KR20080085323A - Method and system for transmitting data in a communication system - Google Patents

Abstract

A method and a system for transmitting data in a communication system are provided to increase the capacity of a signaling link by measuring the channel state between a BS(Base Station) and an RS(Relay Station) and the channel state between the RS and an MS(Mobile Station) and selecting a signal transport scheme according to the measured channel states. An RS receives data through an available frequency band, and measures a channel state at the available frequency band(501). The RS confirms the measured channel state(503). In case the measured channel state is bad, the RS selects the first transport scheme(505). If the measured channel state is good, the RS calculates an eigenvalue or a mutual information value(509). If the calculated value is larger than a threshold(511), the RS selects the second transport scheme(513). Using the selected transport scheme, the RS transmits data to a BS or an MS which provides a relay path(507).

Description

METHOD AND SYSTEM FOR TRANSMITTING DATA IN A COMMUNICATION SYSTEM}

1 is a diagram showing the structure of a CR communication system according to an embodiment of the present invention.

2 is a diagram schematically illustrating an RS structure for measuring a channel state in a communication system according to an exemplary embodiment of the present invention.

3 is a diagram schematically illustrating another structure of an RS for measuring a channel state in a communication system according to an exemplary embodiment of the present invention.

4 is a diagram illustrating an apparatus for transmitting and receiving an RS in a communication system according to an embodiment of the present invention.

5 is a diagram illustrating a process for an RS to select a transmission scheme in a communication system according to an exemplary embodiment of the present invention.

The present invention relates to a communication system, and more particularly, to a data transmission method and system in a wireless recognition (CR) communication system.

In the next generation communication system, active researches are being conducted to provide users with services having high quality of service (QoS: Quality of Service, hereinafter referred to as 'QoS'). In particular, in the current generation communication system, a wireless local area network (WLAN) system and a wireless metropolitan area network (WMAN) will be referred to as "WMAN". Research is being actively conducted to support high-speed services in a form of guaranteeing mobility and QoS in a broadband wireless access (BWA) communication system such as a system). .

The BWA communication system efficiently uses the limited resources because a plurality of cells constituting the communication system divide a limited resource, that is, a frequency resource, a code resource, a time slot resource, and the like. Should be used. In particular, the demand for wireless resources is increasing day by day due to the rapid development of wireless communication systems and the emergence of various services. However, due to the allocation of almost all frequency bands that are currently commercially available, there is a very shortage of frequency resources for new wireless platforms. Given the current frequency usage, few GHz bands, especially low frequency bands, have little room for use. In order to solve such a frequency shortage problem, a CR communication system based on the CR method has been proposed. The CR communication system detects a frequency band to which a frequency is allocated but is not actually used, and efficiently shares and uses the frequency band. This CR communication system is a communication system that can be used in conjunction with the next generation communication system currently being studied. A representative communication system of such a CR communication system is an IEEE 802.22 WRAN (Wireless Regional Area Networks) system. The IEEE 802.22 WRAN system adopts CR technology in a TV frequency band, and intends to use an unused TV band for data transmission and reception. will be.

However, in the CR communication system, even when the secondary system secures and uses the frequency resource, if the primary system intends to use the frequency band used by the CR communication system, the secondary system Should empty the frequency band immediately. Here, the main system means a communication system having a right to use a legal frequency band.

In addition, the sub-system measures the strength of the received signal in the frequency band selected by the sub-system itself to select and use a frequency band not used by the main system as described above. That is, the secondary system measures the strength of the received signal in the frequency band to detect a frequency band in which the frequency is assigned to the primary system but is not actually used. Then, the sub system detects that the main system is not used in the predetermined frequency band through the measured strength of the received signal, and selects and uses the detected frequency band. In this case, the signal received by the sub system may include not only a transmission / reception signal of the main system but also an interference signal, for example, a transmission / reception signal of another sub system. If the received signal has a predetermined level or more, another signal may exist. That is, it is determined that the other system uses a predetermined frequency band in which the signal strength is measured for use by the sub system.

