JP7006892B2 - Transmission circuit, transmission equipment, distortion correction method - Google Patents

Description

The present invention relates to a transmission circuit and a transmission device that correct the distortion generated in the RF unit.

In recent years, in order to expand the transmission capacity, the number of values in the QAM (Quadrature Amplitude Modulation) modulation method is increasing. As the number of values increases, the interval between signal points with respect to the average power becomes narrower, and the error rate increases.

In order to reduce the error rate, technological improvements such as sophistication of error correction methods and prevention of deterioration of transmission quality due to phase noise are being made. For example, as a signal level adjusting device, a communication device, and a signal level adjusting method, a method of calculating an unbalanced component after a fast Fourier transform by FFT (Fast Fourier Transform) and controlling the transmission level of each carrier is known. (Patent Document 1).

Further, as a loopback delay estimation device and a loopback delay estimation method, there is known a technique of detecting the phase difference between the original signal and the feedback signal and correcting the initial phase by using complex arithmetic processing (Patent Document 2).

Further, there is known a technique of detecting a phase difference between an original signal and a feedback signal and correcting an initial phase by using a digital radio receiver complex arithmetic processing (Patent Document 3).

Japanese Unexamined Patent Publication No. 2005-159940 Japanese Unexamined Patent Publication No. 2006-186863 Japanese Unexamined Patent Publication No. 2008-199200

However, the above-mentioned conventional technique is intended for correction on the receiver side, and cannot be directly applied to the improvement of transmission quality on the transmitter side.

The transmission signal is affected by distortion generated in a power amplifier, a transmission line, or the like in the RF section of the transmission device. As described above, by increasing the number of QAMs, the signal point interval with respect to the average power becomes narrower, so that the error rate becomes higher. Therefore, in order to increase the number of QAMs, a transmission device having high accuracy is required. However, in order to reduce the error rate, it is necessary to suppress the influence of distortion in the RF section by using a high-quality power amplifier or the like.

The present invention has been made in view of such conventional problems, and provides a distortion correction method for effectively improving the transmission quality in a transmitting device regardless of the power amplifier quality of the RF unit and the like. It is an issue to be solved.

In order to solve the above problems, the present invention is a transmission circuit that receives an RF signal and performs correction processing for correcting distortion generated in the RF portion of the transmission device, and generates a transmission signal based on the transmission data. It is characterized by including a signal generation unit, a data storage unit that receives an RF signal based on the transmission signal, and a distortion correction unit that generates a distortion correction coefficient based on the RF signal and corrects the transmission signal. ..

With such a configuration, in the transmission device composed of the signal generation section and the RF section, the distortion depending on the transmission line of the transmission line of the RF section is corrected by the signal generation section of the transmission device and transmitted through the RF section. The signal to be transmitted can be transmitted with higher transmission quality.

In a preferred embodiment of the present invention, the RF signal is at least a signal obtained by power-amplifying the output signal from the transmission circuit by the power amplifier of the RF unit.
With such a configuration, the distortion depending on the transmission line of the transmission line of the RF section and / or the distortion depending on the characteristics of the power amplifier is corrected by the signal generation section of the transmission device, and the signal transmitted through the RF section. Can be transmitted with higher transmission quality.

In a preferred embodiment of the present invention, the distortion correction unit is a Fourier transform unit that Fourier transforms the orthogonal component and the in-phase component of the RF signal, and at least a part of the signal points obtained from the processing result in the Fourier transform unit. It is provided with a distortion correction coefficient generation unit that generates the distortion correction coefficient based on power and phase, and a distortion correction coefficient addition unit that corrects each signal point of the transmission signal based on the distortion correction coefficient. It is characterized by.

In a preferred embodiment of the present invention, the distortion correction coefficient generation unit has the power and phase of the reference point for performing correction, and the power and phase at at least a part of the signal points obtained from the processing result of the Fourier transform unit. Based on the above, it is characterized in that the power ratio and the phase angle difference for moving the signal point are calculated as the distortion correction coefficient.

In a preferred embodiment of the present invention, a plurality of pilots are provided in the reference unit according to the signal type generated by the signal generation unit, and the distortion correction coefficient addition unit includes the power and phase of the reference point and the said. The distortion correction coefficient is calculated based on the power and phase of the pilot signal, and the distortion correction coefficient addition unit performs correction processing on each signal point of the transmission signal using the distortion correction coefficient. It is characterized by.
With such a configuration, it is possible to calculate the power ratio and the phase angle difference that need to be corrected according to the position of the pilot symbol whose insertion position is predetermined in the constellation, and it is more accurate and efficient. Can be corrected.

