CN101951308B - Self-adaptive transmission method of vehicle speed mobile MIMO-SCFDE system - Google Patents
Self-adaptive transmission method of vehicle speed mobile MIMO-SCFDE system Download PDFInfo
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Abstract
The invention discloses a self-adaptive transmission method of a vehicle speed mobile multiple input multiple output single carrier frequency domain equalization (MIMO-SCFDE) system. In the method, the combination of a simple precoding method and frequency selection is adopted to withstand channel rank deficiency and the system performance can commonly be superior to a non-self-adaptive MIMO-SCFDE system. The method of the invention has low feedback rate and can effectively solve the problems that a large amount of feedback information is needed to be passed back frequently under the condition of time-varying channel as well as the amount of the feedback information is large and the system performance is difficult to be ensured in the self-adaptive frequency-selecting block transmission method in the existing mobile MIMO broadband wireless channel. In the invention, a frequency domain sub-channel which is equalized to be amplified and has low noise is selected to transmit the information so as to cause Bit Error Rate (BER) performance not to be worsened excessively, and the BER performance has simple controllability. The method of the invention can preferably solve the problems of the excessive feedback information amount on the premise of ensuring the system performance and frequency selectivity and time selective fading.
Description
Technical field
The present invention relates to the adaptive transmission method that a kind of speed of a motor vehicle moves MIMO-SCFDE, belong to the many antennas wideband digital communications method in the broadband wireless communication technique field.
Background technology
The communication technology has obtained tremendous development since nearest decades, particularly nineteen nineties, people's daily life and development and national economy have been produced far-reaching influence.Spectrum efficiency and complexity are two important goals that the radio communication research field is pursued for many years always.Multiple-input and multiple-output (hereinafter to be referred as MIMO:Multiple-inputMulltple-output) utilizes and to enrich in the scattering environments the uncorrelated characteristic of channel between the different antennae; Obtain the high channel capacity; Thereby can obtain the conventional single-antenna technology spectrum efficiency that is beyond one's reach; But along with the increase of transmission rate, complexity that the antenna number that only relying on increases mimo system is brought and the problem in the physics realization become and are difficult to solve, and increasing transmission bandwidth is the feasible means that address this problem; After transmission bandwidth increased, the complexity of the equilibrium that the time delay expansion brings in the rich multipath environment was the problem that the wideband MIMO system must solve.Piecemeal transmission technology based on Cyclic Prefix (hereinafter to be referred as CP:Cyclic Prefix) mainly comprises OFDM (hereinafter to be referred as OFDM:Orthogonal Frequency DivisionMultiplexing) and single carrier frequency domain equalization (hereinafter to be referred as SC-FDE:Single Carrier with FrequencyDomain Equalization); Can effectively solve the difficulty of the balanced aspect that time delay expansion caused with simple frequency-domain equilibrium method, can use FFT (hereinafter to be referred as FFT:FastFourier Transform) and invert fast fourier transformation (hereinafter to be referred as IFFT:Inverse Fast FourierTransform) based on the main operation of the frequency-domain equilibrium method of CP) completion.Therefore, in conjunction with based on the wideband MIMO of CP piecemeal transmission technology: MIMO-OFDM and MIMO-SCFDE are considered to the ripe main support technology of future wireless system physical layer.
Up to the present; Many broadband wireless communications standards based on the MIMO-OFDM framework have been arranged; IEEE802.11n for example, the 54Mbps that can the transmission rate of WLAN be provided by 802.11a and 802.11g is provided to 300Mbps even 600Mbps, has benefited from exactly MIMO and OFDM technology are combined; Both improved wireless transmission quality, transmission rate is greatly improved.MIMO-OFDM/MIMO-SCFDE is also chosen as transmission standard by 36PP LTE and WiMax.
In ofdm system, through the conceptual description system of subchannel commonly used, so-called k subchannel is exactly with subcarrier f
kBe a channel at center, for explaining conveniently, deserving to be called and stating subchannel is the frequency domain subchannel.Though the SC-FDE system does not have the notion of subcarrier; But therefore the signal processing mode of employing and OFDM all fours, copies OFDM to introduce the notion of frequency domain subchannel; Meaning is identical with the frequency domain subchannel of OFDM, and its equilibrium is also independently carried out on each frequency domain subchannel.Different with OFDM is: the input of SC-FDE is accomplished on time domain, and therefore that N sample point of time-domain signal is corresponding time-domain position is a N time domain subchannel.
Introduce the basic structure of MIMO-SCFDE system earlier, system's number of transmit antennas and reception antenna number are respectively N
TAnd N
RAt transmitting terminal, bit stream is divided into N after passing through Space Time Coding successively
TThe road independent data; Every circuit-switched data is assigned to (establishing number of subchannels is N) on a series of subchannels through after the sign map; Then before every frame data of each antenna, insert Cyclic Prefix to eliminate intersymbol interference, use the MIMO technology that each subcarrier is served transmitting antenna then.At receiving terminal, receive N
RAt first to remove Cyclic Prefix behind the SC-FDE signal of road; Then do the FFT conversion that N is ordered respectively according to reception antenna; Transform from the time domain to frequency domain; Then this frequency-region signal is delivered to balance module and carry out equilibrium, at last signal after the equilibrium is IFFT and obtains the time domain sample point and carry out symbol detection, obtain original bit stream after the decoding when empty.
For system of broadband wireless communication, in order to satisfy the demand of various data services, system need provide than higher transmission rate.Along with the rising of transmission rate, it is big that the transmission signals bandwidth becomes, the correlation bandwidth that surpasses channel often far away, and this moment, channel will the frequence of exposure selectivity.Frequency-selective channel mainly shows the influence of block transmission system: the multipath transmisstion of signal or time delay expansion can cause frequency selective fading; Signal propagation in frequency selective fading channels can cause some spectrum component of signal to be attenuated very lowly; Exist under the situation about declining deeply a little at channel; The influence that signal receives is bigger, so that signal generation distortion, and influences systematic function.Under mobile environment, make a start and receive end relatively move and the diversity on ground causes arriving signal generation Doppler frequency shift.Because Doppler effect, keeping under the constant situation of tranmitting frequency, can make receive signal power in time passing and change, thereby channel can the decline of presentative time selectivity.
