CN101064545A - Method for switching equal information quantity based transmission mode - Google Patents

Abstract

The invention discloses a transmission mode switch mode based on equal information, firstly it obtains the real space channel matrix, and obtains the Signal-to-Noise by feedback, according to the total number of sending antennas and all transmission mode, and combines the number of antennas and the different transmission mode to form different transmission mode, and decides the equal information matrix of real information channel for each transmission mode according to the transmission mode and real channel matrix, and calculates the equal information according to the equal channel matrix and the Signal-to-Noise, and at last chooses the mode with biggest equal information to transmit according to the transmission mode. The method in the invention can realize the switch between the different transmission modes.

Description

A kind of transmission mode switching method based on equal information quantity

Technical field

The present invention relates to a kind of transmission mode switching method, relate in particular to the transmission mode switching method of a kind of multiple-input and multiple-output (MIMO) communication system.

Background technology

Mimo system uses a plurality of (Nt) transmitting antennas and a plurality of (Nr) reception antenna transmission data.Can resolve into Ns space channel by a described Nt transmitting antenna and Nr the formed mimo channel of reception antenna, Ns≤min{Nt wherein, Nr}.Ns after a decomposition space channel is independently each other, therefore can transmit Ns data flow independently simultaneously, and this makes mimo system that bigger throughput or higher reliability arranged.General, select to use the decision of which kind of MIMO pattern (diversity, multiplexing or mixed mode) both can make also and can make by transmit leg by the recipient.If determine to use which kind of MIMO pattern by the recipient, then the recipient need feed back to transmit leg to pattern.If use which kind of MIMO pattern by the transmit leg decision, then need: in the FDD/TDD system, recipient's feeding back channel state information is given transmit leg; Perhaps in the TDD system, transmit leg uses reciprocity to estimate channel status.

Because a plurality of channels can be launched independent data flow simultaneously, therefore just there is multiple different emission mode.Common emission mode has two kinds, i.e. diversity mode and multiplexer mode.Feasible diversity emission mode is at present: (1) space and time diversity (space-time diversity) pattern, specific descriptions can be referring to paper: A simple Transmit Diversity Technique for Wireless Communications (S.M.Alamouti, IEEE JSAC, Oct.1998); (2) postpone diversity (delay diversity) pattern, specific descriptions can be referring to paper: Performance of closed Loop Transmit Diversity withFeedback Delay (B.Raghothaman, Thirty-Fourth Asilomar Conference onSignals, Systems and Computers, 2000); (3) day line options (Antenna selection) pattern, specific descriptions can be referring to papers: and Antenna selection for spatial multiplexing withlinear receivers (R.W.Health, IEEE Comm, April.2001).

And multiplexing, promptly spatial reuse is meant the different data flow of emission on a plurality of antennas, requires recipient's antenna number to be no less than the antenna number of emission side.Three kinds of transmission modes the most basic are: space and time diversity, postpone diversity, and spatial reuse, the relation between this three is arranged side by side.In the common mimo system or use diversity individually, or use multiplexing individually.Because day line options does not have too big difference with spatial reuse in system's realization,, between them, switch then so existingly merged diversity and multiplexing MIMO transmission mode combines these two kinds of patterns.But for space and time diversity or postpone for the diversity, they realize having different significantly with the system of spatial reuse, do not carry out so common mimo system combines space and time diversity or delay diversity and spatial reuse.Yet space and time diversity can with the spatial reuse use that combines, and form multiple different transmission mode according to the degree of combination.Space and time diversity or postpone to divide the raising of set pair systematic function to realize by reducing the error rate is generally used for channel condition and is not under the enough good situation, and for example correlation between channels is more intense; And spatial reuse is to realize by improving the quantity that sends data to the raising of systematic function, is generally used under the reasonable situation of channel condition, and for example correlation between channels is lower.

Therefore, raising for systematic function, and select suitable transmission mode according to different channel conditions, just need a kind of method technically, promptly can or postpone diversity and be combined together to form multiple different transmission mode, and can between different transmission modes, switch according to the change of channel condition with spatial reuse space diversity.

Summary of the invention

Technical problem to be solved by this invention just provides a kind of transmission mode switching method that is used for multiple-input-multiple-output communication system, transmission modes such as space and time diversity, spatial reuse are combined, between them, switch according to the change of channel status or signal to noise ratio.

