KR20090061234A - Method for transmitting multi-level threshold based channel quality indicator - Google Patents

Abstract

A method for transmitting a multi-level threshold based channel quality indicator is provided to report a CQI in consideration of various threshold levels, thereby reducing signaling overhead in a transceiving terminal and flexibly operating a system. Channel quality of each sub band is compared with a plurality of threshold levels. The sub bands is formed by grouping a predetermined number of sub carriers. A sub band having channel quality more than each threshold level is selected per each threshold level. Location information and CQI(channel quality indicator) information of the selected sub band are generated. The location information and CQI information are transmitted to a base station.

Description

Method for Transmitting Multi-Level Threshold Based Channel Quality Indicator

The present invention relates to a method for transmitting a channel quality indicator in a mobile communication system, and more particularly, to a method for generating and transmitting a channel quality indicator based on multiple threshold levels.

It is efficient to feed back channel information for efficient communication. To this end, downlink channel information is usually sent uplink and uplink channel information is sent downlink. This channel information is referred to as a channel quality indicator, that is, a CQI (Channel Quality Indicator). This CQI can be generated in several ways. For example, there is a method of quantizing and raising a channel state as it is, a method of calculating and raising an SINR, and a method of notifying a state in which a channel is actually applied, such as a modulation coding scheme (MCS).

Among the various CQI generation methods, in fact, many CQIs can be generated based on MCS. An example of this is CQI generation for a transmission scheme such as HSDPA in 3GPP. As such, when the CQI is generated based on the MCS, in detail, the MCS includes a modulation scheme, a coding scheme, and a coding rate according thereto. Therefore, since the CQI needs to be changed according to the change in the modulation scheme and the coding scheme, at least one CQI is required per codeword unit.

If MIMO is applied to the system, the number of required CQIs also changes. That is, since a MIMO system generates multiple channels using multiple antennas, multiple codewords are usually available. Therefore, multiple CQIs must be used. When a plurality of CQIs are used in this way, the amount of control information accordingly increases proportionally.

1 is a conceptual diagram for generating and transmitting a CQI.

The terminal 100 measures downlink quality and reports the selected CQI value to the base station through the uplink control channel. The base station 200 performs downlink scheduling (terminal selection, resource allocation, etc.) according to the reported CQI. Here, the CQI value includes a signal to interference and noise ratio (SINR), a carrier to interference and noise ratio (CINR), a bit error rate (BER), a frame error rate (FER), and the like, which are converted into transmittable data. Can be mentioned. In addition, in the MIMO system, information in which the RI (Rank Information), the Precoding Matrix Information (PMI), etc., reflects the channel state may be added to the CQI value.

In the mobile communication system, link adaptation is used to maximize the given channel capacity of a channel. Such link adaptation provides a method of adjusting a modulation and coding set (MCS) and a transmission power according to a given channel. In order to perform such link adaptation in the base station, the user must feed back channel quality information to the base station.

If the frequency band used by the system exceeds the coherence bandwidth, the channel shows a drastic change in the system bandwidth. In particular, in a multi-carrier system such as orthogonal frequency division multiplexing (hereinafter referred to as "OFDM"), several sub-carriers exist within a given bandwidth and are modulated through each subcarrier. Symbol) is transmitted, the optimal channel transmission is to transmit the channel information for each subcarrier. Therefore, in a multicarrier system having a large number of subcarriers, the feedback amount of channel information is rapidly increased.

