KR100634580B1 - Apparatus for sending pilot beacon signal for hard hand-off in wcdma communication system - Google Patents

Abstract

A pilot beacon transmission device for hard hand-off in a WCDMA(Wideband Code Division Multiple Access) communication system is provided to generate a pilot beacon signal by combining a signal up-converted in frequency converters with a main signal, amplify the pilot beacon signal, and output the amplified signal through an antenna, thereby preventing the number of available frequencies of a base station from being decreased and preventing the capacity of the base station from being reduced by removing unnecessary overhead channels. A receiving unit(410) receives the main signal of a base station. A signal generating unit(420) extracts a CPICH(Common Pilot Channel) signal from the main signal outputted from the receiving unit(410) and generates a combined signal by combining an SCH(Synchronization Channel) signal with a pre-generated BCH(Broadcast Channel). Frequency converters(430,440) up-convert the combined signal generated in the signal generating unit(420) by the frequency of a pilot beacon signal. A signal combiner(450) generates the pilot beacon signal by combining the combined signal up-converted in the frequency converters(430,440) with the main signal. An output amplifier(460) amplifies the pilot beacon signal and outputs the amplified signal through an antenna.

Description

Apparatus for sending pilot beacon signal for hard hand-off in WCDMA communication system

1 illustrates a handoff method in a mobile communication system according to the prior art.

2 illustrates a frame structure in a compression mode.

3 is a view showing a pilot beacon or a pilot pilot frequency handoff method according to an embodiment of the present invention.

4 is a view schematically showing the structure of a pilot beacon transmission apparatus according to an embodiment of the present invention.

5 is a view schematically showing the structure of a signal generator according to an embodiment of the present invention.

6A is a diagram schematically illustrating a structure of a pilot beacon signal generator 600 which generates a synchronization channel signal according to an exemplary embodiment of the present invention.

6B is a diagram schematically illustrating a structure of a pilot beacon signal generator 650 for extracting a synchronization channel signal from a main signal according to another exemplary embodiment of the present invention.

7 is a view schematically showing the structure of a pilot beacon signal generator 700 according to another preferred embodiment of the present invention.

8 is a diagram illustrating a pilot beacon signal generator 800 extended to a plurality of sectors according to another exemplary embodiment of the present invention.

<Description of the symbols for the main parts of the drawings>

400: pilot beacon transmission device

410: receiver

420: signal generator

500: downconverter 510; A / D Converter

520: pilot beacon signal generator 530: D / A converter

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to handoff in a mobile communication system, and more particularly, to a pilot beacon transmission apparatus for smooth hard handoff in a WCDMA base station.

When a mobile communication terminal (MS) moves out of a serving cell or sector area to another cell or sector area in a mobile communication system, handing off of switching a call path to a moved cell or sector to maintain a call state This is called hand-off or hand over.

1 is a view showing a handoff method in a mobile communication system according to the prior art. Referring to FIG. 1, the mobile communication terminal compares the threshold value for the pilot channel strength received from the base station with the pilot channel strength of the neighboring base station that it continues to measure. When the comparison value is a value that requires handoff at a specific time point, the mobile communication terminal performs handoff under control of the responsible system. The signal transmitted from the base station 2 112 is connected to the mobile communication terminal at reference numeral '120' during the handoff period. The signal transmitted from the base station 1 (110) is terminated at the reference numeral '124' out of the hand off period.

The method is widely used in the base station of the CDMA method, there is a disadvantage that the movement between frequencies (FA) is not free. For example, an 8 FA base station is installed in a city where traffic volume is high. Even in a suburban residential area where there is not much call volume, an 8 FA base station is often required. As a result, investment inefficiency occurs, which is a problem caused by designing a wireless network such that handoffs between frequencies that are not reliable in urban areas do not occur.

In this way, since the movement between frequencies is not free, the urban section is installed by unifying the number of FAs collectively, and installing the FA number by reducing the number of FAs. At the boundary, various methods are used to efficiently perform hard handoff between frequencies.

