CN106941471A - A kind of IQ imbalance compensation methods for differential coding ofdm system - Google Patents

Abstract

The invention belongs to wireless communication technology field, it is related to a kind of IQ imbalance compensation methods for differential coding ofdm system.The method of the present invention mainly carries out Combined estimator using the compensating parameter of subcarrier and mirror image subcarrier, in compensation system I the unbalanced methods of Q.The present invention propose a kind of differential space-time coding ofdm system I Q imbalance compensation methods, including：Estimate the compensating parameter in subcarrier and subcarrier mirror image, update compensation matrix, primary carrier is compensated with compensation matrix.The present invention is not on the premise of accuracy is lost, and the data of two subcarriers are commonly used for estimating a compensation vector, and convergence of algorithm speed can reach twice of generalized linear algorithm.

Description

A kind of IQ imbalance compensation methods for differential coding ofdm system

Technical field

The invention belongs to wireless communication technology field, it is related to a kind of IQ imbalance compensations for differential coding ofdm system Method.

Background technology

With the popularization of high-speed radiocommunication system, a large amount of emerging content of multimedia and application scenarios increase people couple In the demand of several Gbps even more highs rate communications.In order to provide enough transmission bandwidths, conventional 6GHz to new opplication scene Following communications band can not meet demand, therefore increasing scholar will study center of gravity and be transferred to and possesses a large amount of frequencies The millimeter wave frequency band and Terahertz frequency range of spectrum resource.Simultaneously as the transmission services species that mobile communications network is carried is all the more Abundant, there is obvious isomery characteristic in wireless network, and same station terminal equipment needs to support multiple network type, for example, move honeybee Nest system, fixed wireless LAN, short-distance wireless LAN and Position Fixing Navigation System etc..It means that user terminal Transceiver need the system with flexibility to adapt to heterogeneous networks and different frequency range.But, realizing high band communication While with system flexibility is ensured, Analog Circuit Design must be in system linearity degree, circuit bandwidth, complexity and power consumption side Face is weighed.The wireless communication system of design low cost low-power consumption is that the work of a great challenge, the especially system are needed Possess high band, the communication capacity of super large bandwidth.Due to cost limitation, complicated circuit structure and excellent performance are expensive Device is no longer applicable；In addition, in the application scenarios of similar heterogeneous network, for the circuit of the special design optimization of particular frequency bands, Or can not also be used for the circuit of single device or single scene optimization.For control device overall volume and cost, especially Applied to the circuit in multiple-input and multiple-output (Multiple-input Multiple-output, MIMO) system, single set radio frequency Cost, power consumption and the volume of circuit are all strictly limited.Factors above causes the radio-frequency front-end of transceiver to there are many performance flaws Defect.Such as direct current biasing, I Q uneven (In-phase Quadrature Imbalance) and phase noise etc..

QPSK is a kind of conventional baseband modulation, and its principle is that baseband signal is divided into parallel two paths of signals, In-phase branch (In-phase Branch, I roads) and quadrature branch (Quadrature Branch, Q roads) are referred to as, is passed through respectively Two orthogonal local oscillation signals are crossed to be modulated to radio frequency and be transmitted；In receiving terminal, receiver generates two orthogonal sheets Shake signal, is separated two paths of signals using coherent demodulation, extracts baseband signal.In real system, due to I Q two-way vibration letter Number synthesized, then obtained by Hilbert transform by crystal oscillator and phaselocked loop, the amplitude of two-way oscillator signal is difficult to accomplish complete phase Together, phase difference is nor 90 °, cause I Q two paths of data occur crosstalk.In low-frequency range system, because system working frequency range is low, I Q energy imbalances it is not serious；But, the widely used Direct Conversion Receiver of high band system is especially employing high-order In the system of modulation, I Q imbalance turn into limitation receiver performance key factor.On the other hand, I the responses of the branch roads of Q two exist Ideally should be completely the same, however, due to high band system bandwidth increase, I the branch road device frequencies of Q two response be difficult Realize it is completely the same, this be cause I the unbalanced another sources of Q.

