JP3615839B2 - Transmitter - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a transmitter used for radio communication, and more particularly to a burst wave transmitter used in a time division multiple access communication (TDMA) system.
[0002]
[Prior art]
As mobile communication means such as cellular phones generally permeate, radio resources are becoming scarce and effective use of frequencies by digitally modulated waves has been achieved. That is, at present, π / 4 shift differential QPSK modulation is used in the mobile phone system, but this modulation method modulates information only to the phase, so that transmission efficiency is poor.
[0003]
In order to solve this problem, 16QAM, which modulates not only the phase but also the amplitude, and M16QAM, which is a modification of 16QAM, are applied to mobile communications.
For example, M16QAM is adopted in the digital MCA system, and high transmission efficiency is realized.
[0004]
However, in the method of modulating not only the frequency but also the amplitude as in M16QAM, distortion due to the non-linearity of the amplifier tends to occur, resulting in interference with adjacent channels and an increase in transmission error rate.
Therefore, it is necessary to compensate for the non-linearity, but in order to compensate for the non-linearity of the amplifier due to environmental changes, a transmission apparatus that feeds back the output of the amplifier has already been proposed.
[0005]
FIG. 2 is a functional diagram of a conventional transmission device. For example, a digital signal generated by a digital signal processing unit 21 constituted by a DSP is converted into an analog signal by D / A converters 221 and 222, and a low-pass filter 223 is obtained. And 224 to the orthogonal transformer 251.
D / A converters 221 and 222 are driven by a clock output from clock oscillator 225.
[0006]
In the quadrature modulator 251, the analog signal is quadrature modulated by the two-phase intermediate frequency generated by the first PLL 241 and the phase shifter 242 that operate based on the reference frequency output from the reference oscillator 231.
In the first mixer 252, the output of the quadrature modulator 251 is mixed with the local oscillation frequency generated by the second PLL 243 that operates based on the reference frequency output from the reference oscillator 231 , and passes through the bandpass filter 261. Is amplified by the amplifier 262.
[0007]
The amplified signal is extracted from the directional coupler 263 and mixed with the local oscillation frequency generated by the second PLL 243 operating based on the reference frequency output from the reference oscillator 231 in the second mixer 281. The signal is supplied to the quadrature demodulator 281 through the low-pass filter 282.
In the quadrature demodulator 283, the output of the low-pass filter 282 is quadrature modulated by the two-phase intermediate frequency generated by the first PLL 241 and the phase shifter 242 that operate based on the reference frequency output from the reference oscillator 231.
The quadrature demodulated signals are converted into digital signals by the A / D converters 293 and 294 via the low-pass filters 291 and 292 and fed back to the digital signal processing unit 21.
[0008]
The A / D converters 293 and 294 are driven by a clock whose time is shifted from the D / A converters 221 and 222 to the A / D converters 293 and 294 by the clock shifter 295 by the clock oscillator 225.
For example, in the 1500 MHz band used in a digital MCA system, it is difficult to avoid deterioration of accuracy in the case of direct quadrature demodulation. Thus, the intermediate frequency band is used in this way.
[0009]
Therefore, for example, 200 MHz is selected as the intermediate frequency output from the first PLL, and 1300 MHz is selected as the local oscillation frequency output from the second PLL 232.
Therefore, the output of the first mixer is 1300 ± 200 MHz, and only the signal in the 1500 MHz band is supplied to the amplifier 262 by the bandpass filter 261 .
[0010]
The output of the second mixer 281 is 1500 ± 1300 MHz, only the 200 MHz band signal is output from the low-pass filter 282, and the original baseband signal is output from the quadrature demodulator 251.
[0011]
[Problems to be solved by the invention]
As described above, in the conventional transmission device, since the information is once modulated at the intermediate frequency and then further modulated at the local oscillation frequency, not only the configuration is complicated, but also the transmission device is increased in size and height. Pricing is inevitable.
Furthermore, the quadrature demodulator generally has low accuracy, and it is necessary to correct the characteristics of the quadrature demodulator in order to sufficiently compensate the distortion characteristics.
[0012]
The present invention has been made in view of the above problems, and it is an object of the present invention to provide a transmission apparatus that can compensate for nonlinear characteristics with high accuracy, and that can be reduced in size and price.
