JP2018033125A - Distortion compensation device and coefficient update method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of a transmission signal.SOLUTION: A distortion compensation device 10 comprises a distortion compensation unit 50, a feedback coefficient calculation unit 66, a clip processing unit 62, and an update unit 61. The distortion compensation unit 50 generates a distortion compensation signal from a transmission signal using a distortion compensation coefficient, and inputs the generated distortion compensation signal to a power amplifier 34. The feedback coefficient calculation unit 66 calculates a feedback coefficient on the basis of an output signal from the power amplifier 34. The clip processing unit 62 outputs the feedback coefficient calculated by the feedback coefficient calculation unit 66 when an absolute value of the feedback coefficient is not more than a threshold value. The clip processing unit 62 also outputs a feedback coefficient whose absolute value becomes the threshold value or lower when the absolute value of the feedback coefficient calculated by the feedback coefficient calculation unit 66 is greater than the threshold value. The update unit 61 updates the distortion compensation coefficient using an error between the transmission signal and the output signal, a predetermined step coefficient, and the feedback coefficient.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a distortion compensation apparatus and a coefficient updating method.

  The wireless transmission device is provided with a power amplifier that amplifies the power of the transmission signal. Generally, in a wireless transmission device, a power amplifier is operated near a saturation region of the power amplifier in order to increase the power efficiency of the power amplifier. However, when the power amplifier is operated near the saturation region, the nonlinear distortion of the power amplifier increases. When the nonlinear distortion increases, the signal quality such as the leakage power ratio (Adjacent Channel Leakage Ratio: hereinafter ACLR) to the adjacent channel deteriorates. Therefore, in order to suppress this nonlinear distortion, the wireless transmission apparatus is provided with a distortion compensating apparatus that compensates for the nonlinear distortion.

  One of the distortion compensation methods used in the distortion compensation device is a “digital predistortion method”. In a digital predistortion distortion compensation device, a transmission signal is preliminarily multiplied by a distortion compensation coefficient having the inverse characteristic of nonlinear distortion of a power amplifier, and the transmission signal multiplied by the distortion compensation coefficient is input to the power amplifier. Thereby, the nonlinear distortion in the output signal output from the power amplifier is canceled. The distortion compensation coefficient is stored in an LUT (Look Up Table) in association with an address calculated from the transmission signal.

  Further, it is known that a phenomenon called a memory effect occurs in a power amplifier having high power efficiency. The memory effect is a phenomenon in which an output with respect to an input of an amplifier at a certain time is affected by an input at a past time. In order to suppress the memory effect, distortion compensation is performed using a transmission signal before a predetermined sample. The distortion compensation coefficient in the LUT is sequentially updated so that the difference between the signal obtained by feeding back the output signal from the power amplifier and the transmission signal before distortion compensation becomes small. As a method for updating the distortion compensation coefficient, for example, a method such as NLMS (Normalized Least-Mean-Square) is known.

  By the way, the signal fed back from the power amplifier includes noise components such as thermal noise of ADC (Analog to Digital Converter), for example. Therefore, when the power of the fed back signal is small, the signal-to-noise ratio (hereinafter referred to as the S / N ratio) is small, and the influence of the noise component is large. Therefore, when the fed back signal is small, the update amount of the distortion compensation coefficient calculated based on the fed back signal may be a value greatly different from a desired value.

  In order to avoid this, when the address value calculated from the transmission signal before distortion compensation is less than the threshold value, the distortion compensation coefficient corresponding to the address less than the threshold value is not used by clipping the address with the threshold value. Techniques for doing so are known.

International Publication No. 2003/103163 International Publication No. 2003/103167

  By clipping the address corresponding to the transmission signal before distortion compensation with a predetermined threshold, the signal quality such as ACLR when the amplitude of the transmission signal is small is improved to some extent, but the signal quality is still poor. Therefore, further improvement in signal quality is required.

  The technique disclosed in the present application improves the quality of a transmission signal.

  In one aspect, a distortion compensation device that compensates for distortion generated in a power amplifier includes a distortion compensation unit, a calculation unit, a clip processing unit, and an update unit. The distortion compensation unit generates a distortion compensation signal by performing a predetermined calculation on the transmission signal using the distortion compensation coefficient, and inputs the generated distortion compensation signal to the power amplifier. The calculation unit calculates a feedback coefficient based on the output signal output from the power amplifier. The clip processing unit outputs the feedback coefficient calculated by the calculation unit when the absolute value of the feedback coefficient calculated by the calculation unit is equal to or less than the threshold value. Further, when the absolute value of the feedback coefficient calculated by the calculation unit is larger than the threshold value, the clip processing unit outputs a feedback coefficient whose absolute value is equal to or less than the threshold value. The update unit updates the distortion compensation coefficient using an error between the transmission signal and the output signal, a predetermined step coefficient, and the feedback coefficient output from the clip processing unit.

  According to one embodiment, the quality of a transmission signal can be improved.

FIG. 1 is a block diagram illustrating an example of a distortion compensation apparatus according to the first embodiment. FIG. 2 is a diagram illustrating an example of a threshold value in the first embodiment. FIG. 3 is a diagram illustrating an example of a relationship between an address and a distortion compensation coefficient. FIG. 4 is a diagram for explaining an example of a feedback signal convergence process. FIG. 5 is a flowchart illustrating an example of the coefficient update process according to the first embodiment. FIG. 6 is a block diagram illustrating an example of a distortion compensation apparatus according to the second embodiment. FIG. 7 is a diagram illustrating an example of a threshold value in the second embodiment. FIG. 8 is a flowchart illustrating an example of coefficient update processing according to the second embodiment. FIG. 9 is a diagram illustrating an example of threshold calculation timing in the third embodiment. FIG. 10 is a diagram illustrating another example of threshold calculation timing in the third embodiment. FIG. 11 is a block diagram illustrating an example of a distortion compensation apparatus according to the fourth embodiment. FIG. 12 is a diagram illustrating an example of a feedback coefficient distribution in the fourth embodiment. FIG. 13 is a flowchart illustrating an example of coefficient update processing according to the fourth embodiment. FIG. 14 is a block diagram illustrating an example of a distortion compensation apparatus according to the fifth embodiment. FIG. 15 is a diagram illustrating an example of a product distribution of the absolute value of the feedback coefficient and the step coefficient according to the fifth embodiment. FIG. 16 is a flowchart illustrating an example of coefficient update processing according to the fifth embodiment. FIG. 17 is a block diagram illustrating an example of a distortion compensation apparatus according to the sixth embodiment. FIG. 18 is a diagram illustrating an example of a product distribution of the absolute value of the feedback coefficient and the step coefficient according to the sixth embodiment. FIG. 19 is a flowchart illustrating an example of coefficient update processing according to the sixth embodiment. FIG. 20 is a block diagram illustrating an example of a distortion compensation apparatus according to the seventh embodiment. FIG. 21 is a block diagram illustrating an example of a distortion compensation apparatus according to the eighth embodiment. FIG. 22 is a diagram illustrating an example of hardware of the distortion compensation apparatus.

  Hereinafter, embodiments of a distortion compensation apparatus and a coefficient updating method disclosed in the present application will be described in detail with reference to the drawings. The following examples do not limit the disclosed technology. In addition, the embodiments can be appropriately combined within a range in which processing contents are not contradictory.

[Configuration of Distortion Compensation Device 10]
FIG. 1 is a block diagram illustrating an example of a distortion compensation apparatus 10 according to the first embodiment. The distortion compensation apparatus 10 in this embodiment includes an RF (Radio Frequency) digital unit 20, an RF analog unit 30, and an antenna 40. The RF digital unit 20 includes a distortion compensation unit 50 and a coefficient update unit 60.

  The RF analog unit 30 includes a DAC (Digital to Analog Converter) 31, a mixer 32, an oscillator 33, a power amplifier 34, a coupler 35, a mixer 36, and an ADC 37.

  The DAC 31 converts the distortion-compensated transmission signal output from the distortion compensator 50 from a digital signal to an analog signal. Then, the DAC 31 outputs the signal converted into the analog signal to the mixer 32. The mixer 32 uses the local signal output from the oscillator 33 to perform processing such as modulation and up-conversion on the signal output from the DAC 31. Then, the mixer 32 outputs the processed signal to the power amplifier 34. The power amplifier 34 amplifies the signal output from the mixer 32 with a predetermined amplification factor. The signal amplified by the power amplifier 34 is transmitted from the antenna 40.

  A part of the signal amplified by the power amplifier 34 is fed back via the coupler 35. The mixer 36 performs processing such as down-conversion and demodulation on the signal fed back through the coupler 35 using the signal output from the oscillator 33. The ADC 37 converts the signal demodulated by the mixer 36 from an analog signal to a digital signal. Then, the ADC 37 outputs the feedback signal converted into the digital signal to the coefficient updating unit 60. A feedback signal output from the ADC 37 is defined as Fb (t). The feedback signal Fb (t) is an example of an output signal output from the power amplifier 34.

  The distortion compensation unit 50 includes a distortion compensation processing unit 51, an address generation unit 52, and an LUT (Look Up Table) 53. The address generation unit 52 generates a plurality of transmission signals Tx (t-j) having different delay amounts based on a baseband transmission signal Tx (t) generated by a BB (Base Band signal) processing device. Then, the address generation unit 52 generates an address for each of the transmission signals Tx (t−j) having a plurality of different delay amounts including the transmission signal Tx (t) having a delay amount of zero. In the transmission signal Tx (t−j), j represents a delay amount and takes a value of 0 to N. Then, the address generation unit 52 outputs the address generated for each transmission signal Tx (t−j) to the LUT 53 and the coefficient update unit 60. In the present embodiment, the address generation unit 52 generates an address corresponding to the amplitude of the transmission signal Tx (t−j). The amplitude of the transmission signal Tx (t-j) is an example of the magnitude of the transmission signal Tx (t-j). That is, the value of the address generated by the address generation unit 52 is a value corresponding to the magnitude of the transmission signal Tx (t−j). As another example, the address generation unit 52 may generate an address according to the magnitude of the delay signal power.

