KR100870656B1 - Method and apparatus for detecting the ack/nack feedback singal in a digital communication system - Google Patents

Abstract

The present invention relates to an apparatus and method for detecting ACK / NACK feedback information in a digital communication system. The present invention relates to comparing a received response signal with a predetermined threshold value and reducing an ACK or NACK response signal determination error according to the comparison result. An apparatus and method are provided.

An apparatus for detecting ACK / NACK feedback information in a digital communication system according to the present invention includes a signal quality measuring unit measuring a signal quality parameter of a received response signal, and a signal quality comparing unit comparing the measured signal quality parameter and a first threshold value. And a decoding operation unit configured to calculate a correlation coefficient by decoding the received response signal and determine whether the signal quality parameter is equal to or greater than the first threshold, and determine whether the signal quality parameter is ACK or NACK.

Mobile communication, ACK / NACK, threshold, signal quality, decoding

Description

ACC / NAC feedback information detection device and method in a digital communication system {METHOD AND APPARATUS FOR DETECTING THE ACK / NACK FEEDBACK SINGAL IN A DIGITAL COMMUNICATION SYSTEM}

1 shows a general process of ACK and NACK response signals on a response signal channel according to the prior art.

FIG. 2 illustrates a general process performed when the ACK and NACK signals on a response signal channel are misjudged according to the prior art.

3 is a block diagram of an ACK / NACK feedback receiver 300 in a digital communication system according to the present invention.

4 illustrates a symbol structure for an uplink (UL) partial usage of subchannels (UL) PUSC channel mode as an example according to the IEEE 802.16d / e standard.

5 illustrates a combination of code vectors corresponding to ACK and NACK according to the IEEE 802.16d / e standard.

6 shows an orthogonal modulation index in an uplink ACK channel.

7 is a block diagram of the decoding operation unit 500 and illustrates an example of a decoding process in detail.

8 is a graph illustrating a simulation result of measuring an average cost by using the apparatus and method for detecting ACK / NACK feedback information according to the present invention.

9 is a graph illustrating another simulation result of measuring an average cost by using the apparatus and method for detecting ACK / NACK feedback information according to the present invention.

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

310: signal quality measurement unit

320: signal quality comparison unit

330: decoding operation unit

The present invention relates to an apparatus and method for detecting ACK / NACK feedback information in a digital communication system. The present invention relates to comparing a received response signal with a predetermined threshold and accurately determining an ACK or NACK response signal according to a result of the comparison. An apparatus and method are provided.

Today's remarkable development of mobile communication provides various communication services to users, and terminal and network technologies for supporting such communication services are changing day by day.

In a mobile communication system, a terminal exchanges a large amount of data (for example, packet data) with a base station, and a receiving side selects an ACK response signal or a NACK response signal to the transmitting side in order to confirm whether the packet is normally received. Will be sent as an enemy.

1 illustrates a general process for transmitting ACK and NACK response signals on a ACK channel, according to the prior art.

As shown in Fig. 1, packets are sequentially transmitted from the transmitting side (base station) to the receiving side (terminal) through the downlink DL, and the receiving side uplinks the ACK response signal whenever each packet is received. Is transmitted to the sender through If the transmitting side transmits a packet (Tx Packet2) but is not properly received at the receiving side, the receiving side transmits a NACK response signal to the transmitting side. When the transmitting side receives the NACK signal, the transmitting side retransmits the previously transmitted packet. This retransmission process may continue until the sender receives the ACK signal or may be repeatedly performed within a predetermined number of times.

However, due to various factors, the terminal and the base station may incorrectly detect ACK as NACK or NACK as ACK when receiving a response signal of ACK / NACK.

In general, if the ACK signal is incorrectly judged as a NACK signal, the sender retransmits (retransmits) the packet data. Therefore, the same packet is transmitted two or more times, which wastes channel resources. Since the packet was received correctly, ignoring the retransmitted packet may not cause a big problem for the whole network. However, when the sender misjudges the NACK signal as an ACK signal, the retransmission process of the sender does not occur. As a result, the sender deletes the previously transmitted packet from the buffer and transmits a new packet. It can cause serious problems that cannot be delivered to the receiver and lost. Even if it is possible to recover lost packet data in the upper layer of the network, this may cause a fatal transmission and reception delay.

