CN101304300A - Method and device for quantizing multiuser MIMO system channel based on limiting feedback - Google Patents

Abstract

The invention discloses a channel quantification method for a multi-user MIMO system based on limited feedback and a device thereof, which belongs to the technical field of wireless transmission. The method comprises the following steps: according to a channel state message, from a codebook choosing a codeword which has the smallest angle with the codebook and calculating an quantification error; choosing a codeword vector which has the smallest angle with the quantification error from the codebook; projecting a channel vector to the space formed by the two chosen codeword vectors, calculating and obtaining a compound proportion factor; quantifying the compound proportion factor by a pre-generated quantification step set. A receiver device comprises a channel state message obtaining unit, a channel vector qualification unit, a quantification message feedback unit. A sender device comprises a feedback message reconstruction unit and a pre-coding unit. The method and the device of the invention can reduce the quantification error and improve the capacity performance of the system and has the advantages of small codebook and low complexity with same rate and capacity.

Description

Multiuser MIMO system channel quantization method and device based on Limited Feedback

Technical field

The present invention relates to a kind of method and apparatus of radio transmission technical field, specifically is a kind of multiuser MIMO system channel quantization method and device based on Limited Feedback.

Background technology

Use many antennas on transmitter and receiver, promptly constituted multiple-input and multiple-output (MIMO) mode, this transmission means can strengthen the reliability of wireless connections and increase the capacity of wireless communication system.In the comparatively serious wireless environment of electromagnetic interference, have M for one _TTransmit antennas and M _RThe system of root reception antenna, the contribution that the MIMO transmission means improves channel capacity, with number of transmit antennas and reception antenna number, less relatively numerical value is linear.Therefore, the MIMO technology has become the outstanding alternative of following wide-band mobile communication system.

Precoding technique can better overcome the decline of channel to signal at the fading characteristic of wireless channel with the feasible signal that sends of the mode of weighting, better follows the tracks of the variation of channel status, is one of effective ways that improve the mimo system performance.In the last few years, because the development of MIMO technology makes precoding technique become the important research direction of wireless communication field.Precoding technique was conceived to improve the message transmission rate of radio communication, became the part of IEEE 802.16e standard in 2005, comprised the method for precoding of open loop and closed loop.In the 3GPP standard, also used method for precoding based on the Limited Feedback of precoding.

Because the capacity of mimo system is relevant with the minimum antenna number of transmitting terminal and receiving terminal, and in real system, the mobile terminal is owing to the restriction of volume and power, and the quantity of antenna suffers restraints, and the base station is then not limited.Therefore, for implementation space diversity in this case, (Broadcast Channel, research BC) has caused academia's extensive interest to the multiuser MIMO broadcast channel in recent years.Existing result of study shows, (Dirty Paper Coding DPC) can reach the capacity territory of MIMO broadcast channel to dirty paper code.Yet, realize that at transmitting terminal and receiving terminal the required extra complexity of DPC is high.And the problem of how to construct DPC sign indicating number practical, that reach power system capacity is not resolved so far.

It is low that the linear predictive coding technology has a computation complexity, realizes simple advantage.Existing result of study shows, close-to zero beam is shaped, and (Zero-foring Beamforming ZFBF) can eliminate interference between each user antenna, and performance is near optimum.

In actual FDD system, CSI can be obtained by the channel estimating of receiver, and is transferred to transmitter by feedback channel.But,, generally can not can only represent CSI by the information of feedback limit bit with whole CSI message transmission to transmitter because the bandwidth of feedback channel is limited.Because the information with limit bit quantizes CSI, exists the error of quantification.The performance that causes precoding is compared with the ideal situation of the complete known CSI of transmitting terminal, and bigger loss is arranged.