  The LUT 53 stores a distortion compensation coefficient associated with an address for each transmission signal Tx (t−j) having a different delay amount. The LUT 53 outputs the distortion compensation coefficient associated with the address output from the address generation unit 52 to the distortion compensation processing unit 51 for each transmission signal Tx (t−j). Each distortion compensation coefficient in the LUT 53 is updated at any time by the coefficient updating unit 60. The LUT 53 is an example of a table.

  The distortion compensation processing unit 51 generates a plurality of transmission signals Tx (t−j) having different delay amounts based on the transmission signal Tx (t) output from the BB processing device. Then, the distortion compensation processing unit 51 outputs the distortion signal output from the LUT 53 to the transmission signal Tx (tj) for each of the transmission signals Tx (tj) having a plurality of different delay amounts including the transmission signal Tx (t) having the delay amount of 0. Multiply the compensation factor. Then, the distortion compensation processing unit 51 generates the transmission signal Tx ′ (t) after distortion compensation by adding the transmission signal Tx (t−j) multiplied by the distortion compensation coefficient. The distortion-compensated transmission signal Tx ′ (t) is output to the DAC 31 and input to the power amplifier 34. The distortion compensation processing unit 51 is an example of a multiplication unit. Further, the transmission signal Tx ′ (t) after distortion compensation is an example of a distortion compensation signal.

The coefficient updating unit 60 calculates a distortion compensation coefficient update amount for each of a plurality of transmission signals Tx (tj) having different delay amounts, and updates the distortion compensation coefficient in the LUT 53 with the calculated update amount. The updated distortion compensation coefficient h _j (p) for the transmission signal Tx (tj) delayed by j samples is calculated based on the following equation (1), for example.
Here, in the above equation (1), h ^′ _j (p) is a distortion compensation coefficient before update, and μ is a step coefficient. In the above equation (1), the error e (t) is calculated based on, for example, the following equation (2) using the transmission signal Tx (t) and the feedback signal Fb (t).

In the above equation (1), the feedback coefficient C _j is calculated based on, for example, the following equation (3) using the feedback signal Fb (tj) corresponding to the transmission signal Tx (tj) delayed by j samples. The
In the above equation (3), Fb ^* (tj) is a conjugate complex number of Fb (tj).

In particular, the feedback coefficient C ₀ calculated from the feedback signal Fb (t) for the transmission signal Tx (t) with a delay amount of 0 (that is, j = 0) is expressed by, for example, the following equation (4). .

In the distortion compensation coefficient updating process, the coefficient updating unit 60 according to the present embodiment performs a clipping process so that the absolute value of the feedback coefficient C _j is equal to or less than a predetermined threshold C _{th for} each transmission signal Tx (tj). Hereinafter, the details of the coefficient updating unit 60 in the present embodiment will be described.

  For example, as shown in FIG. 1, the coefficient update unit 60 in this embodiment includes an update unit 61, a clip processing unit 62, a holding unit 63, a threshold creation unit 64, an absolute value calculation unit 65, a feedback coefficient calculation unit 66, and a subtraction. A container 67 is provided.

The feedback coefficient calculator 66 uses the feedback signal Fb (tj) output from the ADC 37 to perform a calculation based on the above-described equation (3), thereby transmitting the transmission signal Tx (tj) corresponding to the feedback signal Fb (tj). ) To calculate the feedback coefficient C _j every time. Then, the feedback coefficient calculation unit 66 outputs the calculated feedback coefficient C _j to the clip processing unit 62 and the absolute value calculation unit 65. The feedback coefficient calculation unit 66 is an example of a calculation unit.

The absolute value calculator 65 calculates the absolute value | C _j | of the feedback coefficient C _j output from the feedback coefficient calculator 66 for each transmission signal Tx (tj). Then, the absolute value calculation unit 65 outputs the absolute value | C _j | calculated for each transmission signal Tx (tj) to the clip processing unit 62 and the threshold value creation unit 64.

The holding unit 63 stores a threshold value C _th for each transmission signal Tx (tj). For each transmission signal Tx (tj), the threshold generation unit 64 sets the threshold C _th based on the address output from the address generation unit 52 and the absolute value | C _j | output from the absolute value calculation unit 65. create. The threshold value creation unit 64 is an example of a threshold value calculation unit. For example, the threshold value creation unit 64 performs the following processing for the first predetermined number of samples (for example, 100 samples) of each transmission signal Tx (tj) at each predetermined timing.

First, the threshold value creating unit 64 initializes the value of the threshold value C _th of each transmission signal Tx (tj) in the holding unit 63 to zero. Then, the threshold value creation unit 64 refers to the address from the address generation unit 52 for each transmission signal Tx (tj), and the transmission signal Tx (tj) whose absolute value | C _j | is larger than the threshold value A _th. ) Is determined from the feedback signal Fb (tj) corresponding to the absolute value | C _j |. The threshold value A _th of the address is preset in the threshold value creating unit 64 by the administrator of the distortion compensation apparatus 10 or the like.

The absolute value | C _j | is the absolute value calculated from the feedback signal Fb (tj) corresponding to the transmission signal Tx to be a threshold value A _th is greater than the address (tj) | C _j | a case where the threshold generating portion 64 is The absolute value | C _j | is compared with the threshold value C _th stored in the holding unit 63 for each transmission signal Tx (tj). When the absolute value | C _j | is greater than the threshold C _th stored in the holding unit 63, the threshold creating unit 64 sets the absolute value | C _j | as the threshold C _th in the holding unit 63. To store. Thus, when the determination is completed for a predetermined number of samples of each transmission signal Tx (tj), a threshold value C _th as illustrated in FIG. 2 is stored in the holding unit 63 for each transmission signal Tx (tj), for example. Will be.

FIG. 2 is a diagram illustrating an example of a threshold value in the first embodiment. FIG. 2 shows an example of the distribution of the absolute value | C ₀ | calculated from the feedback signal Fb (t) corresponding to the transmission signal Tx (t) whose delay amount is 0. Note that the absolute value | C _j | calculated from the feedback signal Fb (tj) corresponding to the transmission signal Tx (tj) of another delay amount also has the same distribution as in FIG. In this embodiment, for example, as shown in FIG. 2, the absolute value corresponding to the threshold A _th larger address | C ₀ | in value the maximum absolute value | a (eg, point 70 in FIG. 2 | C ₀ The absolute value | C ₀ |) shown is used as the threshold value C _th .

Here, an example of a method for determining the address threshold _Ath will be described. FIG. 3 is a diagram illustrating an example of a relationship between an address and a distortion compensation coefficient. The feedback signal Fb (t) fed back from the power amplifier 34 includes a noise component due to, for example, thermal noise of the ADC 37. In the power amplifier 34, the transmission signal Tx ′ (t) after distortion compensation is amplified with a predetermined amplification factor. Therefore, when the amplitude of the transmission signal Tx (t) is small, that is, generated from the transmission signal Tx (t). When the address value is small, the power of the feedback signal Fb (t) is small. When the power of the feedback signal Fb (t) is small, the SN ratio is small, and the influence of the noise component is large.

  The power amplifier 34 generally has a nonlinear characteristic in a saturation region where the amplitude of the input signal is large, but has a linear characteristic in a region where the amplitude of the input signal is small. Therefore, ideally, for example, as shown by a broken line in FIG. 3, in a region where the amplitude of the input signal is small, the distortion compensation coefficient becomes a constant value (for example, 1).

However, when the amplitude of the transmission signal Tx (t) is small, i.e., when the address value of the transmission signal Tx (t) is small, the influence of the noise component included in the feedback signal Fb (t) increases. For example, as shown by the solid line in FIG. 3, the distortion compensation coefficient is updated to a value different from the ideal value. In the present embodiment, when the address of the transmission signal Tx (t) is reduced, for example, the value of the address at which the distortion compensation coefficient starts to deviate from the ideal value is determined in advance as the threshold value _Ath . As an example of a specific value, for example, an upper limit address in a range of about 40% from the smallest address value in the entire range of address values may be used as the threshold value _Ath . For example, when the entire address range is 1 to 100, an address value of 40 may be used as the threshold value _Ath .

The clip processing unit 62 receives the feedback coefficient C _j from the feedback coefficient calculation unit 66 and the absolute value | C _j | of the feedback coefficient C _j from the absolute value calculation unit 65 for each transmission signal Tx (tj). Then, the clip processing unit 62 compares the absolute value | C _j | received from the absolute value calculating unit 65 with the threshold value C _th in the holding unit 63 for each transmission signal Tx (tj). When the absolute value | C _j | is equal to or smaller than the threshold C _th , the clip processing unit 62 outputs the feedback coefficient C _j received from the feedback coefficient calculation unit 66 to the update unit 61.

On the other hand, when the value of the absolute value | C _j | is larger than the value of the threshold value C _th , the clip processing unit 62 executes clip processing for calculating a feedback coefficient C _j ^′ based on the following equation (5).

The feedback coefficient C _j ^′ calculated based on the above equation (5) has the absolute value | C _j ′ | which is the magnitude of the feedback coefficient C _j ^′ equal to the threshold C _th and the phase is the original feedback coefficient C _j. Is the same phase. Then, the clip processing unit 62 outputs the feedback coefficient C _j ^′ after the clip processing to the update unit 61.

Thus, for example, as shown in FIG. 2, the feedback coefficient C ₀ (for example, the point 71) whose absolute value | C ₀ | is larger than the value of the threshold C _th maintains the phase of the feedback coefficient C _0. Clipping is performed so that the absolute value is equal to the threshold value C _th .

