CN100392998C - Intelligent antenna downstream wave-packet formation method combined with space hour block coding - Google Patents

Abstract

The present invention relates to a method for forming a downstream wave beam of an intelligent antenna combined with space time block coding, and discloses a method for forming a downstream wave beam of an intelligent antenna. A device used by the method is composed of a space time block coding device 1, N wave beam forming units 2 and a mobile station 3, wherein the 2 is composed of a wave beam forming device 2-1 and M base station antennas 2-2, the mobile station 3 is composed of a time space block decoding device 3-1 and at least one mobile station antenna 3-2, the distance between two adjacent base station antennas 2-2 arranged in a same wave beam forming unit 2 is less than or equal to half of a wavelength of a carrier wave of an emission signal of the base station antennas 2-2, and the distance between two adjacent wave beam forming units 2 is longer than or equal to ten times of the wavelength of the carrier wave of the emission signal of the base station antenna 2-2. The method is realized by the following steps: input signals firstly pass the space time block coding device 1 to generate N paths of parallel output signals; the output signals are respectively transmitted to the wave beam forming device 2-1 to be weighted, and then weighted signals are output; the weighted signals are respectively emitted by the base station antennas 2-2; the 3 uses a maximum likelihood algorithm to carry out time space decoding. Besides, the present invention overcomes the defect that a code error rate is greatly fluctuant following the change of a signal DOA and angle expansion in the prior art.

Description

Smart antenna downlink wave beam formation method in conjunction with space-time block code

Technical field:

The present invention relates to a kind of formation method of smart antenna downlink wave beam, be specifically related to smart antenna downlink wave beam formation method in conjunction with space-time block code.

Background technology:

In wireless communication system, co-channel interference (CCI) and intersymbol interference (ISI) are two principal elements of limiting telecommunication capacity and message transmission rate.Third generation radio communication mainly adopts code division multiple access access (CDMA) technology to improve message capacity and message transmission rate.Cdma system is an interference limiting system, the multipath fading, the multiple access that are subject to wireless channel disturb (MAI) and intersymbol interference (ISI), the signal to noise ratio that improves the user can not reach by increasing transmitter power simply, treatment technology became the important subject in the cdma system when therefore, many antennas were with sky.The multi-antenna technology that comprises smart antenna and MIMO (many inputs/many outputs) etc., processing of the time domain of signal and spatial domain processing are combined, effectively utilize electric wave spatial transmission characteristic to break through the restriction of power system capacity and communication quality, improved systematic function greatly, become one of research focus of wireless communication field gradually, and the breach that is regarded as addressing the above problem.Studies show that MIMO Space Time Coding technology and intelligent antenna beam formation technology are two kinds of important means that realize that the communication system spatial domain is optimized.Traditional Space Time Coding technology is when bringing significant diversity gain and spatial reuse effect, because use many antenna emissions, intersymbol interference (ISI) and inter-user interference (MUI) have been increased to a certain extent, and the advantage of beam-forming technology is to reduce ISI and suppress MUI, but wave beam forms the channel that but can not form a plurality of mutual separations, is difficult to realize the raising of power system capacity on matter by spatial reuse.When antenna array unit number increased, it is very responsive that single beam-forming technology reaches the deviation of estimating at angle (DOA) for signal wave, and a little disturbance will reduce the performance of system greatly; And for MIMO Space Time Coding system, its receiver decoding complexity can sharply rise along with the increase of bay quantity, to realizing bringing very big difficulty.Find out that thus different multi-antenna technologies is applicable to different communication systems, any single technology all is difficult to satisfy future mobile communication system for the data transmission rate, the system's high power capacity and the high-quality requirement of communicating by letter.

At present, existing document proposes two kinds of technology in conjunction with the thought that realizes, Fig. 1 has provided based on the wave beam formation of smart antenna and system block diagram (the list of references Zhong Lei of STBC (space-time block code) association schemes, Francois P.S.Chin, Ying-Chang Liang.Combined Beamforming withSpace-Time Block Coding for Wireless Downlink Transmission.2002 IEEE56th Vehicular Technology Conference.2002,4:24 ~ 28. are translated as: the wave beam of radio downlink transmission forms and the space-time block code combination technology.The 56th communication technology meeting of IEEE in 2002).What it adopted is the structure of the single array emission of M array element, and bay is λ/2 at interval.Input signal s (n) at first passes through the space-time block code device, produces the parallel output s of two-way ₁(n) and s ₂(n).Then, s ₁(n) and s ₂(n) sent into two Beam-formers respectively and be weighted, output signal is finished stack through signal synthesizer, at last by a M array element array emission.In two adjacent moment, wave beam forms transmitting and can be expressed as respectively on the array:

$x_1=x\left(t\right)=w_1^H{s}_1+w_2^H{s}_2---\left(1\right)$

$x_2=x(t+T)=w_1^H(-s_2^{*})+w_2^H{s}_1^{*}---\left(2\right)$

In the formula, w ₁, w ₂For wave beam forms weight vector.

