CN105791182B - IQ imbalances and channel joint estimation method suitable for MIMO-OFDM systems - Google Patents
IQ imbalances and channel joint estimation method suitable for MIMO-OFDM systems Download PDFInfo
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- CN105791182B CN105791182B CN201610137200.0A CN201610137200A CN105791182B CN 105791182 B CN105791182 B CN 105791182B CN 201610137200 A CN201610137200 A CN 201610137200A CN 105791182 B CN105791182 B CN 105791182B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/32—Carrier systems characterised by combinations of two or more of the types covered by groups H04L27/02, H04L27/10, H04L27/18 or H04L27/26
- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/36—Modulator circuits; Transmitter circuits
- H04L27/362—Modulation using more than one carrier, e.g. with quadrature carriers, separately amplitude modulated
- H04L27/364—Arrangements for overcoming imperfections in the modulator, e.g. quadrature error or unbalanced I and Q levels
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0202—Channel estimation
- H04L25/024—Channel estimation channel estimation algorithms
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/0264—Arrangements for coupling to transmission lines
- H04L25/028—Arrangements specific to the transmitter end
- H04L25/0284—Arrangements to ensure DC-balance
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2602—Signal structure
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L27/00—Modulated-carrier systems
- H04L27/26—Systems using multi-frequency codes
- H04L27/2601—Multicarrier modulation systems
- H04L27/2647—Arrangements specific to the receiver only
- H04L27/2655—Synchronisation arrangements
- H04L27/2657—Carrier synchronisation
Abstract
The invention belongs to wireless communication technology field, it is related to a kind of IQ imbalances in the MIMO-OFDM systems of the phase and amplitude imbalance interference of same phase and quadrature branch by receiver and channel joint estimation method.The invention mainly includes steps：Pilot signal estimation IQ balances using the domains DATA and channel joint response；IQ amplitudes, which are solved, using the joint response of estimation mismatches the factor and the phase mismatch factor；Then IQ imbalances are compensated；Channel estimation is carried out using the long training sequence after compensation.The present invention can be obviously improved the performance for the MIMO-OFDM systems interfered by IQ imbalances, reliably restore channel response.In addition, the present invention has very strong practicability and portability.
Description
Technical field
The invention belongs to wireless communication technology field, be it is a kind of be related to by the same phase of receiver and the phase of quadrature branch and
A kind of IQ imbalances in the MIMO-OFDM systems of amplitude imbalance interference and channel joint estimation method.
Background technology
Spectrum utilization efficiency how is improved, communication system channel capacity is increased, fights the influence of radio channel multi-path decline,
High speed data transfer, which is communication system of new generation, under adaptation broadband wireless context to solve the problems, such as.OFDM technology has frequency band
Utilization rate is high, mitigating frequency-selective fading is strong and keeps the potentiality and advantage of higher transmission rate.And MIMO technology then may be used
To enable under conditions of being slightly increased frequency spectrum resource and excess power, power system capacity exponentially increases, performance greatly carries
It rises.So MIMO and OFDM technology are combined into a kind of inevitable trend.
It is channel estimation in terms of one important research of MIMO-OFDM systems, the accuracy of channel estimation directly affects whole
The performance of a system.When receiving terminal carries out coherent demodulation and space-time decoding, it is required for accurate channel state information.In order to extensive
The signal sent is recurred, receiving terminal needs to estimate the status information of channel, and the signal received is corrected and is restored.
In a wireless communication system, transmitter and receiver both ends inevitably exist with mutually quadrature branch between
The unmatched situation of phase and amplitude, i.e. IQ is uneven, this generates channel the orthogonality between destroying ofdm system subcarrier
Image interference causes the overall performance of system to decline.
Currently, had the algorithm of many maturations about the research that channel estimation and IQ imbalances are estimated, but IQ is uneven
The algorithm comparison of weighing apparatus and channel Combined estimator is few, and the algorithm in MIMO-OFDM systems can be applied even more fewer and fewer.Therefore,
Studying a kind of IQ imbalances can be suitably used for MIMO-OFDM systems and channel Combined estimator algorithm is one and has very much reality meaning
The work of justice and challenge.
