JP2000278345A - Modem - Google Patents

Abstract

(57) [PROBLEMS] To provide a modem capable of accurately compensating a DC offset existing in a baseband of a modulation system and a demodulation system by adding a minimum circuit. A switching unit that switches between a reference signal and a baseband signal, an adder that receives an output of the switching unit and compensates for a modulation system DC offset, and an adder
3. A quadrature modulator 106 for modulating a signal obtained by converting the output of the analog-to-analog converter 3 into a carrier frequency, and a distributor 10 for distributing the modulated signal
8, a switch 109 for turning on / off passage of one of the distributed modulation signals as a feedback modulation signal, a quadrature demodulation unit 110 for quadrature demodulating the feedback modulation signal, and a demodulation system DC offset by inputting a signal obtained by digitally converting the quadrature demodulation signal. , And a DC offset estimator 114 for estimating the DC offset of the modulation system and the demodulation system using the reference signal and the output of the adder 113.
C offset compensation can be performed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique for compensating for a DC offset in a modem for digital radio communication.

[0002]

2. Description of the Related Art Conventionally, in a transmission apparatus used for wireless communication, if the efficiency of a transmission system amplifier is increased in order to save power of a wireless terminal, a large amount of nonlinear distortion in the transmission system is likely to occur. For this reason, it is necessary to perform nonlinear distortion compensation by some method. One method is to perform nonlinear distortion compensation of amplitude and phase by referring to a distortion compensation table using the value of a transmission baseband signal. Have been.

FIG. 6 shows a block diagram of a conventional transmitting apparatus. 601 is a transmission digital orthogonal baseband signal. Reference numeral 602 denotes a lookup table for nonlinear distortion compensation.
3 is amplitude distortion compensation data, and 604 is phase distortion compensation data. 605 is a D / A converter for converting digital data into an analog value, and 606 is a converted analog quadrature baseband signal. 607 is a low-pass filter for limiting the band of the transmission signal, and 608 is a band-limited quadrature baseband signal. 609 is a quadrature modulator, 610
Is a modulation signal. 611 is a gain control amplifier for compensating for amplitude distortion, 612 is a modulation signal for which amplitude distortion has been compensated, 613 is a phase shifter for compensating for phase distortion, 614 is a modulation signal for which amplitude and phase shift distortion have been compensated, and 615 is a transmission system. 616 is a transmission modulation signal.

[0004] The operation of the transmitting apparatus configured as described above will be described below. First, the transmission digital quadrature baseband signal 601 is transmitted to the D / A converter 60.
5, the signal is converted into an analog value, band-limited by a low-pass filter 607, and then quadrature-modulated by a quadrature modulator 609 to become a modulated signal 610. At the same time, the amplitude distortion compensation data 603 and the phase distortion compensation data 604 are obtained by referring to the reference table 602 using the value of the transmission digital orthogonal baseband signal 601 as an address. Next, the gain control amplifier 611
Performs amplitude distortion compensation using the amplitude distortion compensation data 603,
The phase shifter 613 performs phase distortion compensation using the phase distortion compensation data 604, and modulates the amplitude and phase distortion of the modulated signal 6.
Get 14. Finally, the modulated signal 614 having undergone the amplitude and phase distortion compensation is amplified by the transmission system amplifier 615, and the transmitted modulated signal 616 is output.

[0005]

However, since the signal density has been improved as in recent years, there has been a need for a method for improving the accuracy by using a modulation / demodulation device based on a modulation technique using a feedback loop as a transmission device. In such a modulation and demodulation device, a DC offset present in a baseband signal of a modulation system or a demodulation system becomes a problem. Therefore, a DC offset compensation technique for compensating the DC offset with high accuracy is required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a technique for compensating a DC offset existing in a modulation system of a modulation / demodulation device and a baseband of the demodulation system with high accuracy by adding a minimum circuit.

[0007]

In order to solve this problem, the present invention provides a feedback loop from a modulation system to a demodulation system and means for connecting / disconnecting the signal. The DC offset of the system and the demodulation system is estimated with high accuracy, and the DC offset of each system is adjusted.

As a result, extremely high-precision DC offset compensation becomes possible by adding a minimum circuit.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 of the present invention is a modulation / demodulation device provided in a communication device of a radio communication system using a digital modulation system, wherein a reference signal for compensating for a DC offset is provided. , A switching means for switching between the reference signal and the digital baseband signal, a first adding means for receiving an output of the switching means and compensating for a modulation system DC offset, D / A conversion means for analog-converting the output of the addition means, quadrature modulation means for modulating the analog-converted quadrature baseband signal to a carrier frequency, distribution means for distributing the modulated signal, and feedback of the distributed one Switch means for turning on / off passage as a modulation signal, quadrature demodulation means for quadrature demodulating the feedback modulation signal, and quadrature demodulated quadrature baseband signal A / D conversion means for performing digital conversion, second addition means for receiving the digitally converted quadrature baseband signal and compensating for a DC offset in a demodulation system, and using the reference signal and the output of the second addition means. And a DC offset estimating means for estimating a DC offset of a modulation system and a demodulation system. The DC offset of a modulation system and a demodulation system are separated by connecting / disconnecting a feedback signal. Has the effect of compensating with high accuracy. Further, by keeping the amplitude constant, the influence of distortion generated in an amplifier or the like can be minimized, and more accurate compensation can be performed. in addition,
By making the reference signal a constant value, it is possible to minimize the power leaked from the terminal when estimating the DC offset.

According to a second aspect of the present invention, there is provided a modulation / demodulation device provided in a communication device of a radio communication system using a digital modulation system, wherein a reference signal generating means for generating a reference signal for compensating for a DC offset. Vector generating means for generating a reference signal offset vector, first adding means for adding the reference signal and the reference signal offset vector, and switching for switching between the output of the first adding means and a digital baseband signal Means, an output of the switching means, a second addition means for compensating for a DC offset in a modulation system, a D / A conversion means for converting the output of the second addition means into an analog signal, Orthogonal modulating means for modulating a baseband signal to a carrier frequency, distributing means for distributing the modulated signal; Switch means for turning on / off the passage, quadrature demodulation means for quadrature demodulating the feedback modulated signal, A / D conversion means for digitally converting the quadrature demodulated quadrature baseband signal, and digitally converted quadrature baseband signal A third adder for inputting a signal to compensate for a demodulation system DC offset, and estimating a DC offset of a modulation system and a demodulation system using an output of the first addition unit and an output of the third addition unit. A modulation / demodulation device comprising a DC offset estimating means, which separates a DC offset of a modulation system and a demodulation system by connecting / disconnecting a feedback signal, and further separates a reference signal and a signal obtained by adding a reference offset vector to a reference signal. By taking the difference between the feedback signals, an extremely accurate DC offset can be achieved. In addition, by making the amplitude constant, the influence of distortion generated in an amplifier or the like can be minimized, and more accurate compensation can be performed. In addition, by making the reference signal a constant value, it becomes possible to minimize the power leaked from the terminal when estimating the DC offset. In addition, since the magnitude of the reference signal and the reference offset vector influence the magnitude of the power leaked from the terminal at the time of DC offset estimation, the reference offset vector is made sufficiently small to suppress the leakage power, and in addition, an amplifier or the like is used. The effect of the generated distortion can also be suppressed. Further, by inverting the sign of the reference offset vector, it is possible to achieve the same performance with half the size.

According to a third aspect of the present invention, there is provided a modulation / demodulation device provided in a communication device of a wireless communication system using a digital modulation system, wherein a reference signal generating means for generating a reference signal for compensating for a DC offset. Vector generating means for generating a reference signal offset vector, first adding means for adding the reference signal and the reference signal offset vector, and switching for switching between the output of the first adding means and a digital baseband signal Means, an output of the switching means, a second addition means for compensating for a DC offset in a modulation system, a D / A conversion means for converting the output of the second addition means into an analog signal, Orthogonal modulating means for modulating a baseband signal to a carrier frequency, distributing means for distributing the modulated signal; A / D conversion means for performing digital conversion, orthogonal demodulation means for orthogonally demodulating a feedback digital modulation signal, and estimating a DC offset of a modulation system using an output of the first addition means and an output of the orthogonal demodulation means. A modulation / demodulation device comprising DC offset estimating means, wherein the quadrature demodulation unit is digitally configured to eliminate the DC offset of the demodulation system in principle, thereby further improving the accuracy of estimating the DC offset of the modulation system. have. In addition, by making the amplitude constant, the influence of distortion generated in an amplifier or the like can be minimized, and more accurate compensation can be performed. In addition, by making the reference signal a constant value, it becomes possible to minimize the power leaked from the terminal when estimating the DC offset. In addition, since the size of the reference signal and the reference offset vector affects the amount of power leaked from the terminal when estimating the DC offset,
By making the reference offset vector sufficiently small, it is possible to suppress the leakage power and also suppress the influence of distortion generated in an amplifier or the like. Also, by inverting the sign of the reference offset vector, equivalent performance can be reduced by half.
It is possible to achieve with.

According to a fourth aspect of the present invention, there is provided a modulation / demodulation device provided in a communication device of a radio communication system using a digital modulation system, wherein reference signal generation means for generating a reference signal for compensating for a DC offset. Vector generating means for generating a reference signal offset vector, first adding means for adding the reference signal and the reference signal offset vector, and switching for switching between the output of the first adding means and a digital baseband signal Means, input of the output of the switching means, second addition means for compensating for a DC offset of the modulation system, D / A conversion means for converting the output of the second addition means into analog, and oscillation as a frequency source Means, quadrature modulation means for modulating the analog-converted quadrature baseband signal based on the output of the oscillation means to a carrier frequency, Distributing means for distributing, quadrature demodulating means for quadrature demodulating one of the divided signals as a feedback modulation signal based on the output of the oscillating means, and turning on / off the output of the oscillating means to the quadrature demodulating means. Switch means, A / D conversion means for digitally converting the orthogonally demodulated quadrature baseband signal, third adding means for inputting the digitally converted quadrature baseband signal and compensating for a demodulation system DC offset, Using the outputs of the first addition means and the third addition means, the modulation system and the demodulation system
A modulation / demodulation device comprising a DC offset estimating means for estimating a C offset, wherein a DC offset of a modulation system and a DC offset of a demodulation system are separated by connecting / disconnecting a frequency source of a quadrature demodulation unit. Taking the difference between the feedback signal and the signal to which the reference offset vector has been added has the effect that a very high-precision DC offset is possible. In addition, this configuration eliminates the need for an extra switch in the demodulation system, and thus has the effect of eliminating the effect on the received signal. In addition, by making the amplitude constant, the influence of distortion generated in an amplifier or the like can be minimized, and more accurate compensation can be performed.
In addition, by making the reference signal a constant value, it becomes possible to minimize the power leaked from the terminal when estimating the DC offset. In addition, since the magnitude of the reference signal and the reference offset vector influence the magnitude of the power leaked from the terminal at the time of DC offset estimation, the reference offset vector is made sufficiently small to suppress the leakage power, and in addition, an amplifier or the like is used. The effect of the generated distortion can also be suppressed. Also, by inverting the sign of the reference offset vector,
Equivalent performance can be achieved with half the size.