On the other hand, the channel state of the frequency band is variable while the frequency system sensed by the sub system is selected and used, that is, while data is transmitted through the frequency band. When the channel state of the frequency band selected and used by the sub-system is changed in this way, a method of transmitting data corresponding to the channel state is required. In particular, in the CR communication system, when a secondary system uses a multi-hop relay scheme through a relay station (RS), a channel state of an available frequency band is used. There is a need for a method of transmitting data correspondingly.

Accordingly, the present invention provides a method and system for transmitting data in a communication system.

The present invention also provides a data transmission method and system in a radio-cognitive communication system employing a multi-hop relay scheme.

A method of the present invention for achieving the above objects comprises a first system having a usage right for a first frequency band and a second system having no use right for the first frequency band. In the transmission method, the step of the relay station of the second system to measure the channel state of the frequency band usable in the first frequency band, the step of selecting a transmission method in accordance with the measured channel state, and the selected Transmitting data using a transmission method.

A system of the present invention for achieving the above objects comprises a first system having usage rights for a first frequency band and a second system having no usage rights for the first frequency band. In the transmission system, the relay station of the second system measures the channel state of the frequency band usable in the first frequency band, selects a transmission method according to the measured channel state, and uses the selected transmission method. And transmitting data.

Hereinafter, the operation principle of the preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. In addition, 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. Terms to be described later are terms defined in consideration of functions in the present invention, and may be changed according to intentions or customs of users or operators. Therefore, the definition should be made based on the contents throughout the specification.

The present invention proposes a data transmission method and system in a communication system. Here, in the embodiment of the present invention to be described later, IEEE 802.16 communication system which is an Institute of Electrical and Electronics Engineers (IEEE) 802.22 communication system and a broadband wireless access (BWA) communication system. Orthogonal Frequency Division Multiplexing (OFDM) or Orthogonal Frequency Division Multiple Access (OFDMA) Although a Cognitive Radio (CR) communication system will be described as an example, the data transmission method and system proposed by the present invention can be applied to other communication systems.

The present invention also provides a first system having a right to use a frequency band, that is, a second system that does not have a right to use the predetermined frequency band when the primary system does not use the predetermined frequency band. That is, the present invention proposes a method and system for allocating the predetermined frequency band so that a secondary system can use the predetermined frequency band, and transmitting the data in the allocated frequency band by the secondary system.

In addition, the present invention proposes a data transmission method and system in a CR communication system using a multi-hop relay scheme. In an embodiment of the present invention to be described later, the secondary system is a base station (BS: base station, referred to as "BS") and the mobile terminal (MS) through a relay station (RS: referred to as "RS") : In a CR communication system that provides a multi-hop relay path between mobile stations, when a main system having a use right for a predetermined frequency band does not use the predetermined frequency band, it does not have a use right for the predetermined frequency band. The sub system allocates a frequency band to be usable, measures the channel state of the allocated frequency band, and transmits data through a predetermined transmission method corresponding to the measured channel state.

In the CR communication system according to an embodiment of the present invention, which will be described later, a sub system may use a first transmission method such as decoding and forwarding (DF: Decode and Forward, DF) when the measured channel state is poor. The data is transmitted using the method, and if the measured channel state is good, the parameter is calculated according to the measured channel state, and the parameter is compared with a threshold set according to the communication environment and system. According to the comparison result, data is transmitted using the first transmission method, for example, the DF method, or a second transmission method, for example, an amplify and forward (AF) method. Transmit data. In this case, the parameter may be an eigen value or a mutual information value.

More specifically, as a result of the comparison between the parameter and the threshold value, if the parameter is larger than the threshold value, that is, if the eigenvalue or mutual information value is larger than the threshold value, it is determined that the measured channel state is good. Data is transmitted using two transmission methods. On the other hand, as a result of comparing the parameter with the threshold value, if the parameter is smaller than the threshold value, that is, if the eigenvalue or mutual information value is smaller than the threshold value, the measured channel state is determined to be poor and the first transmission scheme is determined. Send data using.