Suppose that physical channel is a flat fading channel, comprise distinguishable path, L bar space, the channel fading coefficient of every paths and Bo Da angle are (h _l(t), θ _l), l=1,2 ..., L.Channel response can be expressed as:

$H\left(t\right)=\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{h}_l\left(t\right)a\left({\mathrm{\θ}}_l\right)=\underset{l=1}{\overset{L}{\mathrm{\Σ}}}{\mathrm{\α}}_l{e}^{j{\mathrm{\φ}}_l}a\left({\mathrm{\θ}}_l\right)---\left(3\right)$

Wherein, α _l, φ _lBe respectively the amplitude of fading and phase place, a (θ _l) reach angle θ for ripple _lThe time down link array steering vector, promptly

$a{\left({\mathrm{\θ}}_l\right)=[1,e^{\mathrm{j\π}\sin {\mathrm{\θ}}_l},...,e^{j(M-1)\mathrm{\π}\sin {\mathrm{\θ}}_l}]}^T$

(4)

Therefore, the received signal of travelling carriage can be expressed as:

$y_1=y\left(t\right)=w_1^{H}H\left(t\right)s_1+w_2^{H}H\left(t\right)s_2+n_1---\left(5\right)$

$y_2=y(t+T)=w_1^{H}H\left(t\right)(-s_2^{*})+w_2^{H}H\left(t\right)s_1^{*}+n_2---\left(6\right)$

In the formula, the cycle of T indication code metasymbol, y ₁And y ₂Represent t and t+T received signal constantly respectively, n ₁And n ₂The expression additive white Gaussian noise.

Suppose ${\mathrm{\β}}_1\left(t\right)=w_1^{H}H\left(t\right),$ ${\mathrm{\β}}_2\left(t\right)=w_2^{H}H\left(t\right),$ Form weight vector w by suitable selection wave beam ₁And w ₂, can guarantee β ₁(t) and β ₂(t) be two incoherent equivalent channel complex gains.Like this, the maximum-likelihood decoding algorithm of Space-Time Block Coding just can be applied to and recover s emission signal s (n) in this scheme.The weight vector of launching beam is chosen according to the receiving terminal maximum signal noise ratio principle, and its cost function is as follows:

J＝E[|β ₁(t)| ²+|β ₂(t)| ²] (7)

$E\left[{\mathrm{\β}}_1\left(t\right){\mathrm{\β}}_2^{*}\left(t\right)\right]=0---\left(8\right)$

$w_1^H{w}_1+w_2^H{w}_2=1---\left(9\right)$

Under the condition that satisfies formula (8), formula (9), the receiving terminal maximum signal to noise ratio obtains by maximization (10) formula.Wherein, formula (8) has guaranteed β ₁(t) and β ₂(t) uncorrelated mutually, formula (9) has guaranteed transmitting power normalization.

Here use the method for singular value decomposition to find the solution cost function.The downlink channel covariance matrix (Downlink Channel Covariance Matrix DCCM) can be expressed as:

R＝E[H(t)H ^H(t)] (10)

The average power in the distinguishable path of hypothesis space L bar is all identical, i.e. E|h _l(t) | ²=1/L then has:

$R=1/L\underset{l=1}{\overset{L}{\mathrm{\Σ}}}a\left({\mathrm{\θ}}_l\right)a^H\left({\mathrm{\θ}}_l\right)---\left(11\right)$

Two eigenvalue of maximum characteristic of correspondence vectors of downlink channel covariance matrix are separating of cost function (7), have so just obtained two weight vector w ₁And w ₂, and then can carry out maximum-likelihood decoding to received signal.Have than great fluctuation process but the problem that this technical scheme exists is the error rate to be changed with signal DOA (ripple reaches angle) and angle spread (AS), be in when travelling carriage under the state of rapid movement, systematic function is stable inadequately.