According to a fifth aspect of the present invention, there is provided a modulation / demodulation device provided in a communication device of a radio communication system using a digital modulation method, wherein reference signal generation means for generating a reference signal for compensating for a DC offset. Vector generating means for generating a reference signal offset vector, first adding means for adding the reference signal and the reference signal offset vector, and switching for switching between the output of the first adding means and a digital baseband signal Means, second output means for inputting the output of the switching means to compensate for the DC offset of the modulation system, D / A conversion means for converting the output of the second addition means into analog, and a frequency source for the modulation section. A first oscillating means, and a quadrature for modulating a quadrature baseband signal obtained by the analog conversion based on an output of the first oscillating means to a carrier frequency. Adjusting means, a distributing means for distributing the modulated signal, a second oscillating means serving as a frequency source of the demodulation section, and one selected from an output of the first oscillating means and an output of the second oscillating means. Frequency source selection means, quadrature demodulation means for quadrature demodulating one of the distributed signals based on the output of the frequency source selection means as a feedback modulation signal, and A / D for digitally converting the quadrature demodulated quadrature baseband signal
Conversion means; third addition means for inputting the digitally converted quadrature baseband signal to compensate for a DC offset in a demodulation system; and modulation using the output of the first addition means and the output of the third addition means. A modulation / demodulation device including a DC offset estimating means for estimating a DC offset of a system and a demodulation system. When a plurality of frequency sources are prepared, a DC offset of a modulation system and a demodulation system are separated by switching a frequency source of a quadrature demodulation unit. Further, by taking the difference between the reference signal and the feedback signal with respect to the signal obtained by adding the reference offset vector to the reference signal, an extremely high-precision DC offset can be achieved. In addition, this configuration eliminates the need for an extra switch in the demodulation system, and thus has the effect of eliminating the effect on the received signal. In addition, by making the amplitude constant, the influence of distortion generated in an amplifier or the like can be minimized, and more accurate compensation can be performed. In addition, by making the reference signal a constant value, it becomes possible to minimize the power leaked from the terminal when estimating the DC offset. In addition, since the magnitude of the reference signal and the reference offset vector influence the magnitude of the power leaked from the terminal at the time of DC offset estimation, the reference offset vector is made sufficiently small to suppress the leakage power, and in addition, an amplifier or the like is used. The effect of the generated distortion can also be suppressed. Further, by inverting the sign of the reference offset vector, it is possible to achieve the same performance with half the size.

[0014] Also, as in the sixth aspect, the modulation / demodulation device according to any one of the first to fifth aspects, wherein the reference signal has a constant amplitude, has the same effect.

[0015] Also, as in the seventh aspect, the modulation / demodulation device according to any one of the first to fifth aspects, wherein the reference signal has a constant value, has the same effect.

According to another aspect of the present invention, the magnitude of the reference signal offset vector is 1/100 or less of the maximum amplitude of the baseband signal. Has the same effect.

[0017] Also, as in the ninth aspect, the modulation / demodulation device according to any one of the second to fifth aspects, wherein only the sign of the reference signal offset vector is inverted before and after the switching, the same effect is obtained. Have.

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIG.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a modulation / demodulation device according to a first embodiment of the present invention.
In FIG. 1, reference numeral 101 denotes a reference signal generation unit, 102 denotes a baseband switching unit, 103 denotes a modulation system DC compensation adder,
4 is a D / A converter, 105 is a modulation signal band limiting filter, 106 is a quadrature modulator, 107 is an amplifier, 108 is a distributor, 109 is a switch, 110 is a quadrature demodulator, 111
Is a demodulated signal band limiting filter, 112 is an A / D converter,
113 is a demodulation system DC compensation adder, 114 is a DC offset estimator, 151 is a modulation system digital baseband signal, 152 is a reference switching signal, 153 is a reference signal, and 154.
Is a baseband switching signal, 155 is a transmission digital baseband signal, 156 is a transmission system DC compensation signal, 157 is a transmission DC compensation digital baseband signal, 158 is a transmission analog baseband signal, 159 is a transmission band limited analog baseband signal, 160 is a transmission modulation signal, 16
1 is a transmission amplification modulation signal, 162 is an output modulation signal, 163
Is a distribution modulation signal, 164 is a feedback control signal, 165 is a feedback modulation signal, 166 is a feedback analog baseband signal,
67 is a feedback band limited analog baseband signal, 168
Is a feedback digital baseband signal, 169 is a feedback system D
A C compensation signal 170 is a demodulation system digital baseband signal.

The operation of the modem configured as described above will be described with reference to FIG.

A reference signal that enables the calculation of the DC offset is stored in the reference signal generator 101 in advance. The baseband switching unit 102 includes a DC offset estimation unit 114
, The modulation system digital baseband signal 151 is selected during normal operation, and the reference signal 153 is selected during DC offset estimation. At the time of DC offset estimation, the selected reference signal 153 is output to the transmission digital baseband signal 155, and the modulation system DC compensation signal 156, which is the modulation system DC offset estimation value estimated by the DC offset estimator 114, and the modulation system D
The C offset is added in the C compensation adder 103, and the DC offset of the modulation baseband signal is compensated.

The DC offset compensated transmission DC baseband signal 157 is converted into an analog signal by the D / A converter 104, and a transmission analog baseband signal 158 is output. The transmission analog baseband signal 158 is band-limited by the transmission band limiting filter 105 and the transmission band-limited analog baseband signal 1
59, which is quadrature-modulated by the quadrature modulator 106 to become a transmission modulation signal 160. The transmission modulation signal 160 is transmitted to the amplifier 10
7 and becomes a transmission amplification modulation signal 161, and the transmission amplification modulation signal 161 is distributed to the output modulation signal 162 and the distribution modulation signal 163 in the distributor 108.

The switch 109 is a DC offset estimator 1
In response to the feedback control signal 164 from the demodulator 14, when the demodulation system DC offset signal is estimated, disconnection is performed, and at other times, connection is controlled, and the feedback modulation signal 165 is output. Quadrature demodulation section 110 quadrature demodulates feedback modulation signal 165 and outputs feedback analog baseband signal 166. The feedback analog baseband signal 166 is the demodulated signal band limiting filter 1
The signal is band-limited by 11 and becomes a feedback band-limited analog baseband signal 167, and is further converted into a digital signal by the A / D converter 112 to become a feedback digital baseband signal 168. Demodulation system DC compensation adder 113 adds demodulation system DC compensation signal 169 output from DC offset estimating section 114 and feedback digital baseband signal 168, and outputs demodulation system digital baseband signal 170.

Next, the DC offset estimating operation will be described in more detail. DC offset estimating section 114
It controls the switching unit 102 to select the reference signal 153 through the baseband switching signal 154. Further demodulation system D
At the time of C offset estimation, control is performed such that switch 109 is cut off through feedback control signal 164 so that reference signal 153 for demodulation DC offset estimation is output to reference signal generation section 101 through reference control signal 152.

Further, the demodulation system DC compensation signal 169 becomes 0,
The modulation system DC compensation signal 156 is set to the latest estimated value or 0. Reference signal generating section 101 outputs a reference signal 153 for demodulation system DC offset estimation. The transmission digital baseband signal 155 that has passed through the
The transmission DC compensated digital baseband signal 157 to which the modulation DC compensation signal 156 estimated by the C offset estimating unit 114 is added is analog-converted, and then quadrature-modulated and output to the transmission modulation signal 161 through the amplifier 107. A part of the transmission modulation signal 161 becomes a distribution modulation signal 163 by the distributor 108 and is input to the switch 109.

Since the switch 109 is disconnected by the feedback control signal 164 when estimating the DC offset of the demodulation system, no signal is transmitted to the feedback modulation signal 165. At this time, the feedback analog baseband signal 166 from the quadrature demodulation unit 110 indicates the origin of the demodulation quadrature baseband.
This means that the value digitally converted by the A / D converter 112 is the origin of the demodulation system orthogonal baseband signal. The DC offset estimating unit 114 outputs 0 to the demodulation system DC compensation signal 167, and calculates the demodulation system DC offset estimation value so that the obtained demodulation system digital baseband signal 170 becomes the origin of the demodulation system orthogonal baseband.

At this time, the demodulation system digital baseband signal 170 is sampled a plurality of times and averaged to obtain an A / D signal.
It goes without saying that the conversion error of the conversion unit 112 and the influence of system noise can be reduced. According to the configuration of the present invention, the reference signal 153 for estimating the DC offset of the demodulation system is not limited.
By setting 53 as the origin (the origin is a signal that minimizes the power of the output modulation signal 162), the output modulation signal 1
62 is minimized and the switch 109
, The leakage power to the feedback modulation signal 165 is also minimized, so that more accurate estimation is possible.

Naturally, by increasing the accuracy of the modulation system DC compensation signal 156, the leakage power from the output modulation signal 162 is reduced and the leakage power from the switch 109 to the feedback modulation signal 165 is suppressed. At the time of offset estimation, it is desirable to set the modulation system DC compensation signal 156 to the latest modulation system DC offset estimation value. After the demodulation system DC offset estimation is completed as described above, the operation shifts to the modulation system DC offset estimation operation.

At the time of the modulation system DC offset estimating operation, the DC offset estimating section 114 outputs the baseband switching signal 154
Through the switch 102 to select the reference signal 153. Further, control is performed such that switch 109 is connected through feedback control signal 164 so that reference signal 153 for modulation system DC offset estimation is output to reference signal generating section 101 through reference control signal 152.

The demodulation system DC compensation signal 169 is set to the estimated value obtained by the demodulation system DC offset estimation, and the modulation system DC compensation signal 156 is set to the latest estimated value or 0. Reference signal generating section 101 outputs reference signal 153 for estimating DC offset of modulation system. A modulation DC compensation signal 156 estimated by the DC offset estimator 114 is added to the transmission digital baseband signal 155 that has passed through the switch 102.
DC compensation digital baseband signal 15
7 is converted into an analog signal, and then quadrature-modulated.
Is output to the transmission modulation signal 161 through A part of the transmission modulation signal 161 becomes a distribution modulation signal 163 by the distributor 108 and is input to the switch 109.

Since the switch 109 is connected by the feedback control signal 164 when estimating the DC offset of the modulation system, the distributed modulation signal 163 is orthogonally demodulated through the feedback modulation signal 165, and the feedback analog baseband signal 166 corresponding to the transmission modulation signal 161 is obtained. Is output. The feedback analog baseband signal 166 is band-limited by the band-limiting filter 111 as a pre-process of digital conversion, and is digitally converted by the A / D converter 112 to become a feedback digital baseband signal 168. The latest digital demodulation system DC is applied to this feedback digital baseband signal 168.
The DC offset of the demodulation system is compensated by adding the compensation signal 169, and the demodulation system digital baseband signal 170 is obtained.

DC offset estimating section 114 generates reference signal 1
A modulation DC compensation signal 156 is newly calculated from 53, the modulation DC compensation signal 156, and the demodulation digital baseband signal 170. Various methods are conceivable for this calculation. If the phase rotation and the amplification factor from the modulation system to the demodulation system are clear, the demodulation system digital baseband signal 170 can be input as an inverse function thereof.