In mobile broadband wireless communication, channel exists frequency selectivity and time selectivity simultaneously, can produce direct influence to the performance of system.In order to make communication system obtain preferable performance; Must take certain measure to alleviate the influence of selectivity decline to communication system; The method that alleviates time selectivity commonly used has the robust modulation technology, error correction coding and interleaving technology etc., but system's realization is complicated, spectrum efficiency is low.The method that alleviates frequency selectivity commonly used has: time domain equalization technology and based on the piecemeal transmission technology of frequency domain equalization comprises OFDM and SC-FDE.In OFDM and SC-FDE technology, adopt the CP technology can be under certain condition the inter-block-interference that causes of the multipath transmisstion of erasure signal fully.But, just mean that a part of signal can receive serious decay, has restricted the performance of system when existing in the channel when declining deeply.Thereby should be avoided in these subchannels that decline deeply and upload information.
Technology for self-adaptively transmitting is the effective measures that tackle the broadband mobile channel; Its main thought is the channel condition information (hereinafter to be referred as CSI:Channel State Information) that feeds back to through receiving terminal; Come adaptively characteristic changing signal transmitted, thereby improve the reliability and the validity of communication according to channel.In the OFDM and SC-FDE system of fixed modulation mode; Can consider subchannel is adopted the mode of Adaptive Modulation; Make system initiatively avoid the serious subcarrier that declines, simultaneously through improving the transmission rate of the good subcarrier of transmission conditions, compensation is because the serious subcarrier that declines can't transmit the decline of the transmission rate that data bring; Can also dynamically adjust the transmitting power of each number of sub-carrier simultaneously, further improve systematic function.
Moving the subject matter that the MIMO broadband wireless channel faces is: the time, frequently, empty selectivity.When utilizing the adaptive technique of channel condition information CSI to alleviate effectively, frequently, empty selectivity is to the influence of system, thereby more reliably more effectively communicate.But in mimo system, feedback information volume increases along with the increase of carrier number and number of antenna fast.
At present many methods that reduce the back information amount based on MIMO-OFDM have been arranged: the 1st type is sub-clustering (clustering); Be about to carrier wave and be divided into some bunches; Have stronger frequency dependence in bunch, will on other carrier frequency point of this bunch, share by the pre-coding matrix that the pilot tone point obtains; The 2nd type of scheme is to utilize the pre-coding matrix at all pilot tone point places to carry out interior (interpolation) processing of inserting, to obtain the corresponding pre-coding matrix of other carrier frequency point; The 3rd type of scheme is adaptive tracing (tracking) algorithm to pre-coding matrix, promptly utilizes the frequency domain correlation of pre-coding matrix that some pilot tone points place obtains and carrier wave bunch to do the adaptive tracing of the pre-coding matrix of other carrier wave bunch correspondence.Sub-clustering is a basic scheme, and interior insert rises to cost with complexity and get certain performance boost in return, and the adaptive tracing scheme is pursued littler feedback data rate and be cost with few performance loss of trying one's best.But in time varying channel, CSI can change along with the variation of channel.In mobile radio telecommunications, a large amount of feedback informations needs passback continually, brings very big burden to whole communication system, has a strong impact on the efficient of communication system.Therefore at present based on the precoding algorithm of MIMO-OFDM, still only be applicable to the static time varying channel that perhaps becomes slowly.
Publication number is that the Chinese invention patent application of 101719816A discloses a kind of " realizing the method for low feedback velocity of self-adaptive MIMO-SCFDE system ", and the low feedback velocity method of this self-adaptive MIMO-SCFDE may further comprise the steps:
(1) for N
T* N
RAdaptive MIMO systems, N
TThe expression number of transmit antennas, N
RExpression reception antenna number; Receive end according to non-ideal factor (non-ideal factor comprises the nonlinear characteristic of synchronous error, channel estimation errors and the device etc.) performance loss that causes of channel condition information, system, the modulation system that is adopted and desired system errored bit performance, from whole N frequency domain subchannel, select available M
SThe best order S of subchannel and definite channel matrix; Have only the available frequency domain subchannel to upload the transmission information symbol; And other frequency domain subchannels do not transmit information symbol for the forbidding subchannel; Generate subchannel identification information and channel sequence information then, and this subchannel identification information and channel sequence information sent to via feedback channel make a start;
(2) make a start according to the modulation system that is adopted and subchannel identification information and channel sequence information, form S original equivalent time domain Frame, through M
SPoint FFT (FFT); The equivalent time domain sign reversing of initial data frame is become equivalent frequency domain symbol, and the frequency domain subchannel mapping matrix according to subchannel label information and channel sequence information and receiving-transmitting sides agreement should be mapped to M after the precoding of equivalence frequency domain symbol then
SOn the individual available frequency domain subchannel, generate N
TIndividual N dimension frequency domain vector utilizes N point IFFT (invert fast fourier transformation) to change back to time domain again, and the while was by N after serial to parallel conversion added CP
TIndividual transmitting antenna sends;
(3) receive end with N
RAfter the Frame that individual reception antenna receives removes CP, utilize FFT to transform to frequency domain, select M according to subchannel identification information and frequency domain subchannel inverse mapping matrix
SIndividual available frequency domain subchannel is to the signal of last transmission, generates balanced matrix according to channel sequence information and channel condition information then and carries out equilibrium, and conversion rules out transmission information after returning equivalent time domain.
