JP2003023665A - Mobile communication unit and channel retrieval method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mobile terminal that can enhance a call hit rate in the operation at the outside of a zone, and a channel retrieval method. SOLUTION: The mobile terminal is provided with wireless communication sections 11-14 that transmit/receive a CDMA signal, a base band modem section 17 that modulates/demodulates the CDMA signal to be transmitted/received into a transmission signal, and a CPU 18 that controls the transmission/reception of the CDMA signal. The mobile terminal conducts channel retrievals for a plurality of times in a way that the resolution of the first channel retrieval is highest or/and the first channel retrieval time is longest when the mobile terminal is discriminated to be outside the zone of a base station, and the mobile terminal conducts channel retrievals for a plurality of number of times in a way that the resolution of the first channel retrieval is highest or/and the first channel retrieval time is longest when the electric field strength of the received signal is a prescribed value or below or the system is lost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mobile communication device and a channel search method applied to a mobile communication system using a code division multiple access (CDMA) system.

[0002]

2. Description of the Related Art In recent years, as a multiple access method in a mobile communication system, code division multiple access (CDMA: Code D) is used.
A connection method called ivision Multiple Access) has been proposed. In this CDMA system, a signal modulated by spread spectrum is multiplexed and transmitted on a wireless transmission path (hereinafter referred to as a channel) set using a code unique to each user at the same wireless frequency.

Spread spectrum is roughly classified into a direct spread system (DS system) and a frequency hopping system (FH system). Among them, the DS method modulates a carrier wave using a PN signal (pseudo noise) code having a bit rate higher than the information rate to be communicated, spreads the frequency, and transmits.
On the receiving side, only the signal having the same bit string as the PN code is extracted from the received radio waves and demodulated into information data. This makes it possible to remove the interference component and noise superimposed on the transmission line during demodulation by spreading the spectrum.

A mobile terminal such as a mobile phone applied to the CDMA system starts capturing a control channel before making a call (outgoing call), receiving a call (incoming call), and transmitting / receiving a message. Then, the configuration information and timing information of the captured channel are acquired, and the position registration information and the like are acquired in synchronization with the timing of the captured channel.

By the way, the received electric field strength of the channel may be significantly lowered depending on the terrain and the surrounding environment such as a building. When the received electric field strength of the channel is low, it is determined that the channel cannot be captured even though the channel radio wave is received, and the out-of-range operation is performed.

In this out-of-range operation, the mobile terminal searches for a channel at a certain search cycle. A conventional channel search method during out-of-service operation will be described below with reference to FIG.

The mobile terminal searches the channel radio waves transmitted from the base station by activating two types of scans, full scan and microscan.

The full scan is a method of scanning at a high resolution to capture a channel, and for example, 360 ° scanning is performed with a fine rotation width of a rotation angle of 45 ° or less around an antenna of a mobile terminal. Also, this full scan
This also includes the case where the scan time is extended.

Micro-scan is a method of scanning at a low resolution to capture a channel. For example, a micro scan is performed with a rotation width of 45 ° or more around an antenna of a mobile terminal.
Rotate by 60 °.

As shown in FIG. 6, in the conventional channel search, five scans are activated per state, but the first four channel searches are performed by microscan and only the fifth scan is performed by full scan. .

[0011]

However, in the conventional channel search method for the out-of-service operation, the first four scans are performed by the microscan, and therefore, there are cases where the channels that can be captured by the full scan cannot be captured. As a result, the probability that a channel can be captured decreases during the first four scan times, and even if a line connection request (hereinafter referred to as a call event) is received from the user, the call event is canceled. There was a problem.

Further, the channel radio wave from the base station is RS
The signal is converted to SI (Received Signal Strength Indicaror) signal and the received electric field strength is evaluated. If the received electric field strength falls below a certain threshold, it takes a long time until the received electric field strength exceeds the threshold again. Even if a call event is detected, the channel cannot be captured, and as a result, the call event is canceled.

Further, when the system is lost as a result of the calling operation, the calling event once issued is discarded by the algorithm and the user has to call again. Therefore, it is necessary to reduce the labor. .

Therefore, the present invention has been proposed in view of the above problems, and an object thereof is to provide a mobile terminal device and a channel search method capable of improving a call success rate during out-of-service operation. To do.