  The subtractor 67 calculates the error e (t) by executing the calculation shown in the above equation (2). Then, the subtractor 67 outputs the calculated error e (t) to the update unit 61.

The updating unit 61 receives the feedback coefficient C _j from the clip processing unit 62, receives the error e (t) from the subtractor 67, and reads out the distortion compensation coefficient h ^′ _j (p) before update from the LUT 53. Then, the updating unit 61 calculates the updated distortion compensation coefficient h _j (p) by executing the calculation shown in the above-described equation (1). Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p). In this embodiment, the step coefficient μ is preset in the update unit 61 by the administrator of the distortion compensation apparatus 10 or the like. The updating unit 61 ^'when receiving from the clip processing unit 62, in the above (1), the feedback coefficient C _j in place of the feedback coefficient C ^_j' feedback coefficient C _j using a distortion of the updated A compensation coefficient h _j (p) is calculated.

  Here, as shown in FIG. 4, for example, in the process of updating the distortion compensation coefficient, the distortion compensation coefficient of the feedback signal 80 is updated so as to approach the transmission signal 81 on the IQ plane. FIG. 4 is a diagram for explaining an example of the convergence process of the feedback signal 80. When the S / N ratio of the feedback signal 80 is small, for example, as shown in FIG. 4, the feedback signal 80 varies within a range 83 centering on the transmission signal 81. Therefore, the feedback signal 80 may exist at a position away from the transmission signal 81 which is a correct solution when viewed at a certain moment.

In contrast, in the present embodiment, in the distortion compensation coefficient update process, the clipping process is performed so that the absolute value | C _j | of the feedback coefficient C _j is equal to or less than a predetermined threshold value C _th . Thereby, for example, as shown in FIG. 4, the feedback signal 80 fluctuates within a range 82 that is narrower than the range 83 with the transmission signal 81 as the center. Therefore, the feedback signal 80 is present at a position closer to the range 83 when viewed at a certain moment. Thereby, the distortion component contained in the feedback signal 80, that is, the signal output from the power amplifier 34 is reduced, and the characteristics such as ACLR are improved.

[Coefficient update processing]
FIG. 5 is a flowchart illustrating an example of the coefficient update process according to the first embodiment. The distortion compensation apparatus 10 executes the coefficient update process shown in FIG. 5 at every predetermined timing. For example, when the distortion compensation apparatus 10 transmits a DL (DownLink) signal in a mobile communication system such as LTE (Long Term Evolution), the distortion compensation apparatus 10 performs the coefficient update process shown in FIG. 5 for each frame, for example. Run. In the following flowchart, the transmission signal Tx (tj) and the feedback signal Fb (tj) delayed by j samples will be described, but the same processing is performed for each delayed signal from j = 0 to N.

First, the feedback coefficient calculation unit 66 initializes a variable s for counting sampling data of the transmission signal Tx (tj) to 0 (S100). Further, the threshold creating unit 64 initializes the value of the threshold C _th in the holding unit 63 to 0 (S100).

Next, the feedback coefficient calculation unit 66 selects sampling data of the feedback signal Fb (tj) corresponding to the sampling data of the sth transmission signal Tx (tj) (S101). Then, the feedback coefficient calculation unit 66 calculates the feedback coefficient C _j by executing the calculation shown in the above equation (3) using the sampling data of the feedback signal Fb (tj) selected in step S101. (S102). Then, the feedback coefficient calculation unit 66 outputs the calculated feedback coefficient C _j to the absolute value calculation unit 65.

Next, the absolute value calculator 65 calculates the absolute value | C _j | of the feedback coefficient C _j output from the feedback coefficient calculator 66 (S103). Then, the absolute value calculation unit 65 outputs the calculated absolute value | C _j | to the clip processing unit 62 and the threshold value creation unit 64.

Next, the clip processing unit 62 and the threshold value creating unit 64 determine whether or not the value of the variable s is equal to or less than the specified value s _num (S104). In the present embodiment, the specified value s _num is 100, for example. If the value of the variable s is equal to or less than a specified value s _num (S104: Yes), the threshold value generating portion 64, the value A of the address of the s-th transmission signal Tx (tj) is greater than the threshold value A _th address It is determined whether or not (S105). s th value A of the address of the transmission signal Tx (tj) is less than or equal to the threshold value A _th address (S105: No), the clip processing unit 62 executes the process shown in step S108.

On the other hand, the value A of the address of the s-th transmission signal Tx (tj) is greater than the threshold value A _th address (S105: Yes), the threshold value generating portion 64 reads out the threshold value C _th from the holding portion 63. Then, the threshold value creation unit 64 determines whether or not the absolute value | C _j | of the feedback coefficient C _j output from the absolute value calculation unit 65 is greater than the threshold value C _th (S106). When the absolute value | C _j | is equal to or smaller than the threshold C _th (S106: No), the updating unit 61 executes the process shown in step S108.

On the other hand, when the absolute value | C _j | is larger than the threshold C _th (S106: Yes), the threshold creating unit 64 outputs the absolute value | C _j of the feedback coefficient C _j output from the absolute value calculating unit 65. The value of the threshold value C _th in the holding unit 63 is replaced with the value of | (S107).

Next, the clip processing unit 62 outputs the feedback coefficient C _j output from the feedback coefficient calculation unit 66 to the update unit 61. The updating unit 61 calculates the updated distortion compensation coefficient h _j (p) by executing the calculation shown in the above-described equation (1) using the feedback coefficient C _j output from the clip processing unit 62. To do. Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p) (S108).

Next, the feedback coefficient calculation unit 66 increases the variable s by 1 (S109). Then, the feedback coefficient calculation unit 66 determines whether or not the value of the variable s is larger than s _max that is the maximum value of the variable s (S110). In this embodiment, s _max is the number of samples in one frame, for example 1000. When the value of the variable s is less than or equal to the value of s _max (S110: No), the feedback coefficient calculation unit 66 executes the process shown in step S101 again. On the other hand, when the value of the variable s is larger than the value of s _max (S110: Yes), the distortion compensation apparatus 10 ends the process shown in this flowchart.

In step S104, when the value of the variable s is larger than the specified value s _num (S104: No), the clip processing unit 62 determines that the address value A of the sth transmission signal Tx (tj) is the address threshold _Ath . It is determined whether it is smaller than the value (S111). s th value A of the address of the transmission signal Tx (tj) is the case at least the threshold value A _th address (S111: No), the clip processing unit 62 executes the process shown in step S108.

On the other hand, when the value A of the address of the s-th transmission signal Tx (tj) is smaller than the threshold value A _th of the address (S111: Yes), the clip processing unit 62 reads the threshold value C _th from the holding unit 63. Then, the clip processing unit 62 determines whether or not the absolute value | C _j | of the feedback coefficient C _j output from the absolute value calculation unit 65 is larger than the threshold C _th (S112). When the absolute value | C _j | is equal to or smaller than the threshold C _th (S112: No), the clip processing unit 62 executes the process shown in step S108.

On the other hand, when the value of the absolute value | C _j | is larger than the value of the threshold value C _th (S112: Yes), the clip processing unit 62 executes the calculation shown in the above equation (5) (S113). Thus, clipped feedback coefficient C _j ^'are created such that the absolute value while maintaining the phase of the feedback coefficient C _j is the threshold value C _th. Then, the clip processing unit 62 outputs the feedback coefficient C _j ^′ to the update unit 61.

Next, the updating unit 61 uses the feedback coefficient C _j ^′ output from the clip processing unit 62 to perform the calculation shown in the above-described equation (1), thereby updating the distortion compensation coefficient h _j ( p) is calculated. Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p) (S114). Then, the threshold value creation unit 64 and the feedback coefficient calculation unit 66 execute the process shown in step S109.

[Effect of Example 1]
As is clear from the above description, the distortion compensation apparatus 10 according to the present embodiment includes the LUT 53, the feedback coefficient calculation unit 66, the clip processing unit 62, and the update unit 61. The LUT 53 stores distortion compensation coefficients. The feedback coefficient calculation unit 66 calculates a feedback coefficient C _j based on the output signal from the power amplifier 34. The clip processing unit 62 outputs the feedback coefficient C _j calculated by the feedback coefficient calculation unit 66 when the absolute value | C _j | of the feedback coefficient C _j calculated by the feedback coefficient calculation unit 66 is equal to or less than the threshold value C _th. To do. Further, clipping processing unit 62, the absolute value of the feedback coefficient C _j calculated by the feedback coefficient calculation unit 66 | C _j | is larger than the threshold value C _th, the feedback coefficient absolute value is equal to or less than the threshold C _th C _j ' Is output. The updating unit 61 uses the error between the transmission signal before distortion compensation and the output signal output from the power amplifier 34, a predetermined step coefficient, and the feedback coefficient output from the clip processing unit 62 to generate distortion in the LUT 53. Update the compensation factor. Thereby, the distortion compensation apparatus 10 can improve the quality of the signal transmitted from the distortion compensation apparatus 10.

Further, in the distortion compensation apparatus 10 of the present embodiment, the clip processing unit 62, when the absolute value | C _j | of the feedback coefficient C _j calculated by the feedback coefficient calculation unit 66 is larger than the threshold C _th , the feedback coefficient C _{For j} , a clip coefficient is executed to calculate a feedback coefficient whose absolute value is the threshold value C _th . The clip processing in the present embodiment is, for example, processing for multiplying the threshold C _th by a value obtained by dividing the feedback coefficient C _j calculated by the feedback coefficient calculation unit 66 by the absolute value | C _j | of the feedback coefficient C _j . As a result, the continuity of the phase of the feedback coefficient C _j ′ is maintained even after the clip processing is executed, and signal quality deterioration can be suppressed.

