JP2012175573A - Microwave transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact, lower-power-consumption microwave transmission device with a distortion compensating function.SOLUTION: Transmission data from a transmission data modulation processing part 1 is input to a DPD processing part 20, and a distortion-preprocessed digital signal is converted by a DAC 2 into an analog signal, which is input to a power amplifier 8 through a VGA 9. A signal generated by detecting a signal output by the power amplifier 8 by amplifying the input signal is input to the VGA 9 as a signal for gain control signal, the VGA 9 performs automatic gain control so that the input detection signal has a constant value to perform gain distortion compensation, a microwave wireless device is made small in device scale, and thus the microwave transmission device is provided which has low power consumption.

Description

  Embodiments described herein relate generally to a small-sized microwave transmission device used in a wireless relay device, a small wireless device, or the like.

  In recent years, the introduction of digital wireless communication devices has progressed, and in addition to mobile communication purposes such as LTE (Long Term Evolution), introduction to wireless relay devices that wirelessly relay broadband signals for the purpose of relaying digital broadcast program signals has also progressed. It is out. Since these broadband signals need to operate not only with a wide band but also with linearity, a distortion compensation circuit is incorporated. FF (Feed Forward) is known as an effective distortion compensation method for a high-frequency amplifier. The FF requires a sub-amplifier for extracting and amplifying the distortion component, a phase adjustment circuit for synthesizing the distortion component and the main signal, and the circuit scale becomes large. Instead, recently, predistortion compensation (PD) that compensates by changing output characteristics in advance according to the input level is used.

FIG. 6 is a block diagram showing an example of a configuration of a distortion compensation circuit used in a transmitter of a conventional microwave repeater.
In FIG. 6, a transmitter s1 performs predetermined processing in a transmission data modulation processing unit 1, performs analog conversion in a DAC (digital analog conversion unit) 2, and uses a quadrature modulator 3 and a local mixer 4 to perform, for example, QPSK using an IF signal. Etc. are applied. The modulated IF signal is further input to the mixer 7, converted to an RF signal having a transmission frequency by the mixer 5, and input to the power amplifier 8 through the BPF 6 and the predistortion circuit (PD) 100. As the predistortion circuit (PD) 100, a non-linear component such as a diode is inserted into the circuit to compensate for output distortion and the like. However, there is a disadvantage that the compensation range is not wide. Problems such as increased power will occur.

  In order to improve this and compensate distortion efficiently, DPD (Digital) to which a pre-distortion circuit that adds and amplifies the required distortion by referring to the table data corresponding to the input level in advance is added. Pre-Distortion) is adopted. By monitoring this output and referring to the correction data table, an adaptive (compensation) DPD (for example, Patent Document 1) that performs processing more accurately in a wider range may be introduced.

  However, since ADPD compares and references the digital data whose output is monitored with the compensation data stored in the memory, the same receiving circuit and digital conversion circuit as the receiver are required for monitoring. In addition, there is a problem in miniaturization and efficiency improvement due to power consumption.

JP 2001-285091 A

  Since the transmitter using the conventional ADPD method compares and references the digital data whose output is monitored with the compensation data stored in the memory, the same receiving circuit and digital conversion circuit as the receiver are required for monitoring. Since the scale of the apparatus increases and power consumption occurs, there are problems in miniaturization and efficiency improvement.

  The present invention has been made to solve the above problems, and an object of the present invention is to provide a microwave transmitter having a small and low power consumption and a distortion compensation function.

  In order to achieve the above object, the microwave transmission device of the present embodiment includes an input digitally encoded transmission signal, and an LUT in which data for predistortion compensation of the input transmission signal is stored. In a microwave transmission apparatus that amplifies and transmits a transmission signal that has been subjected to predistortion compensation on the input transmission signal by comparing and referring to the above, the input transmission signal that has been subjected to predistortion compensation is subjected to power amplification and output. A power amplifier, a detection signal output means for outputting a detection signal obtained by detecting a part of the output of the power amplifier, a temperature sensor for outputting temperature data obtained by measuring the temperature of the power amplifier, and the predistortion compensation. The LUT storing the data to be processed as a list corresponding to changes in the temperature data, the digitally encoded transmission signal, and the temperature data are input. A DPD processing unit that checks the level of the input transmission signal and the temperature data, and outputs the digital transmission signal that has been predistorted and compared to the LUT to the power amplifier; and the predistortion compensation The modulated digital transmission signal is input, the modulation means for converting the input digital transmission signal into an analog transmission signal subjected to the required modulation, and the detection signal is input as a gain control signal. A gain adjusting means for controlling a gain for amplifying the analog transmission signal to be output to the power amplifier so that the reception level of the detection signal is a predetermined level that is inserted between a modulation means and the power amplifier. It is characterized by comprising.

