ES2735528T3 - Feedback methods and apparatus for channel quality indication in a communication system - Google Patents

Abstract

A communication method, the method comprising the steps of: obtaining channel quality estimates for a plurality of transmission channels; determine, on a first node, a first channel quality indication index depending on an estimate of channel quality of a first transmission channel, and a second channel quality indication index depending on an estimate of channel quality of a second transmission channel; determining a differential channel quality indication index of the second channel quality indication index with reference to the first channel quality indication index depending on a differential compression scheme; and transmitting, through the first node, the first channel quality indication index and the differential channel quality indication index to a second node using a correlation of the differential channel quality indication index with a bit representation, a number of bits for the first channel quality indication index being greater than a number of bits for the differential channel quality indication index, and where the correlation is a complement two correlation scheme.

Description

DESCRIPTION

Methods and apparatus for feedback of channel quality indication in a communication system Background of the invention

1. Field of the invention

The present invention relates to methods and apparatus for feedback of an indication of channel quality in a communication system.

2. Description of the related technique

Table 1 shows an example of a Channel Quality Indication ( CQI) table. Each CQI index in the table represents the channel condition estimated by a mobile station (ie, user equipment or UE). For a given channel condition, the most appropriate CQI index is selected and fed back by the mobile station. As an example, as shown in Table 1, if an index CQI 9 is reported, the UE recommends modulation and coding (Modulation and Coding Scheme, MCS) as phase-shift keying quadrature (Quadrature Phase -Shift Keying, QPSK), 1/4 of code speed (64/256 = 1/4). Note that this recommendation only serves as an input for the base station (ie Node B) to make a programming decision. Node B may or may not follow the EU recommendation. Note also that there are several ways to build the table. For example, the table can be constructed with a subset of the columns as shown in table 1. As an example, the table can consist of the CQI index column, the modulation column and the code rate column . Or, alternatively, the table may consist of the index column of c Q i, the transport block size column ( Transport Block Size, TBS) nominal and (optionally) the modulation column.

Table 1. An example of a CQI table

At present, when a UE feeds a selected CQI index from table 1, the UE has to use 5 bits for the CQI index, which creates a large overhead for the control signal.

WO 2007/112371 A1 discloses a feedback of channel status information for sub-band programming and MIMO in a wireless communication system. Channel quality indicator (CQI) values are obtained for the multiple spatial channels in the multiple subbands. The CQI values are differentially encoded from beginning to end of the multiple spatial channels and the multiple subbands to obtain differential CQI information.

The LG Electronics document: "CQI Overhead Reduction for MIMO in Spatial Domain", 3GPP Draft; R1-0715454, 3rd Generation Association Project (3GPP), Mobile Competence Center; 650, Route Des Lucioles; F-06921 Sophia-Antipolis Cedex; France, vol. RAN w G1, No. St. Julian; 200700403, April 3, 2007 (04-04-2007) refers to the reduction of CQI overhead for MIMO in the space domain. The maximum number of code words for downlink MIMO was decided to be two for a UE. Therefore, the total number of CQI notifications could be two. To reduce the transmission overhead of CQI, it was proposed that one of two CQI notifications be represented in a differential type. Instead of transmitting the c Q i for each code word, the CQI for the first code word and a differential CQI are transmitted with a reduced number of bits in a differential CQI notification scheme.

WO 2009/022873 A2 refers to the transmission of channel quality information in a MIMO system. When multiple code words CQI are transmitted, a specific CQI is selected as a reference. For other CQI, a difference value is transmitted for the reference value. The transmission of differential CQIs can reduce many more bits than in the transmission of the actual value, resulting in the reduction of transmission overhead.

Document CN 101 043 291 A refers to a feedback control technique in an OFDM system. The number of subcarriers is N. In the first example, the transmitter and receiver need to previously establish the signal-to-noise ratio and the NCS. The receiver detects the average of each sub-band data stream that corresponds to the signal-to-noise ratio of the entire band.

The object of the present invention is the provision of a more efficient communication technique that saves bandwidth.

This object is solved by the subject matter of the independent claims.

Preferred embodiments are defined in the dependent claims.

Summary

Therefore, an object of the present invention is the provision of an improved method and apparatus for feedback of a CQI index.

In accordance with one aspect of the present invention, a sub-table is established from an original channel quality indication table. When a channel quality indication index is selected from the channel quality indication sub-table, an index is notified within the sub-table of the selected channel quality indication index.

In accordance with another aspect of the present invention, channel quality estimates are obtained for a plurality of transmission channels. A first channel quality indication index is determined depending on a channel quality estimate of a first transmission channel, and a second channel quality indication index is determined depending on a channel quality estimate of a second channel. of transmission. A differential channel quality indication index of the second channel quality indication index is determined with reference to the first channel quality indication index depending on a differential compression scheme. Then, the first channel quality indication index and the differential channel quality indication index are notified.