[0015]

When transmitting and receiving a CDMA signal, a pilot of an optimum channel for transmitting the CDMA signal with a base station is searched in advance. Further, during out-of-range operation, the channel radio wave transmitted from the base station is searched by invoking two types of scans, a high-resolution full scan and a low-resolution microscan, a plurality of times.

The present inventor, when capturing the channel radio wave transmitted from the base station during the out-of-range operation, activates the full scan and then the micro scan,
Focusing on the fact that the call success rate can be remarkably improved, a mobile communication device and a channel search method for performing the channel search a plurality of times in which the resolution of the first channel search is the highest and / or the first channel search time is the longest. Invented Further, the present inventor notices that the call success rate can be further improved by invoking a full scan at the time of detecting a call event or at the time of a decrease in the received electric field strength, and further after the system is lost. Invented a communication device and a channel search method shown in FIG.

That is, the portable communication device according to the present invention is
Code division multiple access (C) with a base station connected to a public communication network
A mobile communication device for transmitting / receiving a (DMA) signal, a wireless communication unit for transmitting / receiving the CDMA signal, a baseband modulation / demodulation unit for modulating / demodulating the transmitted / received CDMA signal to a transmission signal, and a control for controlling transmission / reception of the CDMA signal. A plurality of channels for which the resolution of the initial channel search is the highest and / or the initial channel search time is the longest when the control means is determined to be out of the service area of the base station. Characterized by performing a search.

This mobile communication device has the highest resolution of the first channel search and / or the longest channel search time when it is determined to be out of the service area of the base station. I do. For example, in the case of activating the scan 5 times for channel search, 1
The fourth time is performed by full scan, and the remaining four times are performed by microscan for channel search.

Further, the portable communication device according to the present invention has a code division multiple connection (CDM) with a base station connected to a public communication network.
A) A portable communication device for transmitting and receiving a signal, comprising the above CD
Radio communication means for transmitting and receiving MA signals, and CD for transmitting and receiving
Baseband modulation / demodulation means for modulating / demodulating an MA signal up to a transmission signal, and performing a plurality of channel searches, and the above CDM
A control unit for controlling transmission / reception of the A signal and an operation unit for the user to operate are provided, and the control unit receives a line connection request from the operation unit to improve the resolution of the channel search, and / or It is characterized by increasing the channel search time.

Further, the portable communication device according to the present invention has a code division multiple connection (CDM) with a base station connected to a public communication network.
A) A portable communication device for transmitting and receiving a signal, comprising the above CD
Radio communication means for transmitting and receiving MA signals, and CD for transmitting and receiving
Baseband modulation / demodulation means for modulating / demodulating an MA signal up to a transmission signal, and performing a plurality of channel searches, and the above CDM
A control means for controlling transmission / reception of the A signal, wherein the control means improves the resolution of the channel search and / or the channel search time when the electric field strength of the received signal from the base station is a predetermined value or less. It is characterized by increasing.

Further, the portable communication device according to the present invention is connected with a base station connected to a public communication network by code division multiple connection (CDM).
A) A portable communication device for transmitting and receiving a signal, comprising the above CD
Radio communication means for transmitting and receiving MA signals, and CD for transmitting and receiving
Baseband modulation / demodulation means for modulating / demodulating an MA signal up to a transmission signal, and performing a plurality of channel searches, and the above CDM
A control means for controlling transmission / reception of the A signal, wherein the control means improves the resolution of the channel search and / or increases the channel search time when the system is lost.

The channel search method according to the present invention is based on a code division multiple access (CDM) with a base station connected to a public communication network.
A) Wireless communication unit that sends and receives signals, and CDM that sends and receives
A channel search method applied to a mobile communication device including a baseband modulation / demodulation unit that modulates / demodulates an A signal to a transmission signal and a control unit that controls transmission / reception of the CDMA signal, wherein the channel search method is determined to be out of range of the base station. In this case, the resolution of the first channel search is the highest and / or the first channel search time is the longest, and a plurality of channel searches are performed.

According to this channel search method, the resolution of the first channel search is the highest and / or the first channel search time is the longest when it is determined to be out of the range of the base station. I do. For example, when the scan is activated 5 times for the channel search, the first time is performed by the full scan and the remaining 4 times is performed by the micro scan.

Also, the channel search method according to the present invention is
Code division multiple access (C) with a base station connected to a public communication network
A wireless communication unit for transmitting / receiving a (DMA) signal, and C for transmitting / receiving
A channel search method applied to a mobile communication device comprising a baseband modulation / demodulation unit for modulating / demodulating a DMA signal to a transmission signal, and a control means for controlling transmission / reception of the CDMA signal, comprising: It is characterized by improving search resolution and / or increasing channel search time.