At this time, for example, the reference signal 153 for estimating the DC offset of the modulation system is arranged on each axis on the orthogonal plane of the baseband signal at an equal distance from the origin (for example, (a, 0) (0, a ) (−a, 0) (four points indicated by (0, −a)), and the modulation system DC compensation signal 156 such that the vector sum of the demodulation system digital baseband signal 170 corresponding to each reference signal 153 converges to the origin. Can be estimated by updating. These reference signals 153 are 4
It is obvious that the present invention is not limited to the point, and that the output vector sum should be 0.

Further, by arranging the reference signal 153 on the circumference which is an aggregate having a constant amplitude from the origin, the calculation can be performed regardless of the amplification rate and the amount of phase rotation from the modulation system to the demodulation system. It is possible to minimize the influence of linear distortion mainly generated in the amplifier 107 and perform highly accurate DC offset estimation with little influence on signal delay generated from the modulation system to the demodulation system.

Further, even if the reference signal 153 is at a fixed point, it is possible to perform DC offset. By setting this fixed point as the origin, the power leaked from the output modulation signal 162 at the time of DC offset estimation is minimized. Become.

(Embodiment 2) FIG. 2 is a block diagram showing a configuration of a modulation / demodulation device according to a second embodiment of the present invention.
2, reference numeral 201 denotes a reference signal generator, 202 denotes a vector generator, 203 denotes a reference signal offset adder, and 20 denotes a reference signal offset adder.
4 is a baseband switching unit, 205 is a modulation DC compensation adder, 206 is a D / A conversion unit, 207 is a modulation signal band limiting filter, 208 is a quadrature modulation unit, 209 is an amplifier, 21
0 is a distributor, 211 is a switch, 212 is a quadrature demodulator,
213 is a demodulation signal band limiting filter, 214 is an A / D converter, 215 is a demodulation DC compensation adder, 216 is a DC offset estimator, 251 is a modulation digital baseband signal, 252 is a reference switching signal, and 253 is a reference. Signal 2
54 is a reference signal offset vector, 255 is a reference offset signal, 256 is a baseband switching signal, 257 is a transmission digital baseband signal, and 258 is a modulation system DC.
Compensation signal, 259 is transmission DC compensation digital baseband signal, 260 is transmission analog baseband signal, 26
1 is a transmission band limited analog baseband signal, 262 is a transmission modulation signal, 263 is a transmission amplification modulation signal, 264 is an output modulation signal, 265 is a distribution modulation signal, 266 is a feedback control signal, 267 is a feedback modulation signal, and 268 is feedback. An analog baseband signal, 269 is a feedback band limited analog baseband signal, 270 is a feedback digital baseband signal, 271 is a demodulation system DC compensation signal, and 272 is a demodulation system digital baseband signal.

The operation of the modem configured as described above will be described with reference to FIG.

A reference signal capable of calculating a DC offset is stored in the reference signal generator 201 in advance. The baseband switching unit 204 includes a DC offset estimation unit 216
According to the baseband switching signal 256 from the base station, the modulation system digital baseband signal 251 is selected in the normal state, and the reference offset signal 255 is selected in the DC offset estimation.
At the time of DC offset estimation, the selected reference offset signal 255 is the transmission digital baseband signal 25.
7 is added to the modulation DC compensation signal 258, which is the modulation DC offset estimation value estimated by the DC offset estimator 216, in the modulation DC compensation adder 205, and the DC offset of the modulation baseband signal is compensated. Is done.

The transmission DC compensated baseband signal 259 with the DC offset compensated is converted into an analog signal by the D / A converter 206, and the transmission analog baseband signal 260 is output. The transmission analog baseband signal 260 is band-limited by the transmission system band-limiting filter 207 and the transmission band-limited analog baseband signal 2
61, which is quadrature-modulated by the quadrature modulator 208 to become a transmission modulation signal 262. The transmission modulation signal 262 is
9 and becomes a transmission amplification modulation signal 263, and the transmission amplification modulation signal 263 is distributed to the output modulation signal 264 and the distribution modulation signal 265 in the distributor 210.

The switch 211 is a DC offset estimator 2
In response to the feedback control signal 266 from the DC / DC converter 16, control is performed such that the signal is disconnected when the demodulation system DC offset signal is estimated, and the signal is connected otherwise, and the feedback modulation signal 267 is output. Quadrature demodulation section 212 performs quadrature demodulation on feedback modulation signal 267 and outputs feedback analog baseband signal 268. The feedback analog baseband signal 268 is a demodulated signal band limiting filter 2
13, is converted into a feedback band limited analog baseband signal 269 by the A / D converter 214 and converted into a digital signal to form a feedback digital baseband signal 270. The demodulation system DC compensation adder 215 adds the demodulation system DC compensation signal 271 output from the DC offset estimator 216 and the feedback digital baseband signal 270, and outputs a demodulation system digital baseband signal 272.

Next, the DC offset estimation operation will be described in more detail. The DC offset estimating unit 216 includes:
The switching unit 204 is controlled to select the reference offset signal 255 through the baseband switching signal 256. Further, at the time of demodulation system DC offset estimation, the reference control signal 252 is used.
To output the reference signal 253 for demodulation system DC offset estimation to the reference signal generation unit 201, to output the reference signal offset vector 254 for demodulation system DC offset estimation to the vector generation unit 202, and to provide the feedback control signal Control is performed so that the switch 211 is disconnected through 266.

The demodulation system DC compensation signal 271 is set to 0,
The modulation system DC compensation signal 258 is set to the latest estimated value or 0. The reference signal generator 201 outputs a reference signal 253 for demodulation system DC offset estimation, and the vector generator 202 outputs a reference signal offset vector 254 for demodulation system DC offset estimation. Reference signal offset adder 20
3 is a reference signal 253 and a reference signal offset vector 25
4 and outputs a reference offset signal 255. After the transmission DC compensated digital baseband signal 259 obtained by adding the modulation system DC compensation signal 258 estimated by the DC offset estimating unit 216 to the transmission digital baseband signal 257 passed through the switching unit 204 is analog-converted,
The quadrature modulated signal 263 is transmitted through the amplifier 209 and transmitted.
Is output to. A part of the transmission amplification modulation signal 263 becomes a distribution modulation signal 265 by the distributor 210 and is input to the switch 211.

When estimating the DC offset of the demodulation system, the switch 211 is disconnected by the feedback control signal 266, so that no signal is transmitted to the feedback modulation signal 267. At this time, the feedback analog baseband signal 268 from the quadrature demodulation unit 212 indicates the origin of the demodulation system quadrature baseband.
This means that the value digitally converted by the A / D converter 214 is the origin of the demodulation orthogonal baseband signal. The DC offset estimating unit 216 outputs 0 to the demodulation system DC compensation signal 271 and calculates the demodulation system DC offset estimation value so that the obtained demodulation system digital baseband signal 272 becomes the origin of the demodulation system orthogonal baseband.

At this time, the demodulation system digital baseband signal 272 is sampled a plurality of times and averaged to obtain an A / D signal.
It goes without saying that the conversion error of the conversion unit 214 and the influence of system noise can be reduced. Further, according to the configuration of the present invention, the reference offset signal 255 for estimating the DC offset of the demodulation system is not limited. Signal), the leakage power from the output modulation signal 264 is minimized, and the leakage power to the feedback modulation signal 267 through the switch 211 is also minimized, so that more accurate estimation is possible. Therefore, it is desirable that both the reference signal 253 for demodulation system DC offset estimation and the reference signal offset vector 254 be 0.

Naturally, by increasing the accuracy of the modulation system DC compensation signal 258, the leakage power from the output modulation signal 264 is reduced and the leakage power from the switch 211 to the feedback modulation signal 267 is also suppressed. It is desirable that the modulation system DC compensation signal 258 be set to the latest modulation system DC offset estimation value during the offset estimation.

After the demodulation system DC offset estimation is completed as described above, the operation shifts to the modulation system DC offset estimation operation.

In procedure 1 of the modulation system DC offset estimation operation, the DC offset estimation unit 216 controls the switching unit 204 to select the reference offset signal 255 through the baseband switching signal 256. Further, reference control signal 2
The switch 211 through the feedback control signal 266 so as to output the reference signal 253 and the reference signal offset vector 254 for the modulation system DC offset estimation procedure 1 to the reference signal generation unit 201 and the vector generation unit 202 through the control signal 52.
Is controlled to be connected.

The demodulation system DC compensation signal 271 is set to the estimated value obtained by the demodulation system DC offset estimation, and the modulation system DC compensation signal 258 is set to the latest estimated value or 0. Reference signal generating section 201 outputs reference signal 253 for estimating modulation system DC offset. Vector generating section 202 outputs 0 as reference signal offset vector 254. The reference offset signal 255 output by adding the reference signal 253 and the reference signal offset vector 254 by the reference signal offset adder 203 passes through the switching unit 204 and becomes a transmission digital baseband signal 257. The transmission digital baseband signal 257 is supplied to a DC offset estimating section 216.
Is added to the modulation system DC compensation signal 258 estimated, and becomes a transmission DC compensation digital baseband signal 259.
09 to the transmission amplification modulation signal 263.
A part of the transmission amplification modulation signal 263 becomes a distribution modulation signal 265 by the distributor 210 and is input to the switch 211.

Since the switch 211 is connected by the feedback control signal 266 when estimating the DC offset of the modulation system, the distributed modulation signal 265 is orthogonally demodulated through the feedback modulation signal 267, and the feedback analog baseband signal corresponding to the transmission amplification modulation signal 263 is obtained. 268 is output. This feedback analog baseband signal 268 is band-limited by a demodulation signal band-limiting filter 213 as a pre-process of digital conversion, and is digitally converted by an A / D converter 214 to become a feedback digital baseband signal 270. The latest demodulation system DC compensation signal 271 is added to this feedback digital baseband signal 270 to compensate for the DC offset of the demodulation system, and the demodulation system digital baseband signal 2
72 is obtained. The DC offset estimating unit 216 stores the data obtained here.

Next, in the procedure 2 of the modulation system DC offset estimation, the DC offset estimation unit 216 controls the switching unit 204 to select the reference offset signal 255 through the baseband switching signal 256. Further, the reference signal generation unit 201 and the vector generation unit 202 are supplied with the reference signal 253 and the reference signal offset vector 254 for the modulation system DC offset estimation procedure 2 through the reference control signal 252.
, So that the switch 211 is connected through the feedback control signal 266.

The demodulation system DC compensation signal 271 is set to the estimated value obtained by the demodulation system DC offset estimation, and the modulation system DC compensation signal 258 is set to the latest estimated value or 0. Reference signal generating section 201 performs modulation system DC offset estimation procedure 1
And outputs the same reference signal 253 as that of the reference signal. The vector generation unit 202 adds the modulation system D to the reference signal offset vector 254.
A vector for the C offset estimation procedure 2 is output. The reference offset signal 255 output by adding the reference signal 253 and the reference signal offset vector 254 by the reference signal offset adder 203 passes through the switching unit 204 and becomes a transmission digital baseband signal 257.

