mobile station 63a of a request for content analysis of the recognized frequency f4 by sending a "signal content analysis frequency" message in the broadcast information (S35).

Upon receiving this broadcast information (S36), the mobile station 63a recognizes that the frequency code for f4 is stored in the "signal content analysis frequency" and switches its frequency synthesizer to f4 (S37), receives and demodulates f4 from the base station 61e, and analyzes its content (S38). Upon recognizing that f4 is a high-precision transmission wave (S39), the mobile station 63a switches its frequency synthesizer to f1-1 (S40) and reports the analysis result that f4 is a high-precision transmission wave to the base station 61a via a "signal content analysis result report" message on the uplink control channel (SCCH) (S41).

Upon receiving this report (S42), the base station 61a receives f4 from the base station 61e and corrects its own reference frequency based on this (S43).

Next, a fifth embodiment of the present invention will be described with reference to FIGS.

Figure 16 shows the overall configuration of a mobile communications system according to a fifth embodiment of the present invention. In Figure 16, 61a denotes a base station without a high-precision reference frequency oscillator, 61e denotes a base station with a high-precision reference frequency oscillator, 63 denotes a mobile station located in radio zone E and communicating with base station 61e, A and E denote the radio zones of base stations 61a and 61e, respectively, f4-1 denotes the frequency of the transmission wave from base station 61e to mobile station 63, f4-2 denotes the frequency of the transmission wave from mobile station 63 to base station 61e, f5 denotes the frequency of unwanted foreign waves in the same frequency band as frequencies f4-1 and f4-2.

Base station 61a measures the surrounding electric field level in its own receiving frequency band and detects the presence of nearby transmission waves at frequencies f4-2 and f5. Base station 61a then analyzes the signal content of frequencies f4-2 and f5, determining that frequency f4-2 is a transmission wave used by mobile station 63 for a call and that the call is with base station 61e, which has a highly accurate reference frequency oscillator. Base station 61a then recognizes that frequency f5 is an unanalyzable external wave. Base station 61a then corrects its own reference frequency for frequency f4-2 and transmits a signal containing the frequency-corrected content as its own base station transmission wave.

As a result, even in an environment where base station 61a is located outside the radio zones of other base stations and cannot directly receive the transmissions of those other base stations, it can correct its own frequency to the frequencies of those other base stations without having to incorporate a demodulation function for the base station's transmissions. This facilitates the design of base station 61a's location (when installing a base station, factors such as the number of base stations, base station transmission output, and frequencies used by each base station must be considered as determining factors such as traffic and radio zone size) and the securing of installation locations.

In this fifth embodiment, the mobile station 63 is communicating with base station 61e, which has a high-precision reference frequency oscillator. However, this also applies to base stations that have already been frequency-corrected. Furthermore, even if wireless zones A and E are discontinuous, the same effect can be achieved within the range where the transmission wave of frequency f4-2 from mobile station 63 reaches base station 61a. This allows the frequency precision of base station 61a to be matched to that of base station 61e. Therefore, when mobile station 63 moves from wireless zone E to wireless zone A, mobile station 63 can enter wireless zone A in a short time without having to correct its own reference frequency to that of base station 61a in order to receive a control signal.

In the fifth embodiment, the low-precision frequency base station may intercept the uplink radio waves of a mobile station in communication and correct its own reference frequency in the following specific example.

That is, if the radio zones of high-precision frequency base stations and low-precision frequency base stations use the PDC system (compliant with RCR STD-27), a mobile communications system operator could operate the system by dividing the color codes of communication channels, as shown in Figure 17, into those for high-precision frequency base stations and those for low-precision frequency base stations. For example, the color codes for high-precision frequency base stations could be 1 to 128 (decimals), and those for low-precision frequency base stations could be 129 to 255 (decimals). Note that the shaded areas in Figure 17 indicate scrambled portions.

In this case, the operation of the low-accuracy frequency base station 61a in FIG. 16a proceeds as follows:

Base station 61a measures the upstream field level in the vicinity and detects the presence of upstream radio waves from mobile stations communicating with other base stations. It then receives and demodulates these upstream radio waves, analyzes their contents, and obtains a color code.

The base station 61a then determines whether the acquired color code is within the range of 1 to 128, thereby determining that the uplink radio wave is a transmission wave from a mobile station 63 communicating with the high-precision frequency base station 61e, and corrects its own reference frequency based on the frequency of the transmission wave from this mobile station.

Next, a sixth embodiment of the present invention will be described with reference to FIG.

This sixth embodiment is an example of applying the base station frequency correction method of the mobile communications system of the present invention to a case where multiple low-precision frequency base stations are installed to establish a service area in a location, such as an underground mall or indoors, where radio waves from an outdoor high-precision frequency base station cannot reach.

