KR100784334B1 - Apparatus and method for handoff between neighboring two frequency allocation in cellular environments - Google Patents

Abstract

An apparatus and method for sharing and handing off two adjacent frequency bands in a broadband wireless system having a frequency reuse factor of N. When communicating with a first base station, when a signal from a second base station is received, Checking whether the frequency bands of the second base station are adjacent to each other; and if the frequency bands of the two base stations are adjacent to each other, measuring and comparing the strengths of the signals of the two base stations; ) Is less than or equal to the strength PSn of the second base station, requesting handoff to the first base station, and receiving partial resources simultaneously from the two base stations according to the handoff request, the two frequency bands. Including the process of receiving the signal simultaneously, the handset between the two base stations to use the adjacent frequency without disconnection of the call It is possible to perform a handoff to another base station and improve the call quality by reducing the ping pong phenomenon.

Band sliding, frequency sharing, handoff, adjacent frequency band

Description

Apparatus and method for handoff between two adjacent frequency bands in a cellular environment {APPARATUS AND METHOD FOR HANDOFF BETWEEN NEIGHBORING TWO FREQUENCY ALLOCATION IN CELLULAR ENVIRONMENTS}

1 is a diagram illustrating a procedure for performing a handoff according to the prior art;

2 illustrates a structure for performing a handoff according to the prior art;

3 is a diagram illustrating a structure for simultaneously receiving data from two base stations having adjacent frequency bands according to the present invention;

4 is a block diagram of a base station for allowing a terminal to simultaneously receive and handoff two adjacent frequency bands according to the present invention;

5 is a block diagram of a terminal for supporting band sliding according to the present invention;

6 is a diagram illustrating an operation procedure of a mobile communication terminal during handoff according to an embodiment of the present invention; and

7 is a diagram illustrating a handoff procedure in a broadband wireless system according to an embodiment of the present invention.

The present invention relates to an apparatus and a method for performing a handoff between two adjacent frequency bands in a cellular environment. In particular, two base stations are adjacent to a frequency band (Frequency Allocation: FA) in a cellular environment having a frequency reuse factor of N. ), An apparatus and a method for handoff between two adjacent base stations by sharing the two adjacent frequency bands.

The cellular system is a concept proposed to overcome the limitation of the service area and the limitations of the subscriber capacity. The cellular system is divided into several small areas, that is, two cells that are sufficiently far from each other, so that they are spatially frequencyd by using the same frequency band. Make it reusable. Therefore, it is a mobile communication method to secure sufficient subscribers by increasing the number of spatially distributed channels.

The handoff is a technique for continually maintaining the connected call when the terminal moves from a cell in which the terminal communicates with another cell to ensure mobility of the terminal in the cellular system.

1 illustrates a procedure for performing a handoff according to the prior art. The following description describes a mobile assisted handoff (MAHO) method in which a terminal measures a pilot signal strength of a source base station and neighboring base stations, and provides the measured result to the source base station to determine handoff. Here, the source base station refers to a base station with which the terminal is currently communicating, and the adjacent base station refers to a base station located around the source base station and transmitting a pilot signal to the terminal.

Referring to FIG. 1, first, in step 101, the terminal determines whether a unique pilot signal is received from the neighbor base station. If the pilot signal is received from the neighboring base station, the terminal proceeds to step 103 and measures the strength PS of the received pilot signal.

In step 105, the terminal compares the strength of the received pilot signal with a predetermined reference value. If the strength of the received pilot signal is smaller than the reference value (PS <reference value), the terminal returns to step 101 and checks whether a pilot signal is received from another neighboring base station.

If the strength of the received pilot signal is greater than or equal to a reference value (PS> reference value), the terminal proceeds to step 107 and generates a PSMM (Pilot Strength Measurement Message) message and transmits it to the source base station. Here, the PSMM message is a message indicating that the terminal needs to handoff to the source base station. In addition, the PSMM message includes a PN (Pseudo Noise) offset of an adjacent base station whose strength of the received pilot signal exceeds a reference value and the strength of the measured pilot signal. At this time, the source base station determines the handoff to the neighboring base station according to the result of comparing the received pilot signal strength and the reference value and the handoff request of the terminal and transmits the handoff decision message to the terminal.