Find through literature search prior art, " the Multiple Antenna Broadcast Channels With Shape Feedback and LimitedFeedback " that Peilu Ding etc. deliver on IEEE Transaction onSignal Processing (2007 the 55th the 7th phases of volume, 3417-3428 page or leaf).Proposed the method for precoding of Limited Feedback in this article, wherein the concrete grammar of channel quantitative is: receiver user at first estimates channel state vectors; From the code book of constructing in advance, select then and the code word of channel state vectors, come the channel state vectors of representative of consumer apart from minimum; At last selected codeword number is fed back to transmitter, generate pre-coding matrix by transmitter.Its deficiency is: in order to reduce the error of quantification, must increase the size that quantizes code book.Increase codebook size and mean, system strengthens the demand of code book memory space, and in the quantizing process, the increase of computation complexity.

Summary of the invention

The objective of the invention is to overcome deficiency of the prior art, a kind of multiuser MIMO system channel quantization method and device based on Limited Feedback is provided, can reduce the error of quantification, the volumetric properties of raising system, when reaching identical speed and capacity, it is little that the present invention has an employed code book, the advantage that complexity is low.

The present invention is achieved by the following technical solutions:

A kind of multiuser MIMO system channel quantization method that the present invention relates to based on Limited Feedback, it is at first according to channel condition information, selects the code word with its angle minimum from code book, and calculates quantization error; From code book, select code word vector again with quantization error angle minimum; Channel vector is done projection to the space that two code word vectors selecting constitute, calculate the compound proportion factor; With the quantization step set that generates in advance the compound proportion factor is quantized.

Said method of the present invention comprises the steps:

Step 1, each user is according to channel condition information, from code book C ₁The last code word w that selects optimum ₁, to channel vector h _iQuantize, and calculate the quantification error e _i

Described from code book C ₁The last code word w that selects optimum ₁, its method is: traversal is selected the code word with channel vector angle minimum.

Described calculating quantizes error e _i, be the difference of code word vector and channel vector.

$w_1=\arg \underset{w_1\∈C_1}{\max }\left|h_i^H{w}_1\right|=\arg \underset{w_1\∈C_1}{\min }{\sin }^2(\∠(h_i,w_1))---\left(1\right)$

$e_i=h_i-\left(h_i^H{w}_1\right)w_1$

Step 2 is from code book C ₂The middle code word w that selects optimum ₂, to quantization error e _iQuantize.

Described from code book C ₂The middle code word w that selects optimum ₂, its method is: traversal is selected the code word with quantisation error vector angle minimum.

$w_2=\arg \underset{w_2\∈C_2}{\max }\left|e_i^H{w}_2\right|=\arg \underset{w_2\∈C_2}{\min }{\sin }^2(\∠(e_i,w_2))---\left(2\right)$

Step 3, computer memory span (w ₁, w ₂) orthogonal basis obtain w ₁And w ' ₂Wherein, w ₁And w ₂Be the code word vector of selecting in step 1 and the step 2, find the solution the compound proportion factor-alpha:

$\mathrm{\α}=\frac{{w_2^{\′}}^H{h}_i}{w_1^H{h}_i}---\left(3\right)$

Wherein, in the channel state vectors after the compound proportion factor-alpha is represented to quantize, w ₁Component and w ' ₂The ratio of component.

Step 4, real part and the imaginary part to the compound proportion factor-alpha quantizes respectively.The symbol of representing real part (imaginary part) with 1 bit information.With selecting to have constructed the quantization step set in advance, the absolute value of real part (imaginary part) is quantized.Select and the shortest quantization step of real part (imaginary part) absolute value Euclidean distance, quantize its size.

Step 5 is with w ₁And w ₂At code book C ₁And C ₂In numbering, and the quantitative information of compound proportion factor-alpha feeds back to transmitting terminal.