In this case, as shown in Figure 18, low-precision frequency base stations 81a, 81b, and 81c are installed in a building 100 where radio waves from an outdoor high-precision frequency base station 81e cannot reach, and communication is performed with a mobile station 83 within this building 100. Here, the low-precision frequency base stations 81a, 81b, and 81c form a PDC radio zone, and each low-precision frequency base station stores unique serial number information in a memory (not shown).

These low-precision frequency base stations 81a, 81b, and 81c are installed so that their serial numbers are arranged in ascending order, such as 001, 005, and 007, for the base stations 81a, 81b, and 81c in consecutive radio zones.

Each low-precision frequency base station transmits its own serial number information in a newly defined extended information element called "own serial number information" within its broadcast information.

Meanwhile, each low-precision frequency base station measures the downlink field level of the surrounding low-precision frequency base stations, and receives, demodulates, and analyzes the broadcast information to obtain the serial numbers of the surrounding low-precision frequency base stations from the broadcast information of the surrounding low-precision frequency base stations. It then compares the obtained serial numbers with its own serial number, selects the base station with a serial number smaller than its own, and corrects its own reference frequency based on the transmitted signal from that base station.

By having each low-accuracy frequency base station periodically perform such an operation, the reference frequency accuracy of the base stations 81 a, 81 b, and 81 c in the building 100 can be made uniform.

If the reference frequency accuracy of each low-accuracy frequency base station is off by +(1× ^10-6 ) with respect to the absolute frequency accuracy, when mobile station 83 enters building 100 from outdoors or is turned on inside building 100 and enters the radio zone of base station 81a, a frequency pull-in operation (an operation to slightly shift the receiving frequency of the mobile station in order to receive a transmission wave emitted from a transmitter with a different frequency accuracy than the mobile station, thereby making it possible to receive the transmission wave) is required, and it takes several seconds for mobile station 83 to enter a state where it can be located within the range. At this time, the reference frequency accuracy of mobile station 83 becomes +(1× ^10-6 ) when it enters the radio zone of base station 81a.

Thereafter, when the mobile station 83 moves to the radio zone of the adjacent base station 81b, the frequency accuracy in the radio zone of the base station 81b is already +(1×10 ⁻⁶ ), so the mobile station 83 can be present in the radio zone of the base station 81b without performing a frequency pull-in operation. Therefore, zone transfer and handover can be performed in a short time.

Thus, in environments such as indoors or underground malls, even if the base station frequency accuracy deviates from the absolute frequency accuracy, effective results can be obtained by relatively aligning the frequency accuracy between base stations.

As described above, according to the present invention, each base station corrects its own reference frequency against a highly accurate reference frequency or against a frequency-corrected transmission wave based on the content of the received signal, the identification result from the mobile station, or the identification result of the transmission wave from a mobile station currently communicating with another base station. This eliminates the need for expensive, large, highly accurate reference frequency oscillators, enabling the construction of high-quality, economical mobile communication service areas using inexpensive, compact base station equipment. This is effective in implementing mobile communication systems such as mobile telephone systems and cordless telephone systems that employ microcells or picocells, which require multiple base station equipment to ensure a service area. Furthermore, because frequency accuracy is improved and uniform throughout the entire mobile communication service area, smooth radio zone transitions are possible in a short time while the mobile station is idle or in a call.

───────────────────────────────────────────────────── Continued from the front page (81) Designated States: EP (AT, BE, CH, DE, DK, ES, FR, GB, GR, IE, IT, LU, M, C, NL, PT, SE), JP, US (72) Inventor: Masaaki Yoshimi 4-2-414 Hatori, Fujisawa City, Kanagawa Prefecture (72) Inventor: Tatsuaki Wakabayashi 94-2-5-201 Nagasawa, Yokosuka City, Kanagawa Prefecture (Note) This publication is based on the publication published internationally by the International Bureau of International Patent Office (WIPO). Please note that the effect of the international publication of the Japanese-language patent application (Japanese-language utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act), and is unrelated to this publication.

Claims (50)

