CN102710308B - Codebook designing method for reducing feedback information cost in pre-coding MIMO (Multiple Input Multiple Output) system - Google Patents
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Abstract
The invention discloses a codebook designing method for reducing feedback information cost in a pre-coding MIMO (Multiple Input Multiple Output) system. The method comprises the steps of (1) selecting optimal code words w0 from an initial codebook C0 by a receiver according to the current channel vector h0, and feeding reference numbers of the w0 back to an emitter; (2) generating a tapered codebook Calpha(w0) at the emitter and the receiver according to the initial codebook C0, the optimal code words w0 in step 1 and contraction-expansion factors alpha; (3) selecting optimal reference numbers w1 from the tapered codebook Calpha(w0) by the receiver according to the current channel vector h1, wherein the method for selecting the optimal code words w1 is same as the method for selecting the optimal code word vector w0 in the step 1, and feeding the reference numbers of the optimal code words w1 back to the emitter; and (4) selecting optimal code words wi (wherein i=1, 2?-) according to the current channel information hi (wherein i=1, 2?-) of the emitter and the receiver, and converting the tapered codebook Calpha(wi-1) to the optimal tapered codebook Calpha(wi) (wherein i=1, 2?-). According to the method, the size of the feeding-back codebook can be changed according to the channel information, and when the same system channel capacity is achieved, the fed-back bandwidth is reduced, and the cost on feed-back information can be reduced.
Description
Technical Field
The invention relates to a method in the technical field of wireless transmission, in particular to a codebook design method for reducing feedback information overhead in a precoding MIMO system.
Background
Multiple antennas are used in the transmitter and the receiver, that is, a Multiple-Input Multiple-Output (MIMO) transmission model is formed, and the MIMO transmission mode can increase the reliability of wireless connection and increase the capacity of a wireless communication system. In an environment with severe electromagnetic interference, for one ownerRoot transmitting antenna andin a receiving antenna system, the MIMO transmission mode improves channel capacity, and is linear with a relatively small number of transmitting antennas and receiving antennas. Therefore, MIMO technology is a preferred scheme for future broadband mobile communication systems.
In recent years, due to the development of MIMO technology, precoding technology has become an important research direction in the field of wireless communication. The precoding technique has been part of the IEEE 802.16e standard in 2005, including open-loop and closed-loop precoding methods, with a view to increasing the transmission rate of wireless communication. Precoding methods based on limited feedback of precoding are also used in the 3GPP standards.
Since the channel capacity of the MIMO system is related to the minimum number of antennas of the transmitter and the receiver, in the actual MIMO system, the number of antennas is constrained due to the limitations of the volume and power of the mobile terminal, and the number of antennas in the base station is not limited thereby. The existing research results show that Dirty Paper Coding (DPC) can reach the capacity domain of the MIMO broadcast channel. However, the additional complexity required to implement DPC at both the transmitter and receiver is extremely high. And how to construct a practical DPC code that achieves system capacity has not been solved so far.
The linear precoding technique has the advantages of low computational complexity and simple realization. The existing research results show that Zero-forcing Beamforming (ZFBF) can eliminate the interference between the antennas of each user, and the performance approaches to the optimum.
In a practical FDD system, CSI may be obtained by channel estimation at the receiver and transmitted to the transmitter via a feedback channel. However, since the bandwidth of the feedback channel is limited, it is generally impossible to transmit all CSI information to the transmitter, and CSI can only be represented by feeding back limited bits of information. Since the CSI is quantized with a limited bit of information, there is a quantization error. Resulting in a large loss of precoding performance compared to the ideal case where the CSI is completely known to the transmitter.
A literature search in the prior art shows that "Giannakis Design and Analysis of Transmit-beam based on Limited-Rate feed" published by Pengfei Xia et al in IEEE Transmission Signal Processing (vol 54, vol 5, p. 1053 & 1863, 2006). The text provides a precoding method of limited feedback, and provides a specific implementation method of a Lloyd codebook: firstly, selecting an initial codebook, randomly generating a large number of initial sequences as samples, then respectively comparing the generated training sequences with the code words of the initial codebook, dividing the training sequences into range intervals of each code word according to the distance between the training sequences, and finally selecting the center of each interval as a new code word according to the average position of the training sequences. The disadvantages are that: the codebook size is fixed, and for time-dependent channels, a large amount of feedback bandwidth is wasted, i.e., feedback information overhead is increased.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a codebook design method for reducing feedback information overhead in a precoding MIMO system.
The invention is realized by the following technical scheme:
the invention relates to a codebook design method for reducing feedback information overhead in a precoding MIMO system.