The subsequent signal processing is the same as in the modulation system procedure 1. The DC offset estimating unit 216 stores the demodulated digital baseband signal 272 obtained as a result. The DC offset estimator 216 newly generates a modulation DC compensation signal 258 from the reference offset signal 255, the modulation DC compensation signal 258, the demodulation digital baseband signal 272 according to the procedure 1, and the demodulation digital baseband signal 272 according to the procedure 2. calculate.

Next, the procedure for calculating the DC offset will be described while treating each baseband signal as a vector. When estimating the demodulation system DC offset, switch 2
11 is obtained by averaging the feedback digital baseband signal 270 demodulated at that time.
When estimating the demodulation system DC offset, the transmission modulation signal 26
2 is closer to 0, the leakage power of the switch 211 is suppressed, so that the accuracy can be improved. After estimating the demodulation system DC offset, the process proceeds to the estimation of the modulation system DC offset.

When estimating the modulation system DC offset, the DC offset estimation unit 216 connects the switch 211 and sets the demodulation system DC compensation signal 271 to the demodulation system DC offset estimated value obtained earlier. The value of the modulation system DC compensation signal 258 is not particularly limited, but is set to 0 in this description.

Next, a vector sum is calculated for each of the results of the demodulation system digital baseband signal 272 obtained in the procedures 1 and 2. (Hereinafter, the procedure 1 vector sum and the procedure 2 vector sum) These demodulation system DC offsets are compensated for by the demodulation system DC compensation signal 271.

The procedure 1 and procedure 2 obtained as described above are expressed by a linear transformation using the gain and phase rotation of an amplifier or the like from a modulation system to a demodulation system as a transformation vector to the sum of the vectors given by the orthogonal modulation unit 208. (Hereinafter, this conversion vector is called a loop vector). The vector provided to the quadrature modulation unit 208 can be separated into a reference offset signal 255 and a modulation DC offset component. For simplicity, the vector sum of the reference signal 253 is set to 0 and the reference at the time of procedure 1 is used. Assuming that the signal offset vector 254 is 0, at this time, the procedure 1 vector sum is equal to a linear transformation of the modulation system DC offset component by a loop vector.

Similarly, since the vector sum of the procedure 2 is the sum of the reference signal offset vector 254 and that of the procedure 1, the difference between them is equal to the one obtained by linearly transforming the reference signal offset vector 254 with the loop vector. . As a result, the loop vector can be calculated by multiplying the difference between the procedure 2 vector sum and the procedure 1 vector sum by the reciprocal of the reference signal offset vector 254. Further, the modulation system DC offset component can be calculated by multiplying the sum of the procedure 1 vectors by the reciprocal of the loop vector.

In this method, since a loop vector is calculated from a difference between a feedback signal and a known vector which is a reference signal offset vector 254, various error factors such as a DC offset of a modulation system and a demodulation system are removed, and a highly accurate loop vector is obtained. Calculation becomes possible.

In the above description, the vector sum of the reference signal 253 is assumed to be 0, but it is possible to estimate the modulation system DC offset even if it is not 0. Also, reference signal 2
By making the amplitude of 53 constant, the influence of linear distortion generated in the amplifier 209 and the like is minimized, and highly accurate DC offset estimation is enabled. Further, by arranging the reference signal 253 on the circumference, the influence of a loop vector and the like can be reduced.

The above effect is effective even when the reference signal 253 has a constant value. In particular, by setting the reference signal 253 to a constant value, the capacity of the reference signal generating unit can be reduced, and the size of the reference signal offset vector can be reduced. By doing so, it is possible to suppress the power leaking from the output modulation signal 264 to the outside of the device or the internal elements during the DC offset estimation operation to a minimum value. The magnitude of the reference signal offset vector 254 is related to the accuracy of the DC offset estimation, but if it is too large, it is affected by linear distortion of an amplifier or the like.

Although the accuracy is affected, it is sufficient that the magnitude is small relative to the maximum amplitude that can be output by the system, and the magnitude of the reference signal offset vector 254 is set to 100 minutes of the maximum amplitude. By setting the value from about 1 to less than about 1, it is possible to suppress the leakage power at the time of DC offset estimation to -40 dBc or less with respect to the maximum output power.

Further, in procedure 1, it is assumed that the magnitude of the reference signal offset vector 254 is 0. However, the phase is inverted by 180 degrees with respect to the reference signal offset vector 254 given in procedure 2, so that the same magnitude is obtained. by doing,
Double precision can be obtained with the same vector magnitude, and leakage power can be further reduced with the same precision.

The reference signal offset vector 254
Although is not particularly limited, since the reciprocal thereof is used in the calculation, it is obvious that setting this vector on the axis facilitates the calculation processing.

(Embodiment 3) FIG. 3 is a block diagram showing a configuration of a modem device according to a first embodiment of the present invention.
3, reference numeral 301 denotes a reference signal generator, 302 denotes a vector generator, 303 denotes a reference signal offset adder, 30
4 is a baseband switching unit, 305 is a modulation DC compensation adder, 306 is a D / A conversion unit, 307 is a modulation signal band limiting filter, 308 is a quadrature modulation unit, 309 is an amplifier, 31
0 is a distributor, 311 is a band limiting filter, 312 is A /
D conversion unit, 313 is a quadrature demodulation unit, 314 is a demodulation signal band limiting filter, 316 is a DC offset estimation unit, 351
Is a modulation system digital baseband signal, 352 is a reference switching signal, 353 is a reference signal, 354 is a reference signal offset vector, 355 is a reference offset signal, 356 is a baseband switching signal, 357 is a transmission digital baseband signal, and 358 is modulation. System DC compensation signal, 359 is a transmission DC compensation digital baseband signal, 360 is a transmission analog baseband signal, 361 is a transmission band limited analog baseband signal, 362 is a transmission modulation signal, 363 is a transmission amplification modulation signal, and 364 is output modulation. The signal 365 is a feedback modulation signal, 366 is a feedback variable band limited return signal, 367 is a feedback digital modulation signal, 368 is a feedback digital baseband signal, and 369 is a demodulation system digital baseband signal.

The operation of the modem configured as described above will be described with reference to FIG.

A reference signal enabling calculation of the DC offset is stored in the reference signal generating section 301 in advance. The baseband switching unit 304 includes a DC offset estimation unit 316
According to the baseband switching signal 356 from the base station, the modulation system digital baseband signal 351 is selected during normal operation, and the reference offset signal 355 is selected during DC offset estimation.
At the time of DC offset estimation, the selected reference offset signal 355 is transmitted digital baseband signal 35.
7 is added to the modulation DC compensation signal 358, which is the modulation DC offset estimation value estimated by the DC offset estimating unit 316, in the modulation DC compensation adder 305, and the DC offset of the modulation baseband signal is compensated. Is done.

The transmission DC compensated baseband signal 359 whose DC offset has been compensated is converted into an analog signal by the D / A converter 306, and a transmission analog baseband signal 360 is output. The transmission analog baseband signal 360 is band-limited by the transmission system band-limiting filter 307 and the transmission band-limited analog baseband signal 3
61, which is orthogonally modulated by the orthogonal modulation unit 308 to become a transmission modulation signal 362. The transmission modulation signal 362 is
The power is amplified at 9 and becomes a transmission amplification modulation signal 363, and the transmission amplification modulation signal 363 is distributed to the output modulation signal 364 and the feedback modulation signal 365 in the distributor 310.

The feedback modulation signal 365 is applied to the band limiting filter 3
11, the feedback band-limited modulated signal 366 is band-limited.
become. The A / D converter 312 outputs the feedback band limited modulated signal 3
66 is converted to a digital signal and a feedback digital modulation signal 367
And converted into a feedback digital baseband signal 368 by the quadrature demodulation unit 313. The feedback digital baseband signal 368 is applied to the demodulated signal band limiting filter 314.
The demodulated digital baseband signal 369 is obtained by band limitation.

Next, the DC offset estimating operation will be described in more detail. In the procedure 1 of the modulation system DC offset estimation operation, the DC offset estimation unit 316 controls the switching unit 304 to select the reference offset signal 355 through the baseband switching signal 356. Further, the reference signal generation section 301 and the vector generation section 302 transmit the reference signal 353 and the reference signal offset vector 354 for the modulation system DC offset estimation procedure 1 through the reference control signal 352.
Is controlled to be output.

The modulation system DC compensation signal 358 is set to the latest estimated value or 0. The reference signal generation section 301 outputs a reference signal 353 for estimating a modulation system DC offset. Vector generating section 302 outputs 0 to reference signal offset vector 354. The reference signal 353 and the reference signal offset vector 354 are added to the reference signal offset adder 3.
The reference offset signal 355 added and output at 03 is
The signal passes through the switching unit 304 and becomes a transmission digital baseband signal 357. Transmission digital baseband signal 357
Is added to the modulation system DC compensation signal 358 estimated by the DC offset estimating unit 316 to become a transmission DC compensation digital baseband signal 359. This signal is analog-converted, quadrature-modulated, and then transmitted through the amplifier 309. 363. A part of the transmission amplification modulation signal 363 is divided by the distributor 310 into the feedback modulation signal 36.
It becomes 5.

The feedback modulated signal 365 fed back through the distributor 310 is passed through the band-limited filter 311 for pre-processing of analog-to-digital conversion.
66, and becomes a feedback digital modulation signal 367 by the A / D conversion unit 312. Feedback digital modulation signal 367
Are orthogonally demodulated by an orthogonal demodulation unit 313, and a feedback digital baseband signal 368 corresponding to the transmission amplification modulation signal 363 is output. The feedback analog baseband signal 368 is band-limited by the demodulated signal band-limiting filter 314, and then becomes a demodulated digital baseband signal 369. The DC offset estimating unit 316 stores the data obtained here.

Procedure 2 in Modulation System DC Offset Estimation
Then, the DC offset estimating unit 316 controls the switching unit 304 to select the reference offset signal 355 through the baseband switching signal 356. Further, control is performed such that reference signal 353 and reference signal offset vector 354 for modulation system DC offset estimation procedure 2 are output to reference signal generation section 301 and vector generation section 302 through reference control signal 352.

The modulation system DC compensation signal 358 is set to the latest estimated value or 0. Reference signal generating section 301 has the same reference signal 3 as used for modulation system DC offset estimation procedure 1.
53 is output. Vector generating section 302 outputs a vector for modulation system DC offset estimation procedure 2 to reference signal offset vector 354. Reference offset signal 355 output by adding reference signal 353 and reference signal offset vector 354 in reference signal offset adder 303
Pass through the switching unit 304 and become a transmission digital baseband signal 357.

The subsequent signal processing is the same as in the modulation system procedure 1. The DC offset estimating section 316 stores the demodulated digital baseband signal 369 obtained as a result. The DC offset estimating unit 316 newly generates a modulation DC compensation signal 358 from the reference offset signal 355, the modulation DC compensation signal 358, the demodulation digital baseband signal 369 according to the procedure 1, and the demodulation digital baseband signal 369 according to the procedure 2. calculate.

