CN115250218B - Broadband signal IQ imbalance and channel flatness calibration method - Google Patents
Broadband signal IQ imbalance and channel flatness calibration method Download PDFInfo
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- H04L25/00—Baseband systems
- H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
- H04L25/06—Dc level restoring means; Bias distortion correction ; Decision circuits providing symbol by symbol detection
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- H—ELECTRICITY
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- 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
- H04L27/38—Demodulator circuits; Receiver circuits
- H04L27/3845—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier
- H04L27/3854—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier using a non - coherent carrier, including systems with baseband correction for phase or frequency offset
- H04L27/3863—Compensation for quadrature error in the received signal
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- H04L27/34—Amplitude- and phase-modulated carrier systems, e.g. quadrature-amplitude modulated carrier systems
- H04L27/38—Demodulator circuits; Receiver circuits
- H04L27/3845—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier
- H04L27/3854—Demodulator circuits; Receiver circuits using non - coherent demodulation, i.e. not using a phase synchronous carrier using a non - coherent carrier, including systems with baseband correction for phase or frequency offset
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Abstract
The invention belongs to the field of communication, and particularly relates to a broadband signal IQ imbalance and channel flatness calibration method. The method comprises the following steps: a calibration method comprising the steps of: determining M designated frequency points in a broadband signal center frequency point range, and calculating amplitude relative errors and phase relative errors on each frequency point under the condition that an image rejection ratio is met by a transmission signal; determining a calibration factor according to the calibration model; generating a signal after IQ imbalance compensation, and adjusting the amplitude of the baseband signal to measure the uneven parameters of the channel; the IQ imbalance of M points and the channel amplitude-frequency response are fitted into a response function on the whole broadband interval, and a calibration filter bank is constructed; IQ imbalance and channel flatness compensation are carried out on the baseband signal. On the premise of open loop of the system, the method can well inhibit sideband image and can effectively improve broadband signal quality.
Description
Technical Field
The invention belongs to the field of communication, and particularly relates to a broadband signal IQ imbalance and channel flatness calibration method.
Background
In a direct up-conversion radio frequency transmitter system, an analog quadrature modulator is used to up-convert the complex signal of the baseband to the desired radio frequency band. Because there is no ideal quadrature modulator in reality, the quadrature modulator is affected by factors such as precision error and temperature drift of the device, and the quadrature modulator inevitably has problems such as gain, phase imbalance, etc., and can generate image signals. Therefore, calibration of IQ imbalance is required in system design. Wherein I refers to in-phase and Q refers to quadrature.
For imbalance calibration of IQ-modulators, it is common to split the two cases, open loop and closed loop. The closed loop is based on the receiver in the transmitter to down-convert the radio frequency signal to the baseband, and realize the self-adaptive compensation in the digital domain, the closed loop calibration method based on feedback has the advantage of real-time calibration, but the hardware structure and algorithm are extremely complex, and the realization cost is extremely high. Open loop means that there is no receiver inside the transmitter and IQ calibration can only rely on a spectrometer or a power meter, which has the advantage of no need of special hardware equipment and is relatively simple to implement.
In the prior art, based on IQ imbalance calibration under the open loop condition, IQ imbalance is compensated by adjusting respective DC bias, gain and relative phase difference of IQ channels in a D/A device, and only aiming at single frequency point signals. However, in actual engineering, as conditions such as working temperature, frequency change, aging of devices and the like occur, an adjustment value is continuously changed, a compensation effect is also continuously deteriorated, and if a narrowband calibration scheme is still adopted for unbalanced calibration on a broadband signal, performance is greatly reduced. Therefore, a method for calibrating IQ imbalance and channel flatness of a wideband signal based on open loop conditions is needed.
Disclosure of Invention
The invention aims to provide a broadband signal IQ imbalance and channel flatness calibration method based on an open loop condition.