Thereafter, upon receiving the handoff determination message, the terminal proceeds to step 109 to perform a handoff to the neighbor base station, and the terminal terminates the present algorithm.

2 illustrates a structure for performing a handoff according to the prior art. The following description shows the change of the frequency band used in the handoff of the terminal of FIG.

Referring to FIG. 2, the terminal 203 in communication with the base station 1 201 using the FA1 211 frequency band uses the same FA1 213 frequency band as the base station 1 201. Then, when the terminal 203 receives the pilot signal of the base station 2 (205), it performs the process shown in FIG. As a result of performing the process of FIG. 1, when performing a handoff to the base station 2 205, the terminal 203 uses the FA2 214 according to the frequency band FA2 215 used by the base station 2 205. Will be used.

As described above, when a handoff is performed between base stations using different frequency bands in a cellular environment having a frequency reuse factor of N, the terminal temporarily stops communication with a source base station and accesses a frequency band of an adjacent base station to perform communication. Break and make process. That is, since the call channel is disconnected and a call is attempted with a new call channel, there is a problem that the call is temporarily disconnected at the transition point between the cell.

Accordingly, an object of the present invention is to provide an apparatus and method for performing a handoff in the cellular environment without disconnection of a call.

Another object of the present invention is to provide an apparatus and method for eliminating disconnection of a call by sharing adjacent frequency bands of two base stations having adjacent frequency bands in a cellular environment having a frequency reuse factor of N.

It is still another object of the present invention to provide an apparatus and method for minimizing a ping-pong phenomenon by sharing adjacent frequency bands of two base stations having adjacent frequency bands in a cellular environment having a frequency reuse factor of N.

According to a first aspect of the present invention for achieving the above objects, a base station apparatus for handoff in a broadband wireless system, the handoff confirmation unit for confirming whether the terminal is to receive the two adjacent frequency bands at the same time, and When the terminal simultaneously receives two adjacent frequency bands, the terminal includes a subcarrier mapper for mapping control information to subcarriers of a predetermined interval so that the terminal can simultaneously receive two adjacent frequency bands.

According to a second aspect of the present invention, a terminal apparatus for handoff in a broadband wireless communication system is a hand that determines handoff according to the strength of a signal simultaneously received from a first base station and a second base station using adjacent frequency bands. A frequency controller for selecting a carrier for receiving signals of the two base stations simultaneously according to the decision of the handoff determining unit, a local oscillator for generating a carrier selected by the frequency controller, and a carrier generated in the local oscillator And a multiplier for generating a baseband signal by multiplying the received signal with the received signal.

According to a third aspect of the present invention, a method of operating a terminal for handoff in a broadband wireless system includes receiving two base stations when a signal from a second base station using an adjacent frequency band is received during communication with the first base station. Calculating a difference between signal strengths and comparing it with a reference value; requesting a handoff to simultaneously allocate resources from the first base station and the second base station when the difference between the two signal strengths is smaller than the reference value; And receiving signals of two frequency bands simultaneously from the two base stations according to the handoff request.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In describing the present invention, when it is determined that a detailed description of a related known function or configuration may unnecessarily obscure the subject matter of the present invention, the detailed description thereof will be omitted.

In the present invention, in the cellular environment having a frequency reuse factor of N, base stations having adjacent frequency bands (Frequency Allocation: hereinafter referred to as FA) share adjacent frequency bands of the base stations to minimize the ping-pong phenomenon of the terminal. An apparatus and method for performing a handoff without a disconnection phenomenon. Here, the ping-pong phenomenon refers to a phenomenon in which cells are moved without selecting one cell in an area in which signals of two cells or more cells can be simultaneously received.

In addition, in the following description, band sliding refers to a handoff method of sliding a frequency band of a terminal to simultaneously receive two frequency bands in order to simultaneously receive two adjacent frequency bands and simultaneously communicate with two base stations. do.

In the following description, for example, a handoff including a band sliding is determined and requested by the terminal, but a handoff including the band sliding may be determined by a source base station.