On the other hand, in order to reduce the increase in the feedback amount of the channel information as described above, a method of transmitting a channel quality indicator for each subcarrier group (Subcarrier Group) or subband (Subband) formed by grouping a plurality of subcarriers, specific A method of setting a threshold and transmitting a channel quality indicator only for a subcarrier group or subband indicating channel quality above the threshold has been proposed. In particular, in the above-described threshold-based channel quality indicator transmission scheme, it is very important to select a threshold level appropriately since the width / number of subbands selected may vary according to the selected threshold level. In other words, if a high threshold level is selected, only subbands having relatively high channel quality are selected, so that the amount of transmission that needs to be fed back can be reduced when the channel environment is good, but when the channel environment is poor, the number of users to be supported It may not be possible to support it, and if you select a low threshold level, you may select subbands with relatively low channel quality, thereby increasing the amount of transmission that needs to be fed back, but a sufficient number of channels may be used even in a bad channel environment. It can have the advantage of supporting users.

Therefore, it is effective to select the optimal threshold level in accordance with various environments such as the channel state or the number of users in the base station. However, in order to change the threshold level continuously in this manner, a large number of measurements and calculations are required, and accordingly, there is a disadvantage in that signaling of a transmission / reception period is required.

An object of the present invention for solving the above problems is to propose a method for effectively transmitting the channel state information in order to reduce the total amount of transmission when the channel state information is to be transmitted efficiently in the frequency selective channel.

More specifically, in the above-described threshold-based channel quality indicator transmission method, as described above, rather than setting and using the threshold level variably according to the channel environment, the transmission and reception by reporting the channel quality indicator in consideration of various threshold levels. To reduce the signaling overhead of the stage and to provide a way to operate the system flexibly.

In addition, in order to perform the above-described multi-threshold level-based channel quality indicator transmission method, a method of generating a channel quality indicator and a method of transmitting location information of a subband generating a channel quality indicator are provided.

In one aspect of the present invention for solving the above problems, there is provided a method for a user equipment to transmit a channel quality indicator (CQI). According to an embodiment of the present invention, a method for transmitting channel quality indicators includes: (a) comparing a channel quality in each of subbands formed by grouping a predetermined number of subcarriers with a plurality of threshold levels, and then selecting each of the plurality of subbands. Selecting subbands having channel quality equal to or greater than a threshold level for each threshold level, (b) generating location information of the subbands selected for each threshold level and channel quality indicator information in the selected subband, And (c) transmitting the generated location information and channel quality indicator information to a base station.

In the step (a), when selecting the plurality of subbands, when the subbands having channel quality equal to or greater than each threshold level are sequentially selected from the highest threshold level to the lowest threshold level among the plurality of threshold levels, It is preferable to optimize the amount of channel quality information transmission except for subbands having channel quality above the previous threshold level among subbands having channel quality above each threshold level.

In addition, the channel quality indicator information generated in the step (b) may be generated by calculating the channel quality information of the subbands selected in the step (a) by considering an arithmetic mean value or channel capacity for each threshold level. Do.

In addition, the location information of the subbands generated in the step (b) may be represented through a bitmap, and in particular, the bitmap may include a channel quality of each of the plurality of subbands and a plurality of thresholds. Most preferably, it is set to indicate the result of comparison with each level.

According to the embodiments of the present invention as described above, in transmitting the channel state information in the frequency selective channel, it is possible to reduce the overall transmission amount and effectively transmit the channel state information.

More specifically, in the above-described threshold-based channel quality indicator transmission method, as described above, rather than setting and using the threshold level variably according to the channel environment, the transmission and reception by reporting the channel quality indicator in consideration of various threshold levels. The signaling overhead of the stage can be reduced and the system can be operated flexibly.

In addition, when generating a channel quality indicator to perform the above-described multi-threshold level-based channel quality indicator transmission method, by transmitting the average value for each threshold level, the multi-threshold level transmission scheme can be more effectively operated while reducing the amount of channel quality information. In addition, the overhead may be further reduced by setting to indicate whether the position information of each subband is selected or not selected among the multiple threshold levels.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The detailed description, which will be given below with reference to the accompanying drawings, is intended to explain exemplary embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. For example, the following description will be described with reference to specific examples applied to the above-described 3GPP LTE system for clarity, but the present invention is not only a 3GPP LTE system but also any communication requiring feedback of downlink channel quality information in general. Applicable to the system.