Next, the procedure for calculating the DC offset will be described while treating each baseband signal as a vector. At the time of the modulation system DC offset estimation, the DC offset estimation unit 316 sets the value of the modulation system DC compensation signal 358 to 0 in this description, although not particularly limited.

Next, a vector sum is calculated for each of the results of the demodulation system digital baseband signal 369 obtained in Procedure 1 and Procedure 2 (hereinafter referred to as Procedure 1 vector sum and Procedure 2 vector sum).

The procedure 1 and procedure 2 obtained as described above are expressed by a linear transformation using the gain and phase rotation of an amplifier or the like from a modulation system to a demodulation system as a transformation vector to the sum of the vectors given by the quadrature modulator 308. (Hereinafter, this conversion vector is called a loop vector). The vector provided to the orthogonal modulation section 308 can be separated into a reference offset signal 355 and a DC offset component of a modulation system. To simplify the description, the vector sum of the reference signal 353 is set to 0, and the reference at the time of procedure 1 is set to 0. Assuming that the signal offset vector 354 is 0, the procedure 1 vector sum is equal to a linearly converted DC offset component of the modulation system using a loop vector.

Similarly, the procedure 2 vector sum is obtained by adding the reference signal offset vector 354 to the procedure 1 and therefore the difference between them is equal to the result of the linear transformation of the reference signal offset vector 354 by the loop vector. . As a result, a loop vector can be calculated by multiplying the difference between the procedure 2 vector sum and the procedure 1 vector sum by the reciprocal of the reference signal offset vector 354. Further, the modulation system DC offset component can be calculated by multiplying the sum of the procedure 1 vectors by the reciprocal of the loop vector.

In this method, since a loop vector is calculated from a difference between a feedback signal and a known vector which is a reference signal offset vector 354, various error factors such as a DC offset of a modulation system are removed, and a highly accurate calculation can be performed. Becomes

In the above description, the vector sum of the reference signal 353 is assumed to be 0, but it is possible to estimate the modulation system DC offset even if it is not 0. Also, reference signal 3
By keeping the amplitude of 53 constant, the influence of linear distortion generated in the amplifier 309 and the like is minimized, and highly accurate DC offset estimation is enabled. Further, by arranging the reference signal 353 on the circumference, the influence of a loop vector and the like can be reduced.

The above effect is effective even when the reference signal 353 has a constant value. In particular, by setting the reference signal 353 to a constant value, the capacity of the reference signal generating unit can be reduced, and the size of the reference signal offset vector can be reduced. By doing so, it is possible to suppress the power leaked from the output modulation signal 364 to the outside of the device or internal elements during the DC offset estimation operation to a minimum value. The magnitude of the reference signal offset vector 354 is related to the accuracy of the DC offset estimation, but if it is too large, it is affected by linear distortion of an amplifier or the like.

Although the accuracy is affected, it is sufficient that the magnitude is small relative to the maximum amplitude that can be output from the system. By setting from about 1 to less than 1, it is possible to suppress the leakage power at the time of DC offset estimation to -40 dBc or less with respect to the maximum output power.

Further, in procedure 1, it is assumed that the magnitude of reference signal offset vector 354 is 0. However, the phase is inverted by 180 degrees with respect to reference signal offset vector 354 given in procedure 2, so that the magnitude is the same as that of reference signal offset vector 354. by doing,
Double precision can be obtained with the same vector magnitude, and leakage power can be further reduced with the same precision.

The reference signal offset vector 354
Although is not particularly limited, since the reciprocal thereof is used in the calculation, it is obvious that setting this vector on the axis facilitates the calculation processing.

(Embodiment 4) FIG. 4 is a block diagram showing a configuration of a modem according to a first embodiment of the present invention.
4, reference numeral 401 denotes a reference signal generator, 402 denotes a vector generator, 403 denotes a reference signal offset adder,
04 is a baseband switching unit, 405 is a modulation DC compensation adder, 406 is a D / A conversion unit, 407 is a modulation signal band limiting filter, 408 is an oscillator, 409 is a quadrature modulation unit,
10 is an amplifier, 411 is a distributor, 412 is a switch,
13 is a quadrature demodulator, 414 is a demodulation signal band limiting filter, 415 is an A / D converter, 416 is a demodulation DC compensation adder, 417 is a DC offset estimator, 451 is a modulation digital baseband signal, and 452 is a reference. Switching signal,
453 is a reference signal, 454 is a reference signal offset vector, 455 is a reference offset signal, 456 is a baseband switching signal, 457 is a transmission digital baseband signal, 458 is a modulation DC compensation signal, and 458 is a transmission DC compensation digital baseband signal. 460, a transmission analog baseband signal, 461, a transmission band limited analog baseband signal, 462, an oscillation signal, 463, a transmission modulation signal, 465, a transmission amplification modulation signal, 465, an output modulation signal, 466, a feedback modulation signal, 467 Is an oscillation signal switching signal, 468 is a demodulation oscillation signal, 469 is a feedback analog baseband signal, 470 is a feedback band limited analog baseband signal, 471 is a feedback digital baseband signal, 472 is a demodulation system DC compensation signal, and 473 is demodulation. System digital baseband signal That.

The operation of the modem configured as described above will be described with reference to FIG.

A reference signal capable of calculating the DC offset is stored in the reference signal generation unit 401 in advance. The baseband switching unit 404 includes a DC offset estimation unit 417
According to the baseband switching signal 456 from the base station, the modulation system digital baseband signal 451 is selected during normal operation, and the reference offset signal 455 is selected during DC offset estimation.
At the time of DC offset estimation, the selected reference offset signal 455 is the transmission digital baseband signal 45.
7 and a modulation DC compensation signal 458, which is a modulation DC offset estimation value estimated by the DC offset estimating unit 417, and a modulation DC compensation adder 405 to compensate for the DC offset of the modulation baseband signal. Is done.

The transmission DC compensated baseband signal 459 in which the DC offset has been compensated is converted into an analog signal by the D / A converter 406, and the transmission analog baseband signal 460 is output. The transmission analog baseband signal 460 is band-limited by the transmission band limiting filter 407 and the transmission band-limited analog baseband signal 4
The quadrature modulator 409 quadrature modulates the transmission band limited analog baseband signal 461 using the oscillation signal 462 from the oscillator 408 and outputs a transmission modulation signal 463. The transmission modulation signal 463 is power-amplified by the amplifier 410 to become a transmission amplification modulation signal 464, and the transmission amplification modulation signal 464 is distributed to the output modulation signal 465 and the feedback modulation signal 466 in the distributor 411.

The DC offset estimating section 417 controls the switch 412 through the oscillation signal switching signal 467 so as to disconnect the switch 412 when estimating the demodulation DC offset and connect the switch 412 when estimating the modulation DC offset. Using the demodulation oscillation signal 468 from the switch 412, the quadrature demodulation unit 413 performs quadrature demodulation on the feedback modulation signal 466 and outputs a feedback analog baseband signal 469. The feedback analog baseband signal 469 is output to the demodulated signal band limiting filter 4.
The signal is band-limited by the A / D converter 415 and converted into a digital signal by the A / D converter 415 to be a feedback digital baseband signal 471. The demodulation system DC compensation adder 416 adds the demodulation system DC compensation signal 472 output from the DC offset estimator 417 and the feedback digital baseband signal 471 to output a demodulation system digital baseband signal 473.

Next, the DC offset estimation operation will be described in more detail. The DC offset estimator 417 calculates
The switching unit 404 is controlled to select the reference offset signal 455 through the baseband switching signal 456. Further, when estimating the DC offset of the demodulation system, the reference control signal 452 is used.
To output the reference signal 453 for demodulation system DC offset estimation to the reference signal generation unit 401, to output the reference signal offset vector 454 for demodulation system DC offset estimation to the vector generation unit 402, and to switch the oscillation signal. The switch 412 is controlled to be turned off through a signal 467.

The demodulation system DC compensation signal 472 is set to 0,
The modulation system DC compensation signal 458 is set to the latest estimated value or 0. The reference signal generator 401 outputs a reference signal 453 for demodulation system DC offset estimation, and the vector generator 402 outputs a reference signal offset vector 454 for demodulation system DC offset estimation. Reference signal offset adder 40
3 is a reference signal 453 and a reference signal offset vector 45
4 and outputs a reference offset signal 455. After the transmission DC compensated digital baseband signal 459 obtained by adding the modulation system DC compensation signal 458 estimated by the DC offset estimating section 417 to the transmission digital baseband signal 457 passed through the switching section 404 is converted into an analog signal,
The quadrature demodulation unit 409 outputs the oscillation signal 4 output from the oscillator 408.
Quadrature modulation is performed using the signal 62, and output to the transmission amplification modulation signal 464 through the amplifier 410. A part of the transmission amplification modulation signal 464 becomes a feedback modulation signal 466 by the distributor 411 and is input to the quadrature demodulation unit 413.

When estimating the DC offset of the demodulation system, since the switch 412 is disconnected by the oscillation signal switching signal 467, the quadrature demodulation unit 413 does not operate. At this time, the feedback analog baseband signal 4
Reference numeral 69 indicates the origin of the demodulation system orthogonal base band. This is A
The value digitally converted by the / D conversion unit 415 is the origin of the demodulation orthogonal baseband signal. The DC offset estimating unit 417 outputs 0 to the demodulation system DC compensation signal 472.
, And the demodulation system DC offset estimated value is calculated so that the obtained demodulation system digital baseband signal 473 becomes the origin of the demodulation system orthogonal baseband.

At this time, the demodulation system digital baseband signal 473 is sampled a plurality of times and averaged, so that the A / D
It goes without saying that the conversion error of the conversion unit 415 and the influence of system noise can be reduced. Further, according to the configuration of the present invention, the reference offset signal 455 for estimating the DC offset of the demodulation system is not limited. Signal from the output modulation signal 465 is minimized. Therefore, the reference signal 45 for demodulation system DC offset estimation is used.
It is desirable that both 3 and the reference signal offset vector 454 be 0.

Naturally, the leakage power from the output modulation signal 465 can be suppressed by increasing the precision of the modulation DC compensation signal 458. It is desirable to set the offset estimation value. Also, in this method, unlike the configuration in which switches are arranged in the signal sequence of the demodulation system, since the method controls the oscillation signal for quadrature demodulation,
It has the feature that it is not affected by switch leakage power.

After the demodulation system DC offset estimation is completed as described above, the operation shifts to the modulation system DC offset estimation operation.

In the first procedure of the DC offset estimation operation of the modulation system, the DC offset estimation unit 417 controls the switching unit 404 to select the reference offset signal 455 through the baseband switching signal 456. Further, reference control signal 4
The switch 4 through the oscillation signal switching signal 467 so as to output the reference signal 453 and the reference signal offset vector 454 for the modulation system DC offset estimation procedure 1 to the reference signal generation unit 401 and the vector generation unit 402 through 52.
12 is connected.