In order to achieve the aim of the invention, the invention adopts the following technical scheme: a calibration method for IQ imbalance and channel flatness of broadband signals includes the following steps:
m frequency points appointed in the range of the broadband signal center frequency point are determined, and the amplitude relative error delta a and the phase relative error on each frequency point under the condition that the image rejection ratio is met are calculated by a transmitting signal
Determining a calibration factor according to the calibration model;
generating a signal after IQ imbalance compensation, and adjusting the amplitude of the baseband signal to measure the uneven parameters of the channel;
the IQ imbalance of M points and the channel amplitude-frequency response are fitted into a response function on the whole broadband interval, and a calibration filter bank is constructed;
IQ imbalance and channel flatness compensation are carried out on the baseband signal.
Preferably, the calibration factor a' is as follows:
wherein I (t) is the in-phase component of the baseband signal, deltaa is the relative error in amplitude,is the phase relative error.
Preferably, the method specifically comprises the following steps:
(1) M baseband frequency points in a certain bandwidth range are determined by taking the center frequency as the center;
(2) Calculating calibration parameters Δa and Δa for the transmitted signalWherein Δa is the amplitude relative error, +.>Is the relative error of phase;
(3) Generating a calibrated signal;
(4) Judging whether the power of the signal meets a set channel flatness power threshold or not;
(5) If the power of the signal meets the error allowable range, calculating the image rejection ratio of the signal;
(6) Judging whether the image rejection ratio meets a set minimum threshold;
(7) Repeating step (4) when the image rejection ratio meets a minimum threshold;
(8) Recording the calibration parameters Deltaa,And baseband signal amplitude;
(9) Adding 1 to the index value of the index of the baseband frequency point subscript; judging whether the index value is equal to M;
(10) If not, repeating the steps 2-9; if equal, the calibration is ended.
Preferably, in step (1), the baseband frequency point near the center frequency is 1.1MHz.
Preferably, in step (4), if the power of the signal is not within the error allowable range, the baseband signal amplitude is adjusted, and steps (3) and (4) are repeated until the power meets the requirement.
Preferably, in step (6), if the image rejection ratio does not meet the minimum threshold, the calibration parameters Δa and Δb are comparedA two-dimensional search is performed until a minimum threshold is met.
Preferably, the method for obtaining the calibration parameter Δa includes the following steps:
let baseband signal [ I (t) Q (t)]＝[cosw 0 t 0]Obtaining w c +w 0 Power value P at frequency point 1 dBm；
Let baseband signal [ I (t) Q (t)]＝[0 cosw 0 t]Obtaining w c +w 0 Power value P at frequency point 2 dBm；
w c +w 0 The calibration parameters Δa on the frequency points are:
wherein w is c Is the carrier frequency.
Preferably, the calibration parametersThe acquisition method of (1) comprises the following steps:
letting the baseband signalAcquisition of w c +w 0 Power value P at frequency point 3 dBm；
w c +w 0 Calibration parameters at frequency pointsThe method comprises the following steps: />
Wherein w is c Is the carrier frequency.
Preferably, the signal after calibration in step (3) is as follows:
where y' (t) is the calibrated signal, I (t) is the in-phase component of the baseband signal, Q (t) is the quadrature component of the baseband signal, cos (w) c t)、sin(w c t) is the IQ two-way component of the quadrature modulator, w c For the carrier frequency, Δa is the amplitude relative error,is the phase relative error, t is the sampling time.
Correspondingly, the communication circuit for calibrating the IQ imbalance of the broadband signal comprises at least one processor, wherein the calibration method is arranged in at least one processor, and the calibration of the IQ imbalance of the broadband signal and the flatness of the channel can be completed based on the calibration method.
The invention has the following beneficial effects: the invention provides a broadband signal IQ imbalance and channel flatness calibration method. On the premise of open loop of the system, the spectrum analyzer is used for measuring IQ imbalance parameters and channel unevenness parameters corresponding to all narrowband components of the broadband signal, and compensation is carried out on the baseband, so that sideband mirror images can be well restrained, and the broadband signal quality is effectively improved.
Drawings
FIG. 1 is a block diagram of a wideband signal IQ imbalance and channel flatness calibration implementation;
FIG. 2 is a schematic diagram of an analog quadrature modulation circuit;
FIG. 3 is a schematic diagram of an IQ imbalance calibration model;
FIG. 4 is a schematic diagram of an IQ imbalance plus channel flatness compensation calibration model;
FIG. 5 is a diagram of the image rejection ratio before single tone signal misalignment;
FIG. 6 is a diagram showing the image rejection ratio after calibration of a tone signal;
fig. 7 is a schematic diagram of demodulation before QPSK misalignment;
fig. 8 is a schematic diagram of demodulation after QPSK calibration.