FIG. 2 illustrates a general process performed when a wrong ACK and NACK signal on a response signal channel according to the prior art.

As shown in FIG. 2, when the receiver transmits a NACK signal to a packet transmitted by the transmitter (Tx Packet2), if the transmitter misjudges it as an ACK signal, the transmitter does not retransmit the previously transmitted packet. Otherwise, a new packet (Tx Packet3) is transmitted. Therefore, a problem occurs that a packet (Tx Packet2) for an incorrect ACK is lost.

Several techniques have already been proposed to reduce the likelihood of erroneous ACK / NACK response signals.

In US Pat. No. 6,317,418, when a base station transmits packet data to a terminal, the terminal determines the signal quality of the packet data and determines whether to request retransmission according to the determination result. In other words, if the signal quality does not reach the required level, the terminal requests retransmission to the base station, and the base station retransmits the packet data, combines the retransmitted packet data with the previously transmitted data, and restores the signal quality. Checking again determines whether to resend. However, in the present patent, as described above, there is a problem that the likelihood that a terminal misjudges an ACK or NACK signal transmitted to a base station is not reduced.

As another technique, Korean Patent Laid-Open Publication No. 2005-0122282 proposes a method for improving the reliability of ACK / NACK signal determination. In the present patent application, the terminal deletes the data in the buffer until the NDE is received in the subsequent scheduling assignment message even after receiving the ACK / NACK information by using an indicator “NDE” inserted in the scheduling assignment message (indicatior). By not flushing, the reliability of the ACK / NACK judgment can be increased. However, the present patent application has a problem that it may cause a decrease in transmission efficiency due to overload in that the indicator should be further transmitted.

As another technique, Korean Laid-Open Publication No. 2003-0059982 discloses a power control method for an ACK / NACK signal in an Automatic Repeat Request (ARQ) system. In the present patent application, the ACK / NACK sent to the transmitting side is transmitted at different power levels according to the contents according to the result of determining the quality of the received signal at the receiving side. Therefore, it is possible to reduce the power consumption for transmitting the ACK / NACK signal. However, in the present application, power control must be performed, resulting in unnecessary load on the terminal and the network, and there is a concern that the transmission efficiency is lowered.

Accordingly, the present invention is to solve the problems of the prior art described above, to propose a new technique that can minimize the packet data loss due to the misjudge of the response signal, and also improve the transmission efficiency.

The present invention has been made to improve the prior art as described above, and an object thereof is to prevent a problem in that packet data is lost by misrecognizing a reception response signal.

Another object of the present invention is to improve the accuracy of ACK / NACK response signal determination.

Another object of the present invention is to simplify the decoding operation step and to reliably determine the feedback information.

Another object of the present invention is to reduce network load and improve transmission efficiency through accurate determination of ACK / NACK feedback information.

In order to achieve the above object and solve the above-mentioned problems of the prior art, the ACK / NACK feedback information detection apparatus in a digital communication system according to an aspect of the present invention, the signal quality for measuring the signal quality parameter of the received response signal Measuring unit; A signal quality comparison unit for comparing the measured signal quality parameter with a first threshold value and processing the received response signal as a predetermined one of ACK or NACK when the signal quality parameter is less than the first threshold value; And a decoding calculator configured to determine an ACK or a NACK by decoding the received response signal and calculating a decoded signal when the signal quality parameter is equal to or greater than the first threshold.

According to another aspect of the present invention, a method for detecting ACK / NACK feedback information in a digital communication system includes measuring signal quality parameters of a received response signal; Comparing the measured signal quality parameter with a first threshold value; And when the signal quality parameter is less than the first threshold, determine the received response signal as a predetermined one of ACK or NACK, and when the signal quality parameter is greater than or equal to the first threshold, decode the received response signal to decode the received response signal. Or determining as NACK.