MIMO technology is a kind of wide variety of multiple antenna transmission technique.The space diversity brought using channel fading characteristic Effect, MIMO transmission technology can realize the lifting of channel capacity.In the case where not increasing transmission power, transmitting terminal can when Between dimension and Spatial Dimension co-design launch scenario, this technology is referred to as Space-Time Codes (Space-time Coding,STC).In design coding criterion, it is contemplated that the situation that receiving terminal antenna number is fixed, many Space-Time Codes are all Seek to provide maximum transmitting diversity exponent number M.Many scholars think that noncoherent communication is suitable as the supplement of coherent communication technology Technology is applied to the 5th third-generation mobile communication net.However, when realizing noncoherent communication systems using inexpensive device, sending and receiving end is still The non-ideal characteristic problem of radio-frequency devices can be faced.For example, in the large-scale low-cost application scenarios such as Internet of Things, manufacturer without Method is individually debugged to each equipment.Therefore, in the incoherent system of Unknown Channel information, how digital compensation is utilized Algorithm compensates worth research to radio frequency non-ideal characteristic.At present for I Q imbalance compensation algorithms be mainly generalized linear Backoff algorithm, because channel condition is more severe, although the algorithm can compensation I to a certain degree Q it is uneven, but it receives Hold back speed very slow, and compensation poor-performing.

The content of the invention

Differential space-time coding can realize complete space diversity while avoiding channel estimation expense.It is serious in frequency selectivity In channel, Space Time Coding combination ofdm system can effectively eliminate intersymbol interference.However, using inexpensive device Part realizes Space-time Block Code System, especially with Direct Conversion transceiver, can face serious I Q imbalance problems.Therefore originally Invention proposes a kind of method of estimation based on parameter, by the way that the compensating parameter of mirror image subcarrier and primary signal subcarrier is entered Row Combined estimator, the data of two subcarriers are commonly used for estimating a compensation vector, on the premise of accuracy is not lost, Convergence of algorithm speed can reach twice of generalized linear algorithm.

The technical scheme is that：

A kind of IQ imbalance compensation methods for differential coding ofdm system, define differential coding ofdm system and contain The differential space-time coding signal sent on K subcarrier, k-th of subcarrier is：

Wherein z_n(k)=[z_2n-1(k) z_2n(k)] 2n-1 and 2n received for receiver in k-th of subcarrier The signal vector of OFDM symbol composition, matrix S_n(k) n-th of DSTC signal matrix in k-th of subcarrier transmission is represented, each Signal needs two OFDM symbol transmission, S_n(k) it is unitary matrice, the symbol of its i-th row j row is represented in the 2n-2+j OFDM symbol Number k subcarriers, i, j=1,2；The symbol sent by i-th antenna, v_2n-1And v (k)_2n(k) represent in k-th of subcarrier On frequency domain additive noise, scalar lambda_i(n) i=1,2 is represented on subcarrier k from i-th antenna of transmitting terminal to the frequency of reception antenna Domain impulse response；S_n(k) information matrix U is passed through_n(k) obtained according to differential coding rule：

S_n(k)=S_n-1(k)U_n(k)

Define transceiver exist simultaneously I Q it is uneven, the Equivalent Base-Band signal after down coversion is：

Expand to：

Wherein, matrix A_t/r,B_t/rFor I the uneven parameter alphas of Q_t/r、β_t/rThe diagonal matrix of composition, its form is：

It is characterised in that it includes following steps：

S1, set the compensation matrix of k-th of subcarrier as：

The compensation matrix of the K-k+2 subcarrier is：

Wherein, channel componentWithInverse matrix is conjugated each other, i.e.,：

Restriction relation between mirror image subcarrier is：

Wherein

Sending and receiving end I Q imbalance compensations matrix should meet：

It is equivalent to：

Signal matrixWithRecover in such a way：

S2, estimation sending and receiving end I the uneven parameter γ of Q_tAnd γ_r：

Restriction relation according to S1, γ_tAnd γ_rDirectly it can solve in the following manner：

S3, by k-th of subcarrier and its mirror image subcarrier, i.e., the K-k+2 subcarrier is as one group of target, in two sons One of subcarrier is selected in carrier waveEstimated；According to the subcarrier of selectionInformation, pass through generalized linear algorithm Obtain compensation matrixThen utilizeEquivalent relation in S1, obtains the mirror image matrix of compensation matrix

S4, the information according to another non-selected subcarrier in step S3, to square by the way of RLS iterative algorithms Battle arrayIt is updated, recycles after updatingEquivalent relation according to S1 updates

S5, using reset mode of the compensation matrix after renewal according to S1 signal matrix is carried out I Q compensate；

S6, next group of subcarrier of selection, until complete to the I of all signals Q compensate.