Detailed Description
The invention provides a broadband signal IQ imbalance and channel flatness calibration method based on an open loop condition, wherein a flow chart is shown in figure 1, and the method specifically comprises the following steps:
1. the method comprises the steps of taking a center frequency as a center, and determining M baseband frequency points in a certain bandwidth range according to actual requirements, wherein the baseband frequency points close to the center frequency are selected according to requirements, such as 1MHz and 1.1MHz;
2. transmitting three sets of signals to calculate the calibration parameters Δa and ΔaWherein Δa is the amplitude relative error, +.>Is the relative error of phase; the signals are arranged in three groups to derive 2 calibration parameters Δa and +.>Is calculated according to the formula;
3. generating a calibrated signal;
4. judging whether the power of the signal meets a set channel flatness power threshold or not;
5. if the power is not within the allowable range of the error (does not meet the threshold), the amplitude of the baseband signal is adjusted, and the steps 3 and 4 are repeated until the power meets the requirement;
6. if the allowable range of the error is met (the threshold is met), calculating the image rejection ratio IRR of the signal;
7. judging whether IRR meets a set minimum threshold;
8. if the error is not within the allowable range, the calibration parameters delta a and delta bAnd (4) performing two-dimensional search until the minimum threshold is met, and then repeating the step (4) and the step (5) until the power requirement is met in the step (5). Wherein, the two-dimensional search is a mature prior art known in the art and is not an improvement point of the present invention, and is not described herein in detail;
9. recording the calibration parameters Deltaa,And baseband signal amplitude;
10. adding 1 to the index value of the index of the baseband frequency point subscript;
11. judging whether the index value is equal to M;
12. if not, repeating the steps 2-11;
13. if equal, the calibration is ended.
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. The technical means used in the examples are conventional means well known to those skilled in the art unless otherwise indicated. The obtained data are all average values obtained after at least 3 repetitions, and each repetition is obtained as effective data.
Examples
As shown in fig. 2, typical analog quadrature modulation, also known as IQ modulation, refers to digital baseband signals having in-phase and quadrature components, respectively, that are digital-to-analog convertedAnd modulating and adding two paths of same-frequency non-ideal orthogonal carrier signals of the orthogonal modulator to realize modulation technology of the modulated signals after low-pass filtering, wherein I (t) is an in-phase component of a base band signal, Q (t) is an orthogonal component of the base band signal, DAC is a digital-to-analog converter, LPF is a low-pass filter, cos (w c t)、sin(w c t) is the IQ two-way component of the quadrature modulator, w c For the carrier frequency, Δa is the amplitude relative error,t is the sampling time and y (t) is the modulated signal, which is the phase relative error.
The ideal quadrature modulator mathematical expression is:
y(t)＝I(t)cos(w c t)+Q(t)sin(w c t) (1)
written in matrix form as follows:
however, in practice, there is no ideal device, and there are a certain amplitude relative error Δa and phase relative error in the two paths of modulator IQSo that the expression of the actual output signal is:
written in matrix form as follows:
to remove the amplitude and phase imbalance, a calibration factor a' is introduced at baseband, where:
the signal after calibration by introducing the calibration factor a' is shown in formula (5), and the predistortion processing is performed on the digital baseband part, which is specifically as follows: the in-phase component of the digital baseband signal is updated to be the result of multiplying the original quadrature component Q (t) by the calibration coefficient D and then adding to the original in-phase component I (t), the quadrature component of the digital baseband signal is updated to be the result of multiplying the original quadrature component Q (t) by the calibration coefficient C, and the calibration model is shown in fig. 3.
For unbalanced calibration of wideband signals, C, D at this time still satisfies the above formula, but is in the form of a filter. The response values of the filter at different frequency points are unbalance calibration parameters of corresponding baseband frequency points, namelyWhere f is the baseband frequency point.