[Claims] 1. A mobile communications system comprising multiple base stations that form multiple radio zones and whose transmit and receive frequency accuracy is not always uniform, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, characterized by comprising: a high-precision frequency base station device having a high-precision frequency oscillator; and a low-precision frequency base station device having a low-precision frequency oscillator other than the high-precision frequency base station device, which receives transmission waves from the high-precision frequency base station device at a transmission frequency with a predetermined frequency accuracy, and controls its own transmission and reception frequency to match the frequency accuracy of the received transmission waves. 2. The mobile communications system according to claim 1, wherein the low-precision frequency base station device comprises: a frequency reference circuit that generates a reference frequency that serves as a basis for the transmission and reception frequencies of the base station in accordance with the frequency precision of the received transmission waves from other base stations; and a frequency synthesizer that controls the transmission and reception frequencies of the base station based on the reference frequency generated by the frequency reference circuit, thereby causing the transceiver to perform transmission and reception. 3. The mobile communications system described in claim 1 is characterized in that the high-precision frequency reference station device transmits a transmission wave containing frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high, and the low-precision frequency base station device determines that the transmission wave received from the high-precision frequency base station device is a high-precision frequency based on the frequency accuracy information contained in the transmission wave, and controls the reference frequency that serves as the basis for its own transmission and reception frequencies to match the frequency accuracy of the received transmission wave. 4. A base station device for each base station in a mobile communication system consisting of multiple base stations that form multiple radio zones and whose transmit and receive frequency accuracy is not always uniform, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, comprising: a receiving means for receiving transmission waves from other base stations at a transmission frequency with a predetermined frequency accuracy; a frequency control means for controlling the transmit and receive frequency of the base station to match the frequency accuracy of the transmission wave received by the receiving means; and a transceiver that transmits and receives at the transmit and receive frequency controlled by the frequency control means. 5. The base station apparatus according to claim 4, wherein the frequency control means comprises: a frequency reference circuit that generates a reference frequency that serves as a reference for the transmission and reception frequencies in accordance with the frequency accuracy of the transmission wave received by the receiving means; and a frequency synthesizer that controls the transmission and reception frequencies of the base station based on the reference frequency generated by the frequency reference circuit, thereby causing the transceiver to perform transmission and reception. 6. The base station apparatus according to claim 4, wherein the frequency control means controls the transmitting and receiving frequencies of the transceiver to match the frequency accuracy of the transmission waves received by the receiving means, and then transmits transmission waves including frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high; and the receiving means determines that the received transmission waves are of a high-accuracy frequency based on the frequency accuracy information included in the transmission waves from the other base station, and causes the frequency control means to control the reference frequency that serves as the basis for the transmitting and receiving frequencies of the transceiver to match the frequency accuracy of the received transmission waves. 7. A mobile communications system comprising multiple base stations forming multiple radio zones whose transmit and receive frequency accuracy is not always uniform, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, comprising: a high-precision frequency base station device having a high-precision frequency oscillator; a mobile station device that receives transmission waves from the high-precision frequency base station device at a transmission frequency with a predetermined frequency accuracy, controls a reference frequency that serves as the basis for its own transmission and receive frequency to match the frequency accuracy of the received transmission wave, and transmits and receives data to and from the base station at a transmission and receive frequency based on the controlled reference frequency; and a low-precision frequency base station device other than the high-precision frequency base station device that has a low-precision frequency oscillator and receives transmission waves from a mobile station device that transmits and receives data at a transmission and receive frequency based on the controlled reference frequency, controls a reference frequency that serves as the basis for its own transmission and receive frequency to match the frequency accuracy of the received transmission wave, and transmits and receives data to and from the mobile station at a transmission and receive frequency based on the controlled transmission and receive frequency. 8. The mobile communication system according to claim 7, wherein the mobile station device comprises a buffer means for storing a control variable required to correct the mobile station's reference frequency to match the frequency accuracy of the transmission wave from the high-precision frequency base station device, and a control means for controlling the mobile station's reference frequency based on the control variable stored in the buffer means. 9. The mobile communication system according to claim 8, wherein the mobile station device includes additional buffer means for storing an additional control variable required to correct its own reference frequency to match the frequency accuracy of the transmission wave from the low-accuracy frequency base station device, and the control means controls its own reference frequency based on the control variable stored in the additional buffer means to enable the mobile station device to communicate with the low-accuracy frequency base station device, and then controls its own reference frequency based on the control variable stored in the buffer means. 10. The mobile communications system of claim 7, wherein the high-precision frequency base station device transmits transmission waves including frequency precision information indicating that the frequency precision of the transmission frequency is high; the mobile station device determines that the received transmission waves from the high-precision frequency base station device are of a high-precision frequency based on the frequency precision information included in the transmission waves, and adjusts its own reference frequency to match the frequency precision of the received transmission waves, and then transmits transmission waves including frequency precision information indicating that the frequency precision of the transmission frequency is high; and the low-precision frequency base station device determines that the received transmission waves from the mobile station device are of a high-precision frequency based on the frequency precision information included in the transmission waves, and adjusts its own reference frequency to match the frequency precision of the received transmission waves. 