CN111355501B - System and method for correcting quadrature error of broadband transmitter of TDD system - Google Patents
System and method for correcting quadrature error of broadband transmitter of TDD system Download PDFInfo
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- CN111355501B CN111355501B CN202010167146.0A CN202010167146A CN111355501B CN 111355501 B CN111355501 B CN 111355501B CN 202010167146 A CN202010167146 A CN 202010167146A CN 111355501 B CN111355501 B CN 111355501B
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
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- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
- H04B1/02—Transmitters
- H04B1/04—Circuits
- H04B1/0475—Circuits with means for limiting noise, interference or distortion
Abstract
The invention discloses a system and a method for correcting quadrature errors of a broadband transmitter of a TDD system. The method includes transmitter IQ imbalance initialization correction and transmitter IQ imbalance tracking correction. The invention solves the problem of IQ imbalance introduced by a transmitter and irrelevant to frequency in a TDD system, is not influenced by IQ imbalance of a receiver, and improves the IQ imbalance correction accuracy of the transmitter.
Description
Technical Field
The invention belongs to the technical field of communication, and particularly relates to a system and a method for correcting quadrature errors of a broadband transmitter of a TDD system.
Background
With the rapid development of the internet, multimedia and wireless communications, the demand for high quality, high rate wireless services is increasing, however, the available spectrum resources are becoming scarce. The Time Division Duplex (Time Division Duplex) mode becomes more and more popular, and the current 3G, 4G and 5G have corresponding Time Division Duplex (Time Division Duplex) modes. For the rf transceiving system, the tdd mode may also simplify the design of the rf transceiving system. Such as: frequency Division duplexing (Frequency Division Duplex) requires the integration of two local oscillators, and the transmitter and the receiver require different local oscillators. In TDD mode, the transmitter and receiver share a local oscillator. For broadband signals, many corrections require a feedback channel, such as DPD, so that an auxiliary receiving channel needs to be integrated in FDD mode, and the receiving channel can be used as the auxiliary receiving channel in TDD mode, thereby reducing hardware resources and power consumption.
At present, the commonly used radio frequency receiver structures mainly include a superheterodyne receiver and a zero intermediate frequency receiver. As the most traditional receiver architecture, the super-heterodyne receiver architecture is the most mature receiver architecture at present, and can obtain excellent performance after being carefully designed. However, the hardware circuit is too complex, and an off-chip band-pass filter with better performance is required, so that the defects of higher device cost, larger volume and power consumption, lower integration level and the like are caused, and further development and application of the filter are severely restricted. As a novel receiver architecture, compared with a superheterodyne receiver, the zero intermediate frequency receiver has the advantages of simple circuit structure, easy integration, low cost and low power consumption, is more suitable for consumer electronics and multimode communication platforms, and has gained very wide attention and research in recent years.
However, zero-if architecture receivers also have some inherent drawbacks, such asThe performance of the receiver is affected by direct current bias caused by local oscillator leakage and interference leakage, IQ imbalance caused by inconsistency of IQ two-path analog devices (LPF and frequency mixer) and circuit characteristics. The problem of IQ imbalance is more difficult to solve compared with direct current bias, particularly under high bandwidth, the IQ imbalance comprises two parts, the first part is IQ imbalance related to frequency and mainly caused by delay or amplitude inconsistency of two paths I and Q; the second part is IQ imbalance independent of frequency, mainly composed of local oscillator signal I path cos (w)lot) and Q lysin (w)lot) is not exactly 90 degrees and the difference in amplitude between the two results.
Some correction techniques are to form an inner loop between the transmitter and the receiver, and this scheme needs to estimate and correct the IQ imbalance and dc of the receiver, and then estimate and correct the parameters of the dc and imbalance of the transmitter. A disadvantage of this scheme is that IQ imbalance and dc estimation error of the receiver affect the estimation of the dc and imbalance parameters of the transmitter.
Another correction technique is to form an internal loop between the transmitter and the receiver, and proposes to correct the IQ imbalance at the receiving end first, then correct the IQ imbalance at the transmitting end, and adjust the relative delay of the two local oscillators of the LO and the low-pass filter in the simulation.
Another correction technique is to perform envelope detection after the transmitter mixer, perform ADC sampling and frequency reduction on the envelope, and then perform IQ imbalance parameter estimation. This scheme requires additional ADC and digital down conversion processing, which increases resources and power consumption and cost, and does not account for frequency-dependent quadrature errors at high bandwidths.
Disclosure of Invention
The present invention is directed to solve the problem of IQ imbalance correction for a high bandwidth transmitter in a TDD system, which is not enough in the prior art. The problem of IQ imbalance introduced by a transmitter and irrelevant to frequency in a TDD system is solved, the IQ imbalance of the receiver is not influenced, and the IQ imbalance correction accuracy of the transmitter is improved.