The key to the imbalance calibration of the wideband signal is how to obtain two imbalance parameters, the steps of which are as follows:
(1) Let baseband signal [ I (t) Q (t)]＝[cosw 0 t 0]Obtaining w c +w 0 Power value P at frequency point 1 dBm；
(2) Let baseband signal [ I (t) Q (t)]＝[0 cosw 0 t]Obtaining w c +w 0 Power value P at frequency point 2 dBm；
(3) Calculating w c +w 0 Amplitude imbalance parameters at frequency bins:
(4) Letting the baseband signalAcquisition of w c +w 0 Power value P at frequency point 3 dBm；
(5) Calculating w c +w 0 Amplitude imbalance parameters at frequency bins:
wherein w is c Is the carrier frequency, w 0 For baseband frequency, P 1 、P 2 、P 3 dBm is the power unit for signal power.
After IQ imbalance calibration is completed according to the steps, the image rejection ratio of all frequency points in the required bandwidth meets a threshold value. However, the amplitude-frequency response of the RF link is different, which causes distortion of the amplitude-frequency response of the signal, and further measurement of the amplitude-frequency response between channels is required. The method adopted by the invention is to enable the power of all frequency points at the output end to be consistent by adjusting the amplitude value of the baseband signal, and the specific steps are shown in figure 1. The only difference between the IQ imbalance and the channel flatness calibration is that the digital baseband signal is added with amplitude information, that is, the in-phase component of the digital baseband signal is updated to be the result of multiplying the original quadrature component Q (t) by the calibration coefficient D and then multiplying the result of adding the original in-phase component I (t) by the calibration coefficient E, and the quadrature component of the digital baseband signal is updated to be the result of multiplying the original quadrature component Q (t) by the calibration coefficient C and then multiplying the calibration coefficient E, as shown in fig. 4.
In order to verify the validity and correctness of the above method, the following is verified by a narrowband signal and a wideband signal, respectively.
(1) Narrowband signal verification
The DDS is used for generating a quadrature signal of 1.1MHz as an IQ baseband signal, the quadrature signal is up-converted to a center frequency of 5GHz by an analog quadrature modulator after D/A, and an output signal is tested by using a Keysight 9030 spectrometer, and the result is shown in figure 5. At this time, the image rejection ratio is 39.49dB, the amplitude and phase imbalance parameters are measured by the above method, the original signal is compensated, the output signal is measured after compensation as shown in fig. 6, at this time, the image rejection ratio is 65.09dBm, and it can be seen that IQ imbalance has been well compensated.
(2) Broadband signal verification
The DDS is used for respectively generating quadrature signals of-500 MHz to 500MHz and stepping 5MHz, the amplitude, the phase imbalance parameter and the channel unevenness parameter of an IQ modulator in the bandwidth of 1GHz at the carrier frequency of 10GHz are measured as IQ baseband signals, and the demodulation condition of a QPSK signal with the symbol rate of 120Msps without IQ imbalance and channel flatness calibration is shown in fig. 7, so that a desired constellation diagram is changed into a rectangle from a square and is in a trapezoid shape. Fig. 8 shows demodulation after IQ imbalance and channel flatness compensation, and it can be seen that constellation distortion, EVM degradation, etc. are significantly improved.
The above embodiments are only illustrative of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention, and various modifications, variations, alterations, substitutions made by those skilled in the art to the technical solution of the present invention should fall within the protection scope defined by the claims of the present invention without departing from the spirit of the design of the present invention.