In a preferred embodiment of the present invention, the strain correction coefficient addition unit is based on the distortion correction coefficient calculated using the signal included in the reference unit at a certain time point, and the corresponding signal in the reference unit generated thereafter. It is characterized by performing correction processing.
With such a configuration, it is not necessary to calculate the correction coefficient each time a signal is generated, and the distortion of the signal can be efficiently corrected.

In a preferred embodiment of the present invention, the distortion correction unit is characterized in that the distortion correction coefficient is updated at a predetermined timing.
With such a configuration, the correction coefficient can be updated to a more appropriate latest value when the influence of distortion on the transmission line or the power amplifier changes due to changes such as the ambient temperature and humidity. For example, by updating at predetermined time intervals, it is possible to calculate a correction coefficient corresponding to changes in the surrounding environment.

In a preferred embodiment of the present invention, the transmission signal of the reference unit is an OFDM symbol.
At least a part of the distortion correction coefficient calculated based on the pilot carrier is used for correction of at least one carrier of the carrier adjacent to the pilot carrier.
With such a configuration, it is possible to correct a data symbol or the like whose position is unknown in the signal generation unit. Further, since it is not necessary to calculate the correction coefficient for the symbols of all carriers, the correction coefficient can be calculated effectively.

The present invention is a transmission device, characterized in that it includes the transmission circuit and an RF unit.

The present invention is a distortion correction method for an RF signal that receives an RF signal and performs correction processing for correcting the distortion generated in the RF unit.
In the signal generator, the process of generating a transmission signal based on the transmission data,
Processing to output the generated transmission signal to the RF section and receive the RF signal from the RF section,
The distortion correction unit is characterized by comprising a process of generating a distortion correction coefficient based on the received RF signal and adding correction to the transmission signal based on the distortion correction coefficient.

INDUSTRIAL APPLICABILITY According to the present invention, it is possible to provide a distortion correction method for effectively improving the transmission quality in a transmitting device.

It is a functional block diagram of the transmission device which concerns on one conventional embodiment. This is a constellation of an IF signal generated in a signal generation unit of a transmission device according to a conventional embodiment. It is a power spectrum of the IF signal generated in the signal generation part of the transmission equipment which concerns on one conventional embodiment. It is the constellation of the RF signal in the RF part of the transmission equipment which concerns on one conventional embodiment. It is a power spectrum of the RF signal in the RF part of the transmission equipment which concerns on one conventional embodiment. It is a functional block diagram of the transmission device which concerns on embodiment of this invention. This is a CP carrier constellation according to an embodiment of the present invention. It is a figure which shows the constellation at the time of correcting a signal point which concerns on embodiment of this invention. This is an example of a distortion correction coefficient table according to an embodiment of the present invention. It is a processing flowchart of the transmission circuit which concerns on embodiment of this invention.

Hereinafter, the transmission device according to the embodiment of the present invention will be described with reference to the drawings. The embodiments shown below are examples of the present invention, and the present invention is not limited to the following embodiments, and various configurations can be adopted.

For example, in the present embodiment, the configuration, operation, and the like of the transmission device will be described, but a transmission circuit, a transmission method, and the like having the same configuration can also exert the same effect.

In describing a specific example, this example exemplifies a case where a transmission wave is configured by 1721 carriers on the frequency axis as a transmission carrier for performing multi-carrier communication by OFDM (Orthogonal Frequency Division Multiplexing). In addition, based on ARIB STD-B57 2.0 version, the transmission parameter is 2048 points of FFT points in the standard full mode, the carrier modulation method is 16QAM, and the pilot is CP (Continual Pilot). Standards, transmission parameters, and pilots are arbitrary, and the present invention is not limited to the above configuration.

Further, in the present embodiment, the case where distortion correction is performed on the digital signal output from the signal generation unit is illustrated, but distortion correction may be performed on the analog signal.

<Conventional transmitter>
FIG. 1 is a functional block diagram of a transmission device of the prior art in one embodiment. The transmission device 1C includes a signal generation unit 2C, an RF unit 3C, and an antenna ANT.

The signal generation unit 2C includes a signal generation unit 4, a guard interval addition unit 6, an inverse Fourier transform unit 7, a DA converter 8, and a modulation unit 9.

