Wireless transmitter

Abstract

The present invention provides a wireless transmitter capable of automatically controlling the switching of distortion compensation operations. [Solution] An IF-TTL according to one embodiment of the present invention comprises a power amplifier 29 that amplifies the power of an input signal, a pre-distortion compensator 25 positioned in front of the power amplifier 29 and performing distortion compensation for distortion generated by the power amplifier 29, and a bit determination circuit 31 that determines whether or not there is a time variation in the input signal based on the state of a predetermined bit position when the input signal is represented in bits, and controls the pre-distortion compensator 25 so that distortion compensation is not performed when it is determined that there is no time variation in the input signal (i.e., when the input signal is determined to be CW).

Description

[[Technical Field]]

[0001] The present invention relates to a wireless transmission device that amplifies and transmits OFDM modulated waves. [[Background Art]]

[0002] Conventionally, wireless transmission devices such as broadcast wave repeaters and IF (Intermediate Frequency)-TTL (Transmitter to Transmitter Link) devices have been used in terrestrial digital broadcasting systems. In wireless transmission devices for terrestrial digital broadcasting, an OFDM (Orthogonal Frequency Division Multiplexing) modulated signal is used as the modulation signal.

[0003] An OFDM modulated signal has a large PAPR (Peak to Average Power Ratio) of about 12 dB, and is greatly affected by the non-linear characteristics of a power amplifier. Therefore, in these wireless transmission devices, a built-in pre-distortion compensator arranged at the front stage of the power amplifier is used to perform distortion compensation on distortion caused by the non-linear characteristics of the power amplifier. As an input signal to the pre-distortion compensator, a modulated wave such as an OFDM modulated wave is normally input, but a CW (Continuous Wave) may also be input for purposes such as data measurement. However, when the input signal changes from a modulated wave to CW, the distortion compensation operation by the pre-distortion compensator rarely diverges, which may result in excessive output.

[0004] Conventional techniques related to the present invention include the following. For example, Patent Document 1 discloses an invention in which a coefficient related to third-order intermodulation distortion, a coefficient related to fifth-order intermodulation distortion, and a coefficient related to seventh-order intermodulation distortion are calculated from an error signal obtained by taking the difference between an input signal and an output signal of a power amplifier and the input signal, and a distortion compensation signal having an opposite phase with respect to the phase and gain of intermodulation distortion is generated according to these coefficients. [[Prior Art Literature]] [[Patent Literature]]

[0005] [Patent Document 1] Japanese Patent Publication No. 2010-183633 [Overview of the project] [Problems that the invention aims to solve]

[0006] Figure 1 shows an example configuration of an IF-TTL, which is an example of a conventional wireless transmission device. The illustrated IF-TTL includes an SG (Signal Generator) 11, a pre-distortion compensator 12, a frequency converter 13, a power amplifier 14, and a BPF (Band Pass Filter) 15. The SG 11 is a device connected for data measurement, and an OFDM modulated wave or CW signal is input from the SG 11 as the signal for measurement.

[0007] When changing the signal input from SG11 from OFDM modulated wave to CW, it is necessary to switch the distortion compensation operation to "stop" or "none (disabled)" beforehand to prevent the distortion compensation operation from diverging and resulting in excessive output. Furthermore, after changing the signal input from SG11 back from CW to OFDM modulated wave, it is necessary to switch the distortion compensation operation back to "start" or "on (enabled)" to resume it. However, providing the control signal to the pre-distortion compensator to control the switching of the distortion compensation operation required the user to manually or remotely operate the radio transmitter, which was a cumbersome task for the user.

[0008] This invention has been made in view of the above-mentioned conventional circumstances, and aims to provide a wireless transmission device capable of automatically controlling the switching of distortion compensation operation. [Means for solving the problem]

[0009] A wireless transmission device according to one aspect of the present invention is a wireless transmission device that amplifies and transmits an OFDM modulated wave, and is characterized by comprising: a power amplifier for amplifying the power of an input signal; a pre-distortion compensator arranged in front of the power amplifier and performing distortion compensation for distortion generated by the power amplifier; and a distortion compensation control unit that determines whether or not there is a time variation in the input signal and controls the pre-distortion compensator so that distortion compensation is not performed when it is determined that there is no time variation in the input signal.