The DF scheme, which is the first transmission scheme, refers to a scheme in which an RS providing a relay path between the BS and the MS decodes and demodulates a signal received from the BS or the MS, and then signs and modulates the signal. More specifically, when the channel state of the available frequency band of the sub-system, that is, the channel state of the relay path between the BS and the MS is poor, the code and modulation scheme used by the BS or the MS when transmitting data to the RS, Means a method of transmitting data using different codes and modulation schemes. That is, when the data is received, the DF method performs decoding and demodulation corresponding to the code and modulation method applied to the received data, and then uses a code and modulation method different from the code and modulation method applied to the received data. The data is transmitted by applying the decoded and demodulated data.

The AF method, which is the second transmission method, refers to a method in which an RS providing a relay path between the BS and the MS amplifies and transmits the strength of a signal received from the BS or the MS. More specifically, when the channel state of the relay path between the BS and the MS is good, the code and modulation scheme used by the BS or the MS when transmitting data to the RS are the same, and the data is transmitted by amplifying the strength of the transmission signal. Means the way. That is, in the AF method, when data is received, the data is amplified by the transmission power of the received data.

Next, the CR communication system in the communication system according to the embodiment of the present invention will be described with reference to FIG. 1.

1 is a diagram illustrating a structure of a CR communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 1, the CR communication system includes cell 1 110, which is a primary system, and cell 2 150, which is a secondary system cell, and has a right to use a predetermined resource, that is, a frequency band, in cell 1 110. That is, it includes a main system having a usage right, and a sub-system that does not have a right to use the frequency band when the main system does not use the frequency band in cell 2 (150). do. The primary system includes BS1 112, which is a primary BS, and MS1 114, which is a primary MS that receives communication service from the BS1 112, and the secondary system is a secondary BS. BS2 152, which is a secondary BS, and an MS2 154, which is a secondary MS receiving communication service from the BS2 152, and an RS providing a multi-hop relay path between the BS2 152 and MS2 154. 156).

At this time, the RS 156 of the secondary system searches for a predetermined frequency band that is not used by the primary system, that is, an available frequency band of the secondary system, in a frequency band in which the primary system has a usage right. Accordingly, the sub system transmits and receives data using the available frequency band of the sub system searched in the frequency band to which the main system has authority to use, that is, BS2 152 and RS 156 of the sub system. , And MS2 154 transmits and receives data using the available frequency band.

At this time, when the secondary system transmits and receives data using the available frequency band, BS2 152, RS 156, and MS2 154 of the secondary system can determine the channel state of the available frequency band. Measure and transmit data using the first transmission method or the second transmission method according to the measured channel state as described above, and hereinafter, a relay path between the BS and the MS of the secondary system for convenience of description. A case in which an RS providing a WB transmits data by measuring a state of a channel and transmitting data using one of the above-described transmission schemes corresponding to the measured channel state will be described.

 Then, when transmitting and receiving data of the sub system, the RS 156 of the sub system measures the channel state of the usable frequency band.

In other words, when the RS 156 of the secondary system receives data from BS2 152 or MS2 154 of the secondary system through the available frequency band, it detects a spectrum or energy in the available frequency band. Measure the channel state.

As a result of measuring the channel state, if the channel state is poor, the RS 156 transmits data to the BS2 152 or the MS2 154 providing the relay path through the first transmission method, that is, the DF method. do. In other words, as described above, when the RS 156 of the secondary system receives data from the BS2 152 or the MS2 154, a code and modulation scheme applied to the received data, that is, the BS2 152 or After the MS2 154 performs decoding and demodulation corresponding to the code and modulation scheme applied at the time of data transmission, the data obtained by performing decoding and demodulation on a code and modulation scheme different from the code and modulation scheme applied to the received data is performed. In this case, the data received from the BS2 152 or the MS2 154 is transmitted to the MS or BS.

On the other hand, when the channel state is good, the RS 156 calculates a parameter such as an Eigen value or Mutual Information value according to the measured channel state. Then, the first transmission method or the second transmission method is selected according to the calculated parameter, and the data is transmitted to the BS2 152 or the MS2 154 providing a relay path using the selected transmission method. .