According to another aspect of the present invention, a method for detecting ACK / NACK feedback information in a digital communication system includes an inner product of a received response signal and an ACK channel code vector, or an inner product of an NACK channel code vector and an ACK channel code vector. Calculating an intermediate value based on a difference of an inner product, comparing the intermediate value with a threshold value, and determining whether the received response signal is ACK / NACK based on a comparison result with the threshold value; The threshold value is determined in consideration of the dispersion of the noise signal and the transmission power.

3 is a block diagram of an ACK / NACK feedback receiver 300 in a digital communication system according to the present invention. Hereinafter, the function of each component will be described in detail with reference to FIG. 3.

The ACK / NACK feedback information detecting apparatus of the present invention may be installed in a digital communication system such as a communication terminal or a base station wireless communication device, and the digital communication system may use at least one of the IEEE 802.16d / e standard, WiBro, and WiMAX. It may be based on the system.

For reference, the term "communication terminal" herein refers to a PDC (Personal Digital Cellular) phone, PCS (Personal Communication Service) phone, PHS (Personal Handyphone System) phone, CDMA-2000 (1X, 3X) phone, WCDMA (Wideband) CDMA phone, Dual Band / Dual Mode phone, Global Standard for Mobile (GSM) phone, Mobile Broadband System (MBS) phone, Digital Multimedia Broadcasting (DMB) terminal, Smart phone, Devices that may include communication functions, such as orthogonal frequency division multiplexing (OFDM), orthogonal frequency division multiplexing access (OFDMA) communication terminals, personal digital assistants (PDAs), hand-held PCs, notebook computers, laptop computers , Mobile terminals such as WiBro terminals, MP3 players, MD players, etc., and International Mobile Telecommunication-2000 (IMT-2000) terminals that provide international roaming services and extended mobile communication services. Handheld A portable electric and electronic device, which refers to a wireless communication device, is an orthogonal frequency division multiplexing access (OFDMA) module, a code division multiplexing access (CDMA) module, a bluetooth module, an infrared communication module (infrared data association), a wired or wireless LAN card. And a predetermined communication module such as a wireless communication device equipped with a GPS chip in order to enable location tracking through a global positioning system (GPS), and a terminal capable of performing a predetermined operation by mounting a microprocessor. It is interpreted as a generic concept.

As illustrated in FIG. 3, the ACK / NACK feedback information detecting apparatus 300 may include a signal quality measuring unit 310, a signal quality comparing unit 320, and a decoding calculating unit 330. The apparatus for detecting ACK / NACK feedback information according to an embodiment of the present invention 300 includes an ASIC, a digital signal processor (DSP), a field-programmable gate array (FPGA), a programmable array logic (PAL), and a complex programmable logic device (CPLD). ), GAL (Generic Array Logic) and the like.

The signal quality measuring unit 310 measures signal quality parameters of the received response signal. Depending on whether the data (packet) sent from the transmitting side is normally received, the receiving side transmits the ACK or NACK response signal to the transmitting side using an ACK channel (response signal channel) or the like.

In one example, a typical OFDM transceiver includes a serial / parallel converter, an FFT or IFFT device, and a frequency converter. In the serial-to-parallel converter of the transmitting end, the response signal data streams input in series are converted into parallel data streams by the number of subcarriers, and each parallel data stream is inverse Fourier transformed by an IFFT unit. In addition, the inverse Fourier transformed data is converted into serial data and transmitted through frequency conversion. The receiving side receives the response signal transmitted through the wired or wireless channel and outputs the response signal through a demodulation process, which is an inverse process of the transmitting end.

Accordingly, the signal quality measuring unit 310 according to the present invention may use a signal that has undergone a predetermined preprocessing process of transitioning a baseband received signal to a frequency domain by performing FFT conversion using an FFT device.

As an example of the signal quality parameter according to the present invention, at least one of carrier signal to noise and interference ratio (CINR), path loss, and attenuation may be used. have.

4 illustrates a symbol structure for an uplink (UL) partial usage of subchannels (UL) PUSC channel mode as an example according to the IEEE 802.16d / e standard. The basic unit constituting the UL PUSC is a tile having a structure of 4 (subcarrier) * 3 (symbol), and a pilot subcarrier is located at four corners on the tile.

