JP2015050484A - Distortion compensation device and transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent accuracy of estimation from degrading by average power changing within a frame in a DTMB system.SOLUTION: An identification signal generation part of a distortion compensation device generates an identification signal for identifying each frame header and frame body comprising a signal frame of an inputted broadcast transport stream of a DTMB system on the basis of each average power of the frame header and frame body and outputs it to a compensation part. The compensation part has a digital predistorter which superimposes distortion that has a distortion characteristic to be an opposite characteristic of the distortion characteristic of a power amplifier connected to a rear stage of a baseband signal corresponding to a broadcast transport stream, performs distortion estimation by using data corresponding to a data section of the same average power of signal frames on the basis of the output data of the digital predistorter, a feedback signal of a transmission signal outputted by the power amplifier, and an identification signal, and performs distortion compensation by the digital predistorter.

Description

  Embodiments described herein relate generally to a distortion compensation apparatus and a transmission apparatus.

  In a power amplifier (Power Amplifier: PA) that amplifies a linear modulation wave or a plurality of modulation waves, it is necessary to reduce nonlinear distortion as much as possible in order to suppress unnecessary radio wave (spurious) radiation and increase power efficiency. In order to solve this, various types of distortion compensation are used, and a digital predistortion system is known as one of them.

JP 2002-232325 A

  By the way, in the digital predistortion method, in order to estimate the distortion of the power amplifier from the original signal (transmission signal) and the feedback signal, the estimation process is performed when a continuous signal sequence of a certain length is used in the distortion estimation signal processing. In order to perform correctly, it is necessary to match the power (average power) of the original signal and the feedback signal used for signal processing.

  Even in the digital predistortion system, the average power does not change in a frame or between frames in the ISDB-T (Integrated Services Digital Broadcasting-Terrestrial) system, but in the DTMB (Digital Terrestrial Multimedia Broadcast) system, the frame header Are mapped by NRZ (Non-Return-to-Zero) BPSK, and the average power is twice that of the frame body (= data section).

  Here, since the length of the frame body is not constant, the DTMB method has a problem that when a signal sequence including a frame header is used for signal processing, an error in average power is large and a correct estimated value cannot be obtained.

  The present invention has been made in view of the above, and provides a distortion compensation apparatus and a transmission apparatus that can prevent estimation accuracy from deteriorating due to a change in average power in a frame in the DTMB scheme. It is intended to provide.

The identification signal generation unit of the distortion compensation apparatus according to the embodiment uses the frame header and the frame based on the average power of each of the frame header and the frame body constituting the signal frame of the input DTMB broadcast transport stream. An identification signal for identifying the body is generated and output to the compensation unit.
The compensation unit includes a digital predistorter that superimposes a distortion having a distortion characteristic opposite to that of the power amplifier connected to the subsequent stage on a baseband signal corresponding to the broadcast transport stream. Based on the output data, the feedback signal obtained by feeding back the transmission signal output from the power amplifier, and the identification signal, the data corresponding to the data section with the same average power is used for distortion estimation in the signal frame, and distortion estimation is performed. Distortion compensation is performed by a digital predistorter.

FIG. 1 is a schematic configuration block diagram of a transmission apparatus according to an embodiment. FIG. 2 is an explanatory diagram of a data format of a DTMB broadcast transport stream. FIG. 3 is an explanatory diagram of the relationship between the amplitude (power) of the signal frame SGF and time.

Next, embodiments will be described with reference to the drawings.
FIG. 1 is a schematic configuration block diagram of a transmission apparatus according to an embodiment.
The transmission device 10 is a DTMB (Digital Terrestrial Multimedia Broadcast) transmission device, and is roughly classified into a baseband I signal IBB, a baseband Q signal QBB, and encoding and digital modulation of a broadcast transport stream (TS). A modulation unit 11 that generates and outputs an identification signal FFTGP, which will be described later, a compensation unit 12 that compensates for nonlinear distortion of the power amplifier using a digital predistortion method, and a baseband I signal IBB that has been compensated for nonlinear distortion by the compensation unit 12 And a quadrature modulation unit 13 that performs quadrature amplitude modulation based on the baseband Q signal QBB and outputs a quadrature modulation signal, power amplification of the quadrature modulation signal output by the quadrature modulation unit 13, and transmission signal Power amplifier 14 that radiates into the space as a transmission radio wave (electromagnetic wave) A part of the transmission signal of the antenna 15 for transmission and the power amplifier 14 is detected as a feedback signal, and a quadrature demodulation unit 16 for quadrature demodulation and a reference signal for quadrature modulation to the quadrature modulation unit 13 are output, And a synthesizer 17 that outputs a reference signal for orthogonal demodulation to the demodulator 16.