In this case, when a terminal receives the first channel quality indication index and the differential channel quality indication index, the terminal obtains the second channel quality indication index depending on the first channel quality indication index. received, the index of differential channel quality indication received and the differential compression scheme.

The differential compression scheme can be established by

(? SB, í - Q ^sb , / - Q ^wb ,

where Qsbj indicates the differential channel quality indication index, Qwb indicates the first channel quality indication index and Qsb, í indicates the second channel quality indication index.

Alternatively, the differential compression scheme that is established by

^{Q sb} , ^í - min I ^ SB , max, max [lSB , min, ^{[Q sb í ~ Q wb])),}

where Qsbj indicates the differential channel quality indication index, Qwb indicates the first channel quality indication index, Qsb, í indicates the second channel quality indication index, / sB, max and IsB, min respectively indicates the upper and lower limits of the differential channel quality indication index, and L indicates a resolution value.

The values of the upper and lower limits of the differential channel quality indication index, / sB, max e / sB, min can be adjusted depending on the value of the first channel quality indication index, Qwb.

As an additional alternative, the differential compression scheme can be established by:

^{Q sb} ,, - min I ^ SB , max, max [lSB , min, ^{[Qw b ¡Q sb í])),}

As an additional alternative, the differential compression scheme can be established by:

^{Sb Q} ,, - min I ^ SB, m Ix max {LSB min, ^{[Q sb í ~ wb A])),}

where A indicates a offset value.

The displacement A can be determined depending on the first index of the Q ^wb channel quality indication, with the displacement A being established by:

A - max (min (QwB - I ^wb , min Default value), Q ^wb + / ^sb , max - / ^wb , m max)

where / ^wb , max e / wB, min respectively indicate the upper and lower limits of the first index of channel quality indication, and Apor defect indicates a certain default offset.

The first channel quality indication index may include more bits than the differential channel quality indication index.

In accordance with yet another aspect of the present invention, channel quality estimates are obtained for a broadband channel and at least one sub-band channel. Depending on the channel quality estimates, a broadband channel quality indication index, and at least one sub-band channel quality index corresponding to the at least one sub channel is determined. band. Then, at least one differential channel quality indication index corresponding to the at least one subband channel quality indication index is determined with reference to the broadband channel quality indication index depending on a differential compression scheme. Finally, the broadband channel quality indication index and the at least one differential channel quality indication index are notified.

In accordance with yet another aspect of the present invention, a broadband channel quality indication (CQI) index and a sub-band CQI index in each sub-band that corresponds to each of a plurality of words of code depending on the channel quality estimates. A first broadband CQI index that corresponds to a first code word is selected as a first reference, and a broadband delta CQI index for each of the other broadband CQI indices that correspond to The other code words are determined with reference to the first broadband CQI index depending on a differential compression scheme. In each sub-band, a sub-band differential CQI index for the sub-band CQI index that corresponds to the first code word is determined with reference to the first broadband CQI index depending on the compression scheme differential. A sub-band delta CQI index for each of the other sub-band CQI indices that correspond to the other code words is determined with reference to the sub-band differential CQI index depending on the compression scheme differential. Finally, the broadband CQI index that corresponds to the first code word is reported, and the broadband delta CQI indexes that correspond to the other code words. The sub-band differential CQI index that corresponds to the first code word, and the sub-band delta CQI indexes that correspond to the other code words are reported in each sub-band.

The broadband CQI index may contain more bits than each sub-band differential CQI index, and each sub-band differential CQI index comprises more bits than each sub-band delta CQI index.

CQI indices can be notified by using a different number of bits in different transmission formats.

In accordance with a further aspect of the present invention, a plurality of channel quality indication indices is determined depending on the channel quality estimates. An average channel quality indication index is calculated based on the plurality of channel quality indication indices. A differential channel quality indication index is determined for each of the plurality of channel quality indication indices with reference to the average channel quality indication index depending on a differential compression scheme. Then, the average channel quality indication index and the plurality of differential channel quality indication indices can be notified with one of the differential channel quality indication indices that are being omitted from the transmission. Then, on the receiver side, the plurality of channel quality indication indices can be obtained depending on the average channel quality indication index and the differential channel quality indication indices with one of them. The invention is defined by the appended claims. Embodiments that do not fall within the scope of the claims are to be construed as useful examples to understand the invention.

Brief description of the drawings

A more complete assessment of the invention, and many of the concomitant advantages thereof, will be immediately apparent when it is best understood by reference to the following detailed description when considered in conjunction with the accompanying drawings, in which similar reference symbols indicate the same or similar components, where:

Figure 1 (a) schematically illustrates a method for calculating a complete CQI index as an embodiment in accordance with the principles of the present invention;

Figure 1 (b) schematically illustrates a method for calculating a differential / delta CQI index as an embodiment in accordance with the principles of the present invention;

Figure 1 (c) schematically illustrates a method for calculating a differential / delta CQI index as another embodiment in accordance with the principles of the present invention;

Figure 2 schematically illustrates a scheme for obtaining a differential CQI in frequency and space as an embodiment in accordance with the principles of the present invention;

Figure 3 schematically illustrates a scheme for obtaining a differential CQI in frequency and space as another embodiment in accordance with the principles of the present invention; Y

Figure 4 schematically illustrates a scheme for obtaining a differential CQI in frequency and space as yet another embodiment in accordance with the principles of the present invention.