Step 6, transmitting terminal be according to feedback information, the channel vector after reconstruct quantizes

${\hat{h}}_i=w_1+\widehat{\mathrm{\α}}{w}_2^{\′}$

$w_2^{\′}=\frac{w_2-\left(w_1{w}_2^H\right)w_1}{\left|\right|w_2-\left(w_1{w}_2^H\right)w_1\left|\right|}---\left(4\right)$

$\widehat{\mathrm{\α}}=s_{\mathrm{re}}{\widehat{\mathrm{\α}}}_{\mathrm{re}}+s_{\mathrm{im}}{\widehat{\mathrm{\α}}}_{\mathrm{im}}$

Wherein, s _ReAnd s _ImBe respectively the symbol of compound proportion factor-alpha real part and imaginary part; s _ReAnd s _ImBe respectively the quantization step size of compound proportion factor-alpha real part and imaginary part absolute value.

Described code book C ₁And C ₂, its structure may further comprise the steps:

1. step determines transmitting terminal number of transmit antennas M, and code book C ₁Size

And code book C ₂Size

Step 2., from M dimension space unit ball, picked at random

Individual vector constitutes code book C ₁Select code book C ₁Before

Individual vector constitutes code book C ₂

The set of described compound proportion factor-alpha real part (imaginary part) quantization step, its structure may further comprise the steps:

1. step by Matlab (mathematics laboratory) emulation, determines code book C ₁With code book C ₂Down, the approximate statistical characteristic of compound proportion factor-alpha real part (imaginary part);

Step 2., according to the size of selected quantization step set, the approximate statistical characteristic of compound proportion factor-alpha real part (imaginary part) absolute value.The set of search structure quantization step makes average quantization error minimum.

Based on said method, the present invention relates to a kind of device that quantizes based on the multiuser MIMO system channel of Limited Feedback, comprising: receiving end device and the transmitting terminal device that is mated, wherein:

Described receiving end device comprises:

The channel condition information acquiring unit obtains channel condition information;

The channel vector quantifying unit, the channel condition information that the channel status acquiring unit is obtained quantizes.From code book, select two code word vectors respectively, and calculate the compound proportion factor.Linear combination with code word comes the quantization means channel vector;

The quantitative information feedback unit, with the numbering of two code word vectors in code book, and the quantized result of the compound proportion factor feeds back to transmitting terminal;

Described transmitting terminal device comprises:

The feedback information reconfiguration unit receives the channel quantitative information that feeds back.Calculate the quantized result of reconstruct channel vector;

Precoding unit, the channel condition information according to after each user's quantification calculates corresponding pre-coding matrix.

Method step of the present invention is finished by the cooperation of transmitting end device and receiving end device.Transmitting end device comprises feedback information reconfiguration unit and precoding unit; Transmitting end device comprises the channel condition information acquiring unit, channel vector quantifying unit and quantitative information feedback unit.After receiving terminal receives the information of transmitting end device emission, finish a series of tasks of quantification of the obtaining of channel condition information, channel vector, feedback information is launched; After transmitting end device receives feedback information, finish tasks such as feedback information reconstruct, pre-coding matrix calculating, and use the pre-coding matrix that calculates that the data of preparing to transmit are carried out precoding, finally form missile information.

The corresponding relation of the functional unit of said apparatus and the inventive method performing step is: the quantification of channel vector in receiving terminal channel vector quantifying unit completing steps one, step 2, step 3 and the step 4; Quantitative information feedback unit completing steps five; Transmitting terminal feedback information reconfiguration unit completing steps six.

The present invention proposes a kind of new channel quantitative method, adopts the linear combination of two code words to come the quantized channel vector, thereby has reduced the error that quantizes, and has improved the performance of multi-user pre-coding.With respect to existing method, under same performance, the present invention has lower code book storage demand and lower computation complexity, be well suited for using in the reality, can be the third generation (3G), super three generations (B3G), the 4th generation (4G) cellular mobile communication and the technical scheme of systems such as Digital Television, WLAN (wireless local area network), wireless wide area network important theory foundation and concrete implementation method are provided.

Description of drawings

Fig. 1 has the multi-user MIMO system schematic diagram of launching precoding.

Fig. 2 is a real system device schematic diagram.

Fig. 3 is a channel vector quantizing process flow chart.