Further, the channel search method according to the present invention is
Code division multiple access (C) with a base station connected to a public communication network
A wireless communication unit for transmitting / receiving a (DMA) signal, and C for transmitting / receiving
A channel search method applied to a mobile communication device comprising a baseband modulation / demodulation unit for modulating / demodulating a DMA signal to a transmission signal, and a control means for controlling transmission / reception of the CDMA signal, the electric field of a received signal from a base station. If the intensity is below a certain value, improve the resolution of channel search, or
And increasing the channel search time.

Further, the channel search method according to the present invention is
Code division multiple access (C) with a base station connected to a public communication network
A wireless communication unit for transmitting / receiving a (DMA) signal, and C for transmitting / receiving
A channel search method applied to a mobile communication device, comprising a baseband modulation / demodulation unit for modulating / demodulating a DMA signal to a transmission signal, and a control means for controlling transmission / reception of the CDMA signal, wherein the channel is lost when system lost. It is characterized by improving search resolution and / or increasing channel search time.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, the mobile terminal 1 applied to the mobile communication system of the CDMA system will be described. Figure 1
It is a block diagram of a mobile terminal 1. As shown in FIG. 1, the mobile terminal 1 includes an antenna 11 and an antenna duplexer 12.
, Wireless transmission unit 13, wireless reception unit 14, and oscillator 15
, RSSI detector 16, baseband modulator / demodulator 17
A CPU 18, a memory 19, an operation unit 20, and a voice processing unit 21.

The antenna 11 is connected to the antenna duplexer and inputs / outputs the CDMA signal transmitted / received to / from the base station from the antenna duplexer.

The antenna duplexer 12 is a base station and a CDMA.
Since the antenna 11 shares the functions of both the antenna for transmitting a signal and the antenna for receiving a CDMA signal, it is composed of, for example, a dielectric filter or the like, one of which is connected to the antenna 11 and the other of which is connected. Is connected to the wireless transmission unit 13 and the wireless reception unit 14. The mobile terminal 1 may have a configuration without the antenna duplexer 12.

The radio transmitter 13 frequency-converts the CDMA signal in the intermediate frequency band input from the baseband modulator / demodulator 17 to the radio frequency band, and outputs it to the antenna duplexer 12.

The radio receiver 14 frequency-converts the CDMA signal in the radio frequency band input from the antenna duplexer 12 to the intermediate frequency band, and outputs it to the baseband modulator / demodulator 17.

The radio transmitter 13 and the radio receiver 14
Are each connected to an oscillator 15 and supplied with a local oscillator frequency signal.

The RSSI detector 16 is connected to the radio receiver 14, converts the channel radio wave from the base station into an RSSI signal, and evaluates the received electric field strength.

The baseband modulator / demodulator 17 is connected between the radio transmitter 13 and the radio receiver 14 and the voice processor 21 by C.
It inputs and outputs a DMA signal and performs processing such as spectrum spreading, digital modulation / demodulation, multiplexing, information source coding, and transmission path coding. For example, when transmitting a CDMA signal,
The transmission signal input from the voice processing unit 21 is A / D converted and multiplied by a PN code to perform spectrum spreading. When receiving a CDMA signal, only a signal having the same bit string as the multiplied PN code is extracted, demodulated into a transmission signal, and output to the voice processing unit 21. As a result, the interference component and noise superimposed on the transmission path can be removed by spreading the spectrum during demodulation.

The CPU 18 has a baseband modulator / demodulator 17
Is connected to and controls input / output of signals. Also this CP
The U 18 is connected to the memory 19 and reads out and executes the program stored in the memory 19.

The memory 19 is, for example, a flash memory and stores data at a designated address. Further, the memory 19 stores the priority order of channels to be tried for acquisition, a program defining a channel search method described later, and the like.

The operation unit 20 includes a power switch, dial keys, various function setting buttons, etc., and is operated by the user.

The voice processing unit 21 is connected to the baseband modulation / demodulation unit 17, and performs voice coding / combining processing and amplification of voice input / output via a microphone and a speaker.