Further, the distortion compensating apparatus 10 of this embodiment, the clip processing unit 62, a predetermined number of transmission signal Tx (tj) output signal addresses in the sample corresponding to the threshold A _th larger than the transmission signal Tx (tj) of The maximum value of the absolute value | C _j | of the feedback coefficient C _j calculated based on is used as the threshold value C _th . Thereby, the distortion compensation apparatus 10 can improve the quality of the signal transmitted from the distortion compensation apparatus 10.

[Configuration of Distortion Compensation Device 10]
FIG. 6 is a block diagram illustrating an example of the distortion compensation apparatus 10 according to the second embodiment. The distortion compensation apparatus 10 in the present embodiment is different from the distortion compensation apparatus 10 in the first embodiment in the configuration of the coefficient update unit 60. Except for the points described below, in FIG. 6, blocks denoted by the same reference numerals as those in FIG. 1 have the same or similar functions as the blocks shown in FIG.

The coefficient update unit 60 in this embodiment includes an update unit 61, a clip processing unit 62, a threshold value creation unit 64, an absolute value calculation unit 65, a feedback coefficient calculation unit 66, and a subtractor 67. The threshold creating unit 64 creates a threshold C _th based on the absolute value | C _j | output from the absolute value calculating unit 65.

Specifically, the threshold value creation unit 64 calculates the absolute value calculated from the feedback signal Fb (tj) for the first predetermined number of samples (for example, 100 samples) of each transmission signal Tx (tj) at each predetermined timing. The average value C _ave is calculated using | C _j |. Then, for each transmission signal Tx (tj), the threshold generation unit 64 calculates a threshold C _th by adding a predetermined offset C _off to the calculated average value C _ave , for example, as shown in FIG. . FIG. 7 is a diagram illustrating an example of a threshold value in the second embodiment. Then, the threshold value creation unit 64 outputs the threshold value C _th calculated for each transmission signal Tx (tj) to the clip processing unit 62.

The offset C _off is, for example, in a standard environment, the feedback signal Fb (tj) corresponding to the transmission signal Tx (tj) of the address where the threshold C _{th of} each transmission signal Tx (tj) is equal to or greater than the threshold A _th. Is set to a value that is the maximum value of the absolute value | C _j | The value of the offset C _off is set in advance in the threshold creating unit 64 by the administrator of the distortion compensation device 10 or the like.

Here, in each transmission signal Tx (tj), in the feedback coefficient C _j is instantaneous noise by temporarily absolute value | some cases the value increases feedback coefficient C _j is present | C _j . In such a case, if the maximum value of the absolute value | C _j | corresponding to an address equal to or greater than the threshold value A _th is determined as the threshold value C _th , the absolute value | temporarily increased due to instantaneous noise | C _j | is determined as the threshold value C _th . In this case, the threshold C _th is fixed at a large value until the next calculation of the threshold C _th is performed. If the threshold value C _th is fixed at a large value, the absolute value | C _j | of the feedback coefficient C _j after the clip process is not so small, and the quality of the signal transmitted from the distortion compensation device 10 is not so improved. .

On the other hand, in the distortion compensation apparatus 10 of the present embodiment, the threshold value creation unit 64 uses the feedback signal Fb (tj) corresponding to the transmission signal Tx (tj) for the first predetermined number of samples of each transmission signal Tx (tj). The average value C _ave is calculated for | C _j | Then, the threshold value creating unit 64 calculates the threshold value C _th by adding a predetermined offset C _off to the calculated average value C _ave . Thus, in the process of calculating the threshold C _th, the absolute value becomes temporarily large value by instantaneous noise | C _j | change in the threshold C _th according to the impact is kept low. Thereby, the quality of the signal transmitted from the distortion compensation apparatus 10 can be improved more stably.

[Coefficient update processing]
FIG. 8 is a flowchart illustrating an example of coefficient update processing according to the second embodiment. The distortion compensation apparatus 10 executes the coefficient update process shown in FIG. 8 at every predetermined timing. For example, when the distortion compensation apparatus 10 transmits a DL signal in a mobile communication system such as LTE, the distortion compensation apparatus 10 executes a coefficient update process illustrated in FIG. 8 for each frame, for example. In the following flowchart, the transmission signal Tx (tj) and the feedback signal Fb (tj) delayed by j samples will be described, but the same processing is performed for each delayed signal from j = 0 to N.

First, the feedback coefficient calculation unit 66 initializes a variable s for counting sampling data of the transmission signal Tx (tj) to 0 (S200). Then, the feedback coefficient calculation unit 66 selects sampling data of the feedback signal Fb (tj) corresponding to the sampling data of the sth transmission signal Tx (tj) (S201). Then, the feedback coefficient calculation unit 66 determines whether or not the value of the variable s is less than the specified value s _num (S202). In the present embodiment, the specified value s _num is 100, for example.

When the value of the variable s is less than the specified value s _num (S202: Yes), the feedback coefficient calculation unit 66 uses the sampling data of the feedback signal Fb (tj) selected in step S201, and the above (3) Perform the operation shown in the expression. Thereby, the feedback coefficient C _j is calculated (S203). Then, the feedback coefficient calculation unit 66 outputs the calculated feedback coefficient C _j to the absolute value calculation unit 65.

Next, the absolute value calculating unit 65 calculates the absolute value | C _j | of the feedback coefficient C _j output from the feedback coefficient calculating unit 66 (S204). Then, the absolute value calculation unit 65 outputs the calculated absolute value | C _j | to the threshold value creation unit 64. The threshold creating unit 64 holds the absolute value | C _j | output from the absolute value calculating unit 65.

Next, the clip processing unit 62 outputs the feedback coefficient C _j output from the feedback coefficient calculation unit 66 to the update unit 61. The updating unit 61 calculates the updated distortion compensation coefficient h _j (p) by executing the calculation shown in the above-described equation (1) using the feedback coefficient C _j output from the clip processing unit 62. To do. Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p) (S205).

Next, the feedback coefficient calculation unit 66 increases the variable s by 1 (S206). Then, the feedback coefficient calculation unit 66 determines whether or not the value of the variable s is larger than s _max that is the maximum value of the variable s (S207). In this embodiment, s _max is the number of samples in one frame, for example 1000. When the value of the variable s is less than or equal to the value of s _max (S207: No), the feedback coefficient calculation unit 66 executes the process shown in step S201 again. On the other hand, when the value of the variable s is larger than the value of s _max (S207: Yes), the distortion compensation apparatus 10 ends the process shown in this flowchart.

In step S202, when the value of the variable s is greater than or equal to the specified value s _num (S202: No), the feedback coefficient calculation unit 66 determines whether or not the value of the variable s is equal to the specified value s _num (S208). . When the value of the variable s is equal to the specified value s _num (S208: Yes), the feedback coefficient calculation unit 66 uses the sampling data of the feedback signal Fb (tj) selected in step S201, and the above equation (3) The operation shown in is executed. Thereby, the feedback coefficient C _j is calculated (S209). Then, the feedback coefficient calculation unit 66 outputs the calculated feedback coefficient C _j to the absolute value calculation unit 65.

Next, the absolute value calculator 65 calculates the absolute value | C _j | of the feedback coefficient C _j output from the feedback coefficient calculator 66 (S210). Then, the absolute value calculation unit 65 outputs the calculated absolute value | C _j | to the clip processing unit 62 and the threshold value creation unit 64.

Next, the threshold value generating portion 64, the absolute value outputted from the absolute value calculating section 65 | and the absolute value is held | | C _j C _j | and using the absolute value | C _j | average value _Cave is calculated (S211). Then, the threshold value creating unit 64 calculates the threshold value C _th by adding the offset C _off to the average value C _ave (S212). Then, the threshold creating unit 64 outputs the calculated threshold C _th to the clip processing unit 62.

Next, the clip processing unit 62 determines whether the absolute value | C _j | of the feedback coefficient C _j output from the absolute value calculation unit 65 is greater than the value of the threshold C _th output from the threshold generation unit 64. Is determined (S213). When the absolute value | C _j | is equal to or smaller than the threshold C _th (S213: No), the clip processing unit 62 executes the process shown in step S205.

On the other hand, when the value of the absolute value | C _j | is larger than the value of the threshold value C _th (S213: Yes), the clip processing unit 62 executes the calculation shown in the above equation (5) (S214). Thus, while maintaining the phase of the feedback coefficients C _j, clip processing to be clipped is performed so that the absolute value of the feedback coefficient C _j is the threshold value C _th. Then, the clip processing unit 62 outputs the feedback coefficient C _j ^′ clipped with the threshold value C _th to the update unit 61.

Next, the updating unit 61 uses the feedback coefficient C _j ^′ output from the clip processing unit 62 to perform the calculation shown in the above-described equation (1), thereby updating the distortion compensation coefficient h _j ( p) is calculated. Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p) (S215). Then, the threshold value creation unit 64 and the feedback coefficient calculation unit 66 execute the process shown in step S206.

[Effect of Example 2]
As is clear from the above description, in the distortion compensation apparatus 10 of the present embodiment, the clip processing unit 62 calculates the absolute value of the feedback coefficient calculated based on the output signal corresponding to the transmission signal in a predetermined number of transmission signal samples. A value obtained by adding a predetermined offset C _off to the average value C _ave is used as the threshold value C _th . Thereby, the quality of the signal transmitted from the distortion compensation apparatus 10 can be improved more stably.

In the first and second embodiments described above, for example, as described with reference to FIG. 5 or FIG. 8, every first period such as one frame period, the first second period within the first period is included. The threshold value C _th is calculated using the sample. Then, in the first period, the clipping process is performed using the threshold value C _th calculated in the second period in the remaining period after the second period has elapsed. In contrast, in Example 3, the first threshold value C _th calculated in the second period within the first period, the threshold C _th is calculated in the first second period in the next first time period It is used for the clip processing until it is done.

