CN100591065C - Differential west space-time modulation constellation mapping method in multiple antenna orthogonal frequency division multiplexing - Google Patents

Abstract

The method comprises: mapping 0,1 binary bits into L=2RM form symbols - Zk, Zk=0, 1, ....L-1; the mapping is used for making the bits become a form adapted to be transmitted; the information symbol Zkis made with the unitary space-time constellation mapping and is mapped as MXM unitary matrix VAk; each column of the matrix is sent out through its corresponding antenna; taking time block as unit,namely the space-time constellation Xk sent in the time block of number k symbol is the product of the constellation Xk-1 sent in previous time slot and the unitary constellation VZk obtained by unitary constellation mapping; at receiving end, the receiving signals are combined into 2MXM matrix which is decoded using maximum likelihood to get the sending information.

Description

Differential west space-time modulation constellation mapping method in the multi-antenna orthogonal frequency division multiplexing system

Technical field

The present invention relates to a kind of modulation signal constellation mapping scheme when being used for duplicating multi-antenna orthogonal frequency division (OFDM) system differential west space, belong to communication technical field.

Background technology

The continuous development of mobile communication and people are growing to communication requirement, require to realize on effective frequency spectrum resource the quick transmission of integrated service, need the high technology of spectrum efficiency.MIMO (Multiple InputMultiple Output) technology, promptly adopt a plurality of antennas at transmitting terminal and receiving terminal, can under the situation that does not increase bandwidth, increase exponentially the capability of communication system and the availability of frequency spectrum, thereby obtain concern more and more widely.OFDM (Orthogonal Frequency Division Modulation) technology is a kind of multi-carrier transmission technology, utilizes the orthogonality between the multicarrier, efficiently utilizes frequency spectrum resource.MIMO and OFDM combine, made full use of the time, frequency, the three kinds of diversity techniques in space make wireless system to noise, the tolerance limit of interference and multipath increases greatly, effectively overcome the harmful effect of multipath effect and frequency selective fading, improved the reliability of transmission, increased power system capacity, improve the availability of frequency spectrum, now become the hot spot technology of the 4th third-generation mobile communication.

In recent years, people had carried out extensive studies to Space Time Coding.Space Time Coding commonly used has: trellis code STTC (Space-Time Trellis Codes), Space-Time Block Coding STBC (Space-Time Block Codes) and hierarchical space-time code BLAST (Bell Labs Layered Space-Time Architecture) when empty.These Space Time Coding all need channel information, and this just need send from transmitted from transmitter to receiver trains bit or pilot frequency sequence to carry out channel estimating.Yet channel estimating becomes more and more difficult when very fast or transmitting antenna number is more in decline, and this will seriously restrict the application of these Space Time Coding.Thereby Hochwald and Marzetta have proposed a kind of unitary space-time coding without any need for channel information.Because constellation method for designing complexity in the unitary blank time code, the constellation structures generalization is poor, the searching algorithm complexity height of key parameter in the constellation, therefore on the basis of unitary blank time code, Hochwald has proposed a kind of differential west space time-code DUSTM in conjunction with differential modulation (DifferentialUnitary Space-Time Modulation) again.This method is to come out in the conceptive amplification of single antenna DPSK (Differentialphase-shift keying), this method constellation design is simple, constellation is represented succinctly, and the searching algorithm moderate complexity, therefore becomes the focus of people's research in recent years.

Summary of the invention

Technical problem: the purpose of this invention is to provide differential west space-time modulation constellation mapping method in a kind of multi-antenna orthogonal frequency division multiplexing system, this method is based on the maximized design criterion of diversity product, adjust step-size in search, enlarge the search volume scope, constellation mapping method improves during to traditional differential west space, the diversity product is increased, improved systematic function.