3 illustrates a structure for simultaneously receiving data from adjacent base stations having different frequency bands according to the present invention.

Referring to FIG. 3, data of two adjacent base transceiver systems (301, 303) using different FAs (FA1 311 and FA2 313) is used to shift a frequency band used by the terminal 305. The structure which receives simultaneously is shown.

When the base station 1 301 uses the FA1 311 and the base station 2 303 uses the FA2 313, the terminal 305 simultaneously receives data of the base stations 301 and 303. The frequency band 315 used to move is moved. That is, the terminal 305 moves the frequency band 315 to simultaneously receive the FA1 311 and the FA2 313 which are the frequency bands of the base stations 301 and 303.

As shown in FIG. 3, in order for the terminal 305 to successfully communicate with the two base stations 301 and 303, a frame structure transmitted from the base stations may receive a structure for receiving data using only the partial band. You must support. That is, even if the terminal 305 receives a portion of the band, it must support a frame structure that can include the preamble and control information of the frame.

Although not shown, in order to receive data using only some bands of the base stations 301 and 303 in the terminal 305, the control information is placed on subcarriers of adjacent portions of the two frequency bands. That is, since the terminal 305 receives data using some adjacent bands of the frequency bands of the two base stations 301 and 303, the base stations 301 and 303 may transmit the control information to some bands received by the terminal. It must include the minimum bandwidth of the preamble to distinguish the base station. At this time, in order to distinguish the base station, the preamble is repeatedly mapped to the entire frequency band of the base station to form a frame.

4 is a block diagram of a base station for allowing a terminal to simultaneously receive and handoff two adjacent frequency bands according to the present invention.

As shown in FIG. 4, the base station includes a band sliding checker 400, an encoder 401, a modulator 403, a subcarrier mapper 405, a subcarrier mapping controller 407, and an inverse fast fourier transform (IFFT). It includes a calculator 409, a parallel / series converter 411, a digital / analog converter 413, a multiplier 415, and a local oscillator 417.

First, the encoder 401 channel-codes and outputs information data provided from a medium access control (MAC) layer at a corresponding code rate. The modulator 403 modulates the data provided from the encoder 401 in a corresponding modulation scheme and outputs the modulated data. Here, the modulation scheme may be Binary Phase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 16 Quadrature Amplitude Modulation (16QAM), or 64QAM.

The subcarrier mapper 405 maps the data provided from the modulator 403 to subcarrier mapping under the control of the subcarrier mapping controller 407 and outputs the subcarrier mapping. When the partial resource allocation request message is received from the mobile switching center, the band sliding checker 400 outputs a band sliding control signal to the subcarrier mapping controller 407 so that the terminal can perform band sliding. When the subcarrier mapping controller 407 receives the band sliding control signal from the band sliding checker 400, the subcarrier mapping controller 407 receives the control information so that the terminal can simultaneously perform the band sliding by receiving the signals of the base station and the other base station. A control signal is generated for mapping a frequency band to an adjacent predetermined subcarrier. In this case, the control signal is output to the subcarrier mapper 405.

The IFFT operator 409 converts the data provided from the subcarrier mapper 405 into inverse fast Fourier transform and converts data in the frequency domain into time sample data. The parallel / serial converter 411 converts the parallel data provided from the IFFT operator 409 into serial data and outputs the serial data. The digital / analog converter 413 converts the digital signal provided from the parallel / serial converter 411 into an analog signal, and the multiplier 415 converts the analog baseband signal provided from the digital / analog converter 413. The local oscillator 417 converts the signal into a high frequency band signal so as to be multiplied by the signal and outputs the signal through an antenna.

5 is a block diagram of a terminal receiving data simultaneously in two adjacent frequency bands according to the present invention.

Referring to FIG. 5, the terminal includes a handoff determiner 500, a frequency controller 501, a local oscillator 503, a multiplier 505, an analog / digital converter 507, a serial / parallel converter 509. And a fast fourier transform (FFT) operator 511, a subcarrier demapper 513, a demodulator 515, and a decoder 517.