  The compensation unit 12 generates a distortion having a reverse characteristic to the distortion characteristic of the power amplifier 14 using the baseband I signal IBB and the baseband Q signal QBB, the identification signal FFTGP described later, and the distortion estimation data Ddis described later. A digital predistorter 21 that outputs the distortion superimposed baseband I data xI and the distortion superimposed baseband Q data xQ superimposed on each of the I signal IBB and the baseband Q signal QBB; The first D / A converter 22-1 that performs analog conversion and outputs a distortion superimposed baseband I signal and the digital / analog conversion of the distortion superimposed baseband Q data xQ to output a distortion superimposed baseband Q signal By the second D / A converter 22-2 and the orthogonal demodulator 16 A first A / D converter 23-1 that performs analog / digital conversion of the demodulated feedback baseband I signal and outputs feedback baseband I data yI, and a feedback baseband Q signal demodulated by the quadrature demodulation unit 16 And a second A / D converter 23-2 that performs analog / digital conversion and outputs feedback baseband Q data yQ.

  Further, the compensation unit 12 receives the distortion superimposed baseband I data xI, the identification signal FFTGP, the distortion superimposed baseband Q data xQ, the feedback baseband I data yI, and the feedback baseband Q data yQ, and performs gain calculation. 24, the identification signal FFTGP, the distortion superimposed baseband I data xI and the distortion superimposed baseband Q data xQ are input, and the feedback baseband I data yI and the feedback baseband Q for the baseband I signal IBB and the baseband Q signal QBB are input. Based on the calculation result of the delay estimation / correction unit 25 that generates and outputs delay correction data xI_dlycmp and delay correction data xQ_dlycmp for estimating and correcting the delay amount (delay time) of the data yQ, Delay The gain correction unit 26 that outputs the data xI_dlycmp and the delay correction data xQ_dlycmp by performing gain correction, the delay correction data xI_dlycmp, the delay correction data xQ_dlycmp, the feedback baseband I data yI, and the feedback baseband Q data yQ that have been gain-corrected. And a distortion estimation unit 27 that estimates distortion characteristics of the power amplifier 14 and outputs distortion estimation data Ddis to the digital predistorter 21.

Here, prior to a specific operation description, a data format of a DTMB broadcast transport stream will be described.
FIG. 2 is an explanatory diagram of a data format of a DTMB broadcast transport stream.

As shown in FIG. 2, the DTMB system broadcast transport stream is configured as a calendar day frame CDF including 1440 minute frames MF0 to MF1439, corresponding to 24-hour continuous broadcasting.
The minute frames MF0 to MF1439 include 480 super frames SF0 to SF479, respectively.

  Further, each super frame SF0 to SF479 includes a first frame FF representing the head of each super frame SF0 to SF479 and a plurality of signal frames SGF having a frame length of 555.6 μsec, 578.703 μsec, or 625 μsec. .

  Here, the signal frame SGF includes a frame header FH representing the head of the signal frame SGF, and a frame body FB including a data block which is actual data of the broadcast data.

FIG. 3 is an explanatory diagram of the relationship between the amplitude (power) of the signal frame SGF and time.
As shown in FIG. 3, the frame header FH of the signal frame SGF converts the PN signal (pseudorandom signal) into NRZ (Non Return to Zero): 1 and 0 are “Hi” level or “Lo” level. It is represented by a voltage opposite to each other in voltage, and between encoded bits is mapped to a binary signal of a binary encoding system that does not return to a zero (reference) voltage, and RZ (Return to Zero [Return to Zero [ Zero return]: Binary encoding method in which 1 and 0 are represented by voltages opposite to each other of “Hi” level or “Lo” level voltage, and the encoded bits are returned to zero (reference) voltage) The signal has a power twice that of the frame body FB mapped to the binary signal.

  Therefore, in the present embodiment, the identification signal generation unit 11A provided in the modulation unit 11 calculates the average power per unit time of the signal frame SGF, and the signal frame SGF included in the input broadcast transport stream is calculated. An identification signal FFTGP for identifying the frame header FH and the frame body FB is generated.

Next, the operation of the embodiment will be described.
First, the modulation unit 11 performs encoding and digital modulation of a broadcast transport stream (TS) to generate a baseband I signal IBB and a baseband Q signal QBB.
In parallel with this, the identification signal generator 11A calculates the average power per unit time of the signal frame SGF, and calculates the frame header FH and the frame body FB of the signal frame SGF included in the input broadcast transport stream. An identification signal FFTGP for identification is generated.
Then, the modulation unit 11 outputs the generated baseband I signal IBB, baseband Q signal QBB, and an identification signal FFTGP described later to the digital predistorter 21.

