KR102240375B1 - Calibration factor determining device, calibration factor determining method, device and method for CQI feedback using the same - Google Patents

Abstract

A method for determining a correction factor for link quality estimation by a correction factor determination apparatus, which is effective in receiving a plurality of CQI indexes and a correction parameter candidate group of each CQI index as an input, and including a plurality of SNRs for each CQI index. Define the interval. After generating a plurality of channels for each of the plurality of SNRs included in the valid section, and checking the actual BLER (Block Error Rate) and the effective BLER from the additive noise of each generated channel, the plurality of effective BLERs and A value at which the difference between a plurality of actual BLERs is minimum is derived as a correction factor.

Description

Calibration factor determining device, calibration factor determining method, terminal, and CQI feedback method using the same {Calibration factor determining device, calibration factor determining method, device and method for CQI feedback using the same}

The present invention relates to an apparatus for determining a correction factor, a method for determining a correction factor, a terminal, and a CQI feedback method using the same.

With the development of mobile communication systems, as the number of users increases rapidly, environments experienced by terminals are diversified, and the amount of data traffic is rapidly increasing. Each terminal determines an appropriate link quality for a fading channel through Fast Link Adaptation (FLA), determines a channel quality indicator (CQI), and feeds it back to the base station.

Since the channel is frequency-selective and has a property of visually changing, the base station determines a modulation order and coding rate (MCS: Modulation and Coding Scheme) suitable for the current channel condition based on the CQI transmitted from the terminal. In addition, the base station delivers information to be transmitted to the terminal according to the modulation order and coding rate.

Here, as the CQI fed back from the terminal to the base station is higher, the base station increases the modulation order or coding rate. In the opposite case, the base station maintains the reliability of communication between the terminal and the base station by reducing the modulation order and the coding rate.

In order for the UE to select an appropriate CQI for the current channel in fast link adaptation, it is necessary to calculate an effective signal-to-noise ratio (SNR). The effective SNR is a value that expresses the characteristics of a channel as a constant through a link quality metric (LQM).

In the current fast link adaptation scheme, an exponential effective SNR metric (EESM) and a mutual information effective SNR metric (MIESM) are widely used. In the fast link adaptation scheme, the correction factor used by the system to calculate the effective SNR is used to adjust the accuracy of the physical layer link abstraction (PLA).

The optimal correction factor can predict an accurate block error rate (BELR) for a given channel, and allows the terminal to select a reliable CQI. However, the correction factor previously derived by the system is a correction factor derived by performing physical layer link abstraction in a limited channel environment without considering various characteristics of mobile communication.

Accordingly, the present invention provides a calibration factor determination device and a calibration factor determination method for deriving a calibration factor from an improved calibration procedure, and a CQI feedback device and method for feeding back a CQI selected by a terminal to a base station using the derived calibration factor. do.

As a method for determining a correction factor for link quality estimation by the calibration factor determination apparatus, which is one characteristic of the present invention for achieving the technical problem of the present invention,

Receiving a plurality of CQI indexes and correction parameter candidate groups of each CQI index as an input, and defining a valid period including a plurality of SNRs for each of the CQI indexes, a plurality of SNRs included in the valid period Generating a plurality of channels for each, generating additive noise for each of the generated channels, confirming actual block error rates (BLERs) and effective BLERs from the additive noise, and validating a plurality of It includes the step of deriving a value at which the difference between the BLERs and the plurality of actual BLERs is minimum as a correction factor.

The valid period may be defined such that the BLER of each CQI index is between 0.9 and 0.001.

The defining of the effective period includes calculating a noise variance for each of the plurality of SNRs, and the effective SNR may be calculated based on the generated channels, the noise variance, and the calibration parameter candidate group. .

Checking the valid BLER,

Generating the additive noises from the channel state information for each of the channels, decoding a received signal including the additive noises, and confirming the actual BLER, and additive white Gaussian for each channel It may include the step of checking the effective BLERs by mapping the effective SNR to the noise-BLER lookup table.

