U.S. patent application number 09/968024 was filed with the patent office on 2003-04-10 for transmission apparatus.
This patent application is currently assigned to MATSUSHITA ELECTRIC INDUSTRIAL CO., Ltd.. Invention is credited to Matsuoka, Akihiko, Misaizu, Kouei, Orihashi, Masayuki, Sagawa, Morikazu, Takahashi, Kenichi.
Application Number | 20030067995 09/968024 |
Document ID | / |
Family ID | 26565227 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030067995 |
Kind Code |
A1 |
Matsuoka, Akihiko ; et
al. |
April 10, 2003 |
Transmission apparatus
Abstract
A wireless communication system includes an amplitude limiting
section that limits an amplitude of a sequence of signals input for
transmission and a nonlinear distortion compensating section
compensates nonlinear distortion of the sequence of signals output
from the amplitude limiting section. A digital wireless
communication method is also provided.
Inventors: |
Matsuoka, Akihiko;
(Yokohama-shi, JP) ; Orihashi, Masayuki;
(Ichikawa-shi, JP) ; Sagawa, Morikazu; (Tokyo,
JP) ; Takahashi, Kenichi; (Kawasaki-shi, JP) ;
Misaizu, Kouei; (Yokohama-shi, JP) |
Correspondence
Address: |
GREENBLUM & BERNSTEIN, P.L.C.
1950 ROLAND CLARKE PLACE
RESTON
VA
20191
US
|
Assignee: |
MATSUSHITA ELECTRIC INDUSTRIAL CO.,
Ltd.
Osaka
JP
|
Family ID: |
26565227 |
Appl. No.: |
09/968024 |
Filed: |
October 2, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09968024 |
Oct 2, 2001 |
|
|
|
09101443 |
Jul 15, 1998 |
|
|
|
6418173 |
|
|
|
|
09101443 |
Jul 15, 1998 |
|
|
|
PCT/JP97/04132 |
Nov 13, 1997 |
|
|
|
Current U.S.
Class: |
375/296 |
Current CPC
Class: |
H03F 1/3294 20130101;
H03C 3/406 20130101; H03F 2200/57 20130101; H03F 1/3247 20130101;
H03F 2201/3233 20130101; H04L 27/368 20130101; H03F 1/3258
20130101 |
Class at
Publication: |
375/296 |
International
Class: |
H04K 001/02; H04L
025/03; H04L 025/49 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 19, 1996 |
JP |
JP8-307685 |
Nov 19, 1996 |
JP |
JP8-307686 |
Claims
What is claimed:
1. A digital wireless communication system comprising: an amplitude
limiting section that limits an amplitude of a sequence of signals
input for transmission; and a nonlinear distortion compensating
section that compensates nonlinear distortion of the sequence of
signals output from said amplitude limiting section.
2. A digital wireless communication system according to claim 1,
wherein the compensated sequence of signals output from said
nonlinear distortion compensating section is converted to radio
frequency signals and amplified for transmission.
3. A method for digital wireless communication comprising: limiting
an amplitude of a sequence of signals input for transmission; and
compensating nonlinear distortion of the amplitude limited sequence
of signals.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Continuation of U.S. application Ser.
No. 09/101,443, filed Jul. 15, 1998, which was the National Stage
of International Application No. PCT/JP97/04132, filed Nov. 13,
1997, the contents of which are herein incorporated by reference in
their entireties. The International Application was not published
under PCT Article 21(2) in English.
TECHNICAL FIELD
[0002] The present invention relates to a nonlinear distortion
compensating technique in a transmission apparatus for digital
radio communications.
BACKGROUND ART
[0003] In recent years, a mobile communication system using a
digital modulation method has vigorously been researched and
developed. If a high efficiency amplifier is employed in the
transmission system in order to attempt to save power at a radio
transceiver, nonlinear distortions frequently result therefrom. As
a means, there is a method for compensating nonlinear distortions
of amplitude and phase with reference to a distortion compensating
table, by using an amplitude value of transmission base band
signals.