Further, a method for calibrating quadrature error of a wideband transmitter in a TDD system includes an initial calibration of transmitter IQ imbalance and a tracking calibration of transmitter IQ imbalance, wherein the initial calibration of transmitter IQ imbalance includes the following steps:
s11: the signal generator generates a test signal and sends a plurality of groups of test tone signals through the signal sending module;
s12: the test signal only passes through the I path or the Q path of the signal receiving module after passing through the quadrature error correction circuit;
s13: carrying out transmitter IQ imbalance parameter estimation on the test signal after the test signal passes through an analog-to-digital converter;
s14: pre-compensating in a signal sending module, and adjusting a pre-compensation coefficient of a sending end;
further, the transmitter IQ imbalance tracking correction comprises the steps of:
s21: when in normal service, a service signal of a transmitting end passes through a signal receiving module mixer, a low-pass filter and an analog-to-digital conversion circuit;
s22: IQ imbalance parameter estimation is carried out in a digital domain;
s23: the method comprises the following steps of configuring local oscillation frequency points of a transmitter and local oscillation frequency points of a receiver: the local oscillation frequency point of the emitter is f _ tx, the receiver adopts an auxiliary local oscillation, the local oscillation frequency point is f _ rx, and f _ tx-f _ rx is not equal to 0;
s24: carrying out digital frequency conversion, wherein the frequency conversion frequency point is- (f _ tx-f _ rx);
s25: and pre-compensating in the signal sending module, and adjusting the sending end to pre-compensate the complex filter.
A TDD system broadband transmitter quadrature error correction system comprises a signal generator, a signal sending module, a signal receiving module, a quadrature error correction circuit and a digital frequency conversion module; the signal receiving module is also provided with a switch circuit for selecting a transmitter IQ imbalance initialization correction mode or a transmitter IQ imbalance tracking correction mode of the system; the signal generator is connected with the signal sending module, the signal sending module is connected with the orthogonal error correction circuit and the signal receiving module, the orthogonal error correction circuit is connected with the switch circuit in the signal receiving module, the signal receiving module is connected with the digital frequency conversion module, and the digital frequency conversion module is connected with the transmitting end precompensation module in the signal sending module; and a local oscillator and an auxiliary local oscillator are also arranged between the frequency mixers of the signal sending module and the signal receiving module.
Further, the digital frequency conversion module generates orthogonal sine and cosine signals through a digital oscillator.
Further, the quadrature error correction circuit employs an envelope detector for extracting envelope information of the radio frequency signal.
The invention has the beneficial effects that: the problem of IQ imbalance introduced by a transmitter and irrelevant to frequency in a TDD system is solved, the IQ imbalance of the receiver is not influenced, and the IQ imbalance correction accuracy of the transmitter is improved. The accuracy of transmitter IQ imbalance estimation is effectively improved, and the robustness of the system is ensured.
Drawings
FIG. 1 is a block diagram of the system of the present invention.
Fig. 2 is a flow chart of transmitter IQ imbalance correction.
Fig. 3 is a flow chart of IQ imbalance initialization correction for a transmitter.
Fig. 4 is a block diagram of IQ imbalance tracking correction of a transmitter.
Detailed Description
In order to more clearly understand the technical features, objects, and effects of the present invention, embodiments of the present invention will now be described with reference to the accompanying drawings.
The switching circuit controls two operating modes: mode 1: an IQ imbalance initialization correction mode of a transmitter is that a signal generated by a signal generator passes through an orthogonal error correction circuit, only passes through an I path or a Q path of a receiving side circuit, passes through an ADC (analog to digital converter), then carries out parameter estimation of IQ imbalance of a transmitting end, and carries out pre-compensation at a digital end of the transmitter, wherein the IQ imbalance irrelevant to frequency is mainly solved in the mode 1; mode 2: in normal service, the transmitter IQ imbalance tracking and correcting mode is that the service signal of the transmitting end passes through the receiving mixer, the LPF and the ADC, IQ imbalance parameter estimation is carried out in a digital domain, and precompensation is carried out at the digital end of the transmitter. The mode 1 is mainly used for carrying out initialization correction on IQ imbalance of a transmitting end when the surrounding environment is changed greatly, namely initial power-on is solved, or the environment temperature exceeds a threshold or the local oscillation frequency point change exceeds the threshold; the mode 2 is to solve the IQ imbalance irrelevant to the frequency on one hand, and to track and correct the IQ imbalance of the transmitting end for ensuring the service quality when the IQ imbalance is changed due to factors such as the environmental temperature and the like during the normal service operation on the other hand. During normal service operation, the transmitter and the receiver share one local oscillator, and during IQ imbalance tracking and correction of the transmitter, the receiver uses an auxiliary local oscillator to receive data of the transmitter to perform IQ imbalance estimation and correction, and the specific implementation flow is shown in fig. 2.
A block diagram of the IQ imbalance initialization correction process for the mode 1 transmitter is shown in fig. 3. The signal generator of the transmitter is used for sending a test single tone signal, the test single tone signal passes through the pre-compensation coefficient module, different imbalance values are preset in the pre-compensation coefficient module, the test single tone signal passes through the orthogonal detection circuit and then is detected at the receiving end, and finally the optimal I-path direct current, Q-path direct current, gain and phase imbalance values are searched. In order to ensure the accuracy of the test, several groups of frequency points can be generated within the bandwidth by sending the test single-tone signal frequency points, and then the average is carried out, so that the estimation accuracy is improved.