First, when a signal is simultaneously received from base stations using two adjacent frequency bands, the handoff determiner 500 determines whether to perform the sliding of the band using the received signal. That is, when the absolute value of the difference between the two received signals is compared with a preset reference value, when the absolute value of the difference between the two signals is smaller than the reference value (| PSs-PSn | <reference value), the band sliding is performed. Decide If the absolute value of the difference between the two signals is greater than or equal to the reference value (| PSs-PSn | ≥ reference value), the handoff determiner 500 moves the handoff to the base station having the greater signal strength among the two signals. Decide what to turn off. Here, the handoff determination unit 500 determines the handoff or band sliding and requests handoff and band sliding to the mobile switching center through the source base station. Then, the handoff and the band sliding are performed according to the acceptance message of the handoff or the band sliding from the mobile switching center.

The frequency controller 501 generates a control signal for selecting a frequency band to be used by the terminal. That is, since the terminal uses a constant bandwidth, the terminal generates a control signal for selecting the center frequency of the terminal, that is, the carrier wave. Furthermore, when a band sliding execution signal is received from the handoff determining unit 500 according to the present invention, as shown in FIG. 3, a carrier for selecting a frequency band for simultaneously receiving data from the two base stations is selected. Generate a control signal. The local oscillator 503 generates a center frequency of the terminal, that is, a carrier wave under the control of the frequency controller 501. Here, the carrier is selected to include a preamble of a minimum bandwidth for distinguishing each control information and the base station in the two adjacent frequency bands.

The multiplier 505 multiplies the signal received through the antenna and the carrier wave provided by the local oscillator 503 to generate a frequency band for receiving the signals of the two base stations simultaneously. The analog / digital converter 507 receives the output signal of the multiplier 505 and converts the analog signal into a digital signal and outputs the digital signal. Here, the digital signal is time sample data.

The serial / parallel converter 509 converts the serial data provided from the analog / digital converter 507 into parallel data for FFT conversion and outputs the parallel data. The FFT converter 511 receives parallel data from the serial / parallel converter 509 and performs fast Fourier transform to output data in a frequency domain.

The subcarrier demapper 513 extracts subcarrier values carrying actual data from the output signal from the FFT operator 511, that is, from the subcarrier values. According to the present invention, the actual data of each frequency band is extracted using control information carried on subcarriers of a predetermined section of the two adjacent frequency bands.

The demodulator 515 demodulates and outputs the data provided from the subcarrier demapper 513 in a corresponding demodulation scheme, and the decoder 517 performs channel decoding on the data demodulated by the demodulator 515 at a corresponding code rate. Restore the data.

6 illustrates an operation procedure of a mobile communication terminal for handoff according to an embodiment of the present invention. In the following description, it is assumed that the frequency bands of the source base station and the adjacent base station use adjacent frequency bands. Here, the source base station refers to a base station in communication with the terminal, and the neighboring base station refers to a base station located around the source base station and transmitting a pilot signal to the terminal.

Referring to FIG. 6, the terminal first checks whether a pilot signal is received from the neighboring base station during communication with the source base station in step 601. When the pilot signal of the neighboring base station is received, the terminal proceeds to step 603 to measure the strength PSs of the pilot signal of the source base station and the strength PSn of the pilot signal of the neighboring base station.

In step 605, the terminal calculates a difference between the PSs and PSn so that the absolute value of the difference between the PSs and PSn is greater than or equal to a reference value (│PSs − PSn ≧ a reference value). In step 601, it is checked whether pilot signals are received from other neighbor base stations.

If the PSs is smaller than the absolute value of the difference of PSn (│PSs-PSn | <reference value), the terminal proceeds to step 607 and transmits a band sliding request message for handoff to the source base station. .

After transmitting the band sliding request message for the handoff, the terminal proceeds to step 609 to determine whether resources are simultaneously allocated from the source base station and the neighboring base station. In this case, resource allocation from the two base stations (source base station and neighboring base station) is performed by the source base station receiving the band sliding request message for the handoff by handoff to a mobile switching center (hereinafter referred to as MSC). Request band sliding for Upon receiving the band sliding request, since the frequency bands of the two base stations are adjacent to each other, the MSC requests the two base stations to allocate partial resources to the terminal in order to perform band sliding. Thereafter, the two base stations receiving the partial resource allocation request allocate the partial resources to the terminal. In addition, the band sliding is a method for partially sharing the frequency bands of the neighboring base station and the source base station.