[0013]
[Means for Solving the Problems]
As shown in the block diagram of FIG. 1, the transmission device according to claim 1 generates a transmission signal and performs distortion compensation on the transmission signal based on the feedback signal, and outputs from the signal processing unit 11. Digital / analog conversion means 12 for converting the transmitted digital signal into a transmission analog signal, a reference frequency oscillation means 13 for oscillating a reference frequency, and a first carrier wave based on the reference frequency oscillated by the reference frequency oscillation means 13. First carrier generation means 14 to be generated, modulation means 15 for modulating the first carrier generated by the first carrier generation means 14 by the transmission analog signal output from the digital / analog conversion means 12, and output of the modulation means 15 A second carrier for generating a second carrier wave based on the reference frequency oscillated by the reference frequency oscillation means 13 The generating means 17, the frequency converting means 18 for converting the frequency of the output of the amplifying means 16 by the second carrier wave generated by the second carrier wave generating means 17, and the output of the frequency converting means 18 being analog / digital converted to obtain a feedback signal An analog / digital conversion means for generating , wherein the signal processing means generates a feedback signal by orthogonally demodulating the digitally converted signal, and based on the feedback signal The transmission signal is subjected to distortion compensation.
[0014]
Transmitting apparatus according to claim 2, further comprising a conversion timing regulating means for regulating the conversion timing of the analog / digital converting means 19 based on the reference frequency oscillated by the reference frequency oscillation means 13.
The transmission apparatus according to claim 3 further includes conversion timing regulation means for adjusting the conversion timing of the digital / analog conversion means 12 and the analog / digital conversion means 19 based on the reference frequency oscillated by the reference frequency oscillation means 13. .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3 is a block diagram of a first embodiment of the transmission apparatus according to the present invention. In the digital signal processing unit 31 which is a DSP, for example, a baseband transmission signal is generated.
This transmission signal is converted into an analog signal by the D / A converters 321 and 322, and then the harmonics are removed by the low-pass filters 323 and 324.
[0016]
The D / A converters 321 and 322 are driven by a clock generated by a common clock oscillator 325.
Reference frequency oscillated by the reference frequency oscillator 331 is converted into a carrier wave of 1496MHz in a first PLL (phase locked loop) 341 is converted into a carrier wave orthogonal to each other in more phase shifters 342, the quadrature modulator 2 51 Quadrature modulation is performed by the transmission signal from which harmonics have been removed by the low-pass filters 323 and 324.
[0017]
That is, the transmission signal is directly converted into a signal of 1496 MHz in the quadrature modulator. This signal is amplified by the amplifier 3 9 1 and output to an antenna (not shown), and is fed back to the digital signal processing unit 31 via the directional coupler 3 9 2.
Mixing that is, the output of the directional coupler 3 9 2 are input to the mixer 381, second carrier generated in PLL343 which operates on the basis of the reference frequency oscillated from the reference frequency oscillator 331 (e.g., 1495.95MHz) Then, it is directly converted into a 50 KHz band signal.
[0018]
The 50 KHz band signal is supplied to the A / D converter 391 via the low pass filter 382, converted into a digital signal, and fed back to the digital signal processing unit 31.
The A / D converter 391 is driven by a clock obtained by shifting the clock oscillated by the clock oscillator 325 by a predetermined amount by the clock shifter 392.
[0019]
This shift amount is determined as an amount corresponding to the time until the signal leaves the D / A converters 321 and 322 and reaches the A / D converter 391, and ensures the synchronism of the signals processed in the digital signal processing unit 31. To do.
As described above, according to the first embodiment, a baseband signal is directly converted into a 1500 MHz band signal, and a 50 KHz band signal that can be easily subjected to digital signal processing is extracted from the 1500 MHz band signal. Compared to the conventional transmission apparatus, it is possible to reduce the step of analog conversion processing.
[0020]
Therefore, not only can the transmission apparatus be reduced in size and price, but also the quadrature demodulator can perform digital signal processing unlike the prior art, so that the signal processing accuracy can be improved.
However, since the reference frequency oscillator and the clock oscillator operate independently, it is difficult to ensure simultaneity between the transmission signal and the feedback signal.
[0021]
FIG. 4 is a configuration diagram of the second embodiment, and a frequency divider 326 is installed in place of the clock oscillator 325.
The frequency divider 326 divides the reference frequency oscillated by the reference frequency oscillator 331 and generates a clock for driving the D / A converters 321 and 322 and the A / D converter 391.