FIG. 9 is a diagram illustrating an example of threshold calculation timing in the third embodiment. In the third embodiment, for example, as illustrated in FIG. 9, first, the threshold value C _th is calculated using a sample in the first second period b in the first period a. The calculated threshold C _th is used for clip processing in the period c until the threshold C _th is calculated in the first second period b ′ in the next first period a ′. Then, the threshold C _th calculated using the samples in the first second period b ′ in the first period a ′ is the first second period b ″ in the next first period a ″. Is used for clip processing in the period c ′ until the threshold value C _th is calculated.

In the third embodiment, the first period a and the second period b are arbitrarily set. For example, in an environment where communication traffic varies greatly, the first period a may be set shorter than the second period b. As a result, the threshold value C _th can be updated as needed in response to changes in the communication environment. On the other hand, in an environment where fluctuations in communication traffic do not vary so much, the first period a may be set longer than the second period b. Thereby, the update frequency of the threshold value _Cth is reduced, and the processing load of the distortion compensation apparatus 10 is reduced.

Further, the second period b may overlap with another second period b, for example, as shown in FIG. FIG. 10 is a diagram illustrating another example of threshold calculation timing in the third embodiment. For example, as shown in FIG. 10, the threshold value C _th calculated in the second period b ₁ is used for clipping the period c ₁ to threshold C _th is calculated in the following second period b ₂ . Similarly, the threshold value C _th calculated in the second period b ₂ is used for the clipping process in the period c ₂ until the threshold value C _th is calculated in the next second period b ₃ .

[Effect of Example 3]
As is clear from the above description, in the distortion compensation apparatus 10 of the present embodiment, the threshold value C _th calculated in the first second period in the first period is the first threshold value in the next first period. This is used for clip processing until the threshold C _th is calculated in the period 2. Thereby, the quality of the signal transmitted from the distortion compensation apparatus 10 can be improved more stably.

[Configuration of Distortion Compensation Device 10]
FIG. 11 is a block diagram illustrating an example of the distortion compensation apparatus 10 according to the fourth embodiment. Distortion compensating apparatus 10 in this embodiment, if the value of the address of the transmission signal Tx (t) is equal to or less than the threshold value A _th, using the threshold C _th calculated based on the magnitude of the transmission signal Tx (t) The point that the feedback coefficient C _j is clipped is different from the distortion compensation apparatus 10 in the first embodiment. Except for the points described below, in FIG. 11, blocks denoted by the same reference numerals as those in FIG. 1 have the same or similar functions as the blocks shown in FIG.

The threshold value creation unit 64 determines whether or not the value of the address output from the address generation unit 52 is greater than the threshold value _Ath . When the value of the address output from the address generation unit 52 is larger than the threshold value A _th , the threshold value creation unit 64 outputs the maximum value as the threshold value C _th to the clip processing unit 62.

When the value of the address output from the address generation unit 52 is equal to or less than the threshold value A _th , the threshold value creation unit 64 creates the threshold value C _th based on, for example, the following equation (6). Then, the threshold creating unit 64 outputs the created threshold C _th to the clip processing unit 62.
In the above equation (6), α and β are predetermined constants.

The clip processing unit 62 receives the feedback coefficient C _j from the feedback coefficient calculation unit 66 and the absolute value | C _j | of the feedback coefficient C _j from the absolute value calculation unit 65 for each transmission signal Tx (tj). Then, the clip processing unit 62 compares the absolute value | C _j | received from the absolute value calculating unit 65 with the threshold C _th output from the threshold creating unit 64 for each transmission signal Tx (tj). When the absolute value | C _j | is equal to or smaller than the threshold C _th , the clip processing unit 62 outputs the feedback coefficient C _j received from the feedback coefficient calculation unit 66 to the update unit 61.

On the other hand, when the value of the absolute value | C _j | is larger than the value of the threshold value C _th , the clip processing unit 62 calculates the feedback coefficient C _j ^′ based on the above equation (5). Then, the clip processing unit 62 outputs the feedback coefficient C _j ^′ after the clip processing to the update unit 61.

Thereby, the distribution of the feedback coefficient becomes, for example, as shown in FIG. FIG. 12 is a diagram illustrating an example of a feedback coefficient distribution in the fourth embodiment. FIG. 12 shows an example of the distribution of the absolute value | C ₀ | calculated from the feedback signal Fb (t) corresponding to the transmission signal Tx (t) whose delay amount is 0. Note that the absolute value | C _j | calculated from the feedback signal Fb (tj) corresponding to the transmission signal Tx (tj) of another delay amount has the same distribution as that in FIG. In Example 4, for example, as shown in FIG. 12, the threshold value A _th following address, absolute value of the feedback coefficient C _j | C _j | value becomes less than the threshold value C _th, the divergence of the feedback coefficient C _j is suppressed Has been. This suppresses deterioration of distortion compensation accuracy at a small address.

[Coefficient update processing]
FIG. 13 is a flowchart illustrating an example of coefficient update processing according to the fourth embodiment. The distortion compensation apparatus 10 starts the coefficient update process illustrated in FIG. 13 at a predetermined timing. For example, when the distortion compensation apparatus 10 starts transmission of a DL signal in a mobile communication system such as LTE, the distortion compensation apparatus 10 starts coefficient update processing illustrated in FIG. 13, for example. In the following flowchart, the transmission signal Tx (tj) and the feedback signal Fb (tj) delayed by j samples will be described, but the same processing is performed for each delayed signal from j = 0 to N.

First, the feedback coefficient calculation unit 66 uses the sampling data of the feedback signal Fb (tj) corresponding to the sampling data of the transmission signal Tx (tj) to execute the calculation shown in the above equation (3). A feedback coefficient C _j is calculated (S220). Then, the feedback coefficient calculation unit 66 outputs the calculated feedback coefficient C _j to the clip processing unit 62.

Next, the threshold value creation unit 64 determines whether or not the value of the address output from the address generation unit 52 is greater than the threshold value A _th (S221). When the address value output from the address generation unit 52 is greater than the threshold value A _th (S221: Yes), the threshold value creation unit 64 outputs the maximum value as the threshold value C _th to the clip processing unit 62. Since the absolute value | C _j | received from the absolute value calculator 65 is smaller than the threshold C _th output from the threshold _generator 64, the clip processor 62 updates the feedback coefficient C _j received from the feedback coefficient calculator 66. To the unit 61.

The updating unit 61 calculates the updated distortion compensation coefficient h _j (p) by executing the calculation shown in the above-described equation (1) using the feedback coefficient C _j output from the clip processing unit 62. To do. Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p) (S222). Then, the feedback coefficient calculation unit 66 executes the process shown in step S220 again.

On the other hand, when the value of the address output from the address generation unit 52 is equal to or less than the threshold value A _th (S221: No), the threshold value creation unit 64 creates the threshold value C _th based on the above equation (6) ( S223). Then, the threshold creating unit 64 outputs the created threshold C _th to the clip processing unit 62. The clip processing unit 62 determines whether or not the absolute value | C _j | received from the absolute value calculation unit 65 is larger than the threshold value C _th output from the threshold value creation unit 64 (S224). When the absolute value | C _j | is equal to or less than the threshold value C _th (S224: No), the clip processing unit 62 outputs the feedback coefficient C _j received from the feedback coefficient calculation unit 66 to the update unit 61. And the update part 61 performs the process shown to step S222.

On the other hand, when the absolute value | C _j | is larger than the threshold value C _th (S224: Yes), the clip processing unit 62 calculates the feedback coefficient C _j ^′ based on the above-described equation (5) (S225). Then, the clip processing unit 62 outputs the feedback coefficient C _j ^′ to the update unit 61. The updating unit 61 uses the feedback coefficient C _j ^′ output from the clip processing unit 62 to perform the calculation shown in the above-described equation (1), thereby obtaining the updated distortion compensation coefficient h _j (p). calculate. Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p) (S226). Then, the feedback coefficient calculation unit 66 executes the process shown in step S220 again.

[Effect of Example 4]
As is clear from the above description, in the distortion compensation apparatus 10 of the present embodiment, when the address value of the transmission signal Tx (t) is equal to or less than a predetermined value, the calculation is performed based on the magnitude of the transmission signal Tx (t). The feedback coefficient C _j is clipped using the threshold value C _th . Thereby, the quality of the signal transmitted from the distortion compensation apparatus 10 can be improved more stably.

[Configuration of Distortion Compensation Device 10]
FIG. 14 is a block diagram illustrating an example of the distortion compensation apparatus 10 according to the fifth embodiment. The distortion compensator 10 in the present embodiment performs the process of switching the step coefficient μ according to the address value of the transmission signal Tx (tj) instead of the process of clipping the feedback coefficient C _j in the first embodiment. Different from the distortion compensation apparatus 10. Except for the points described below, in FIG. 14, blocks denoted by the same reference numerals as those in FIG. 1 have the same or similar functions as the blocks shown in FIG.

The coefficient updating unit 60 in this embodiment includes an updating unit 61, a feedback coefficient calculating unit 66, a subtracter 67, and a step coefficient switching unit 68. The feedback coefficient calculation unit 66 calculates a feedback coefficient C _j for each transmission signal Tx (tj) by performing a calculation based on the above-described equation (3) using the feedback signal Fb (t) output from the ADC 37. . Then, the feedback coefficient calculation unit 66 outputs the calculated feedback coefficient C _j to the update unit 61. The subtractor 67 calculates the error e (t) by executing the calculation shown in the above equation (2), and outputs the calculated error e (t) to the update unit 61.

The step coefficient switching unit 68 acquires the address generated by the address generation unit 52 for each transmission signal Tx (tj). Then, step coefficient switching unit 68, for each transmission signal Tx (tj), determines the value of the address is whether greater than a predetermined threshold value A _th. That is, the step coefficient switching unit 68 determines whether or not the amplitude of the transmission signal Tx (tj) is greater than a predetermined value for each transmission signal Tx (tj) having a different delay amount. Note that the threshold A _th is derived from noise in the section from the amplifier to the ADC, and is thus set based on a measured value of the magnitude of noise in this portion.