[0004] A description is given of a conventional transmission
apparatus which compensates nonlinear distortions by using such a
method.
[0005] FIG. 10 is a main block diagram of a conventional
transmission apparatus. In FIG. 10, amplitude calculating section
1001 calculates amplitude information 1010 of transmission signals
1009 (transmission digital quadrature base band of I and Q
channels), and compensation table 1002 outputs distortion
compensating coefficient 1011. The distortion compensating section
1003 outputs a distortion compensating signal 1012 according to the
transmission signal 1009 and distortion compensating coefficient
1011. The outputted distortion compensation signal 1012 is
quadrature-modulated by quadrature modulating section 1004, and the
modulated signal 1013 is amplified by amplifier 1005, wherein
amplified RF signal 1014 is outputted.
[0006] Furthermore, demodulating section 1007 demodulates feedback
RF signal 1016 fed back from coupler 1006 to feedback base band
signal 1017, and estimating section 1008 updates the distortion
compensation coefficient of compensation table 1002 on the basis of
a distortion compensation coefficient 1018, transmission signal
1009 and feedback base band signal 1017. Through the abovementioned
actions, amplified RF signal 1015 for which nonlinear distortion
compensation is carried out is outputted from the coupler 1006.
[0007] In addition thereto, as a method to compensate nonlinear
distortions in the transmission system, there is a method having a
digital filter to which a ROM (Read-only-memory) is attached,
wherein compensation is carried out by applying in advance
distortions to compensate nonlinear distortions generated in an
amplifier by the digital filter.
[0008] The main block diagram of a conventional transmission
apparatus in which this method is employed is shown in FIG. 11.
Hereinafter, a description is given to this apparatus.
[0009] In FIG. 11, digital filter 1102 in which digital signals
1101 is inputted gives to the digital signal 1101 distortions to
compensate nonlinear distortion components generated in radio
frequency power amplifier 1105, by using distortion information
stored in a ROM in advance.
[0010] The digital signal 1101 to which distortion to be
compensated is given is digital-analog converted and modulated by
quadrature modulating section 1103 and inputted into the radio
frequency power amplifier 1105 via transmission section 1104. In
the radio frequency power amplifier 1105, since distortion of the
inputted digital signal are compensated in advance, distortions
generated at the radio frequency power amplifier 1105 are cancelled
by those for compensation.
[0011] Furthermore, instead of ROM, there is still another method
to compensate nonlinear distortions, in which a RAM (Random Access
Memory) having compensation coefficients stored therein in order to
compensate nonlinear distortion components is used, by varying the
compensation coefficients of the RAM in compliance with amplitudes
of digital signals.
[0012] Furthermore, Unexamined Japanese Patent Publication No.
290321 of 1992 discloses a method for controlling actions of a
digital filter by feeding outputs of a radio frequency power
amplifier back to the digital filter.
[0013] However, in the conventional example shown in FIG. 10, it is
necessary that signals having the maximum amplitude is suppressed
less than the maximum output of amplifier 1005, and this results in
a lowering of efficiency in the amplifier 1005.
[0014] In the conventional example shown in FIG. 11, since it is
necessary to provide a memory table such as a ROM or RAM in which
compensation coefficients are stored to compensate nonlinear
distortion components, and this results in an increase of the scale
of transmission circuits themselves.
DISCLOSURE OF INVENTION
[0015] It is therefore an object of this invention to provide a
transmission apparatus capable of easily controlling leak power and
easily improving the efficiency of power amplification and cable of
compensating nonlinear distortions generated in a transmission
system amplifier without any use of a memory table such as a ROM or
RAM.
[0016] The first aspect of the invention resides in a transmission
apparatus having a nonlinear distortion compensating circuit, which
includes an amplitude limiting function for transmission quadrature
base band signals by adding an amplitude calculating section, an
amplitude limiting table and an amplitude limiting section thereto.