The following detailed description includes specific details in order to provide a thorough understanding of the present invention. However, one of ordinary skill in the art appreciates that the present invention may be practiced without these specific details. In some instances, well-known structures and devices are omitted or shown in block diagram form, centering on the core functions of each structure and device, in order to avoid obscuring the concepts of the present invention. In addition, the same components will be described with the same reference numerals throughout the present specification.

As described above, an embodiment of the present invention provides a method for generating and transmitting a channel quality indicator by reducing the amount of feedback of channel quality information and the amount of position information of a frequency band corresponding to the channel quality information in a mobile communication system. I would like to. To this end, in general, we will look at the various methods that can be considered in order to reduce the overhead in general CQI generation and transmission.

First, a method of changing the unit of channel information transmission is possible. For example, in the OFDM scheme, channel information transmitted for each subcarrier is bundled into one subcarrier group, and channel information is transmitted in the corresponding group unit. That is, in the OFDM method using 2048 subcarriers, if 12 subcarriers are collected and formed into one subcarrier group, a total of 171 subcarrier groups are formed, and thus the amount of channel information actually transmitted is reduced from 2048 to 171.

In the following description of the present invention, when a frequency band is divided into subcarriers as in the OFDM scheme, one or more subcarriers are grouped into one group, and the CQIs are reported by dividing the subcarrier group units. The basic unit of the method is defined as "CQI subcarrier group" or "CQI subband".

On the other hand, if the frequency band is not distinguished with each subcarrier, the entire frequency band is divided into some frequency bands, and the CQI is generated based on the divided frequency bands, and the divided frequency bands for the CQI generation are generated. It is also defined as "CQI subband".

In addition, such a CQI subband may also be referred to simply as a "subband".

Next, a method of generating CQI by compressing channel information is possible. For example, in the OFDM scheme, channel information for each subcarrier is compressed and transmitted using a specific compression scheme. As the compression method, methods such as a discrete cosine transform (DCT) may be considered.

In addition, a method of generating a CQI by selecting a corresponding frequency band for generating channel information is possible. For example, instead of transmitting channel information for every subcarrier in the OFDM scheme, a Best-M scheme for selecting and transmitting the best M among subcarriers or subcarrier groups may be possible.

When transmitting the CQI by selecting the frequency band, the actual transmitted part can be largely divided into two parts. The first is the CQI value part and the second is the CQI index part.

2 is a diagram for describing a method of generating a CQI by selectively setting a CQI subband in a frequency domain.

In the graph shown at the top of FIG. 2, the horizontal axis represents the frequency axis and the vertical axis represents the CQI value in each frequency domain. In addition, in the upper graph of FIG. 2, the horizontal axis is divided into subband units in which a plurality of subcarriers are grouped, and an index is assigned to each subband.

The frequency band selective CQI scheme consists of three parts. The first step is to select a frequency band for generating CQI, that is, a CQI subband. The second step is to manipulate and generate and transmit CQI values of the selected frequency bands. Third, the index of the selected frequency band, that is, CQI subbands is transmitted.

FIG. 2 shows examples of a best-m scheme and a threshold-based scheme as an example of selecting a CQI subband in a first step.

The Best-M scheme is a method of selecting M CQI subbands having good channel states. In the example shown in FIG. 2, the CQI subbands having good channel states are selected using the Best-3 scheme. An example of selecting is shown. In addition, the threshold-based scheme is a technique for selecting a CQI subband having a channel state higher than a predetermined threshold. In the example of FIG. 2, the CQI sub-index of indexes 5 and 6 higher than the threshold T is shown. An example of selecting a band is shown.