In such scheme, channel is fast fading channel in system, and the parameter Estimation described in step S2 is first to estimate γ_r, Recycle γ_rEstimate γ_t, to improve accuracy；Due to compensation matrixWithIn a DSTC-OFDM data It has been updated twice in block, so the convergence rate of estimation is twice of generalized linear algorithm.

Further, in the step S3, subcarrierSystem of selection be：

The beneficial effects of the invention are as follows：Under the channel circumstance of rapid fading, its performance of the backoff algorithm based on parameter Estimation It is substantially better than the performance of generalized linear, especially in the case where I Q imbalances are more serious.And as channel quickly becomes Change, generalized linear convergence of algorithm speed is far from enough to be caused tracking performance to decline and can introduce delay error.By contrast, base Effectively increase convergence rate in the method for parameter Estimation, can better compensate for transmitting terminal I the performance brought of Q imbalances damage Lose.

Brief description of the drawings

Fig. 1 for exist I the unbalanced DSTC-OFDM system models figures of Q；

Fig. 2 be fast fading channel sending and receiving end I Q imbalance compensation performance maps；Wherein, (a) is when using QPSK modulation systems The contrast signal of the inventive method and generalized linear methods；(b) it is the inventive method and broad sense line when using 8PSK modulation mode Property method contrast signal；

Fig. 3 for the present invention the I based on parameter Q imbalance compensation method flow diagrams.

Embodiment

Below in conjunction with the accompanying drawings, technical scheme is described in detail：

As shown in figure 3, being the schematic flow sheet of the method for the present invention, it is base band that the method for the present invention, which needs the data inputted, Signal Z ' (k) andAnd loop initialization number of times t=0 is provided with, according to default threshold value Nini, be less than in t etc. Γ is utilized when threshold value_c(k) andMore new estimation γ_tAnd γ_r, due to sending and receiving end I Q imbalances be it is almost unchanged, because This estimated result is all effective within some time.The method of the present invention is more than after threshold value primarily directed to cycle-index, tool The method of body is described in detail in the content of the invention.

As shown in Fig. 2 the present invention compare under two kinds of modulation systems different compensation ways to I the unbalanced error codes of Q Can, be specifically configured in the present invention receiving terminal I Q injustice be set to κ_r(dB)=1dB, φ_r=5 °, and transmitting terminal has carried out two kinds Set, respectively reasonable level I Q it is uneven：Amplitude imbalance κ_t(dB)=0.5dB, unbalance in phase φ_t=3 °, correspondence mirror As rejection ratio 18dB；And serious I Q it is uneven：Amplitude imbalance κ_t=1dB, amplitude imbalance φ_t=5 °, correspondence mirror image suppression System than 11.6dB, even if by Fig. 2 it can be found that do not deposit I Q it is uneven, the receiving terminal bit error rate compares slow fading channel situation It has been deteriorated that, because fast-changing channel circumstance no longer meets the static channel characteristic required for differential space-time coding.With it is wide Adopted linear compensation algorithm is compared, and performance of the backoff algorithm based on parameter Estimation in fast fading channel is substantially more preferable, especially Transmitting terminal I the uneven more serious situations of Q.Clearly as transmitting terminal I Q imbalance compensation matrix optimal values with channel it is fast The change of speed, generalized linear convergence of algorithm speed not enough causes tracking performance to decline and introduces delay error.By contrast, base Improve convergence rate in the method for estimation of parameter, can more preferably compensate transmitting terminal I the performance loss that brings of Q imbalances.But by In fast fading channel non-stationary property for I the influence that brings of Q imbalance compensation performances can not eliminate, in compensation Afterwards, residual performance loss is still larger.