The step of deriving the correction factor may further include confirming the channel in which the valid BLER and the actual BLER derived by the correction factor are confirmed as a current channel to be used by the terminal.

As a correction factor determination device for determining a correction factor for estimating link quality, which is another feature of the present invention for achieving the technical problem of the present invention,

A channel generator that generates a virtual channel, obtains an effective SNR for all stored CQI indexes, determines an effective period for an effective SNR based on channel state information for the virtual channel, and determines a plurality of valid SNRs included in the effective period. Valid section definition unit that checks the actual block error rates (BLERs) and effective BLER of the SNRs of SNRs, noise calculated for each of the plurality of channels generated, and calibration to check the calibration parameter candidate group based on the valid section A factor candidate group verification unit, and a calibration factor determination unit that calculates an effective SNR using the calibration parameter candidate groups, and determines a calibration factor using the effective BLER verified using the effective SNR and the actual BLER verified through the calculated noise. Includes.

The channel generator may generate a plurality of channels for each of a plurality of effective SNRs included in the valid period.

The valid interval defining unit may define an effective SNR of each CQI index to be between 0.9 and 0.001.

The correction factor determiner may estimate the effective BLER for the channel by mapping the effective SNR to an additive white Gaussian noise-BLER lookup table.

The correction factor determination unit may derive a value at which a difference between a plurality of effective BLERs and a plurality of actual BLERs is minimum, as the correction factor.

As a method of feeding back CQI for a channel to a base station by a terminal interworking with a correction factor determination apparatus, which is another feature of the present invention for achieving the technical problem of the present invention,

Receiving a calibration factor for a channel used by the terminal from the calibration factor determination device, checking the current CQI for the channel based on the received calibration factor, and feeding back the current CQI to the base station, the current Predicting a next CQI for a next channel after the channel, and calculating a difference between the predicted CQI and a current CQI, and feeding back the calculated difference value as a CQI for the next channel to the base station.

In the step of feeding back to the base station, the difference between the predicted CQI and the current CQI is converted into a binary number, and a 3-bit CQI for a next channel may be fed back.

According to the present invention, the apparatus for determining a calibration factor may derive a calibration factor in consideration of an actual channel state rather than a limited channel environment through an improved calibration procedure.

In addition, the terminal may feed back an accurate CQI value for a wide SNR range by using the calibration factor derived by the calibration factor determination apparatus.

In addition, when the UE feeds back the CQI to the base station, it may feed back with a reduced number of bits than the number of bits used for conventional CQI feedback.

1 is an exemplary diagram showing a general fast link adaptation mechanism.
2 is an exemplary diagram for a conventional effective SNR and effective BLER.
3 is an exemplary diagram for a correction factor derivation process.
4 is an exemplary diagram of a communication system environment according to an embodiment of the present invention.
5 is a structural diagram of an apparatus for determining a correction factor according to an embodiment of the present invention.
6 is an exemplary diagram of a graph showing an effective SNReff interval according to an embodiment of the present invention.
7 is a structural diagram of a terminal according to an embodiment of the present invention.
8 is a flowchart illustrating a method of determining a correction factor and feedback CQI according to an embodiment of the present invention.
9 is a flowchart of a method of deriving a correction factor according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present invention. However, the present invention may be implemented in various different forms and is not limited to the embodiments described herein. In the drawings, parts irrelevant to the description are omitted in order to clearly describe the present invention, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the specification, when a part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

In the present specification, a terminal is a mobile station (MS), a mobile terminal (MT), a subscriber station (SS), a portable subscriber station (PSS), and a user device (User Equipment, UE), an access terminal (AT), and the like, and may include all or part of functions such as a mobile terminal, a subscriber station, a mobile subscriber station, and a user equipment.