The realization of the low feedback velocity method of above-mentioned self-adaptive MIMO-SCFDE is based on the static channel environment; Under the broadband wireless mobile environment, the time-varying characteristics of channel are to the most important restraining factors of system's error performance.The low feedback velocity method of above-mentioned self-adaptive MIMO-SCFDE does not provide the update strategy that when channel status changes, how to upgrade passback CSI, can not solve the time-varying characteristics of channel, can not directly apply to time varying channel; For the time changing environment, also to consider the influence of time selective fading simultaneously, need take suitable self adaptation passback strategy, make the MIMO-SCFDE system under mobile condition, still can obtain the compromise between performance and the feedback information volume.
LTE is very good to ambulant support, but does not adopt adaptive technique during its fast moving, exchanges the availability of system for the spectrum efficiency of sacrificial system.
Summary of the invention
For overcoming the deficiency of prior art, the present invention provides a kind of speed of a motor vehicle to move the adaptive transmission method of MIMO-SCFDE system.
For realizing above-mentioned purpose, the present invention adopts following technical scheme:
A kind of speed of a motor vehicle moves the adaptive transmission method of MIMO-SCFDE system, and this method may further comprise the steps:
(1) for N
T* N
RSelf-adaptive MIMO-SCFDE system, after receiving-transmitting sides is set up communication, receive end according to current state information of channel, desired system errored bit performance, from whole N frequency domain subchannel, select available M
SThe best order S of subchannel and definite channel matrix generates subchannel identification information and channel sequence information, and this subchannel identification information and channel sequence information sent to via feedback channel makes a start;
(2) make a start according to the modulation system that is adopted and subchannel identification information and channel sequence information, form S original equivalent time domain Frame, through M
SPoint FFT becomes equivalent frequency domain symbol with the equivalent time domain sign reversing of initial data frame, and the frequency domain subchannel mapping matrix of arranging according to subchannel label information and channel sequence information and receiving-transmitting sides then should be mapped to M after the precoding of equivalence frequency domain symbol
SOn the individual available frequency domain subchannel, generate N
TIndividual N dimension frequency domain vector utilizes N point IFFT to change back to time domain again, and the while was by N after serial to parallel conversion added CP
TIndividual transmitting antenna sends;
(3) receive end with N
RAfter the Frame that individual reception antenna receives removes CP, utilize FFT to transform to frequency domain, select M according to subchannel identification information and frequency domain subchannel inverse mapping matrix
SThe signal that transmits on the individual available frequency domain subchannel generates balanced matrix according to channel sequence information and channel condition information then and carries out equilibrium, and conversion is returned equivalent time domain and accomplished judgement;
(4) receive end and carry out the channel condition information that channel estimating obtains upgrading; According to the self-adaptive decision rule; Judge whether to need to upgrade subchannel label information and channel sequence information; Upgrade if desired, receive end and upgrade subchannel label information and channel sequence information, and feed back to through backward channel and to make a start according to the requirement of system's error performance; When sending new frame data on the transmitting antenna, make a start and always carry out signal transformation according to up-to-date subchannel label information and the channel sequence information received.
The said channel condition information method of obtaining is used: training frames adds method, the decision-feedback of decision-feedback tracking and follows the tracks of method that adds frequency pilot sign or the method for using channel estimating.
The said channel condition information method of obtaining is followed the tracks of the method that adds frequency pilot sign with decision-feedback, and its concrete implementation method is: adopt number of pilot symbols to equal Cyclic Prefix, pilot tone is inserted and is adopted the dressing pilot tone; Pilot tone is evenly distributed in the subchannel; It is known that pilot tone point is gone up the information D of sending; Frequency domain according to pilot tone point place receives signal, calculates the characteristic of channel at this pilot tone point place, and the characteristic of channel on the non-pilot tone point subcarrier is to obtain according to the characteristic of channel on the pilot sub-carrier is carried out interpolation; Thereby obtain the channel condition information of all subchannels.
The said concrete implementation method that needs to upgrade subchannel label information and channel sequence information that judges whether is: according to the errored bit performance that system requirements reaches, determine the scope of the balanced back signal to noise ratio that need reach, according to the subchannel number M
SMonitor out the balanced back signal to noise ratio snr of every frame with channel sequence number S
Post, and and SNR
ReqMake comparisons, determine whether in the signal to noise ratio scope that limits; If in set scope, keep current channel logo information D and channel sequence information B constant; Otherwise according to SNR
Post>=SNR
Req, maximization M
S* S chooses the available subchannels number M again
SWith channel sequence number S, and form new channel logo information D and channel sequence information B, made a start channel logo information after upgrading and order information retransmission then; SNR wherein
ReqFor adopting behind certain modulation system and the taking into account system non-ideal factor signal to noise ratio after the pairing equivalent time domain equilibrium of desired system errored bit performance; SNR
PostBe signal to noise ratio after the equilibrium; SNR
PreBe signal to noise ratio before balanced.
For the ease of better expression, symbol used among the present invention is carried out the part explanation:
N
T: the transmitting antenna number; N
R: the reception antenna number; N: the length that does not add a protection frame SC-FDE frame at interval; M
S: selected frequency domain subchannel number; Lowercase is represented time domain and equivalent time domain symbol, and capitalization is represented frequency domain and equivalent frequency domain symbol; N: n (refers to n the moment in frame data of transmission antennas transmit) constantly, n=0, and 1 ..., N-1; M: m time-domain symbol (referring to m time-domain symbol in primary signal one frame that transmitting antenna will launch), m=0,1 ..., M
S-1; K: k frequency domain subchannel, k=0,1 ..., N-1; Q: transmitting terminal is preceding q the frequency domain subchannel of spectrum transformation not, q=0, and 1 ..., M
S-1; I: the i transmit antennas, i=1,2 ..., N
TJ: j root reception antenna, j=1,2 ..., N
RD: make a start before the precoding or receive the end equilibrium after d data flow, d=1,2 ..., S.
Making a start,
Be carved into M when representing on the d transmit antennas from first equivalence
SThe original equivalent time domain symbol that individual equivalence engraves the time is M
STie up original equivalent time domain Frame.