Summary of the invention:

The purpose of this invention is to provide a kind of smart antenna downlink wave beam formation method, with signal DOA and angle spread (AS) variation the stable inadequately shortcoming of systematic function under the state that is in rapid movement than great fluctuation process, when travelling carriage is arranged to overcome the prior art error rate in conjunction with space-time block code.The employed equipment of method of the present invention is by space-time block code device 1, N wave beam forms unit 2 and travelling carriage 3 compositions, each wave beam forms unit 2 and is made up of a Beam-former 2-1 and M antenna for base station 2-2, time grouping decoder 3-1 and at least one mobile portable antennas 3-2 form travelling carriage 3 by sky, be arranged on same wave beam and form the carrier wavelength that the distance between adjacent two antenna for base station 2-2 in the unit 2 transmits smaller or equal to half antenna for base station 2-2, adjacent two wave beams form the carrier wavelength that the distance between the unit 2 transmits more than or equal to ten times of antenna for base station 2-2, this method realizes as follows: one, input signal s (n) at first passes through space-time block code device 1, produces the parallel output signal s in N road ₁(n), s ₂(n) ..., s _N(n); Two, output signal s ₁(n), s ₂(n) ..., s _N(n) sent into N Beam-former 2-1 respectively and be weighted, the signal x after the output weighting ₁(n), x ₂(n) ..., x _N(n); Three, the signal x after the weighting ₁(n), x ₂(n) ..., x _N(n) M the antenna for base station 2-2 that forms in the unit 2 by each wave beam respectively launches, altogether N * M bay; The emission vector signal is expressed as: $x_i\left(n\right)=w_i^H{s}_i\left(n\right),$ I=1,2 ..., N is w wherein _iBe weighing vector, the wave beam arrival travelling carriage 3 that each wave beam forms unit 2 generations has only a paths, is designated as (h _i(t), θ _i), h wherein _i(t) and θ _i(i=1,2 ..., N) represent that respectively channel fading coefficient and signal wave reach the angle; The signal that travelling carriage 3 receives is that N road wave beam forms unit 2 launching beam signals and noise sum; Decipher when four, grouping decoder 3-1 uses maximum likelihood algorithm to carry out sky during empty in the travelling carriage 3, thereby recover to transmit; Space-time block code device 1 selects for use Alamouti STBC scheme to encode in step 1.

As can be seen, technical scheme of the present invention is to develop on traditional STBC (space-time block code) system-based and come.The transmit diversity of conventional art uses many bays to realize at transmitting terminal, and each bay is replaced by a wave beam formation unit 2 in the technical solution of the present invention, launches by multi-beam and realizes transmit diversity.Base station end N wave beam forms spacing between the unit 2 enough big (about 10 times more than the signal wavelength), can regard as separate with the interchannel that guarantees each subarray arrival reception antenna; And the array element distance that each wave beam forms in the unit 2 still is λ/2 (λ is a carrier wavelength), the high correlation between guaranteeing to receive in the array, transmit.From the framework of whole system, each subarray is equivalent to a little antenna system, has finished the function that wave beam forms; And whole transmitter can be regarded a big mimo system as, has finished the effect of transmit diversity.This implementation that the present invention proposes had both solved two kinds of technology and had combined for the contradiction requirement of antenna structure, had realized simultaneously that again wave beam forms and the effect of transmit diversity.

Description of drawings:

Fig. 1 is the structural representation of background technology, Fig. 2 is a structural representation of the present invention, Fig. 3 is SNR=10dB, the array gain comparison diagram of background technical scheme and technical solution of the present invention under AS=10 ° of condition, Fig. 4 is SNR=10dB, the array gain comparison diagram of background technical scheme and technical solution of the present invention under AS=50 ° of condition, Fig. 5 is the BPSK modulation, AS=10 °, during SNR=10dB, the performance chart that the error rate changes with center DOA, Fig. 6 is the BPSK modulation, AS=50 °, during SNR=10dB, the performance chart that the error rate changes with center DOA, Fig. 7 is the BPSK modulation, AS=10 °, in the time of DOA=0 °, the curve chart that the error rate changes with SNR, Fig. 8 is the BPSK modulation, AS=50 °, in the time of DOA=0 °, the curve chart that the error rate changes with SNR.