[0010] In the above-described wireless transmission device, the distortion compensation control unit can determine whether or not there is a time variation in the input signal based on the state of a predetermined bit position when the input signal is represented in bits.

[0011] Furthermore, in the above-described wireless transmission device, the predetermined bit position may be a bit position where the bit value is "1" when the input signal is an OFDM modulated wave, and where the bit value is always "0" when the input signal is a continuous wave.

[0012] Furthermore, in the above-described wireless transmission device, the distortion compensation control unit can determine whether or not there is a time variation in the input signal based on the state of the derivative value obtained by performing a differential operation on the input signal.

[0013] Furthermore, in the above-described wireless transmission device, the distortion compensation control unit can determine whether or not there is a time variation in the input signal based on the state of a predetermined bit position when the input signal is represented in bits and the state of the derivative value obtained by performing a differential operation on the input signal. [Effects of the Invention]

[0014] According to the present invention, it is possible to provide a wireless transmission device that can automatically control the switching of distortion compensation operations. [Brief explanation of the drawing]

[0015] [Figure 1] This figure shows an example of a conventional IF-TTL configuration. [Figure 2]This figure shows an example of the IF-TTL configuration according to the first embodiment. [Figure 3] This figure shows example waveforms of the real and imaginary components of an OFDM modulated or continuous wave baseband signal. [Figure 4] This figure shows an example waveform where the real and imaginary components of an OFDM modulated or continuous wave baseband signal have been replaced with bitwise representations. [Figure 5] This figure shows an example of the IF-TTL configuration according to the second embodiment. [Figure 6] This figure shows an example of the waveform of the derivative obtained by differentiating the real and imaginary components of an OFDM modulated or continuous wave baseband signal. [Figure 7] This figure shows an example of the IF-TTL configuration according to the third embodiment. [Modes for carrying out the invention]

[0016] This invention focuses on the fact that OFDM modulated waves fluctuate rapidly over time, while CW (continuous wave) waves fluctuate very little over time. In general terms, it determines whether an input signal is an OFDM modulated wave or a CW wave by checking for the presence or absence of time fluctuations in the input signal, and automatically switches the distortion compensation operation according to the result. The invention will be described in detail below with reference to several embodiments. In the following explanation, IF-TTL will be used as an example, but this invention can also be applied to other types of wireless transmission devices that amplify and transmit OFDM modulated waves (for example, broadcast wave relay devices).

[0017] (First embodiment) Generally, while the PAPR of an OFDM modulated wave is approximately 12 dB, the PAPR of a CW is approximately 3 dB. The first embodiment utilizes this property to distinguish between an OFDM modulated wave and a CW. Fig. 1 shows a configuration example of an IF-TTL according to the first embodiment. The illustrated IF-TTL includes an SG21, an AGC (Automatic Gain Control) circuit 22, an ADC (Analog to Digital Converter) 23, a quadrature demodulator 24, a predistortion compensator 25, a quadrature modulator 26, a DAC (Digital to Analog Converter) 27, a frequency converter 28, a power amplifier 29, a BPF 30, and a bit decision circuit 31.

[0018] The SG21 is a device connected for data measurement, and an OFDM modulated wave or a CW is input from the SG21 as a measurement signal. The signal input from the SG21 is controlled to have a constant RMS (Root Mean Square) via the AGC circuit 22, and then converted from an analog signal to a digital signal by the ADC 23. The signal converted into a digital signal is converted into a baseband signal through quadrature demodulation processing by the quadrature demodulator 24. The predistortion compensator 25 performs distortion compensation processing on the signal converted into the baseband signal to compensate for distortion generated in the power amplifier 29. The signal after the distortion compensation processing undergoes quadrature modulation processing by the quadrature modulator 26, and is then converted from a digital signal to an analog signal by the DAC 27. The signal converted into an analog signal undergoes frequency conversion by the frequency converter 28, is then power-amplified by the power amplifier 29, and is output from an antenna via the BPF 30.