11. A mobile station device for a mobile station in a mobile communication system consisting of multiple base stations forming multiple radio zones and having non-uniform transmission and reception frequency accuracy, and a mobile station that moves within the multiple radio zones and communicates via the multiple base stations, comprising: means for receiving transmission waves from the base stations and determining whether the received transmission waves are of high-precision frequencies; means for controlling a reference frequency that serves as the basis for the transmission and reception frequencies of the mobile station to match the frequency accuracy of the transmission waves received by the receiving and determining means; transmission and reception means for transmitting and receiving signals to and from the base stations at transmission and reception frequencies based on the reference frequency controlled by the controlling means. 12. The mobile station device according to claim 11, wherein said control means includes buffer means for storing a control amount required to correct the reference frequency of said mobile station in accordance with the frequency accuracy of the transmission wave of said high-precision frequency, and controls the reference frequency of said mobile station based on the control amount stored in said buffer means. 13. The mobile station device according to claim 12, wherein the control means includes additional buffer means for storing an additional control variable required to correct the local station's reference frequency to match the frequency accuracy of received transmission waves other than the high-precision frequency transmission wave, and after controlling the local station's reference frequency based on the additional control variable stored in the additional buffer means, controls the local station's reference frequency based on the control variable stored in the buffer means. 14. The mobile station device according to claim 11, wherein the transmitting/receiving means transmits a transmission wave including frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high after the controlling means adjusts the reference frequency of the station to match the frequency accuracy of the received transmission wave. 15. A base station device for each base station in a mobile communication system consisting of multiple base stations forming multiple radio zones and having variable transmission and reception frequency accuracy, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, comprising: means for receiving transmission waves from the mobile stations and determining whether the received transmission waves are of high-precision frequencies; means for controlling a reference frequency that serves as the basis for the transmission and reception frequencies of the base station itself to match the frequency accuracy of the transmission waves received by the receiving and determining means; transmitting and receiving means for transmitting and receiving signals to and from the mobile stations at transmission and reception frequencies based on the reference frequency controlled by the controlling means. 16. The base station apparatus according to claim 15, wherein the control means includes buffer means for storing a control amount required to correct the base station's reference frequency to match the frequency accuracy of the transmission wave from the mobile station, and the base station controls the base station's reference frequency based on the control amount stored in the buffer means. 17. A mobile communications system comprising multiple base stations forming multiple radio zones, each with varying transmission and reception frequency accuracy, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, wherein the base station equipment of each base station comprises: a receiving means for receiving transmission waves from other base stations at a transmission frequency with a predetermined frequency accuracy and determining whether the received transmission waves are of a high-precision frequency based on frequency accuracy information contained in the transmission waves; a frequency control means for, when the receiving means determines that the received transmission waves are of a high-precision frequency, controlling a reference frequency that serves as the basis for the transmission and reception frequencies of the base station to match the frequency accuracy of the transmission waves received by the receiving means; and a transmitting means for, after the frequency control means has controlled the base station's reference frequency to match the frequency accuracy of the transmission waves received by the receiving means, transmitting transmission waves containing frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high, at a transmission frequency based on the reference frequency controlled by the frequency control means. 18. A mobile communications system comprising multiple base stations forming multiple radio zones whose transmit and receive frequency accuracy is not always uniform, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, wherein the base station device of each base station detects the presence or absence of transmission waves from other base stations, notifies mobile stations within its own radio zone of the transmission frequency of the detected transmission wave, and has the mobile station identify whether the detected transmission wave is a high-precision frequency and return the identification result; frequency control means, when the identification result returned from the mobile station indicates that the detected transmission wave is a high-precision frequency, controls the reference frequency that serves as the basis for the transmit and receive frequency of the own station to match the frequency accuracy of the detected transmission wave; and transmission means, after the frequency control means adjusts the own station's reference frequency to match the frequency accuracy of the detected transmission wave, transmits transmission waves containing frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high, at a transmission frequency based on the reference frequency controlled by the frequency control means; wherein the mobile station device A mobile communication system comprising: an identification means for receiving a transmission wave having a transmission frequency notified by the receiving means of the currently serving base station and identifying whether the received transmission wave has a high-precision frequency based on frequency accuracy information contained in the received transmission wave; and an identification result return means for returning the identification result obtained by the identification means to the currently serving base station. 19. A mobile communications system comprising multiple base stations forming multiple radio zones whose transmit and receive frequency accuracy is not always uniform, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, wherein the base station equipment of each base station comprises: Identification means for detecting the presence or absence of transmission waves from mobile stations communicating with other base stations, and for identifying whether the detected transmission waves are of high-precision frequencies based on frequency accuracy information contained in the detected transmission waves; Frequency control means for, when the identification means identifies the detected transmission waves as of high-precision frequencies, controlling the reference frequency that serves as the basis for the transmit and receive frequencies of the base station to match the frequency accuracy of the detected transmission waves. 