As an example according to the present invention, the CINR may be measured using four pilot signals or eight data signals per tile. For the CINR measurement, the pilot signal or the data signal is squared to obtain a power value, and the power value is accumulated for a plurality of symbols for a predetermined time, thereby further increasing accuracy. As another example, the CINR may be measured using both the pilot signal and the data signal.

As another example, in a multi-input multi-output (MIMO) based system, the CINR can be measured by combining all pilot signals received through several antennas, or depending on the situation, The CINR may be measured by selecting a specific antenna among antennas of.

The signal quality comparing unit 320 compares the signal quality parameter measured by the signal quality measuring unit 310 with a predetermined first threshold value. The signal quality comparison unit 320 estimates the channel quality of the ACK channel by measuring the signal quality parameter, and if the channel quality is not good below the threshold value, determines that the decoding result of the response signal itself is unreliable. . Accordingly, when the signal quality parameter is less than or equal to the first threshold value, the response signal may be regarded as a predetermined signal of NACK or ACK, and processing thereof may be performed immediately. The method for calculating the first threshold value will be described later in detail.

The decoding operator 330 determines whether to decode the digital received signal according to a result of the comparison with the first threshold of the signal quality comparator 320. That is, when the signal quality parameter is greater than or equal to the threshold, it is determined that the ACK channel is good, and finally, whether the ACK / NACK is determined by decoding the received response signal to generate a decoded signal.

5 illustrates a combination of code vectors corresponding to ACK and NACK according to the IEEE 802.16d / e standard.

According to the IEEE 802.16d / e standard, an uplink ACK channel provides feedback for downlink hybrid ARQ. The channel transmits an ACK or NACK response signal as feedback information to the base station for downlink packet data. One ACK channel occupies 1/2 subchannel, which corresponds to three pieces of 4x3 uplink tiles when in PUSC channel mode. The even half subchannel consists of a piece of Tile (0), Tile (2), and Tile (4), and the odd half subchannel consists of Tile (1), Tile (3), and Tile ( 5) can be composed of pieces.

If the corresponding downlink packet is successfully received successively, the response bit of the ACK channel is set to "0" (ACK), otherwise it is set to "1" (NACK). This 1-bit response bit is encoded into 3 code-words for the 8-ary alphabet as shown in FIG. 5 for error protection.

The uplink ACK channel is orthogonally modulated in a QPSK manner. As shown in FIG. 6, one UL ACK channel has three uplink tiles each having eight elements, thereby forming a code vector having 24 elements.

FIG. 7 is a block diagram of the decoding operation unit 330 and illustrates an example of a decoding process in detail.

As shown in FIG. 7, a code vector received through the UL ACK channel described above calculates an inner-product of each of the code vectors corresponding to ACK and NACK, and obtains a difference to obtain a correlation coefficient ( R _Δ ). Can be obtained.

Correlation estimate of the signal and the ACK and NACK in the ACK channel received code (i.e., a vector dot product) difference, _△ R is not and determine the NACK is greater than a second threshold value of λ is determined, if the ACK.

Hereinafter, a detailed operation will be described by taking an example of setting the first threshold value to minimize the risk or the average cost due to the determination error by using the signal-to-noise ratio (SNR) as the signal quality parameter.

First, two hypotheses about response signal judgment, H ₀ and H ₁ ,

H ₀ : ACK sent

H ₁ : When calculating the average cost for the error of judgment that the NACK was transmitted

Equation 1 below.

[Equation 1]

here,

to be. The input r of the decoding operation unit for the signal received through the white Gaussian noise channel may be expressed by Equation 2 below.

[Formula 2]

here,

를 ACK/NACK의 판단을 위한 시험통계(test statistic)로 사용할 경우, 가설 H _K 에 대한 R _△의 확률밀도함수 (Probability Density Function; pdf) R _{△ │} H _K 는 가우시안 pdf를 가지며 평균과 분산(

)은 다음과 같이 구할 수 있다.to be. The difference between the inner product of the NACK channel code vector and the inner product of the ACK channel code vector, i.e.,

Is used as a test statistic for the determination of ACK / NACK, the probability density function of R _△ for hypothesis H _K is R _{△ │} H _K has Gaussian pdf, mean and variance (

) Can be obtained as

Therefore, the probability density function of R _△ for the hypothesis H _k can be expressed as Equation 3 below.