A block diagram of a mode 2 transmitter IQ imbalance tracking correction is shown in fig. 4. In the TDD system, when the normal service works, the transmitting end and the receiving end are time-shared, therefore, the orthogonal error of the transmitting end can be tracked and corrected through a receiver channel. The y (t) signal of the receiver through the ADC is affected by IQ imbalance at the receiving side. In order to avoid the influence of IQ imbalance of a receiving side, an auxiliary local oscillation frequency point for a receiver local oscillation is f _ rx, a transmitter local oscillation frequency point is f _ tx, and the receiver local oscillation frequency point and the transmitter local oscillation frequency point have frequency offset difference, namely f _ tx-f _ rx is not 0, so that the influence of IQ imbalance of the receiver can be eliminated. The channel estimation in fig. 4 not only includes the signal filter g1(t)g2The estimation of (t) also includes the estimation of dc (t).
The invention solves the problem of IQ imbalance introduced by a transmitter and irrelevant to frequency in a TDD system, is not influenced by IQ imbalance of a receiver, and improves the IQ imbalance correction accuracy of the transmitter.
The foregoing shows and describes the general principles and broad features of the present invention and advantages thereof. It will be understood by those skilled in the art that the present invention is not limited to the embodiments described above, which are described in the specification and illustrated only to illustrate the principle of the present invention, but that various changes and modifications may be made therein without departing from the spirit and scope of the present invention, which fall within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and equivalents thereof.
Claims (6)
1. A method for calibrating quadrature error of wideband transmitter in TDD system includes initialization calibration of transmitter IQ imbalance and tracking calibration of transmitter IQ imbalance,
the transmitter IQ imbalance initialization correction comprises the steps of:
s11: the signal generator generates a test signal and sends the test signal through the signal sending module;
s12: the test signal only passes through the I path or the Q path of the signal receiving module after passing through the quadrature error correction circuit;
s13: carrying out transmitter IQ imbalance parameter estimation on the test signal after the test signal passes through an analog-to-digital converter;
s14: pre-compensating in a signal sending module, and adjusting a pre-compensation coefficient of a sending end;
the transmitter IQ imbalance tracking correction comprises the steps of:
s21: when in normal service, a service signal of a transmitting end passes through a signal receiving module mixer, a low-pass filter and an analog-to-digital conversion circuit;
s22: IQ imbalance parameter estimation is carried out in a digital domain;
s23: the method comprises the following steps of configuring local oscillation frequency points of a transmitter and local oscillation frequency points of a receiver: the local oscillation frequency point of the emitter is f _ tx, the receiver adopts an auxiliary local oscillation, the local oscillation frequency point is f _ rx, and f _ tx-f _ rx is not equal to 0;
s24: carrying out digital frequency conversion, wherein the frequency conversion frequency point is- (f _ tx-f _ rx);
s25: and performing precompensation on the signal sending module, and adjusting the precompensation complex filter.
2. The method as claimed in claim 1, wherein the frequency points of the test signal in step S11 have multiple groups.
3. The method of claim 1, wherein the test signal of step S11 is a tone signal.
4. A TDD system broadband transmitter quadrature error correction system is characterized by comprising a signal generator, a signal sending module, a signal receiving module, a quadrature error correction circuit and a digital frequency conversion module; the signal receiving module is also provided with a switch circuit for selecting a transmitter IQ imbalance initialization correction mode or a transmitter IQ imbalance tracking correction mode of the system; the signal generator is connected with the signal sending module, the signal sending module is connected with the orthogonal error correction circuit and the signal receiving module, the orthogonal error correction circuit is connected with the switch circuit in the signal receiving module, the signal receiving module is connected with the digital frequency conversion module, and the digital frequency conversion module is connected with the transmitting end precompensation module in the signal sending module; a local oscillator and an auxiliary local oscillator are also arranged between the frequency mixers of the signal sending module and the signal receiving module; sending a test single tone signal by a signal generator of a transmitter, passing through a pre-compensation coefficient module, presetting different imbalance values by the pre-compensation coefficient module, detecting the signal at a receiving end after passing through an orthogonal detection circuit, and finally searching the optimal I path direct current, Q path direct current, gain and phase imbalance values; tracking and correcting the orthogonal error of the transmitting end through a receiver channel; in order to avoid the influence of IQ imbalance on a receiving side, an auxiliary local oscillation frequency point for a receiver local oscillation is f _ rx, a transmitter local oscillation frequency point is f _ tx, and the frequency deviation of the auxiliary local oscillation frequency point and the transmitter local oscillation frequency point is f _ tx and is f _ tx not 0, so that the influence of IQ imbalance of the receiver is eliminated.
5. The TDD system wideband transmitter quadrature error correction system of claim 4, wherein said digital frequency conversion module generates quadrature sine and cosine signals by means of a digital oscillator.
6. The TDD system wideband transmitter quadrature error correction system of claim 4, wherein said quadrature error correction circuit employs an envelope detector for extracting envelope information of the RF signal.
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