20. A mobile communication method in a mobile communication system comprising multiple base stations forming multiple radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, comprising: a step of transmitting a transmission wave at a transmission frequency with a predetermined frequency accuracy from a high-precision frequency base station device having a high-precision frequency oscillator; and a step of receiving the transmission wave from the high-precision frequency base station device and controlling its own transmission and reception frequency to match the frequency accuracy of the received transmission wave, in a low-precision frequency base station device other than the high-precision frequency base station device. 21. The mobile communications system according to claim 20, wherein the low-precision frequency base station device generates a reference frequency that serves as a reference for its own transmission and reception frequencies in a frequency reference circuit that matches the frequency precision of the transmission waves received from the high-precision frequency base station, and controls the transmission and reception frequencies of its own station based on the reference frequency generated by the frequency reference circuit in a frequency synthesizer, causing the transceiver to transmit and receive. 22. The mobile communications system described in claim 20, characterized in that the high-precision frequency base station device transmits transmission waves including frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high, and the low-precision frequency base station device determines that the received transmission waves are of a high-precision frequency based on the frequency accuracy information included in the transmission waves from the high-precision frequency base station device, and controls the reference frequency that serves as the basis for its own transmission and reception frequencies to match the frequency accuracy of the received transmission waves. 23. A mobile communication method for a mobile communication system comprising multiple base stations forming multiple radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that moves within the multiple radio zones and communicates via the multiple base stations, comprising: a high-precision frequency base station device having a high-precision frequency oscillator, transmitting a transmission wave at a transmission frequency with a predetermined frequency accuracy; a mobile station device receiving the transmission wave from the high-precision frequency base station device, controlling a reference frequency that serves as a basis for the transmission and reception frequency of the mobile station to match the frequency accuracy of the received transmission wave, and transmitting and receiving signals to and from the base station at a transmission and reception frequency based on the controlled reference frequency; a low-precision frequency base station device other than the high-precision frequency base station device, having a low-precision frequency oscillator, receiving a transmission wave from a mobile station device that transmits and receives signals at a transmission and reception frequency based on the controlled reference frequency, controlling a reference frequency that serves as a basis for the transmission and reception frequency of the mobile station to match the frequency accuracy of the received transmission wave, and transmitting and receiving signals to and from the mobile station at a transmission and reception frequency based on the controlled transmission and reception frequency. 24. The mobile station device according to claim 23, wherein the mobile station device stores in a buffer means a control variable required to correct the mobile station's reference frequency to match the frequency accuracy of the transmission wave from the high-precision frequency base station device, and controls the mobile station's reference frequency based on the control variable stored in the buffer means. 25. The mobile station device according to claim 24, wherein the mobile station device stores in an additional buffer means an additional control variable required to correct its own reference frequency to match the frequency accuracy of the transmission wave from the low-precision frequency base station device, controls its own reference frequency based on the additional control variable stored in the additional buffer means to enable the mobile station device to communicate with the low-precision frequency base station device, and then controls its own reference frequency based on the control variable stored in the buffer means. 26. The mobile communications system of claim 23, wherein the high-precision frequency base station device transmits transmission waves including frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high; the mobile station device determines that the received transmission waves are of a high-precision frequency based on the frequency accuracy information included in the transmission waves from the high-precision frequency base station device, adjusts its own reference frequency to match the frequency accuracy of the received transmission waves, and then transmits transmission waves including frequency accuracy information indicating that the frequency accuracy of the transmission frequency is high; and the low-precision frequency base station device determines that the received transmission waves are of a high-precision frequency based on the frequency accuracy information included in the transmission waves from the mobile station device, and adjusts its own reference frequency to match the frequency accuracy of the received transmission waves. 27. A mobile communications method for a mobile communications system comprising multiple base stations forming multiple radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, comprising: a step in which, in the base station equipment of each base station, a transmission wave from another base station at a transmission frequency having a predetermined frequency accuracy is received, and based on frequency accuracy information contained in the received transmission wave, the received transmission wave is determined to be a high-precision frequency; a step in which, when it is determined in the receiving and determining step that the received transmission wave is a high-precision frequency, the base station equipment of each base station controls a reference frequency that serves as the basis for its own transmission and reception frequency to match the frequency accuracy of the received transmission wave; and, after adjusting its own reference frequency to match the frequency accuracy of the received transmission wave in the controlling step, the base station equipment of each base station transmits a transmission wave containing frequency accuracy information indicating that the transmission frequency has high precision, at a transmission frequency based on the reference frequency controlled in the controlling step. 28. A mobile communication method for a mobile communication system consisting of multiple base stations forming multiple radio zones with varying transmission and reception frequency accuracy, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, comprising: a step in which, in each base station's base