When the value of the address is larger than the predetermined threshold A _th , the step coefficient switching unit 68 outputs the first value of the step coefficient μ ₀ to the update unit 61. On the other hand, when the address value is equal to or smaller than the predetermined threshold A _th , the step coefficient switching unit 68 outputs the second value step coefficient μ ₁ , which is smaller than the first value, to the updating unit 61. Note that the values of the step coefficients μ ₀ and μ ₁ are stored in advance in the memory of the distortion compensation apparatus 10 by an administrator of the distortion compensation apparatus 10 or the like.

The updating unit 61 receives the feedback coefficient C _j from the clip processing unit 62, receives the error e (t) from the subtractor 67, and receives the step coefficient μ ₀ or μ ₁ from the step coefficient switching unit 68. Further, the update unit 61 reads out the distortion compensation coefficient h ^′ _j (p) before update from the LUT 53. Then, the updating unit 61 calculates the updated distortion compensation coefficient h _j (p) by executing the calculation shown in the above-described equation (1). Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p).

Thus, in this embodiment, the update processing of the distortion compensation coefficient for the following transmission signal value threshold A _th address, the value of the address is applied to the threshold A _th larger transmission signal A step coefficient μ ₁ having a value smaller than the step coefficient μ ₀ is used. As a result, for example, as shown in FIG. 15, the value of the product of the absolute value | C ₀ | of the feedback coefficient C ₀ and the step coefficient μ is reduced in the transmission signal Tx (t) having an address equal to or less than the threshold A _th . FIG. 15 is a diagram illustrating an example of a product distribution of the absolute value | C ₀ | of the feedback coefficient C ₀ and the step coefficient μ in the fifth embodiment.

Thus, the address value is the threshold A _th less transmission signal Tx (tj), i.e., the update amount of the distortion compensation coefficient for the amplitude is small transmission signal Tx (tj) is computed smaller. For this reason, in the distortion compensation coefficient update process for the transmission signal Tx (tj) having a small amplitude, the influence of noise can be suppressed to a low level. Thereby, the distortion compensation apparatus 10 can improve the quality of the signal transmitted from the distortion compensation apparatus 10.

[Coefficient update processing]
FIG. 16 is a flowchart illustrating an example of coefficient update processing according to the fifth embodiment. The distortion compensation apparatus 10 performs the coefficient update process shown in FIG. 16 at every predetermined timing. For example, when the distortion compensation apparatus 10 transmits a DL signal in a mobile communication system such as LTE, the distortion compensation apparatus 10 executes a coefficient update process illustrated in FIG. 16 for each frame, for example. In the following flowchart, the transmission signal Tx (tj) and the feedback signal Fb (tj) delayed by j samples will be described, but the same processing is performed for each delayed signal from j = 0 to N.

First, the feedback coefficient calculation unit 66 initializes a variable s for counting sampling data of the transmission signal Tx (tj) to 0 (S300). Then, the feedback coefficient calculation unit 66 selects sampling data of the feedback signal Fb (tj) corresponding to the sampling data of the sth transmission signal Tx (tj) (S301). Then, the feedback coefficient calculation unit 66 calculates the feedback coefficient C _j by executing the calculation shown in the above equation (3) using the sampling data of the feedback signal Fb (tj) selected in step S301. (S302). Then, the feedback coefficient calculation unit 66 outputs the calculated feedback coefficient C _j to the update unit 61.

Next, the step coefficient switching unit 68 refers to the value of the address generated by the address generation unit 52, and determines whether or not the value A of the address is greater than a predetermined threshold _Ath (S303). If the value A of the address is larger than a predetermined threshold value A _th (S303: Yes), the step coefficient switching section 68, a step coefficient mu, and outputs the step coefficient mu ₀ of the first value to the update unit 61 (S304) . On the other hand, when the value A of the address is equal to or smaller than the predetermined threshold A _th (S303: No), the step coefficient switching unit 68 sets the step coefficient μ as the step coefficient μ to a value smaller than the first value of the step coefficient μ ₀ . The step coefficient μ ₁ having a value of 2 is output to the update unit 61 (S305).

Next, the updating unit 61 receives the feedback coefficient C _j from the feedback coefficient calculation unit 66, receives the error e (t) from the subtractor 67, and receives the step coefficient μ from the step coefficient switching unit 68. Further, the update unit 61 reads out the distortion compensation coefficient h ^′ _j (p) before update from the LUT 53. Then, the update unit 61 calculates the updated distortion compensation coefficient h _j (p) by executing a calculation based on the above-described equation (1). Then, the updating unit 61 updates the distortion compensation coefficient h ^′ _j (p) in the LUT 53 with the calculated distortion compensation coefficient h _j (p) (S306).

Next, the feedback coefficient calculation unit 66 increases the variable s by 1 (S307). Then, the feedback coefficient calculation unit 66 determines whether or not the value of the variable s is larger than s _max that is the maximum value of the variable s (S308). In this embodiment, s _max is 1000, for example. When the value of the variable s is less than or equal to the value of s _max (S308: No), the feedback coefficient calculation unit 66 executes the process shown in step S301 again. On the other hand, when the value of the variable s is larger than the value of s _max (S308: Yes), the distortion compensation apparatus 10 ends the processing shown in this flowchart.

[Effect of Example 5]
As is clear from the above description, the distortion compensation apparatus 10 according to the present embodiment includes the LUT 53, the feedback coefficient calculation unit 66, and the update unit 61. The LUT 53 stores distortion compensation coefficients. The feedback coefficient calculation unit 66 calculates a feedback coefficient based on the output signal from the power amplifier 34. The update unit 61 uses the error between the transmission signal before distortion compensation and the output signal output from the power amplifier 34, a predetermined step coefficient, and the feedback coefficient output from the feedback coefficient calculation unit 66 in the LUT 53. Update distortion compensation coefficient. In addition, when the updating unit 61 updates the distortion compensation coefficient corresponding to the transmission signal whose magnitude is equal to or less than the predetermined value, the update coefficient 61 is used to update the distortion compensation coefficient corresponding to the transmission signal whose magnitude is larger than the predetermined value. The distortion compensation coefficient is updated using the step coefficient μ ₁ having a value smaller than μ ₀ . Thereby, the distortion compensation apparatus 10 can improve the quality of the signal transmitted from the distortion compensation apparatus 10.

[Configuration of Distortion Compensation Device 10]
FIG. 17 is a block diagram illustrating an example of the distortion compensation apparatus 10 according to the sixth embodiment. The distortion compensation apparatus 10 in the present embodiment is different from the distortion compensation apparatus 10 in the fifth embodiment in that the distortion compensation coefficient is updated using a step coefficient corresponding to the address value of the transmission signal. Except for the points described below, in FIG. 17, blocks denoted by the same reference numerals as those in FIG. 14 have the same or similar functions as the blocks shown in FIG.

The coefficient update unit 60 includes an update unit 61, a feedback coefficient calculation unit 66, a subtractor 67, and a step coefficient calculation unit 69. The step coefficient calculation unit 69 acquires the address generated by the address generation unit 52 for each transmission signal Tx (tj) having a different delay amount. Then, the step coefficient calculation unit 69 determines for each transmission signal Tx (tj) whether the value of the address is greater than a predetermined threshold _Ath . That is, the step coefficient calculation unit 69 determines whether or not the amplitude of the transmission signal Tx (t) is greater than a predetermined value for each transmission signal Tx (t) having a different delay amount.

If the address value is greater than the predetermined threshold A _th , the step coefficient calculation unit 69 outputs the step coefficient μ ₀ to the update unit 61. On the other hand, when the address value is equal to or smaller than the predetermined threshold A _th , the step coefficient calculation unit 69 calculates the step coefficient μ ₁ based on the following equation (7), and updates the calculated step coefficient μ ₁ to the update unit 61. Output to.
In the above equation (7), α and β are predetermined constants, and are preset in the step coefficient calculation unit 69 by the administrator of the distortion compensation apparatus 10 or the like. As α and β, for example, values are selected such that the value of the step coefficient μ ₁ is smaller than the value of the step coefficient μ ₀ in the transmission signal Tx (t) whose address value is equal to or less than the threshold value A _th. The

The update unit 61 receives the feedback coefficient C _j from the feedback coefficient calculation unit 66, receives the error e (t) from the subtractor 67, and receives the step coefficient μ from the step coefficient calculation unit 69. Further, the update unit 61 reads out the distortion compensation coefficient h ^′ _j (p) before update from the LUT 53. Then, the update unit 61 calculates the aforementioned items (1) distortion compensation coefficient h _j (p) after updated based on the formula, the calculated distortion compensation coefficients h _j (p) by the distortion compensation coefficient h in the LUT 53 ^' _j (p) is updated.

As described above, in this embodiment, in the distortion compensation coefficient update process, the step coefficient μ ₁ calculated based on the above-described equation (7) is set for the transmission signal whose address value is equal to or less than the threshold value A _th. Applied. As a result, for example, as shown in FIG. 18, the value of the product of the absolute value | C ₀ | of the feedback coefficient C ₀ and the step coefficient μ is reduced in the transmission signal Tx (t) with an address equal to or less than the threshold A _th . FIG. 18 is a diagram illustrating an example of a product distribution of the absolute value | C ₀ | of the feedback coefficient C ₀ and the step coefficient μ in the sixth embodiment.

Thus, the address value is the threshold A _th less transmission signal Tx (tj), i.e., the update amount of the distortion compensation coefficient for the amplitude is small transmission signal Tx (tj) is computed smaller. For this reason, in the distortion compensation coefficient update process for the transmission signal Tx (tj) having a small amplitude, the influence of noise can be suppressed to a low level. Thereby, the distortion compensation apparatus 10 can improve the quality of the signal transmitted from the distortion compensation apparatus 10.