Invention content
Goal of the invention：In view of the deficiencies of the prior art, present invention aims at provide one kind can be suitably used for MIMO-OFDM systems
The IQ imbalances and channel joint estimation method of system.
Technical solution：For achieving the above object, the technical solution adopted by the present invention is：
A kind of IQ imbalances and channel joint estimation method suitable for MIMO-OFDM systems includes mainly IQ uneven
Estimation and compensation, channel estimation, are as follows：
(1) baseband signal received is synchronized, including Timing Synchronization, carrier frequency synchronization and sampling clock are same
Step；
(2) signal after synchronization is parsed, extract the long training sequence in signal and is inserted in data word
The pilot signal of section；
(3) the pilot signal estimation IQ imbalances of extraction and channel joint response are utilized；
(4) the joint response obtained according to estimation solves IQ amplitudes and mismatches the factor and the phase mismatch factor；
(5) it mismatches the factor using the IQ amplitudes acquired and phase mismatches factor pair data and carries out IQ imbalance compensations；
(6) channel estimation is carried out using the long training sequence after IQ imbalance compensations.
In step (3) by the reception signal frequency domain expression formula for the MIMO-OFDM systems interfered by IQ imbalances be zk=sk
Γk+Vk, wherein skIndicate the frequency-region signal sent on k-th of subcarrier, ΓkIndicate IQ imbalances on k-th of subcarrier and
Channel joint response, VkIndicate the white Gaussian noise on k-th of subcarrier；The IQ balances and letter estimated using pilot signal
Road joint response is Γk=(sk Hsk)-1sk Hzk。
IQ amplitudes in step (4) mismatch factor g and phase mismatches factor φ and acquired according to following formula：
Wherein, g1For ΓkIn the 1st and the 2nd element ratio, g2For ΓkIn the 4th and the 3rd element ratio
Value,Expression takes the real part of expression formula,Expression takes the imaginary part of expression formula.
IQ imbalance compensation formula in step (5) are：
Wherein, Yk(n) indicate that the frequency domain not influenced by IQ imbalances on k-th of subcarrier of n-th of OFDM symbol connects
The collection of letters number, Ck(n) indicate the compensation on k-th of subcarrier of n-th of OFDM symbol reception signal after IQ imbalances,
The algorithm of channel estimation includes in step (6)：
(6.1) it is rung using compensating the unbalanced long training sequences of IQ and estimate initial channel frequency based on LS criterion
It answers；
(6.2) become to change commanders using IDFT and estimate that obtained channel frequency domain response transforms to time domain and obtains time domain impulse response；
(6.3) noise in maximum posteriori criterion estimation signal subspace is utilized；
(6.4) the channel time domain shock response obtained in step (6.2) is subtracted into the signal that estimation obtains in step (6.3)
Noise in subspace obtains updated channel impulse response；
(6.5) updated channel impulse response is obtained into the channel frequency of all subcarriers by DFT transform to frequency domain
Response.
Step responds time domain impulse in (6.2)Resolve into two parts：
V (n) is also divided into two
PointWherein, W is Fourier transform matrix,Indicate n-th of OFDM symbol
Channel frequency domain response estimation value, LCPIndicate that the length of OFDM symbol cyclic prefix, K indicate the number of OFDM symbol subcarrier, v
(n) time domain white Gaussian noise, () are indicated-1Expression inverts to expression formula, ()TIt indicates to carry out transposition to expression formula,WithDefinition difference it is as follows：
The noise in maximum posteriori criterion estimation signal subspace is utilized in step (6.3)
Wherein, X (n) indicates the frequency sent
Domain signal, ()HExpression takes conjugate transposition to expression formula,Indicate the variance of white Gaussian noise.
By estimating and removing the noise of signal subspace in step (6.4), noise is utmostly reduced to channel estimation
Influence, the calculation formula of updated channel time domain shock response is：
Advantageous effect：Compared with prior art, it is uneven to propose a kind of IQ can be suitably used for MIMO-OFDM systems by the present invention
Weighing apparatus and channel joint estimation method, method estimate IQ imbalances and channel joint response first with the pilot signal in the domains DATA,
Then it solves the IQ amplitudes mismatch factor using the joint response of estimation and phase mismatches the factor, then IQ imbalances are mended
It repays, finally carries out channel estimation using the long training sequence after compensation.The present invention, which can be obviously improved, to be interfered by IQ imbalances
The performance of MIMO-OFDM systems, reliably restores channel response.In addition, the present invention has very strong practicability and portability.