In asynchronous WCDMA, the compression mode is a representative method. 2 is a diagram illustrating a frame structure of a compression mode. Two RF receiver circuits must be present in the mobile terminal for inter-frequency handoff to search for other adjacent cells during a call. However, since this is impractical, the mobile communication terminal incorporating one RF receiving circuit performs a compression mode in which a call is temporarily suspended during a call in order to search for cells of different frequencies. Referring to FIG. 2, the mobile communication terminal temporarily changes a frequency to another adjacent frequency cell to search for a possibility of handoff with an adjacent cell during a temporarily suspended transmission gap length (TGL). This method increases the transmission data rate of the frame, changes the spreading factor to a low value, and increases the output by the lowered confidence gain. In addition, a search for adjacent cell frequencies within a few kilohertz requires a good PLL. In addition, since the transmission data rate increases, there is a problem in that a probability of an error of data increases.

When moving from an asynchronous (WCDMA) network to a synchronous (CDMA) network, handoff is impossible because of different communication systems. At this time, a device for generating a pilot beacon signal is installed in the cell of the synchronous base station. The mobile communication terminal compares the strengths of the pilot beacon signal and the actual asynchronous base station signal so that the pilot beacon signal can be handed off to the synchronous network when the strength of the pilot beacon is greater than a predetermined size. Of course, the mobile communication terminal is preferably a dual mode terminal designed to be used in both asynchronous and synchronous networks. However, in this scheme, when there is only a pilot beacon signal, the mobile communication terminal stays in the asynchronous mode for a predetermined time because there is no information on the synchronous network base station. If no information is received from the base station after searching for a certain time, the synchronous modem is initialized and communication is performed by shifting to the synchronous network mode. That is, since the mobile communication terminal is located in the asynchronous network, the mobile terminal is initially set up in the asynchronous network mode and searches for a pilot signal, but after a certain time, if no information about the base station is found, the mobile communication terminal is automatically set to transition to the synchronous network. There is a problem that should be present.

Accordingly, an object of the present invention for solving the above problems is to provide an apparatus for transmitting a pilot beacon in a WCDMA communication system for inter-frequency hard handoff in an asynchronous WCDMA system.

Another object of the present invention is to provide an apparatus for transmitting a pilot beacon in a WCDMA communication system which can prevent the number of available frequencies of a base station from decreasing and prevents a decrease in capacity of the base station.

Another object of the present invention is to provide an apparatus for transmitting a pilot beacon in a WCDMA communication system that can lower the error rate occurring in the compression mode.

Another object of the present invention is to provide a pilot beacon transmission apparatus in a WCDMA communication system that can reduce the delay time when the transition from the asynchronous network to the synchronous network.

In order to achieve the above object, according to an aspect of the present invention, an apparatus for generating a pilot beacon signal in an asynchronous network (WCDMA) communication system, comprising: a receiving unit for receiving a main signal of a base station; A signal generator for extracting a common pilot channel (CPICH) signal from the main signal output from the receiver and generating a synthesized signal obtained by synthesizing a synchronization channel (SCH) signal and a previously generated broadcast channel (BCH) signal; A frequency converter configured to up-convert the synthesized signal generated by the signal generator to a frequency of the pilot beacon signal; A signal synthesizer configured to synthesize the up-converted composite signal and the main signal by the frequency converter to generate the pilot beacon signal; And an output amplifier for amplifying the pilot beacon signal and outputting the same through an antenna. When the pilot beacon signal is greater than or equal to a predetermined size, the mobile communication terminal hands off to a communication frequency of the base station corresponding to the broadcast channel signal. The pilot beacon transmission apparatus may be provided in which a frequency of the pilot beacon signal is a communication frequency of a base station where the mobile communication terminal is located before handoff.

Preferably, the signal generation unit, a down converter for down converting the frequency of the main signal to an IF frequency; An A / D converter converting the down-converted main signal into a digital signal; A pilot beacon signal generator for extracting the common pilot channel signal from the digital signal using a scramble code and synthesizing the sync channel signal and the broadcast channel signal; And a D / A converter converting the synthesized signal into an analog signal.

The pilot beacon signal generation unit may further include: a correlator for searching for the scramble code from the digital signal and extracting the common pilot channel signal using correlation; And a channel synthesizer for synthesizing the sync channel signal, the broadcast channel signal, and the common pilot channel signal, wherein the scramble code may be known in advance by the pilot beacon signal generator.

The sync channel signal may be a signal of a sync channel extracted from the main signal or a signal of a separate sync channel previously generated by the signal generator, and the broadcast channel signal may be system information of the base station or a communication frequency of the base station. It may be a signal including information.