Technical scheme: modulator approach when differential west space-time modulation constellation mapping method adopts traditional differential west space in the multi-antenna orthogonal frequency division multiplexing system of the present invention, the tenth of the twelve Earthly Branches, a kind of comparatively simple optimum unitary group sign indicating number design---diagonal angle unitary group sign indicating number was adopted in the design of constellation, this design adopt diagonal matrix as the tenth of the twelve Earthly Branches constellation when empty, and guarantee that constellation set constitutes a cyclic group, the parameter of constellation is selected when empty at the tenth of the twelve Earthly Branches, adopt the method for adjusting step-size in search, the search volume is expanded to the method for decimal scope from integer range, the diversity product is increased, obtain more excellent diagonal angle unitary group sign indicating number design parameter.

Improved parameter searching method is to expand the search volume to the decimal scope from integer range, 0,0.01,0.02 ... 1,1.01,1.02 ..., find the u that makes diversity gain ζ maximum among the L-1} ₁..., u _mValue.

Differential west space-time modulation constellation mapping method is in the multi-antenna orthogonal frequency division multiplexing system of the present invention: at transmitting terminal, 0,1 binary message bit is mapped to L=2 ^RMThe information symbol Z of system _k, Z _k=0,1 ... .L-1, mapping is for information bit being done the form that is fit to transmission that is transformed into; Information symbol Z _kCarry out constellation mapping at the tenth of the twelve Earthly Branches again, be mapped as M * M unitary matrice Each row of matrix are gone out by the antenna transmission of correspondence; With the time block is unit, constellation X when promptly the transmission in k symbol time piece is empty _kTransmission constellation X for previous time block _K-1With the unitary matrice that the tenth of the twelve Earthly Branches, constellation mapping obtained

Product; At receiving terminal, the sets of signals of reception is synthesized 2M * Metzler matrix, adopts maximum likelihood method to decipher, and obtains transmission information; Wherein: L is the system number, and R is a data rate, and M is a number of transmit antennas, k=1,2,3 ...

At transmitting terminal, information symbol Z _kCarrying out tenth of the twelve Earthly Branches constellation mapping is the unitary matrice of M * M

Adopt diagonal matrix as constellation at the tenth of the twelve Earthly Branches, and guarantee that constellation set constitutes a cyclic group, its mathematical expression is as follows: the generator matrix V of definition cyclic group ₁, it is a L unit root of unit matrix, that is:

Wherein: u _m∈ 0 ..., L-1} is the parameter that will design; M=0,1 ..., M; J represents imaginary part, and π represents circumference ratio; Each element in the constellation set can be expressed as:

$V_l=V_1^l---2)$

l＝0，…，L-1。

Adopt maximum likelihood method decoding, the estimated value of information symbol at receiving terminal

Can be expressed as:

${\hat{Z}}_k=\arg \underset{l=0,...,L-1}{\max }\left\{{\left|\right|Y_{k-1}+V_l^H{Y}_k\left|\right|}_F\right\}=\arg \underset{l=0,...,L-1}{\max }\left\{\mathrm{Retr}\right\{V_l{Y}_{k-1}{Y}_k^H\left\}\right\}---3)$

Wherein Re represents to get real part, tr{ } expression " mark " computing, || || _FNorm, X are got in expression ^HThe complex-conjugate matrix of representing matrix X,

Expression makes l=0 ..., L-1 gets maximum operation, Y _kK the symbol that expression receives.

u _mSetting adopt diversity product maximization criterion design criterion, promptly

Seek suitable u ₁..., u _m∈ 0 ..., L-1} makes diversity gain ζ big as far as possible;

$\mathrm{\ζ}=\arg \underset{l=1,...,L-1}{\max }\left\{{\left|\underset{m=1}{\overset{M}{\mathrm{\Π}}}\sin \left(\frac{\mathrm{\π}{u}_{m}l}{L}\right)\right|}^{1/M}\right\}---\left(4\right)$

Expression quadrature computing, | | the expression delivery,

Expression makes l=1 ..., L-1 gets minimum operation; The sine value computing is asked in sin () expression; In parameters u _mSearch procedure in, make l=1 ..., L-1, calculating formula (4) is got its minimum value and is composed to a variable gama, if this variable gama greater than variable ζ, gives variable ζ with variable gama assignment, is both and preserves u this moment _mValue give variable U _m, make u _m∈ 0 ..., L/2} repeats above step, searches maximum variable ζ and its corresponding U _mValue can be adjusted step-size in search, expands the search volume to the decimal scope from integer range, and the diversity product increases, and obtains more excellent diagonal angle constellation at the tenth of the twelve Earthly Branches.