Claims (2)

1. a kind of IQ imbalance compensation methods for differential coding ofdm system, define differential coding ofdm system and contain K The differential space-time coding signal sent on individual subcarrier, k-th of subcarrier is：

Wherein2n-1 and the 2n OFDM symbol received for receiver in k-th of subcarrier The signal vector of composition, matrix S_n(k) n-th of DSTC signal matrix in k-th of subcarrier transmission is represented, each signal needs Two OFDM symbol transmission, S_n(k) it is unitary matrice, the symbol of its i-th row j row represents k in the 2n-2+j OFDM symbol Carrier wave, i, j=1,2；The symbol sent by i-th antenna, v_2n-1And v (k)_2n(k) frequency domain on k-th of subcarrier is represented Additive noise, scalar lambda_i(n) i=1,2 represents to ring from i-th antenna of transmitting terminal to the frequency domain impulse of reception antenna on subcarrier k Should；S_n(k) information matrix U is passed through_n(k) obtained according to differential coding rule：

S_n(k)=S_n-1(k)U_n(k)

Define transceiver exist simultaneously I Q it is uneven, the Equivalent Base-Band signal after down coversion is：

$\begin{array}{c}{Z}_{n-1}^{\′}\left(k\right)=\left(A_t{A}_r\mathrm{\Λ}\left(k\right)+B_t^{*}{B}_r\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\right)S_{n-1}\left(k\right)+A_r{V}_{n-1}\left(k\right)+B_r{\stackrel{\‾}{V}}_{n-1}\left(k\right)\\ +\left(A_r{B}_t\mathrm{\Λ}\left(k\right)+A_t^{*}{B}_r\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\right){\stackrel{\‾}{S}}_{n-1}\left(k\right)\end{array}$

Expand to：

$\begin{array}{c}{Z}_n^{\′}\left(k\right)=\left(A_t{A}_r\mathrm{\Λ}\left(k\right)+B_t^{*}{B}_r\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\right)S_n\left(k\right)+\left(A_r{B}_t\mathrm{\Λ}\left(k\right)+A_t^{*}{B}_r\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\right){\stackrel{\‾}{S}}_n\left(k\right)\\ +A_r{V}_n\left(k\right)+B_r{\stackrel{\‾}{V}}_n\left(k\right)\\ =\left(A_t{A}_r\mathrm{\Λ}\left(k\right)+B_t^{*}{B}_r\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\right)S_{n-1}\left(k\right)U_n\left(k\right)\\ +\left(A_r{B}_t\mathrm{\Λ}\left(k\right)+A_t^{*}{B}_r\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\right){\stackrel{\‾}{S}}_n\left(k\right)+A_r{V}_n\left(k\right)+B_r{\stackrel{\‾}{V}}_n\left(k\right),\end{array}$

Wherein, matrix A_t/r,B_t/rFor I the uneven parameter alphas of Q_t/r、β_t/rThe diagonal matrix of composition, its form is：

$A_{t/r}=\left[\begin{array}{cc}{\mathrm{\α}}_{t/r}& 0\\ 0& {\mathrm{\α}}_{t/r}^{*}\end{array}\right],B_{t/r}=\left[\begin{array}{cc}{\mathrm{\β}}_{t/r}& 0\\ 0& {\mathrm{\β}}_{t/r}^{*}\end{array}\right]$

It is characterised in that it includes following steps：

S1, set the compensation matrix of k-th of subcarrier as：

${\mathrm{\Γ}}_c\left(k\right)\≈-\left(A_r{B}_t\mathrm{\Λ}\left(k\right)+A_t^{*}{B}_r\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\right){\left(A_r^{*}{A}_t^{*}\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\right)}^{-1}=-A_r{B}_t\mathrm{\Λ}\left(k\right)\stackrel{\‾}{\mathrm{\Λ}}{\left(k\right)}^{-1}{\left(A_r^{*}{A}_t^{*}\right)}^{-1}+B_r{\left(A_r^{*}\right)}^{-1}{\mathrm{\Γ}}_c\left(k\right)$

The compensation matrix of the K-k+2 subcarrier is：

${\stackrel{\‾}{\mathrm{\Γ}}}_c\left(k\right)\≈-A_r{B}_t\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\mathrm{\Λ}{\left(k\right)}^{-1}{\left(A_r^{*}{A}_t^{*}\right)}^{-1}+B_r{\left(A_r^{*}\right)}^{-1}$