Thereby, it is possible to easily improve the efficiency of
amplification section with distortions of the entire system
limited.
[0017] The second aspect of the invention is such that nonlinear
distortion compensation is carried out on the basis of nonlinear
distortion compensation coefficients calculated by an approximation
equation in a compensation coefficient calculating section.
Thereby, it is possible to compensate nonlinear distortions
generated by amplifier in the transmission system without any use
of a memory table such as a ROM or RAM, and it is possible to make
a nonlinear distortion compensating section small-sized.
[0018] Furthermore, this invention is constructed so that it is
provided with a first amplitude calculating section for calculating
the first amplitude value of transmission quadrature base band
signals; an amplitude limiting table for storing amplitude limiting
information corresponding to the first amplitude value; a first
amplitude limiting section for limiting the amplitude of the
transmission quadrature base band signals by using the amplitude
limiting information; a quadrature modulating section for
outputting RF signals by quadrature-modulating the transmission
quadrature base band signals, the amplitude of which is limited;
and an amplification section for amplifying the RF signals.
[0019] With this construction, it is possible to improve the
efficiency of an amplifying section with distortion components
limited, by executing distortion compensation of an amplifier with
respect to limited signals, the maximum amplitude of which is
distorted by the transmission quadrature base band signals.
[0020] Furthermore, the invention is constructed so that it is
provided with a first amplitude calculating section for calculating
the first amplitude value from transmission quadrature base band
signals; a limiting coefficient calculating section for calculating
an amplitude limiting coefficient corresponding to the first
amplitude value; a second amplitude limiting section for limiting
the amplitude of the transmission quadrature base band signal by
using the amplitude limiting coefficient; a quadrature modulating
section for quadrature-modulating the transmission quadrature base
band signals to output RF signals, the amplitude of which is
limited; and an amplification section for amplifying the RF
signals.
[0021] With this construction, the amplitude limiting coefficient
is calculated on the basis of amplitude information of the
transmission quadrature base band signals, whereby it is possible
to improve the efficiency of amplifier by limiting the amplitude of
transmission signals in compliance with the amplitude limiting
coefficient with the distortion components limited, without adding
any memory thereto.
[0022] Furthermore, this invention is constructed so that it is
provided with a power calculating section for calculating a power
value of transmission quadrature base band signals; a compensation
coefficient calculating section for calculating a nonlinear
distortion compensation coefficient according to approximation
equation set in advance using the power value; a distortion
compensating section for carrying out nonlinear distortion
compensation of the transmission quadrature base band signals by
using the nonlinear distortion compensation coefficient; a
quadrature modulating section for quadrature-modulating
transmission quadrature base band signals, the distortion of which
is compensated; and an amplifier for amplifying the quadrature
modulation signal.
[0023] With this construction, with only slight memory capacity, it
is possible to compensate nonlinear distortion which is generated
at an amplifier of transmission system.
[0024] Furthermore, the invention is constructed so that it is
provided with a power calculating section for calculating a power
value of transmission quadrature base band signals; a compensation
coefficient calculating section for calculating an amplitude
distortion compensation coefficient by an approximation equation
set in advance by using the power value; a quadrature modulating
section for quadrature-modulating the transmission quadrature base
band signals; and an amplitude distortion compensating section for
compensating amplitude distortions of quadrature modulation signals
using the amplitude distortion compensation coefficient.
[0025] With this construction, it is possible to compensate
amplitude distortions, which is generated at an amplifier of
transmission system, with simple calculations and slight memory
capacity.