In order to achieve the above objects, according to another aspect of the present invention, in an apparatus for generating a pilot beacon signal used for handoff from an asynchronous network communication system to a synchronous network (CDMA) communication system, receiving the main signal of the base station A receiving unit, wherein the base station follows the synchronous network communication system scheme; A signal generator configured to separately generate a common pilot channel signal, a sync channel signal, and a broadcast channel signal to generate a synthesized signal; A frequency converter configured to up-convert the synthesized signal generated by the signal generator to a frequency of the pilot beacon signal; A signal synthesizer configured to synthesize the up-converted composite signal and the main signal by the frequency converter to generate the pilot beacon signal; And an output amplifier for amplifying the pilot beacon signal and outputting the same through an antenna. When the pilot beacon signal is greater than or equal to a predetermined size, the mobile communication terminal hands off to a communication frequency of the base station corresponding to the broadcast channel signal. The pilot beacon transmission apparatus may be provided in which a frequency of the pilot beacon signal is a communication frequency of a base station where the mobile communication terminal is located before handoff.

Preferably, the broadcast channel signal is a signal including system information of the base station or communication frequency information of the base station, and the mobile communication terminal includes an asynchronous modem and a synchronous modem at the same time, and is handed to the communication frequency of the base station. When off, the synchronous modem may be initialized and turned on.

Other objects, specific advantages and novel features of the present invention will become more apparent from the following detailed description and the preferred embodiments associated with the accompanying drawings. Hereinafter, exemplary embodiments of a pilot beacon transmission device for hard handoff in a WCDMA communication system according to the present invention will be described in detail with reference to the accompanying drawings. The same or corresponding components are given the same reference numerals and redundant description thereof will be omitted.

FIG. 3 is a diagram illustrating a frequency beoff method for pilot beacon or dummy pilot according to an embodiment of the present invention. Hereinafter, the pilot beacons or dummy pilots will be described collectively as pilot beacons. Even in the hard handoff between frequencies, the mobile communication terminal 300 should be able to grasp the access to the adjacent base station by itself. Therefore, it is necessary to install a pilot beacon transmitter that transmits only pilot signals that do not include a communication channel in adjacent base stations.

In synchronous (CDMA), the mobile communication terminal 300 communicates with the frequency f1 in cell A of the base station 1110. The mobile communication terminal 300 knows that the adjacent base station 2 112 is transmitting the pilot beacon signal of f1, and when detecting the f1 pilot beacon signal, the mobile station 300 checks the frequency information by the f1 dummy call channel and returns to the f2 frequency. By communicating, it is hard handed off.

In the asynchronous WCDMA scheme, there is a blind mode similar to the synchronous method. However, unlike in CDMA, in WCDMA, there is no calling channel for confirming frequency information. When the mobile communication terminal 300 determines a broadcast channel (BCH), the mobile communication terminal 300 moves to the corresponding frequency within a short time. Let's do it. The broadcast channel includes a plurality of system information blocks (SIBs), and when the base station carries blind mode information on specific system information and transmits the blind mode information, the mobile communication terminal 300 transmits the corresponding system information from the corresponding system information of the broadcast channel to the corresponding cell. Get information about The hard handoff is performed by acquiring frequency information of the corresponding cell among the information about the corresponding cell.

In FIG. 3, base station 1 110 communicates at a frequency f1 in cell A, and adjacent base station 2 112 communicates at a frequency f2 in cell B. The mobile communication terminal 300 communicates with the base station 1 110 at a frequency f1 in the cell A, and transmits a signal of a pilot cell having a frequency f1 transmitted from the cell B of the adjacent base station 2 112. Detect (310). When the signal size of the pilot cell is greater than or equal to the threshold value, the mobile communication terminal 300 performs handoff. At this time, the system information included in the broadcast channel of the signal in the pilot cell is checked. Based on the result of the check, it is found that the communication frequency of the neighboring base station 2 112 is f2, and the frequency is changed to f2, that is, the hard handoff is performed 320 to perform continuous communication. If adjacent base station 3 (not shown) is communicating at the same frequency f2, soft handoff is performed (330).

4 is a view schematically showing the structure of a pilot beacon transmission apparatus according to an embodiment of the present invention, Figure 5 is a diagram schematically showing the structure of a signal generator according to an embodiment of the present invention.