Beneficial effect: modulator approach when the present invention is based on differential west space, the constellation mapping scheme has obtained the diversity gain bigger than traditional scheme when having proposed improved differential west space.This method based on diversity gain maximization design criterion, adopts the diagonal angle unitary group sign indicating number of cyclic group in system design, adjust the step-size in search of constellation parameter, enlarge the search volume, traditional constellation parameter design is improved, increased diversity gain, improved systematic function.With two one multiaerial systems of receiving is example, and as can be seen from Table 1, when message transmission rate is that R is 1bit/s/Hz, promptly during L=4, adopting the value of the maximum diversity gain that improved plan obtains is 0.74767, and originally the value that obtains of scheme is 0.7071; When R is 2bit/s/Hz, promptly during L=16, adopting the value of the maximum diversity gain that improved plan obtains is 0.39552, and the value that original scheme obtains is 0.3826.From performance map 5, also as can be seen, the performance of the system of the constellation mapping that the employing improved plan obtains will be got well about 1-3dB among Fig. 6.

Description of drawings

Modulating system integrated stand composition when Fig. 1 is the MIMO-OFDM differential west space,

Modulating system transmitting terminal block diagram when Fig. 2 is difference empty,

Modulating system receiving terminal block diagram when Fig. 3 is difference empty,

Fig. 4 is constellation parameter search process flow diagram when empty at the tenth of the twelve Earthly Branches,

Fig. 5 is that the systematic function simulation result of the listed parameter of table 1 compares (L=4),

Fig. 6 is that the systematic function simulation result of the listed parameter of table 1 compares (L=16).

Embodiment

The integral frame of MIMO-OFDM of the present invention system as shown in Figure 1, what suppose to adopt is two one structures of receiving.The serial information bit stream of input is divided into p parallel data stream, wherein p is a carrier number, modulation (DUSTM) when each line data flow point does not carry out differential west space, the output result's who modulates when each goes differential west space then first line data and second line data merge respectively, carry out inverse-Fourier transform (IFFT), add Cyclic Prefix (CP) again, and the string conversion, on two antennas, send simultaneously, at receiving terminal, carry out a series of anti-change, adopt maximum likelihood method (ML) to carry out demodulation.

The concrete scheme of modulation is as described below during differential west space:

1) at transmitting terminal, modulation scheme can be divided into following a few step and carries out during differential west space, as shown in Figure 2:

1. information symbol mapping: moment t=kM+1 (k=0,1 ...), RM information bit is mapped to L=2 ^RMThe information symbol Z of system _k, i.e. Z _k∈ 0,1 ..., L-1};

The tenth of the twelve Earthly Branches constellation mapping: constellation set omega when structure tenth of the twelve Earthly Branches is empty, by L=2 ^RMThe unitary matrice of individual M * M constitutes, Ω={ V ₀, V ₁..., V _L-1, V wherein _l∈ ^{M * M}And

The diagonal angle unitary group sign indicating number that the design adopts in the technical scheme to be mentioned based on cyclic group, information symbol Z _kBe mapped to unitary matrice

3. difference sends: modulation is the expansion of DPSK under many antennas situation during difference empty, and its process of transmitting is unit with the time block, i.e. constellation X during the transmission sky in k symbol time piece _kTransmission constellation X for previous time block (k-1 time block) _K-1With the unitary matrice that the tenth of the twelve Earthly Branches, constellation mapping obtained

Product, that is:

X ₀=I _M, k=1,2 ... 4) I wherein _MUnit for M * M.