If resources are not simultaneously allocated from the two base stations, the terminal returns to step 601 and checks whether pilot signals are received from other neighbor base stations.

On the other hand, when the terminal performs a band sliding and is allocated resources simultaneously from the two base stations, the terminal proceeds to step 611 to share the resources of the source base station and the neighboring base station to communicate with the two base stations at the same time.

In step 613, the terminal measures the strength of pilot signals of the two base stations.

After measuring the strengths of the pilot signals of the two base stations, the terminal proceeds to step 615 to compare the strengths (PSs, PSn) of the pilot signals of the two base stations, the PSs is greater than PSn, the PSs and PSn If the absolute value of the difference is greater than or equal to the reference value ((PSs> PSn) & (│PSs-PSn│> reference value)), the terminal proceeds to step 617 to move the center frequency to the frequency band of the source base station. The resource of the source base station is allocated to communicate with the source base station. Hereinafter, the terminal ends the present algorithm.

If the condition of step 615 is not satisfied, the terminal proceeds to step 619 in which the PSs are smaller than PSn, and whether the absolute value of the difference between the PSs and PSn is greater than or equal to the reference value ((PSs <PSn). ) & (│PSs-PSn│ ≥ reference value)). If the condition of step 619 is satisfied, the terminal proceeds to step 621 to move the center frequency to the frequency band of the neighboring base station to receive the resources of the neighboring base station to communicate with the neighboring base station. Hereinafter, the terminal ends the present algorithm.

On the other hand, if the condition of step 619 is not satisfied, that is, the absolute value of the difference between the PSs and PSn is smaller than the reference value (│PSs-PSn | <reference value), the terminal proceeds to step 623 and the two base stations It communicates with the source base station and the adjacent base station by sharing the frequency of the signal. Hereinafter, the terminal ends the present algorithm.

7 illustrates a handoff procedure in a cellular system according to an embodiment of the present invention. In the following description, it is assumed that the frequency bands of the source base station and the adjacent base station use adjacent frequency bands. Here, the source base station refers to a base station communicating with the terminal, and the neighboring base station refers to base stations located around the source base station and transmitting pilot signals to the terminal.

Referring to FIG. 7, when a pilot signal of a neighboring base station 720 is received in a situation in which the terminal 700 communicates with the source base station 710 (step 701), the two base stations (the source base station 710 and the neighboring base station) are received. The difference of the pilot signal magnitude of 720 is calculated and compared with a reference value. If the absolute value of the difference between the two signal strengths is smaller than the reference value (| RSs-RSn | <reference value), the terminal 700 includes a measurement result of the pilot signal magnitudes of the two base stations 710 and 720. A band sliding request message is transmitted to the source base station 710 (step 703).

The source base station 710 receiving the band sliding request message from the terminal 700 performs a band sliding for handoff to a mobile switching center (hereinafter referred to as MSC) 730. Request (step 705). The MSC 730 uses the two base stations 710 and 720 when the band sliding request message is received from the source base station 710. The frequency sliding is determined by checking the frequency (step 707). In this case, the band sliding scheme of the MSC 730 is determined to perform band sliding when the two base stations 710 and 720 have adjacent frequency bands. If the two base stations 710 and 720 do not have adjacent frequency bands, it is determined to perform hard handoff.

If the MSC 730 selects the band sliding, the MSC 730 requests the two base stations 710 and 720 to allocate the partial resource to the terminal 700 (step 709). Thereafter, when the two base stations 710 and 720 receive a resource allocation request from the MSC 730, the two base stations allocate resources to the terminal 700 according to the request (step 711).

Thereafter, the terminal 700 performs the band sliding as shown in FIG. 3 and simultaneously allocates resources from the two base stations 710 and 720 to simultaneously communicate with the two base stations 710 and 720. (Step 713).