[0026] Furthermore, the invention is constructed so that it is
provided with a power calculating section for calculating a power
value of transmission quadrature base band signals; a compensation
coefficient calculating section for calculating an amplitude
distortion compensation coefficient by an approximation equation
set in advance by using the power value; a quadrature modulating
section for quadrature-modulating the transmission quadrature base
band signals; an amplitude distortion compensating section for
compensating amplitude distortions of quadrature modulation signals
by using the amplitude distortion compensating coefficient; an
amplifier for amplifying modulation signals; a distributor for
distributing output of the amplifier; a quadrature demodulator for
carrying out quadrature demodulate with one of the outputs of the
distributor inputted; and a coefficient updating section which
calculates an error by comparing quadrature demodulate signals with
the power value and updates the value of coefficients of the
approximation equation on the basis of the error.
[0027] With this construction, it is possible to very accurately
compensate amplitude distortions by lowering the error of amplitude
distortion compensation data calculated by an approximation
equation through a feedback loop.
BRIEF DESCRIPTION OF DRAWINGS
[0028] FIG. 1 is a main block diagram of a transmission apparatus
according to a first embodiment of the invention,
[0029] FIG. 2 is a main block diagram of a transmission apparatus
according to a second embodiment of the invention,
[0030] FIG. 3 is a main block diagram of a transmission apparatus
according to a third embodiment of the invention,
[0031] FIG. 4 is a main block diagram of a transmission apparatus
according to a fourth embodiment of the invention,
[0032] FIG. 5 is a main block diagram of a transmission apparatus
according to a fifth embodiment of the invention,
[0033] FIG. 6 is a main block diagram of a transmission apparatus
according to a sixth embodiment of the invention,
[0034] FIG. 7 is a main block diagram of a transmission apparatus
according to a seventh embodiment of the invention,
[0035] FIG. 8 is a main block diagram of a transmission apparatus
according to a eighth embodiment of the invention,
[0036] FIG. 9 is a main block diagram of a transmission apparatus
according to a ninth embodiment of the invention,
[0037] FIG. 10 is a main block diagram of a conventional
transmission apparatus, and
[0038] FIG. 11 is a main block diagram of another conventional
apparatus other than the above apparatus.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] Hereinafter, a detailed description is given of embodiments
of a transmission apparatus according to the invention.
[0040] (Embodiment 1)
[0041] FIG. 1 is a main block diagram of a transmission apparatus
according to a first embodiment of the invention.
[0042] A transmission apparatus illustrated in FIG. 1 comprises
first amplitude calculating section 101, amplitude limiting table
102, amplitude limiting section 103, nonlinear distortion
compensating section 104, quadrature modulating section 108,
amplification section 109, etc.
[0043] Nonlinear distortion compensating section 104 has second
amplitude calculating section 105, compensating table 106 using a
RAM, distortion compensating section 107, coupler 110, demodulating
section 111, and estimating section 112.
[0044] Furthermore, in FIG. 1, reference number 113 indicate a
transmission signal (Transmission digital quadrature base band
signal in I and Q channel), reference number 114 indicate amplitude
information of the transmission signal, reference number 115
indicate an amplitude limiting coefficient, reference number 116
indicate an amplitude limiting signal, reference number 117
indicate limiting amplitude information, reference number 118
indicate a distortion compensation coefficient, reference number
119 indicate a distortion compensation signal, reference number 120
indicate an RF signal, reference number 121 indicate an amplitude
RF signal, reference number 122 indicate an output signal,
reference number 123 indicate a feedback RF signal, reference
number 124 indicate a feedback base band signal, and reference
number 125 indicate a coefficient updating signal.
[0045] A description is given of the actions of a transmission
apparatus constructed as described above.
[0046] The first amplitude calculating section 101 calculates
amplitude information 114 on the basis of transmission signal 113
and outputs it. In amplitude limiting table 102, proper amplitude
limiting information is stored in advance with respect to a
modulation method designed on the basis of noise margin and leak
power value as its entirety, and amplitude limiting coefficient 115
is outputted in response to amplitude information 114.
[0047] Amplitude limiting section 103 limits the amplitude of
transmission signal 113 in accordance with the amplitude limiting
coefficient 115 and outputs an amplitude limiting signal 116 thus
obtained. The amplitude limiting executed herein is to limit the
protrudent amplitude in only a slightly short time. Furthermore, it
is clear that the leak power of amplitude limiting signal 116 can
be designed in advance on the basis of a modulation method and
amplitude limiting information.