station device, detects the presence or absence of transmission waves from other base stations and notifies a mobile station located within the base station's radio zone of the transmission frequency of the detected transmission waves; a step in which, in the mobile station's mobile station device, receives transmission waves with the transmission frequency notified from the currently located base station in the detection and notification step, and identifies whether the received transmission waves are of a high-precision frequency based on frequency accuracy information included in the received transmission waves; a step in which, in the mobile station's mobile station device, returns the identification result obtained in the receiving and identification step to the currently located base station; When the identification result returned from the mobile station in the returning step indicates that the detected transmission wave has a high-precision frequency, the base station device of each base station controls the reference frequency that serves as the basis for its own transmission and reception frequency to match the frequency precision of the detected transmission wave; and, after adjusting the reference frequency in the controlling step to match the frequency precision of the detected transmission wave, the base station device of each base station transmits a transmission wave containing frequency precision information indicating that the frequency precision of the transmission frequency is high, at a transmission frequency based on the reference frequency controlled in the controlling step. 29. A mobile communications system comprising multiple base stations forming multiple radio zones, each with varying transmission and reception frequency accuracy, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, comprising: a base station device at each base station detects the presence or absence of transmission waves from a mobile station communicating with another base station, and identifies whether the detected transmission waves are of a high-precision frequency based on frequency accuracy information contained in the detected transmission waves; and, when the detected transmission waves are identified as of a high-precision frequency in the detection and identification step, controls the base station device at each base station to adjust its reference frequency, which serves as the basis for its own transmission and reception frequencies, to match the frequency accuracy of the detected transmission waves. 30. A mobile communications system comprising multiple base stations that form multiple radio zones and whose transmit and receive frequency accuracy is not always uniform, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, wherein the multiple base stations are in a predetermined order and have means for mutually notifying each other of information indicating the predetermined order, and each base station receives transmission waves from other base stations, determines whether to perform frequency correction based on the predetermined order, and, if it determines that frequency correction is required, controls its own transmission and reception frequencies to match the frequency accuracy of the received transmission waves, characterized in that the mobile communications system. 31. A base station device for each base station in a mobile communications system comprising multiple base stations forming multiple radio zones, the base stations having varying transmission and reception frequency accuracy, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, the multiple base stations being in a predetermined order, and having means for communicating information indicating the predetermined order with each other, the base station device comprising: receiving means for receiving transmission waves from other base stations; frequency control means for determining whether to perform frequency correction based on the predetermined order, and, if it is determined that frequency correction is required, for controlling the transmission and reception frequency of the base station to match the frequency accuracy of the transmission wave received by the receiving means; and a transceiver for transmitting and receiving at the transmission and reception frequency controlled by the frequency control means. 32. A mobile communications system comprising multiple base stations forming multiple radio zones whose transmit and receive frequency accuracy is not always uniform, and a mobile station that moves within the multiple radio zones and communicates via the multiple base stations, comprising: a mobile station device that receives transmission waves from one of the multiple base stations, controls a reference frequency that serves as the basis for its own transmit and receive frequency to match the frequency accuracy of the received transmission waves, and transmits and receives signals to and from the base station at a transmit and receive frequency based on the controlled reference frequency; and a base station device that receives transmission waves from the mobile station device that transmits and receives signals at a transmit and receive frequency based on the controlled reference frequency, controls a reference frequency that serves as the basis for its own transmit and receive frequency to match the frequency accuracy of the received transmission waves, and transmits and receives signals to and from the mobile station at a transmit and receive frequency based on the controlled transmit and receive frequency. 33. The mobile communications system according to claim 32, wherein the plurality of base stations are arranged in a predetermined order, the mobile station device of the mobile station transmits a transmission wave containing information indicating that the mobile station's transmission wave has controlled a reference frequency for a certain base station and the predetermined order, and the base station device of each base station determines whether to perform frequency correction based on the predetermined order, and controls the reference frequency when it determines that frequency correction is necessary. 34. A base station device for each base station in a mobile communication system consisting of multiple base stations forming multiple radio zones and having non-uniform transmission and reception frequency accuracy, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, comprising: means for receiving transmission waves from the mobile station and determining whether the received transmission waves are based on a reference frequency controlled for one of the multiple base stations; means for controlling the reference frequency that serves as the basis for the transmission and reception frequencies of the base station to match the frequency accuracy of the transmission waves received by the receiving and determining means; transmission and reception means for transmitting and receiving signals to and from the mobile station at a transmission and reception frequency based on the reference frequency controlled by the controlling means. 35. The base station apparatus according to claim 34, wherein the plurality of base stations are in a predetermined order, the mobile station transmits a transmission wave including information indicating that the transmission wave of the mobile station controls a reference frequency for a certain base station and the predetermined order, the base station apparatus of each base station further determines whether to perform frequency correction based on the predetermined order using the receiving and determining means, and when it determines that frequency correction is to be performed, the base station apparatus controls the reference frequency using the controlling means. 