For channel,
Be k frequency domain subchannel gains between i transmit antennas and l root reception antenna; A
kBe the channel matrix of k frequency domain subchannel, wherein the capable i column element of l does
I=1,2 ..., N
T, l=1,2 ..., N
R, k=0,1 ..., N-1.
After receiving terminal removed CP, j root reception antenna received
J=1,2 ..., N
R, each value in the vector representes that respectively first is to N signal that constantly receives on the j root reception antenna.First constantly receives useful signal to N on
expression j root reception antenna,
represent on the j root reception antenna the useful symbol of frequency domain that first receives to N the frequency domain subchannel.First receives noise component(s) to N the moment on
expression j root reception antenna, and
wherein
is noise variance.
With
Represent that respectively first of n sampling time is to N
RTime domain useful signal part and time domain noise section that the root reception antenna receives.N=0,1 ..., N-1;
Represent on k the frequency domain subchannel first to N
RThe useful frequency-region signal that the root reception antenna receives, wherein
Represent on k the frequency domain subchannel first to N
TThe frequency-region signal that transmit antennas sends, noise component(s) does
Represent on k the frequency domain subchannel first to N
RThe frequency domain frequency domain noise that the root reception antenna receives.k＝0，1，…，N-1。According to the subchannel identification information, select the symbol that transmits on the available frequency domain subchannel
Wherein
Represent k
qOn the individual available frequency domain subchannel from first to N
RThe noise of receiving on the individual reception antenna, k
q∈ 0,1 ..., N-1} is the label of available frequency domain subchannel, q=0, and 1 ..., M
S-1; The signal that receives noise pollution on q the available frequency domain subchannel carries out the ZF equilibrium, is equivalent to
M-P contrary
The difference premultiplication
With
Obtain
With
Represent the noise component(s) on balanced q the available frequency domain subchannel.M
SObtain behind the some IFFT
With
D=1,2 ..., S;
Represent the noise component(s) of m the equivalence moment of balanced back first transmit antennas to the S transmit antennas, m=0,1 ..., M
S-1.
This method performing step is following:
(1) for N
T* N
RSelf-adaptive MIMO-SCFDE system, after receiving-transmitting sides is set up communication, receive end according to current state information of channel, desired system errored bit performance, from whole N frequency domain subchannel, select available M
SThe best order S of subchannel and definite channel matrix generates subchannel identification information and channel sequence information, and this subchannel identification information and channel sequence information sent to via feedback channel makes a start;
(2) make a start according to the modulation system that is adopted and subchannel identification information and channel sequence information, form S original equivalent time domain Frame, through M
SPoint FFT becomes equivalent frequency domain symbol with the equivalent time domain sign reversing of initial data frame, and the frequency domain subchannel mapping matrix of arranging according to subchannel label information and channel sequence information and receiving-transmitting sides then should be mapped to M after the precoding of equivalence frequency domain symbol
SOn the individual available frequency domain subchannel, generate N
TIndividual N dimension frequency domain vector utilizes N point IFFT to change back to time domain again, and the while was by N after serial to parallel conversion added CP
TIndividual transmitting antenna sends;
(3) receive end with N
RAfter the Frame that individual reception antenna receives removes CP, utilize FFT to transform to frequency domain, select M according to subchannel identification information and frequency domain subchannel inverse mapping matrix
SThe signal that transmits on the individual available frequency domain subchannel generates balanced matrix according to channel sequence information and channel condition information then and carries out equilibrium, and conversion is returned equivalent time domain and accomplished judgement;
(4) receive end and carry out the channel condition information that channel estimating obtains upgrading; Based on the self-adaptive decision rule; Judge whether to need to upgrade subchannel label information and channel sequence information; Upgrade if desired; Receive end group and upgrade subchannel label information and channel sequence information, and feed back to through backward channel and to make a start in the requirement of system's error performance;
When sending new frame data on the transmitting antenna, make a start and always carry out signal transformation according to up-to-date subchannel label information and the channel sequence information received.
Detailed step:
(1) step is for N
T* N
RAdaptive MIMO systems, after receiving-transmitting sides is set up communication, receive end according to current state information of channel, desired system errored bit performance, from whole N frequency domain subchannel, select available M
SThe best order S of subchannel and definite channel matrix generates subchannel identification information and channel sequence information, and this subchannel identification information and channel sequence information sent to via feedback channel makes a start;
Wherein channel condition information is the channel matrix of all frequency domain subchannels, the channel matrix A on each frequency domain subchannel
k, k=0,1 ..., N-1, the available diverse ways that obtains of CSI realize, for example can add the method for decision-feedback tracking or the method that the decision-feedback tracking adds frequency pilot sign with training frames, also can use the method for channel estimating etc.The best order of channel matrix is meant and satisfies systematic function, can make system spectral efficiency reach maximum number of antenna.Select available M
SThe criterion of the best order S of subchannel and definite channel matrix is following; According to the modulation system that system adopted; Should under the desired errored bit performance of system, transmit information symbol as much as possible, promptly let the product M of selected available frequency domain number of subchannels under best order and this order of channel matrix as far as possible
S* S or spectrum efficiency
Maximum.The error performance of system by equilibrium after signal to noise ratio decision, for the self-adaptive MIMO-SCFDE system that uses zero forcing equalization, balanced before signal to noise ratio snr
PreFor:
Balanced back signal to noise ratio snr
PostFor:
The best order of channel matrix and the selection of available frequency domain subchannel are following: satisfying
Down, maximization M
S* S, wherein: M
SBe available subchannels number, M
S∈ 0,1 ..., N}, S ∈ 1,2 ..., N
T, q=0,1 ..., M
S-1,
Be the average power of information symbol,
Be noise variance, SNR
ReqFor adopting behind certain modulation system and the taking into account system non-ideal factor signal to noise ratio after the pairing equivalent time domain equilibrium of desired system errored bit performance;
The method of the best order information of generation subchannel identification information and channel matrix is following: have only available subchannels to upload the transmission information symbol, and other frequency domain subchannels are for forbidding not transmission symbol of subchannel, D={D (k), k=0,1 ..., N-1, wherein D (k
q)=1 expression k
qSubchannel is an available subchannels, k
q∈ 0,1 ..., N-1}, q=0,1 ..., M
S-1, D (k)=0 expression k subchannel is unavailable subchannel, k ≠ k
qThe method of the best order information of mark generation channel matrix is following: at first need generate log2 (N
T) the channel sequence information B of bit, such as working as N
T=4 o'clock B={00,01,10, the best order that 11} identifies selected channel matrix successively is 1,2,3,4.Therefore feedback information has comprised subchannel identification information D and channel sequence information B.