  The digital predistorter 21 generates a distortion having a characteristic opposite to that of the power amplifier 14 using a baseband I signal IBB, a baseband Q signal QBB, and an identification signal FFTGP, which will be described later, and generates a baseband I signal IBB and a baseband. Superimposed on each of the Q signals QBB, the distortion superimposed baseband I data xI is output to the first D / A converter 22-1, and the distortion superimposed baseband Q data xQ is output to the second D / A converter 22-2.

The first D / A converter 22-1 performs digital / analog conversion of the distortion superimposed baseband I data xI and outputs the distortion superimposed baseband I signal to the orthogonal modulation unit 13.
Further, the second D / A converter 22-2 performs digital / analog conversion of the distortion superimposed baseband Q data xQ, and outputs the distortion superimposed baseband Q signal to the orthogonal modulation unit 13.

  As a result, the quadrature modulation unit 13 uses the digital predistorter 21 to compensate for non-linear distortion, that is, the baseband I signal IBB, the baseband Q signal QBB, and the synthesizer 17 on which the distortion characteristic opposite to that of the power amplifier 14 is superimposed. Based on the outputted reference signal for quadrature modulation, quadrature modulation is performed and a quadrature modulation signal is outputted to the power amplifier 14.

  The power amplifier 14 amplifies the power of the quadrature modulation signal output from the quadrature modulation unit 13 to generate a transmission signal, and radiates the transmission signal to the space as a transmission radio wave (electromagnetic wave) via the antenna 15 and transmits it.

  On the other hand, the quadrature demodulation unit 16 detects a part of the transmission signal of the power amplifier 14 as a feedback signal, performs quadrature demodulation based on the reference signal for quadrature demodulation output from the synthesizer 17, and outputs the first A / D converter 23-. 1 and the second A / D converter 23-2.

The first A / D converter 23-1 performs analog / digital conversion of the feedback baseband I signal demodulated by the quadrature demodulation unit 16 and outputs the feedback baseband I data yI to the gain calculation unit 24 and the distortion estimation unit 27. To do.
Similarly, the second A / D converter 23-2 performs analog / digital conversion of the feedback baseband Q signal demodulated by the quadrature demodulator 16, and converts the feedback baseband Q data yQ into a gain calculator 24 and a distortion estimator. 27.

  The gain calculation unit 24 receives the identification signal FFTGP, distortion superimposed baseband I data xI, distortion superimposed baseband Q data xQ, feedback baseband I data yI, and feedback baseband Q data yQ, and transmits a transmission signal and a feedback signal. Perform gain calculation.

  Further, the delay estimation / correction unit 25 receives the identification signal FFTGP, the distortion superimposed baseband I data xI, and the distortion superimposed baseband Q data xQ, and provides feedback baseband I data for the baseband I signal IBB and the baseband Q signal QBB. The delay correction data xI_dlycmp and delay correction data xQ_dlycmp for estimating and correcting the delay amount (delay time) of yI and feedback baseband Q data yQ are generated and output to the gain correction unit 26.

  Here, the acquisition timing of the distortion superimposed baseband I data xI and distortion superimposed baseband Q data xQ used in the gain calculation unit 24 and the delay estimation / correction unit 25 will be described with reference to FIG. 3 again.

  As shown in FIG. 3, the signal frame SGF includes a frame header FH and a frame body FB. As described above, the average power of the frame header FH is twice that of the frame body FB.

  As a result, the identification signal FFTGP output from the identification signal generator 11A is at the “Hi” level in the frame header FH portion where the average power is high, and is at the “Lo” level in the frame body FB portion where the average power is low. .

  Therefore, the gain calculation unit 24 and the delay estimation / correction unit 25 have the predetermined time T2 from the time t2 when the predetermined time T1 has elapsed from the time t1 when the identification signal FFTGP output from the identification signal generation unit 11A becomes the “Lo” level. The distortion superimposed baseband I data xI and distortion superimposed baseband Q data xQ that are used for gain calculation and delay estimation / correction are acquired during a period of time t3.

  As a result, the gain calculation unit 24 and the delay estimation / correction unit 25 perform the distortion superimposed baseband I data xI and the distortion at the timing at a predetermined position from the top of the frame body FB in which the average power is reliably at the “Lo” level. Superimposed baseband Q data xQ can be acquired. That is, since the acquisition position of the distortion superimposed baseband I data xI and the distortion superimposed baseband Q data xQ does not span the “Hi” level region and the “Lo” level region in the signal frame SGF, Gain calculation and delay estimation can be performed accurately. In other words, since data is not compared between regions having different average powers, accurate calculation and estimation can be performed.

  As a result, the gain correction unit 26 appropriately performs gain correction of the delay correction data xI_dlycmp and the delay correction data xQ_dlycmp based on the calculation result of the gain calculation unit 24, and outputs the gain correction unit 27 to the distortion estimation unit 27. Based on the delay correction data xI_dlycmp, the delay correction data xQ_dlycmp, the feedback baseband I data yI, and the feedback baseband Q data yQ that have been gain-corrected, the distortion characteristics of the power amplifier 14 are estimated, and the digital predistorter 21 Will be output.