[Equation 3]

는 다음 수식 4와 같다.If ACK / NACK is judged only by the magnitude of the correlation coefficient calculated internally without considering the signal quality, the average cost shown in Equation 1

Is the same as Equation 4.

[Equation 4]

On the other hand, if the received response signal is considered as ACK or NACK unconditionally, the average cost is as follows.

[Equation 5]

는 신호의 크기와 잡음전력의 함수이며, 평균비용

와

은 사전에 정해진 확률(a priori probability) P ₀와 P ₁과 그에 해당하는 비용에 의해 미리 결정되는 값이다. 따라서 신호 품질비교에 적용되는 임계값은

또는

중 작은 값이

와 같아지는 신호대 잡음비로 결정하면 된다. 즉, 제1임계값

를 결정하는 신호의 크기 A와 잡음전력 s ²는 다음의 조건을 만족시켜야 한다.Average cost in the conventional method of determining ACK / NACK without a signal quality comparison unit, i.e., according to the constant λ

Is a function of signal magnitude and noise power, and average cost

Wow

Is a value determined by a priori probability P ₀ and P ₁ and corresponding cost. Therefore, the threshold applied to the signal quality comparison

or

Of the smaller values

This is determined by the signal-to-noise ratio equal to. That is, the first threshold

The magnitude of the signal A and the noise power s ² to determine the following conditions must be satisfied.

[Equation 6]

And the first threshold value g can be calculated by numerical method from Equations 4, 5 and 6. Therefore, the hypothesis test for ACK / NACK determination can be expressed in two cases as follows.

[Formula 7]

According to Equation 7, the C _ACK may be large or the C _NACK may be large depending on the system or operation service, and for each, the signal is regarded as NACK when the quality of the signal falls below the first threshold (select H ₁ ). Or ACK (H ₀ selection), and when the quality of the signal is greater than the first threshold, it is determined as ACK or NACK compared to the second threshold.

The ACK / NACK feedback transmission method according to the present invention may be implemented in the form of program instructions that can be executed by various computer means and recorded in a computer readable medium. The computer readable medium may include program instructions, data files, data structures, etc. alone or in combination. Program instructions recorded on the media may be those specially designed and constructed for the purposes of the present invention, or they may be of the kind well-known and available to those having skill in the computer software arts. Examples of computer readable recording media include magnetic media such as hard disks, floppy disks, and magnetic tape, optical media such as CD-ROMs, DVDs, and magnetic disks such as floppy disks. -Magneto-Optical Media, and hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, flash memory, and the like. The medium may be a transmission medium such as an optical or metal wire, a waveguide, or the like including a carrier wave for transmitting a signal specifying a program command, a data structure, or the like. Examples of program instructions include not only machine code generated by a compiler, but also high-level language code that can be executed by a computer using an interpreter or the like. The hardware device described above may be configured to operate as one or more software modules to perform the operations of the present invention, and vice versa.

8 is a graph illustrating a simulation result of measuring an average cost by using the apparatus and method for detecting ACK / NACK feedback information according to the present invention. First, in the case of determining ACK / NACK as one step that does not consider the signal quality as a conventional method, the average cost for error, the average cost for the two-stage decision proposed in the present invention, and the theoretical minimum according to the Bayes judgment method The cost is shown. As the conditions used in this simulation, P ₁ is assumed to be 0.1, C ₀₁ is 50, and C ₁₀ is 1, and accordingly, it is regarded as NACK when the signal quality is lower than the first threshold value (about -10.6 dB). It can be seen that the average cost reduction effect according to the present invention when the signal quality is lower than the first threshold is well represented. In addition, even though the determiner minimizes the complexity by fixing the second threshold l to 0, it can be seen that there is no significant difference from the theoretical minimum cost.