Wherein, channel componentWithInverse matrix is conjugated each other, i.e.,：

$\[\mathrm{\Λ}\left(k\right)\stackrel{\‾}{\mathrm{\Λ}}{\left(k\right)}^{-1}\]*\stackrel{\‾}{\mathrm{\Λ}}\left(k\right)\mathrm{\Λ}{\left(k\right)}^{-1}=I$

Restriction relation between mirror image subcarrier is：

${\stackrel{\‾}{\mathrm{\Γ}}}_c\left(k\right)-{\mathrm{\Γ}}_r={\mathrm{\Γ}}_t{\[{\left({\mathrm{\Γ}}_c\right(k)-{\mathrm{\Γ}}_r)}^{*}\]}^{-1}{\mathrm{\Γ}}_t^{*}$

Wherein

Sending and receiving end I Q imbalance compensations matrix should meet：

${\stackrel{\‾}{\mathrm{\Γ}}}_c\left(k\right)={\mathrm{\Γ}}_t{\[{\left({\mathrm{\Γ}}_c\right(k\left)\right)}^{*}\]}^{-1}{\mathrm{\Γ}}_t^{*}$

It is equivalent to：

$\left\{\begin{array}{c}{\[{\stackrel{\‾}{\mathrm{\Γ}}}_c\left(k\right)\]}_{1,1}=|{\mathrm{\γ}}_t{|}^2{\[{\left({\mathrm{\Γ}}_c^{*}\right(k\left)\right)}^{-1}\]}_{1,1}\\ {\[{\stackrel{\‾}{\mathrm{\Γ}}}_c\left(k\right)\]}_{1,2}={{\mathrm{\γ}}_t}^2{\[{\left({\mathrm{\Γ}}_c^{*}\right(k\left)\right)}^{-1}\]}_{1,2}\end{array}\right.$

Signal matrixWithRecover in such a way：

$\left[\begin{array}{c}{\hat{S}}_n\left(k\right)\\ {\widehat{\stackrel{\‾}{S}}}_n\left(k\right)\end{array}\right]=\left[\begin{array}{cc}I& {\mathrm{\Γ}}_c\left(k\right)\\ {\stackrel{\‾}{\mathrm{\Γ}}}_c\left(k\right)& I\end{array}\right]\left[\begin{array}{c}{Z}_n^{\′}\left(k\right)\\ {\stackrel{\‾}{Z}}_n^{\′}\left(k\right)\end{array}\right];$

S2, estimation sending and receiving end I the uneven parameter γ of Q_tAnd γ_r：

Restriction relation according to S1, γ_tAnd γ_rDirectly it can solve in the following manner：

$\[{\mathrm{\γ}}_t,{\mathrm{\γ}}_r\]=\underset{{\mathrm{\γ}}_t,{\mathrm{\γ}}_r}{\mathrm{argmin}}|{\stackrel{\‾}{\mathrm{\Γ}}}_c\left(k\right)-{\mathrm{\Γ}}_r-{\mathrm{\Γ}}_t{\[{\left({\mathrm{\Γ}}_c\right(k)-{\mathrm{\Γ}}_r)}^{*}\]}^{-1}{\mathrm{\Γ}}_t^{*}{|}^2;$

S3, by k-th of subcarrier and its mirror image subcarrier, i.e., the K-k+2 subcarrier is as one group of target, in two subcarriers The middle one of subcarrier of selectionEstimated；According to the subcarrier of selectionInformation, obtained by generalized linear algorithm Compensation matrixThen utilizeEquivalent relation in S1, obtains the mirror image matrix of compensation matrix S4, the information according to another non-selected subcarrier in step S3, to matrix by the way of RLS iterative algorithms It is updated, recycles after updatingEquivalent relation according to S1 updates

S5, using reset mode of the compensation matrix after renewal according to S1 signal matrix is carried out I Q compensate；

S6, next group of subcarrier of selection, until complete to the I of all signals Q compensate.

2. a kind of IQ imbalance compensation methods for differential coding ofdm system according to claim 1, its feature exists In, in the step S2, subcarrierSystem of selection be：