JP2003018661A - Mobile radio terminal and control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mobile radio terminal and a control circuit which prevents the delay of detecting a pilot signal or the consumption of battery power even in the presence of jamming waves. SOLUTION: A controller 140 integrates and controls blocks of the mobile radio terminal apparatus such that a receiver 103 receives known frequencies f1, f2, f3, f4, f5,... one after another to detect a frequency at which a received electric field intensity exceeding a predetermined threshold is obtained, and controls a CDMA signal processor 106 so as to apply an inverse diffusion process to only radio signals of the detected frequency for trying to receive a pilot signal, thereby detecting a communicable cell. But priority will not be given to the cell detection at those frequencies at which no pilot signal having a sufficient reception intensity level is obtained as a result of the reverse diffusion process, even if reception field intensities over the predetermined threshold are obtained at the frequencies.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile radio terminal used in a mobile radio communication system such as a car telephone system or a mobile telephone system which employs a code division multiple access system.

[0002]

As is well known, in a mobile communication system in which a mobile station, that is, a mobile radio terminal and a base station are wirelessly connected by a code division multiple access system, a radio zone called a cell is used as a unit for a communication area. Is formed.

Then, the mobile station receives a pilot signal from a base station forming a cell in which the mobile station is located or a cell in the vicinity thereof, and detects a communicable cell from the received intensity level, so-called cell search. There is.

In this cell search, the mobile station sequentially receives known frequencies f1, f2, f3, f4, f5, ... As shown in FIG. 5, and obtains a reception electric field strength equal to or higher than a preset threshold th1. Is detected, the despreading process is performed only on the radio signal having the frequency at which the received electric field strength equal to or more than the threshold value th1 is obtained, the pilot signal is tried to be received, and the communicable cell is detected.

In the example of FIG. 5, at the frequency f4, since the received electric field strength equal to or higher than the preset threshold th1 is obtained, the despreading process is applied to the radio signal received at this frequency f4 to receive the pilot signal. Try.

However, as shown in FIG. 3, even when an interfering wave is present at the frequency f2, the conventional mobile station obtains a received electric field strength equal to or higher than a preset threshold th1, so that the interfering wave is present. The radio signal received at the frequency f2 is despread and an attempt is made to receive a pilot signal.

Such erroneous detection of the frequency to be received causes erroneous detection every time the frequency is detected in a specific environment in which an interfering wave constantly exists, resulting in useless despreading processing. Not only is signal detection delayed, but battery power is wasted. This problem has become more serious in recent years with the widespread use of devices using personal computers and low-power radios.

[0008]

A mobile radio terminal of a conventional mobile communication system, when detecting a frequency to be received, erroneously detects a frequency in which an interfering wave exists and is received at this erroneously detected frequency. Since the despreading process is performed on the wireless signal, the path detection is delayed and the battery power is wasted.

The present invention has been made to solve the above problems, and a mobile radio terminal and control circuit capable of preventing delay in path detection and waste of battery power even in the presence of interfering waves. The purpose is to provide.

[0010]

In order to achieve the above object, the present invention according to claim 1 is a mobile radio terminal wirelessly connecting to a base station by a code division multiple access system,
A first detection unit that monitors the electric field strength of the radio signal and detects a frequency at which the electric field strength equal to or higher than a preset first threshold is obtained, and the strength of the signal received from the base station based on the demodulation result of the radio signal. Of the frequencies detected by the second detection means and the first detection means, the frequency at which the intensity detected by the second detection means is less than the second threshold value set in advance is the first The detection means is controlled to be used in a non-priority manner, and the control means for detecting the frequency used for communication is provided.

According to a fourth aspect of the present invention, in a control circuit of a mobile radio terminal wirelessly connecting to a base station by a code division multiple access system, the electric field strength of a radio signal is monitored to be equal to or higher than a preset first threshold value. Detecting means for detecting the frequency at which the electric field strength of the base station is obtained, second detecting means for detecting the strength of the signal received from the base station from the demodulation result of the radio signal, and the first detecting means. Out of the frequency
The frequency at which the intensity detected by the second detection means is less than the preset second threshold is controlled to be used in the first detection means in a non-priority manner, and the frequency used for communication is detected. And a means.

In the mobile radio terminal and the control circuit configured as described above, the strength of the signal received from the base station is preset based on the demodulation result even if the electric field strength has a frequency equal to or higher than the preset first threshold value. Frequencies less than the second threshold are controlled to be used in the first detecting means in a non-priority manner, and frequencies used for communication are detected.