The mobile terminal 1 according to the present invention applied to this CDMA system starts capturing the control channel before making a call, receiving a call, and transmitting / receiving a message. Then, the configuration information and timing information of the captured channel are acquired, and the position registration information and the like are acquired in synchronization with the timing of the captured channel.

By the way, the received electric field strength of the channel may be significantly lowered depending on the terrain and the surrounding environment such as a building. When the received electric field strength of the channel is low, it is determined that the channel cannot be captured even though the channel radio wave is received, and the out-of-range operation is performed. In the out-of-service operation, the mobile terminal searches for a channel at a certain search cycle.

A channel searching method when the mobile terminal 1 to which the present invention is applied is out of service will be described below with reference to FIG.

The mobile terminal 1 searches the channel radio waves transmitted from the base station by activating two types of scans, full scan and microscan.

The full scan is a method of scanning at a high resolution and capturing a channel, and the microscan is a method of scanning at a low resolution and capturing of a channel. Incidentally, the level of resolution is distinguished based on parameters such as scan rotation angle and scan time.

As shown in FIG. 2, channel search is performed in three types of states (DZ_S0,
DZ_S1, DZ_S2). The channel search cycle is the shortest in DZ_S0, DZ_S1, DZ_
It becomes longer as time goes on with S2. If the optimum channel cannot be captured even after shifting to the DZ_S2 state, the channel search is continued based on the timing of the DZ_S2 state.

In each state, the mobile terminal 1 performs scanning for channel search five times. The first scan is a full scan. The second to fifth scans are microscans. Note that this scan is performed for all channels. For example,
When there are two channels, A channel and B channel,
When the scanning is completed for both the A channel and B channel frequencies, one scan is completed.

The scan interval is 5.12 seconds in the DZ_S0 state and 1 in the DZ_S1 state.
At 0.24 second intervals, the DZ_S2 state is 20.48.
Scan each second.

The number of scans and the scan interval are merely examples and can be set arbitrarily.

That is, the mobile terminal 1 to which the present invention is applied
Can perform the first scan at the highest resolution and / or take the longest time, thus increasing the probability of capturing the optimal channel in the first scan. As a result, compared to the conventional mobile terminal that performs the full scan for the first time in the fifth time, the call success rate can be further increased especially in the scan time zones from the first time to the fourth time.

Next, the call-out event monitoring cycle in each state will be described by taking the DZ_S0 state as an example.

FIG. 3 is an enlarged view of the DZ_S0 state in the time axis direction. The mobile terminal 1 activates the scan at a cycle of 5.12 seconds, and monitors the calling event at a cycle of 1.28 seconds. That is, the call event is monitored four times in one scan cycle. This calling event is monitored by TCXO (Temperature CompensatedX't
al Oscillator) Start up only the power supply.

Regarding the calling event monitoring cycle,
It can be reset to any cycle within the range of the scan interval.

Next, a channel search method at the time of detecting a calling event will be described with reference to FIG. 4 by taking the DZ_S0 state as an example.

First, when the operation shifts to the out-of-range operation, DZ_S0
The state is entered (step ST1), and a scan for channel search is activated at an interval of 5.12 seconds as shown in FIG. At the same time, the TCXO power supply is turned on at intervals of 1.28 seconds to monitor the calling event (step ST2).

When a calling event is detected, the mobile terminal 1
Monitors the call-out event and interrupts all microscans, and performs channel search by full scan (steps ST3 to ST4). As a result of the channel search by the full scan, if the pilot of the optimum channel can be captured (step ST5), the transmission path can be established with the base station, and the call is successful (step ST6).

On the other hand, when the optimum channel cannot be captured, the full scan is activated again to search the channel. This channel search is performed a specified number of times (for example, 6
When the pilot of the optimum channel cannot be captured even after repeating the above times, it is determined that the call has failed and the state shifts to the DZ_S1 state (step ST7).

The mobile terminal 1 to which the present invention is applied not only performs each state for the first time, but also issues a full scan anew when a calling event is detected to perform channel search. This allows
Even when the channel has not been captured yet at the time of detecting the call-out event, the probability of capturing the channel can be increased by invoking the full scan. Also,
This full scan is performed for all base stations in the vicinity, so even if a weak radio wave channel is captured from the base station when a call event is detected, a reliable radio wave can be captured again. The electric field strength of can be optimized.

That is, the mobile terminal 1 to which the present invention is applied
Can trigger an optimal channel acquisition by invoking a full scan when a call event is detected.
Further, since the received radio waves can be optimized, the call success rate can be further increased.