More specifically, as a result of the comparison between the parameter and the threshold value, if the parameter is larger than the threshold value, that is, if the eigenvalue or mutual information value is larger than the threshold value, it is determined that the measured channel state is good. Data is transmitted using two transmission methods. In other words, as described above, when the RS 156 of the secondary system receives data from the BS2 152 or the MS2 154, the RS 156 amplifies the transmission power of the received data to transmit data, that is, the BS or The data received from the MS is transmitted to the MS or BS.

On the other hand, as a result of the comparison between the parameter and the threshold value, if the parameter is less than the threshold value, that is, if the eigen value or mutual information value is less than the threshold value is determined that the measured channel state is poor and the first transmission scheme Send data using. Next, a case of measuring a channel state of a frequency band usable by an RS in a communication system according to an exemplary embodiment of the present invention will be described with reference to FIGS. 2 and 3.

2 is a diagram schematically illustrating an RS structure for measuring a channel state in a communication system according to an exemplary embodiment of the present invention. 2 is a diagram illustrating a case in which an RS senses energy in the usable frequency band and measures a channel state, and FIG. 3 to be described later is a diagram in which RS senses a spectrum in the usable frequency band and a channel state. Is a diagram illustrating a case of measuring.

Referring to FIG. 2, the RS is an RF processor 201 for RF processing a signal received from a BS or an MS providing a relay path through an available frequency band, and energy of a signal output from the RF processor 201. And an energy sensor 203 for detecting the channel state and calculating a parameter corresponding to the measured channel state.

The RS inputs a signal received from a BS or an MS providing a relay path through an available frequency band to the RF processor 201 for RF processing, and transmits the RF processed signal to the energy sensor 203. The energy sensor 203 receiving the signal detects energy from the received signal to measure a channel state, calculates a parameter corresponding to the measured channel state, and transmits the parameter to the channel parameter calculator 205.

Next, another structure of an RS for specifying a channel state in a communication system according to an exemplary embodiment of the present invention will be described with reference to FIG. 3.

3 is a diagram schematically illustrating another structure of an RS for measuring a channel state in a communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the RS performs a high-speed RF processor 301 for RF processing a signal received from a BS or an MS providing a relay path through an available frequency band, and a signal output from the RF processor 301. An FFT device 303 for performing a Fourier Transform (FFT) process, a spectrum sensor 305 for detecting a spectrum of the FFT-processed signal and measuring channel conditions; And a channel parameter calculator 307 for calculating a parameter corresponding to the measured channel state.

The RS inputs a signal received from a BS or MS providing a relay path through an available frequency band to the RF processor 301 for RF processing, and transmits the RF processed signal to the FFT device 303. The FFT unit 303 performs FFT processing on the signal received from the RF processor, and then transfers the signal to the spectrum sensor 305. The spectrum sensor 305 receiving the FFT-processed signal detects a spectrum from the received signal to measure a channel state, calculates a parameter corresponding to the measured channel state, and transmits the parameter to the channel parameter calculator 307. do.

Next, a transmission / reception apparatus of an RS in a communication system according to an embodiment of the present invention will be described with reference to FIG. 4.

4 is a diagram illustrating an apparatus for transmitting and receiving an RS in a communication system according to an exemplary embodiment of the present invention.

Referring to FIG. 4, the RS includes a transmitter and a receiver.

First, the receiver includes a radio frequency (RF) processor 401 and an analog / digital converter (ADC) 403. The transmission mode processor 405, the header extractor 407, the symbol copier 409, the switches 411, 413, 421, and the cyclic prefix remover 415. A Fast Fourier Transform (FFT) group 417, a decoder and demodulator 419, an energy sensor 445, a spectrum sensor 447, A channel parameter calculator 423 and a transmission mode selector 425.