Thereafter, the terminal 700 measures the strengths of the pilot signals of the two base stations 710 and 720 and provides the measurement result to the source base station 710 (step 715). In other words, the terminal 700 compares the PSs of the pilot signal of the source base station with the PSs of the pilot signal of the neighboring base station, and the PSs are smaller than the PSn, and the difference between the PSs and the PSn. If the absolute value of is greater than or equal to a predetermined reference value ((PSs < PSn) & (│PSs-PSn > &gt; reference value)), the source base station 710 is requested to handoff to the neighboring base station 720. . Here, although not shown, the terminal 700 is the measurement result, if the PSs is greater than PSn, the absolute value of the difference between the PSs and PSn is greater than or equal to the reference value ((PSs> PSn) & (│ PSs-PSn | reference value)), requesting to handoff to the source base station 710. Further, when the measurement result is smaller than the absolute value of the difference between the PSs and PSn (| PSs-PSn | <reference value), it is requested to communicate by sharing the frequency of the two base stations. That is, it requests to maintain the band sliding.

Thereafter, when the source base station 710 receives the handoff request from the terminal 700, the source base station 710 requests the MSC 730 to handoff the terminal 700 (step 717).

Upon receiving the handoff request from the source base station 710, the MSC 730 indicates to perform handoff to the two base stations 710 and 720 (step 719). The neighboring base station 720 receiving the handoff indication of the MSC 730 recognizes that the terminal 700 is to be handed off, and the source base station 710 sends the neighboring base station 720 to the terminal 700. In step 721, handoff is indicated.

Thereafter, the terminal 700 performs handoff to the neighbor base station 720 to communicate with the neighbor base station 720.

The above-described embodiment has been described with an example of determining the handoff or the band sliding in the terminal and requesting the mobile switching center. In another embodiment, the terminal transmits a result of measuring the strength of the signal from the source base station and the adjacent base station to the source base station. The source base station receiving the strength measurement results of the two base stations may determine a handoff or band sliding of the terminal and request the mobile switching center.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications are possible without departing from the scope of the present invention. Therefore, the scope of the present invention should not be limited to the described embodiments, but should be determined not only by the scope of the following claims, but also by the equivalents of the claims.

As described above, in a cellular environment with a frequency reuse factor of N, another base station that shares two adjacent frequencies of two base stations with adjacent frequency bands and uses adjacent frequencies without disconnection of the call during handoff between the two base stations. Handoff can be performed and the call quality can be improved by reducing the ping pong phenomenon. In addition, when receiving the same data from two base stations at the same time, there is an advantage that the diversity effect can be obtained.

Claims (21)