[0019] Here, the baseband signal output from the quadrature demodulator 24 will be described. FIG. 3 shows waveform examples of real components and imaginary components of a baseband signal of an OFDM modulated wave or a continuous wave. In FIG. 3, (a) is a waveform example related to the real component of the baseband signal of the OFDM modulated wave, (b) is a waveform example related to the imaginary component of the baseband signal of the OFDM modulated wave, (c) is a waveform example related to the real component of the CW baseband signal, and (d) is a waveform example related to the imaginary component of the CW baseband signal. The effective value of any of these signals is 8192, but since they are displayed separately for the real component and the imaginary component, they appear to be multiplied by 1 / √2. According to FIG. 3, in the case of CW, the signal value is stable at approximately 5800, whereas in the case of an OFDM modulated wave, the signal value fluctuates greatly and may exceed 20,000.

[0020] FIG. 4 shows waveform examples obtained by replacing the real components and imaginary components of the baseband signal of an OFDM modulated wave or a continuous wave with bit representation. In FIG. 4, (a) is a waveform example related to the real component of the baseband signal of the OFDM modulated wave, (b) is a waveform example related to the imaginary component of the baseband signal of the OFDM modulated wave, (c) is a waveform example related to the real component of the CW baseband signal, and (d) is a waveform example related to the imaginary component of the CW baseband signal. Here, the vertical axis of the graph in FIG. 4 indicates the minimum number of bits required to represent the signal value of each component in bits. In other words, when the signal value of each component is represented in bits, it indicates the maximum value of the position of a bit whose bit value is "1".

[0021] As shown in Figure 4, in the case of CW, there is a signal up to the 12th bit, but no signal from the 13th bit onward. In contrast, in the case of OFDM modulated waves, there is a signal up to the 14th bit. Therefore, if there is a signal only up to the 12th bit, it should be determined to be CW, and otherwise it should be determined to be an OFDM modulated wave. Accordingly, the bit determination circuit 31 determines whether it is an OFDM modulated wave or CW by observing the bit representation of the baseband signal output from the quadrature demodulator 24.

[0022] Because the time variation of OFDM modulated waves is extremely fast, if it can be confirmed that a signal value with 13 or more bits used occurs a predetermined number of times within a very small time frame (e.g., 1 microsecond), it can be said to be an OFDM modulated wave; otherwise, it is CW. Whether or not a signal value has 13 or more bits used can be determined by various methods. For example, by observing the 13th bit of the bit representation value, if the bit value is "1", it can be determined that the signal value has 13 or more bits used. As another example, by identifying the maximum value of the bit position with a bit value of "1", if the maximum value is greater than or equal to a threshold (=13), it can be determined that the signal value has 13 or more bits used.

[0023] In this example, the 13th bit value is observed to make a determination, but any bit position that can accurately determine whether the signal is OFDM modulated or CW should be observed, and the observed bit position will vary depending on the system environment, etc. The observed bit position is, for example, a bit position where the bit value can be "1" when the input signal is OFDM modulated, and a bit position where the bit value is always "0" when the input signal is CW. Furthermore, there may be multiple observed bit positions; for example, a predetermined number of bit positions from the 13th bit onward may be observed, and if any of the bit values ​​are "1", it may be determined that the signal value uses 13 bits or more.

[0024] The bit determination circuit 31 provides a control signal to the pre-distortion compensator 25 to switch distortion compensation to "off (disabled)" when it detects a change from OFDM modulated wave to CW. It also provides a control signal to the pre-distortion compensator 25 to switch distortion compensation operation to "on (enabled)" when it detects a change from CW to OFDM modulated wave. Alternatively, instead of switching distortion compensation to "on" or "off," the distortion compensation operation may be switched to "start" or "stop."

[0025] As described above, the IF-TTL according to the first embodiment includes a power amplifier 29 that amplifies the power of the input signal, a pre-distortion compensator 25 positioned before the power amplifier 29 and performing distortion compensation for distortion generated by the power amplifier 29, and a bit determination circuit 31 that determines whether or not there is a time variation in the input signal based on the state of predetermined bit positions when the input signal is represented in bits, and controls the pre-distortion compensator 25 so that distortion compensation is not performed when it is determined that there is no time variation in the input signal (i.e., when the input signal is determined to be CW). With this configuration, it is possible to accurately and quickly determine whether the input signal is an OFDM modulated wave or CW, and to automatically switch the distortion compensation operation according to the result.