The method comprises the following steps:
step one, a receiver carries out channel estimation according to the current channel vectorFrom the initial codebookTo select the optimal code wordWill beThe index number is fed back to the transmitter;
step two, according to the initial codebook in the step oneAnd an optimal codewordAnd scaling factorGenerating a tapered codebook at both the transmitter and receiver ends；
Step three, the receiver carries out the operation according to the current channel vectorFrom conical codebooksTo select the optimal code wordSelecting the optimal code wordMethod and step one for selecting optimal code word vectorThe same method, will optimize the code wordThe index number is fed back to the transmitter;
step four, the transmitter and the receiver according to the current channel information(wherein) Selecting the optimal code word(wherein) Conical codebookTransforming into a tapered codebook(wherein)。
The initial codebook in the step one is a Grassmannian codebook or an RVQ codebook, and the transmitter and the receiver respectively adopt the same initial codebook.
The initial codebook in the step oneTo select the optimal code wordSelecting the optimal code wordThe method comprises the following steps: traversing initial codebooksSelecting a channel vector corresponding to the current channel vectorCode word with optimal included angleThe expression is as follows:whereincis an initial codebookThe code word in (b) represents the conjugate transpose, then the receiver feeds back the index number of the optimal code word to the transmitter, and the transmitter feeds back the index number of the optimal code word from the initial codebook according to the information fed back by the receiverThe corresponding codeword is found.
The parameters mentioned in the second stepIs a conical spatial contraction factor, and,whereinoptimal codewords for initial quantizationAnd initial codebookExcept for the optimal codewordExternal firstThe included angle between the code words is set,for optimal code wordAnd conical codebookExcept for the optimal codewordExternal firstAngle between codewords, i.e.
Generating the tapered codebook at the transmitter and receiver end as described in the second stepThe method specifically comprises the following steps:
step one, optimal code words are usedAs a conical codebookA code word of (a);
step two, conical codebookThe rest of code words in the code table are calculated by a formulaGenerating, wherein the weight is calculatedTo solve the problem that the reaction solution is not stable,and obtaining the compound.
The slave codebook described in step three aboveTo select the optimal code wordThe method comprises the following steps: traversing pyramid codebooksSelecting the current channel informationIncluded angle optimized codewordThe expression is as follows:whereinIs an initial codebookThe codeword in (1) represents a conjugate transpose.
The codebook of cones as described in step four aboveTransforming into a tapered codebookThe specific process is as follows:
conical codebookAll code words in the code word and Householder matrix(wherein) Multiplying to obtain a conical codebookOf the code words of (a), wherein,。
compared with the prior art, the method has the advantages that: the invention utilizes the correlation of the actual channel time to ensure that the codebook can adjust the size and the direction of the space of the codebook according to the channel information. The high-efficiency feedback scheme designed by the invention can achieve the effect similar to that of the traditional design scheme by using lower feedback quantity.
Drawings
FIG. 1 is a flow chart of a codebook design method for reducing feedback information overhead in a precoding MIMO system according to the present invention;
FIG. 2 is a diagram of a comparison between the performance of a spherical codebook and the performance of a conventional spherical codebook in the codebook design method for reducing feedback information overhead in a precoding MIMO system according to the present invention (at that time)When the scaling factor takes the optimal value of alpha, alpha = 4);
FIG. 3 is a diagram comparing the performance of a spherical codebook and a conventional spherical codebook (when the performance of the spherical codebook is compared) for the codebook design method for reducing feedback information overhead in a precoding MIMO system of the present inventionWhen α takes the optimum value and α = 4).
Detailed Description
The embodiments of the present invention will be described in detail below with reference to the accompanying drawings: the present example is carried out on the premise of the technical scheme of the present invention, and detailed embodiments, operation processes and experimental results are given, but the scope of the present invention is not limited to the following examples.
As shown in fig. 1, the codebook design method for reducing feedback information overhead in a precoding MIMO system of the present invention specifically includes the following steps:
step one, a receiver carries out channel estimation according to the current channel vectorFrom the initial codebookTo select the optimal code wordWill beIs fed back to the transmitter.
The initial codebookFor Grassmannian codebook, the transmitter and the receiver respectively use the same initial codebook, and the initial codebook is used as the secondary codebookTo select the optimal code wordSelecting the optimal code wordThe method comprises the following steps: traversing initial codebooksSelecting a channel vector corresponding to the current channel vectorCode word with optimal included angleThe expression is as follows:wherein c is an initial codebookThe code word in (b) represents the conjugate transpose, then the receiver feeds back the number of the vector to the transmitter, and the transmitter feeds back the number from the initial codebook according to the information fed back by the receiverFinding out the corresponding code word;
step two, according to the initial codebook in the step oneAnd an optimal codewordAnd a scaling factor alpha, generating a conical codebook at the transmitter and the receiver。
The parameter alpha is a tapered codebook scale factor, and,，
wherein,optimal codewords for initial quantizationAnd initial codebookExcept for the optimal codewordExternal firstThe included angle between the code words is set,for optimal code wordAnd conical codebookExcept for the optimal codewordExternal firstAngle between codewords, i.e.