[0048] Nonlinear distortion compensating section 104 compensates
nonlinear distortions of amplifier 109 almost as in the description
with reference to FIG. 10 in the conventional example.
[0049] That is, the second amplitude calculating section 105
calculates limiting amplitude information 117 from amplitude
limiting signal 116 and outputs it. Compensation table 106 outputs
distortion compensation coefficient 118 in response to limiting
amplitude information 117. Distortion compensating section 107
calculates distortion compensation signal 119 on the basis of
distortion compensation coefficient 118 and amplitude limiting
signal 119. Quadrature modulating section 108 modulates distortion
compensation signals 119 to radio frequency (RF) signals 120 which
are signals of carrier band. Amplifier 109 amplifies the power of
RF signals 120 and outputs amplified RF signals 121.
[0050] Coupler 110 outputs a part of amplified RF signals 121 as a
feedback RF signal 123 and outputs the remaining thereof as output
signals 122. Demodulator 111 demodulates the feedback RF signal 123
to a feedback base band signal 124. The estimating section 112
updates, using the amplitude limiting signal 116 as a target value,
distortion compensation coefficients stored in the compensation
table 106 by a coefficient updating signal 125 in compliance with a
distortion compensation coefficient 118 read by the coefficient
updating signal 125, limiting amplitude information 117 and
feedback base band signal 124.
[0051] As a result, the linearity between amplitude limiting signal
116 and feedback base band signal 124 will be retained by a
distortion compensation coefficient stored in compensation table
106.
[0052] The distortion components of the output signal 122 are
equalized to the distortion components of the amplitude limiting
signal 116. As described above, the amplitude limiting signal 116
can be easily designed on the basis of modulation method and the
amplitude limiting information stored in amplitude limiting table
102, wherein it is possible to control distortion components as the
entire system by the amplitude limiting information.
[0053] In a prior nonlinear distortion compensation technique, the
maximum amplitude signal is assigned to the maximum output value of
an amplifier. However, since signals having the maximum amplitude
have a very low ratio of existence, they will not exert any great
influence as leak power even though the maximum amplitude signals
are slightly distorted. Therefore, if the amplitude of the maximum
amplitude signals is limited and its average amplitude is
relatively raised, it becomes possible to improve the amplification
efficiency of an amplifier.
[0054] Thus, according to the first embodiment, since the amplitude
of signals having a great amplitude is limited before carrying out
nonlinear distortion compensation, the maximum amplitude value is
lowered, wherein the amplifier 121 has an allowance to improve the
mean power.
[0055] On the other hand, distortion components, the amplitude of
which is limited, can be designed in advance on the basis of its
modulation system and limiting properties, the leak power resulting
from the nonlinearity outside the signal band can be suppressed
less than the prescribed level, wherein the area of nonlinearity of
the amplifier 121 is used to cause the efficiency of power
amplification to be improved.
[0056] Thus, since it is possible to easily control the distortion
components, it is possible to construct a more efficient
transmission apparatus than that according to the prior nonlinear
distortion compensation technique.
[0057] Generally, suppression of signals having a great amplitude
is effective in improving the efficiency. However, it is also
possible to secure the same effect by elongating signals having a
small amplitude. Furthermore, by making the amplitude width narrow
by a combination of the former and the latter, the efficiency can
be further improved.
[0058] (Embodiment 2)
[0059] FIG. 2 is a main block diagram of a transmission apparatus
according to a second embodiment of the invention. However, parts
in the second embodiment illustrated in this drawing, which
correspond to those of the first embodiment illustrated in FIG. 1
are given the same reference numbers, and the description thereof
is omitted.