The signal generation unit 4 maps the input transmission data to each OFDM subcarrier using digital modulation such as BPSK or QAM, and adds an OFDM pilot. Then, a guard interval is added by the guard interval addition unit 6 and output to the inverse Fourier transform unit 7.

The inverse Fourier transform unit 7 applies an inverse Fourier transform to the input frequency domain signal to convert it into a time domain signal. The converted signal is converted into an IF (Intermediate Frequency) signal through the DA converter 8 and the modulation unit 9, and is output to the RF unit 3C.

The RF unit 3C includes an amplifier 31, a bandpass filter 32, an upconverter 33, and a power amplifier 34. The IF signal that is modulated and output after the inverse Fourier transform by the inverse Fourier transform unit 7 in the signal generation unit 2C is input to the RF unit 3C. The input IF signal is converted into an output signal via the upconverter 33 and the power amplifier 34 through the transmission line of the transmission line of the RF unit 3C, and is transmitted from the antenna ANT. The IF signal is frequency-converted in the upconverter 33 and power-amplified in the power amplifier 34.

2 and 3 are constellation and power spectra of the IF signal generated by the signal generation unit 2C of the transmission device 1C. 4 and 5 are constellations and power spectra of an output signal (RF signal) that has passed through the transmission line of the RF unit 3C, the upconverter 33, and the power amplifier 34.

The constellation of the IF signal generated from the signal generation unit 2C of the transmission device 1C is a high-quality signal with no distortion and no frequency characteristics can be seen from the power spectrum. On the other hand, the output signal converted by the RF unit 3C is affected by the frequency characteristics of the transmission line, the power amplifier, and the like constituting the RF unit 3C. As a result, the constellation is distorted, resulting in a poor quality signal with frequency characteristics in the power spectrum.

<Transmitting device of the present invention>
FIG. 6 is a functional block diagram of a transmitting device according to an embodiment of the present invention. The transmitting device 1 includes a signal generation unit 2, an RF unit 3, and an antenna ANT.

The signal generation unit 2 includes a signal generation unit 4, a distortion correction unit 5, a guard interval addition unit 6, an inverse Fourier transform unit 7, a DA converter 8, a modulation unit 9, and a data storage unit 10. ing.

The RF unit 3 includes an amplifier 31, a bandpass filter 32, an up converter 33, a power amplifier 34, a directional coupler 35, a down converter 36, and an AD converter 37.

<Distortion correction unit>
The distortion correction unit 5 includes a Fourier transform unit 51, a distortion correction coefficient generation unit 52, and a distortion correction coefficient addition unit 53.

After the inverse Fourier transform from the signal generation unit 2 to the inverse Fourier transform unit 7, the modulated and output signal (reference unit signal) is sent to the RF unit 3. The output signal (RF signal) output from the power amplifier 34 of the RF unit 3 is input to the down converter 36 by the directional coupler 35, down-converted by the down converter 36, digitally converted by the AD converter 37, and is a signal. It is input to the generation unit 2.

<Calculation of distortion correction coefficient>
The data of the orthogonal component and the in-phase component of the output signal (RF signal) returned through the directional coupler 35 are stored in the data storage unit 10. Then, the output signal data is input to the Fourier transform unit 51, Fourier transformed into a signal in the frequency domain, and the strain correction coefficient generation unit 52 generates the distortion correction coefficient.

In the Fourier transform unit 51, the output signal data (signal data of the reference unit) is Fourier transformed at 2048 points, and the frequency component of each carrier from the carrier index 0 to 1720 is calculated. Here, the carriers of the carrier indexes 0, 8, 16, 24 ... 1712, 1720 are CP carriers.

FIG. 7 is a diagram when CP carriers are extracted from the output signal data and plotted on an IQ plane. As shown in the illustrated example, each carrier of the output signal data is plotted with amplitude fluctuation and phase rotation due to the frequency characteristic of the RF unit 3. CP indicates the plotted pilot and P0 indicates the reference point for correcting the distortion.

In this example, among the calculated output signal data of each CP carrier, the point where the in-phase component becomes the maximum is used as the reference point. The method for determining the reference point is arbitrary, for example, the point where the absolute value of the orthogonal component is the smallest among the output signal data of each CP carrier is used as the reference point, or the carrier index of each CP carrier and the specified amplitude are used as the reference point. Therefore, the coordinates of the pilot designated as the standard (± 4/3 in this example) may be used as the reference point.