Referring to FIG. 4, the pilot beacon transmission apparatus 400 includes a receiver 410, a signal generator 420, frequency converters 430 to 440, a signal synthesizer 450, and a power amplifier (LPA) 460. do.

The pilot beacon transmitting device 400 receives a main signal from the base station, extracts a common pilot channel (CPICH) and a broadcast channel, synthesizes the synchronization signal (SCH), and generates a pilot beacon signal. Send.

Here, channels of WCDMA used in the present invention are as follows.

The common pilot channel (CPICH) is composed of a primary pilot channel and a secondary pilot channel. The primary pilot channel acts like a pilot channel in the CDMA scheme and provides the phase reference for all channels (but not the secondary channel). And only one channel exists. The secondary pilot channel serves as a secondary pilot channel in the CDMA scheme, supports a smart antenna function to concentrate the antenna beam in a specific region, and a plurality of channels may be used. The secondary common pilot channel can be used as the phase reference of the secondary common control channel and the designated channel. The synchronization channel (SCH) is a channel having the most basic synchronization information that a mobile communication terminal should first acquire. It consists only of the primary sync code and the secondary sync code that have not been scrambled. It is transmitted through an antenna through carrier modulation, frequency reverse conversion, and amplification along with other scrambled physical channels. The broadcast channel (BCH) is a channel used to transmit information related to a specific system or cell to all mobile communication terminals in the cell.

The receiver 410 is a part that receives the main signal from the base station. The main signal received from the base station is a signal including a common pilot channel or a synchronization channel.

The signal generator 420 extracts a common pilot channel signal in order to obtain information of a base station in charge of a cell in which the pilot beacon transmission apparatus 400 is located. After analyzing the information of the base station, a common pilot channel signal is synthesized with a separate sync channel signal (or a sync channel signal extracted from the base station signal) and a broadcast channel signal including blind mode information.

The frequency converter 430 up-converts the frequency of the pilot beacon signal generated by the signal generator 420 to have the F1 frequency, which is the communication frequency of the base station in charge of the cell where the mobile communication terminal 300 is located.

Another frequency converter 440 upconverts the main signal to have a frequency F2, which is a communication frequency of a base station to which the main signal is to be moved.

The signal synthesizer 450 may transmit the pilot beacon signal having the F1 frequency and the main signal having the F2 frequency.

The power amplifier 460 amplifies a signal output from the signal synthesizer 450 and transmits the signal through an antenna.

Referring to FIG. 5, the signal generator 420 includes a down converter 500, an A / D converter 510, a pilot beacon signal generator 520, and a D / A converter 530.

The down converter 500 drops the frequency of the signal output from the receiver 410 to the IF frequency.

The A / D converter 510 converts a signal dropped to the IF frequency into a digital signal using a system clock.

The pilot beacon signal generator 520 includes a correlator 521 and a channel synthesizer 522. The correlator 521 finds the scramble code from the converted digital signal, extracts an original signal that has not been scrambled based on the scramble code, and extracts a common pilot channel signal from the original signal. The method for determining the scramble code may determine the scramble code used by the base station in charge of the cell to be pre-installed as the pilot beacon transmitting device 400 is installed in a specific base station. Another method obtains scramble code group information of the base station to which the pilot beacon transmission apparatus 400 belongs through correlation through the correlator 521. The scramble code group of the base station to which the base station belongs to each includes eight scramble codes. Therefore, the scramble codes can be identified through all eight scramble codes through a search process. The above process is the most general matter for the mobile communication terminal to acquire the initial synchronization and the scramble code in the WCDMA communication system.

The channel synthesizer 522 generates a sync channel signal based on the extracted common pilot channel signal. The sync channel signal may be extracted from the main signal received by the receiver 410 or may be generated separately. The broadcast channel signal in the main signal is typically intended to undergo hard handoff in compression mode in the WCDMA scheme, which is not used in the present invention. Instead, channel synthesizer 522 pre-generates the new broadcast channel signal set to blind mode. A common pilot channel signal extracted from the main signal, a sync channel signal extracted or newly generated from the main signal, and a previously generated broadcast channel signal are synthesized. The other channel is preferably removed because it is not necessary for handoff.

The D / A converter 530 converts the signal synthesized by the channel synthesizer 522 into an analog signal and outputs the analog signal.