36. A mobile communications system comprising multiple base stations forming multiple radio zones whose transmit and receive frequency accuracy is not always uniform, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, wherein the base station equipment of each base station comprises: a receiving means for receiving transmission waves from other base stations and determining whether the received transmission waves have been frequency-corrected based on frequency accuracy information contained in the received transmission waves; a frequency control means for, when the receiving means determines that the received transmission waves have been frequency-corrected, controlling a reference frequency that serves as the basis for the transmit and receive frequencies of the base station to match the frequency accuracy of the transmission waves received by the receiving means; and a transmitting means for, after the frequency control means has adjusted the base frequency of the base station to match the frequency accuracy of the transmission waves received by the receiving means, transmitting transmission waves that include frequency accuracy information indicating that the frequency accuracy of the transmission frequency has been frequency-corrected, at a transmission frequency based on the reference frequency controlled by the frequency control means. 37. The mobile communications system of claim 36, wherein the plurality of base stations are in a predetermined order, and the system has means for mutually notifying each other of information indicating the predetermined order, and the base station device of each base station further determines, based on the predetermined order, whether or not to perform frequency correction using the receiving means, and when it is determined that frequency correction is to be performed, the frequency control means controls the reference frequency. 38. A mobile communications system consisting of multiple base stations forming multiple radio zones whose transmit and receive frequency accuracy is not always uniform, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, wherein the base station equipment of each base station includes: a receiving means for detecting the presence or absence of transmission waves from other base stations, notifying mobile stations within the base station's radio zone of the transmission frequency of the detected transmission wave, and having the mobile station identify whether the detected transmission wave has been frequency-corrected and return the identification result; a frequency control means for adjusting the reference frequency that serves as the basis for the transmit and receive frequency of the base station to match the frequency accuracy of the detected transmission wave when the identification result returned from the mobile station indicates that the detected transmission wave has been frequency-corrected; and a transmitting means for transmitting transmission waves at a transmission frequency based on the reference frequency controlled by the frequency control means, including frequency accuracy information indicating that the frequency accuracy of the transmission frequency has been frequency-corrected, after the frequency control means adjusts the base frequency of the base station to match the frequency accuracy of the detected transmission wave; A mobile communication system characterized in that the mobile station device of the mobile station receives a transmission wave at a transmission frequency notified by the receiving means of the currently serving base station and has an identification means for identifying whether the received transmission wave has been frequency-corrected based on frequency accuracy information included in the received transmission wave, and an identification result return means for returning the identification result obtained by the identification means to the currently serving base station. 39. A mobile communications system according to claim 38, wherein the plurality of base stations are arranged in a predetermined order, the identification means of the mobile station device further determines whether or not frequency correction should be performed at the base station currently serving the mobile station based on the predetermined order, and the frequency control means of each base station device controls the reference frequency when the identification result returned from the mobile station indicates that frequency correction should be performed. 40. A mobile communications system comprising multiple base stations forming multiple radio zones whose transmit and receive frequency accuracy is not always uniform, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, wherein the base station equipment of each base station comprises: a discrimination means for detecting the presence or absence of transmission waves from mobile stations communicating with other base stations, and for discriminating whether the detected transmission waves have been frequency-corrected based on frequency precision information contained in the detected transmission waves; and a frequency control means for, when the discrimination means determines that the detected transmission waves have been frequency-corrected, controlling the reference frequency that serves as the basis for the transmit and receive frequencies of the base station to match the frequency precision of the detected transmission waves. 41. The mobile communications system of claim 40, wherein the plurality of base stations are arranged in a predetermined order, the mobile station transmits a transmission wave including frequency accuracy information and information indicating the predetermined order regarding the other base station with which it is currently communicating, the base station device of each base station further determines, using the identification means, whether or not to perform frequency correction based on the predetermined order, and when it determines that frequency correction should be performed, the frequency control means controls the reference frequency. 42. A mobile communications method for a mobile communications system comprising multiple base stations forming multiple radio zones, the base stations having varying transmission and reception frequency accuracy, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, the multiple base stations being in a predetermined order, and having means for mutually notifying each other of information indicating the predetermined order, comprising: a step of receiving, in the base station equipment of each base station, a transmission wave from another base station; a step of determining, in the base station equipment of each base station based on the predetermined order, whether or not to perform frequency correction, and, if it is determined that frequency correction should be performed, adjusting the transmission and reception frequency of the base station to match the frequency accuracy of the received transmission wave, and performing transmission and reception. 