[Coefficient update processing]
FIG. 19 is a flowchart illustrating an example of coefficient update processing according to the sixth embodiment. The distortion compensation apparatus 10 executes a coefficient update process shown in FIG. 19 at every predetermined timing. Except for the points described below, in FIG. 19, the processes denoted by the same reference numerals as those in FIG. 16 are the same as the processes shown in FIG.

In step S303, the step coefficient calculation unit 69 refers to the value of the address generated by the address generation unit 52, and determines whether or not the value A of the address is greater than a predetermined threshold value _Ath (S303). If the value A of the address is larger than a predetermined threshold value A _th (S303: Yes), the step coefficient calculation unit 69 outputs the step coefficient mu ₀ as step factor mu to update unit 61 (S304). On the other hand, when the address value A is equal to or smaller than the predetermined threshold A _th (S303: No), the step coefficient calculating unit 69 calculates the step coefficient μ ₁ calculated based on the above-described equation (7) as the step coefficient μ. Is output to the updating unit 61 (S310). Then, the update unit 61 executes the process shown in step S306.

[Effect of Example 6]
As is clear from the above description, in the distortion compensation apparatus 10 of the present embodiment, the updating unit 61 determines the magnitude of the transmission signal when updating the distortion compensation coefficient corresponding to the transmission signal whose magnitude is a predetermined value or less. The distortion compensation coefficient is updated using the step coefficient calculated based on this. Thereby, in the distortion compensation coefficient update process for a transmission signal having a small amplitude, the influence of noise can be suppressed low, and the quality of the signal transmitted from the distortion compensation apparatus 10 can be improved.

[Configuration of Distortion Compensation Device 10]
FIG. 20 is a block diagram illustrating an example of the distortion compensation apparatus 10 according to the seventh embodiment. The distortion compensation apparatus 10 according to the present embodiment is based on the ratio between the absolute value | C _j | of the feedback coefficient C _j and the threshold C _th when the address value of the transmission signal Tx (t) is equal to or less than the threshold A _th. The difference from the distortion compensation apparatus 10 in the sixth embodiment is that the step coefficient μ is changed. Except for the points described below, in FIG. 20, blocks denoted by the same reference numerals as those in FIG. 1 or FIG. 17 have the same or similar functions as the blocks shown in FIG. 1 or FIG. Description is omitted.

The holding unit 63 stores a threshold value C _th for each transmission signal Tx (tj) in advance. The absolute value calculation unit 65 calculates the absolute value | C _j | of the feedback coefficient C _j output from the feedback coefficient calculation unit 66 for each transmission signal Tx (tj), and calculates the calculated absolute value | C _j | And output to the step coefficient calculation unit 69.

The step coefficient calculation unit 69 acquires the address generated by the address generation unit 52 for each transmission signal Tx (tj) having a different delay amount. Then, the step coefficient calculation unit 69 determines for each transmission signal Tx (tj) whether the value of the address is greater than a predetermined threshold _Ath . If the address value is greater than the predetermined threshold A _th , the step coefficient calculation unit 69 outputs the step coefficient μ ₀ to the update unit 61.

On the other hand, when the address value is equal to or smaller than the predetermined threshold A _th , the step coefficient calculation unit 69 calculates the threshold C _th in the holding unit 63 and the absolute value | C _j | output from the absolute value calculation unit 65. For example, the step coefficient μ ₁ is calculated based on the following equation (8). Then, the step coefficient calculation unit 69 outputs the calculated step coefficient μ ₁ to the update unit 61.

[Effect of Example 7]
As is apparent from the above description, in the distortion compensation apparatus 10 of the present embodiment, the step coefficient calculation unit 69 calculates the absolute value of the feedback coefficient C _j when the address value of the transmission signal Tx (t) is equal to or less than the threshold value A _th. The step coefficient μ is changed based on the ratio between the value | C _j | and the threshold value C _th . Thereby, in the distortion compensation coefficient update process for a transmission signal having a small amplitude, the influence of noise can be suppressed low, and the quality of the signal transmitted from the distortion compensation apparatus 10 can be improved.

[Configuration of Distortion Compensation Device 10]
FIG. 21 is a block diagram illustrating an example of the distortion compensation apparatus 10 according to the eighth embodiment. The eighth embodiment is an embodiment according to the combination of the first embodiment and the seventh embodiment. That is, the distortion compensation apparatus 10 in the present embodiment specifies the maximum value among the absolute values | C _j | of the feedback coefficients C _j corresponding to addresses larger than the threshold A _th as the threshold C _th . The distortion compensation apparatus 10 according to the present embodiment sets the ratio of the absolute value | C _j | of the feedback coefficient C _j to the threshold C _th when the address value of the transmission signal Tx (t) is equal to or less than the threshold A _th. Based on this, the step coefficient μ is changed. Except for the points described below, in FIG. 21, blocks with the same reference numerals as those in FIG. 1 or FIG. 17 have the same or similar functions as the blocks shown in FIG. 1 or FIG. Description is omitted.

The absolute value calculation unit 65 calculates the absolute value | C _j | of the feedback coefficient C _j output from the feedback coefficient calculation unit 66 for each transmission signal Tx (tj), and calculates the calculated absolute value | C _j | And output to the threshold generation unit 64 and the step coefficient calculation unit 69. The threshold creating unit 64 creates a threshold C _th for each predetermined period using samples of the feedback coefficient C _j corresponding to the first predetermined number of transmission signals Tx (tj) included in the predetermined period. Specifically, the threshold creating unit 64 creates the maximum value among the absolute values | C _j | of the feedback coefficients C _j corresponding to addresses larger than the threshold A _th as the threshold C _th . Then, the threshold creating unit 64 stores the created threshold C _th in the holding unit 63. The holding unit 63 stores the threshold value C _th created by the threshold value creating unit 64 for each transmission signal Tx (tj).

The step coefficient calculation unit 69 acquires the address generated by the address generation unit 52 for each transmission signal Tx (tj) having a different delay amount, and determines whether or not the value of the address is greater than a predetermined threshold _Ath. . If the address value is greater than the predetermined threshold A _th , the step coefficient calculation unit 69 outputs the step coefficient μ ₀ to the update unit 61.

On the other hand, when the address value is equal to or smaller than the predetermined threshold A _th , the step coefficient calculation unit 69 calculates the threshold C _th in the holding unit 63 and the absolute value | C _j | output from the absolute value calculation unit 65. For example, the step coefficient μ ₁ is calculated based on the above-described equation (8). Then, the step coefficient calculation unit 69 outputs the calculated step coefficient μ ₁ to the update unit 61.

Note that the threshold value creating unit 64, for each transmission signal Tx (tj), the average value C of the absolute values | C _j | of the feedback coefficients C _j corresponding to the transmission signal Tx (tj), as in the second embodiment. A value obtained by adding a predetermined offset C _off to _ave may be created as the threshold value C _th .

[Effect of Example 8]
As is apparent from the above description, in the distortion compensation apparatus 10 of the present embodiment, the threshold value creating unit 64 creates the threshold value C _th using the feedback coefficient C _j for each predetermined period. Further, when the value of the address of the transmission signal Tx (t) is equal to or less than the threshold value A _th , the step coefficient calculation unit 69 performs a step based on the ratio between the absolute value | C _j | of the feedback coefficient C _j and the threshold value C _th. Change the coefficient μ. Thereby, in the distortion compensation coefficient update process for a transmission signal having a small amplitude, the influence of noise can be suppressed low, and the quality of the signal transmitted from the distortion compensation apparatus 10 can be improved.

[hardware]
The distortion compensation apparatus 10 in the first to eighth embodiments described above is realized by hardware as shown in FIG. 22, for example. FIG. 22 is a diagram illustrating an example of hardware of the distortion compensation apparatus 10. For example, as illustrated in FIG. 22, the distortion compensation apparatus 10 includes an interface circuit 11, a memory 12, a processor 13, a wireless circuit 14, and an antenna 40.

  The interface circuit 11 is an interface for performing wired communication with the BB processing device. The radio circuit 14 includes a power amplifier 34 and the like. The radio circuit 14 performs processing such as up-conversion on the signal output from the processor 13, amplifies the processed signal by the power amplifier 34, and transmits it from the antenna 40. Further, the radio circuit 14 performs processing such as down-conversion on a part of the signal amplified by the power amplifier 34 and feeds back the processed signal to the processor 13. The radio circuit 14 includes, for example, a DAC 31, a mixer 32, an oscillator 33, a power amplifier 34, a coupler 35, a mixer 36, an ADC 37, and the like.

  The memory 12 stores, for example, various programs and data for realizing the functions of the distortion compensation unit 50 and the coefficient update unit 60. The processor 13 implements the functions of the distortion compensation unit 50 and the coefficient update unit 60, for example, by executing the program read from the memory 12.

  22 includes one processor 13, one radio circuit 14, and one antenna 40. However, the processor 13, the radio circuit 14, and the antenna 40 each include the distortion compensation apparatus. Two or more each may be provided in 10.

  Further, not all programs and data in the memory 12 need be stored in the memory 12 from the beginning. For example, a program, data, or the like is stored in a portable recording medium such as a memory card inserted into the distortion compensation apparatus 10, and the distortion compensation apparatus 10 acquires and executes the program, data, etc. from such a portable recording medium. You may do it. In addition, the distortion compensation apparatus 10 acquires and executes the program from another computer or server device storing the program, data, etc. via a wireless communication line, public line, Internet, LAN, WAN, or the like. May be.

<Others>
The disclosed technology is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist.