For solving the problems of the technologies described above, the invention provides a kind of transmission mode switching method based on equal information quantity, the transmission mode that is used for multiple-input-multiple-output communication system is switched, and comprises the steps:

(1) according to transmitting antenna sum Nt, and all emission modes that can adopt, various antenna amounts in the Nt scope are made up with the different emission modes that can adopt, form different transmission modes, every kind of unique antenna number and emission mode of having determined one group of actual use of transmission mode;

(2) calculate actual spatial channel matrix H and signal to noise ratio snr;

(3),, determine the equivalent channels matrix H equ of H at each transmission mode according to described each transmission mode and described actual channel matrix H;

(4), calculate the equal information quantity Cequ of each transmission mode correspondence according to the equivalent channels matrix H equ and the signal to noise ratio snr of each transmission mode correspondence;

(5) according to the different equal information quantity Cequ of all transmission mode correspondences, therefrom select the pattern of equal information quantity maximum to transmit.

All emission modes in the described step (1) comprise: diversity mode, multiplexer mode and mixed mode.

Spatial channel matrix H in the described step (2) is calculated and is fed back to emission side by receiving side signal, is perhaps estimated by the reciprocity of signal emission side use channel.

The signal to noise ratio snr of described step (2) is measured and is fed back to emission side by receiving side signal.

A kind of transmission mode switching method of the present invention based on equal information quantity, exactly different transmission modes is combined, under the situation that the signal to noise ratio or the channel status of mimo system changes, can select best transmission mode to transmit by their equal information quantity relatively.Because the transmission rate difference of different mode just can change transmission rate so switch, thereby help Adaptive Transmission speed in mimo system, has promptly improved the performance of system.

Description of drawings

Fig. 1 is the matrix notation schematic diagram according to the transmission mode of an antenna of the described use of the embodiment of the invention;

Fig. 2 is the matrix notation schematic diagram according to the transmission mode of two antennas of the described use of the embodiment of the invention;

Fig. 3 is the matrix notation schematic diagram according to the transmission mode of three antennas of the described use of the embodiment of the invention;

Fig. 4 is the matrix notation schematic diagram according to the transmission mode of four antennas of the described use of the embodiment of the invention;

Fig. 5 is the matrix notation schematic diagram according to the described transmission mode of the embodiment of the invention;

Fig. 6 is the schematic diagram that concerns according to described amount of information of the embodiment of the invention and signal to noise ratio;

Fig. 7 is the flow chart that switches according to the described transmission mode of the embodiment of the invention.

Embodiment

Different transmission modes can provide different transmission rates, and this can realize from two aspects, promptly adopt different antenna number and diversity or multiplexing use.Because, for Nt transmitting antenna, when carrying out the signal transmission, not necessarily to all use certain time slot, and may only use a part of antenna that more performance is arranged on the contrary, this depends at that time channel condition and signal to noise ratio.So scheme is formed different pattern lists according to the antenna number of the actual use of pattern, travels through the pattern list of all feasible antenna number then, therefrom selects the pattern an of the best.For the selection of transmission mode, be on the basis of comparing its equal information quantity, to carry out.The equal information quantity here comprises: one used equivalent channels in the amount of information that compares different transmission mode, and equivalent channels can be expressed as the form of received signal vector/emission signal vector; Its two because the once complete transmission of different transmission modes may comprise different time slots, for example spatial reuse only needs a time slot space diversity then to need two at least, so align on time slot for different transmission mode.

Changing method based on equal information quantity comprises following several steps: (1) estimates actual space channel H; (2) measure signal to noise ratio snr; (3) to the actual spendable antenna number (iCurAntNum) of transmission signals, from its pattern list, select iCurMod pattern, and calculate its equivalent channels matrix H equ according to the space channel H of reality, 1≤iCurAntNum≤Nt wherein, 1≤iCurMod≤iModNum[iCurAntNum], iModNum[iCurAntNum] be iCurAntNum the actual pairing pattern sum of antenna number that uses; (4) according to the equal information quantity of equivalent channels matrix and snr computation present mode (Cequ[iCurAntNum] [iCurMod]); (5) select the pattern of equal information quantity maximum, i.e. [iSelAntNum, iSelMod]=argmax (Cequ), wherein iSelAntNum and iSelMod represent the antenna number and the pattern of maximum equal information quantity correspondence.

Be equivalent to provide best transmission mode after finishing above step, physically signal launched again, just finished the switching of transmission mode.