43. A mobile communication method in a mobile communication system comprising multiple base stations forming multiple radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that moves within the multiple radio zones and communicates via the multiple base stations, comprising: a step in the mobile station device of the mobile station receiving a transmission wave from one of the multiple base stations, controlling a reference frequency that serves as the basis for the transmission and reception frequency of the mobile station to match the frequency accuracy of the received transmission wave, and transmitting and receiving signals to and from the base station at a transmission and reception frequency based on the controlled reference frequency; and a step in the base station device of each base station receiving a transmission wave from a mobile station device that transmits and receives signals at a transmission and reception frequency based on the controlled reference frequency, controlling a reference frequency that serves as the basis for the transmission and reception frequency of the mobile station to match the frequency accuracy of the received transmission wave, and transmitting and receiving signals to and from the mobile station at a transmission and reception frequency based on the controlled transmission and reception frequency. 44. The mobile communication system according to claim 43, wherein the plurality of base stations are arranged in a predetermined order, the mobile station device of the mobile station transmits a transmission wave containing information indicating that the transmission wave of the mobile station is a control of the reference frequency for a certain base station and the predetermined order, the base station device of each base station determining whether to perform frequency correction based on the predetermined order, and controlling the reference frequency when it determines that frequency correction is necessary. 45. A mobile communications method for a mobile communications system comprising multiple base stations forming multiple radio zones, the transmission and reception frequency accuracy of which is not always uniform, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, comprising: a step in each base station's base station device receiving transmission waves from other base stations and determining whether the received transmission waves have been frequency-corrected based on frequency accuracy information contained in the received transmission waves; a step in each base station's base station device, when it is determined in the receiving and determining step that the received transmission waves have been frequency-corrected, controlling a reference frequency that serves as the basis for the base station's own transmission and reception frequencies to match the frequency accuracy of the received transmission waves; and a step in each base station's base station device, after adjusting the base station's own reference frequency to match the frequency accuracy of the received transmission waves in the controlling step, transmitting transmission waves containing frequency accuracy information indicating that the frequency accuracy of the transmission frequency has been frequency-corrected, at a transmission frequency based on the reference frequency controlled in the controlling step. 46. A mobile communications system according to claim 45, wherein the plurality of base stations are in a predetermined order relationship and have means for mutually notifying each other of information indicating the predetermined order relationship, and wherein the base station equipment of each base station further determines whether to perform frequency correction based on the predetermined order relationship in the receiving and determining step, and when it determines that frequency correction should be performed, controls the reference frequency in the controlling step. 47. A mobile communication method for a mobile communication system consisting of multiple base stations forming multiple radio zones with varying transmission and reception frequency accuracy, and a mobile station that communicates through the multiple base stations while moving within the multiple radio zones, comprising: a step in each base station's base station device detecting the presence or absence of transmission waves from other base stations and notifying a mobile station located within the base station's radio zone of the transmission frequency of the detected transmission waves; a step in the mobile station's mobile station device receiving transmission waves with the transmission frequency notified from the currently located base station in the detection and notification step, and identifying whether the received transmission waves have been frequency corrected based on frequency accuracy information included in the received transmission waves; and a step in the mobile station's mobile station device returning the identification result obtained in the receiving and identification step to the currently located base station. When the identification result returned from the mobile station in the returning step indicates that the detected transmission wave has been frequency-corrected, the base station device of each base station controls the reference frequency that is the basis for the transmission and reception frequency of the base station to match the frequency accuracy of the detected transmission wave; and, after adjusting the reference frequency in the controlling step to match the frequency accuracy of the detected transmission wave, the base station device of each base station transmits a transmission wave at a transmission frequency based on the reference frequency controlled in the controlling step, the transmission wave including frequency accuracy information indicating that the frequency accuracy of the transmission frequency has been frequency-corrected. 48. A mobile communication system according to claim 47, wherein the plurality of base stations are arranged in a predetermined order, the mobile station device of the mobile station further determines whether or not frequency correction should be performed at the base station currently serving the mobile station based on the predetermined order in the identifying step, and the base station device of each base station controls the reference frequency in the controlling step when the identification result returned from the mobile station indicates that frequency correction should be performed. 49. A mobile communications system comprising multiple base stations forming multiple radio zones and having non-uniform transmission and reception frequency accuracy, and mobile stations that communicate through the multiple base stations while moving within the multiple radio zones, comprising: a base station device at each base station detects the presence or absence of transmission waves from mobile stations communicating with other base stations, and identifies whether the detected transmission waves have been frequency-corrected based on frequency accuracy information contained in the detected transmission waves; and, when the detected transmission waves are identified as frequency-corrected in the detection and identification step, the base station device at each base station adjusts the reference frequency that serves as the basis for the transmission and reception frequencies of the base station to match the frequency accuracy of the detected transmission waves. 50. The mobile communications system according to claim 49, wherein the plurality of base stations are arranged in a predetermined order, the mobile station transmits a transmission wave including frequency accuracy information and information indicating the predetermined order regarding the other base stations with which it is currently communicating, the base station device of each base station further determines whether or not to perform frequency correction based on the predetermined order in the detecting and identifying step, and controls the reference frequency in the controlling step when it determines that frequency correction should be performed.