[0022]
That is, according to the second embodiment, it is possible to strictly maintain the simultaneity of modulation, frequency conversion, D / A conversion and A / D conversion, and further improve the accuracy of signal processing.
In the bidirectional communication device, the transmission device and the reception device are used in combination, but the present invention can also be applied to the reception device.
FIG. 5 is a block diagram of the third embodiment. A transmission signal output via the directional coupler 392 is radiated from the antenna 52 via the antenna duplexer 51.
[0023]
A reception signal received by the antenna 52 is guided to the reception mixer 53 via the antenna duplexer 51.
In the reception mixer 53, the reception signal (for example, 1544 MHz) is mixed with a carrier wave (for example, 1495.95 MHz) generated by the second PLL 343 and converted into a signal of 1544 ± 1495.95 MHz.
[0024]
Here, the 48.05 MHz signal is selected and guided to the receiving unit 54, whereby the high frequency processing unit of the receiving unit 54 can be omitted.
[0025]
【The invention's effect】
According to the transmission device of the first aspect, not only the transmission device can be reduced in size and price, but also the demodulation signal processing accuracy can be improved.
According to the transmission apparatus of the second aspect, it is possible to strictly maintain the simultaneity of modulation, frequency conversion, D / A conversion, and A / D conversion, and further improve the accuracy of signal processing.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a transmission apparatus according to the present invention.
FIG. 2 is a configuration diagram of a conventional transmission apparatus.
FIG. 3 is a configuration diagram of the first embodiment.
FIG. 4 is a configuration diagram of a second embodiment.
FIG. 5 is a configuration diagram of a third embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 11 ... Digital signal processing means 12 ... Digital / analog conversion means 13 ... Reference frequency oscillation means 14 ... First carrier generation means 15 ... Modulation means 16 ... Amplification means 17 ... Second carrier generation means 18 ... Frequency conversion means 19 ... Analog / Digital conversion means

Claims (2)

A signal processing means for generating a transmission signal and performing distortion compensation on the transmission signal based on the feedback signal;
Digital / analog conversion means for converting a transmission digital signal output from the signal processing means into a transmission analog signal;
A reference frequency oscillation means for oscillating a reference frequency;
First carrier wave generating means for generating a first carrier wave based on the reference frequency oscillated by the reference frequency oscillating means;
Modulation means for modulating the first carrier wave generated by the first carrier wave generation means by a transmission analog signal output from the digital / analog conversion means;
Amplifying means for amplifying the output of the modulating means;
Second carrier wave generating means for generating a second carrier wave based on the reference frequency oscillated by the reference frequency oscillating means;
Frequency conversion means for frequency-converting the output of the amplification means by the second carrier wave generated by the second carrier wave generation means;
A transmitting apparatus comprising, an analog / digital converting means for analog / digital conversion of the output of the frequency converter, together with the signal processing means generates a feedback signal by quadrature demodulation of the digital converted signal ,
A transmission apparatus further comprising conversion timing regulation means for adjusting the conversion timing of the analog / digital conversion means based on the reference frequency oscillated by the reference frequency oscillation means. A signal processing means for generating a transmission signal and performing distortion compensation on the transmission signal based on the feedback signal;
Digital / analog conversion means for converting a transmission digital signal output from the signal processing means into a transmission analog signal;
A reference frequency oscillation means for oscillating a reference frequency;
First carrier wave generating means for generating a first carrier wave based on the reference frequency oscillated by the reference frequency oscillating means;
Modulation means for modulating the first carrier wave generated by the first carrier wave generation means by a transmission analog signal output from the digital / analog conversion means;
Amplifying means for amplifying the output of the modulating means;
Second carrier wave generating means for generating a second carrier wave based on the reference frequency oscillated by the reference frequency oscillating means;
Frequency conversion means for frequency-converting the output of the amplification means by the second carrier wave generated by the second carrier wave generation means;
A transmitting apparatus comprising, an analog / digital converting means for analog / digital conversion of the output of the frequency converter, together with the signal processing means generates a feedback signal by quadrature demodulation of the digital converted signal ,
A transmission apparatus further comprising conversion timing regulation means for adjusting the conversion timing of the digital / analog conversion means and the analog / digital conversion means based on the reference frequency oscillated by the reference frequency oscillation means.
that's all

Images