For example, in Embodiments 1 to 4 and 8 described above, the threshold value C _th of the feedback coefficient C _j is created for each transmission signal Tx (tj), but the disclosed technique is not limited thereto. As another example, the threshold C _th created from the feedback coefficient C ₀ for the transmission signal Tx of the delay amount is 0 (t) is also used as a threshold C _th of the transmission signal Tx of the other delayed signals (tj) Good. Thereby, the processing load _concerning creation of the threshold value C _th can be reduced.

Further, in each of the above-described embodiments, a distortion compensation coefficient is obtained for each amplitude or power of a transmission signal, and a method of performing distortion compensation using the obtained distortion compensation coefficient (LUT method) has been described as an example. The disclosed technique is not limited to this. For example, in the case of a method (series method) in which a distortion compensation coefficient is not generated for each amplitude or power of a transmission signal but a distortion compensation signal is generated by series expansion using the amplitude or power of the transmission signal as an argument. Similarly, the disclosed technology can be applied. In the series method, for example, the distortion compensation signal u (t) is generated based on the following equation (9).
In the above equation (9), h _{i, j, k} is an example of a distortion compensation coefficient. h _{i, j, k} is updated by the coefficient updating unit 60 as needed.

In each of the above-described embodiments, the feedback coefficient C _j is calculated based on the above-described equation (3), but the disclosed technique is not limited thereto. The feedback coefficient C _j may be calculated based on the following formula (10) or formula (11), for example.

Similarly, in each of the above-described embodiments, the feedback coefficient C ₀ is calculated based on the above-described equation (4), but the disclosed technique is not limited thereto. The feedback coefficient C ₀ may be calculated based on, for example, the following expression (12) or (13).

In each of the embodiments described above, the address threshold _Ath is a fixed value, but the disclosed technique is not limited thereto. For example, according to the power of the distortion compensation signal is input to the power amplifier 34, of the two thresholds A _th different values, one threshold value A _th may be selected. Specifically, when the power value of the distortion compensation signal is equal to or greater than a predetermined threshold value P _th , the threshold value A _th having the larger value of the two threshold values A _th is selected, and the power value of the distortion compensation signal is selected. Is less than the threshold value P _th , the threshold value A _th having the smaller value is selected. The threshold value P _th is, for example, an intermediate value between the maximum value of power that can be input to the power amplifier 34 and the minimum value of power of the transmission signal input to the power amplifier 34, for example, 1 (maximum value−minimum value). / 2 is set. When the communication traffic is high, the power of the transmission signal input to the power amplifier 34 is increased, and when the communication traffic is low, the power of the transmission signal input to the power amplifier 34 is decreased. Therefore, the distortion compensation apparatus 10 can switch the threshold value A _th in accordance with a change in communication traffic.

DESCRIPTION OF SYMBOLS 10 Distortion compensation apparatus 11 Interface circuit 12 Memory 13 Processor 14 Radio | wireless circuit 20 RF digital part 30 RF analog part 31 DAC
32 Mixer 33 Oscillator 34 Power amplifier 35 Coupler 36 Mixer 37 ADC
40 Antenna 50 Distortion Compensation Unit 51 Distortion Compensation Processing Unit 52 Address Generation Unit 53 LUT
60 coefficient update unit 61 update unit 62 clip processing unit 63 holding unit 64 threshold generation unit 65 absolute value calculation unit 66 feedback coefficient calculation unit 67 subtractor 68 step coefficient switching unit 69 step coefficient calculation unit 70 point 71 point 80 feedback signal 81 transmission Signal 82 Range 83 Range

Claims (16)

In a distortion compensation device that compensates for distortion generated in a power amplifier,
A distortion compensation unit that generates a distortion compensation signal by performing a predetermined operation on the transmission signal using a distortion compensation coefficient, and inputs the generated distortion compensation signal to the power amplifier;
A calculation unit for calculating a feedback coefficient based on an output signal output from the power amplifier;
When the absolute value of the feedback coefficient calculated by the calculation unit is less than or equal to a threshold value, the feedback coefficient calculated by the calculation unit is output, and the absolute value of the feedback coefficient calculated by the calculation unit is larger than the threshold value A clip processing unit that outputs a feedback coefficient whose absolute value is equal to or less than the threshold;
A distortion unit, comprising: an update unit that updates the distortion compensation coefficient using an error between the transmission signal and the output signal, a predetermined step coefficient, and a feedback coefficient output from the clip processing unit. Compensation device. The clip processing unit
When the absolute value of the feedback coefficient calculated by the calculation unit is larger than the threshold, the absolute value is equal to or less than the threshold by multiplying the threshold by a value obtained by dividing the feedback coefficient by the absolute value of the feedback coefficient. The distortion compensation apparatus according to claim 1, wherein a coefficient is calculated.   The apparatus further comprises a threshold value calculation unit that calculates the threshold value based on an absolute value of the feedback coefficient calculated from the output signal corresponding to the transmission signal for each predetermined number of samples of the transmission signal. Item 3. The distortion compensation device according to Item 1 or 2. The threshold value calculation unit
Calculating a maximum value of an absolute value of a feedback coefficient calculated based on the output signal corresponding to the transmission signal having a magnitude greater than a predetermined value among a predetermined number of samples of the transmission signal as the threshold value; The distortion compensation apparatus according to claim 3, wherein The threshold value calculation unit
In a predetermined number of samples of the transmission signal, a value obtained by adding a predetermined offset to the average value of the absolute values of the feedback coefficients calculated based on the output signal corresponding to the transmission signal is calculated as the threshold value. The distortion compensation apparatus according to claim 3, wherein   The distortion compensation apparatus according to claim 1, further comprising a threshold value calculation unit that calculates the threshold value based on a magnitude of the transmission signal for each sample of the transmission signal. In a distortion compensation device that compensates for distortion generated in a power amplifier,
A distortion compensation unit that generates a distortion compensation signal by performing a predetermined operation on the transmission signal using a distortion compensation coefficient, and inputs the generated distortion compensation signal to the power amplifier;
A calculation unit for calculating a feedback coefficient based on an output signal output from the power amplifier;
An update unit that updates the distortion compensation coefficient using an error between the transmission signal and the output signal, a predetermined step coefficient, and the feedback coefficient;
The update unit
When updating the distortion compensation coefficient corresponding to the transmission signal whose magnitude is less than or equal to a predetermined value, the step coefficient used for updating the distortion compensation coefficient corresponding to the transmission signal whose magnitude is greater than the predetermined value A distortion compensation apparatus, wherein the distortion compensation coefficient is updated using the step coefficient having a small value. The update unit
Updating the distortion compensation coefficient using the step coefficient calculated based on the magnitude of the transmission signal when the distortion compensation coefficient corresponding to the transmission signal having a magnitude equal to or less than the predetermined value is updated; The distortion compensation apparatus according to claim 7. A step coefficient calculation unit that calculates the step coefficient based on a ratio between an absolute value of the feedback coefficient calculated from the output signal corresponding to the transmission signal and a predetermined constant for each predetermined number of samples of the transmission signal Further comprising
The update unit
The distortion compensation coefficient is updated using the step coefficient calculated by the step coefficient calculation unit when the distortion compensation coefficient corresponding to the transmission signal having a magnitude equal to or less than the predetermined value is updated. The distortion compensation apparatus according to claim 7.   Threshold calculation for calculating the maximum value of the absolute value of the feedback coefficient calculated based on the output signal corresponding to the transmission signal whose magnitude is larger than a predetermined value among the predetermined number of samples of the transmission signal as the constant The distortion compensation apparatus according to claim 9, further comprising a unit.   Threshold calculation for calculating, as the constant, a value obtained by adding a predetermined offset to an average value of absolute values of feedback coefficients calculated based on the output signal corresponding to the transmission signal in a predetermined number of samples of the transmission signal The distortion compensation apparatus according to claim 9, further comprising a unit.   The distortion compensation apparatus according to any one of claims 4, 6, 7, 8, 9, and 10, wherein the magnitude of the transmission signal is an amplitude or power of the transmission signal. The distortion compensation unit
A table for storing the distortion compensation coefficient;
The distortion compensation apparatus according to claim 1, further comprising: a multiplication unit configured to generate the distortion compensation signal by multiplying the transmission signal by the distortion compensation coefficient. The distortion compensation unit
The distortion compensation apparatus according to claim 1, wherein the distortion compensation signal is generated by series-expanding the transmission signal using the distortion compensation coefficient. In a coefficient updating method executed by a distortion compensator that compensates for distortion generated in a power amplifier,
The distortion compensator is
A distortion compensation signal is generated by performing a predetermined operation on the transmission signal using a distortion compensation coefficient, and the generated distortion compensation signal is input to the power amplifier.
Calculate a feedback coefficient based on the output signal output from the power amplifier,
When the absolute value of the calculated feedback coefficient is less than or equal to the threshold value, the calculated feedback coefficient is output,
When the absolute value of the calculated feedback coefficient is larger than the threshold, a feedback coefficient that outputs the absolute value equal to or less than the threshold is output.
A coefficient updating method, comprising: performing a process of updating the distortion compensation coefficient using an error between the transmission signal and the output signal, a predetermined step coefficient, and the feedback coefficient. In a coefficient updating method executed by a distortion compensator that compensates for distortion generated in a power amplifier,
The distortion compensator is
A distortion compensation signal is generated by performing a predetermined operation on the transmission signal using a distortion compensation coefficient, and the generated distortion compensation signal is input to the power amplifier.
Calculate a feedback coefficient based on the output signal output from the power amplifier,
Using the error between the transmission signal and the output signal, a predetermined step coefficient, and the feedback coefficient, a process of updating the distortion compensation coefficient is executed,
In the updating process,
When updating the distortion compensation coefficient corresponding to the transmission signal whose magnitude is less than or equal to a predetermined value, the step coefficient used for updating the distortion compensation coefficient corresponding to the transmission signal whose magnitude is greater than the predetermined value A coefficient updating method, wherein the distortion compensation coefficient is updated using the step coefficient having a small value.