Meanwhile, FIG. 2 illustrates an example of an individual transmission method and an average transmission method as an example of a method of generating and transmitting CQI values in a second step. The separate transmission method is a method of transmitting all CQI values of the CQI subband selected in the first step. Therefore, in the individual transmission scheme, as the number of selected CQI subbands increases, the CQI values to be transmitted also increase. Meanwhile, the average transmission method is a method of transmitting an average of CQI values of the selected CQI subband. Therefore, the average transmission method has the advantage that the CQI value to be transmitted is one irrespective of the number of the selected CQI subbands, while transmitting the average of several CQI subbands, so that the accuracy is inferior. Here, the method of calculating the average may be a simple arithmatic average method or an average method in consideration of channel capacity.

In FIG. 2, the CQI generation and transmission method in the second step is described using an example in which CQI subbands 5, 6, and 9 are selected by the Best-3 method in the first step. That is, in the second step, when the separate transmission method is used, the CQI values 7, 6, and 5 of the subbands 5, 6, and 9 are generated / transmitted separately, respectively. , 9 shows an example in which 6 arithmetic average of each CQI value is generated / transmitted.

In FIG. 2, a bitmap index scheme and a general combination index scheme are illustrated as examples of a method of transmitting an index of a CQI subband in a third step. Bitmap indexing is a method of allocating one bit for every CQI subband, assigning 1 if the corresponding CQI subband is used, and 0 if not used, indicating which CQI subband is used. it means. This bitmap index method has a disadvantage in that the number of bits as many as the total CQI subbands is required. However, the bitmap index method has an advantage that it can always be represented by a certain number of bits regardless of how many CQI subbands are used. On the other hand, the combination index method is a method of determining how many CQI subbands are used and mapping the number of combinations corresponding to the number of CQI subbands used in the total CQI subbands to each index. In more detail, when there are a total of N CQI subbands and M CQI subband indices among the N are used for CQI generation, the total number of possible combinations is as follows.

The number of bits for representing the number in the case of Equation 1 may be determined by Equation 2 below.

)In the example of FIG. 2, since three CQI subbands are selected from a total of 11 CQI subbands, the number of possible cases is ₁₁ C ₃ = 165, and the number of bits for indicating the 165 is 8 bits. (

)

An embodiment of the present invention to be described below relates to a method of more efficiently improving a threshold-based CQI transmission method among the above-described CQI generation and transmission schemes. To this end, a general threshold-based CQI transmission method will be described in more detail.

The threshold based CQI generation technique is a technique for selecting a CQI subband having a channel state over a predetermined threshold level. Since the width / number of CQI subbands selected according to the threshold level becomes wrong, selection of the threshold level is very important in this scheme. In addition, when the CQI subband is selected, CQI subbands having a good channel environment to a relatively bad channel environment are selected according to high and low threshold levels.

More detailed description is as follows. That is, by selecting a CQI subband having a channel environment that exceeds the threshold level by the high threshold level, only the CQI subband having a good channel environment is selected. As a result, the number of targets to be transmitted is reduced. However, when the channel environment is not good, too few CQI subbands are selected and reported, so that the base station does not contend with many users in one CQI subband, thereby providing sufficient multiuser diversity. (Multiuser diversity) has a disadvantage that may not support the number of users.

On the other hand, since the CQI subband having a channel environment over the threshold level is selected by the low threshold level, the CQI subband larger or larger than the channel environment represented by the threshold level is selected. Since the CQI subband is selected by a low threshold level, a large amount is selected from subbands having a relatively good channel environment to subbands having a relatively bad channel environment. Therefore, although the transmission target may have a disadvantage of increasing, it may have an advantage of supporting a sufficient number of users even when the channel environment is not good.

Therefore, it is effective to select the optimal threshold level according to various environments such as the channel state or the number of users in the base station. However, in order to variably change the threshold level as described above, many measurements and calculations may be required as described above, and accordingly, signaling of a transmission / reception period may be required.