Detailed description of the invention

In the present invention, methods and apparatus are proposed to improve performance and reduce feedback overload of channel quality indication in a communication system.

Aspects, features and advantages of the invention are immediately apparent from the following detailed description, simply by illustrating a number of particular embodiments and implementations, including the best mode contemplated for carrying out the invention. The invention is also capable of other embodiments, and of different embodiments, and its various details can be modified in various obvious aspects, all without departing from the scope of the invention. Therefore, the drawings and description should be considered as illustrative, not restrictive. The invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings. In the following illustrations, downlink channel quality indication (CQI) feedback on the uplink of 3GPP LTE systems is used as an example. However, the technique illustrated in the present case can certainly be used in feedback of uplink CQI in the downlink in LTE systems and other systems whenever applicable.

In a first embodiment according to the principles of the present invention, a communication station creates a sub-table of CQI by selecting a subset of entries in the CQI table and notifying a CQI index or infers the channel quality from of a CQI index based on the CQI sub-table. In other words, the communication station notifies the index within the sub-table of the CQI index, instead of notifying the index within the original CQI index table.

In a first secondary embodiment of the first embodiment according to the principles of the present invention, a sub-table of CQI can be constructed by selecting the rows with the CQI indices 16-31. If such a CQI sub-table is used for the CQI notification of a UE, the UE will only need 4 bits to notify the index within the CQI index sub-table, which reduces the overhead. Note that the dynamic range covered by this sub table is reduced to half the dynamic range of the original table. This example is shown in table 2.

T l 2. n m l - l I

In a second secondary embodiment of the first embodiment in accordance with the principles of the present invention, a sub-table can be constructed by selecting the rows with even number of CQI indices as 0, 2, ..., 30. Again, only 4 bits are necessary to notify an index within the sub-table of CQI index (before CQI compression considerations). This sub-table can have the same dynamic range as that of the original or similar table, but with a less fine resolution. This example is shown in table 3.

T l. r m l - l I

In a third secondary embodiment of the first embodiment according to the principles of the present invention, a sub-table can be constructed by selecting several rows of CQI indices from the original table. Then, a few more rows can be added to the sub-table to increase the resolution of the sub-table above the resolution of the original table. For example, the indexes of CQI 3, 4, 5, 6, 7, 8, 9, 10 can be selected to construct the sub-table. A few rows can be added to the sub-table to increase the resolution. This example is shown in table 4.

T l 4. r m l - l I

In a second embodiment according to the principles of the present invention, different CQI tables constructed from the same original CQI table are used to notify (in the UE) or to interpret (at the base station) different types of CQI . In other words, communication stations can use the same CQI table with different resolution and / or different dynamic range to notify or interpret different types of CQI. In many cases, a UE can notify more than one type of CQI to the base station. Examples of different types of CQI CQI wideband CQI transmission diversity, CQI average, c Q i of subband CQI -Multiple Multiple Input Output (Multiple Input Multiple Output, MIMO), etc. Different CQI tables can be used for these different types of CQI. These different CQI tables can be constructed independently, or they can be constructed from the same original CQI table. For example, a UE can notify both broadband CQI and sub-band CQI. Because the present invention focuses on the case in which the different CQI tables are constructed from the same original table, no examples are provided in which the CQI tables for the sub-band CQI and the CQI Broadband are built independently. The broadband CQI is averaged over a set of subbands, which usually cover a large bandwidth. To reduce the overhead of the CQI notification, a differential compression scheme is used. With this approach, the differences between sub-band CQI and broadband CQI, which is called differential sub-band CQI, are reported together with the broadband CQI. In this case, the broadband CQI is notified using a full CQI, the sub-band CQI can be notified using a differential CQI. As another example, a UE can notify a CQI for the MIMO code word 1 and the MIMO code word 2. In that case, a complete CQI can be notified for the CQI of the MIMO code word 1, while that the difference between the CQI for the code word of MIMO 1 and the code word 2 can be reported as a differential CQI. As another example, a UE can notify the CQI of one or multiple MIMO code words using a complete CQI and notify the gain due to the cancellation of successive interference as a differential CQI. The cancellation of successive interference usually increases the CQI of the second MIMO code word to be more than the CQI of the first MIMO code word. In that case, the gain can be seen as a differential CQI between the c Q i of the first MIMO code word and the CQI of the second MIMO code word. Usually, a complete CQI is notified with a larger number of bits while a differential sub-band CQI is notified with a smaller number of bits. This differential compression reduces the number of bits needed to notify more than one CQI. Because the complete CQI is used as a reference for the differential CQI, sometimes notifying the complete CQI with a higher resolution and / or a larger dynamic range is preferable to notifying the differential CQI. For example, 5 bits can be used for a full CQI notification while 3 bits can be used for a differential CQI. A CQI table with 32 entries as shown in table 1 can be used to notify a complete CQI. The differential compression approach can be seen as the construction of a smaller CQI sub-table from the original CQI table to notify the differential CQI. As an example, assuming that the full CQI index is 22, a 3-bit differential CQI sub-table can be constructed by selecting 8 rows around the CQI index 22 from the original CQI table.