Claims (5)
1. A calibration method for IQ imbalance and channel flatness of broadband signals is characterized in that: the method comprises the following steps:
determining M designated frequency points in the range of the center frequency point of the broadband signal, and calculating the amplitude relative error delta a and the phase relative error on each frequency point under the condition of meeting the image rejection ratio by the transmitted signal
Determining a calibration factor according to the calibration model;
generating a signal after IQ imbalance compensation, and adjusting the amplitude of the baseband signal to measure the uneven parameters of the channel;
the IQ imbalance of M points and the channel amplitude-frequency response are fitted into a response function on the whole broadband interval, and a calibration filter bank is constructed;
IQ imbalance and channel flatness compensation are carried out on the baseband signal;
the method specifically comprises the following steps:
(1) The method comprises the steps of taking a center frequency as a center, and determining M baseband frequency points in a certain bandwidth range according to actual requirements, wherein the baseband frequency points close to the center frequency are selected according to requirements;
(2) Calculating the calibration parameters Deltaa and Deltaa by transmitting three sets of signalsWherein Δa is the amplitude relative error, +.>Is the relative error of phase; the signals are arranged in three groups to derive 2 calibration parameters Δa and +.>Is calculated according to the formula;
the acquisition steps are as follows:
let baseband signal [ I (t) Q (t)]＝[cosw 0 t 0]Obtaining w c +w 0 Power value P at frequency point 1 dBm；
Let baseband signal [ I (t) Q (t)]＝[0 cosw 0 t]Obtaining w c +w 0 Power value P at frequency point 2 dBm；
Calculating w c +w 0 Amplitude imbalance parameters at frequency bins:
letting the baseband signalAcquisition of w c +w 0 Power value P at frequency point 3 dBm；
Calculating w c +w 0 Amplitude imbalance parameters at frequency bins:
wherein w is c Is the carrier frequency, w 0 For baseband frequency, P 1 、P 2 、P 3 dBm is the power unit of the signal power;
(3) Generating a calibrated signal;
(4) Judging whether the power of the signal meets a set channel flatness power threshold or not;
(5) If the threshold is not met, the amplitude of the baseband signal is adjusted, and the step 3 and the step 4 are repeated until the power meets the requirement;
(6) If the threshold is met, calculating the image rejection ratio IRR of the signal;
(7) Judging whether IRR meets a set minimum threshold;
(8) If the error is not within the allowable range, the calibration parameters delta a and delta bPerforming two-dimensional search until the minimum threshold is met, and then repeating the step 4 and the step 5 until the power requirement is met in the step 5;
(9) Recording the calibration parameters Deltaa,And baseband signal amplitude;
(10) Adding 1 to the index value of the index of the baseband frequency point subscript;
(11) Judging whether the index value is equal to M;
(12) If not, repeating the steps 2-11;
(13) If equal, the calibration is ended.
2. The method according to claim 1, wherein: the calibration factor a' is as follows:
3. the method according to claim 1, wherein: in the step (1), the baseband frequency point close to the center frequency is 1MH or 1.1MHz.
4. The method according to claim 1, wherein: the calibrated signal of step (3) is as follows:
where y' (t) is the calibrated signal, I (t) is the in-phase component of the baseband signal, Q (t) is the quadrature component of the baseband signal, cos (w) c t)、sin(w c t) is the IQ two-way component of the quadrature modulator, w c For the carrier frequency, deltaa is the amplitude relative error,is the phase relative error, t is the sampling time.
5. A communication circuit for calibrating wideband signal IQ imbalance, comprising: the communication circuit comprises at least one processor, wherein the calibration method of any one of claims 1-4 is arranged in at least one processor, and the calibration of the IQ imbalance and the channel flatness of the broadband signal can be completed based on the calibration method.
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| US6421398B1 (en) * | 2000-01-28 | 2002-07-16 | Alcatel Canada Inc. | Modulation system having on-line IQ calibration |
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| US7035341B2 (en) * | 2001-08-10 | 2006-04-25 | Maxim Integrated Products, Inc. | Quadrature gain and phase imbalance correction in a receiver |
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| US11128501B2 (en) * | 2007-07-30 | 2021-09-21 | HuWoMobility, Inc. | Method for fast convergence calibration of radio-frequency transceivers |
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| US6421398B1 (en) * | 2000-01-28 | 2002-07-16 | Alcatel Canada Inc. | Modulation system having on-line IQ calibration |
| KR20050066953A (en) * | 2003-12-26 | 2005-06-30 | 한국전자통신연구원 | Apparatus for compensation dc offset and i/q gain and phase imbalance and compensation system using it |
| CN105656834A (en) * | 2015-12-21 | 2016-06-08 | 武汉虹信通信技术有限责任公司 | Digital correction method for IQ channel mismatch of novel broadband receiver |
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