Description of the drawings
Fig. 1 is MIMO-OFDM receiver flow charts.
Fig. 2 is IEEE 802.11ac physical layer frame structure figures.
Fig. 3 is the implementation flow chart of IQ imbalances of the present invention and channel Combined estimator algorithm.
Fig. 4 is influence diagram of the IQ imbalances to channel estimation results.
Fig. 5 is the planisphere before and after IQ imbalance compensations.
Fig. 6 is the algorithm MSE performance charts of IQ imbalances of the present invention and channel Combined estimator.
Specific implementation mode
Further description is done to the present invention in the following with reference to the drawings and specific embodiments.
Fig. 1 is that MIMO-OFDM receives flow chart.Receiver end signal processing includes mainly：Timing Synchronization, SISO-
OFDM channel estimation and equalizations, signal field parsing, MIMO Frequency Estimations and compensation, MIMO-OFDM channel estimation and equalizations,
DATA field parses.
Fig. 2 is IEEE 802.11ac physical layer frame structure schematic diagrames.It is leading (VHT) by legacy preamble, ultra-high throughput
And DATA field composition.Legacy preamble ensure that the back compatible with 802.11a/n.L-STF is that Legacy practices sequence, is used
It is corrected in automatic growth control (Automatic Gain Control, AGC), Timing Synchronization and frequency.L-LTF is that tradition is long
Training sequence is mainly used for more accurate Frequency offset estimation and time synchronization, also be used for for receive and equilibrium L-SIG fields with
And VHT-SIG-A fields, generate channel estimation parameter.L-SIG is legacy signaling field, is used for transmission data transmission rate and length
Spend information.VHT-SIG-A is VHT PPDU signaling fields, carries the information of decoding VHT PPDU, is for single user PPDU numbers
It is designed according to format.VHT-STF is used for the fine tuning of automatic growth control and time synchronization when MIMO transmission.VHT-LTF is used for
Channel estimation parameter, decoding VHT-SIG-B field and equalization data field are obtained when MIMO transmission.VHT-SIG-B is carried
The specific information of data frame.The domains DATA carry the useful information of user's transmission, it contains certain number of pilot signal, can
To be used for estimating IQ imbalances and tracking time varying channel.
Fig. 3 is the implementation flow chart of IQ imbalances of the present invention and channel Combined estimator algorithm, as shown in figure 3, the present invention is real
It applies a kind of suitable for the IQ imbalances of MIMO-OFDM systems and the specific implementation step master of channel joint estimation method disclosed in example
Including：
Step1：The baseband signal received is synchronized, including Timing Synchronization, carrier frequency synchronization and sampling clock
It is synchronous.
Step2：Signal after synchronization is parsed, the long training sequence in signal is extracted and is inserted in data
The pilot signal of field.