In the present specification, a base station (BS) is an access point (AP), a radio access station (RAS), a node B (Node B), a base transceiver station (BTS), and an MMR ( Mobile Multihop Relay)-BS, and the like, and may include all or part of functions such as an access point, a wireless access station, a node B, a base station for transmission and reception, and an MMR-BS.

Hereinafter, an apparatus for determining a correction factor, a method for determining a correction factor, a terminal, and a CQI feedback method according to an embodiment of the present invention will be described in detail with reference to the drawings. Before describing an embodiment of the present invention, a general fast link adaptation mechanism will be described with reference to FIG. 1.

1 is an exemplary diagram for a general fast link adaptation mechanism.

The goal of fast link adaptation is to maximize the throughput of data traffic of the communication system while maintaining the target BLER in response to changing channel conditions. In the fast link adaptation scheme used in the terminal as shown in FIG. 1, the terminal estimates an appropriate CQI value based on current channel state information (CSI), and feeds back the estimated CQI value to the base station.

In an Orthogonal Frequency Division Multiplexing (OFDM) system, the UE _{calculates the SNR of subcarriers including CSI as an effective SNR (SNR eff} ) (S10). When calculating the effective SNR, the terminal calculates the effective SNR representing the characteristics of the current channel using a link quality metric (LQM).

The terminal maps the calculated effective SNR (SNR _eff ) to an additive white Gaussian noise-BLER look-up table to estimate _{an effective BLER (BLER eff) for a given channel state.} (S20). Since the UE estimates the effective BLER from the effective SNR in various ways, detailed descriptions are omitted in the embodiment of the present invention.

The UE determines the CQI for the maximum rate at which a signal is transmitted without errors between the UE and the base station while maximizing the throughput of the system while satisfying the condition of the target BLER using the estimated effective BLER. Here, the target BLER condition is described as an example of 0.1, but is not necessarily limited as such.

The terminal feeds back the determined CQI to the base station (S30). As a result, through the CQI fed back to the base station, each terminal can provide a communication service to a user while maintaining a quality of service (QoS).

_{Here, the effective SNR (SNR eff} ) of the fast link adaptation calculated by the terminal in step S10 is calculated through Equation 1 below.

Here, P is the total number of subcarriers in the OFDM system generated per channel, SNR _p is the SNR of each of the subcarriers, and β is a correction factor. f _m (·) uses a BICM (bit interleaved coding and modulation) capacity curve as a compression function, and the shape of the curve is determined according to the modulation order m.

Here, the effective SNR calculated by the terminal and the estimated effective BLER will be described with reference to FIG. 2.

2 is an exemplary diagram for a conventional effective SNR and effective BLER.

Figure 2 (a) shows an example in which the effective SNR is calculated using MIESM when the modulation order m = 4 (16QAM), and Figure 2 (b) shows the effective BLER estimated using the effective SNR. An example is illustrated.

As shown in (a) of FIG. 2, the terminal divides the SNRs of each of the plurality of OFDM subcarriers generated in one channel by a predefined correction factor (β). Then, values derived by dividing the SNR by a correction factor are mapped to a compression function to calculate a BICM channel capacity.

The terminal calculates the average of the values mapped to the compression function, and multiplies the value obtained by applying the inverse function of the compression function by a correction factor again to obtain an effective SNR (SNR _eff ). Here, the compression function is described by using a known BICM (Bit Interleaved Coding and Modulation) capacity curve as an example, but is not necessarily limited as such.

Then, the UE estimates the _{BLER eff} using the BLER curve corresponding to each CQI and the calculated effective SNR (SNR _{eff) in the AWGN channel.} That is, as shown in (b) of FIG. 2, the terminal estimates the effective BLER corresponding to the effective SNR by using the AWGN-BLER curve corresponding to each CQI. Then, the last CQI value that satisfies the effective BLER ≤ target BLER (=0.1) is determined as the CQI value in the corresponding channel, and is fed back to the base station.