The RF processor 401 converts an RF signal received through the multiple antennas from the BS or the MS into a baseband signal, outputs the baseband signal, and transmits the signal to the ADC 403. The ADC 403 converts the baseband analog signal provided from the RF processor 401 into a digital signal and transmits the digital signal to the transmission mode processor 405.

The transmission mode processor 405 is configured to transmit from the ADC 403 according to a transmission mode transmitted from the BS or the MS, for example, a transmission mode such as diversity, multiplexing, beam forming, or the like. The received digital signal is processed and transmitted to the header extractor 407 and the symbol copier 409.

The header extractor 407 extracts a header from the signal received from the transmission mode processor 405 and transmits the header to the first switch 411. In addition, the symbol copier 409 copies the entire symbol of the signal processed by the transmission mode processor 405 and transmits it to the first switch 411.

The first switch 411 selectively transfers the signals of the header extractor 407 and the symbol copier 409 under the control of the transmission mode selector 425. That is, the output signal of the header extractor 407 is transmitted to the CP remover 415 to select a transmission method for the received signal. Next, when the transmission scheme of the received signal is selected, the entire received symbol copied by the symbol copier 409 is transmitted to the second switch 413.

The second switch 413 transmits a signal provided from the symbol copier 409 to the CP remover 415 or the power amplifier 427 according to the transmission scheme selected by the transmission scheme selector 425. That is, when the determined transmission scheme is the second transmission scheme, the signal provided from the symbol copier 409 is transmitted to the power amplifier 427. On the other hand, when the determined transmission scheme is the first transmission scheme, the signal received from the symbol copier 409 is transmitted to the CP remover 415.

The CP remover 415 is a protection included in the output signal of the header extractor 407 provided from the first switch 411 or the output signal of the symbol copier 409 provided from the second switch 413. The interval (Cyclic Prefix) is removed and transmitted to the FFT unit 417.

The FFT unit 417 performs a fast Fourier transform on the time domain signal received from the CP remover 415, converts the signal in the frequency domain into a signal in the frequency domain, and outputs the signal to the decoder in the frequency domain.

The decoder and demodulator 419 decodes and demodulates a signal in the frequency domain provided from the FFT 417 according to a decoding and demodulation scheme and transmits the demodulated signal to the third switch 421.

The third switch 421 is configured to convert the signal decoded and demodulated by the decoder and demodulator 419 under the control of the transmission mode selector 425 into the code and modulator 437 of the channel parameter calculator 423 or the transmitter. To send). That is, when the transmission scheme is determined using the decoded and demodulated signal, the transmission is transmitted to the channel parameter calculator 423. In addition, when the decoded and demodulated signal is transmitted to the BS or the MS according to the determined transmission scheme, the decoded and demodulated signal is transmitted to the code and modulator 437 of the transmitting apparatus.

The energy sensor 445 measures a channel state by energy sensing a signal in a time domain provided from the CP remover 415. Next, the measured channel state parameter information is transmitted to the channel parameter calculator 423.

The spectrum sensor 447 measures a channel state by spectrum-detecting a signal in a frequency domain provided through the FFT device 417. Next, the measured channel state parameter information is transmitted to the channel parameter calculator 423.

The channel parameter calculator 423 calculates the decoded and demodulated header information provided from the third switch 421 and the channel parameters provided from the energy sensor 445 or the spectrum sensor 447. Eigenvalues are calculated. In addition, the channel parameter calculator 423 generates a control signal for controlling the transmission mode processor 405 and the power amplifier 427 of the transmission device by using the measured channel parameter. To send).

The transmission method selector 425 selects a transmission method for the received signal by comparing the eigenvalues provided from the channel parameter calculator 423 with a predetermined threshold value. In addition, the transmission method selector 425 generates control information for controlling the switches 411, 413, 421, 429, 431 of the transceiver. In other words, a control signal for controlling the first switch 411 and the third switch 421 is generated to select a transmission method of the received signal. When the transmission method is selected, the control method according to the selected transmission method is used. A control signal for controlling the first switch 411 and the second switch is generated. The transmitter generates a control signal for controlling the fourth switch 429 and the fifth switch 431 to map the signals to be relayed according to the first antenna or the second transmission scheme for each antenna.