[0026] (Second example) Figure 5 shows an example of the configuration of an IF-TTL according to the second embodiment. The illustrated IF-TTL comprises an SG21, an AGC circuit22, an ADC23, a quadrature demodulator24, a pre-distortion compensator25, a quadrature modulator26, a DAC27, a frequency converter28, a power amplifier29, a BPF30, and a differential decision circuit32. In other words, the IF-TTL according to the second embodiment is configured to include a differential decision circuit32 instead of the bit decision circuit31 in the IF-TTL according to the first embodiment.

[0027] In the second embodiment, differentiation is used to determine whether the signal is OFDM modulated or CW. Figure 6 shows examples of waveforms of the derivative values ​​obtained by differentiating the real and imaginary components of the baseband signal of an OFDM modulated or continuous wave. In Figure 6, (a) is an example of a waveform related to the real component of the baseband signal of an OFDM modulated wave, (b) is an example of a waveform related to the imaginary component of the baseband signal of an OFDM modulated wave, (c) is an example of a waveform related to the real component of the baseband signal of a CW, and (d) is an example of a waveform related to the imaginary component of the baseband signal of a CW.

[0028] As is clear from Figure 6, in the case of CW, the derivative value is almost zero because there is no fluctuation in the signal value, whereas in the case of OFDM modulated waves, the derivative value can exceed 4000 because the fluctuation in the signal value is large. Therefore, the derivative determination circuit 32 determines whether it is an OFDM modulated wave or CW by observing the derivative value obtained by differentiating the baseband signal output from the quadrature demodulator 24. Since the time fluctuation of OFDM modulated waves is very fast, if it can be confirmed that a derivative value of a threshold (e.g., 1000) or more occurs a predetermined number of times within a very small time frame (e.g., 1 μs), it can be said that it is an OFDM modulated wave; otherwise, it is CW.

[0029] The differential decision circuit 32 provides a control signal to the pre-distortion compensator 25 to switch distortion compensation to "off (disabled)" when it detects a change from OFDM modulated wave to CW. It also provides a control signal to the pre-distortion compensator 25 to switch distortion compensation operation to "on (enabled)" when it detects a change from CW to OFDM modulated wave. Alternatively, instead of switching distortion compensation to "on" or "off," the distortion compensation operation could be switched to "start" or "stop."

[0030] As described above, the IF-TTL according to the second embodiment includes a power amplifier 29 that amplifies the power of the input signal, a pre-distortion compensator 25 positioned before the power amplifier 29 to perform distortion compensation for distortion generated by the power amplifier 29, and a differential determination circuit 32 that determines whether or not there is a time variation in the input signal based on the state of the differential value obtained by differentiating the input signal, and controls the pre-distortion compensator 25 so that distortion compensation is not performed when it is determined that there is no time variation in the input signal (i.e., when the input signal is determined to be CW). With this configuration, it is possible to accurately and quickly determine whether the input signal is an OFDM modulated wave or CW, and to automatically switch the distortion compensation operation according to the result.

[0031] (Third embodiment) Figure 7 shows an example of the configuration of an IF-TTL according to the third embodiment. The illustrated IF-TTL includes an SG21, an AGC circuit22, an ADC23, a quadrature demodulator24, a pre-distortion compensator25, a quadrature modulator26, a DAC27, a frequency converter28, a power amplifier29, a BPF30, a bit decision circuit31, a differential decision circuit32, and a logic operation circuit33. In other words, the IF-TTL according to the third embodiment is a combination of the IF-TTL according to the first embodiment and the IF-TTL according to the second embodiment.

[0032] In the third embodiment, the bit determination circuit 31 determines whether the signal is an OFDM modulated wave or CW by observing the bit representation of the baseband signal output from the quadrature demodulator 24. The differential determination circuit 32 also determines whether the signal is an OFDM modulated wave or CW by observing the derivative obtained by differentiating the baseband signal output from the quadrature demodulator 24. Finally, the logic operation circuit 33 performs a logical AND operation of the determination results from the bit determination circuit 31 and the differential determination circuit 32 to make a final determination as to whether the signal is an OFDM modulated wave or CW. Specifically, if the bit determination circuit 31 determines that the signal is CW and the differential determination circuit 32 also determines that the signal is CW, the input signal from SG21 is determined to be CW; otherwise, the input signal from SG21 is determined to be an OFDM modulated wave.