The functional block diagram of the microwave transmitter concerning the Example of this invention. The functional block diagram of the 1st modification of the microwave transmitter concerning the Example of this invention. The functional block diagram of the 2nd modification of the microwave transmitter concerning the Example of this invention. The block diagram which shows the structural example which performs the APC loop of the microwave transmitter concerning the Example of this invention digitally. The functional block diagram of the digital processing APC loop comprised on a small scale. The block diagram which shows one example of a structure of the distortion compensation circuit used for the transmitter of the conventional microwave relay apparatus.

  Embodiments of the present invention will be described below with reference to the drawings.

  In mobile phone base stations with a transmission output of several tens of watts, an adaptive digital predistorter (ADPD) method is used to compensate for distortion characteristics of the power amplifier at the final stage, and distortion compensation accuracy and compensation amount Both are excellent, but there is a problem that the structure of the apparatus becomes complicated and expensive. In addition, in the ADPD method, the RF receiver circuit and signal processing to be mounted for performing distortion detection consume about several watts of power, and the transmission output power as a target of the present invention is a small microwave of about several watts or less. In the transmission apparatus, there is a case where an effect for reducing power consumption cannot be obtained.

  The microwave transmission device according to the embodiment of the present invention is applied to a microwave transmission device in which the number of transmission carriers and the transmission power are constant at about several W, such as a relay device. The DPD processing unit stores distortion compensation data acquired in advance in an LUT (Look Up Table), and adds and multiplies compensation data as a fixed coefficient to the modulation data for transmission to obtain power. A DPD that compensates for distortion generated in an amplifier, and is hereinafter referred to as a fixed coefficient DPD. Therefore, although the distortion compensation performance of the fixed coefficient type DPD is inferior to that of the ADPD system, it is unnecessary to observe the output distortion of the transmission power amplifier in real time and to obtain distortion compensation data by calculation as in the ADPD system. The structure becomes simple and the power consumption of the processing circuit can be suppressed.

FIG. 1 is a functional block diagram of a microwave transmission apparatus according to an embodiment of the present invention.
In FIG. 1, a microwave transmission device S includes a transmission data modulation processing unit 1, a DAC (digital / analog conversion unit) 2, a quadrature modulator 3, a local oscillator 4, a local oscillator 5, a BPF 6, a mixer 7, and a power amplifier (PA). 8, a VGA (variable gain amplifier) 9, a detector 10, a coupler 11, a DPD (Digital Pre-distortion) processing unit 20, a temperature sensor 21, and an LUT (look-up table) 22.

  Although the description of the parts having the same circuit configuration as that of the transmitter s1 in FIG. 6 is omitted, a DPD processing unit 20 is inserted between the transmission data modulation processing unit 1 and the DAC 2, and the output of the quadrature modulator 3 is VGA 9 And the output of VGA9 is input to PA8. Temperature information is input to the DPD processing unit 20 from the temperature sensor 21 attached in the vicinity of the PA 8.

  The transmission data modulation processing unit 1 converts input transmission data into digital data such as I-phase data and Q-phase data for generating a modulation signal such as PSK or QAM in the quadrature modulator 3. The converted transmission data is input to the DPD processing unit 20.

  The DPD processing unit 20 reads the data for setting the distortion compensation amount for the transmission data signal input from the transmission data modulation processing unit 1 written in advance in the LUT 22 in an internal memory (not shown), performs arithmetic processing, and performs PA8. Distortion compensation is performed to reduce the output distortion. In this distortion compensation, a plurality of compensation amounts corresponding to temperature information input from the temperature sensor 21 are selected from the distortion compensation pattern candidate data prepared in the LUT 22, and the phase distortion change accompanying the temperature change in the PA 8 is corrected.

  Data subjected to distortion compensation calculation by the DPD processing unit 20 is converted from a digital signal to an analog signal by the DAC 2. The quadrature modulator 3 performs quadrature modulation on the analog signal input from the DAC 2 by the IF band local oscillation signal output from the IF processing local oscillator 4 and outputs the result as an IF band signal. The IF band signal is input to a variable gain amplifier (VGA) 9 and is input to the mixer 7 after gain adjustment.