Therefore, according to the mobile radio terminal and the control circuit having the above-mentioned structure, the first radio wave which is preset by the interfering wave is used.
Even if there is an interfering wave, unnecessary reception processing for the radio signal of the frequency at which this interfering wave exists is performed because the frequency at which the received electric field strength equal to or higher than the threshold is obtained is non-priority used for communication. Can be suppressed, delay in path detection can be prevented, and waste of battery power due to unnecessary processing can be prevented.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a mobile radio terminal according to a first embodiment of the present invention will be described. FIG. 1 shows the configuration thereof. The mobile radio terminal shown in this figure has a CDMA (Code Division Multiple A) interface with a base station BS.
ccess) method for wireless communication.

The radio frequency signal received by the antenna 101 from the space is input to the antenna duplexer 102. The antenna duplexer 102 includes a reception filter 102a and a transmission filter 102b.

Of the radio frequency signals input from the antenna 101, the radio frequency signal transmitted from the base station BS is
After passing through the reception filter 102a, the reception unit (RX) 1
It is output to 03. It should be noted that this radio frequency signal is not input to the transmission unit 105 described later by the transmission filter 102b.

The receiving section 103 mixes the radio frequency signal with the receiving local oscillation signal input from the frequency synthesizer (SYN) 104 to frequency-convert it into an intermediate frequency signal.

The frequency of the received local oscillation signal generated by the frequency synthesizer 104 is controlled by the control unit 140.
Controlled by the control signal from. In addition, the receiving unit 10
3 has a function of detecting the received electric field strength of the radio signal of the frequency designated by the control unit 140.

The intermediate frequency signal obtained by the receiving unit 103 is subjected to quadrature demodulation processing in the CDMA signal processing unit 106 and then despreading processing to receive a predetermined format corresponding to the data rate. Converted to data,
The data is output to the voice code processing unit 107, and the data indicating the data rate is output to the control unit 140.

The voice code processing unit 107 subjects the received data obtained by the CDMA signal processing unit 106 to decompression processing according to the received data rate notified from the control unit 140, and the processing result is PCM. It is output to the code processing unit 108.

The PCM code processing unit 108 decodes the received data expanded by the voice code processing unit 107 to obtain an analog reception signal. This analog reception signal is supplied to the amplifier 10
After being amplified at 9, the speaker 110 outputs a loud sound.

On the other hand, the input voice of the speaker is input as an analog transmission signal through the microphone (M) 111, is amplified to an appropriate level by the amplifier 112, and then is input to the PC.
The M code processing unit 108 performs PCM coding processing, and outputs it to the voice code processing unit 107 as transmission data.

The voice code processing unit 107 detects the energy amount of the input voice from the transmission data output from the PCM code processing unit 108, determines the data rate based on the detection result, and notifies the control unit 140. Then, the transmission data is compressed into a burst signal having a format corresponding to the data rate and output to the CDMA signal processing unit 106.

The CDMA signal processing unit 106 responds to the burst signal compressed by the voice code processing unit 107 as follows.
Spreading processing is performed using a PN code corresponding to the transmission channel. Then, the processing result is subjected to quadrature modulation processing and output to the transmission section (TX) 105 as a quadrature modulation signal.

The transmitting unit 105 combines the quadrature modulated signal with the transmitting local oscillation signal to convert it into a radio frequency signal, and based on the transmission data rate notified by the control unit 140,
Only the effective part of the radio frequency signal is high frequency amplified and output to the antenna duplexer 102. The transmission local oscillation signal is generated by the frequency synthesizer 104 and is an oscillation signal having a frequency according to the control signal from the control unit 140.

The radio frequency signal from the transmission section 105 input to the antenna duplexer 102 is the transmission filter 102b.
As a result, only the radio frequency signal in the transmission band is transmitted to the antenna 101.
And is radiated into space toward the base station BS. The radio frequency signal in this transmission band is not input to the reception unit 103 by the reception filter 102a.

The control unit 140 includes a CPU, ROM and R
It has an AM and the like, and the CPU has the R
In accordance with a control program and control data stored in the OM, the respective units of the mobile radio terminal device are centrally controlled.

The main control is the receiving section 103,
Frequency synthesizer 104, transmitter 105 and CDM
The A signal processing unit 106 is controlled so that the C
There is communication control in which a communication link is established by wireless communication of the DMA system and communication is performed through a mobile communication network in which the base station BS is accommodated.