Next, a channel search method when the received electric field strength of channel radio waves is low will be described with reference to FIG.

Channel radio waves from the base station are converted into RSSI signals to evaluate the received electric field strength. When the received electric field strength evaluated from this RSSI signal is small (that is, in FIG.
If the received electric field strength is lower than a certain threshold (as shown in Fig. 4), the optimal channel cannot be acquired, and the transmission path cannot be established with the base station. Will end up.

When the reception electric field strength drops to the threshold (for example, -98 dBm) at which the calling event is canceled, the mobile terminal 1 activates the full scan a prescribed number of times until the optimum channel can be captured.

As a result, even if the optimum channel has not been acquired yet, the probability that the optimum channel can be acquired can be increased by invoking the full scan, and the transmission path can be established with the base station. . Therefore,
Even if a call-out event is detected during the time period when the received electric field strength falls below the threshold, it is possible to make a call with a high probability.

In particular, as shown in FIG. 5, since the RSSI signal fluctuates in time series, once it falls below the above threshold, it takes a considerable time to rise above the threshold again in a weak electric field, and the calling event is canceled. In some cases, the time period is extended for a long time. Even in such a case, by activating the above-described full scan, the call event success rate can be further improved.

Further, when a call-out event is detected when the received electric field intensity drops below the above threshold,
Since the optimum channel cannot be captured, not only the outgoing call event is canceled but also the system is lost.

The mobile terminal 1 to which the present invention is applied activates the full scan a prescribed number of times even after the system is lost. With this, even if the system is lost once,
The optimal channel can be captured and the calling event can be rescued from the system lost. As a result, the calling event issued once is not wasted, and the user does not need to call again, so that the labor can be reduced.

The mobile terminal 1 to which the present invention is applied is not limited to the above embodiment. If the resolution of the first channel search is the highest and / or if the first channel search time is the longest, not only the three types of states described in the above embodiment but also different channel search periods and channel search pattern states The present invention is also applicable to a mobile terminal composed of

[0067]

As described in detail above, the portable communication device and the channel search method according to the present invention are capable of performing the first scan at the highest resolution or / or during the out-of-service operation.
Also, since it can be performed over the longest time, the probability that the optimum channel can be captured in the first scan can be improved. As a result, compared to the conventional mobile terminal that performs the full scan for the first time in the fifth time, the call success rate can be further increased especially in the scan time zones from the first time to the fourth time.

Further, in the portable communication device and the channel search method according to the present invention, it is possible to try to capture an optimum channel by further invoking a full scan when a call event is detected, and to optimize the received radio wave. As a result, the call success rate can be further increased.

Further, in the portable communication device and the channel search method according to the present invention, when the received electric field strength is equal to or lower than the predetermined value, the full scan can be further activated to capture the optimum channel. Can be further enhanced, and by re-acquiring reliable channel radio waves,
The reception radio wave can be optimized.

Further, in the portable communication device and the channel search method according to the present invention, the optimum channel can be captured by further invoking the full scan after the system is lost, so that the calling event can be rescued from the system lost. You can

[Brief description of drawings]

FIG. 1 is a diagram showing a block configuration diagram of a mobile terminal to which the present invention is applied.

FIG. 2 is a diagram for explaining channel search timing of a mobile terminal to which the present invention has been applied.

FIG. 3 is a diagram for explaining a call-out event monitoring cycle of a mobile terminal to which the present invention is applied.

FIG. 4 is a diagram for explaining channel search at the time of detecting a calling event of a mobile terminal to which the present invention is applied.

FIG. 5 is a diagram for explaining a channel search method when the received electric field strength of channel radio waves is low.

FIG. 6 is a diagram for explaining a conventional channel search method during out-of-service operation.