An apparatus for controlling handoff in a base station of a broadband wireless system, A handoff confirmation unit which checks whether the terminal receives the signals of the first base station and the second base station using the adjacent frequency band by handoff at the same time; When the terminal simultaneously receives signals of two adjacent frequency bands, the terminal includes a subcarrier mapper that maps control information to subcarriers of an adjacent portion of the two frequency bands so that the terminal can simultaneously receive signals of two adjacent frequency bands. Device characterized in that. The method of claim 1, An encoder for receiving information data from a medium access control (MAC) layer and encoding at a predetermined code rate, And a modulator for modulating the data encoded by the encoder by a predetermined modulation scheme and providing the modulated data to the subcarrier mapper. The method of claim 1, And the handoff confirming unit checks whether the terminal simultaneously receives signals of two adjacent frequency bands through a partial resource allocation request message received from a mobile telephone exchange. The method of claim 1, The control information, characterized in that it comprises a preamble and channel assignment information. The method of claim 1, And the subcarrier mapper repeatedly maps the preamble to the entire frequency band of the base station. The method of claim 1, And the subcarrier mapper maps channel allocation information to subcarriers of a portion of a portion of the band where the two frequency bands are adjacent to each other. The method of claim 1, An IFFT operator for performing inverse fast Fourier transform (IFFT) on the data mapped to the subcarrier into a signal in a time domain; A digital / analog converter for converting the output signal of the IFFT operator into an analog signal; And converting the baseband analog output signal of the digital-to-analog converter into a radio frequency (RF) signal and outputting the RF signal to the terminal through an antenna. A handoff device in a terminal of a broadband wireless communication system, A handoff determining unit which determines a handoff according to the strength of a signal simultaneously received from a first base station and a second base station using adjacent frequency bands; A frequency controller for selecting a carrier for simultaneously receiving signals of the two base stations according to the determination of the handoff decision unit; A local oscillator for generating a carrier selected by the frequency controller; And a multiplier for generating a baseband signal by multiplying a carrier signal generated by the local oscillator and a received signal. The method of claim 8, The handoff determination unit, And when the absolute value of the difference between the signal strengths received from the two base stations is smaller than a preset reference value, determine that the signals of the two base stations are simultaneously received. The method of claim 8, And the frequency controller selects a carrier to include channel allocation information of each channel in the two adjacent frequency bands used by the two base stations and a minimum bandwidth preamble for distinguishing the two base stations. The method of claim 8, An analog / digital converter for converting the baseband signal output from the multiplier into a digital signal; An FFT operator for fast Fourier transform (FFT) of the digital signal provided from the analog / digital converter; And a subcarrier demapping unit for extracting actual data from the output signal of the FFT operator using control information in which two frequencies used by the two base stations are mapped to subcarriers of an adjacent portion. A method for handoff at a terminal of a broadband wireless system, When a signal of a second base station using an adjacent frequency band is received during communication with the first base station, calculating a difference between received signal strengths of the two base stations and comparing the signal with a reference value; Requesting handoff to simultaneously allocate resources from the first base station and the second base station when the difference between the two signal strengths is smaller than a reference value; And simultaneously receiving signals of a frequency band used by the first base station and a frequency band used by the second base station according to the handoff request. The method of claim 12, When simultaneously receiving signals of two frequency bands used by the first base station and the second base station, Measuring and comparing the strengths of the signals of the two frequency bands; Requesting handoff to the second base station if the strength of the first base station signal is less than the strength of the second base station signal and the absolute value of the difference between the two signal strengths is greater than or equal to the reference value. It further comprises a method. The method of claim 13, Requesting handoff to the first base station when the strength of the first base station signal is greater than the strength of the second base station signal and the absolute value of the difference between the two signal strengths is greater than or equal to the reference value. Method comprising a. The method of claim 13, And if the absolute value of the difference between the two signal strengths is less than the reference value, maintaining the simultaneous reception of the signals of the two frequency bands. A method of operating a broadband wireless system for handoff by sharing two adjacent frequency bands, When the terminal receives a signal from a second base station during communication with the first base station, requesting a handoff to the mobile switching center through the first base station by comparing the signal strengths of the two base stations; When the handoff request is received, checking the frequency bands of the two base stations and requesting allocation of partial resources from the two base stations to the terminal when the frequency bands of the two base stations are adjacent; , The two base stations allocate resources to the terminal according to a resource allocation request of the mobile switching center; And when the terminal is simultaneously allocated resources from the two base stations, sharing the frequency bands of the two base stations. The method of claim 16, The process of requesting a handoff from the terminal, Calculating a difference between signal strengths of the two base stations and comparing them with a reference value; Requesting a handoff to simultaneously allocate resources from the first base station and the second base station to the mobile switching center via the first base station when the difference between the signal strengths of the two base stations is smaller than the reference value. Characterized in that the method. The method of claim 16, And the mobile switching center instructing the two base stations to perform hard handoff when the frequency used by the two base stations is not adjacent to each other. The method of claim 16, When the terminal shares the frequency bands of the two base stations, comparing and measuring the strengths of the signals of the two base stations; The terminal further comprises the step of maintaining receiving the signals of the two base stations at the same time, if the difference between the two base station signal strength is less than the reference value. The method of claim 19, The terminal further includes the step of requesting handoff to the first base station when the strength of the first base station signal is greater than the strength of the second base station signal and the difference between the two signal strengths is greater than or equal to the reference value. Characterized in that. The method of claim 19, The terminal further includes the step of requesting handoff to the second base station when the strength of the second base station signal is greater than the strength of the first base station signal and is greater than or equal to the next reference value of the two signal strengths. How to characterized.

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