Next, the transmitter includes a power amplifier 427, switches 429 and 431, a digital / analog converter (DAC) 433, an RF processor 435, A code and modulator 437, an Inverse Fast Fourier Transform (IFFT) device 439, a CP inserter 441, and a transfer mode processor 443 Include.

When the transmission method is selected as the second transmission method, the power amplifier 427 amplifies and outputs the received signal provided from the second switch 413 under the control of the channel parameter calculator 423. Transfer to the fourth switch 429.

The fourth switch 429 performs a function of mapping a signal amplified by the power amplifier 427 to a corresponding antenna path under the control of the transmission mode selector 425.

When the transmission scheme is selected as the first transmission scheme, the code and modulator 437 encodes the decoded and demodulated received signals provided from the third switch 421, and modulates the modulated signals according to a predetermined modulation scheme. And transmit to the IFFT device 439.

The IFFT unit 439 performs an inverse fast Fourier transform on the signal provided from the code and the modulator 437, converts the signal into a time domain signal, and outputs the transformed time domain signal to the CP inserter 441.

The CP inserter 441 inserts and outputs a guard interval in the data provided from the IFFT unit 439 to remove noise and transmits it to the transmission mode processor 443.

The transmission mode processor 443 receives the signal provided from the CP inserter 441 according to the transmission mode, for example, transmission modes such as diversity, multiplexing, beam forming, and the like. The output is converted and transmitted to the fifth switch 431.

The fifth switch 431 performs a function of mapping a signal provided from the transmission mode processor 443 to a corresponding antenna path under the control of the transmission mode selector 425 and transmits the signal to the DAC 433.

The DAC 433 receives a digital signal for each antenna provided from the fourth switch 429 or the fifth switch 431 and converts the digital signal into an analog signal, and transmits the converted analog signal to the RF processor 435.

The RF processor 435 converts each antenna baseband signal provided from the DAC 433 into an RF signal and transmits the RF signal to the MS through the multiple antennas.

As described above, the energy sensor 445 and the spectrum sensor 447 measure a channel state, calculate a eigenvalue corresponding to the measured channel state, and select a predetermined transmission scheme, or the eigen The transmission method is selected by calculating the mutual information value as well as the value. Here, the mutual information value may be expressed as in Equation 1 below.

은 상호 정보값을 의미하고, 상기

은 단위행렬을 의미하며, 상기

는 수신신호의 신호 대 잡음비(SNR: Signal to Noise Ratio)를 의미하며, 상기

는 송신 안테나의 수를 의미한다.Where

Means mutual information value,

Means unit matrix, and

Denotes a signal-to-noise ratio (SNR) of the received signal.

Denotes the number of transmit antennas.

를 고유값으로 표현하면 하기 수학식 2와 같이 나타낼 수 있다.If the BS knows the channel state, the mutual information value of Equation 1 is

When expressed as an eigenvalue, it can be expressed as Equation 2 below.

은 상호 정보값을 의미하고, 상기

는 수신신호의 SNR를 의미하며, 상기

는 송신 안테나의 수를 의미한다. 또한

은 m 번째 가장 큰

의 고유값을 의미하며, n은 상기 H에 대한 순위를 의미한다. 이렇게 사용 가능한 주파수 대역에서 채널 상태를 측정한 상기 에너지 센싱기(445)와 상기 스펙트럼 센싱기(447)는, 상기 수학식 1 및 수학식 2에서 설명한 바와 같이 채널 상태에 상응하여 상호 정보값 및 고유값을 산출한다.Where

Means mutual information value,

Denotes the SNR of the received signal, and

Denotes the number of transmit antennas. Also

Is m-th largest

Means an eigenvalue of, and n means a rank for H. As described above in Equation 1 and Equation 2, the energy sensor 445 and the spectrum sensor 447 measuring the channel state in the usable frequency band correspond to mutual information values and intrinsic values. Calculate the value.