As described above, according to the present embodiment, since the distortion superimposed baseband I data xI and the distortion superimposed baseband Q data xQ are obtained from a constant region in the signal frame SGF, the average power is always maintained. The distortion superimposed baseband I data xI and the distortion superimposed baseband Q data xQ can be acquired from a substantially constant part, and the power of the original signal and the feedback signal is the same (including cases where they are considered to be the same in the implementation) and is stable. Correct distortion estimation can be performed.
As a result, the non-linear distortion of the power amplifier 14 can be reduced, and the spurious radiation of the broadcast radio wave radiated from the antenna 15 can be suppressed to increase the power efficiency.

  In the above description, the distortion superimposed baseband I data xI and the distortion superimposed baseband Q data xQ are acquired at the timing of the frame body FB at a predetermined position from the head of the frame body FB whose average power is at the “Lo” level. However, the distortion superimposition baseband I data xI and the distortion superimposition baseband Q data xQ are acquired at a timing at a predetermined position from the head of the frame header FH whose average power is “Hi” level. It is also possible.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

DESCRIPTION OF SYMBOLS 10 Transmitter 11 Modulator 11A Identification signal generator 12 Compensator 13 Orthogonal modulator 14 Power amplifier 15 Antenna 16 Orthogonal demodulator 17 Synthesizer 21 Digital predistorter 22-1 and 22-2 D / A converter (digital / analog conversion) Part)
23-1, 23-2 A / D converter (analog / digital converter)
24 gain calculation unit 25 delay estimation / correction unit 26 gain correction unit 27 distortion estimation unit Ddis distortion estimation data FB frame body FFTGP identification signal FH frame header IBB baseband I signal QBB baseband Q signal SGF signal frame xI distortion superimposed baseband I Data xI_dlycmp Delay correction data xQ Distortion superimposed baseband Q data xQ_dlycmp Delay correction data yI Feedback baseband I data yQ Feedback baseband Q data

Claims (5)

An identification signal generator for generating an identification signal for identifying the frame header and the frame body based on the average power of each of the frame header and the frame body constituting the signal frame of the DTMB broadcast transport stream When,
A digital predistorter that superimposes a distortion having a distortion characteristic opposite to the distortion characteristic of a power amplifier connected in a subsequent stage to a baseband signal corresponding to the broadcast transport stream, and output data of the digital predistorter Based on the feedback signal obtained by feeding back the transmission signal output from the power amplifier and the identification signal, distortion estimation is performed using data corresponding to a data section having the same average power in the signal frame for distortion estimation. A compensation unit for compensating for distortion by the digital predistorter;
A distortion compensation apparatus comprising: The data corresponding to the data section is data corresponding to either the frame header or the frame body.
The distortion compensation apparatus according to claim 1. The compensation unit calculates a gain of the transmission signal and the feedback signal corresponding to the output data of the digital predistorter based on the identification signal;
A delay estimation / correction unit for estimating a delay time of the feedback signal corresponding to the output data of the digital predistorter based on the identification signal and outputting delay correction data for correcting the gain;
A gain correction unit that corrects the gain of the transmission signal and the feedback signal calculated by the gain calculation unit using the delay correction data;
A distortion estimation unit that estimates a distortion characteristic that is the inverse of the distortion characteristic of the power amplifier, based on the correction result of the gain correction unit and feedback data corresponding to the feedback signal;
A distortion compensation apparatus comprising: An identification signal generator for generating an identification signal for identifying the frame header and the frame body based on the average power of each of the frame header and the frame body constituting the signal frame of the DTMB broadcast transport stream A modulation unit that modulates the broadcast transport stream and outputs a baseband signal;
A digital predistorter for superimposing distortion on the baseband signal, and based on a feedback signal obtained by feeding back output data of the digital predistorter, a broadcast signal output from a power amplifier, and the identification signal; Among them, a compensation unit that performs distortion estimation using data corresponding to a data section having the same average power for distortion estimation, and performs distortion compensation by the digital predistorter,
A transmission modulation unit that modulates the output signal of the compensation unit that has been subjected to the distortion compensation;
A power amplifier that performs power amplification of an output signal of the transmission modulation unit to form the broadcast signal, and radiates the broadcast signal as a broadcast radio wave via an antenna;
A transmission device comprising: A digital / analog converter for performing digital / analog conversion of the output data of the digital predistorter and outputting;
An analog / digital converter that performs analog / digital conversion of a feedback signal that is a part of the broadcast signal and outputs the converted signal,
The transmission modulator modulates the output signal of the digital / analog converter.
The transmission device according to claim 4.

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