The scale factor α characterizes the degree of conical space contraction, i.e.The optimal scaling factor a is determined by the doppler spread and the bandwidth of the feedback channel,byAll code word directions inGathering and shrinking are generated, the shrinking degree is determined by a shrinking factor alpha, and each code word in the codebook is associated withAll included angles are reduced to the originalAnd (4) doubling.
In order to achieve the best communication quality, the invention utilizes the computer to search out the best scaling factor alpha value, and because the computer is used for searching and the searching is carried out in an off-line state, the burden of the calculated amount in the channel quantization process can not be increased. Some different feedback bits B and channel correlation are given in Table 1 and Table 2 belowAnd under the condition of value taking, the corresponding optimal scaling factor alpha value.
Table 1 different feedback bit number B and channel correlationOptimal value of scaling factor alpha corresponding to the value of =0.9
| Channel correlation | Number of feedback bits B | Optimal scale factor alpha value |
| 0.9 | 2 | 1.5 |
| 0.9 | 3 | 2 |
| 0.9 | 4 | 2.5 |
| 0.9 | 5 | 2.5 |
| 0.9 | 6 | 2.5 |
| 0.9 | 7 | 2.5 |
| 0.9 | 8 | 2 |
Table 2 different feedback bit numbers B and channel correlationOptimal value of expansion factor alpha corresponding to the value of =0.95
| Channel correlation | B | Optimal scale factor alpha value |
| 0.95 | 2 | 1.5 |
| 0.95 | 3 | 2.5 |
| 0.95 | 4 | 3 |
| 0.95 | 5 | 3 |
| 0.95 | 6 | 3 |
| 0.95 | 7 | 3 |
| 0.95 | 8 | 3 |
Generating the tapered codebook at the transmitter and the receiverThe method specifically comprises the following steps:
step one, optimal code words are usedAs a conical codebookA code word of (a);
step two, conical codebookThe rest of code words in the code table are calculated by a formulaGenerating, wherein the weight valueBy solving forObtaining;
step three: the receiver is based on the current channel informationFrom conical codebooksTo select the optimal code wordSelecting the optimal code wordThe method and the step oneThe same method, will optimize the code wordThe index number is fed back to the transmitter;
the slave conical codebookTo select the optimal code wordThe method comprises the following steps: traversing pyramid codebooksSelecting the current channel informationCode word with optimal included angleThe expression is as follows:whereinIs an initial codebookCode word in (c) represents a conjugate transpose;
step four, the transmitter and the receiver according to the current channel information(wherein) Selecting the optimal code word(wherein) Conical codebookTransforming into a tapered codebook(wherein)，
The conical codebookTransforming into a tapered codebookThe specific process is as follows:
conical codebookAll code words in the code word and Householder matrix(wherein) Multiplying to obtain a conical codebookOf the code words of (a), wherein, 。
the simulation results of the embodiment of the invention are as follows:
FIG. 2 is a schematic view ofIn MIMO systems, when the channel correlation degreeIn the conventional spherical codebook, the performance of the conical codebook when the scale factor α =4 is compared with the performance of the codebook when the optimal scale factor α value is selected. In fig. 2, the abscissa indicates the number of fed bits, the ordinate indicates the normalized SNR, the curve with squares indicates the pyramid codebook for the optimal scaling factor α value proposed by the present invention, and the curve with triangles above indicates α =4, and the curve with bars indicates the conventional sphere codebook. FIG. 3 is a schematic view ofIn MIMO systems, when the channel correlation degreeIn the conventional spherical codebook, the performance of the conical codebook when the scale factor α =4 is compared with the performance of the codebook when the optimal scale factor α value is selected. In fig. 3, the abscissa represents the number of bits fed back, and the ordinate represents the normalized SNR. The curve with squares represents the pyramid codebook with the best scale factor α value proposed by the present invention, and the curve with triangles above represents the pyramid codebook with scale factor α =4, and the curve with crosses represents the conventional spherical codebook. As can be seen from fig. 2 and fig. 3, when the normalized snr is around 0.89, the overhead required by the conical codebook with the optimal scaling factor α value, the conical codebook with the scaling factor α =4, and the conventional spherical codebook is 5 bits, 6 bits, and 8 bits, respectively, which indicates that the bit difference of the conical codebook with the optimal scaling factor α value proposed by the present invention is 3 bits compared with the conventional codebook, that is, the conical codebook with the optimal scaling factor α value proposed by the present invention saves the overhead of 3 bits compared with the conventional codebook. As can be seen from fig. 2 and 3, the codebook proposed by the present invention can reduce the overhead of feedback information under the same condition as that of the conventional spherical code.