To Nt transmitting antenna and Nr the formed mimo system of reception antenna, communication channel can resolve into Ns space channel, Ns≤min{Nt wherein, Nr}.Suppose that the channel response between Nt transmitting antenna and Nr the reception antenna is H.

The existing model of mimo system can be expressed as:

r＝Hx+n

Wherein, x represents the vector that transmits, and r represents the received signal vector, and n represents noise vector.

The existing Shannon amount of information of mimo system is:

C＝log ₂(det(I+HR _xxH ^H))

Wherein, R _Xx=E (xx ^H) be the covariance matrix that transmits, represented the Power Limitation condition that transmits.Suppose power mean allocation on transmitting, the amount of information of mimo system can be expressed as so:

$C={\log }_2\left(\det (I+\frac{\mathrm{SNR}}{N_t}{\mathrm{HH}}^H)\right)$

Wherein, SNR represents signal to noise ratio, and SNR/Nt represents power mean allocation on Nt transmits.

Below in conjunction with accompanying drawing present embodiment is described in further detail, Nt=Nr=4 in the present embodiment can access similar conclusion for other situation.

Shown in Fig. 1,2,3,4, be the matrix notation schematic diagram of the described different transmission mode of the embodiment of the invention, wherein, the part in all patterns that Fig. 1 represents when being antenna transmission signal of actual use; Part in all patterns that Fig. 2 represents when being two antenna transmission signals of actual use; Part in all patterns that Fig. 3 represents when being three antenna transmission signals of actual use; Part in all patterns that Fig. 4 represents when being four antenna transmission signals of actual use.

As shown in Figure 5, be matrix notation schematic diagram according to the described transmission mode of the embodiment of the invention, matrix when it has provided transmit empty, wherein row matrix is represented antenna, time slot is shown in tabulation.Pattern a represents only to use two antennas to transmit, and signal has carried out the Alamouti Space Time Coding of quadrature.Obviously, the signal that decoding schema a is launched only needs an antenna just much of that, under the situation that four reception antennas are arranged, uses maximum gain than merging and is equivalent to receive diversity.Pattern b is illustrated in two pairs of quadrature Space Time Coding signals of emission on four antennas.The signal that decoding schema b is launched needs two antennas at least, can use the maximum gain ratio to merge under the situation that four antennas are arranged.Pattern c is illustrated in four different signals of emission on four antennas, and this mode that transmits is also referred to as spatial reuse.

Channel matrix during present embodiment Nt=Nr=4 is:

$H=\left[\begin{array}{cccc}{h}_{11}& h_{21}& h_{31}& h_{41}\\ h_{12}& h_{22}& h_{32}& h_{42}\\ h_{13}& h_{23}& h_{33}& h_{43}\\ h_{14}& h_{24}& h_{34}& h_{44}\end{array}\right]$

If use pattern a to transmit, the signal that two time slots are received on the i root antenna is so:

r _i1＝h _1iS ₁+h _2iS ₂+n _i1

$r_{i2}=-h_{1i}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="A20061007903900122.png,A20061007903900131.png"\; state="\{\{state\}\}">S</figure-callout>}}_2^{*}+h_{2i}{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="A20061007903900122.png,A20061007903900141.png"\; state="\{\{state\}\}">S</figure-callout>}}_1^{*}+n_{i2}$

Following formula can be expressed as with vector form:

r _i＝H _iS+n _i

Wherein, r _i=[r _I1, r _I2] ^T, n _i=[n _I1, n _I2] ^T, S=[S ₁, S ₂] ^T, $H_i=\left[\begin{array}{cc}{h}_{1i}& h_{2i}\\ h_{2i}^{*}& -h_{1i}^{*}\end{array}\right].$

Obviously, H _i(being equivalent channels matrix H equ) is an orthogonal matrix.Compare formula r=Hx+n and formula r _i=H _iS+n _i, both have similar forms.This explanation uses pattern a to transmit, and channel can be by the equivalence channel that is orthogonal.The signal that all receive on the reception antenna is carried out maximum gain than merging, and this moment, amount of information of equal value can be expressed as:

$\mathrm{Ce}{\mathrm{qu}}_A=\underset{i=1}{\overset{N_t}{\mathrm{\&Sigma;}}}{\log }_2\left(\det (I+\frac{2\mathrm{SNR}}{N_t}{H}_i{H}_i^H)\right)$

The amount of information that system can reach when following formula just was to use pattern a to transmit.