T l. n m l - l I r I if r n i l

Note that, in this case, 3 CQI indices smaller than the full CQI index, the complete CQI index, and 4 CQI indices larger than the full CQI index were selected. By doing this, the constructed CQI sub-table can support both positive and negative differential CQI values.

As another example, the differential CQI sub-table can be constructed around the complete CQI index with a different resolution. For example, the differential CQI sub-table can be constructed with a larger step, for example, by taking one in two CQI indices around the complete CQI index. Assuming again that the complete CQI index is 22, a 3-bit differential CQI sub-table can be constructed by selecting 8 rows around the CQI index 22 from the original CQI table as shown in the table 6.

T l. r m l - l I r I if r n i l

For purposes of illustration, assume that the complete CQI is the broadband CQI and the differential CQI is the sub-band differential CQI. Note that the following embodiments are also applicable when the complete CQI and the differential CQI represent other types of CQI, such as MIMO CQI and MIMO Delta CQI.

Suppose the broadband channel is represented by a matrix á -¡á SB '" ¿ SBr <l á Y where áSB ,

1 is the channel matrix for the sub-band ik. In some cases, intermediate measures such as channel capacity, mutual information, transport block size, or effective signal -to-noise ratio ( SNR) can be obtained from estimates of these channel matrices. The reported broadband CQI index is Q ^wb = q (" ^wb ) and the sub-band CQI index before differential compression is Q ^sb , ^í = q ( ass, i), where q () is the UE measurement function that selects a CQI index based on channel matrices. The reported CQI index for broadband CQI is Q ^wb = q (5 ^wb ), while the notified CQI index for sub-band CQI is (<2 ^sb , ¡= P ( Qsb, í) = p ( q (5 ^sb , ¡)), where p ( ) is the differential compression scheme of the UE for the differential sub-band CQI As an example of this embodiment, the index of c Q i sub-band differential defined as the sub-band CQI index minus the broadband CQI index A mathematical representation Illustrative is as follows,

Q ^sb , ^í = min ^ ISBmax, max {lSB, min, [Qsbíl Qwb])), (1)

where Qsbj is the differential CQI calculated by the transmitter, / sB, max and IsB, min respectively represent the upper and lower limits of the differential CQI index, and L is a certain value to adjust the resolution of the CQI sub-table. Note that the upper and lower limits are applied to ensure that the reported differential CQI index is within the desired range. For example, the upper limit and the lower limit can be set such that / sb , min = IsB, max - 7 to ensure that the differential CQI index can be represented by 3 bits. On the receiver side, the sub-band CQI index can be obtained by adding the differential sub-band CQI index back to the broadband CQI index. An illustrative mathematical representation is as follows,

<3 ^s B, ¡= min (/ WB, max, max (/ we, min, Q ^wb + L x (? ^Sb , ¡)) (2)

where Q ^sb , ¡is the sub-band CQI calculated by what is received based on the ^{Q sb} , ¡received and Q ^wb , ¡, / wB, max, e / wB, min respectively represent the upper and lower limits of the index of CQI broadband. Due to the range limit and transmission error, Qsbj and Q ^sb may not be the same. Without range limit or transmission error, these two quantities would be equal. As an example, you can set / sB, max = 3, / sB, min = -4, / wB, max = 31, e / wB, min = 0 for a 5-bit broadband CQI and a c Q i of sub-band different from 3 bits. L is used to adjust the resolution of the CQI sub-table for the differential sub-band CQI. For example, L = 2 can be set to achieve a larger dynamic range for the differential sub-band CQI. Note that, in order to use 3 bits to represent the differential sub-band CQI with a range of -4 to 3, it is necessary to define a mapping between the 8 binary values and the 8 sub-CQI values. differential band A common correlation is the “complement 2” representation of signed integers, which define the denial of a positive integer by inverting each bit of a positive integer and adding 1 to the result. The correlation for 3-bit signed integers is shown in table 7.