In this communication control, the frequency of the oscillation signal generated by the frequency synthesizer 104 is controlled,
Known frequencies f1, f2, f3, f in the receiving unit 103
4, f5, ... Are sequentially received, and a frequency at which a received electric field strength equal to or higher than a preset threshold value is obtained is detected.

Then, as a result of this detection, the CDMA signal processing unit 106 tries to receive the pilot signal by performing the despreading process only on the radio signal having the frequency at which the received electric field strength equal to or higher than the preset threshold value is obtained. To detect a communicable cell.

Further, in the above-mentioned communication control, the control section 140 obtains a pilot signal having a sufficient reception strength level as a result of the despreading process even if the reception electric field strength is equal to or higher than a preset threshold value. For frequencies that cannot be detected, a new function is provided to perform non-priority cell detection.

The incoming call notifying unit 150 notifies the user of the incoming call under the control of the control unit 140 when an incoming call is addressed to the terminal device. , A light-emitting body 152 for giving notification by light emission, and a vibrating body 153 for giving notification by generating vibration by an eccentric motor or the like.

The storage unit 160 uses, for example, a semiconductor memory such as a ROM or a RAM as a storage medium. The storage medium includes control data of the control unit 140, telephone directory data in which names and telephone numbers are associated with each other, and the like. In addition to storing the data created by the user, an error table storing the frequency at which the interference wave exists is stored.

The user interface section 170 comprises a display section 171 and a key input section 172. Display unit 171
Is, for example, an LCD (Liquid Crystal Display) or the like, and is used to visually indicate to the user the status of the device itself (outgoing / incoming calls, remaining battery level, receiving strength), dial data read from the storage unit 160, and the like. Is.

The key input unit 172 is a key for performing a normal call function related to outgoing / incoming calls such as a ten-key for inputting a dial number, and an incoming call notification method (audible tone /
It is provided with keys for utilizing various settings such as switching between light emission / vibrator / notification) and various functions. A power supply circuit 181 generates a predetermined operating power supply voltage Vcc based on the output of the battery 180 and supplies it to each circuit.

Next, the operation of the mobile radio terminal apparatus having the above configuration will be described. In the following description, the cell detection operation will be described, and the operation after the voice communication or the data communication is started will not be described.

FIG. 2 is a flow chart for explaining the cell detection processing. This processing is performed by the control unit 140, and is repeatedly executed as necessary in preparation for handover or RAKE reception.

First, in step 2a, "1" is set to the parameter n as an initial setting, and the process proceeds to step 2b. In step 2b, it is determined whether or not the frequency fn is recorded in the error table of the storage unit 160. Here, if the frequency fn is recorded in the error table of the storage unit 160, the process proceeds to step 2i, while if it is not recorded, the process proceeds to step 2c.

In step 2c, the receiving section 103 and the frequency synthesizer 104 are controlled to receive the frequency fn, the reception electric field strength of the radio signal of this frequency is detected, and the process proceeds to step 2d.

In step 2d, the received electric field strength of the radio signal of frequency fn detected in step 2c is the threshold th1.
It is determined whether or not the above. Here, if the received electric field strength is equal to or greater than the threshold th1, the process proceeds to step 2e, while if it is less than the threshold th1, the process proceeds to step 2i.

In step 2e, the receiving section 103, the frequency synthesizer 104 and the CDMA signal processing section 106 are controlled to frequency-convert the radio signal of the frequency fn,
The despreading process is performed, and the process proceeds to step 2f.

In step 2f, the pilot signal is tried to be detected based on the result of the despreading process executed in step 2e, and it is determined whether or not the pilot signal can be detected. If the pilot signal can be detected, the process proceeds to step 2g. On the other hand, if the pilot signal cannot be detected, the process proceeds to step 2h.

In step 2g, it is determined whether or not the intensity level (correlation level) of the pilot signal detected in step 2f is equal to or greater than the threshold value th2. Here, when the intensity level of the pilot signal is equal to or higher than the threshold value th2, the process ends. Although detailed description is omitted, thereafter, path detection at the frequency fn is performed as necessary. On the other hand, when the intensity level of the pilot signal is less than the threshold value th2, the process proceeds to step 2i.

In step 2h, the frequency fn is stored in the storage unit 1.
It records in the error table of 60, and it transfers to step 2i. In step 2i, "1" is added to the current parameter n, and the process proceeds to step 2j.