Equally, if use pattern b to transmit, the signal that two time slots are received on the i root antenna is so:

r _i1＝h _1iS ₁+h _2iS ₂+h _3iS ₃+h _4iS ₄+n _i1

$r_{i2}=-h_{1i}{\mathrm{<figure-callout\; id="2"\; label="S"\; filenames="A20061007903900122.png,A20061007903900131.png"\; state="\{\{state\}\}">S</figure-callout>}}_2^{*}+h_{2i}{\mathrm{<figure-callout\; id="1"\; label="S"\; filenames="A20061007903900122.png,A20061007903900141.png"\; state="\{\{state\}\}">S</figure-callout>}}_1^{*}-h_{3i}{\mathrm{<figure-callout\; id="4"\; label="S"\; filenames="A20061007903900132.png,A20061007903900141.png"\; state="\{\{state\}\}">S</figure-callout>}}_4^{*}+h_{4i}{\mathrm{<figure-callout\; id="3"\; label="S"\; filenames="A20061007903900131.png,A20061007903900141.png"\; state="\{\{state\}\}">S</figure-callout>}}_3^{*}+n_{i2}$

Following formula can be expressed as with vector form:

r _i＝A _iS ₁₂+B _iS ₃₄+n _i

Wherein, r _Ij=[r _i, r _j] ^T, S=[S ₁₂, S ₃₄] ^T, n _Ij=[n _i, n _j] ^T, $H_{\mathrm{ij}}=\left[\begin{array}{cc}{A}_i& B_i\\ A_j& B_j\end{array}\right].$

Different with pattern a is to have only formula r _i=A _iS ₁₂+ B _iS ₃₄+ n _iCan't decoded signal, because two unknown numbers are arranged, but have only an equation in this formula.Suppose the signal decoding that uses i and j root antenna to receive, so antenna to (i, the signal that receives on j) is:

r _ij＝H _ijS+n _ij i≠j

Wherein, r _Ij=[r _i, r _j] ^T, S=[S ₁₂, S ₃₄] ^T, n _Ij=[n _i, n _j] ^T, $H_{\mathrm{ij}}=\left[\begin{array}{cc}{A}_i& B_i\\ A_j& B_j\end{array}\right].$

The H of this moment _Ij(being equivalent channels matrix H equ) be orthogonal matrix not necessarily, but with respect to matrix H, H _IjThe order attribute much better, this explanation use pattern b transmission signals can improve systematic function.Equally, carry out maximum gain than merging, the equal information quantity that can access b is:

${\mathrm{Cequ}}_B={\log }_2\left(\det (I+\frac{\mathrm{SNR}}{N_t}{H}_{12}{H}_{12}^H)\right)+{\log }_2\left(\det (I+\frac{\mathrm{SNR}}{N_t}{H}_{34}{H}_{34}^H)\right)$

Pattern c does not use Space Time Coding, directly different signals is launched from different antennas.Its amount of information is exactly the amount of information of mimo system, i.e. formula:

$C={\log }_2\left(\det (I+\frac{\mathrm{SNR}}{N_t}{\mathrm{HH}}^H)\right).$

But pattern c can not directly compare with pattern a, b, because pattern a, b have used two time slots, and pattern c has only used a time slot.So,, on time slot, align to the amount of information of pattern c for the comparison three's of justice amount of information.Therefore, the equal information quantity of alignment back pattern c is:

$\mathrm{Ceq}{u}_C=2\mathrm{lo}{g}_2\left(\det (I+\frac{\mathrm{SNR}}{N_t}{\mathrm{HH}}^H)\right)$

Channel matrix at random is:

$H=\left[\begin{array}{cccc}0.4070& 0.1068& 0.0937& 0.2562\\ 0.1905& 0.0101& 0.3165& 0.3587\\ 0.2461& 0.1364& 0.5137& 0.9897\\ 0.9316& 04622& 0.5030& 0.4335\end{array}\right].$

As shown in Figure 6, be the schematic diagram that concerns according to described amount of information of the embodiment of the invention and signal to noise ratio, this figure has showed the variation of the equal information quantity of pattern a/b/c with SNR, and in order more to clearly illustrate their difference, what provide among the figure is the poor of equal information quantity.As can be seen from the figure, as SNR greater than 21db the time, pattern a is better than pattern b, pattern c, and as SNR less than 19db the time, pattern b is better than pattern a, pattern c, when SNR when 19db is between 21db, pattern c is better than pattern a, pattern b.