In the physical layer abstraction, the _{smaller the difference between the actual BLER (BLER real} ) and the effective BLER (BLER _eff ), the more accurate the prediction of the channel is. Therefore, the correction factor used to calculate the effective SNR (SNR _{eff) is important.} This is because, if the optimum value of the correction factor is used, an accurate link quality can be determined.

A standard calibration procedure for obtaining an optimal calibration factor has been proposed in the past. However, the disadvantage of using standard calibration procedures is that a vast amount of link simulation is required to cover a significant number of channels. For this reason, an average calibration procedure has been proposed and is currently used in many systems.

Here, the average calibration procedure will be described with reference to Table 1.

는 해당 SNR의 잡음 분산, w_n는 발생된 잡음이다. bler(H_k, w_n)은 0 또는 1의 값을 갖는 BLER이다. Here, N _b is the number of correction factor candidates, N _s is the number of generated SNR points, N _c is the number of channels, and N _w is the number of noise occurrences. H _k means the generated channel matrix,

Is the noise variance of the corresponding SNR, and w _n is the generated noise. bler(H _k , w _n ) is a BLER with a value of 0 or 1.

는 주어진 채널 및 잡음에 대한 물리계층에서의 실제 BLER(BLER_real)의 평균값을 나타내며,

는 AWGN-BLER 룩업 LUT 맵핑을 통하여 추정한 BLER인

들의 평균이다. 그리고 β_i는 교정인자 후보들을 의미한다.In this case, the transport block means a subframe of the LTE standard.

Represents the average value of _{the actual BLER (BLER real} ) in the physical layer for a given channel and noise,

Is the BLER estimated through AWGN-BLER lookup LUT mapping.

It is the average of them. And β _i means correction factor candidates.

In the average calibration procedure, the error function ε(·) of Equation 2 is used to calculate the optimal calibration factor.

The general correction factor derivation process described above will be described with reference to FIG. 3.

3 is an exemplary diagram for a correction factor derivation process.

As shown in FIG. 3, in the average calibration procedure, in order to find the optimum value of the calibration factor, the BLER of each CQI generates noise for a limited SNR corresponding to 0.95-0.01, and then a calibration factor is derived. When deriving the correction factor, practically all data obtained from the link level simulation cannot be reflected.

Therefore, only the data generated in the SNR of the ROI is used. This acts as a limitation in that the conventional method for deriving correction factors is limited in the channel environment, that is, only a limited range of the AWGN SNR corresponding to the BLER of 0.95 to 0.01 is considered.

Therefore, in an embodiment of the present invention, effective channels are generated from an SNR range wider than the existing limited SNR range, and an optimal correction factor capable of determining the correct link quality of the channel is to be derived. This will be described with reference to FIG. 4.

4 is an exemplary diagram of a communication system environment according to an embodiment of the present invention.

As shown in FIG. 4, the correction factor determination apparatus 100 for determining a correction factor to be applied to the terminal 200 selects a plurality of correction factors included in the correction factor candidate group one by one for all CQI indexes. Since there are a plurality of calibration factors, the calibration factor determination apparatus 100 virtually generates a channel in order to determine one of the plurality of calibration factors. Since the calibration factor determining apparatus 100 can virtually generate a channel in various ways, it is not limited to any one method in the embodiment of the present invention.

The calibration factor determination apparatus 100 checks channel state information for the generated channel, and defines a valid section from the effective SNR. That is, the calibration factor determination apparatus 100 does not receive channel state information about a channel from the outside, but generates a channel by itself, and checks channel information about the generated channel.

를 도출한다. The calibration factor determination apparatus 100 uses channel information of each of a plurality of channels for each of a plurality of SNRs included in the valid period, noise, and calibration parameter candidate groups received from the outside, and uses the effective SNR (SNR _eff ). Calculate And the calibration factor determination device 100 is the optimal calibration factor from the _{calculated effective SNR (SNR eff) using the error function.}

To derive.