6A is a diagram schematically illustrating a structure of a pilot beacon signal generator 600 which generates a synchronization channel signal according to an exemplary embodiment of the present invention. 6B is a diagram schematically illustrating a structure of a pilot beacon signal generator 650 extracting a synchronization channel signal from a main signal according to another exemplary embodiment of the present invention.

Referring to FIG. 6A, the main signal has a value of 3.84 Mcps (38400 chips (10 ms)). The scramble code is obtained from the correlator 521 through the main signal. The common pilot channel signal is extracted. The sync channel signal is a signal generated by the pilot beacon signal generator 520 itself. The mobile terminal includes the most basic synchronization information to be obtained first, and does not go through channelization and scrambling. The broadcast channel signal including blind mode information in one of the system information is subjected to channelization through an OVSF (orthogonal variable spreading coefficient) code and scrambled through a scramble code. In the WCDMA scheme, an OVSF code whose Walsh code length is changed according to data transmission speed is used for spreading, and a scramble code is used to distinguish cell sectors. The OVSF code widens the bandwidth from bit rate to chip rate. That is, it has a length of 3.84 Mcps that is the same as the main signal. The scramble code inserts a signal without affecting the bandwidth.

The channel synthesizer 522 combines the extracted common pilot channel signal, the separately generated synchronization channel signal, and the broadcast channel signal that has been channelized and scrambled, and outputs the combined channel signal to the D / A converter 530.

The pilot beacon signal generator 650 shown in FIG. 6B is similar to the pilot beacon signal generator 600 shown in FIG. 6A, and there is a difference in generation of a synchronization channel signal. The sync channel signal generator 655 extracts the sync channel signal included in the main signal. The sync channel signal is used as a sync channel signal of the pilot beacon signal. Other parts have the same function and role as those of FIG. 6A.

7 is a view schematically showing the structure of a pilot beacon signal generator 700 according to another embodiment of the present invention. The pilot beacon signal generator 700 shown in FIG. 7 is usable for handoff between asynchronous (WCDMA) networks or handoff between different networks. A pilot beacon signal including a broadcast channel signal including system information of a synchronous (CDMA) network is generated, not just a pilot beacon signal having only strength. Accordingly, the mobile communication terminal moving from the asynchronous network to the synchronous network can immediately switch to the synchronous network mode without time delay by using the system information of the broadcast channel signal included in the pilot beacon signal.

The common pilot channel signal may be extracted from the main signal, but a separate common pilot channel signal may be generated. The sync channel signal may also be extracted from the main signal or may generate a separate signal. Although FIG. 7 illustrates generating the sync channel signal separately, it can also be extracted from the main signal.

When the beacon signal generator 700 shown in FIG. 7 is used in an asynchronous network, the pilot beacon signal generator 600 shown in FIG. 6A or the switch shown in FIG. The pilot beacon signal generator 650 performs the same function. When used in a synchronous network, the switch is in an OFF state. At this time, the common pilot channel signal generation unit 710 does not have a common pilot channel signal in the signal of the synchronous network base station. Create A pilot beacon signal is generated by adding the common pilot channel signal to the newly generated sync channel signal and the broadcast channel signal that has undergone channelization and scrambling. The broadcast channel signal includes information of a synchronization network base station in charge of a cell in which the pilot beacon transmission apparatus is located. The mobile communication terminal receives the pilot beacon signal and checks the information of the synchronization network base station included in the broadcast channel signal. If the size of the pilot beacon signal is greater than or equal to a predetermined size (more than a threshold), the synchronization modem immediately without time delay. It initializes the handset to perform communication with the synchronous network base station.

In order to perform handoff from the asynchronous network to the synchronous network, the process of synchronizing the mobile communication terminal to be able to communicate in the synchronous network will be apparent to those skilled in the art, and thus a detailed description thereof will be omitted.

The pilot beacon signal generators 600 and 650 illustrated in FIGS. 6A to 6B represent one sector in the base station and may extend to other sectors. 8 is a diagram illustrating a pilot beacon signal generator 800 extended to a plurality of sectors according to another exemplary embodiment of the present invention.

Typically, the base station may be divided into three sectors of α, β, and γ sectors at intervals of 120 ° (degree). Each sector may have a different frequency. In this case, the frequency converter illustrated in FIG. 8 may be implemented to have respective frequencies fα, fβ, and fγ. Alternatively, the frequency may be hopped to implement a plurality of frequencies.