Claims (7)
1. A codebook design method for reducing feedback information overhead in a precoding MIMO system is characterized in that the method firstly selects an optimal codeword from an initial codebook according to channel information, and then constructs a conical codebook according to the initial codebook, the optimal codeword and a contraction factor, and comprises the following specific steps:
step one, a receiver carries out channel estimation according to the current channel vectorFrom the initial codebookTo select the optimal code wordWill beThe index number is fed back to the transmitter;
step two, according to the initial codebook in the step oneAnd an optimal codewordAnd scaling factorGenerating a tapered codebook at both the transmitter and receiver ends；
Step three, the receiver carries out the operation according to the current channel vectorFrom conical codebooksTo select the optimal code wordSelecting the optimal code wordMethod and step one for selecting optimal code word vectorThe same method, will optimize the code wordThe index number is fed back to the transmitter;
step four, the transmitter and the receiver according to the current channel informationWhereinSelecting the optimal code wordWhereinConical codebookTransforming into a tapered codebookWherein。
2. The method as claimed in claim 1, wherein the initial codebook in the first step is a Grassmannian codebook or an RVQ codebook, and the transmitter and the receiver respectively use the same initial codebook.
3. Codebook design method for reducing feedback information overhead in precoding MIMO system as claimed in claim 1 or 2The method is characterized in that the initial codebook in the step one isTo select the optimal code wordSelecting the optimal code wordThe method comprises the following steps: traversing initial codebooksSelecting a channel vector corresponding to the current channel vectorCode word with optimal included angleThe expression is as follows:whereincis an initial codebookThe code word in (b) represents the conjugate transpose, then the receiver feeds back the index number of the optimal code word to the transmitter, and the transmitter feeds back the index number of the optimal code word from the initial codebook according to the information fed back by the receiverThe corresponding codeword is found.
4. The method of claim 3, wherein the parameters in step two are used to design a codebook for reducing feedback information overhead in a precoding MIMO systemIs a conical spatial contraction factor, and,whereinoptimal codewords for initial quantizationAnd initial codebookExcept for the optimal codewordExternal firstThe included angle between the code words is set,for optimal code wordAnd conical codebookExcept for the optimal codewordExternal firstAngle between codewords, i.e.
。
5. The method of claim 4, wherein said step two generates the conical codebook at the transmitter and receiver endsThe method specifically comprises the following steps:
step one, optimal code words are usedAs a conical codebookA code word of (a);
step two, conical codebookThe rest of code words in the code table are calculated by a formulaGenerating, wherein the weight valueBy solving for the solution, the method can be used,thus obtaining the product.
6. The method of claim 5, wherein said step three is a codebook design method for reducing feedback information overhead in precoding MIMO systemsTo select the optimal code wordThe method comprises the following steps: traversing pyramid codebooksSelecting the current channel informationIncluded angle optimized codewordThe expression is as follows:whereinIs an initial codebookThe codeword in (1) represents a conjugate transpose.
7. The method of claim 6, wherein said step four is a method of designing a codebook to reduce feedback information overhead in a precoding MIMO systemTransforming into a tapered codebookThe specific process is as follows: conical codebookAll code words in the code word and Householder matrixWhereinMultiplying to obtain a conical codebookOf the code words of (a), wherein, 。
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| CN109361441B (en) * | 2018-10-16 | 2021-08-03 | 南京信息工程大学 | MU-MISO system limited feedback codebook design method based on channel statistical information |
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| CN101252381A (en) * | 2008-04-01 | 2008-08-27 | 东南大学 | Multi-aerial radio communication system high efficiency feedback method based on tree code book |
| CN101304300A (en) * | 2008-05-29 | 2008-11-12 | 上海交通大学 | Method and device for quantizing multiuser MIMO system channel based on limiting feedback |
| WO2009022872A2 (en) * | 2007-08-16 | 2009-02-19 | Lg Electronics Inc. | A method for transmitting codewords in multiple input multiple output system |
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| WO2009022872A2 (en) * | 2007-08-16 | 2009-02-19 | Lg Electronics Inc. | A method for transmitting codewords in multiple input multiple output system |
| CN101252381A (en) * | 2008-04-01 | 2008-08-27 | 东南大学 | Multi-aerial radio communication system high efficiency feedback method based on tree code book |
| CN101304300A (en) * | 2008-05-29 | 2008-11-12 | 上海交通大学 | Method and device for quantizing multiuser MIMO system channel based on limiting feedback |
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