Embodiment:

Embodiment one: specify present embodiment below in conjunction with Fig. 2 to Fig. 8.The employed equipment of present embodiment is by space-time block code device 1, N wave beam forms unit 2 and travelling carriage 3 compositions, each wave beam forms unit 2 and is made up of a Beam-former 2-1 and M antenna for base station 2-2, time grouping decoder 3-1 and at least one mobile portable antennas 3-2 form travelling carriage 3 by sky, be arranged on same wave beam and form the carrier wavelength that the distance between adjacent two antenna for base station 2-2 in the unit 2 transmits smaller or equal to half antenna for base station 2-2, adjacent two wave beams form the carrier wavelength that the distance between the unit 2 transmits more than or equal to ten times of antenna for base station 2-2, this method realizes as follows: one, input signal s (n) at first passes through space-time block code device 1, produces the parallel output signal s in N road ₁(n), s ₂(n) ..., s _N(n); Two, output signal s ₁(n), s ₂(n) ..., s _N(n) sent into N Beam-former 2-1 respectively and be weighted, the signal x after the output weighting ₁(n), x ₂(n) ..., x _N(n); Three, the signal x after the weighting ₁(n), x ₂(n) ..., x _N(n) M the antenna for base station 2-2 that forms in the unit 2 by each wave beam respectively launches; The emission vector signal is expressed as: $x_i\left(n\right)=w_i^H{s}_i\left(n\right),$ I=1,2 ..., N is w wherein _iBe weighing vector, the wave beam arrival travelling carriage 3 that each wave beam forms unit 2 generations has only a paths, is designated as (h ₁(t), θ ₁) ..., (h _N(t), θ _N), h wherein _i(t) and θ _i(i=1,2 ..., N) represent that respectively channel fading coefficient and signal wave reach the angle; The signal that travelling carriage 3 receives is that N road wave beam forms unit 2 launching beam signals and noise sum; Four, at moment t=n, the received signal of travelling carriage 3 is expressed as:

$y\left(n\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{w}_i^H{h}_{i}a\left({\mathrm{\θ}}_i\right)s_i\left(n\right)+\mathrm{\η}---\left(22\right)$

In the formula, a (θ _i) represent that ripple reaches angle θ _iThe time down link array steering vector, η represents additive white Gaussian noise.Decipher when travelling carriage 3 uses maximum likelihood algorithm to carry out sky, thereby recover to transmit.Suitably handle by received signal, can obtain descending channel information, estimate signal DOA (Bo Dajiao) up link.Here consider single user, the situation of state no interference signal, spatial matched filtering can be realized optimum signal processing under the white noise background.As preceding hypothesis, form unit 2 for each wave beam, only come from direction θ in the space _i(i=1,2 ..., the plane wave of N, its direction vector are a (θ _i), as weight vector w _iGet and make a (θ _i) time, array gain $\left|w_i^{H}a\left({\mathrm{\θ}}_i\right)\right|=\left|a{\left({\mathrm{\θ}}_i\right)}^{H}a\left({\mathrm{\θ}}_i\right)\right|=M$ Maximum has realized the guide-localization effect.At this moment, the weighted signal of array Nei Gelu is a coherent superposition, has promptly finished spatial matched filtering.In view of the above, the formation of the optimization wave beam in technical solution of the present invention weight vector can be taken as

w _i=ka (θ _i) k is power normalization coefficient (23)

Under the condition that transmitting power remains unchanged, promptly satisfy $\underset{i=1}{\overset{N}{\mathrm{\Σ}}}{w}_i^H{w}_i=1$ The time, if $w_i^H{w}_i=1/N,$ Can solve

$k=1/\sqrt{N\·M}---\left(24\right)$

In (23) formula, (24) formula substitution (22) formula, then the received signal of travelling carriage can be rewritten as:

$y\left(n\right)=\underset{i=1}{\overset{N}{\mathrm{\Σ}}}\sqrt{\frac{M}{N}}{h}_i{s}_i\left(n\right)+\mathrm{\η}---\left(25\right)$

Suppose the equivalent channel complex gain ${\mathrm{\β}}_i=w_i^H{h}_{i}a\left({\mathrm{\θ}}_i\right),$ Because system configuration has determined transmission channel h ₁, h ₂..., h _NIrrelevance, so β ₁, β ₂..., β _NAlso be incoherent mutually.Therefore, decipher when travelling carriage can use maximum likelihood algorithm to carry out sky, thereby recover to transmit.The present invention has adopted N emission array, and M array element is arranged in each array, altogether N * M bay.