  The mixer 7 frequency-converts the IF band signal into an RF band signal by the RF conversion local signal input from the RF conversion local oscillator 5. The RF band signal is filtered by a bandpass filter (BPF) 6 to remove unwanted signals out of the band, such as local signal leakage and image waves generated during frequency conversion, and the power amplifier (PA) 8 The RF signal from which noise is removed is input, amplified to a required power, and output.

  A part of the RF signal output from the PA 8 is extracted as a monitor signal by the coupler 11 and input to the detector 10. The signal detected by the detector 10 is input to the control signal input terminal of the VGA 9, and the VGA 9 adjusts the gain so that the level of the detection signal is constant, in other words, the RF signal transmission output is constant. . That is, an APC (automatic power control) circuit is constituted by the coupler 11, the detector 10, and the VGA 9, and the gain distortion compensation in the DPD 20 is further compensated.

  Further, the gain change of the power amplifier due to the temperature change can be suppressed small by the amplifier circuit configuration, and the change at the single component level such as the mixer can also be compensated by configuring the APC circuit. In this way, by combining the APC processing at the final stage, it is possible to accurately compensate for distortion by incorporating changes in the output signal in the same manner as ADPD with small size and low power consumption.

  The present invention may change the combination of configuration and processing procedure without departing from the above gist.

2 and 3 are functional block diagrams illustrating first and second modifications of the microwave transmission device.
In FIG. 1, a feedback loop in which the mixer 7 is connected to the output side of the VGA 9 is configured. However, in the example shown in FIG. 2, the frequency conversion to the IF frequency is not performed and the mixer 7 is omitted. The present invention is also applicable to a method of inserting the VGA 9 after the mixer 7 as in the example shown in FIG.

FIG. 4 is a block diagram illustrating an example of a configuration of a microwave transmission device that digitally executes an APC loop.
The microwave transmission device shown in FIG. 4 is provided with an analog-digital converter (ADC) 91, a coefficient generation unit 92, and a multiplier 93 in addition to the configuration shown in FIG. The configuration and processing procedure are basically the same as those of the microwave transmitter of FIG. 1 except that digital processing and the VGA 9 operate as a driver amplifier having a fixed gain value.

  A signal obtained by detecting the output of PA 1 is digitally converted by the ADC 91 and input to the coefficient generation unit 92. The coefficient generation unit 92 examines a table (not shown) that stores a corresponding gain coefficient that corrects a difference between the digitally converted signal and a preset value to, for example, “0”. The gain coefficient is selected and input to the multiplier 93 so as to become (match). That is, when there is a difference from a preset value, the multiplier 93 generates a coefficient for increasing or decreasing the input with respect to the input, and outputs the coefficient to the multiplier 93 so that the difference becomes zero. APC processing is executed in between. In the case of FIG. 1, the VGA 9 performs gain adjustment, whereas in the microwave transmission device of FIG. 4, the coefficient generation unit 92 and the multiplier 93 perform processing corresponding to input level adjustment, that is, gain adjustment.

  FIG. 5 is a functional block diagram of a digital processing APC loop configured on a small scale.

  In FIG. 5, the microwave transmission device is provided with a gate comparator 94 instead of the ADC 91 of FIG. 4. Here, the gate comparator 94 outputs determination information of “+1” to the coefficient generation unit 95 when it is larger than a predetermined level, for example, “−1” when it is smaller.

  When the determination information “+1” is input, the coefficient generation unit 92 is a fixed coefficient that reduces the multiplication coefficient corresponding to the amplification degree with respect to the input level by the multiplier, for example, “0.9”. Is input to the multiplier 93. On the other hand, when it is “−1”, a fixed coefficient to be increased as “1.1” is input to the multiplier 93. This method is advantageous in that it does not use an AD converter as compared with the method shown in FIG.

  Thus, a small microwave transmission device can be realized by combining the APC processing and the fixed coefficient DPD.

  Fixed coefficient type DPD has the effect of accurately compensating for phase distortion, but if combined with gain change compensation caused by temperature change, etc., the number of combinations of phase distortion and amplitude distortion becomes enormous, and computation and control become complicated. . In the microwave transmission apparatus of the present embodiment, the DPD processing unit 20 may mainly perform phase compensation, and gain (amplitude) distortion may be mainly compensated by APC at the subsequent stage. In that case, the microwave transmission device compensates the gain change accompanying the temperature change by the APC processing using the simple gain control that makes the detection signal level of the output monitor constant, and accurately corrects the phase distortion with a small-scale DPD. Let me compensate. As a result, the circuit becomes smaller, and the power amplifier at the final stage can be made smaller and consume less power than the FF system.