Next, a process for the RS to select a transmission scheme in the communication system according to an embodiment of the present invention will be described with reference to FIG. 5.

5 is a diagram illustrating a process for the RS to select a transmission scheme in a communication system according to an embodiment of the present invention.

Referring to FIG. 5, in step 501, the RS receives data through an available frequency band, and measures channel conditions by sensing spectrum or energy in the available frequency band. Then, in step 503, the RS checks the state of the measured channel. If the channel state is good as a result of the checking, the RS proceeds to step 509. If the channel state is poor, the RS proceeds to step 505.

First, if the channel condition is poor, in step 505, the RS selects a first transmission method, and then in step 507, the RS transmits data to a BS or MS providing a relay path using the first transmission method.

On the other hand, if the channel state is good, the RS proceeds to step 509 to calculate a unique value or mutual information value and proceeds to step 511. In step 511, the RS proceeds to step 513 when the calculated eigenvalue or mutual information value is greater than a threshold value, and proceeds to step 505 when the calculated eigenvalue or mutual information value is smaller than a threshold value.

First, if the calculated eigenvalue or mutual information value is larger than the threshold value, the method proceeds to step 513 to select a second transmission method and proceeds to step 507. The RS proceeds to step 507 and transmits data to the BS or MS providing a relay path using the second transmission scheme.

On the other hand, if the calculated eigenvalue or mutual information value is smaller than the threshold, the process proceeds to step 505 to select the first transmission method and proceeds to step 507. The RS proceeds to step 507 and transmits data to the BS or MS providing a relay path using the first transmission scheme.

Meanwhile, in the detailed description of the present invention, specific embodiments have been described, but various modifications may be made 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, the present invention can improve the capacity of the signal link by selecting a signal transmission method corresponding to the measured channel state through channel state measurement between the base station and the relay station, and the relay station and the terminal in the relay station of the CR communication system. There is an advantage.

Claims (14)

A data transmission method in a communication system comprising a first system having a usage right for a first frequency band and a second system having no use right for the first frequency band, Measuring, by the relay station of the second system, a channel state of a frequency band usable in the first frequency band; Selecting a transmission method according to the measured channel state; And transmitting data using the selected transmission method. The method of claim 1, The process of selecting the transmission mode, If the measured channel state is poor, select the first transmission method, If the measured channel condition is good, calculating a parameter corresponding to the measured channel condition. The method of claim 2, The process of selecting the transmission mode, Selecting a second transmission method when the calculated parameter is larger than a threshold value, and selecting a first transmission method when the calculated parameter is smaller than a threshold value. The method of claim 3, The first transmission method is a decode and forward (DF) method, and the second transmission method is an amplify and forward (AF) method. The method of claim 3, And the parameter is an eigen value or mutual information value. The method of claim 1, The measuring of the channel state may include measuring energy by sensing energy in the usable frequency band. The method of claim 1, The measuring of the channel state may include measuring the channel state by detecting a spectrum in the usable frequency band. A data transmission system in a communication system comprising a first system having a usage right for a first frequency band and a second system having no use right for the first frequency band, The relay station of the second system measures a channel state of a frequency band usable in the first frequency band, selects a transmission method according to the measured channel state, and transmits data using the selected transmission method. A data transmission system characterized by the above. The method of claim 8, The relay station of the second system, If the measured channel state is poor, select the first transmission method, And calculating the parameter according to the measured channel state when the measured channel state is good. The method of claim 9, The relay station of the second system, Selecting a second transmission method when the calculated parameter is larger than a threshold value, and selecting a first transmission method when the calculated parameter is smaller than a threshold value. The method of claim 10, The first transmission scheme is a Decode and Forward (DF) scheme, and the second transmission scheme is an Amplify and Forward (AF) scheme. The method of claim 10, And the parameter is an eigen value or mutual information value. The method of claim 8, The relay station of the second system, And measuring channel conditions by sensing energy in the usable frequency band. The method of claim 8, The relay station of the second system, And measuring channel conditions by detecting spectrum in the usable frequency band.

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