Further, the demodulation system DC compensation signal 472 is set to the estimated value obtained by the demodulation system DC offset estimation, and the modulation system DC compensation signal 458 is set to the latest estimated value or 0. The reference signal generation unit 401 outputs a reference signal 453 for estimating a modulation system DC offset. Vector generating section 402 outputs 0 as reference signal offset vector 454. The reference offset signal 455 output by adding the reference signal 453 and the reference signal offset vector 454 by the reference signal offset adder 403 passes through the switching unit 404 and becomes a transmission digital baseband signal 457. The transmission digital baseband signal 457 is converted into a DC offset estimator 417.
Is added to the estimated modulation system DC compensation signal 458 to become a transmission DC compensation digital baseband signal 459. After this signal is converted into an analog signal, the quadrature modulation section 409 uses the oscillation signal 462 output from the oscillator 408 to perform quadrature modulation. The signal is modulated to output a transmission modulation signal 463, and becomes an transmission amplification modulation signal 464 through the amplifier 410. A part of the transmission amplification modulation signal 464 is divided by the divider 411 into the feedback modulation signal 464.
66, which is input to the quadrature demodulation unit 413.

Since the switch 412 is connected by the oscillation signal switching signal 467 when estimating the modulation system DC offset, the oscillation signal 462 is output to the demodulation oscillation signal 468 through the switch 412. The orthogonal demodulation unit 413 orthogonally demodulates the feedback modulation signal 466 using the demodulation oscillation signal 468, and outputs a feedback analog baseband signal 469 corresponding to the transmission amplification modulation signal 464. This feedback analog baseband signal 469 is band-limited by a demodulation signal band-limiting filter 414 as a pre-processing of digital conversion, and is digitally converted by an A / D converter 415 to become a feedback digital baseband signal 471.
The latest demodulation system DC compensation signal 472 is added to this feedback digital baseband signal 471 to compensate for the DC offset of the demodulation system, and the demodulation system digital baseband signal 473 is added.
Get. The DC offset estimating unit 417 stores the data obtained here.

Next, in the procedure 2 for the modulation system DC offset estimation, the DC offset estimation unit 417 controls the switching unit 404 to select the reference offset signal 455 through the baseband switching signal 456. Further, the reference signal generation section 401 and the vector generation section 402 receive the reference signal 453 and the reference signal offset vector 454 for the modulation system DC offset estimation procedure 2 through the reference control signal 452.
Is controlled so that the switch 412 is connected through the oscillation signal switching signal 467 so as to output the output signal.

Also, the demodulation system DC compensation signal 472 is set to the estimated value obtained by the demodulation system DC offset estimation, and the modulation system DC compensation signal 458 is set to the latest estimated value or 0. Reference signal generating section 401 performs modulation system DC offset estimation procedure 1
And outputs the same reference signal 453 as that of the reference signal. Vector generation section 402 modulates reference signal offset vector 454 with modulation system D
A vector for the C offset estimation procedure 2 is output. The reference offset signal 455 output by adding the reference signal 453 and the reference signal offset vector 454 by the reference signal offset adder 403 passes through the switching unit 404 and becomes a transmission digital baseband signal 457.

The subsequent signal processing is the same as the modulation system procedure 1. The DC offset estimating unit 417 stores the demodulated digital baseband signal 473 obtained thereby. The DC offset estimating unit 417 newly generates a modulation DC compensation signal 458 from the reference offset signal 455, the modulation DC compensation signal 458, the demodulation digital baseband signal 473 according to the procedure 1, and the demodulation digital baseband signal 473 according to the procedure 2. calculate.

Next, the procedure for calculating the DC offset will be described while treating each baseband signal as a vector. When estimating the demodulation system DC offset, switch 4
12 is obtained by averaging the feedback digital baseband signal 473 which is orthogonally demodulated at that time.
When estimating the demodulation system DC offset, when the power of the transmission amplification modulation signal 464 is closer to 0, the influence on other elements is suppressed, so that highly accurate estimation is possible. Demodulation system DC
After estimating the offset, the process proceeds to estimating the DC offset of the modulation system.

When estimating the modulation system DC offset, the DC offset estimator 417 connects the switch 412 and sets the demodulation system DC compensation signal 472 to the demodulation system DC offset estimation value obtained earlier. The value of the modulation system DC compensation signal 458 is not particularly limited, but is set to 0 in this description.

Next, a vector sum is calculated for each of the results of the demodulation system digital baseband signal 473 obtained in Procedure 1 and Procedure 2. (Hereinafter, the procedure 1 vector sum and the procedure 2 vector sum) The demodulation system DC offset is compensated for by the demodulation system DC compensation signal 472 in these vector sums.

The procedure 1 and procedure 2 obtained as described above are expressed by a linear transformation using the gain and phase rotation of an amplifier or the like from a modulation system to a demodulation system as a transformation vector to the sum of the vectors given by the quadrature modulator 409. (Hereinafter, this conversion vector is called a loop vector). The vector provided to the quadrature modulation unit 409 can be separated into a reference offset signal 455 and a DC offset component of a modulation system. For simplicity, the vector sum of the reference signal 453 is set to 0, and the reference at the time of procedure 1 is used. Assuming that the signal offset vector 454 is 0, at this time, the procedure 1 vector sum is equal to the one obtained by linearly converting the modulation system DC offset component by the loop vector.

Similarly, since the vector sum of the procedure 2 is obtained by adding the reference signal offset vector 454 compared with the procedure 1, the difference between the two is equal to the value obtained by linearly transforming the reference signal offset vector 454 with the loop vector. . As a result, a loop vector can be calculated by multiplying the difference between the procedure 2 vector sum and the procedure 1 vector sum by the reciprocal of the reference signal offset vector 454. Further, the modulation system DC offset component can be calculated by multiplying the sum of the procedure 1 vectors by the reciprocal of the loop vector.

In this method, since a loop vector is calculated from a difference between a feedback signal and a known vector as a reference signal offset vector 454, various error factors such as DC offset of a modulation system and a demodulation system are removed, and a high-accuracy system is obtained. Calculation becomes possible.

In the above description, the vector sum of the reference signal 453 is assumed to be 0, but it is possible to estimate the modulation system DC offset even if it is not 0. Also, reference signal 4
By keeping the amplitude of 53 constant, the influence of linear distortion generated in the amplifier 410 or the like is minimized, and highly accurate DC offset estimation is enabled. Further, by arranging the reference signal 453 on the circumference, the influence of a loop vector or the like can be reduced.

The above effect is effective even when the reference signal 453 has a constant value. In particular, by setting the reference signal 453 to a constant value, the capacity of the reference signal generating unit can be reduced, and the size of the reference signal offset vector can be reduced. By doing so, it is possible to suppress the power leaked from the output modulation signal 465 to the outside of the device or the internal elements during the DC offset estimation operation to a minimum value. The magnitude of the reference signal offset vector 454 is related to the accuracy of the DC offset estimation, but if it is too large, it is affected by linear distortion of an amplifier or the like.

Although the precision is affected, it is sufficient that the magnitude is small relative to the maximum amplitude that can be output by the system, and the magnitude of the reference signal offset vector 454 is set to 100 minutes of the maximum amplitude. By setting from about 1 to less than 1, it is possible to suppress the leakage power at the time of DC offset estimation to -40 dBc or less with respect to the maximum output power.

Further, in procedure 1, it is assumed that the magnitude of reference signal offset vector 454 is 0. However, the phase is inverted by 180 degrees with respect to reference signal offset vector 454 given in procedure 2, so that the magnitude is the same as that of reference signal offset vector 454. by doing,
Double precision can be obtained with the same vector magnitude, and leakage power can be further reduced with the same precision.

Also, reference signal offset vector 454
Although is not particularly limited, since the reciprocal thereof is used in the calculation, it is obvious that setting this vector on the axis facilitates the calculation processing.

(Embodiment 5) FIG. 5 is a block diagram showing a configuration of a modem device according to a first embodiment of the present invention.

In FIG. 5, reference numeral 501 denotes a reference signal generator,
502 is a vector generator, 503 is a reference signal offset adder, 504 is a baseband switch, 505 is a modulation system DC compensation adder, 506 is a D / A converter, 507 is a modulation signal band limiting filter, and 508 is a modulation system. Oscillator, 509
Is a quadrature modulator, 510 is an amplifier, 511 is a distributor, 51
2 is a demodulation system oscillator, 513 is a switch, 514 is a quadrature demodulation unit, 515 is a demodulation signal band limiting filter, and 516 is A
/ D conversion unit, 517 is a demodulation system DC compensation adder, 518 is a DC offset estimation unit, 551 is a modulation system digital baseband signal, 552 is a reference switching signal, 553 is a reference signal, 554 is a reference signal offset vector, and 555 is The reference offset signal 556 is a baseband switching signal,
57 is a transmission digital baseband signal, 558 is a modulation system DC compensation signal, 559 is a transmission DC compensation digital baseband signal, 560 is a transmission analog baseband signal, 561 is a transmission band limited analog baseband signal,
562 is a modulation system oscillation signal, 563 is a transmission modulation signal, 56
4 is a transmission amplification modulation signal, 565 is an output modulation signal, 566
Is a feedback modulation signal, 567 is an oscillation signal switching signal, 568 is a demodulation system oscillation signal, 569 is a selection oscillation signal, 570 is a feedback analog baseband signal, 571 is a feedback band limited analog baseband signal, and 572 is a feedback digital baseband signal. , 573 a demodulation system DC compensation signal, and 574 a demodulation system digital baseband signal.

The operation of the modem configured as described above will be described with reference to FIG.

A reference signal enabling calculation of a DC offset is stored in advance in reference signal generating section 501. The baseband switching unit 504 includes a DC offset estimation unit 518
According to the baseband switching signal 556 from the base station, the modulation system digital baseband signal 551 is selected in the normal state, and the reference offset signal 555 is selected in the DC offset estimation.
At the time of DC offset estimation, the selected reference offset signal 555 is the transmission digital baseband signal 55
7 and a modulation DC compensation signal 558, which is a modulation DC offset estimation value estimated by the DC offset estimating unit 518, and a modulation DC compensation adder 505 to compensate for the DC offset of the modulation baseband signal. Is done.

The transmission DC compensated baseband signal 559 in which the DC offset has been compensated is converted into an analog signal by the D / A conversion section 506, and the transmission analog baseband signal 560 is output. The transmission analog baseband signal 560 is band-limited by the transmission system band-limiting filter 507 and the transmission band-limited analog baseband signal 5
The orthogonal modulation unit 509 orthogonally modulates the transmission band limited analog baseband signal 561 using the modulation system oscillation signal 562 from the modulation system oscillator 508 and outputs a transmission modulation signal 563. The transmission modulation signal 563 is supplied to the amplifier 510.
The power is amplified by the transmission amplifier 560 and becomes a transmission amplification modulation signal 564. In the distributor 511, the transmission amplification modulation signal 564 is distributed to an output modulation signal 565 and a feedback modulation signal 566.

The DC offset estimating unit 518 connects the switch 513 to the demodulation system oscillation signal 568 through the oscillation signal switching signal 567 when the demodulation system DC offset is estimated, and the modulation system oscillation signal 56 when the modulation system DC offset is estimated.
2 to be connected. Using the selective oscillation signal 569 from the switch 513, the quadrature demodulation unit 514 performs quadrature demodulation on the feedback modulation signal 566 and outputs a feedback analog baseband signal 570. The feedback analog baseband signal 570 is band-limited by the demodulated signal band-limiting filter 515 and the feedback band-limited analog baseband signal 571
And further converted into a digital signal by the A / D converter 516 to become a feedback digital baseband signal 572. Demodulation system DC compensation adder 517 adds demodulation system DC compensation signal 573 output from DC offset estimating section 518 and feedback digital baseband signal 572, and outputs demodulation system digital baseband signal 574.