Table 7. Signed integers and their representation in complement to 2

Alternatively, the sub-band differential CQI index can be defined as the broadband CQI minus the sub-band CQI. An illustrative mathematical representation is as follows,

<3 ^sb , ¡= min (/ s S, ma *, max ^{(¡SB, min,} [QlyB ~ feBÍ])), (3)

On the receiver side, the sub-band CQI index can be obtained by subtracting the differential sub-band CQI from the broadband CQI. An illustrative mathematical representation is as follows,

<3 ^sb , ¡= min (/ wB, max, max (/ wB, min, Q ^wb - L x Q ^sbj )) (4)

As an example, you can set / sB, max = 3, / sB, min = -4, / wB, max = 31, e / wB, min = 0 for a 5-bit broadband CQI and a sub CQI - 3-bit different band. L is used to adjust the resolution of the CQI sub-table for the differential sub-band CQI. For example, L = 2 can be set to achieve a larger dynamic range for the differential sub-band CQI. Note that the negative relationship between the sub-band CQI and the differential sub-band CQI with this alternative. With the complement rule to 2, there are fewer levels (indexes) of quantification above 0 than those below 0 for the differential subband CQI. As a result, there are more levels (indexes) of quantification above the broadband CQI index than those below the broadband CQI index for sub-band CQI, which is advantageous for programming algorithms that favor some channel conditions better.

In a third embodiment according to the principles of the present invention, the upper and lower limit indices for the differential CQI can be adjusted depending on the value of the complete CQI. The complete CQI represents the CQI index that is selected by a UE based on the channel condition. In other words, the range of the differential CQI can be adjusted depending on the value of the complete CQI. For example, suppose that the complete CQI is 5 bits and uses the original CQI table shown in table 1. As an example, if the complete CQI index is 2, the differential CQI sub-table can be constructed as follows:

Table 8. Another example of CQI sub-table for differential CQI

This case corresponds to equation (1) with / SB, max 5 e / SB, m¡n -2. In Table 8, the full CQI index of 2 corresponds to the Qwb in equation (1); the “CQI index” column corresponds to the Qsb, í in equation (1); and, the "Sub-table CQI index" column corresponds to the differential CQI index Qsbj in equation (1). In the example given in table 8, the UE first selects a broadband CQI index of 2 from table 1. Then, the UE constructs a differential CQI sub-table (i.e., table 8 ) by using the broadband CQI index of 2 as a reference. Subsequently, the UE selects a sub band CQI of 3 from the differential CQI sub-table. Finally, the UE notifies a 5-digit broadband CQI index of 2, and a 3-digit sub-band CQI index of 3. Note that, if the UE selects another broadband CQI index, by For example, a broadband CQI index of 5, then, the UE has to construct another differential CQI sub table.

As another example, if the average CQI index (ie, the full CQI index) is 10, the differential CQI sub-table can be constructed as follows:

Table 9. Another example of CQI sub-table for differential CQI

This case corresponds to equation (1) with / sB, max = 4 and IsB, min = -3.

As another example, if the average CQI index is 30, the differential CQI sub-table can be constructed as follows: Table 10. Another example of CQI sub-table for differential CQI

This case corresponds to equation (1) with / SB, max = 1, e / SB, min = -6.

As a first secondary embodiment of the third embodiment according to the principles of the present invention, the sub-band differential CQI index can be defined as the sub-band CQI minus the broadband CQI, plus a displacement. An illustrative mathematical representation is as follows,

<3 ^sb , ¡= min ^ ISB, max, max {lSB, min, [Qsb í ~ ^ wb + A])). (5)

On the receiver side, the sub-band CQI index can be obtained by adding the broadband CQI back to the differential sub-band CQI. An illustrative mathematical representation is as follows,

<? SB, i = min (/ wB, max, max (/ wB, min, Q ^wb -AL x (? ^Sb , ¡)). (6)

By setting a different offset, the range of the differential sub-band CQI can be adjusted. An embodiment is the establishment of a different offset for a different complete CQI value. As an example, suppose the broadband CQI index is 2. When setting / sB, max = 7, / sB, min = 0, and A = 2, the differential sub-band CQI values and their correlation with The indices are shown as follows:

Table 11. Another example of differential subband CQI

As another example, if the broadband CQI index is 10, when setting / sB, max = 7, / sb, min = 0, and A = 3, the values of differential sub-band CQI and its correlation with the indices is shown as follows:

Table 12. Another example of differential subband CQI

As another example, if the broadband CQI index is 30, when setting / sB, max = 7, IsB, min = 0, and A = 6, the differential sub-band CQI values and their correlation with the indices It is shown as follows:

Table 13. Another example of differential subband CQI

As a second secondary embodiment of the third embodiment according to the principles of the present invention, by establishing the displacement appropriately, it is possible to adjust how many levels (indexes) of quantification are above and below the reference level (index of CQI broadband). The offset can be chosen as a function of the full CQI value. An example of such a functional relationship is as follows:

A = max (min ((QwB - AwB ^ Default value), Q ^w B / SB, max - / WB, max) (7)

Note that the default value of Apor default dictates how many CQI indices below the full CQI index can be reported, regardless of the effect of the upper or lower limit of the CQI indices. As an example, suppose that the lower limit and the upper limit for the complete CQI is / wB, min = 0, e / wB, max = 31, respectively; assume that the lower limit and the upper limit for the differential CQI is / SB, min = 0, e / SB, max = 7, respectively; assume that the default offset Apor defect = 3. Equation (7) can be written as

A = max (min (QwB, 3), Qw b- 24). (8)

As an alternative, this equation can be represented as:

Note that, as an alternative, this embodiment can be interpreted as a different differential CQI value calculation depending on the value of the complete CQI. By combining equation (9) and equation (5), and the above-mentioned assumption about the values of the upper and lower limits, the illustrative functional relationship can be represented as

By setting the upper and lower limit appropriately, the number of bits used in the notification of the differential sub-band CQI can be controlled. In the examples shown in Table 11, Table 12 and Table 13, because the differential subband CQI value is set to be 0 ~ 7, the differential subband CQI value can be correlated with the 3-bit differential sub-band CQI field using the binary representation of unsigned integers. An example of this representation is shown in table 14.