Step3：The estimation of IQ imbalances and compensation are carried out to the signal after synchronizing, the IQ imbalances estimation that the present embodiment proposes
Include mainly the joint response of estimation IQ imbalances and channel with backoff algorithm, solve IQ amplitudes and the phase mismatch factor, IQ
It is the step of imbalance compensation, specific as follows：
S1：IQ imbalances are not mismatch g (as unit of dB) and phase not by the amplitude at transmitter and receiver both ends
With caused by φ (as unit of degree), enableOne is interfered by receiver IQ imbalances
MIMO-OFDM systems in, transmitting antenna number is NTX, reception antenna number is NRX, then the i-th (i=1,2 ..., NRX) piece-root grafting
The frequency-domain received signal received on k-th of subcarrier of n-th of OFDM symbol on antenna can be expressed as：
Y′ik(n)=X 'k(n)H′i+αvik(n)+βv-ik(n)*=α Yik(n)+βY-ik(n)* (1)
Wherein,Xjk(n) indicate that jth root emits day
K-th of sub-carrier signal of n-th of the OFDM symbol emitted on line,HjkTable
Show the channel frequency domain response of k-th of subcarrier between i-th and j-th strip link, Yik(n) it is not received by IQ imbalance interference
Signal, vik(n) it is white Gaussian noise.Further abbreviation, receiving frequency-region signal can be expressed as：zk=skΓk+Vik, wherein zk、
sk、Vik、ΓkDefinition difference it is as follows：zk=[Y′ik(n)T,Y′ik(n+1)T,…,Y′ik(n+NTX-1)T]T,sk=[X′1k(n)T,X′1k(n+1)T,…,X′1k(n+NTX-1)T]T,, Vik=[v′ik(n)T,v′ik(n+1)T,…,v′ik(n+NTX-1)T]T, It is carried out using the pilot signal extracted in Step2
Based on the channel estimation of LS criterion, it is Γ that estimation, which obtains IQ imbalances and the joint response of channel,k：
Γk=(sk Hsk)-1sk Hzk (2)
S2：Utilize the Γ in formula (2)kIt solves IQ amplitudes and mismatches factor g and phase mismatch factor φ.Enable ΓkIn the 1st
A and the 2nd element ratio is g1, the ratio of the 4th and the 3rd element is g2, then can obtain
AgainThen
S3：The factor is mismatched using the IQ amplitudes that formula (4) acquires and phase mismatches factor pair data and carries out IQ injustice
Weighing apparatus compensation, IQ imbalance compensation formula are as follows：
Wherein Cik(n) the reception signal after IQ imbalance compensations, Y ' are indicatedik(n) it is to be received by IQ imbalance interference
Signal, Yik(n) it is the reception signal not interfered by IQ imbalances,
Step4：Channel estimation is carried out using the unbalanced long training sequences of IQ were compensated, the channel that the present embodiment proposes is estimated
The step of calculating method, is as follows：
S1：Initial channel frequency domain response is estimated based on LS criterion using the unbalanced long training sequences of IQ were compensated：
S2：Become the channel frequency domain response that estimation obtains of changing commanders using IDFT and transforms to time domain：
S3：It willIt is divided into two parts：
S4：V (n) is also divided into two parts：
S5：The noise of signal subspace is estimated using maximum posteriori criterion：
Formula (10) is asked about v1(n) derivative can obtain：
S6：It will be in S3The noise in the signal subspace that estimation obtains is subtracted, channel estimation value is updated：
S7：It will finally by DFTFrequency domain is transformed to, the channel frequency domain response of all subcarriers is obtained：
Fig. 4 illustrates influence of the IQ imbalances to channel estimation results.Abscissa indicates that frequency, ordinate expression are returned in figure
Channel power (unit after one change：DB), while legend Ideal indicates ideal channel frequency response.It can be with from simulation result
Find out, not compensating the unbalanced channel estimation results of IQ can up and down shake near true channel frequency response, and carry herein
The IQ imbalances and channel estimation method gone out can effectively eliminate this shake that IQ imbalances are brought.
Fig. 5 (a) is the planisphere before IQ imbalance compensations；Fig. 5 (b) is the planisphere after IQ imbalance compensations.From constellation
Figure is as can be seen that the unbalanced presence of IQ can make planisphere thicken, to make the bit error rate of system decline.But by right
Data carry out IQ imbalance compensations, can substantially reduce interference of the IQ imbalances to constellation point, improve the overall performance of system.
Fig. 6 (a) is the statistical chart of mean square error of the different channels estimator in given IQ imbalances；Fig. 6 (b) is different
The statistical chart of the bit error rate of the channel estimator in given IQ imbalances.From simulation result as can be seen that the unbalanced sizes of IQ
Really the result of channel estimation is influenced very big, and IQ imbalances proposed by the present invention and channel Combined estimator algorithm really can be with
Significantly improve the performance of channel estimation.
Specific implementation process of the present invention described in detail above in IEEE 802.11ac MIMO-OFDM systems, but
It is that the present invention is not limited to the specific details in the above embodiment, it within the scope of the technical concept of the present invention, can be to this hair
Bright technical solution carries out a variety of equivalents, these equivalent variations are all within the scope of the present invention.