Next, the DC offset estimating operation will be described in more detail. DC offset estimating section 518 includes:
The switching unit 504 is controlled to select the reference offset signal 555 through the baseband switching signal 556. Further, when estimating the DC offset of the demodulation system, the reference control signal 552 is used.
To output the reference signal 553 for demodulation system DC offset estimation to the reference signal generation unit 501, output the reference signal offset vector 554 for demodulation system DC offset estimation to the vector generation unit 502, and switch the oscillation signal. The control is performed so that the switch 513 is connected to the demodulation oscillation signal 568 through the signal 567.

The demodulation system DC compensation signal 573 is set to 0,
The modulation system DC compensation signal 558 is set to the latest estimated value or 0. The reference signal generator 501 outputs a reference signal 553 for demodulation system DC offset estimation, and the vector generator 502 outputs a reference signal offset vector 554 for demodulation system DC offset estimation. Reference signal offset adder 50
3 is a reference signal 553 and a reference signal offset vector 55
4 and outputs a reference offset signal 555. After the transmission DC-compensated digital baseband signal 559 obtained by adding the modulation DC compensation signal 558 estimated by the DC offset estimator 518 to the transmission digital baseband signal 557 that has passed through the switching unit 504 is converted into an analog signal,
The quadrature demodulation unit 509 performs quadrature modulation using the modulation system oscillation signal 562 output from the modulation system oscillator 508, and
The signal is output to the transmission amplification modulation signal 564 through 0. A part of the transmission amplification modulation signal 564 becomes a feedback modulation signal 566 by the distributor 511 and is input to the quadrature demodulation unit 514.

Since the switch 513 is connected to the demodulation system oscillation signal 568 by the oscillation signal switching signal 567 when estimating the demodulation system DC offset, the feedback modulation signal 566 is quadrature demodulated with the frequency shifted. At this time, the feedback analog baseband signal 57 by the quadrature demodulation unit 514
0 is output as a baseband signal shifted by the difference between the frequency of the orthogonal oscillation signal 562 and the frequency of the demodulation oscillation signal 568 about the demodulation DC offset. If the difference between the frequencies is sufficiently large, the demodulated component of the feedback analog baseband signal 570 is
Therefore, only the demodulation system DC offset component is included in the feedback band limited analog baseband signal 571. The value obtained by digitally converting the feedback band limited analog baseband signal 571 by the A / D converter 516 is the origin of the demodulation system orthogonal baseband signal. The DC offset estimating unit 518 outputs 0 to the demodulation system DC compensation signal 573, and calculates the demodulation system DC offset estimation value so that the obtained demodulation system digital baseband signal 574 becomes the origin of the demodulation system orthogonal baseband.

At this time, the demodulation system digital baseband signal 574 is sampled a plurality of times and averaged to obtain an A / D signal.
It goes without saying that the conversion error of the conversion unit 516 and the influence of system noise can be reduced. Also, in this description, the modulation system oscillation signal 562 and the demodulation system oscillation signal 568
Is assumed to be large, but when the difference is small, the DC offset of the demodulation system can be estimated as follows.

As described above, the feedback analog baseband signal 570 from the quadrature demodulation unit 514 has a baseband signal shifted by the difference between the frequency of the quadrature oscillation signal 562 and the frequency of the demodulation oscillation signal 568 about the demodulation DC offset. Is output as If this frequency difference is small,
The demodulated component of the feedback analog baseband signal 570 passes through the demodulated signal band limiting filter 515, and the feedback band limited analog baseband signal 571 is superimposed on a demodulated DC offset component with a signal shifted in frequency and demodulated. Become. Since the signal demodulated with the frequency shifted is rotated on the orthogonal plane in the baseband, the signal is drawn as a circle centered on the demodulation system DC offset component.

Next, the feedback band limited analog baseband signal 571 is digitally converted by the A / D converter 516 to become a feedback digital baseband signal 572, and a demodulation system DC compensation signal 573 (here, 0 is set). Added and demodulated digital baseband signal 5
74. If the reference offset signal 555 is a constant value, the demodulation system digital baseband signal 5
Since 74 draws a circle centered on the demodulation system DC offset component, the DC offset estimating unit 518 can estimate the demodulation system DC offset by obtaining the center of the demodulation system digital baseband signal 574, that is, calculating the average. is there.

According to the configuration of the present invention, the reference offset signal 555 for estimating the DC offset of the demodulation system is not limited, but the reference offset signal 555 is set at the origin (the origin is defined as the minimum power of the output modulation signal 565). ), The leakage power from the output modulation signal 565 is minimized. Therefore, it is desirable that both the reference signal 553 for demodulation system DC offset estimation and the reference signal offset vector 554 be 0.

Naturally, by increasing the precision of the modulation system DC compensation signal 558, the leakage power from the output modulation signal 565 can be suppressed, so that when the demodulation system DC offset is estimated, the modulation system DC compensation signal 558 is replaced with the latest modulation system DC compensation signal 558. It is desirable to set the offset estimation value. Also, in this method, unlike the configuration in which switches are arranged in the signal sequence of the demodulation system, since the method controls the oscillation signal for quadrature demodulation,
It has the feature that it is not affected by switch leakage power.

After the demodulation system DC offset estimation is completed as described above, the operation shifts to the modulation system DC offset estimation operation.

In the first step of the modulation system DC offset estimation operation, the DC offset estimation unit 518 controls the switching unit 504 to select the reference offset signal 555 through the baseband switching signal 556. Further, the reference control signal 5
A switch 5 through an oscillation signal switching signal 567 so as to output the reference signal 553 and the reference signal offset vector 554 for the modulation system DC offset estimation procedure 1 to the reference signal generator 501 and the vector generator 502 through 52
13 controls the modulation system oscillation signal 562 and the selection oscillation signal 569 to be connected.

Also, the demodulation system DC compensation signal 572 is set to the estimated value obtained by the demodulation system DC offset estimation, and the modulation system DC compensation signal 558 is set to the latest estimated value or 0. The reference signal generating section 501 outputs a reference signal 553 for estimating the DC offset of the modulation system. Vector generating section 502 outputs 0 as reference signal offset vector 554. The reference offset signal 555 output by adding the reference signal 553 and the reference signal offset vector 554 by the reference signal offset adder 503 passes through the switching unit 504 to become a transmission digital baseband signal 557. The transmission digital baseband signal 557 is converted into a DC offset estimator 518.
Is added to the estimated modulation system DC compensation signal 558 to become a transmission DC compensation digital baseband signal 559. After this signal is converted into an analog signal, the quadrature modulator 509 outputs the modulation system oscillation signal 562 output from the modulation system oscillator 508. Are used for quadrature modulation to output a transmission modulation signal 563, which becomes an amplified transmission modulation signal 564 through the amplifier 510. A part of the transmission amplification modulation signal 564 becomes a feedback modulation signal 566 by the distributor 511 and is input to the quadrature demodulation unit 514.

When estimating the modulation system DC offset, the switch 513 connects the modulation system oscillation signal 562 and the selection oscillation signal 569 by the oscillation signal switching signal 567, so that the modulation system oscillation signal 562 is changed to the selection oscillation signal 569 through the switch 513. Is output. Quadrature demodulation section 514 performs quadrature demodulation on feedback modulation signal 566 using selective oscillation signal 569, and outputs feedback analog baseband signal 570 corresponding to transmission amplification modulation signal 564. This feedback analog baseband signal 570 is band-limited by a demodulation signal band-limiting filter 515 as a pre-process of digital conversion, and is digitally converted by an A / D converter 516 to become a feedback digital baseband signal 572. This feedback digital baseband signal 572 has the latest demodulation system D
The DC offset of the demodulation system is compensated by adding the C compensation signal 573 to obtain the demodulation system digital baseband signal 574. The DC offset estimating unit 518 stores the data obtained here.

Next, in the procedure 2 of the DC offset estimation of the modulation system, the DC offset estimation unit 518 controls the switching unit 504 to select the reference offset signal 555 through the baseband switching signal 556. Further, the reference signal generation unit 501 and the vector generation unit 502 transmit the reference signal 553 and the reference signal offset vector 554 for the modulation system DC offset estimation procedure 2 through the reference control signal 552.
The switch 513 is connected to the demodulation system oscillation signal 568 and the selected oscillation signal 5 through the oscillation signal switching signal 567 so as to output
69 is connected.

Also, the demodulation system DC compensation signal 573 is set to the estimated value obtained by the demodulation system DC offset estimation, and the modulation system DC compensation signal 558 is set to the latest estimated value or 0. Reference signal generating section 501 performs modulation system DC offset estimation procedure 1
And outputs the same reference signal 553 as that of the reference signal. Vector generating section 502 applies modulation system D to reference signal offset vector 554.
A vector for the C offset estimation procedure 2 is output. The reference offset signal 555 output by adding the reference signal 553 and the reference signal offset vector 554 by the reference signal offset adder 503 passes through the switching unit 504 to become a transmission digital baseband signal 557.

The subsequent signal processing is the same as the modulation system procedure 1. The DC offset estimating unit 518 stores the demodulated digital baseband signal 574 obtained as a result. The DC offset estimating unit 518 newly generates a modulation DC compensation signal 558 from the reference offset signal 555, the modulation DC compensation signal 558, the demodulation digital baseband signal 574 according to the procedure 1, and the demodulation digital baseband signal 574 according to the procedure 2. calculate.

Next, the procedure for calculating the DC offset will be described while treating each baseband signal as a vector. When estimating the demodulation system DC offset, switch 5
12 is obtained by averaging the feedback digital baseband signal 574 that is orthogonally demodulated at that time.
When estimating the demodulation system DC offset, when the power of the transmission amplification modulation signal 564 is closer to 0, the influence on other elements is suppressed, so that highly accurate estimation is possible. Demodulation system DC
After estimating the offset, the process proceeds to estimating the DC offset of the modulation system.

When estimating the DC offset of the modulation system, the DC offset estimation unit 518 connects the switch 513 and sets the demodulation system DC compensation signal 573 to the demodulation system DC offset estimated value obtained earlier. The value of the modulation system DC compensation signal 558 is not particularly limited, but is set to 0 in this description.

Next, a vector sum is calculated for each of the results of the demodulation system digital baseband signal 574 obtained in Procedure 1 and Procedure 2. (Hereinafter, the procedure 1 vector sum and the procedure 2 vector sum) The demodulation system DC offset is compensated for in these vector sums by the demodulation system DC compensation signal 573.