[0033] The logic circuit 33 provides a control signal to the pre-distortion compensator 25 to switch distortion compensation to "off (disabled)" when a change from OFDM modulated wave to CW is detected. It also provides a control signal to the pre-distortion compensator 25 to switch distortion compensation operation to "on (enabled)" when a change from CW to OFDM modulated wave is detected. Alternatively, instead of switching distortion compensation to "on" or "off," the distortion compensation operation may be switched to "start" or "stop."

[0034] As described above, the IF-TTL according to the third embodiment includes a power amplifier 29 that amplifies the power of the input signal, a pre-distortion compensator 25 positioned before the power amplifier 29 and performing distortion compensation for distortion generated by the power amplifier 29, a bit determination circuit 31 that determines the state of a predetermined bit position when the input signal is represented in bits, a differential determination circuit 32 that determines the state of the differential value obtained by performing a differential operation on the input signal, and a logic operation circuit 33 that determines whether or not there is a time variation in the input signal based on the determination result of the bit determination circuit 31 and the determination result of the differential determination circuit 32, and controls the pre-distortion compensator 25 so that distortion compensation is not performed when it is determined that there is no time variation in the input signal (i.e., when the input signal is determined to be CW). With this configuration, it is possible to accurately and quickly determine whether the input signal is an OFDM modulated wave or CW, and to automatically switch the distortion compensation operation according to the result.

[0035] Although embodiments of the present invention have been described above, these embodiments are merely illustrative and do not limit the technical scope of the present invention. The present invention can take many other embodiments, and various modifications such as omissions and substitutions can be made without departing from the spirit of the invention. These embodiments and their variations are included in the scope and spirit of the invention as described herein, and are included in the scope of the invention and its equivalents as described in the claims.

[0036] Furthermore, the present invention can be provided not only as the devices described above or as systems composed of such devices, but also as methods executed by these devices, programs for a processor to realize the functions of these devices, and storage media for storing such programs in a computer-readable manner. [Industrial applicability]

[0037] The present invention can be used in a wireless transmitting device that amplifies and transmits OFDM modulated waves. [Explanation of Symbols]

[0038] 11: SG, 12: Pre-distortion compensator, 13: Frequency converter, 14: Power amplifier, 15: BPF, 21: SG, 22: AGC circuit, 23: ADC, 24: Quadrature demodulator, 25: Pre-distortion compensator, 26: Quadrature modulator, 27: DAC, 28: Frequency converter, 29: Power amplifier, 30: BPF, 31: Bit decision circuit, 32: Differential decision circuit, 33: Logic operation circuit

Claims

1. In a wireless transmitting device that amplifies and transmits OFDM modulated waves, A power amplifier that amplifies the power of the input signal, A pre-distortion compensator is placed in front of the power amplifier and performs distortion compensation related to the distortion generated by the power amplifier, A wireless transmission device comprising: a distortion compensation control unit that determines whether or not there is a time variation in the input signal, and controls the pre-distortion compensator so that distortion compensation is not performed when it is determined that there is no time variation in the input signal.

2. In the wireless transmission device according to claim 1, The distortion compensation control unit is characterized by determining whether or not there is a time variation in the input signal based on the state of a predetermined bit position when the input signal is represented in bits.

3. In the wireless transmission device according to claim 2, The wireless transmission device is characterized in that the predetermined bit position is a bit position where the bit value can be "1" when the input signal is an OFDM modulated wave, and a bit position where the bit value is always "0" when the input signal is a continuous wave.

4. In the wireless transmission device according to claim 1, The strain compensation control unit is characterized by determining whether or not there is a time variation in the input signal based on the state of the derivative value obtained by performing a differential operation on the input signal.

5. In the wireless transmission device according to claim 1, The distortion compensation control unit is characterized by determining whether or not there is a time variation in the input signal based on the state of a predetermined bit position when the input signal is represented in bits and the state of the derivative value obtained by performing a differential operation on the input signal.

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