Claims (4)
1. a kind of IQ imbalances and channel joint estimation method suitable for MIMO-OFDM systems, which is characterized in that including following
Step：
(1) baseband signal received is synchronized, including Timing Synchronization, carrier frequency synchronization are synchronous with sampling clock；
(2) signal after synchronization is parsed, extract the long training sequence in signal and is inserted in data field
Pilot signal；
(3) the pilot signal estimation IQ imbalances of extraction and channel joint response Γ are utilizedk=(sk Hsk)-1sk Hzk；Wherein, skFor
The frequency-region signal sent on k-th of subcarrier, zkThe frequency-region signal received for the MIMO-OFDM systems interfered by IQ imbalances；
(4) the joint response obtained according to estimation solves IQ amplitudes and mismatches factor g and phase mismatch factor φ；Solution formula
For：
Wherein, g1For ΓkIn the 1st and the 2nd element ratio, g2For ΓkIn the 4th and the 3rd element ratio,Expression takes the real part of expression formula,Expression takes the imaginary part of expression formula；
(5) it mismatches the factor using the IQ amplitudes acquired and phase mismatches factor pair data and carries out IQ imbalance compensations；IQ is not
Balanced compensated formula is：Wherein, Yk(n) indicate that the frequency domain not by the interference of IQ imbalances receives letter
Number, Ck(n) the reception signal after IQ imbalance compensations is indicated,
(6) channel estimation is carried out using the long training sequence after IQ imbalance compensations；Including：
(6.1) initial channel frequency domain response is estimated based on LS criterion using compensating the unbalanced long training sequences of IQ；
(6.2) become to change commanders using IDFT and estimate that obtained channel frequency domain response transforms to time domain and obtains time domain impulse response；
(6.3) noise in maximum posteriori criterion estimation signal subspace is utilized；
(6.4) the channel time domain shock response obtained in step (6.2) is subtracted into the signal subspace sky that estimation obtains in step (6.3)
Between in noise, obtain updated channel impulse response；
(6.5) by updated channel impulse response by DFT transform to frequency domain, the channel frequency for obtaining all subcarriers is rung
It answers.
2. a kind of IQ imbalances and channel joint estimation method suitable for MIMO-OFDM systems according to claim 1,
It is characterized in that：Time domain impulse is responded in the step (6.2)Resolve into two parts： V (n) is also divided into two parts： Wherein, W is Fourier transform matrix,Indicate the channel frequency domain response estimation of n-th of OFDM symbol
Value, LCPIndicate that the length of OFDM symbol cyclic prefix, K indicate that the number of OFDM symbol subcarrier, v (n) indicate time domain white Gaussian
Noise, ()-1Expression inverts to expression formula, ()TIt indicates to carry out transposition to expression formula,WithDefinition respectively such as
Under：
3. a kind of IQ imbalances and channel Combined estimator suitable for MIMO-OFDM systems according to claim 2
Method, it is characterised in that：The noise in maximum posteriori criterion estimation signal subspace is utilized in the step (6.3)Wherein, X
(n) frequency-region signal sent, () are indicatedHExpression takes conjugate transposition to expression formula,Indicate the variance of white Gaussian noise.
4. a kind of IQ imbalances and channel joint estimation method suitable for MIMO-OFDM systems according to claim 3,
It is characterized in that：By estimating and removing the noise of signal subspace in the step (6.4), noise is utmostly reduced to letter
The influence of road estimation, updated channel time domain shock responseCalculation formula be：
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| CN108076002B (en) | 2016-11-10 | 2020-11-03 | 富士通株式会社 | Offset drift compensation device, received signal recovery device, and receiver |
| CN106656884B (en) * | 2016-12-23 | 2019-11-15 | 上海创远仪器技术股份有限公司 | A kind of Vector Signal Analyzer channel compensation method based on frequency domain parameter estimation |
| CN106685864B (en) * | 2017-01-18 | 2019-09-17 | 深圳市极致汇仪科技有限公司 | A kind of composite system channel estimation methods and device suitable for tester |
| CN108650199B (en) * | 2018-04-23 | 2021-01-26 | 东南大学 | Wireless communication receiving end IQ imbalance and channel joint estimation method and device |
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