The calibration factor determination apparatus 100 transmits the derived calibration factor to the terminal 200. The terminal 200 stores the calibration factor received from the calibration factor determination apparatus 100 and estimates a CQI value using the calibration factor. Then, the estimated CQI value is transmitted to the base station 300. Here, the correction factor stored in the terminal 200 is described as an example that does not change, but is not necessarily limited as such.

In such a communication environment, the structure of the calibration factor determination apparatus 100 for determining the calibration factor and the terminal 200 for feeding back CQI to the base station 300 will be described with reference to FIGS. 5 to 7.

5 is a structural diagram of an apparatus for determining a correction factor according to an embodiment of the present invention.

As shown in FIG. 5, the calibration factor determination apparatus 100 operated by at least one processor (not shown) includes an effective section defining unit 110, a channel generating unit 120, and a calibration factor candidate group checking unit ( 130), and a correction factor determination unit 140.

The effective interval defining unit 110 obtains a probability distribution of an effective SNR from a given AWGN SNR for all CQI indexes stored in advance. Since the effective interval defining unit 110 calculates the probability distribution of the effective SNR in the AWGN SNR, detailed descriptions are omitted in the embodiment of the present invention.

The valid period defining unit 110 checks channel state information (CSI) for a virtual channel generated by the channel generating unit 120. Here, the channel state information is already known, and detailed descriptions are omitted in the embodiment of the present invention.

The valid period defining unit 110 checks the SNR of the virtual channel using the checked channel state information and the link quality metric (LQM). _{In order to check the effective SNR (SNR eff} ) from the verified SNR, the valid interval definition unit 110 determines an valid interval for the SNR (hereinafter, referred to as a'SNR valid interval' for convenience of description).

,

)을 유효 SNR의 SNR 유효 구간(

)인 것으로 정의하나, 반드시 이와 같이 한정되는 것은 아니다. In general, the CQI feedback value is determined based on the target BLER of 0.1. Accordingly, the valid interval defining unit 110 sets the SNR valid interval to sufficiently include an effective channel centering on the SNR of which the BLER is 0.1. In the embodiment of the present invention, the SNR valid section set by the valid section definition unit 110 is set in the range corresponding to BLER 0.95 to BLER 0.01, SNR (

,

) To the valid SNR segment (

), but is not necessarily limited as such.

Here, an example of the valid section defined by the valid section defining unit 110 will be first described with reference to FIG. 6.

6 is an exemplary diagram of a graph showing an effective SNReff interval according to an embodiment of the present invention.

For a given AWGN SNR and each CQI, the effective section definition unit 110 obtains a probability distribution of the effective SNR over a plurality of channels. The distribution of the effective SNR for each AWGN SNR follows a Gaussian distribution as shown in FIG. 6. The effective SNR represents a random variable corresponding to the effective SNR of a given AWGN SNR when the channel coefficient is random.

확률이 일정 값 이상이 되도록 하는 AWGN SNR의 범위를 설정한다. 그리고 유효구간 정의부(110)는 설정한 AWGN SNR의 범위에서 SNRmin과 SNRmax를 각각 AWGN SNR의 최소값(또는 SNR 최소값)과 최대값(또는 SNR 최대값)으로 나타낸다. 또한, 유효구간 정의부(110)는 SNR의 분포로부터 확률

가 가중치로 사용되어, 최적의 교정 인자에 대한 총 오차를 계산한다.The valid section definition unit 110

Set the range of AWGN SNR so that the probability becomes more than a certain value. In addition, the valid section defining unit 110 represents the SNRmin and SNRmax in the range of the set AWGN SNR as the minimum value (or SNR minimum value) and the maximum value (or SNR maximum value) of the AWGN SNR, respectively. In addition, the valid section definition unit 110 is the probability from the distribution of the SNR.