The distortion correction coefficient generation unit 52 calculates the distortion of each pilot with respect to this reference point. A case where the signal point A is moved with respect to the signal point C on the IQ plane will be described with reference to FIG. FIG. 8 is a diagram showing a constellation when correcting signal points. In order to move the signal point A to the signal point C, the Fourier transform unit 51 obtains the power and the phase angle of each signal point after Fourier transforming the output signal data.

Equation (1) indicates the distance ( _DA ) from the origin to the signal point A in the IQ plane, that is, the power of the signal point. Here, RE _A indicates the value of the RE axis of the signal point A, and IMA indicates the value of the IM axis of the signal point _A. Equation (2) shows the distance (DC) from the origin to the signal point _C in the IQ plane. Here, REC indicates the value of the RE axis of the signal point _C , and IM _C indicates the value of the IM axis of the signal point C. Equation (3) represents the power ratio α _CA for correcting the power of the signal point A to the power of the signal point C.

Equation (4) represents the phase angle difference θ _CA for correcting the phase angle of the signal point A to the phase angle of the signal point C. Here, θ _C indicates the phase angle of the signal point C, and θ _A indicates the phase angle of the signal point A.

Equation (5) is a determinant when the signal point A is rotated to the signal point C. By expanding the equation (5) and using the power ratio α _CA obtained by the equation (3) and the phase angle difference θ _CA obtained by the equation (4), the signal point A can be moved to the signal point C. can. Equation (6) shows an equation of the amount of movement of common-mode data when the signal point A is moved to the signal point C. Equation (7) shows an equation of the amount of movement of orthogonal data when the signal point A is moved to the signal point C.

As shown in FIG. 9, the calculated distortion correction coefficient is held as a distortion correction coefficient table. The distortion correction coefficient addition unit 53 encodes the transmission data generated by the signal generation unit 4, maps and adds a pilot, and then adds the distortion correction coefficient.

For carriers with a carrier index of 0 to 7, the strain correction coefficients (α0 and θ0 in the illustrated example) of pilot carriers (CP carriers) with a carrier index of 0 are used, and for carriers with a carrier index of 8 to 15, carriers are used. The strain correction coefficient is added using the strain correction coefficients (α1 and θ1 in the illustrated example) of the pilot carrier (CP carrier) having an index of 8.

The signal to which the distortion correction coefficient is added is added with a GI in the guard interval addition unit 6, inverse Fourier transformed by the inverse Fourier transform unit 7, modulated by the modulation unit 9, and transmitted to the RF unit 3 as an IF signal. The constellation of the RF signal based on the distortion-corrected signal is a signal point close to the constellation of the IF signal as shown in FIG.

Next, the operation of the transmission circuit provided with the distortion correction unit will be described with reference to FIG. In step S1, the transmitting device 1 is activated. When the transmitting device is activated, transmission data is generated and input to the signal generation unit 4 (step S2).

When the transmission data is input to the signal generation unit 4, the transmission data is mapped to the constellation (step S3), and an OFDM symbol having a CP as an OFDM format pilot is configured (step S4).

In step S5, it is determined whether or not the calculation condition of the distortion correction coefficient is satisfied. The case where the distortion correction coefficient is calculated is, for example, after the transmission device 1 is started (when the first distortion correction coefficient is calculated) or when the distortion correction coefficient is updated. The distortion correction coefficient is updated, for example, in order to deal with changes in distortion amplitude and phase rotation due to changes in temperature, humidity, and the like after a certain period of time has elapsed.

If the calculation condition of the distortion correction coefficient is satisfied (Yes in step S5), the process proceeds to step S6. When calculating the distortion correction coefficient, the output signal of the OFDM symbol generated in step S4 is converted through the directional coupler 35, the down converter 36, and the AD converter 37 (step S6), and the data is stored as the output signal data of the reference unit. Store in the unit (step S7).

Then, the distortion correction coefficient is calculated based on the stored output signal data of the reference unit (step S8). After the distortion correction coefficient is calculated, the distortion correction coefficient is added to the OFDM symbol generated by the signal generation unit 4 (step S9).

When the distortion correction coefficient is added, the guard interval addition unit 6 adds the guard interval, and the inverse Fourier transform unit 7 applies the inverse Fourier transform to convert the signal into a time domain signal. The converted signal is converted into an IF signal through the DA converter 8 and the modulation unit 9 and output to the RF unit 3C (step S10).