As described above, according to the pilot beacon transmission apparatus in the WCDMA communication system according to the present invention, inter-frequency hard handoff is possible in an asynchronous WCDMA system.

In addition, it is possible to prevent the number of available frequencies of the base station from being reduced and to reduce the capacity of the base station. In addition, the error rate occurring in the compression mode can be reduced.

In addition, the delay time when the transition from the asynchronous network to the synchronous network can be reduced, and since the pilot beacon transmission apparatus does not have any interface with the base station, it can be installed at any position where the base station signal arrives. The base station capacity can be prevented from being reduced by eliminating unnecessary overhead channels that need to be created to generate a channel for handoff, and an increase in load of the power amplifier due to channel copy traffic can be prevented.

Although the above has been described with reference to a preferred embodiment of the present invention, those skilled in the art to which the present invention pertains without departing from the spirit and scope of the present invention as set forth in the claims below It will be appreciated that modifications and variations can be made.

Claims (9)

An apparatus for generating a pilot beacon signal in an asynchronous network (WCDMA) communication system, Receiving unit for receiving the main signal of the base station; A signal generator for extracting a common pilot channel (CPICH) signal from the main signal output from the receiver and generating a synthesized signal obtained by synthesizing a synchronization channel (SCH) signal and a previously generated broadcast channel (BCH) signal; A frequency converter configured to up-convert the synthesized signal generated by the signal generator to a frequency of the pilot beacon signal; A signal synthesizer configured to synthesize the up-converted composite signal and the main signal by the frequency converter to generate the pilot beacon signal; And An output amplifier for amplifying the pilot beacon signal and outputs through the antenna, If the pilot beacon signal is greater than or equal to a predetermined size, the mobile communication terminal hands off to the communication frequency of the base station corresponding to the broadcast channel signal, and the frequency of the pilot beacon signal is determined by the base station where the mobile communication terminal is located before the handoff. Pilot beacon transmission device that is a communication frequency. The method of claim 1, wherein the signal generator, A down converter for down converting the frequency of the main signal to an IF frequency; An A / D converter converting the down-converted main signal into a digital signal; A pilot beacon signal generator for extracting the common pilot channel signal from the digital signal using a scramble code and synthesizing the sync channel signal and the broadcast channel signal; And Pilot beacon transmission device including a D / A converter for converting the synthesized signal into an analog signal. The method of claim 2, wherein the pilot beacon signal generation unit, A correlator for retrieving the scramble code from the digital signal and extracting the common pilot channel signal using correlation; And And a channel synthesizer for synthesizing the sync channel signal, the broadcast channel signal, and the common pilot channel signal. The method of claim 2, And the scramble code is known in advance by the pilot beacon signal generator. The method of claim 1, And the sync channel signal is a signal of a sync channel extracted from the main signal or a signal of a separate sync channel previously generated by the signal generator. The method of claim 1, And the broadcast channel signal is a signal including system information of the base station or communication frequency information of the base station. An apparatus for generating a pilot beacon signal used for handoff from an asynchronous network communication system to a synchronous network (CDMA) communication system, the apparatus comprising: A receiving unit for receiving a main signal of a base station, wherein the base station follows the synchronous network communication system scheme; A signal generator configured to separately generate a common pilot channel signal, a sync channel signal, and a broadcast channel signal to generate a synthesized signal; A frequency converter configured to up-convert the synthesized signal generated by the signal generator to a frequency of the pilot beacon signal; A signal synthesizer configured to synthesize the up-converted composite signal and the main signal by the frequency converter to generate the pilot beacon signal; And An output amplifier for amplifying the pilot beacon signal and outputs through the antenna, If the pilot beacon signal is greater than or equal to a predetermined size, the mobile communication terminal hands off to the communication frequency of the base station corresponding to the broadcast channel signal, and the frequency of the pilot beacon signal is determined by the base station where the mobile communication terminal is located before the handoff. Pilot beacon transmission device that is a communication frequency. The apparatus of claim 7, wherein the broadcast channel signal is a signal including system information of the base station or communication frequency information of the base station. 8. The apparatus of claim 7, wherein the mobile communication terminal includes an asynchronous modem and a synchronous modem at the same time, and initializes and turns on the synchronous modem upon handoff to a communication frequency of the base station.

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