Accordingly, an embodiment of the present invention proposes a method of setting a plurality of threshold levels from the first threshold level setting, and generating and informing a plurality of CQIs according to the plurality of threshold levels set as described above. When the CQI subbands are selected using a plurality of threshold levels as proposed in the present embodiment, it is possible to select a subband indicating good channel quality through a relatively high CQI threshold level, and to select a relatively low threshold level. Through this, it is possible to classify subbands having a relatively poor channel state and select them as necessary.

As described in the present embodiment, a method of transmitting CQI using a plurality of threshold levels will be referred to as a multi-level threshold based CQI generation or transmission scheme.

The above-described multi-level threshold based CQI transmission scheme is briefly described for each execution step as follows. In the CQI transmission method according to the present embodiment, first, a channel quality of each subband formed by grouping a predetermined number of subcarriers is compared with a plurality of threshold levels, and the channel quality of each of the plurality of subbands has a channel quality equal to or greater than each threshold level. A subband is selected for each threshold level. Thereafter, location information of the selected subbands for each threshold level and CQI information of the selected subbands are generated. In this case, the CQI values in the selected subbands may be individually represented as they are, respectively, or may be represented as an arithmetic mean value of each CQI values or an average value considering channel capacity. In addition, as described above, the position information of the selected subbands may indicate each subband index by a general bitmap method or a combination index method.

Lastly, when location information and CQI information are generated as described above, it is transmitted to the base station.

The multi-level threshold based CQI transmission scheme according to the above-described embodiment will be described below with a specific example.

3 is a diagram illustrating a specific example for explaining a method of transmitting a CQI according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating channel quality values in each subband by grouping subcarriers within an entire frequency domain into 12 subbands. In FIG. 3, the horizontal axis represents a frequency axis, and the lower axis represents each subband index and CQI value in each subband. 3, the vertical axis represents CQI value.

3 shows an example in which four threshold levels are set as multiple thresholds. Specifically, four threshold levels show an example in which threshold 1, threshold 2, threshold 3, and threshold 4 are set to 3, 4, 5, and 6, respectively. Doing.

According to the threshold level, reference numeral 301 indicates subbands selected for each threshold level. Therefore, 8, 9 are selected as subband indexes indicating channel quality of the threshold 4 or more, 5, 8, 9, 10 are selected as subband indexes representing the channel quality of the threshold 3 or more, and the sub-bands representing channel quality of the threshold 2 or more. 5, 8, 9, 10, and 11 are selected as band indices, and 4, 5, 6, 7, 8, 9, 10, and 11 are selected as subband indices representing channel quality equal to or greater than the threshold 1.

As another example of threshold setting, a method of relatively determining a threshold value is not considered absolutely. That is, if the foregoing description and the example of FIG. 3 are used as it is, the threshold 4 indicates a channel having a difference of 1 or less from the maximum CQI value having the best channel state, and the threshold 3 is a CQI value with the threshold value of the threshold 4. It is possible to indicate a channel having a difference of 1 or less, and likewise, threshold 2 and threshold 1 may be set so that the difference between CQI values is 1 or less as a comparison target. Here, in order to use the same example as in FIG. 3, the width of the difference in the CQI values between the thresholds is set to 1, but in actual applications, the difference in the various CQI values may be used for each threshold. Like the above threshold setting, the threshold setting can be set not as an absolute value but as a difference value (change range) of the CQI between the threshold values. It should be noted, however, that the highest threshold here represents the difference from the best channel condition.

As described above, when each threshold level is sequentially set according to the degree of the CQI value, the threshold of the next level selected after the highest level threshold includes all subbands selected in the previous step. That is, in the threshold-based CQI generation method, since the selection of the subband basically selects the subband indicating the channel quality above the corresponding threshold, when using a plurality of threshold levels as in the present embodiment, the threshold below the highest threshold level is used. Since the subbands selected in the level include the subbands selected in the previous step, a kind of waste may be generated.