When the transmitting device 1 is stopped (Yes in step S11), the process is terminated. When the transmitting device 1 is activated (No in step S11), the processes of S2 to S10 are repeated, and the IF signal corrected for each reference unit is transmitted to the RF unit 3. Further, the distortion correction coefficient is updated at predetermined time intervals (step S5), and the distortion correction coefficient in step S9 is added using the updated distortion correction coefficient.

1 Transmitter 1C Conventional transmitter 2 Signal generator 2C Conventional signal generator 3 RF section 3C Conventional RF section 31, 31a, 31b Amplifier 32, 32a, 32b, 32c Band pass filter 33 Upconverter 34 Power amplifier 35 direction Sex coupler 36 Down converter 37 AD converter 4 Signal generation unit 5 Distortion correction unit 51 Fourier conversion unit 52 Distortion correction coefficient generation unit 53 Distortion correction coefficient addition unit 6 Guard interval addition unit 7 Inverse Fourier conversion unit 8 DA converter 9 Modulation unit 10 Data storage unit ANT antenna CP pilot (CP)
P0 reference points A and B signal points

Claims (5)

A transmission circuit that corrects distortion that occurs in the RF section of a transmission device.
A signal generator that generates a transmission signal by mapping transmission data using a QAM modulation method and generating an OFDM symbol with pilot symbols arranged at regular intervals in the frequency direction.
A data storage unit that receives an RF signal based on the transmission signal, and
For each of the plurality of pilot symbols arranged in the RF signal, as a distortion correction coefficient for moving the pilot symbol to a reference point which is a reference signal point, the power ratio of the reference point and the pilot symbol in the IQ plane, and the same A distortion correction unit that calculates a phase angle difference, which is a difference between the phase angles of the reference point and the pilot symbol, and corrects the transmission signal based on the distortion correction coefficient.
The RF signal is a signal obtained by power-amplifying the transmission signal with the power amplifier of the RF unit.
The distortion correction unit is arranged in the transmission signal, and the signal point of the pilot symbol continuous with the pilot symbol used for calculating the correction coefficient in the time direction or the frequency direction is used for calculating the correction coefficient. The transmission is corrected based on the distortion correction coefficient of the pilot symbol, and the signal points of the carriers arranged in the transmission signal and continuous in the frequency direction are corrected based on the distortion correction coefficient. circuit. The distortion correction unit performs distortion correction processing on a plurality of OFDM symbols including a subsequent data symbol and a subsequent pilot symbol by using the distortion correction coefficient generated for an OFDM symbol which is a certain pilot symbol. The transmission circuit according to claim 1. The distortion correction unit regenerates the distortion correction coefficient for the OFDM symbol, updates the distortion correction coefficient, and performs distortion correction processing on the subsequent OFDM symbol using the updated distortion correction coefficient. The transmission circuit according to claim 2, wherein the transmission circuit is characterized in that. A transmission device comprising the transmission circuit according to any one of claims 1 to 3 and an RF unit that amplifies the transmission signal with a power amplifier and outputs an RF signal. This is a distortion correction method for RF signals that corrects distortion that occurs in the RF section of a transmitting device.
In the signal generation unit, the transmission data is mapped using the QAM modulation method, an OFDM symbol with pilot symbols arranged at regular intervals in the time and frequency directions is generated, and a transmission signal is generated.
A process of outputting the transmission signal to the RF unit and receiving an RF signal based on the transmission signal from the RF unit.
In the distortion correction unit, for each of the plurality of pilot symbols arranged in the RF signal, as a distortion correction coefficient for moving the pilot symbol to a reference point which is a reference signal point, the reference point and the pilot symbol in the IQ plane are used. It is provided with a process of calculating a phase angle difference which is a difference between the power ratio and the phase angle of the same reference point and the pilot symbol, and correcting the transmission signal based on the distortion correction coefficient.
The RF signal is a signal obtained by power-amplifying the transmission signal with the power amplifier of the RF unit.
The distortion correction unit is arranged in the transmission signal, and the signal point of the pilot symbol continuous with the pilot symbol used for calculating the correction coefficient in the time direction or the frequency direction is used for calculating the correction coefficient. A method for correcting distortion of an RF signal, which comprises correcting based on a distortion correction coefficient of a pilot symbol and correcting signal points of carriers adjacent to the pilot symbol based on the distortion correction coefficient.

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