Space Time Coding be a kind of utilize a plurality of transmitting antennas to information symbol on the time-domain and spatial domain on the combined coding mode, relevant by between the signal of different antennae emission, introducing time domain with the spatial domain, the realization time go up and the space on diversity, thereby obtain significant spatial reuse effect and space diversity gain, and then the performance of raising system, the capacity of increase system.Space Time Coding requires each sub data flow of coding output should experience low relevant or approximate independently fading channel and arrives receiver, and like this, receiving terminal could utilize maximum likelihood algorithm to decipher.So, in the mimo system interval of bay must be enough big (to about 10 more than the wavelength of uniform linear array), could guarantee the irrelevance of the interchannel of different transmit antennas arrival receiver.Simultaneously, the introducing of many antennas has also increased intersymbol interference and inter-user interference to a certain extent.The main purpose that wave beam forms then is by the weighting of aerial array being adjusted the directional diagram of emission or receiving antenna array, on the desired signal direction, form main beam, fall into and on interference radiating way, form zero, make narrow as far as possible wave beam between base station and travelling carriage, form the point-to-point approximate wireless communication link that linearize is arranged, obtain considerable array gain with this, improve systematic function.But beam-forming technology requires to have the correlation of height between all antennas emissions or the signal that receives, thereby requires in the aerial array array element at interval must enough little (uniform linear array is generally half wavelength).Therefore, Space Time Coding will be striven for two or more mutual incoherent channels exactly in conjunction with the key of beam-forming technology, carries out wave beam then and form on each channel.The present invention has complementary advantages Space Time Coding technology and beam-forming technology from application point of view, by both are better improved systematic function and increase power system capacity in conjunction with realizing.Space Time Coding and two kinds of multi-antenna technologies of wave beam formation are combined, make up a kind of new lift-off technology, can obtain wave beam simultaneously and form gain and diversity gain, reduce system complexity and sensitiveness simultaneously, improve the systematic function of whole down link.Thereby the stable inadequately shortcoming of systematic function when overcoming the fluctuation of the prior art error rate than big and travelling carriage high-speed motion.