Fig. 4 is the code book of 12 bits, the approximate statistical performance plot of compound proportion factor-alpha real part (imaginary part).

Fig. 5 is system's speed and capacity simulation curve figure under the MIMO broadcast channel.

Fig. 6 is the different quantization step set speed and capacity simulation curve figure of system down.

Embodiment

Below in conjunction with accompanying drawing embodiments of the invention are elaborated: present embodiment is being to implement under the prerequisite with the technical solution of the present invention, provided detailed execution mode and concrete operating process, but protection scope of the present invention is not limited to following embodiment.

System comprise 1 base station and K user (user 1, and the user 2 ..., user K).There is the K transmit antennas base station, and each receiver user has 1 reception antenna.Among Fig. 1, Z _i(i=1,2 ..., K) for sending to i user's data; T _iBe expressed as the linear predictive coding process that i user sends data; R _iBe expressed as i user's receiver.At each user's receiving terminal, estimate channel state vectors separately, according to pre-designed code book, channel state vectors is quantized then, and, send back the base station by feedback channel.The base station receiving feedback information, each user's of reconstruct channel state vectors according to the channel state vectors of reconstruct, is carried out multi-user pre-coding at last.

(1) the multi-user MIMO system parameter configuration of present embodiment, specific as follows:

Base station number: 1 base station transmit antennas number: 6

Number of users: 6 user's reception antenna numbers: 1

Promptly as shown in Figure 1, the situation of number of users K=6.

Channel model is MIMO broadcast channel (MIMO Broadcast Channel), specifically please refer to " Multiple Antenna Broadcast Channels With Shape Feedback and LimitedFeedback ", IEEE TRANSACTIONS ON SIGNAL PROCESSING, VOL.55, NO.7, July 2007.

(2) code book structure:

The random configuration size is the code book C of 8 bits, 12 bits, 16 bits and 20 bits ₁Promptly according to as among Fig. 3, the flow process of code book structure, structure contains 256,4,096,65,536 and 1,048, the code book collection of 576 code words respectively.

(3) compound proportion factor-alpha quantization step set:

According to as among Fig. 3, the flow process of code book structure is to the code book C of 12 bits ₁, the 6 bit code book C that therefrom select ₂Emulation obtains the approximate statistical characteristic of compound proportion factor-alpha real part (imaginary part).Simulation curve adopts the approximate probability density function curve that obtains compound proportion factor-alpha real part and imaginary part of method of emulation as shown in Figure 4.The statistical property of compound proportion factor-alpha is used to search for optimum quantization step coefficient.Search obtains the quantization step set of two groups of different feedback quantities.

Feed back special number	Quantization step
			4 bits	[0.12，0.33]
6 bits	[0.06，0.18，0.28，0.38]

According to as among Fig. 3, the flow process of code book structure is to the code book C of 8 bits ₁, the 6 bit code book C that therefrom select ₂Emulation obtains the approximate statistical characteristic of compound proportion factor-alpha real part (imaginary part).Search obtains the quantization step set of two groups of different feedback quantities.

Feed back special number	Quantization step
			4 bits	[0.17，0.46]
6 bits	[0.09，0.27，0.41，0.55]

(4) quantification manner parameter:

Mode 1 and mode 2 are used existing channel quantitative mode, adopt 20 bit code books and 16 bit code books respectively, as algorithm performance of the present invention reference relatively.At different feedback quantity sizes, with the different quantification manner 3-6 of algorithm design of the present invention.

(5) system and device

For different quantification manner 3-6, the device of transmitting terminal and receiving terminal is identical, and as shown in Figure 2, base station apparatus comprises feedback information reconfiguration unit and precoding unit.Each user's receiving end device comprises channel condition information acquiring unit, channel vector quantifying unit and quantitative information feedback unit.