Table 14. Unsigned integers and their binary representation

Alternatively, the sub-band differential CQI index can be defined as the broadband CQI minus a sub-band CQI, plus one offset. Similarly, by setting the offset appropriately, you can adjust how many levels (indexes) of quantification are above and below the reference level (broadband CQI index). By setting the upper and lower limit appropriately, the number of bits used in the notification of the differential sub-band CQI can be controlled.

Figures 1 (a), (b) and (c) schematically illustrate different methods for calculating the complete CQI and the differential CQI. The complete CQI can be calculated using the process shown in Figure 1 (a). Specifically, first, channel estimates are obtained, and a channel quality measure such as the effective SNR is calculated. Then, the complete CQI, that is, the first CQI index, is calculated based on the channel estimates and / or the channel quality measures. The differential c Q i can be calculated using the processes shown either in Figure 1 (b) or in Figure 1 (c). In an embodiment according to the principles of the present invention shown in Figure 1 (b), the difference between two channel quality measurements (for example, the difference in SINR) is first calculated, then the index is selected of differential / delta CQI based on the difference between the two channel quality measures. In the present case, a differential CQI table would be necessary to establish the correlation based on the difference between two channel quality measurements, and the differential / delta CQI index. In another embodiment in accordance with the principles of the present invention shown in Figure 1 (c), a second CQI index is selected based on the channel estimates and / or the channel quality measures. Then, the value of the differential CQI index is obtained by subtracting the index of a first CQI that is notified by a complete CQI, to the second CQI index that is notified by said differential CQI. In other words, the differential operation should be carried out on quantified CQI indices, instead of the channel conditions or other intermediate channel quality measures such as effective SINR, mutual information, transport block size, or transport sizes. standardized transport block. This operation can be represented in an equation as follows, Qsb, í - Qsb, í - Q ^wb . (eleven)

Note that it is easy to extend this embodiment by applying the upper limit IsB, max and the lower limit / sB, min. And it is also a simple extension to choose a different resolution level L for the sub-band CQI. Note that, if the differential operation is performed on the channel conditions or other intermediate channel quality measures, both the complete CQI and the differential CQI indices will suffer from independent quantization errors that will accumulate when the differential operation is reversed in the receiver end

In a fourth embodiment in accordance with the principles of the present invention, the UE needs to notify the frequency-selective MIMO CQI. An example is shown in Figure 2. Assume that a UE notifies a CQI for two MIMO code words. In 3GPP LTE, this takes place when the channel range is greater than 1. Note also that, in LTE, a common range from beginning to end of frequency subbands is reported. Therefore, in this example, the channel is assumed to have the same range in multiple subbands and throughout the broadband. As shown in Figure 1, a broadband CQI, Q ^wb , and a broadband delta CQI, D ^wb , are reported for broadband channel conditions. Note that delta CQI is the difference between two CQI values. There may be a variety of different interpretations of the average CQI and differential / delta CQI. For example, if the two CQI notifications (Q ^wb and D ^wb ) represent the CQI for two MIMO code words, the CQI of the MIMO code word 1 (CW1) can be notified by Qwb, and the difference between The CQI of CW1 and CW2 can be notified by D ^wb . On the receiver side, the CQ2 of CW2 can be obtained together from the delta CQI and the broadband CQI, for example, Qwb Dwb. The UE also reports sub-band MIMO CQI. A differential frequency CQI, Qsbj, and a c Q i of sub-band delta, D ^sb , ^í , are reported in sub-band 1. There may be a variety of different meanings and interpretations of these CQI notifications. For example, if the two CQI notifications (Q ^sb , ⁱ and D ^sb , ⁱ ) represent the CQI for two MIMO code words, the difference between the CQ1 of CW1 in sub-band 1 and the cQ i of band Wide (Q ^wb ) can be notified by Q ^sb , ⁱ , and the difference between the CQI of CW1 and CW2 can be notified by D ^sb , ⁱ . On the receiver side, the CQ1 of CW1 can be obtained jointly from the sub-band CQI notification and the broadband CQI notification, for example, Q ^wb + Q ^sb , ⁱ . The CQ2 of CW2 can be obtained jointly from the notification of broadband CQI, notification of sub-band CQI, and CQI of sub-band delta, for example, Qwb Qsb, / + D ^sb , ⁱ . These operations are also illustrated in Figure 2. For example, the arrow from Q ^sb , ⁱ pointing towards Qwb means that Qsb, /, is a differential CQI with respect to the broadband CQI. Similarly, the arrow from D ^sb , ⁱ , which points to Q ^sb , ⁱ , means that D ^sb , ⁱ , is a delta CQI with respect to the sub-band CQI. With this framework, previous embodiments can be extended to the case of differential frequency CQI and MIMO delta CQI.