In order to verify these advantages of the present invention program, the present invention is combined space time coding scheme with the wave beam formation of background technology compare.Space-time block code has been selected 21 classical receipts Alamouti STBC schemes, and two uniform linear arrays are used in the base station, and 3 array elements are arranged in each array, and transmitting antenna adds up to NM=6, and travelling carriage 3 adopts maximum likelihood algorithms decoding.The present invention is the single array structures of 6 array elements, and the background technology scheme then is the two array structures of 3 array elements.Consider the situation of the single reception antenna of single user, promptly ignore the influence of co-channel interference and monkey chatter in the system.Suppose that the user moves in 120 ° of sectors, the channel of experience is the flat Rayleigh fading channel.Two kinds of schemes all are based on the basis of Alamouti STBC scheme wave beam formed and combine realization with the space-time block code technology.Form weight vector and design system model structure by the suitable wave beam of choosing, make that the received signal that arrives travelling carriage is uncorrelated mutually, and then can adopt maximum likelihood algorithm decoding, therefore the diversity gain of two kinds of association schemes can both reach theoretical maximum, receives the full diversity gain that Alamouti STBC scheme can realize for promptly traditional 21.At this moment, the performance difference of two kinds of association schemes just is mainly reflected on the array gain, and following Fig. 3 and Fig. 4 have provided the present invention program respectively and the array gain of background technology scheme under the different angles expansion condition reaches the situation that the angle changes with signal center ripple.Under AS=10 ° of situation of low-angle expansion, as seen from Figure 3, the present invention program's array gain reaches the angular direction for different middle cardiac waves and all keeps stable, greatly about about 1.75dB.On the contrary, the array gain of background technology then has certain fluctuation along with the variation that middle cardiac wave reaches the angle, and when travelling carriage is in the center, sector, in the time of signal DOA=0 °, the array gain maximum of background technology is approximately 1.3dB; Along with signal wave reaches the increase at angle, array gain reduces gradually.Further, under AS=50 ° of condition of wide-angle expansion, observe Fig. 4 and can find that it is stable that the present invention program's array gain still keeps, and the performance when expanding with low-angle is identical.At this moment, the performance of background technology scheme is approached the present invention program, reaches the angle for different middle cardiac waves, and its array gain has only very little fluctuation, also tends towards stability basically.For the background technology scheme, weight vector acts on wave beam simultaneously and forms and two aspects of Space Time Coding.When low-angle was expanded, the correlation of two distinguishable path signals that reaches the base station was stronger, in order to use maximum-likelihood decoding at travelling carriage, must guarantee two-way equivalent channel factor beta ₁And β ₂Be separate, this moment is to two weight vector w ₁And w ₂The constraints chosen stronger, thereby restricted the effect that wave beam forms, the array gain that system is obtained is less.On the contrary, under the wide-angle expansion condition, article two, the correlation of distinguishable path signal a little less than, therefore choosing of weight vector is subjected to the constraint of the uncorrelated condition of equivalent channel less, can make the received signal to noise ratio maximization of travelling carriage as much as possible, optimize the effect that wave beam forms, make system obtain bigger array gain.So, the situation the when array gain that reflects wide-angle when expansion from figure is better than the low-angle expansion on the whole.For technical solution of the present invention, system configuration has guaranteed that the channel of each subarray arrival travelling carriage is incoherent mutually, so wave beam forms the restriction that is not subjected to extra condition of choosing of weight vector.For the wave beam that each subarray forms, it points to, and all the direction with the incoming wave signal is consistent, the size of angle spread no matter, and the array gain that system obtains is always maximum and remains unchanged.Fig. 5 and Fig. 6 have provided AS=10 ° respectively, and SNR=10dB and AS=50 °, under the SNR=10dB condition, the error rate of two kinds of schemes reaches the curve that the angle changes with signal wave.For the ease of relatively, also provided the performance curve that traditional single-antenna transmission, Alamouti STBC and 6 array element intelligent antenna beams form three kinds of schemes simultaneously.Observe Fig. 5 and Fig. 6 and can find that under any DOA and AS condition, the bit error rate performance of two kinds of association schemes all is better than single-antenna transmission, Alamouti STBC and 6 array element intelligent antenna beam formation technology.For the background technology scheme, when low-angle was expanded, its error rate had certain variation.When travelling carriage is positioned at the center, sector, error rate of system is minimum in the time of DOA=0 °; Along with signal wave reaches the increase at angle, the error rate raises gradually.In wide-angle when expansion,, the present invention program's the error rate tends towards stability in [40 °, 40 °] center DOA scope, and the situation when being better than the low-angle expansion.This is because the center DOA of two orthogonal beams that the background technical scheme produces under the low-angle expansion condition is very approaching, and as shown in Figure 3, the influence that this moment, array gain acceptor center DOA changed greatly.Along with the increase of angle spread, array gain reduces with the fluctuation that center DOA changes, and tends towards stability.For the present invention program, under any DOA and AS condition, its bit error rate performance remains stable, and the error rate with the background technology scheme during wide-angle expansion is close in certain DOA scope.This can be interpreted as, and the subarray in the technical solution of the present invention is enough big at interval, has fully guaranteed the irrelevance of the interchannel of two subarray arrival reception antennas.For arbitrarily angled expansion, system is when obtaining complete diversity gain, and array gain also is maximum, so property retention is stable.Fig. 7 and Fig. 8 have provided AS=10 ° respectively, and DOA=0 ° and AS=50 °, under the DOA=0 ° of condition, the curve that the error rate of five kinds of schemes changes with average bit signal to noise ratio.In the error rate is 10 ^-3The time, the SNR of background technical scheme is better than Alamouti STBC respectively and 6 array element wave beams form about 2dB and 4dB under the low-angle expansion condition; Under the wide-angle expansion condition, then reach 5dB and 7dB.Equally, be 10 in the error rate ^-3The time, the SNR of technical solution of the present invention is better than Alamouti STBC respectively and 6 array element wave beams form about 5dB and 7dB, and arbitrarily angled expansion is all remained unchanged.Can find that further along with the raising of SNR, the property retention of technical solution of the present invention is stable, is better than all the time about STBC scheme 5dB; The performance of background technology scheme is then approached STBC gradually, and low-angle its ber curve of when expansion almost overlaps with STBC when SNR＞20dB; In wide-angle when expansion, is along with the raising of SNR, the trend that the also oriented STBC of its performance approaches.This can be interpreted as, and the effect of smart antenna mainly is to form main beam on desired orientation, improves signal gain, suppresses noise, and the STBC transmit diversity is then obvious to opposing multipath fading effect.For the present invention program, the Launch Right vector choose the irrelevance that at first will satisfy equivalent channel, consider to make the received signal to noise ratio maximum of travelling carriage again.Be subjected to the restriction of this constraints, it is optimum that the effect that wave beam forms just can not reach, and its array gain changes along with the power of constraints.In the high s/n ratio interval, received signal power is much larger than noise, and the array gain that smart antenna is introduced is very little with respect to the diversity gain that STBC brings, so the improvement of systematic function is mainly reflected on the STBC that suppresses multipath fading.And for technical solution of the present invention, system configuration has guaranteed that the channel of each subarray arrival travelling carriage is incoherent mutually, so wave beam forms the restriction that is not subjected to extra condition of choosing of weight vector.For the wave beam that each subarray forms, it points to, and all the direction with the incoming wave signal is consistent, has realized optimum signal transmission.The size of angle spread no matter, the array gain that system obtains is always maximum and remains unchanged.