Therefore, in a preferred embodiment of the present invention, when the subbands having the channel quality above each threshold level are selected in the order of the higher threshold levels, the subbands having the channel quality values above the specific threshold level are selected in the previous step. Suggest to choose except those. That is, even if the CQI subbands selected in the previous step have channel quality values equal to or greater than the threshold level of the current step, the CQI subbands are considered to have been represented by the previous step and are omitted and represented in the current subband selection.

In 301 of FIG. 3, the subband index selected according to this preferred embodiment is indicated in bold letters. That is, 8, 9 as a subband index having a channel quality value of threshold 4 or more, 5, 10 as a subband index having a channel quality value of 3 or more threshold, 11 as a subband index having a channel quality value of 2 or more threshold value, 4, 6, and 7 are selected as subband indices having a channel quality value equal to or greater than the threshold 1. FIG.

Meanwhile, reference numeral 302 of FIG. 3 indicates how to represent channel quality values of the selected subbands as shown by reference numeral 301. In the present embodiment, there is no need to particularly suggest a method for representing the CQI values of the selected subbands as described above. However, in one preferred embodiment of the present invention, it is proposed to calculate and calculate an average value for each subband selected according to each threshold level. In this case, the average value may be a simple arithmetic mean or an average value considering channel capacity.

In general, the method of calculating and transmitting the average of the CQI values has the advantage of reducing the transmission amount of the CQI values as described above, but has the disadvantage of not correctly transmitting the CQI values for each subband. However, when the CQI value is averaged for each threshold level and transmitted according to the present embodiment as described above, the average value calculated for each threshold level is not transmitted as a single CQI value in the selected subband. By being transmitted, it is possible to distinguish between subbands representing a relatively high CQI value and subbands representing a relatively low CQI value.

As another example, a method may be considered in which only the average of the CQI values belonging to the CQI subbands corresponding to the highest threshold value or more and the average of the CQI values corresponding to other threshold values are not sent. Let's look at why this is possible. If the threshold is set absolutely, then the channel above the highest threshold may have several values, and therefore must transmit the average of the CQI values. However, since the threshold afterwards can be known which CQI values already exist, it is only necessary to know the CQI subband index corresponding to the threshold, and the CQI average value can be sufficiently calculated by the receiver. As another example, if the threshold is set relatively, the average of the highest CQI value corresponding to the highest threshold should also be transmitted since the receiver does not know, but the difference in CQI from the second higher threshold is determined by the threshold setting originally promised. Can be. That is, the average of the CQI values corresponding to each threshold value is directly obtained at the receiver by the difference between the upper threshold value and the CQI value determined at the threshold setting.

In addition, according to the above-described embodiment, since the total number of transmitted CQI values is equal to or greater than the number of threshold levels, the number of CQI values becomes equal to, and thus, the number of transmitted CQI values can be kept constant.

On the other hand, although not considered in the various method embodiments of transmitting the CQI values, let us consider a further transmittable CQI value. As such a further transmittable CQI value, a method of transmitting an average of CQI values corresponding to a band smaller than the last threshold, that is, a CQI subband not selected anywhere can be considered. The CQI average value of the CQI subband lower than the lowest threshold may be used as an indicator indicating how bad the corresponding channel is.

In FIG. 3, an example showing CQI values of selected subbands as shown by reference numeral 301 for each threshold level is illustrated. Accordingly, 3 for threshold 1, 4 for threshold 2, and 3 for threshold 3 are shown. 5, a CQI value of 6 is generated for the threshold 4. Of course, in the reference numeral 302 of FIG. 3, when the subband is selected by the reference numeral 301, the subbands representing the channel quality values above the threshold level are selected in the order of the higher threshold levels. The method of selecting except for the threshold level of the step is shown.

Next, reference numeral 303 of FIG. 3 exemplarily illustrates a method of indicating position information of selected subbands as shown by reference numeral 301.