9 is a result of another simulation, the conditions used for the simulation, P ₁ is assumed to be 0.01, C ₀₁ is 25, and C ₁₀ is 1, so that the signal quality is less than the first threshold value (about -12.4dB) If low, it is regarded as ACK. Average cost reduction effect according to the present invention is shown to be similar to the previous case.

Hereinafter, the meaning of the first threshold described above will be described once again.

If the quality of the signal is less than or equal to the first threshold value, regardless of the magnitude of the correlation coefficient (or vector dot product), it is determined as NACK (or ACK) and the corresponding action, that is, retransmission (or new packet transmission). In this case, whether to determine as NACK or ACK is determined in advance as a system parameter, which may correspond to a smaller value of C _NACK and C _ACK shown in Equation 5.

For example, the probability that a NACK occurs (that is, the probability that a data transmission fails) is 0.1 (an average of one non-recoverable error occurs when transmitting 10 packets), and the NACK is determined as ACK. For the cost incurred by not retransmitting, i.e., if the C _ACK is 50, the average cost is 0.1x50 = 5 if it is considered unconditionally ACK (no retransmission) without a decision. However, at the same probability, the cost incurred when the ACK is determined to be _NACK and needlessly retransmitted, i.e., if C _NACK is 1, the average cost is (1-0.1) x1 = 0.9 even if retransmitted unconditionally. (In practice, if the retransmission is repeated, the probability of transmission failure decreases, but for convenience, it is assumed to be a constant of 0.1). That is, it is advantageous in terms of average cost that C _NACK <C _ACK is performed and retransmission is performed regardless of the determination.

On the other hand, if the probability of NACK is 0.01 (packet error is about 1%), and the C _ACK is 25, the average cost is 0.01x25 = 0.25 if it is regarded as an ACK (without retransmission) without determination. do. However, if C _NACK is 1 at the same probability, the average cost is (1-0.01) x1 = 0.99 even if retransmission is unconditionally performed regardless of the determination. That is, it is advantageous in terms of average cost that C _NACK > C _ACK does not retransmit.

On the other hand, as another embodiment according to the present invention, if it is determined whether the NACK or ACK on the basis of the yin and yang (that is, the comparison of the size of the NACK and ACK) of the dot product with the NACK code vector minus the dot product with the ACK code vector, When the quality of the signal is good, the average cost will be lower than unconditionally determined by NACK or ACK as described above, but if the signal quality is poor, the average cost may be larger than C _ACK or C _NACK .

Therefore, the first threshold value is determined as a signal-to-noise ratio, in which the smaller of C _ACK and C _NACK and the average cost for comparing the sizes of NACK and ACK are equal.

For example, the dotted line in the figure corresponds to the average cost of the conventional method, the horizontal line corresponding to the average cost (vertical axis) = 0.9 corresponds to the C _NACK , the two curves meet at SN = -10.6dB. Therefore, it can be considered that NSN should be processed unconditionally under SN = -10.6dB. 9 exemplifies a case where it is preferable to process the ACK unconditionally below the first threshold value.

Therefore, the average cost in the present invention is to select the first threshold value so as not to exceed the smaller value of C _ACK and C _NACK , that is, min (C _ACK , C _NACK ).

In the present invention as described above has been described by the specific embodiments, such as specific components and limited embodiments and drawings, but this is provided to help a more general understanding of the present invention, the present invention is not limited to the above embodiments. For those skilled in the art, various modifications and variations are possible from such description.

Therefore, the spirit of the present invention should not be limited to the described embodiments, and all the things that are equivalent to or equivalent to the claims as well as the following claims will belong to the scope of the present invention. .

According to the ACK / NACK feedback transmission apparatus and method according to the present invention, it is possible to alleviate the problem that packet data is lost due to a misjudgment of the reception response signal.

According to the present invention, by determining the authenticity of the NACK response signal through two steps, it is possible to improve the reliability of the determination.

According to the present invention, it is possible to reliably detect the feedback information while simplifying the decoding operation step.

According to the present invention, the reliability of the response signal determination can be improved in consideration of the channel environment.