Suppose that the broadband channel can be represented by a matrix “WD - ^ SB '

where is the channel matrix for the sub-band ik. In simplified cases, some intermediate measures such as channel capacity, mutual information, transport block size, or effective SNR can be obtained from these channel vectors. Assume that the intermediate channel quality measure is the effective SNR, which is indicated by S. Therefore, the intermediate channel quality measure can be obtained from the channel estimation matrices as follows, S ^wb , ^cwi = fi (5 ^wb ), S ^wb , ^cw 2 = f2 (5 ^wb ), S ^sb , ^cw 1, ^í = fi (5 ^sb , ¡), S ^sb , ^cw 2, <- f2 (5 ^sb , ¡) . The reported broadband CQI index can be chosen as Q ^wb -q ( S wB, cwi) and the CQI index of broadband delta reported as D ^wb = p ( q ( SwB, cwi), q ( SwB cw2 )), where q () is the measurement function of the UE that estimate the most appropriate CQI index based on the effective SNR, and p () is the differential compression scheme of the UE. In the simplest form, D ^wb = q (SwB, cw2) - q (SwB, cw i)).

In the fourth embodiment according to the principles of the present invention, the value of the sub-band differential CQI index is obtained by subtracting the broadband CQI index from the sub-band CQI index corresponding to said CQI differential. In other words, the differential operation should be performed on the quantified CQI indices, instead of the channel conditions or other intermediate channel quality measures such as effective SINR, mutual information, or standardized transport block sizes. Note that if the differential operation is performed on the channel conditions or other intermediate channel quality measures, both the broadband CQI and the sub-band differential CQI indices will suffer from independent quantization errors that will accumulate in the obtaining sub-band CQI at the receiver end.

Similarly, the value of the sub-band MIMO delta CQI index is obtained by subtracting the sub-band CQI index for one code word from the sub-band CQI index for the other code word. In other words, the differential operation should be performed on the quantified CQI indices of the MIMO code words, instead of the channel conditions or other intermediate channel quality measures. Note that, although the reference CQI value for the sub-band MIMO delta CQI is the sub-band CQI index for one of the MIMO code words, the sub-band CQI index is not notifies by using a full CQI. Instead, that sub-band CQI index is notified by the use of a differential sub-band CQI. However, the aforementioned embodiments such as using different CQI tables, obtaining different CQI sub-tables from the same original table, adjusting the upper / lower limit and the offset in the calculation of the differential sub-band CQI or The MIMO delta CQI according to the reference CQI value, and so on, are applicable to both the differential sub-band CQI and the calculation of the MIMO delta CQI.

Note that the reference CQI may also have different interpretations. For example, for the MIMO delta CQI, the reference CQI may be the corresponding sub-band CQI of one of the MIMO code words, or a broadband CQI of a MIMO code word.

In a fifth embodiment according to the principles of the present invention, different bit widths are used for the broadband CQI, sub-band differential CQI, and the sub-band MIMO delta CQI. Because broadband CQI serves as a reference for all other CQIs, it is desirable to have a higher resolution for broadband CQI. Similarly, the sub-band differential CQI also serves as an intermediate reference for the sub-band MIMO delta CQI, therefore it is also preferable to have a better resolution for the sub-band differential CQI. For example, 5 bits for the broadband CQI indices, 3 bits for the sub-band differential CQI indices and 2 bits for the sub-band MIMO delta CQI indices could be used. In a sixth embodiment according to the principles of the present invention, different bit widths are used for the same type of CQI in different transmission formats. For example, a broadband CQI can be transmitted either on a physical uplink control channel ( Physical Uplink Control Channel, PUCCH) or on a physical uplink shared channel ( Physical Uplink Shared Channel, PUSCH). Because the resources in a PUCCH are scarcer, transmitting broadband CQI in a PUCCH with a smaller number of bits is preferable to transmitting broadband CQI in a PUSCH. For example, we can use 5 bits to transmit broadband CQI in a PUSCH and 4 bits to transmit broadband CQI in a PUCCH.

In a seventh embodiment according to the principles of the present invention, the CQI of sub-band delta can be taken with respect to a different reference. For example, as shown in Figure 3, the sub-band delta CQI for CW2 is chosen to be the difference between the sub-band CQI for CW2 and the broadband CQI index for CW2. Alternatively, the sub-band delta CQI for CW2 can be taken with respect to the broadband CQI for CW1, as shown in Figure 4. In that case, the broadband CQI for CW1 serves as a reference for all other differential / delta CQI.