In general, the CQI subband index may use a bitmap method or a combined index method. However, when the threshold based method is used in the CQI subband selection method, it is advantageous to use the bitmap method. The reason for this is that the number of CQI subbands selected in the threshold-based CQI generation method varies according to the change in the channel state even if there is no change in the threshold level. This is because the number of indexes is also variable. When the indexes of the CQI subbands selected in this way are variable, the number of bits required for transmission is variable in the combined index method, which is undesirable in designing control information. On the other hand, if the bitmap index scheme is applied, it is possible to transmit the index of the selected CQI subband using a constant number of bits regardless of the number of selected CQI subbands. It is more suitable for.

Therefore, after selecting the CQI subbands for each threshold level, suppose that the bitmap scheme is used as a method of transmitting the indexes of the selected CQI subbands. Then, since one bitmap index is needed for each threshold level, the total number of required bitmap indexes is required by the number of threshold levels. However, the preferred embodiment of the present invention provides an index generation and transmission method suitable for the multi-level threshold based CQI transmission scheme according to the above-described embodiments of the present invention, rather than the general bitmap scheme.

In general, a bitmap index allocates a value of 1 when a CQI subband corresponding to each bit is selected from a bitmap, and assigns a value of 0 when not selected. Therefore, in the case of using such a general bitmap scheme, according to the above-described multilevel threshold based CQI generation and transmission scheme, a bitmap as many as the total threshold levels is required. However, the CQI subbands represented by the respective bits in the bitmaps corresponding to each threshold level are the same. Therefore, there is a waste of forming a bitmap in duplicate for the same subband. Therefore, in this embodiment, not one bit indicates whether a specific CQI subband is selected in each bitmap, but for which threshold level among the multiple threshold levels is selected through one bitmap ( Or a plurality of bits for each subband so as to express the number of bits per subband.

That is, compared with the existing bitmap index method, a plurality of bits are allocated to an index for representing each CQI subband. Through the plurality of bits, a method of informing whether a threshold level of CQI subbands corresponding to the plurality of bits is selected (or not selected by any threshold level) may be considered.

Specifically, for example, as in the case of FIG. 3, there are four threshold levels, and consider the case in which there are 12 CQI subbands. In the conventional method, since 12 bits are required as a bitmap index per threshold and 4 bitmap indexes are required in total, the total number of bits required for the bitmap index is 48 (= 12 * 4). However, according to the present embodiment, two bits (2 = log ₂ 4) are allocated per CQI subband, and the two bits are used to indicate on which threshold level the corresponding CQI subband is selected. It is possible. For example, 0 (= 00) of a combination of 2 bits indicates the highest threshold level (e.g., threshold 4 of FIG. 3), and 1 (= 01) indicates the next highest threshold level (e.g., FIG. Threshold 3 of 3, 2 (= 10) is the next threshold level (e.g., threshold 2 of FIG. 3), and finally 3 (= 11) is the lowest threshold level (e.g., FIG. 3). It is possible to represent the threshold value of 1). Using this proposed method, the total number of bits needed to transmit the CQI index is 24 (= 12 * 2). Thus, there is about 50% bit reduction compared to the conventional method.

On the other hand, in the above-described embodiment, it may be necessary to indicate a case where each subband is not selected by any threshold level as well as by which threshold level. In such a case, the number of bits allocated to each subband can be set so as to additionally indicate a case in which it is not selected by any threshold level. For example, reference numeral 303 of FIG. 3 indicates, in an example using four threshold levels, that each of the subbands is selected by which of the four threshold levels one, two, three, The case where it is set to show through 4 and is not selected by any index level is shown to show through 0. In this case, it can be seen that an additional 1 bit is required to indicate each case for each subband. Preferably, in setting a plurality of threshold levels, the number of bits required by selecting the sum of the number of threshold levels each subband is selected and the number of cases where no threshold level is selected is represented by a power of 2 is reasonable. Can be selected.