(2) step, make a start according to the modulation system that is adopted and subchannel identification information and channel sequence information, form S original M
SThe equivalent time domain Frame is through M
SPoint FFT becomes equivalent frequency domain symbol with the equivalent time domain sign reversing of initial data frame, and the frequency domain subchannel mapping matrix of arranging according to subchannel label information and channel sequence information and receiving-transmitting sides then should be mapped to M after the precoding of equivalence frequency domain symbol
SOn the individual available frequency domain subchannel, generate N
TIndividual N dimension frequency domain vector utilizes N point IFFT to change back to time domain again, and the while was by N after serial to parallel conversion added CP
TIndividual transmitting antenna sends;
Become the concrete implementation method of equivalent frequency domain symbol to be the equivalent time domain sign reversing of initial data frame: to make a start and carry out sign map, form S frame M waiting for transmission according to the modulation system that is adopted
SIndividual equivalent time domain symbol
D=1,2 ..., through M
SPoint FFT, thus equivalent frequency domain symbol obtained
The implementation method of precoding and the mapping of available frequency domain subchannel is: the subchannel mark letter D={D (k) that makes a start and obtain according to feedback, k=0,1 ..., N-1} and channel sequence information B generate frequency domain subchannel mapping matrix P and pre-coding matrix Q, wherein
And the element among the P is (k only
q+ 1, be that other elements of 1 these row is 0 q+1), k
qRepresent k
qIndividual available frequency domain subchannel, k
q∈ 0,1 ..., N-1}, q=0,1 ..., M
S-1, pre-coding matrix Q is the S row of unit matrix, when being chosen at receiving-transmitting sides and before communication, appointing of S row, according to channel sequence information, generates Q, and on q equivalent frequency domain subchannel, precoding is with original equivalent frequency domain symbol
Be transformed to
Frequency domain subchannel mapping matrix P incites somebody to action then
Be mapped to M
SIndividual available frequency domain subchannel k
qOn, generate the N dimensional vector
Wherein
Other
I=1,2 ... N
T, to X
N, iBeing N point IFFT obtains
Add and carry out the D/A conversion behind the CP and carry out carrier modulation again and launch big line by each and send simultaneously.
In (3) step, receive end with N
RAfter the Frame that individual reception antenna receives removes CP, utilize FFT to transform to frequency domain, select M according to subchannel identification information and frequency domain subchannel inverse mapping matrix
SThe signal that transmits on the individual available frequency domain subchannel generates balanced matrix according to channel sequence information and channel condition information then and carries out equilibrium, and conversion rules out transmission information after returning equivalent time domain;
Because the effect of CP, on discrete time-domain, the linear convolution of signal and channel impulse response can convert the product on the discrete frequency domain to, so on k frequency domain subchannel,
And work as k=k
qThe time,
Otherwise
Do not carry information, k
q∈ 0,1 ..., N-1}, q=0,1 ..., M
S-1, k=0,1 ..., N-1;
After receiving terminal removed CP, j root reception antenna received useful signal and partly does
With the reception noise vector
Being N point FFT obtains frequency domain form and is respectively
Then, receive end and generate available frequency domain subchannel inverse mapping matrix P according to the subchannel identification information earlier
T, utilize frequency domain subchannel inverse mapping matrix P
T, select the symbol that on available subchannels, transmits
J=1,2 ..., N
R, promptly only be retained in k
qThe symbol that transmits on the subchannel
k
q∈ 0,1 ..., N-1}, q=0,1 ..., M
S-1; The A that utilizes estimation to obtain
kWith the pre-coding matrix Q that obtains according to channel sequence information, the symbol of selecting is carried out equilibrium, and the frequency domain symbol after the equilibrium is carried out M
SObtain the estimation of d data flow behind the some IFFT
Adjudicate, d=1,2 ..., S.
(4) step; Receive end and carry out the channel condition information that channel estimating obtains upgrading; According to the self-adaptive decision rule, judging whether needs to upgrade subchannel label information and channel sequence information, upgrades if desired; Receive end and upgrade subchannel label information and channel sequence information, and feed back to through backward channel and to make a start according to the requirement of system's error performance; Work as N
TWhen sending new frame data on the individual transmitting antenna, make a start and always carry out signal transformation according to up-to-date subchannel label information and the channel sequence information received.
Under static environment, only obtaining of channel condition information need be in the starting stage of communication, just determines after available subchannels number and the channel sequence information transmission signals continuously.And under mobile environment, channel situation changes constantly, when the various algorithms that are used for static environment can not directly be used under the changing environment.
In time varying channel; Channel condition information changes constantly; Obtain the method for channel condition information and can use different realization methods, for example can add the method for decision-feedback tracking or the method that the decision-feedback tracking adds frequency pilot sign, also can use the method for channel estimating etc. with training frames.What the present invention adopted is that the decision-feedback tracking adds the frequency pilot sign method:
According to demands of different to precision of channel estimation; Can insert the frequency pilot sign of different numbers at frequency domain; The minimal number of frequency pilot sign is the length of channel time domain impulse response, and the insertion frequency pilot sign possibly reach higher precision of channel estimation when many, but will waste more transmitting power and usable spectrum; The simulation result of present embodiment is to adopt number of pilot symbols to equal Cyclic Prefix, and pilot tone is inserted and adopted the dressing pilot tone.Its concrete implementation method is: pilot tone is evenly distributed in the subchannel; It is known that pilot tone point is gone up the information D of sending; Frequency domain according to pilot tone point place receives signal; Calculate the characteristic of channel at this pilot tone point place, the characteristic of channel on the non-pilot tone point subcarrier is to obtain according to the characteristic of channel on the pilot sub-carrier is carried out interpolation.Thereby obtain the channel condition information of all subchannels.