In an eighth embodiment according to the principles of the present invention, if an item CQI number is reported as the average CQI and the differential CQI, one of the item CQIs can be omitted. The receiver can infer the value of the omitted element CQI by the relationship between the average CQI and the element CQI or the relationship between the differential CQI. For example, suppose that,

The UE only needs to notify the average CQI, and (N-1) CQI differentials because ^{w - ¡}

- £ DifCQI,

- £ DifCQI,

, Or equivalently, DifCQIk = (13)

And the base station can use these relationships to obtain the value of element CQI or the omitted differential CQI. This scheme is particularly useful when the item CQI number is small. For example, N = 2, 3, or 4. While the present invention has been shown and described in connection with preferred embodiments, it will be apparent to those skilled in the art that modifications and variations can be made without departing from the scope of the invention such as defined by the appended claims.

Claims (16)

1. A method of communication, the method comprising the stages of: obtain channel quality estimates for a plurality of transmission channels; determine, in a first node, a first channel quality indication index depending on an estimate of channel quality of a first transmission channel, and a second channel quality indication index depending on an estimate of channel quality of a second transmission channel; determining a differential channel quality indication index of the second channel quality indication index with reference to the first channel quality indication index depending on a differential compression scheme; Y transmitting, through the first node, the first channel quality indication index and the differential channel quality indication index to a second node using a correlation of the differential channel quality indication index with a bit representation, being a number of bits for the first channel quality indication index greater than a number of bits for the differential channel quality indication index, and where the correlation is a complement two correlation scheme. 2. The method of claim 1, composed of the differential compression scheme that is established by: Osb, ¡- Qsb, í - Qwb where Qsb indicates the differential channel quality indication index, Qwb indicates the first channel quality indication index and Qsb indicates the second channel quality indication index. 3. The method of claim 1, wherein the differential compression scheme comprises determining the differential channel quality indication index based at least in part on a difference between the first channel quality indication for a first code word and the second channel quality indication for a second code word. 4. The method of claim 1, composed of transmitting the differential channel quality indication index by using a three-bit representation according to the complement correlation scheme to 2. 5. The method of claim 4, wherein the two-complement correlation scheme is established by the following table:

6. The method of claim 1, the first channel quality indication and the second channel quality indication represent an MIMO channel quality indication. 7. A method of communication, the method comprising the steps of: receiving, in a second node from a first node, a first channel quality indication index and a bit representation of a differential channel quality indication index, a number of bits being for the first quality indication index of channel greater than a number of bits for the differential channel quality indication index, the representation of received bits being correlated according to a two-complement correlation scheme; Y obtaining, in the second node, a second channel quality indication index depending on the first channel quality indication index received, the differential channel quality indication index received and a differential compression scheme. 8. A communication device, the device comprising: means for receiving, in a second node from a first node, a first channel quality indication index and a bit representation of a differential channel quality indication index, a number of bits being for the first indication index of channel quality greater than a number of bits for the differential channel quality indication index, the representation of received bits being correlated according to a two-complement correlation scheme; Y means for obtaining, in the second node, a second channel quality indication index depending on the first channel quality indication index received, the differential channel quality indication index received and a differential compression scheme. 9. The apparatus of claim 8, composed of the differential compression scheme that is established by: O ^s B, / - Q ^w BO ^s B, í, where Qs bj indicates the second channel quality indication index, Qwb indicates the first channel quality indication index and Qs bj indicates the differential channel quality indication index. 10. The apparatus of claim 8, wherein the differential compression scheme comprises means for determining the differential channel quality indication index based at least in part on a difference between the first channel quality indication for a first word code and the second channel quality indication for a second code word. 11. The apparatus of claim 8, wherein the received differential channel quality indication index is represented with three bits according to the complement correlation scheme to 2. 12. The apparatus of claim 11, wherein the complement two correlation scheme is being established by the following table:

13. The apparatus of claim 12, the first channel quality indication and the second channel quality indication represent an MIMO channel quality indication. 14. A communication device, the device comprising: means for obtaining channel quality estimates for a plurality of transmission channels; means for determining, in a first node, a first index of channel quality indication depending on an estimate of channel quality of a first transmission channel, and a second index of channel quality indication depending on an estimate of channel quality channel of a second transmission channel; means for determining a differential channel quality indication index of the second indication index of channel quality with reference to the first index of channel quality indication depending on a differential compression scheme; Y means for transmitting, through the first node, the first channel quality indication index and the differential channel quality indication index to a second node using a correlation of the differential channel quality indication index with a bit representation , a number of bits for the first channel quality indication index being greater than a number of bits for the differential channel quality indication index, and where the correlation is a complement two correlation scheme. 15. The apparatus of claim 14, adapted according to one of claims 2 to 6. 16. A computer program product for wireless communications, the computer program product comprising a non-transient computer-readable medium having a program code registered therein, the program code comprising a program code for performing the method of a of claims 1 to 7.