For example, when each subband is selected through a bitmap of 12 subbands as shown in FIG. 3, by using three threshold levels, which threshold level is selected for each subband through two bits. Or it may indicate whether or not selected by any threshold level.

The detailed description of the preferred embodiments of the invention disclosed as described above is provided to enable any person skilled in the art to make and practice the invention. Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art will variously modify and change the present invention without departing from the spirit and scope of the invention as set forth in the claims below. I can understand that you can.

For example, while the description of the preferred embodiments of the present invention as described above has been described with reference to the example of 3GPP LTE in generating and transmitting the CQI, the CQI generation method and user equipment therefor according to the present invention are 3GPP. It can be applied to any system that requires feedback on downlink channel quality, such as not only LTE but also an IEEE 802 series communication method.

In addition, in the above description, a "base station" generally refers to a fixed station for communicating with a user equipment, and includes a node-B, a base transceiver system, and an access point. Or other terminology. In addition, in the above description, "user" is any subject that may be fixed or mobile, and may be any terminal, user terminal (UT), subscriber station (SS), wireless device, or the like. It may also be referred to as other terms of.

Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

According to the multi-threshold level-based CQI generation and transmission method according to the embodiments of the present invention as described above, it is possible to transmit as much channel information as possible while minimizing overhead in generating and transmitting a channel quality indicator. In addition to the 3GPP LTE system described as a specific example in one description, it may be used in any wireless communication system requiring feedback on downlink channel quality.

1 is a conceptual diagram for generating and transmitting a CQI.

2 is a diagram for describing a method of generating a CQI by selectively setting a CQI subband in a frequency domain.

3 is a diagram illustrating a specific example for explaining a method of transmitting a CQI according to an embodiment of the present invention.

Claims (9)

In the method for the user equipment to transmit a Channel Quality Indicator (CQI), (a) comparing the channel quality in each of the subbands formed by grouping a predetermined number of subcarriers with a plurality of threshold levels, and subbands having a channel quality equal to or greater than each threshold level among the plurality of subbands, respectively; Selecting each star; (b) generating location information of the selected subbands and channel quality indicator information in the selected subband for each threshold level; And (c) transmitting the generated location information and channel quality indicator information to a base station. The method of claim 1, In step (a), when selecting the plurality of subbands, when selecting a subband having channel quality equal to or greater than each threshold level sequentially from the highest threshold level to the lowest threshold level among the plurality of threshold levels, And selecting subbands having channel quality equal to or greater than the previous threshold level except subbands having channel quality equal to or greater than each threshold level. The method of claim 1, The channel quality indicator information generated in the step (b) is generated by calculating the channel quality information of the subbands selected in the step (a) by calculating an average value considering the arithmetic mean value or channel capacity for each threshold level. Transmission method. The method of claim 3, wherein The channel indicator information transmitted to the base station in step (c) includes only an average value calculated for the highest threshold level among the plurality of threshold levels. And transmitting the average value calculated for the remaining threshold levels of the plurality of threshold levels. The method of claim 4, wherein The base station determines a mean value for the remaining threshold levels by a fixed channel quality value for each preset threshold level, or a preset difference for each of the plurality of threshold levels and a channel quality value for the highest threshold level and each of the remaining threshold levels. A channel quality indicator transmission method, calculated using values. The method of claim 1, Wherein the plurality of threshold levels are each preset as a predetermined number of different fixed channel quality values. The method of claim 1, The plurality of threshold levels, The channel quality value for the highest threshold level of the plurality of threshold levels is preset to have a predetermined difference value with the highest channel quality value among the channel quality values measured in each of the subbands, And a remaining threshold level of the plurality of threshold levels is preset to have a predetermined difference value from the highest threshold level. The method of claim 1, The location information of the subbands generated in the step (b) is represented through a bitmap, channel quality indicator transmission method. The method of claim 8, And the bitmap is set to indicate a result of comparing a channel quality of each of the plurality of subbands with each of the plurality of threshold levels.

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