In step 2j, it is determined whether or not the parameter n is larger than the maximum value n _max . If the parameter n is larger than the maximum value n _max , the process proceeds to step 2k, while if the parameter n is smaller than the maximum value n max.
If it is less than or equal to _max , the process proceeds to step 2b.

In step 2k, the initial value "1" is set in the parameter n, and the process proceeds to step 2l. Step two
In l, in order to perform cell detection for the frequencies stored in the error table, the reception unit 103, the frequency synthesizer 104, and the CDMA signal processing unit 106 are controlled to frequency-convert the radio signal of the above frequency, and then despread. After processing, the process proceeds to step 2m.

In step 2m, the pilot signal is tried to be detected from the result of the despreading process executed in step 21, and it is determined whether or not the pilot signal can be detected. If the pilot signal can be detected, the process proceeds to step 2n. On the other hand, if the pilot signal cannot be detected, the process proceeds to step 2b.

In step 2n, it is determined whether or not the intensity level (correlation level) of the pilot signal detected in step 21 is equal to or more than the threshold value th2. Here, when the intensity level of the pilot signal is equal to or higher than the threshold value th2, the processing is ended, and thereafter, path detection at the above frequency is performed if necessary.

On the other hand, when the intensity level of the pilot signal is less than the threshold value th2, the process proceeds to step 2b. If there are a plurality of frequencies stored in the error table, the processes of steps 2l, 2m, and 2n are performed for each frequency.

As described above, in the mobile radio terminal having the above configuration, as shown in FIG. 3, even if the frequencies f2 and f4 are such that the received electric field strength equal to or greater than the preset threshold th1 is obtained,
As a result of the despreading process, a frequency f2 at which an interfering wave exists such that a pilot signal having a reception strength level equal to or higher than the threshold th2 cannot be obtained is recorded in an error table of the storage unit 160, and the other frequency f1 is recorded. , F3, f4
When cell detection cannot be performed at f5, cell detection is performed for the frequency f2 recorded in the error table.

That is, even if the frequency at which the received electric field strength is equal to or greater than the preset threshold th1 is obtained, the cell detection is carried out non-prioritize the frequency at which the pilot signal having a sufficient received strength level is not obtained. ing.

Therefore, according to the mobile radio terminal having the above-mentioned configuration, the frequency at which the received electric field strength equal to or higher than the threshold value th1 preset by the interfering wave is obtained is non-prioritized to the cell detection, so that the interfering wave is generated. Even if there is an interference signal, unnecessary despreading processing can be suppressed for a radio signal having a frequency in which this interference wave exists, so delay in path detection can be prevented, and battery power is wasted due to unnecessary processing. Can be prevented.

The present invention is not limited to the above embodiment.

For example, a plurality of error tables recorded in the storage unit 160 are recorded in association with the position information, the position information is acquired from the base station BS, and the cell detection processing is performed according to the position information. The error table used may be switched.

As a second embodiment, a mobile radio terminal that performs such cell detection processing will be described below. Note that the cell detection process described below can also be realized by the same configuration as the case described in the first embodiment, so a description of the configuration will be omitted, but the control unit 140.
Has a function of detecting position information from a received signal from the base station BS, and the storage unit 160 stores a plurality of error tables associated with the position information.

FIG. 4 is a flow chart for explaining the cell detection processing. This processing is performed by the control unit 140, and is repeatedly executed as necessary in preparation for handover or RAKE reception.

First, in step 4a, after detecting the position information from the received signal from the base station BS, the parameter n is set to "1" as an initial setting, and the process proceeds to step 4b. In step 4b, the frequency f is stored in the error table of the storage unit 160 corresponding to the position information detected in step 4a.
It is determined whether n is recorded. Here, when the frequency fn is recorded in the error table,
If it is not recorded, the process proceeds to step 4i.

In step 4c, the receiving section 103 and the frequency synthesizer 104 are controlled to receive the frequency fn, the reception electric field strength of the radio signal of this frequency is detected, and the process proceeds to step 4d.

In step 4d, the received electric field strength of the radio signal of frequency fn detected in step 4c is the threshold value th1.
It is determined whether or not the above. Here, if the received electric field intensity is equal to or greater than the threshold th1, the process proceeds to step 4e, while if it is less than the threshold th1, the process proceeds to step 4i.

In step 4e, the receiving section 103, the frequency synthesizer 104 and the CDMA signal processing section 106 are controlled to frequency-convert the radio signal of the frequency fn,
The despreading process is performed, and the process proceeds to step 4f.