Find relatively that by above technical solution of the present invention has also obtained maximum array gain when obtaining the full diversity gain, its performance is better than traditional single-antenna transmission, and Alamouti STBC and intelligent antenna beam form three kinds of technology.And, under identical condition, the performance of technical solution of the present invention is better than the background technology scheme, the influence that its error rate is not changed by DOA and AS, can keep stable performance when the travelling carriage rapid movement, be a kind of better with wave beam forms and the space-time block code technology combines implementation.

Embodiment two: specify present embodiment below in conjunction with Fig. 2.The difference of present embodiment and execution mode one is: space-time block code device 1 selects for use Alamouti STBC scheme to encode in step 1.In numerous space time coding schemes, (Alamouti is a foreign scholar's a name to Alamouti STBC, Alamouti STBC can be translated into the Alamouti space-time block code) code efficiency of scheme is 1, compare with coded system not, can under the identical bandwidth prerequisite of maintenance, improve the availability of frequency spectrum of system, because advantages such as its coding and decoding is simple, validity and unit encoding efficient have obtained using widely.Beam-forming technology is introduced in the Alamouti STBC system, can be remedied the deficiency of this low order space-time block code, obtain wave beam simultaneously and form gain and diversity gain, improve systematic function greatly.Below provide M array element wave beam and formed the implementation of receiving Alaomouti STBC in conjunction with 21.

Adopt the structure of two array diversity emissions, transmitting antenna adds up to 2M.Coding and transmitting sequence are as shown in table 1.Input signal s (n) is from the two-way parallel signal s of space-time block code device output ₁(n) and s ₂(n), weighing vector w in through Beam-former 2-1 ₁And w ₂Weighting after, respectively from the emission of the subarray of two M array elements.

Table 1Alamouti STBC scheme coding and transmitting sequence

Suppose that each wave beam forms subarray arrival travelling carriage and has only a paths, be designated as (h ₁(t), θ ₁) and (h ₂(t), θ ₂), h wherein _l(t) and θ _l(l=1,2) represent that respectively channel fading coefficient and signal wave reach the angle, and because two spacings in array are enough big, have guaranteed two fading channel h ₁(t), h ₂(t) be incoherent mutually.In two adjacent moment, the received signal of travelling carriage can be expressed as respectively:

$y_1=y\left(t\right)=w_1^H{h}_1\left(t\right)a\left({\mathrm{\θ}}_1\right)s_1+w_2^H{h}_2\left(t\right)a\left({\mathrm{\θ}}_2\right)s_2+n_1---\left(26\right)$

$y_2=y(t+T)=w_1^H{h}_1\left(t\right)a\left({\mathrm{\θ}}_1\right)(-s_2^{*})+w_2^H{h}_2\left(t\right)a\left({\mathrm{\θ}}_2\right)s_1^{*}+n_2---\left(27\right)$

In the formula, the cycle of T indication code metasymbol, a (θ ₁) and a (θ ₂) represent that respectively ripple reaches angle θ ₁And θ ₂The time down link array steering vector, y ₁And y ₂Represent t and t+T received signal constantly respectively, n ₁And n ₂The expression additive white Gaussian noise.

Suppose that at the base station transmit antennas place, descending channel information is known fully, this can estimate by the received signal of up link.Here consider single user, the situation of state no interference signal, spatial matched filtering can be realized optimum signal processing under the white noise background.Then the formation of the optimization wave beam in association schemes weight vector can be taken as

w ₁＝ka(θ ₁) (28)

w ₂＝ka(θ ₂) (29)

Satisfying under the constant condition of transmitting power, promptly $w_1^H{w}_1+w_2^H{w}_2=1,$ If

$w_1^H{w}_1=w_2^H{w}_2=1/2---\left(30\right)$

Can solve

$k=1/\sqrt{2M}---\left(31\right)$

Suppose the equivalent channel complex gain

${\mathrm{\β}}_1\left(t\right)=w_1^H{h}_1\left(t\right)a\left({\mathrm{\θ}}_1\right)---\left(32\right)$

${\mathrm{\β}}_2\left(t\right)=w_2^H{h}_2\left(t\right)a\left({\mathrm{\θ}}_2\right)---\left(33\right)$

By h ₁(t), h ₂(t) irrelevance as can be known, β ₁(t), β ₂(t) also be incoherent mutually.Therefore, travelling carriage can use the maximum-likelihood decoding algorithm to recover to transmit.