The procedure 1 and procedure 2 vector sums obtained as described above are expressed by a linear transformation using the gain and phase rotation of an amplifier or the like from a modulation system to a demodulation system as a transformation vector to the sum of the vectors given by the quadrature modulator 509. (Hereinafter, this conversion vector is called a loop vector). The vector provided to the quadrature modulation unit 509 can be separated into a reference offset signal 555 and a DC offset component of a modulation system. For simplicity, the vector sum of the reference signal 553 is set to 0, and the reference at the time of procedure 1 is used. Assuming that the signal offset vector 554 is 0, the procedure 1 vector sum is equal to the linearly transformed DC offset component of the modulation system using a loop vector.

Similarly, the procedure 2 vector sum is obtained by adding the reference signal offset vector 554 as compared with the procedure 1, and the difference between them is equal to the value obtained by linearly transforming the reference signal offset vector 554 with the loop vector. . As a result, the loop vector can be calculated by multiplying the difference between the procedure 2 vector sum and the procedure 1 vector sum by the reciprocal of the reference signal offset vector 554. Further, the modulation system DC offset component can be calculated by multiplying the sum of the procedure 1 vectors by the reciprocal of the loop vector.

In this method, since a loop vector is calculated from a difference between a feedback signal and a known vector as a reference signal offset vector 554, various error factors such as DC offset of a modulation system and a demodulation system are removed, and a high-precision system is obtained. Calculation becomes possible.

In the above description, the vector sum of the reference signal 553 is assumed to be 0, but it is possible to estimate the modulation system DC offset even if it is not 0. Also, reference signal 5
By making the amplitude of 53 constant, the effect of linear distortion generated in the amplifier 510 or the like is minimized, and highly accurate DC offset estimation is enabled. Also, by arranging the reference signal 553 on the circumference, the influence of a loop vector and the like can be reduced.

The above effect is effective even when the reference signal 553 has a constant value. In particular, by setting the reference signal 553 to a constant value, the capacity of the reference signal generation unit can be reduced, and the size of the reference signal offset vector can be reduced. By doing so, it is possible to suppress the power leaking from the output modulation signal 565 to the outside of the device or the internal elements during the DC offset estimation operation to a minimum value. The magnitude of the reference signal offset vector 554 is related to the accuracy of the DC offset estimation, but if it is too large, it is affected by linear distortion of an amplifier or the like.

Although the precision is affected, it is sufficient that the magnitude is small relative to the maximum amplitude that the system can output, and the magnitude of the reference signal offset vector 554 is set to 100 minutes of the maximum amplitude. By setting from about 1 to less than 1, it is possible to suppress the leakage power at the time of DC offset estimation to -40 dBc or less with respect to the maximum output power. Furthermore, although the magnitude of the reference signal offset vector 554 is assumed to be 0 in the procedure 1, the phase is set to 1 with respect to the reference signal offset vector 554 given in the procedure 2.
By inverting by 80 degrees and having the same magnitude, double precision can be obtained with the same vector magnitude, and leakage power can be further reduced with the same precision.

Also, reference signal offset vector 454
Although is not particularly limited, since the reciprocal thereof is used in the calculation, it is obvious that setting this vector on the axis facilitates the calculation processing.

[0144]

As described above, according to the present invention, it is possible to estimate the DC offset of the modulation system and the demodulation system with high accuracy without adding any circuit. By compensating for the DC offset in this way, the characteristics are not impaired even in a modulation scheme having a high signal density such as quadrature amplitude modulation, and the DC offset is compensated even in a device that forms a feedback system. Thus, it is possible to configure a device having an extremely small error component. Further, when the DC offset is compensated by this method, the power leaked from the device can be suppressed to a very small value. Therefore, the DC offset is compensated for a short period during a period when neither the transmission system nor the demodulation system is used. It becomes possible.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a modem according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a modem according to an embodiment of the present invention;

FIG. 3 is a block diagram illustrating a configuration of a modem according to an embodiment of the present invention.

FIG. 4 is a block diagram illustrating a configuration of a modem according to an embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a modem according to an embodiment of the present invention;

FIG. 6 is a block diagram of a conventional transmission device.

[Explanation of symbols]

101, 201, 301, 401, 501 Reference signal generator 102, 204, 304, 404, 504 Baseband switch 103, 205, 305, 405, 505 Modulation DC
Compensation adders 104, 206, 306, 406, 506 D / A conversion units 105, 207, 307, 407, 507 Modulation signal band limiting filters 106, 208, 308, 409, 509 Quadrature modulation units 107, 209, 309, 410 , 510 amplifiers 108, 210, 310, 411, 511 distributors 109, 211, 412, 513 switches 110, 212, 313, 413, 514 quadrature demodulators 111, 213, 314, 414, 515 demodulated signal band limiting filter 112, 214, 312, 415, 516 A / D converter 113, 215, 416, 517 Demodulation system DC compensation adder 114, 216, 316, 416, 517, 518 DC offset estimator 202, 302, 402, 502 Vector generator 203, 303, 403, 503 Set adder 311 band-limiting filter 408 oscillator 508 modulates system oscillator 512 demodulation system oscillator

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yutaka Murakami 3-10-1 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa Prefecture Inside Matsushita Giken Co., Ltd. (72) Moriiichi Sagawa 3 Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa No. 10-1 Matsushita Giken Co., Ltd. F term (reference) 5K004 AA05 AA08 FF01 FF02 FF06 FH01 FH02 FH06 JF04

Claims (9)

[Claims] 1. A modulation / demodulation device provided in a communication device of a wireless communication system using a digital modulation method, comprising:
Reference signal generating means for generating a reference signal for compensating for an offset, switching means for switching between the reference signal and the digital baseband signal, and first output for inputting an output of the switching means and compensating for a modulation system DC offset. Adding means, and a D / D converter for converting the output of the first adding means into an analog signal.
A conversion means, quadrature modulation means for modulating the analog-converted quadrature baseband signal to a carrier frequency, distribution means for distributing the modulated signal, and a switch for turning on / off passage of the divided one as a feedback modulation signal Means, orthogonal demodulation means for orthogonally demodulating the feedback modulated signal, and A for digitally converting the orthogonally demodulated orthogonal baseband signal.
/ D conversion means, second addition means for inputting the digitally converted quadrature baseband signal to compensate for DC offset in a demodulation system, and a modulation system using the reference signal and the output of the second addition means. A modulation / demodulation device comprising: a DC offset estimating means for estimating a DC offset of a demodulation system. 2. A modulation / demodulation device provided in a communication device of a radio communication system using a digital modulation method, comprising:
Reference signal generating means for generating a reference signal for compensating for an offset, vector generating means for generating a reference signal offset vector, first adding means for adding the reference signal and the reference signal offset vector, Switching means for switching between the output of the first addition means and the digital baseband signal; second addition means for inputting the output of the switching means to compensate for the DC offset of the modulation system; and outputting the output of the second addition means. D / A conversion means for performing analog conversion, quadrature modulation means for modulating the analog-converted quadrature baseband signal to a carrier frequency, distribution means for distributing the modulated signal, and passing the distributed one as a feedback modulation signal. Switch means for turning on / off, quadrature demodulation means for quadrature demodulating the feedback modulated signal, quadrature baseband for quadrature demodulation A / D conversion means for digitally converting the signal, third addition means for inputting the digitally converted quadrature baseband signal and compensating for a DC offset in a demodulation system, output of the first addition means and the third And a DC offset estimating means for estimating the DC offset of the modulation system and the demodulation system using the output of the adding means. 3. A modulation / demodulation device provided in a communication device of a wireless communication system using a digital modulation method, comprising:
Reference signal generating means for generating a reference signal for compensating for an offset, vector generating means for generating a reference signal offset vector, first adding means for adding the reference signal and the reference signal offset vector, Switching means for switching between the output of the first addition means and the digital baseband signal; second addition means for inputting the output of the switching means to compensate for the DC offset of the modulation system; and outputting the output of the second addition means. D / A conversion means for performing analog conversion, quadrature modulation means for modulating the analog-converted quadrature baseband signal to a carrier frequency, distribution means for distributing the modulated signal, and digital conversion using one of the distributed signals as a feedback modulation signal A / D conversion means for performing quadrature demodulation for performing a quadrature demodulation of the feedback digital modulation signal, and an output of the first addition means. Modem apparatus and a DC offset estimating means for estimating a DC offset of the modulation system using the output of the serial quadrature demodulation means. 4. A modulation / demodulation device provided in a communication device of a wireless communication system using a digital modulation method, comprising:
Reference signal generating means for generating a reference signal for compensating for an offset, vector generating means for generating a reference signal offset vector, first adding means for adding the reference signal and the reference signal offset vector, Switching means for switching between the output of the first adding means and the digital baseband signal; second adding means for receiving the output of the switching means to compensate for a DC offset in a modulation system; D / A converting means for performing analog conversion, oscillating means serving as a frequency source, quadrature modulating means for modulating the analog converted quadrature baseband signal to a carrier frequency based on the output of the oscillating means, and distributing the modulated signal. Distribution means; quadrature demodulation means for performing quadrature demodulation based on the output of the oscillating means as one of the divided signals as a feedback modulation signal; Switch means for turning on / off the passage of an output to the quadrature demodulation means, A / D conversion means for digitally converting the quadrature demodulated quadrature baseband signal, and demodulation by inputting the digitally converted quadrature baseband signal Addition means for compensating for the system DC offset, and D for estimating the DC offset of the modulation system and the demodulation system using outputs of the first addition means and the third addition means.
A modulation / demodulation device comprising C offset estimating means. 5. A modulation / demodulation device provided in a communication device of a wireless communication system using a digital modulation method, comprising:
Reference signal generating means for generating a reference signal for compensating for an offset, vector generating means for generating a reference signal offset vector, first adding means for adding the reference signal and the reference signal offset vector, Switching means for switching between the output of the first addition means and the digital baseband signal; second addition means for inputting the output of the switching means to compensate for the DC offset of the modulation system; and outputting the output of the second addition means. D / A conversion means for performing analog conversion, first oscillating means serving as a frequency source of a modulation section, and quadrature for modulating the analog baseband signal converted to analog on the basis of an output of the first oscillating means to a carrier frequency. A modulating unit, a distributing unit for distributing a modulated signal, a second oscillating unit serving as a frequency source of a demodulation unit, an output of the first oscillating unit and the second oscillating unit. Frequency source selecting means for selecting any one of the outputs of the stages, quadrature demodulating means for quadrature demodulating one of the distributed signals based on the output of the frequency source selecting means as a feedback modulation signal, and the quadrature demodulated quadrature baseband A / D conversion means for digitally converting a signal, and a demodulation system D which receives the digitally converted quadrature baseband signal as input.
A third adder for compensating for the C offset; and a DC offset estimator for estimating a DC offset of a modulation system and a demodulation system using an output of the first adder and an output of the third adder. Modem. 6. The modulation / demodulation device according to claim 1, wherein the reference signal has a constant amplitude. 7. The modulation / demodulation device according to claim 1, wherein the reference signal has a constant value. 8. The magnitude of the reference signal offset vector is one hundredth of the maximum amplitude of the baseband signal.
The modulation / demodulation device according to any one of claims 2 to 5, wherein: 9. The method according to claim 2, wherein only the sign of the reference signal offset vector is inverted before and after the switching.
6. The modulation / demodulation device according to any one of claims 1 to 5.