2), suppose that channel fading is sparse in two adjacent time blocks (2M the time interval) to remain unchanged, i.e. H at receiving terminal _k=H _K-1, and represent with H.K the receiving matrix Y that the symbol time piece is interior _kCan be expressed as:

$Y_k=X_{k}H+N_k$

$=V_{Z_k}{X}_{k-1}H+N_k$

$=V_{Z_k}{Y}_{k-1}+N_k-V_{Z_k}{N}_{k-1}---5)$

$=V_{Z_k}{Y}_{k-1}+\sqrt{2}{N}_k^{\′}$

N ' wherein _kFor average is 0, variance is 1 white Gauss noise.According to maximum-likelihood criterion, the estimated value of information symbol can be expressed as:

${\hat{Z}}_k=\arg \underset{l=0,...,L-1}{\max }{\left|\right|Y_{k-1}+V_l^H{Y}_k\left|\right|}_F=\arg \underset{l=0,...,L-1}{\max }\mathrm{Retr}\left\{V_l{Y}_{k-1}{Y}_k^H\right\}---\left(6\right)$

Wherein Re represents to get real part, tr{ } expression " mark " computing, || || _FNorm is got in expression.X ^HThe complex-conjugate matrix of representing matrix X.

3) constellation parameter designing during differential west space: a kind of comparatively simple optimum unitary group sign indicating number design-diagonal angle unitary group sign indicating number is adopted in the design of constellation during differential west space.Its definition is as shown in technical scheme.The search of constellation parameter is promptly sought suitable u based on diversity product maximization criterion ₁..., u _m∈ 0 ..., L-1} makes diversity gain ζ big as far as possible.ζ is suc as formula 3) definition.

In order to reduce amount of calculation, use following simplification criterions:

Since every antenna all to be with respect to other antenna that statistics goes up of equal value, so hypothesis has u in proper order ₁≤ u ₂≤ ... ≤ u _M

2. can suppose u _m＞0, because if u _m=0, m root antenna only can send symbol 1 so, just is equivalent to cut little ice;

3. if u _mUse L-u _mReplace formula 3) can not change, therefore can limit the hunting zone at u _m∈ 0 ..., L/2}.

Concrete search step is seen Fig. 4.At first each initialization of variable is 0, L=2 ^RM, make l=1 ..., L-1, calculating formula 3), get its minimum value and compose to a variable gama, if this variable gama greater than variable G, gives variable G with variable gama assignment, be both and preserve u this moment _mValue give variable U _m, make u _m∈ 0 ..., L/2} repeats above step, searches maximum variable G and its corresponding U _mValue.

Traditional searching method is only for search for u in integer range _mValue, even u _m∈ { 0,1,2 ..., L/2}, step-size in search are 1, improved searching method is adjusted into 0.01 with step-size in search, with the little number space of hunting zone from integer space expansion, i.e. u _m∈ 0,0.01 ..., 1,1.01 ..., L/2}.

Following table has provided and has adopted with two one receipts systems, and R is respectively 1 and 2, i.e. the comparison of the Search Results under constellation size L=4 and 16 situations.From result of calculation as can be seen, the decimal scope with the search volume enlarges can obtain bigger diversity product.We have adopted MALAB that this system is carried out emulation simultaneously, and are as Fig. 5, shown in Figure 6.We are as can be seen from figure, under identical channel condition, to L=4, the systematic function that adopts improved constellation parameter is than the good 2.5dB of systematic function that adopts traditional constellation parameter, to L=16, adopt the systematic function of improved constellation parameter can improve about about 1dB.

Following table is to adopt two one receipts systems, and R is respectively 1 and 2, i.e. the comparison of the Search Results under constellation size L=4 and 16 situations.

Claims (2)

1, differential west space-time modulation constellation mapping method in a kind of multi-antenna orthogonal frequency division multiplexing system is characterized in that: at transmitting terminal, 0,1 binary message bit is mapped to L=2 ^RMThe information symbol Z of system _k, Z _k=0,1 ... .L-1, mapping is for information bit being done the form that is fit to transmission that is transformed into; Information symbol Z _kCarry out constellation mapping at the tenth of the twelve Earthly Branches again, be mapped as M * M unitary matrice

, each row of matrix are gone out by the antenna transmission of correspondence; With the time block is unit, constellation X when promptly the transmission in k symbol time piece is empty _kTransmission constellation X for previous time block _K-1With the unitary matrice that the tenth of the twelve Earthly Branches, constellation mapping obtained

Product; At receiving terminal, adopt maximum likelihood method to decipher, obtain transmission information;