Formula (28), (29), (31) are brought in formula (26), (27), and then the received signal of travelling carriage can be rewritten as:

$y_1=y\left(t\right)=\sqrt{\frac{M}{2}}{h}_1\left(t\right)s_1+\sqrt{\frac{M}{2}}{h}_2\left(t\right)s_2+n_1---\left(34\right)$

$y_2=y(t+T)=\sqrt{\frac{M}{2}}{h}_1\left(t\right)(-s_2^{*})+\sqrt{\frac{M}{2}}{h}_2\left(t\right)s_1^{*}+n_2---\left(35\right)$

Signal that mobile portable antennas receives and the path gain h that obtains by channel estimating ₁, h ₂Through after the linear combination, the estimated signal of generation

For

${\tilde{s}}_1=h_1^{*}{y}_1+h_2{y}_2^{*}---\left(36\right)$

${\tilde{s}}_2=h_2^{*}{y}_1-h_1{y}_2^{*}---\left(37\right)$

With formula (34), (35) substitution formula (36), formula (37), promptly

${\tilde{s}}_1=\sqrt{\frac{M}{2}}({\left|h_1\right|}^2+{\left|h_2\right|}^2)s_1+h_1^{*}{n}_1+h_2{n}_2^{*}---\left(38\right)$

${\tilde{s}}_2=\sqrt{\frac{M}{2}}({\left|h_1\right|}^2+{\left|h_2\right|}^2)s_2+h_2^{*}{n}_1-h_1{n}_2^{*}---\left(39\right)$

At last, the signal of combiner output With the path gain h that obtains by channel estimating ₁, h ₂Grouping decoder 3-1 obtains decoding output through maximum likelihood decision when being sent into sky simultaneously.

Observation type (38), formula (39) can find that the detection signal expression formula of association schemes is similar with the form of traditional AlamoutiSTBC scheme, and difference only is to expect the amplitude difference of received signal.And this difference has embodied just, and association schemes have been owing to introduced the array gain benefit that beam-forming technology is brought with respect to single space-time block code plan, thereby has improved the input signal-to-noise ratio of receiver, has improved systematic function.

Claims (1)

1. in conjunction with the smart antenna downlink wave beam formation method of space-time block code, it is characterized in that the employed equipment of method of the present invention is by space-time block code device (1), N wave beam forms unit (2) and travelling carriage (3) composition, each wave beam forms unit (2) and is made up of a Beam-former (2-1) and M antenna for base station (2-2), travelling carriage (3) by sky time grouping decoder (3-1) and at least one mobile portable antennas (3-2) form, be arranged on same wave beam and form the carrier wavelength that the distance between interior adjacent two antenna for base station (2-2) in unit (2) transmits smaller or equal to half antenna for base station (2-2), adjacent two wave beams form the carrier wavelength that the distance between the unit (2) transmits more than or equal to ten times of antenna for base station (2-2), this method realizes as follows: one, input signal s (n) at first passes through space-time block code device (1), produces the parallel output signal s in N road ₁(n), s ₂(n) ..., s _N(n); Two, output signal s ₁(n), s ₂(n) ..., s _N(n) sent into N Beam-former (2-1) respectively and be weighted, the signal x after the output weighting ₁(n), x ₂(n) ..., x _N(n); Three, the signal x after the weighting ₁(n), x ₂(n) ..., x _N(n) M the antenna for base station (2-2) that forms in the unit (2) by each wave beam respectively launched, altogether N * M bay; The emission vector signal is expressed as: $x_i\left(n\right)=w_i^H{s}_i\left(n\right),i=\mathrm{1,2},...,N$ W wherein _iBe weighing vector, the wave beam arrival travelling carriage (3) that each wave beam forms unit (2) generation has only a paths, is designated as (h _i(t), θ _i), h wherein _i(t) and θ _i(i=1,2 ..., N) represent that respectively channel fading coefficient and signal wave reach the angle; The signal that travelling carriage (3) receives is that N road wave beam forms unit (2) launching beam signal and noise sum; Decipher when four, grouping decoder (3-1) uses maximum likelihood algorithm to carry out sky during empty in the travelling carriage (3), thereby recover to transmit; Space-time block code device (1) selects for use Alamouti STBC scheme to encode in step 1.

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