Is used as the weight to calculate the total error for the optimal correction factor.

Meanwhile, the channel generating unit 120 of FIG. 5 generates a plurality of channels Nc for each of a plurality of SNR values included in the valid period defined by the valid period defining unit 110. At this time, the number of times of channel generation generated by the channel generator 120 is largely set to show the characteristics of all channels, and the number of settings is not limited to any one in the embodiment of the present invention.

In addition, in the embodiment of the present invention, the number of SNR values included in the valid period and the number of channels generated from each of the SNR values are not limited to any one. In addition, since there are various methods of generating a virtual channel by the channel generator 120, the present invention is not limited to any one method.

The channel generator 120 calculates noise for the generated channel. Since there are various methods of calculating noise for a channel generated by the channel generator 120, detailed descriptions are omitted in the embodiment of the present invention.

In addition, the channel generator 120 transmits channel state information for each of the plurality of generated channels to the valid section defining unit 110. Here, the channel state information includes noise information on the calculated channel.

The correction factor candidate group checking unit 130 is based on a plurality of channels generated by the channel generator 120, noise calculated for each channel, and an SNR valid period set by the valid period defining unit 110, N _b correction parameter candidate groups βi are identified. Since there are various methods for the correction factor candidate group checking unit 130 to check the calibration parameter candidate group from a plurality of channels and noise, detailed descriptions are omitted in the exemplary embodiment of the present invention.

The correction factor determination unit 140 calculates the effective SNR from the calibration parameter candidate groups βi checked by the calibration factor candidate group confirmation unit 130. In addition, the correction factor determination unit 140 calculates an error between the actual BLER and the effective BLER using the error function ε(·).

The correction factor determination unit 140 uses the distribution ratio of the effective SNR obtained through the pre-simulation as a weight, and obtains a correction factor that minimizes the error between the actual BLER and the effective BLER. And the correction factor determination unit 140 transmits the obtained correction factor to the terminal 200. Here, the error function ε(·) used by the correction factor determination unit 140 is shown in Equation 3 below.

Here, BLERreal=0 is regarded ^{as BLERreal=10 -5.}

The algorithm for performing the calibration procedure by the calibration factor determination apparatus 100 described above uses the algorithm shown in Table 2 below.

Next, a structure of the terminal 200 that determines or predicts a CQI based on a correction factor for a current channel received from the calibration factor determination apparatus 100 and feeds it back to the base station 300 will be described with reference to FIG. 7.

7 is a structural diagram of a terminal according to an embodiment of the present invention.

As shown in FIG. 7, the terminal 200 includes a processor 210, a communication interface 220, and a memory 230. In the embodiment of the present invention, for convenience of explanation, the above structure is described as an example, but the structure of a general mobile terminal may be further included.

When the processor 210 receives the calibration factor from the calibration factor determination apparatus 100 through the communication interface 220, the CQI value for the current channel using the received calibration factor (hereinafter,'first (Referred to as'CQI value'). Then, the feedback is first to the base station 300 through the communication interface 220. Herein, a method for the processor 210 to check the CQI value using a correction factor is known, and detailed description thereof will be omitted in the embodiment of the present invention.

In addition, the processor 210 predicts a CQI value for the next channel (hereinafter, also referred to as a'second CQI value' for convenience of description). Further, the processor 210 calculates a difference between consecutive CQI values by using the first CQI value and the second CQI value.

The processor 210 applies only the difference between the first CQI value and the second CQI value to the CQI feedback bit, and feeds it back to the base station 300 through the communication interface 220. Further, the difference between the first CQI value, the second CQI value, and the CQI value is temporarily stored in the memory 230. In addition to CQI values, the memory 230 stores various programs and information for executing the terminal 200.

A procedure in which the calibration factor determination apparatus 100 and the terminal 200 described above obtain a calibration factor using a calibration procedure technique and feed back the CQI to the base station 300 will be described with reference to FIG. 8.