In step 4f, the pilot signal is tried to be detected from the result of the despreading process executed in step 4e, and it is determined whether or not the pilot signal can be detected. If the pilot signal can be detected, the process proceeds to step 4g. On the other hand, if the pilot signal cannot be detected, the process proceeds to step 4h.

In step 4g, it is determined whether or not the intensity level (correlation level) of the pilot signal detected in step 4f is equal to or greater than the threshold value th2. Here, when the intensity level of the pilot signal is equal to or higher than the threshold value th2, the process ends. Although detailed description is omitted, thereafter, path detection at the frequency fn is performed as necessary. On the other hand, when the strength level of the pilot signal is less than the threshold value th2, the process proceeds to step 4i.

In step 4h, the frequency fn is recorded in the error table corresponding to the position information detected in step 4a, and the process proceeds to step 4i. In step 4i,
"1" is added to the current parameter n, and the process proceeds to step 4j.

At step 4j, it is determined whether the parameter n is larger than the maximum value n _max . If the parameter n is larger than the maximum value n _max , the process proceeds to step 4k, while if the parameter n is smaller than the maximum value n max.
If it is less than or equal to _max , the process proceeds to step 4b.

In step 4k, the initial value "1" is set in the parameter n, and the process proceeds to step 4l. Step 4
In l, in order to perform cell detection for the frequency stored in the error table corresponding to the position information detected in step 4a, the receiving unit 103 and the frequency synthesizer 10 are used.
4 and the CDMA signal processing unit 106 to control the frequency conversion of the radio signal of the above-mentioned frequency, perform the despreading process, and move to step 4m.

In step 4m, the pilot signal is tried to be detected from the result of the despreading process executed in step 4l, and it is determined whether or not the pilot signal can be detected. If the pilot signal can be detected, the process proceeds to step 4n, while if the pilot signal cannot be detected, the process proceeds to step 4b.

In step 4n, it is determined whether or not the intensity level (correlation level) of the pilot signal detected in step 4l is equal to or greater than the threshold value th2. Here, when the intensity level of the pilot signal is equal to or higher than the threshold value th2, the processing is ended, and thereafter, path detection at the above frequency is performed if necessary. On the other hand, if the intensity level of the pilot signal is less than the threshold value th2, the process proceeds to step 4b.

When there are a plurality of frequencies stored in the error table corresponding to the position information detected in step 4a, the processes of steps 4l, 2m and 2n are executed for each frequency.

As described above, in the mobile radio terminal having the above configuration, the error table to be used is switched according to the position information, and as shown in FIG. 3, the frequency at which the received electric field strength equal to or greater than the preset threshold th1 is obtained. Even if the frequency is f2 or f4, the frequency f2 in which an interfering wave exists such that a pilot signal having a reception intensity level equal to or higher than the threshold th2 cannot be obtained as a result of the despreading process is recorded in the error table corresponding to the position information. Incidentally, frequencies f1 and f other than this
When cell detection cannot be performed at 3, f4 and f5, cell detection is performed at the frequency f2 recorded in the error table.

That is, depending on the location where the mobile radio terminal is located, even if the frequency at which the received electric field strength equal to or greater than the preset threshold th1 is obtained, the frequency at which the pilot signal having a sufficient reception intensity level is not obtained is , Non-priority cell detection is performed.

Therefore, according to the mobile radio terminal having the above-mentioned configuration, even if the frequency at which the interference wave exists changes depending on the location where the mobile radio terminal is located, it is not necessary for the radio signal at the frequency at which the interference wave exists. Since the despreading process can be suppressed, the detection of the pilot signal can be prevented from being delayed for each operating environment of the user, and the power consumption of the battery 180 due to unnecessary processing can be prevented.

The present invention is not limited to the above embodiment. For example, in the second embodiment, the position information is detected from the received signal from the base station BS, but a GPS (Global Positioning System) receiver or the like is provided to acquire the position information, Alternatively, the user may input position information through the key input unit 172 or switch the error table to be used. Needless to say, the present invention can be similarly implemented even if various modifications are made without departing from the scope of the present invention.

[0073]

As described above, according to the present invention, the strength of the signal received from the base station is preset based on the demodulation result even if the electric field strength has a frequency equal to or higher than the preset first threshold value. The frequencies below the second threshold are controlled to be used in the first detecting means in a non-priority manner, and the frequencies used for communication are detected.