[Explanation of symbols]

1 mobile terminal, 11 antennas, 12 antenna duplexer, 13 wireless transmitter, 14 wireless receiver, 15 oscillator, 16 RSSI detector, 17 baseband modulator / demodulator, 18 CPU, 19 memory, 20 operation unit, 21
Voice processing unit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yasutaka Nakata             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation (72) Inventor Hiroshi Tajiri             6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Soni             -Inside the corporation F term (reference) 5K022 EE02 EE21 EE31                 5K067 AA25 CC10 DD23 EE02 EE10                       HH21 JJ11

Claims (10)

[Claims] 1. A portable communication device for transmitting and receiving a code division multiple access (CDMA) signal to and from a base station connected to a public communication network, and wireless communication means for transmitting and receiving the CDMA signal, and a transmission signal for transmitting and receiving the CDMA signal. Up to a baseband modulation / demodulation means for performing modulation / demodulation and a control means for performing channel search and controlling the transmission / reception of the CDMA signal are provided. The control means determines the resolution of the first channel search when the optimum channel cannot be captured. The highest, or /
And a mobile communication device characterized by performing channel search a plurality of times, the channel search time of the first time being the longest. 2. The mobile communication device according to claim 1, wherein the control means performs the channel search a plurality of times based on a plurality of types of states having different channel search cycles. 3. A portable communication device for transmitting / receiving a code division multiple access (CDMA) signal to / from a base station connected to a public communication network, a wireless communication means for transmitting / receiving the CDMA signal, and a transmission signal for transmitting / receiving the CDMA signal. Up to a baseband modulation / demodulation means for performing modulation / demodulation, a control means for performing channel search a plurality of times, and controlling transmission / reception of the CDMA signal, and an operation section for a user to operate, the control means comprising: A mobile communication device, which receives the line connection request and improves the resolution of the channel search and / or increases the channel search time. 4. A portable communication device for transmitting and receiving a code division multiple access (CDMA) signal to and from a base station connected to a public communication network, a wireless communication means for transmitting and receiving the CDMA signal, and a transmission signal for transmitting and receiving the CDMA signal. A baseband modulation / demodulation means for performing modulation / demodulation up to and including a control means for performing a plurality of channel searches and controlling transmission / reception of the CDMA signal, wherein the control means has an electric field strength of a reception signal from the base station equal to or less than a predetermined value. In this case, the mobile communication device is characterized in that the resolution of the channel search is improved and / or the channel search time is increased. 5. A portable communication device for transmitting and receiving a code division multiple access (CDMA) signal to and from a base station connected to a public communication network, and wireless communication means for transmitting and receiving the CDMA signal, and a transmission signal for transmitting and receiving the CDMA signal. Up to a baseband modulation / demodulation means for performing modulation / demodulation and a control means for performing channel search a plurality of times and controlling transmission / reception of the CDMA signal. The control means improves the resolution of the channel search when the system is lost. Or / and increasing the channel search time, a portable communication device. 6. A radio communication unit for transmitting / receiving a code division multiple access (CDMA) signal to / from a base station connected to a public communication network, a baseband modulation / demodulation unit for modulating / demodulating the transmitted / received CDMA signal to a transmission signal, and the CDMA. A channel search method applied to a mobile communication device comprising a control means for controlling signal transmission and reception, wherein the resolution of the first channel search is the highest when the optimum channel cannot be captured, and / or the first channel search is performed. A channel search method comprising performing a channel search a plurality of times, which has the longest channel search time. 7. The channel search method according to claim 6, wherein the channel search is performed a plurality of times based on a plurality of types of states having different channel search periods, and the channel search period of the first state is the minimum. . 8. A radio communication unit for transmitting / receiving a code division multiple access (CDMA) signal to / from a base station connected to a public communication network, a baseband modulation / demodulation unit for modulating / demodulating the transmitted / received CDMA signal to a transmission signal, and the CDMA. A channel search method applied to a mobile communication device comprising a control means for controlling signal transmission / reception, which is capable of improving channel search resolution and / or increasing channel search time in response to a line connection request. Channel search method characterized by. 9. A radio communication unit for transmitting / receiving a code division multiple access (CDMA) signal to / from a base station connected to a public communication network, a baseband modulation / demodulation unit for modulating / demodulating the transmitted / received CDMA signal to a transmission signal, and the CDMA. A channel search method applied to a mobile communication device comprising a control means for controlling signal transmission / reception, wherein when the electric field strength of a received signal from a base station is equal to or lower than a predetermined value, the channel search resolution is improved, And / or a channel search method characterized by increasing the channel search time. 10. A radio communication unit for transmitting / receiving a code division multiple access (CDMA) signal to / from a base station connected to a public communication network, a baseband modulation / demodulation unit for modulating / demodulating the transmitted / received CDMA signal to a transmission signal, and the CDMA. A channel search method applied to a mobile communication device, comprising: a control means for controlling signal transmission / reception, wherein when the system is lost, the resolution of the channel search is improved and / or the channel search time is increased. Channel search method characterized by.