1 Transmission Data Modulation Processing Unit 2 DAC (Digital / Analog Conversion Unit)
3 Quadrature modulator 4 (for IF processing) local oscillator 5 (for RF conversion) local oscillator 6 BPF
7 Mixer 8 Power amplifier (PA)
9 VGA (Variable Gain Amplifier)
DESCRIPTION OF SYMBOLS 10 Detector 11 Coupler 20 DPD processing part 21 Temperature sensor 22 LUT (Look-up table)
91 ADC (analog / digital converter)
92 Coefficient Generator 93 Multiplier 94 Gate Comparator

Claims (5)

The input transmission signal is predistorted by comparing and referring to the input digitally encoded transmission signal and the LUT storing data for predistortion compensation of the input transmission signal. In the microwave transmission device that amplifies the transmission signal and transmits it,
A power amplifier that amplifies and outputs the input predistortion-compensated transmission signal;
A detection signal output means for outputting a detection signal obtained by detecting a part of the output of the power amplifier; and
A temperature sensor that measures the temperature of the power amplifier and outputs the measured temperature data;
An LUT storing the data for performing the pre-distortion compensation as a list corresponding to the change of the temperature data;
The digitally encoded transmission signal and the temperature data are input, the level of the input transmission signal and the temperature data are examined, and the predistortion compensated digital transmission signal is compared with the LUT. A DPD processing unit that generates and outputs to the power amplifier;
Modulation means for inputting the predistortion compensated digital transmission signal, converting the input digital transmission signal to an analog transmission signal subjected to required modulation, and outputting the analog transmission signal;
The analog signal that is input as a gain control signal, is inserted between the modulation means and the power amplifier, and is output to the power amplifier so that a reception level of the detection signal becomes a predetermined level. A microwave transmitter comprising: gain adjusting means for controlling a gain for amplifying a transmission signal. Transmission in which the input transmission signal is predistorted by comparing and referring to the input digitally encoded transmission signal and the LUT in which data for predistortion compensation of the input transmission signal is stored. In a microwave transmission device that amplifies and transmits a signal,
A power amplifier that amplifies and outputs the input predistortion-compensated transmission signal;
A detection signal output means for outputting a detection signal obtained by detecting a part of the output of the power amplifier; and
A temperature sensor that outputs temperature data obtained by measuring the temperature of the power amplifier;
An LUT storing data for predistortion compensation as a list corresponding to changes in the temperature data;
The digitally encoded transmission signal and the temperature data are input, the level of the input transmission signal and the temperature data are examined, and the predistortion compensated digital transmission signal is compared with the LUT. An output DPD processing unit;
The predistortion compensated digital transmission signal from the DPD is input to one terminal, and the gain adjustment signal is input to the other terminal to adjust the predistortion compensated digital transmission signal to the power amplifier. Output multiplier,
Gain adjustment means for receiving the detection signal and generating a gain adjustment signal corresponding to the level of the detection signal so that the input detection signal becomes a predetermined level and outputting the gain adjustment signal to the multiplier When,
Modulation means for inputting the gain-adjusted digital transmission signal, converting the digital transmission signal into an analog transmission signal, generating a transmission signal obtained by performing a required modulation on the converted signal, and outputting the transmission signal to the power amplifier; A microwave transmitter characterized by that.   The microwave transmission device according to claim 1, wherein the transmission signal that is modulated and input to the power amplification device is converted to a frequency that is input to the post-modulation mixer and transmitted.   The microwave transmission apparatus according to claim 1 or 2, wherein the DPD mainly compensates for phase distortion, and mainly compensates for amplitude distortion by the gain adjusting means.   The gain adjusting means further includes a gate comparator for determining whether the level of the input detection signal is higher or lower than a predetermined value. When it is determined that the level is higher than the predetermined value, a gain is gained at a constant rate. A gain adjustment signal for reducing the gain is output to the multiplier, and when it is determined that the gain adjustment signal is lower than a predetermined value, a gain adjustment signal for increasing the gain at a constant rate is output to the multiplier. Item 3. The microwave transmission device according to Item 2.

Images