[0060] A transmission apparatus shown in FIG. 2 is different from
that shown in FIG. 1 in that, as shown at the nonlinear distortion
compensating section 201 of FIG. 2, the second amplitude
calculating section 105 of the nonlinear distortion compensating
section 104 shown in FIG. 1 is omitted, and amplitude information
114 of the transmission signals outputted from the amplitude
calculating section 101 is outputted to the compensation table 106
and estimating section 112.
[0061] In such a construction, amplitude information 114 calculated
by the first amplitude calculating section 101 is outputted to the
compensation table 106 and estimating section 112, and the
compensation table 104 outputs distortion compensation coefficients
118 in compliance with the amplitude information 114.
[0062] Furthermore, using the amplitude limiting signal 116 as a
target value, the estimating section 112 updates the distortion
compensation coefficients stored in the compensation table 106 by a
coefficient updating signal 125 in compliance with distortion
compensation coefficients read from the compensation table 106 by
the coefficient updating signal 125, amplitude information 114, and
feedback base band signal 124. The other actions are the same as
those described in the first embodiment.
[0063] Thus, according to the second embodiment, since the
nonlinear distortion compensating section 201 is constructed with
the amplitude calculating section omitted in addition to securing
the same effects as those of the first embodiment, the
configuration thereof can be further simplified than the first
embodiment. The entire size thereof can be reduced.
[0064] (Embodiment 3)
[0065] FIG. 3 is a main block diagram of a transmission apparatus
according to a third embodiment of the invention. However, parts in
the third embodiment illustrated in this drawing, which correspond
to those of the first embodiment illustrated in FIG. 1 are given
the same reference numbers, and the description thereof is
omitted.
[0066] A transmission apparatus illustrated in FIG. 4 is different
from that shown in FIG. 1 in that a limiting coefficient
calculating section 301 shown in FIG. 2 is provided instead of the
amplitude limiting table 102 shown in FIG. 1 and the amplitude
limiting coefficient 302 calculated by the limiting coefficient
calculating section 301 is outputted to the amplitude limiting
section 103.
[0067] Furthermore, a limiting coefficient calculating section 301
can be achieved by a surplus calculation performance of DSP
(Digital Signal Processor) (not illustrated) which is a component
of the transmission apparatus along with the first amplitude
calculating section 101 and amplitude limiting section 103.
[0068] In such a construction, in limiting coefficient calculating
section 301, a proper amplitude limiting coefficient calculation
method is defined in advance with respect to a modulation system
which is designed on the basis of noise margin and leak power value
as the entire system, and amplitude limiting coefficients 302 are
outputted in compliance with the amplitude information 114. The
amplitude limiting section 103 calculates amplitude limiting
signals 116 on the basis of amplitude limiting coefficient 302 and
transmission signal 113.
[0069] The amplitude limiting signal 116 can be easily designed by
a modulation system and a calculation method defined by the
limiting coefficient calculating section 301, wherein it is
possible to control distortion components as the entire system by
the amplitude limiting coefficient calculation method. The other
actions are the same as those of the first embodiment.
[0070] Thus, according to the third embodiment, limiting
coefficient calculation part 301 which already exists as a
component of the transmission apparatus is provided instead of the
amplitude limiting table 102 constructed using memories such as a
ROM, etc. in addition to securing the same effects as those of the
first embodiment. Therefore, it is possible to further simplify the
apparatus than the first embodiment, and the entire system can be
small-sized.
[0071] (Embodiment 4)
[0072] FIG. 4 is a main block diagram of a transmission apparatus
according to a fourth embodiment of the invention. However, parts
in the fourth embodiment illustrated in this drawing, which
correspond to those of the third embodiment illustrated in FIG. 3
are given the same reference numbers, and the description thereof
is omitted.
[0073] A transmission apparatus illustrated in FIG. 4 is different
from that illustrated in FIG. 3 in that, as shown in the nonlinear
distortion compensating section 201 in FIG. 4, the second amplitude
calculating section 105 of the nonlinear distortion compensating
section 104 shown in FIG. 3 is omitted, and amplitude information
114 of transmission signals outputted from the amplitude
calculation portion 101 is outputted to the compensation table 106
and estimating section 112.