The device of receiving terminal is used for the quantized channel state vector, and the flow process of its work comprises design codebooks, the flow process of quantization step set and the flow process of receiver user quantized channel state information vector in advance as shown in Figure 3.The flow process of code book design is at first determining code book collection C ₁, therefrom select code book collection C then ₂, at last according to C ₁And C ₂, search out optimum quantization step set.The flow process of quantized channel state information vector is, at first extracts channel condition information, travels through code book collection C then ₁Determine code word w ₁, then travel through code book C ₂Determine code word w ₂, again according to the code word w that selects ₁And w ₂, calculate and quantification compound proportion factor-alpha the result of last feedback quantization.

(6) simulation result

The result of emulation such as Fig. 5, shown in Figure 6.Wherein Fig. 5 has compared under the different quantification manners according to the parameter among the embodiment, the speed of whole system and the simulation result of performance.Fig. 6 has compared and has adopted different quantization step set, the speed of whole system and the simulation result of performance according to the parameter among the embodiment.

Mode 1, mode 2 adopt the reference as a comparison of existing quantization method, the new method that mode 3, mode 4 adopt the present invention to propose.As shown in Figure 5, mode 3 is compared with mode 1, mode 4 is compared with mode 2, and the volumetric properties of system is almost completely consistent.But the size of code book that the present invention adopts only is 1/256 of existing method codebook size, therefore, the expense that has lower memory space requirements and quantize to calculate, thus implementation complexity reduced.

Mode 5, mode 6 shown, under fixing code book situation, and the performance of the present invention upper bound.If do not consider the quantification of α, the quantification feedback quantity of mode 6 and mode 2 is identical.But the not only used code book of the present invention is less, and volumetric properties is better than existing method.When SNR=30dB, adopt the new method of 8 bit code books, the speed and capacity of system can reach 10.0bps/Hz; With respect to existing method, adopt 16 bit code books, can only reach 8.1bps/Hz.

Consider the bit information of the quantification of α, feedback quantity of the present invention can increase to some extent.Fig. 6 has compared the code book for 4,096 code words, B ₁=12bit, B ₂Under the situation of=6bit, the different quantification manners of α are to the influence of speed and capacity.Volumetric properties when not quantizing with α is compared, if adopt 4bit information to quantize (table 1, table 2), performance is just more approaching; If adopt 6bit information to quantize, performance is almost consistent.Take all factors into consideration the increase of feedback quantity and the loss of performance, it is just enough generally to adopt 4bit information to quantize α.Along with the increase of codebook size, the average quantization error of α real part (imaginary part) is more and more littler, and the shared proportion of overhead bit of feedback α is also more and more littler, and advantage of the present invention is obvious further.

Claims (10)

1, a kind of multiuser MIMO system channel quantization method based on Limited Feedback is characterized in that, may further comprise the steps:

Step 1, each user is according to channel condition information, from code book C ₁The last code word w that selects optimum ₁, to channel vector h _iQuantize, and calculate the quantification error e _i

Step 2 is from code book C ₂The middle code word w that selects optimum ₂, to quantization error e _iQuantize;

Step 3, computer memory span (w ₁, w ₂) orthogonal basis obtain w ₁And w ' ₂, find the solution the compound proportion factor-alpha;

Step 4, real part and the imaginary part to the compound proportion factor-alpha quantizes respectively;

Step 5 is with w ₁And w ₂At code book C ₁And C ₂In numbering, and the quantitative information of compound proportion factor-alpha feeds back to transmitting terminal;

Step 6, transmitting terminal be according to feedback information, the channel vector after reconstruct quantizes

2, the multiuser MIMO system channel quantization method based on Limited Feedback as claimed in claim 1 is characterized in that, and is in the step 1, described from code book C ₁The last code word w that selects optimum ₁, its method is: traversal is selected the code word with channel vector angle minimum.

3, the multiuser MIMO system channel quantization method based on Limited Feedback as claimed in claim 1 or 2 is characterized in that, in the step 1, described calculating quantizes error e _i, be the difference of code word vector and channel vector.