Therefore, according to the present invention, the frequency at which the received electric field strength equal to or higher than the first threshold value set in advance by the interfering wave is non-priority used for communication, and therefore the interfering wave exists. In this case, it is possible to suppress unnecessary reception processing for a radio signal having a frequency in which this interference wave exists, prevent delay in path detection, and prevent waste of battery power due to unnecessary processing. It is possible to provide a possible mobile wireless terminal.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing a configuration of an embodiment of a mobile radio terminal according to the present invention.

2 is a flow chart for explaining a cell detection process in the first embodiment of the mobile radio terminal shown in FIG.

FIG. 3 is a diagram showing an example of a distribution of received electric field strength when an interfering wave exists at a reception target frequency.

FIG. 4 is a flowchart for explaining a cell detection process in the second embodiment of the mobile radio terminal shown in FIG.

FIG. 5 is a diagram showing an example of a distribution of received electric field strengths of reception target frequencies.

[Explanation of symbols]

101 ... antenna 102 ... Antenna duplexer 102a ... Receiving filter 102b ... filter for transmission 103 ... Receiving unit (RX) 104 ... Frequency Synthesizer (SYN) 105 ... Transmission unit (TX) 106 ... CDMA signal processing unit 107 ... Voice code processing unit 108 ... PCM code processing unit 109 ... Amplifier 110 ... speaker 111 ... Microphone (M) 112 ... Amplifier 140 ... Control unit 150 ... Incoming call notification section 151 ... Sounding body 152 ... luminous body 153 ... Vibrating body 160 ... Storage unit 170 ... User interface section 171 ... Display unit 172 ... Key input section 180 ... Battery 181 ... Power supply circuit BS ... Base station

Claims (6)

[Claims] 1. A mobile radio terminal wirelessly connecting to a base station by a code division multiple access method, wherein the electric field strength of a radio signal is monitored to detect a frequency at which an electric field strength equal to or higher than a preset first threshold value is obtained. 1 detecting means, 2nd detecting means for detecting the strength of the signal received from the base station from the demodulation result of the radio signal, and 2nd detecting of the frequencies detected by said 1st detecting means The frequency at which the intensity detected by the means is less than a preset second threshold is controlled by the first detection means so as to be used in a non-priority manner, and a control means for detecting the frequency used for communication is provided. A mobile radio terminal, comprising: 2. The storage means for storing the frequency at which the intensity detected by the second detection means is less than a preset second threshold value, and the frequency stored by the storage means, The mobile radio terminal according to claim 1, further comprising: a frequency control unit that controls the first detection unit to use it in a non-priority manner. 3. A position information acquisition unit for acquiring position information of the mobile radio terminal, wherein the storage unit has a frequency at which the intensity detected by the second detection unit is less than a preset second threshold value. Is stored in association with the position information acquired by the position information acquisition unit, the frequency control unit, among the frequencies stored in the storage unit, for the frequency corresponding to the position information acquired by the position information acquisition unit The mobile radio terminal according to claim 1, wherein the mobile radio terminal is controlled to be used in a non-priority manner in the first detecting means. 4. A control circuit of a mobile radio terminal wirelessly connecting to a base station by a code division multiple access system, monitors the electric field strength of a radio signal, and determines the frequency at which the electric field strength equal to or higher than a preset first threshold value is obtained. First detecting means for detecting, second detecting means for detecting the intensity of a signal received from a base station from a demodulation result of a radio signal, and the first detecting means for detecting the strength of the signal received from the base station. The frequency at which the intensity detected by the second detecting means is less than the preset second threshold is controlled to be used in the first detecting means in a non-prioritized manner, and the frequency used for communication is detected. And a control circuit. 5. The storage unit stores the frequency at which the intensity detected by the second detection unit is less than a preset second threshold value, and the frequency stored by the storage unit, The control circuit according to claim 4, further comprising a frequency control unit that controls the first detection unit to use it in a non-priority manner. 6. A position information acquisition unit for acquiring position information of the mobile radio terminal, wherein the storage unit has a frequency at which the intensity detected by the second detection unit is less than a preset second threshold value. Is stored in association with the position information acquired by the position information acquisition unit, the frequency control unit, among the frequencies stored in the storage unit, for the frequency corresponding to the position information acquired by the position information acquisition unit 5. The control circuit according to claim 4, wherein the control circuit controls the first detection means to use it in a non-priority manner.