8 is a flowchart illustrating a method of determining a correction factor and feedback CQI according to an embodiment of the present invention.

As shown in FIG. 8, the calibration factor determination apparatus 100 checks the SNR of subcarriers with respect to the signal received in the OFDM system (S100), and derives a calibration factor from the checked SNR (S110).

The calibration factor determination apparatus 100 transmits the calibration factor derived in step S110 to the terminal 200 (S120). The terminal derives an effective SNR for a corresponding channel using the calibration factor derived by the calibration factor determination apparatus 100, and selects a CQI using the effective SNR (S130). The terminal 200 temporarily stores the selected CQI and feeds it back to the base station 300 as the CQI of the current channel (S140). Here, the CQI fed back from the terminal 200 to the base station 300 is referred to as a first CQI.

The terminal 200 predicts a second CQI for the current channel by using the stored first CQI (S150). Here, since there are various methods of predicting the second CQI for the current channel by the terminal 200 using the first CQI, detailed descriptions are omitted in the embodiment of the present invention.

After calculating the difference value between the second CQI and the first CQI (S160), the terminal 200 feeds back only the difference value as a second CQI, which is the CQI of the next channel, to the base station 300 (S170). In this case, a method of feeding back the CQI value from the terminal 200 to the base station 300 in step S170 will be described with reference to Table 3.

The terminal 200 feeds back CQI to the base station 300 using a 3-bit CQI feedback scheme based on time-coherence.

That is, in a low SNR environment, the difference in CQI feedback between channels is not large, and low-level CQIs (CQI 0, CQI 1, and CQI 2) are frequently fed back. In consideration of this, 2-bit CQI feedback is applied to a specific CQI, thereby reducing bits for CQI feedback.

는 2로 계산된다.

는

와 동일하므로,

도 2가 됨을 알 수 있다.As shown in Table 3, it is assumed that _{CQI k -1, which} is a previous CQI value, is determined as 8 from the viewpoint of the terminal 200, _{and that CQI k} is calculated as 10 when the current CQI value is calculated. Then, the difference between the two values

Is calculated as 2.

Is

Is the same as,

It can be seen that FIG. 2 becomes.

를 8로 나눈 나머지인 2를 이진수로 바꾸어 FBk=010을 얻고 이를 기지국(300)으로 전송함으로써, 기존에 4비트로 전송하던 CQI 값을 3비트로 1비트 줄여 전송할 수 있게 된다.The terminal 200

By converting 2, which is the remainder of dividing by 8, into a binary number to obtain FBk = 010 and transmitting it to the base station 300, the CQI value previously transmitted in 4 bits can be reduced by 1 bit to 3 bits.

A method of restoring the CQI by the base station 300 that has received the CQI value transmitted by the terminal 200 will be described with reference to Table 4 below.

가 2임을 확인할 수 있다. 기지국(300)은

는

와 동일하므로,

도 2가 됨을 알 수 있다.As shown in Table 4, when the base station 300 receives the FBk 010 as an input from the terminal 200, the base station 300

It can be seen that is 2. The base station 300 is

Is

Is the same as

It can be seen that FIG. 2 becomes.

Accordingly, the base station 300 confirms that the CQI of the current channel is 10 by adding 2 for the current channel to 8, which is the CQI value for the previous channel transmitted from the terminal 200.

Meanwhile, a procedure for deriving a correction factor by the calibration factor determination apparatus 100 in step S110 will be described in detail with reference to FIG. 9.

9 is a flowchart of a method of deriving a correction factor according to an embodiment of the present invention.

As shown in FIG. 9, the calibration factor determination apparatus 100 defines a valid interval for calculating the effective SNR from the SNR of the subcarriers with respect to the signal received in the OFDM system (S111). The correction factor determination apparatus 100 calculates noise variances corresponding to each of the plurality of SNRs in the defined valid period (S112), and then generates a plurality of channels from each of the plurality of SNRs (S113).