4, the multiuser MIMO system channel quantization method based on Limited Feedback as claimed in claim 1 is characterized in that, and is in the step 2, described from code book C ₂The middle code word w that selects optimum ₂, its method is: traversal is selected the code word with quantisation error vector angle minimum.

5, the multiuser MIMO system channel quantization method based on Limited Feedback as claimed in claim 1 is characterized in that, in the step 3, and described computer memory span (w ₁, w ₂) orthogonal basis obtain w ₁And w ' ₂, it is found the solution the compound proportion factor-alpha and is:

$\mathrm{\α}=\frac{{w_2^{\′}}^H{h}_i}{w_1^H{h}_i}$

In the channel vector after the compound proportion factor-alpha is represented to quantize, w ₁Component and w ' ₂The ratio of component.

6, the multiuser MIMO system channel quantization method based on Limited Feedback as claimed in claim 1, it is characterized in that, in the step 4, the method for the quantification of the described compound proportion factor is to select and compound proportion factor real part or the shortest quantization step of imaginary part absolute value Euclidean distance from the quantization step set.

7, as claim 1 or the 6 described methods that quantize based on the multiuser MIMO system channel of Limited Feedback, it is characterized in that, described compound proportion factor-alpha quantization step set, its structure may further comprise the steps:

1. step by Matlab emulation, determines code book C ₁With code book C ₂Down, the approximate statistical characteristic of compound proportion factor-alpha real part or imaginary part;

Step 2., according to the size of selected quantization step set, the approximate statistical characteristic of compound proportion factor-alpha real part or imaginary part absolute value, the set of search structure quantization step makes average quantization error minimum.

8, want the 1 described method that quantizes based on the multiuser MIMO system channel of Limited Feedback as right, it is characterized in that, in the step 6, described transmitting terminal utilizes the channel vector after feedback information reconstruct quantizes

Be specially:

${\hat{h}}_i=w_1+\widehat{\mathrm{\α}}{w}_2^{\′}$

$w_2^{\′}=\frac{w_2-\left(w_1{w}_2^H\right)w_1}{\left|\right|w_2-\left(w_1{w}_2^H\right)w_1\left|\right|}$

$\widehat{\mathrm{\α}}=s_{\mathrm{re}}{\widehat{\mathrm{\α}}}_{\mathrm{re}}+s_{\mathrm{im}}{\widehat{\mathrm{\α}}}_{\mathrm{im}}$

Wherein, s _ReAnd s _ImBe respectively the symbol of compound proportion factor-alpha real part and imaginary part; s _ReAnd s _ImBe respectively the quantization step size of compound proportion factor-alpha real part and imaginary part.

9, the multiuser MIMO system channel quantization method based on Limited Feedback as claimed in claim 1 is characterized in that, described code book C ₁And C ₂, its structure may further comprise the steps:

1. step determines transmitting terminal number of transmit antennas M, and code book C ₁Size And code book C ₂Size

Step 2., from M dimension space unit ball, picked at random

Individual vector constitutes code book C ₁, select code book C ₁Before Individual vector constitutes code book C ₂

10, a kind of device that quantizes based on the multiuser MIMO system channel of Limited Feedback, comprising: receiving end device and the transmitting terminal device that is mated is characterized in that:

Described receiving end device comprises: the channel condition information acquiring unit, obtain channel condition information;

Described channel vector quantifying unit, the channel condition information that the channel status acquiring unit is obtained quantizes, and selects two code word vectors from code book respectively, and calculates the compound proportion factor, comes the quantization means channel vector with the linear combination of code word; Described quantitative information feedback unit, with the numbering of two code word vectors in code book, and the quantized result of the compound proportion factor feeds back to transmitting terminal;

Described transmitting terminal device comprises: feedback information reconfiguration unit, precoding unit;

Described feedback information reconfiguration unit receives the channel quantitative information that feeds back, and calculates the quantized result of reconstruct channel vector; Described precoding unit, the channel condition information according to after each user's quantification calculates corresponding pre-coding matrix.

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