In time varying channel, transmitting terminal need be known the CSI of renewal, and channel estimating is accomplished at receiving terminal.Therefore rational passback strategy need be set, obtain the compromise between performance and the passback amount.The present invention requires to judge whether that needs upgrade subchannel label information and channel sequence information again according to system's error performance.Its concrete implementation method is: according to the errored bit performance that system requirements reaches, determine the scope of the balanced back signal to noise ratio that need reach, promptly in this scope error code newly can fluctuation the time system acceptable, for example [SNR
Req-2, SNR
Req+ 3].According to the subchannel number M
SMonitor out the balanced back signal to noise ratio of every frame with channel sequence number S:
And and SNR
ReqMake comparisons, determine whether in the signal to noise ratio scope that limits,, to keep current channel logo information D and channel sequence information B constant if in set scope; Otherwise according to
Maximization M
S* S chooses the available subchannels number M again
SWith channel sequence number S, and form new channel logo information D and channel sequence information B, made a start channel logo information after upgrading and order information retransmission then.
Beneficial effect of the present invention: the present invention has adopted a kind of simple method for precoding to combine frequency-selecting to resist the scarce order of channel; And under the same frequency spectrum utilance; Systematic function usually can be far above non-self-adapting MIMO-SCFDE system; Have low feedback velocity, solved effectively under the time varying channel and need return a large amount of feedback informations continually; Through selecting the balanced little frequency domain subchannel transmission information of noise of amplifying to make the errored bit performance can excessively not worsen; The BER of this system (Bit Error Rate, bit error rate) performance has simple controllable property; Overcome the existing problem that the back information amount is big in the adaptive frequency-selecting block transmission method in the MIMO broadband wireless channel, systematic function is difficult to guarantee that moves.The present invention can preferably resolve the excessive problem of feedback back information amount under the prerequisite that guarantees systematic function; Preferably resolve the problem of frequency selectivity and time selective fading.
Description of drawings
Fig. 1 is a system block diagram of realizing method proposed by the invention;
Wherein: 1, information source module, 2, the bit mapping block, 3, FFT module (M
SPoint), 4, precoding and available frequency domain subchannel mapping block, 5, IFFT module (N point), 6, add Cyclic Prefix (CP) module; 7, D/A module, 8, intermediate frequency and rf modulations module, 9, channel, 10, radio frequency and intermediate frequency demodulation module; 11, A/D module, 12, go the CP module, 13, FFT module (N point); 14, available frequency domain subchannel inverse mapping module, 15, balance module, 16, IFFT module (M
SPoint), synchronization module 17, judgement and symbol inverse mapping module, 18, channel estimation module, 19, adaptive frequency-selecting and channel sequence judge module, 20, choose available subchannels and channel sequence module, 21, backward channel, 22.
Embodiment
Below in conjunction with embodiment and description of drawings the present invention is described further:
What provide in an embodiment is the base band simulation result, does not consider the influence of synchronous error, promptly is ideal synchronisation synchronously.Accompanying drawing has provided the system block diagram of realizing the invention method that proposes, and each module effect is following:
Information source module 1: the bit information that generation will be transmitted.The result who passes back according to backward channel 21 and the modulation system number of employing produce and selected available subchannels number M
sS equivalent time domain Frame of corresponding length.
Bit mapping block 2: the data based modulation system that adopts that information source is produced is mapped on the planisphere corresponding points.In the present embodiment, adopted the 4QAM modulation.
FFT module (M
sPoint) 3: original equivalent time domain Frame is transformed to equivalent frequency domain.
Precoding and available frequency domain subchannel mapping block 4: this module generates pre-coding matrix according to the channel sequence information of backward channel module 21, and original equivalent frequency domain information symbol is carried out precoding.In the present embodiment; Receiving-transmitting sides is realized appointing that the column selection mode of getting of pre-coding matrix is former row; The best order that promptly obtains channel according to channel sequence information is S; Pre-coding matrix is
subchannel identification information according to backward channel module 21; Generate frequency domain subchannel mapping matrix and with equivalent frequency domain information sign map to the available frequency domain subchannel; And forbidding frequency domain subchannel does not transmit information symbol, generates the frequency domain information symbolic vector of N dimension.This module need be programmed according to the method that the present invention introduces, and is realized by the general digital signal processing chip.In the present embodiment, receiving-transmitting sides realizes appointing that frequency domain subchannel mapping matrix is for satisfying
And the element among the P is (k only
q+ 1, be that 1 other element of these row is 0 stairstepping matrix q+1).
IFFT module (N point) 5: the frequency-region signal that obtains after the mapping of available frequency domain subchannel is transformed to time domain.
Add CP module 6: every frame data that will obtain add Cyclic Prefix.
D/A module 7: with digital signal conversion is analog signal.
Intermediate frequency and rf modulations module 8: signal is modulated to and carries out the intermediate frequency amplification on the intermediate frequency, does rf modulations again, at last modulated signal is launched by antenna.
Channel 9: the frequency domain selectivity mimo channel of transmission signals.
Radio frequency and intermediate frequency demodulation module 10: the frequency spectrum that reception antenna is received signal is moved low frequency from radio frequency or intermediate frequency.The frequency deviation that causes in need be before the demodulation with Frequency Synchronization data correction signal transmission course.
A/D module 11: analog signal after the demodulation is transformed to digital signal.The A/D conversion need be sampled to analog signal, provides the crystal oscillator of clock signal need follow the crystal oscillator frequency of transmitter D/A module identical, otherwise will cause the sampling rate error.Therefore it is synchronous before the A/D conversion, will to carry out sampling rate.