After generating a plurality of channels, the calibration factor determining apparatus 100 generates encrypted additive noises for each of the channels (S114). In addition, the calibration factor determination apparatus 100 determines BLER _reals by decoding a virtual received signal including additive noises.

_{In addition, the calibration factor determination apparatus 100 checks the BLER eff} by mapping the effective SNR to the additive white Gaussian noise-BLER lookup table (S115), and then calculates the difference between the two values _{BLER real} and BLER _{eff (S116).} The calibration factor determination apparatus 100 derives a value at which the difference between the two values calculated in step S116 is the minimum as a calibration factor (S117).

Although the embodiments of the present invention have been described in detail above, the scope of the present invention is not limited thereto, and various modifications and improvements by those skilled in the art using the basic concept of the present invention defined in the following claims are also provided. It belongs to the scope of rights.

Claims (12)

As a method for determining a correction factor for link quality estimation by a calibration factor determination device,
Receiving a plurality of CQI indexes and a correction parameter candidate group of each CQI index as an input, and defining a valid period including a plurality of SNRs for each of the CQI indexes,
Generating a plurality of channels for each of a plurality of SNRs included in the valid period,
Generating additive noise for each of the generated channels, and confirming actual block error rates (BLER) and effective BLER from the additive noise, and
The step of deriving a value at which the difference between a plurality of effective BLERs and a plurality of actual BLERs is minimum as a correction factor
Correction factor determination method comprising a. The method of claim 1,
The valid interval is a method of determining a correction factor defined so that the BLER of each CQI index is between 0.9 and 0.001. The method of claim 2,
The step of defining the valid interval,
Calculating noise variance for each of the plurality of SNRs
Including,
A method for determining a calibration factor in which an effective SNR is calculated based on the generated channels, the noise variance, and the calibration parameter candidate group. The method of claim 3,
Checking the valid BLER,
Generating the additive noises from channel state information for each of the channels,
Decoding the received signal including the additive noises to check the actual BLER, and
Mapping the effective SNR to an additive white Gaussian noise-BLER lookup table for each channel, and checking the effective BLERs
Correction factor determination method comprising a. The method of claim 4,
The step of deriving the correction factor,
Checking the channel in which the effective BLER derived by the calibration factor and the actual BLER are confirmed as the current channel to be used by the terminal
Correction factor determination method further comprising a. As a calibration factor determination device that determines a calibration factor for link quality estimation,
A channel generator that generates a virtual channel,
Effective SNR for all stored CQI indexes is obtained, an effective period for an effective SNR is determined based on channel state information for the virtual channel, and an actual block error (BLER) for a plurality of SNRs included in the valid period is determined. Rate) and valid section definition section that checks the valid BLER,
A correction factor candidate group confirmation unit that checks a calibration parameter candidate group based on the noise calculated for each of the generated plurality of channels and the valid period, and
A calibration factor determination unit that calculates an effective SNR using the calibration parameter candidate groups and determines a calibration factor using the effective BLER checked using the effective SNR and the actual BLER checked through the calculated noise
Calibration factor determination device comprising a. The method of claim 6,
The channel generator,
A calibration factor determination apparatus for generating a plurality of channels for each of a plurality of effective SNRs included in the valid period. The method of claim 7,
The valid section definition unit,
A correction factor determination device that defines the effective SNR of each CQI index to be between 0.9 and 0.001. The method of claim 8,
The correction factor determination unit,
An apparatus for determining a correction factor for estimating an effective BLER for the channel by mapping the effective SNR to an additive white Gaussian noise-BLER lookup table. The method of claim 9,
The correction factor determination unit,
A calibration factor determination device for deriving a value at which the difference between a plurality of effective BLERs and a plurality of actual BLERs is minimum, as the calibration factor. delete delete

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