Claims (20)

A signal quality measuring unit measuring a signal quality parameter of the received response signal; A signal quality comparison unit for comparing the measured signal quality parameter with a first threshold value and processing the received response signal as a predetermined one of ACK or NACK when the signal quality parameter is less than the first threshold value; And ACK / NACK feedback information in a digital communication system including a decoding operation unit that decodes the received response signal, calculates a decoding signal, and determines an ACK or a NACK when the signal quality parameter is equal to or greater than the first threshold. Detection device. delete The method of claim 1, The first threshold value is determined in consideration of the average cost of the determination error of the ACK or NACK ACK / NACK feedback information detection apparatus in a digital communication system. The method of claim 3, The first threshold value is set so that the average cost for the determination error does not exceed a smaller value among the average costs of considering the received response signal as either ACK or NACK only. NACK feedback information detection device. The method of claim 1, And the first threshold value is determined as a signal-to-noise ratio that satisfies the following equation. [Equation]

The apparatus of claim 1, wherein the signal quality parameter comprises at least one of a CINR, a path loss value, and an attenuation value. Measuring signal quality parameters of the received response signal; Comparing the measured signal quality parameter with a first threshold value; And If the signal quality parameter is less than the first threshold, the received response signal is determined to be a predetermined one of ACK or NACK. If the signal quality parameter is greater than or equal to the first threshold, the received response signal is decoded to decode the received response signal. A method for detecting ACK / NACK feedback information in a digital communication system comprising determining as NACK. The method of claim 7, wherein The step of determining whether to decode the ACK / NACK from the decoded signal, Calculating a correlation coefficient using a difference of a complex product of the decoded signal and each of the code vectors corresponding to ACK and NACK; Comparing the calculated correlation coefficient with a second threshold value; And And determining the NACK when the correlation coefficient is greater than the second threshold as a result of the comparison. The method of claim 8, The step of determining whether to decode the ACK / NACK from the decoded signal, And determining that the correlation coefficient is ACK when the correlation coefficient is smaller than the second threshold value. A computer-readable recording medium having recorded a program for executing the method according to any one of claims 7 to 9. The method according to any one of claims 7 to 9, The first threshold value is determined in consideration of the average cost of the determination error of the ACK or NACK ACK / NACK feedback information detection method in a digital communication system. The method of claim 11, The first threshold value is set so that the average cost for the determination error does not exceed a smaller value among the average costs of considering the received response signal as either ACK or NACK only. How to detect NACK feedback information. The method according to any one of claims 7 to 9, The first threshold value is determined by the signal-to-noise ratio satisfying the following equation, ACK / NACK feedback information detection method in a digital communication system. [Equation]

The method according to any one of claims 7 to 9, And the signal quality parameter comprises at least one of a CINR, a path loss value and an attenuation value. The ACK / NACK in a digital communication system according to any one of claims 7 to 9, wherein the digital communication system is based on at least one of the IEEE 802.16d / e standard, WiBro, and WiMAX. How to detect feedback information. 10. The system according to any one of claims 7 to 9, wherein the digital communication system is a multi-input multi-output (MIMO) based system, and the quality parameter is a signal received through a plurality of antennas. And a CINR obtained by using a signal received through a specific antenna selected from among a plurality of antennas or a CINR obtained by using the ACK / NACK feedback information detection method in a digital communication system. 10. The method according to any one of claims 7 to 9, wherein the received response signal transmits an ACK or NACK for packet data through an ACK channel and is encoded in a code vector form. / NACK How to detect feedback information. The apparatus of claim 1, wherein the digital communication system is based on at least one of the IEEE 802.16d / e standard, WiBro, and WiMAX. The digital communication system of claim 1, wherein the digital communication system is a system based on a multi-input multi-output (MIMO), and the quality parameter is a plurality of CINRs or a plurality of CINRs obtained using signals received through a plurality of antennas. Apparatus for detecting ACK / NACK feedback information in a digital communication system, characterized in that the CINR obtained by using a signal received through a specific antenna selected from the antenna. The apparatus of claim 1, wherein the reception response signal is ACK or NACK for packet data transmitted through an ACK channel and encoded in a code vector form.

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