As shown in Figure 7, be the flow chart that switches according to the described transmission mode of the embodiment of the invention, detailed process is as follows:

Step 701: obtain link channel information H;

Step 702: obtain signal to noise ratio snr;

Step 703: make iCurAntNum equal 1;

Step 704: make iCurMod equal 1 again;

Step 705: from the pattern list of iCurAntNum antenna, select iCurMod pattern, calculate its equivalent channels matrix H equ;

Step 706: according to the equal information quantity Cequ[iCurAntNum of equivalent channels matrix H equ and signal to noise ratio snr calculating present mode] [iCurMod];

Step 707: make the value of iCurMod increase 1;

Step 708: judge whether iCurMod is less than or equal to iModNum[iCurAntNum], if, enter step 705, if not, enter step 709;

Step 709: make the value of iCurAntNum increase 1;

Step 710: judge whether iCurAntNum is less than or equal to Nt, if, enter step 704, if not, enter step 711;

Step 711: select the pattern of equal information quantity maximum, i.e. [iSelAntNum, iSelMod]=argmax (Cequ);

Step 712: finishing switching.

Wherein, the information of the described channel of step 701, can obtain by dual mode: the one, transmit leg obtains channel information by feedback; The 2nd, in the TDD system, transmit leg can use the reciprocity estimating channel information of channel.

Step 702 is described to be the process of obtaining signal to noise ratio, measures and feeds back to transmit leg by the recipient.

Step 705 is described to be the process of calculating the equivalent channels matrix, different transmission modes and actual channel matrix H have determined equivalent channels matrix H equ jointly, for the channel matrix H of current reality, determine to calculate its equal information quantity after the corresponding equivalent channels matrix.

Step 711 is described, is the process of making the transmission mode decision-making according to equal information quantity, promptly selects the pattern of equal information quantity maximum to transmit.

Under the certain situation of bandwidth, two key factors of decision mimo system amount of information are exactly signal to noise ratio and channel matrix.Under the constant situation of channel matrix, along with the change of signal to noise ratio, the change difference of the equal information quantity of different transmission mode, this just makes the situation that can be used in different signal to noise ratios based on the changing method of equal information quantity.

The described method of present embodiment combines different transmission modes exactly, under the situation that the signal to noise ratio or the channel status of mimo system changes, can select best transmission mode to transmit by the equal information quantity of different transmission mode relatively.

Increased amount of system information therefrom, can improve the performance of system from two aspects: the one, at the certain situation decline low error rate of transmitted data amount; The 2nd, under the certain situation of the error rate, improve volume of transmitted data.Because the transmission rate difference of different transmission mode just can change transmission rate so switch, thereby be beneficial to Adaptive Transmission speed in mimo system, to improve the performance of system.

Claims (5)

1, a kind of transmission mode switching method based on equal information quantity, the transmission mode that is used for multiple-input-multiple-output communication system is switched, and it is characterized in that, comprises the steps:

(1) according to transmitting antenna sum Nt, and all emission modes that can adopt, various antenna amounts in the Nt scope are made up with the different emission modes that can adopt, form different transmission modes, every kind of unique antenna number and emission mode of having determined one group of actual use of transmission mode;

(2) calculate actual spatial channel matrix H and signal to noise ratio snr;

(3),, determine the equivalent channels matrix H equ of H at each transmission mode according to described each transmission mode and described actual channel matrix H;

(4), calculate the equal information quantity Cequ of each transmission mode correspondence according to the equivalent channels matrix H equ and the signal to noise ratio snr of each transmission mode correspondence;

(5) according to the different equal information quantity Cequ of all transmission mode correspondences, therefrom select the pattern of equal information quantity maximum to transmit.

2, the method for claim 1 is characterized in that, described all emission modes of step (1) comprise: diversity mode, multiplexer mode and mixed mode.

3, the method for claim 1 is characterized in that, the described spatial channel matrix H of step (2) is calculated and fed back to emission side by receiving side signal.

4, the method for claim 1 is characterized in that, the described spatial channel matrix H of step (2) uses the reciprocity of channel to estimate by signal emission side.

5, the method for claim 1 is characterized in that, the described signal to noise ratio snr of step (2) is measured and fed back to emission side by receiving side signal.

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