Go CP module 12: Cyclic Prefix is removed.At this moment just there is the problem of judging that which frame data begin from, then goes to do regularly synchronously before the CP.
FFT module (N point) 13: the time-domain signal that will remove CP transforms to frequency domain.
Available frequency domain subchannel inverse mapping module 14:, select in the reception signal by M according to the subchannel identification information that backward channel module 21 is sent here
SThe equivalent frequency-region signal that individual available frequency domain subchannel carries.This module need be programmed according to the method that the present invention introduces, and is realized by the general digital signal processing chip.
Balance module 15: the channel sequence information that CSI that sends here with channel estimation module 18 and backward channel module 21 are sent here generates balanced matrix and carries out equilibrium.Present embodiment has adopted ZF balanced.
IFFT module (M
sPoint) 16: the equivalent frequency domain symbol after the equilibrium is transformed to equivalent time domain.
Judgement and symbol inverse mapping module 17: rule out the transmission symbol, and its inverse mapping is become bit information.
Channel estimation module 18: carry out channel condition information and obtain.Adopt decision-feedback to follow the tracks of the method that adds frequency pilot sign in the present embodiment and obtain channel condition information.Backward channel module 21 is utilized the CSI information that estimates; Confirm the order and the available frequency domain subchannel of pre-coding matrix; And send the subchannel identification information that generates to available frequency domain subchannel mapping block and precoding module 4 and available frequency domain subchannel inverse mapping module 14, send channel sequence information to available frequency domain subchannel mapping block and precoding module 4 and balance module 15.To estimate to such an extent that CSI gives balance module 15 simultaneously.
Adaptive frequency-selecting and channel sequence judge module 19: the channel condition information of every frame update that this module transmits according to channel estimation module 18 obtains the channel matrix A of all frequency domain subchannels
k(k=0,1 ..., N-1), best order S that determines and available subchannels number M
sJudge.Can adopt different judgment rules.If judged result is to carry out frequency-selecting again and channel sequence, then available subchannels and 20 work of channel sequence module are chosen in control; Make a start when sending new frame data, always work according to the subchannel label information of nearest acquisition.
According to the system error performance require to judge whether needs again the Adaptive Criterion of frequency-selecting and channel sequence can have multiple, for example:
(a) calculate current balanced back signal to noise ratio; Be designated as actual balanced back signal to noise ratio, liken difference to, be this difference capping and lower limit with the balanced back of expectation noise; If the difference of gained between the upper and lower bound that sets, keeps current channel tag information constant; If the difference of gained has exceeded the upper limit or lower limit, frequency-selecting again; This Adaptive Criterion can guarantee that the error performance of system is in the scope that requires.
(b) if can obtain whole channel condition informations, promptly comprise the channel condition information of available subchannels and no subchannel; Suppose that noise power is certain, calculate current balanced back signal to noise ratio, be designated as actual balanced back signal to noise ratio; Choose in whole subchannels after channel condition information upgrades and make balanced back signal to noise ratio be maximum groups of subchannels, and subchannel number is current available subchannels number, remember that this maximum balanced back signal to noise ratio is a signal to noise ratio after the optimum equalization; Liken noise after the balanced back signal to noise ratio of reality and the optimum equalization to difference, be this difference capping and lower limit, if the difference of gained between the upper and lower bound that sets, keeps current channel tag information constant; If the difference of gained has exceeded the upper limit or lower limit, frequency-selecting again.This Adaptive Criterion can guarantee that also the error performance of system is in the scope that requires.
Choose available subchannels and channel sequence module 20: whether this module need carry out frequency-selecting again and channel sequence by result's decision of adaptive frequency-selecting and channel sequence module 19.Again choose if desired; Then this module work; According to the desired errored bit performance of system, carry out the order of pre-coding matrix and select and the available subchannels selection, generate subchannel label information and channel sequence information simultaneously; Give available frequency domain subchannel inverse mapping module 14 and backward channel 21 during with subchannel label information and channel sequence information of same, beam back the precoding and the available frequency domain subchannel mapping block 4 of making a start through backward channel; This module need be programmed according to the method for introduction of the present invention, has digital signal processing chip to realize.
Backward channel module 21: subchannel label information and channel sequence information passed back make a start.
Synchronization module 22: the way through parameter Estimation (for example: blind estimation and based on the estimation of auxiliary data) obtains the various synchrodatas that system needs.Synchronization module is given radio frequency and intermediate frequency demodulation module 10 with the Frequency Synchronization data; Give A/D module 12 with the sampling rate synchrodata; Regularly synchrodata is given CP module 12.At present embodiment, be assumed to be synchronous ideal.
This instance simulation parameter:
Simulated environment: MATLAB R2009b
Subchannel sum: N=1024
CP length: 256
Modulation system: 2PSK, 4QAM, 16QAM
Selected signal to noise ratio SNR:13dB, the 20dB of on average accepting of emulation
Maximum doppler frequency fd:111Hz, 166Hz, 222Hz
Sampling rate: 20M bps
Simulated channel environment: adopt 4 * 4MIMO time varying channel
Time varying channel: adopt the A model (ITU IMT2000 Vehicular Test Environmentchannel model A) of IMT2000 vehicle environment, can be with reference to international telecommunication union recommendation the M.1225 number (RECOMMENDATION ITU-RM.1225GUIDELINES FOR EVALUATION OF RADIO TRANSMISSION TECHNOLOGIES FOR IMT-2000).
Be used for the signal to noise ratio high 3dB of the training frames of channel estimating in the emulation than normal data frame
Do not consider in the emulation that to the influence of system, the error of promptly supposing all synchronization parameters all is 0 to synchronous error (comprising regularly synchronous error of carrier synchronization error, sampling rate synchronous error and frame); The propagation delay time when not considering backward channel passback subchannel identification information and channel sequence information and the influence of transmission error code suppose that promptly propagation delay time and error code all are 0; Do not consider the influence (for example device non-linear etc.) of other non-ideal factors.