At receiving terminal, suppose that at two adjacent time blocks channel fading is sparse in 2M the time interval remains unchanged, i.e. H _k=H _K-1, and represent the receiving matrix Y in k symbol time piece with H _kCan be expressed as:

$Y_k=X_{k}H+N_k$

$=V_{Z_k}{X}_{k-1}H+N_k$

$=V_{Z_k}{Y}_{k-1}+N_k-V_{Z_k}{N}_{k-1}$

$=V_{Z_k}{Y}_{k-1}+\sqrt{2}{N_k}^{\′}$

N ' wherein _kFor average is 0, variance is 1 white Gauss noise, and according to maximum-likelihood criterion, the estimated value of information symbol can be expressed as:

${\hat{Z}}_k=\arg \underset{l=0,...,L-1}{\max }{\left|\right|Y_{k-1}+V_l^H{Y}_k\left|\right|}_F=\arg \underset{l=0,...,L-1}{\max }\mathrm{Retr}\left\{V_l{Y}_{k-1}{Y}_k^H\right\}$

Wherein Re represents to get real part, and tr{} represents " mark " computing, ‖ ‖ _FNorm, X are got in expression ^HThe complex-conjugate matrix of representing matrix X;

Wherein: L is the system number, and R is a data rate, and M is a number of transmit antennas, k=1,2,3

At transmitting terminal, information symbol Z _kCarrying out tenth of the twelve Earthly Branches constellation mapping is the unitary matrice of M * M

, adopting diagonal matrix as constellation at the tenth of the twelve Earthly Branches, and guarantee that constellation set constitutes a cyclic group, its mathematical expression is as follows: the generator matrix V of definition cyclic group ₁, it is a L unit root of unit matrix, that is:

Wherein: u _m∈ 0 ..., L-1} is the parameter that will design; M=0,1 ..., M; J represents imaginary part, and π represents circumference ratio; Each element in the constellation set can be expressed as:

$V_l=V_1^l---2)$

l＝0，…，L-1；

u _mSetting adopt the design of diversity product maximization criterion, promptly seek

Suitable u ₁..., u _m∈ 0 ..., L-1} makes diversity product ζ big as far as possible;

$\mathrm{\ζ}=\arg \underset{l=1,...,L-1}{\min }\left\{{\left|\underset{m=1}{\overset{M}{\mathrm{\Π}}}\sin \left(\frac{\mathrm{\π}{u}_{m}l}{L}\right)\right|}^{1/M}\right\}---4)$

() expression quadrature computing, || the expression delivery,

Expression makes l=1 ..., L-1 gets minimum operation; The sine value computing is asked in sin () expression; In parameters u _mSearch procedure in, make l=1 ..., L-1, calculating formula (4) is got its minimum value and is composed to a variable gama, if this variable gama greater than variable ζ, gives variable ζ with variable gama assignment, preserves u this moment simultaneously _mValue give variable U _m, make u _m∈ 0 ..., L/2} repeats above search maximum variable ζ and its corresponding U _mThe step of value searches maximum variable ζ and its corresponding U _mValue can be adjusted step-size in search, expands the search volume to the decimal scope from integer range, and the diversity product increases, and obtains more excellent diagonal angle constellation at the tenth of the twelve Earthly Branches.

2. differential west space-time modulation constellation mapping method in the multi-antenna orthogonal frequency division multiplexing system according to claim 1 is characterized in that: adopt maximum likelihood method decoding, the estimated value of information symbol at receiving terminal

Can be expressed as:

${\hat{Z}}_k=\arg \underset{l=0,...,L-1}{\max }{\{\left|\right|Y_{k-1}+V_l^H{Y}_k\left|\right|}_F\}=\arg \underset{l=0,...,L-1}{\max }\{\mathrm{Retr}\left\{V_l{Y}_{k-1}{Y}_k^H\right\}\}---)$

Wherein Re represents to get real part, and tr{} represents " mark " computing, ‖ ‖ _FNorm, X are got in expression ^HThe complex-conjugate matrix of representing matrix X,

Expression makes l=0 ..., L-1 gets maximum operation.

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