Simulation result:
Provide below and adopt the present invention speed of a motor vehicle moveable self-adaption MIMO-SCFDE system that proposes and the contrast of not adopting the MIMO-SCFDE system of adaptive algorithm.When table 1 is 13dB for the average received signal to noise ratio, the adaptive algorithm that the present invention adopts and the comparison of non-self-adapting algorithm.When table 2 is 20dB for the average received signal to noise ratio, the adaptive algorithm that the present invention adopts and the comparison of non-self-adapting algorithm.Can be found out by simulation result: under the same frequency spectrum utilance, the speed of a motor vehicle moveable self-adaption MIMO-SCFDE systematic function that the present invention proposes can be far above non-self-adapting MIMO-SCFDE system.
(1) average received signal to noise ratio: SNR=13dB
Table 1
(2) average received signal to noise ratio: SNR=20dB
Table 2
For avoiding confusion, some nouns or the symbol mentioned in this specification are done following explanation:
1, the frequency domain subchannel notion of frequency domain subchannel: MIMO-SCFDE is equal to the notion of the subcarrier among the MIMO-OFDM.
2, equivalent time domain symbol: M
SReach M before the some FFT
SSymbol behind the some IFFT.
3, equivalent frequency domain symbol: M
SReach M behind the some FFT
SSymbol before the some IFFT.
4, time-domain signal: before the N point FFT and the symbol behind the N point IFFT.
5, frequency-region signal: reach the preceding symbol of N point IFFT behind the N point FFT.
6, the M-P of
matrix is contrary.
Claims (4)
1. the speed of a motor vehicle moves the adaptive transmission method of MIMO-SCFDE, and this method may further comprise the steps:
(1) for N
T* N
RSelf-adaptive MIMO-SCFDE system, after receiving-transmitting sides is set up communication, receive end according to current state information of channel, desired system errored bit performance, from whole N frequency domain subchannel, select available M
SThe best order S of subchannel and definite channel matrix generates subchannel identification information and channel sequence information, and this subchannel identification information and channel sequence information sent to via feedback channel makes a start; Wherein, N
T: the transmitting antenna number; N
R: the reception antenna number; N: the length that does not add a protection frame SC-FDE frame at interval; M
S: selected frequency domain subchannel number;
(2) make a start according to the modulation system that is adopted and subchannel identification information and channel sequence information, form S original equivalent time domain Frame, through M
SPoint FFT becomes equivalent frequency domain symbol with the equivalent time domain sign reversing of initial data frame, and the frequency domain subchannel mapping matrix of arranging according to subchannel label information and channel sequence information and receiving-transmitting sides then should be mapped to M after the precoding of equivalence frequency domain symbol
SOn the individual available frequency domain subchannel, generate N
TIndividual N dimension frequency domain vector utilizes N point IFFT to change back to time domain again, and the while was by N after serial to parallel conversion added cyclic prefix CP
TIndividual transmitting antenna sends;
(3) receive end with N
RAfter the Frame that individual reception antenna receives removes CP, utilize FFT to transform to frequency domain, select M according to subchannel identification information and frequency domain subchannel inverse mapping matrix
SThe signal that transmits on the individual available frequency domain subchannel generates balanced matrix according to channel sequence information and channel condition information then and carries out equilibrium, and conversion is returned equivalent time domain and accomplished judgement;
It is characterized in that; Receive end and carry out the channel condition information that channel estimating obtains upgrading; According to the self-adaptive decision rule, judging whether needs to upgrade subchannel label information and channel sequence information, upgrades if desired; Receive end and upgrade subchannel label information and channel sequence information, and feed back to through backward channel and to make a start according to system's errored bit performance demands; When sending new frame data on the transmitting antenna, make a start and always carry out signal transformation according to up-to-date subchannel label information and the channel sequence information received.
2. a kind of speed of a motor vehicle as claimed in claim 1 moves the adaptive transmission method of MIMO-SCFDE; It is characterized in that, obtain the method for said channel condition information and use: training frames adds method, the decision-feedback of decision-feedback tracking and follows the tracks of method that adds frequency pilot sign or the method for using channel estimating.
3. a kind of speed of a motor vehicle as claimed in claim 2 moves the adaptive transmission method of MIMO-SCFDE; It is characterized in that; The said channel condition information method of obtaining is followed the tracks of the method that adds frequency pilot sign with decision-feedback; Its concrete implementation method is: adopt number of pilot symbols to equal Cyclic Prefix, pilot tone is inserted and is adopted the dressing pilot tone; Pilot tone is evenly distributed in the subchannel; It is known that pilot tone point is gone up the information D of sending; Frequency domain according to pilot tone point place receives signal; Calculate the characteristic of channel at this pilot tone point place, the characteristic of channel on the non-pilot tone point subcarrier is to obtain according to the characteristic of channel on the pilot sub-carrier is carried out interpolation, thereby obtains the channel condition information of all subchannels.
4. a kind of speed of a motor vehicle as claimed in claim 1 moves the adaptive transmission method of MIMO-SCFDE; It is characterized in that; Judge whether that concrete implementation method that need to upgrade subchannel label information and channel sequence information is: the errored bit performance that reaches according to system requirements; Determine the scope of the balanced back signal to noise ratio that need reach, according to the subchannel number M
SMonitor out the balanced back signal to noise ratio snr of every frame with channel sequence number S
Post, and and SNR
ReqMake comparisons, determine whether in the signal to noise ratio scope that limits; If in set scope, keep current channel logo information D and channel sequence information B constant; Otherwise according to SNR
Post>=SNR
Req, maximization M
S* S chooses the available subchannels number M again
SWith channel sequence number S, and form new channel logo information D and channel sequence information B, made a start channel logo information after upgrading and order information retransmission then; SNR wherein
ReqFor adopting behind certain modulation system and the taking into account system non-ideal factor signal to noise ratio after the pairing equivalent time domain equilibrium of desired system errored bit performance; SNR
PostBe signal to noise ratio after the equilibrium.
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