[0074] In such a construction, the amplitude information 114
calculated by the amplitude calculating section 101 is outputted to
the compensation table 106 and estimating section 112, wherein the
compensation table 104 outputs distortion compensation coefficients
118 in compliance with the amplitude information 114.
[0075] Furthermore, using the amplitude limiting signal 116 as a
target value, the estimating section 112 updates distortion
compensation coefficients stored in the compensation table 106 by a
coefficient updating signal 125 in compliance with the distortion
compensation coefficient read from the compensation table 106 by
the coefficient updating signal 125, amplitude information 114 and
feedback base band signal 124. The other actions thereof are the
same as those of the third embodiment.
[0076] Thus, according to the fourth embodiment, it is possible to
obtain effects similar to those of the third embodiment, and since
the amplitude calculating section is omitted from the nonlinear
distortion compensating section 201, it is possible to further
simplify the apparatus than the third embodiment, and the entire
system can be small-sized.
[0077] (Embodiment 5)
[0078] FIG. 5 is a main block diagram of a transmission apparatus
according to a fifth embodiment of the invention. However, parts of
the fifth embodiment shown in FIG. 5, which correspond to those of
the first embodiment shown in FIG. 1, are given the same reference
numbers, and the description thereof is omitted.
[0079] In FIG. 5, reference number 501 is a nonlinear distortion
compensating section, reference number 502 is a threshold value
storing section, reference number 503 is an amplitude comparator,
reference number 504 is a first compensation table, reference
number 505 is a second compensation table, reference number 506 is
a coefficient selecting section, reference number 512 is an
estimating section, reference number 513 is a writing selecting
section, reference number 516 is threshold value information,
reference number 517 is a result of amplitude comparison, reference
number 518 is a first compensation coefficient, reference number
519 is a second compensation coefficient, reference number 520 is a
distortion compensation coefficient, reference number 527 is a
coefficient renewing signal, reference number 528 is a first
updating signal, reference number 529 is a second updating
signal.
[0080] A description is given of the actions of a transmission
apparatus thus constructed. The amplitude calculating section 105
calculates and outputs amplitude information 117 on the basis of
transmission signal 116. The threshold value storing section 502
outputs threshold value information 516. The comparator 503
compares amplitude information 117 with threshold value information
516, and outputs the result 517 of amplitude comparison, which
shows whether the amplitude is grater or smaller than the threshold
value.
[0081] The first compensation table 504 and the second compensation
table 505 output the first compensation coefficient 518 and the
second compensation coefficient 519 in compliance with amplitude
information 117. Coefficient selecting section 506 selects any one
of the first compensation coefficient 518 and the second
compensation coefficient 519 on the basis of the result 517 of
amplitude comparison and outputs distortion compensation
coefficient 520.
[0082] For example, in a case where the result 517 of amplitude
comparison shows that the amplitude is smaller than the threshold
value, the coefficient selecting section 506 selects the first
compensation coefficient 518 and outputs it as distortion
compensation coefficient 520. If it is shown that the amplitude is
greater than the threshold value, the coefficient selecting section
506 selects the second compensation coefficient 519 and outputs it
as distortion compensation coefficient 520. The distortion
compensating section 107 calculates distortion compensation signal
521 on the basis of transmission signal 113 and distortion
compensation coefficient 520 and outputs it to the quadrature
modulating section 108.
[0083] Furthermore, using the transmission signal 514 as the target
value, the estimating section 512 renews a coefficient updating
signal 527 in compliance with the distortion compensation
coefficient read as coefficient updating signal 527 through the
write selecting section 513, amplitude information 515, amplitude
comparison result 517 and feedback base band signal 124 and outputs
the first updating signal 528 or the second updating signal
529.
[0084] The write section section 513 selects the renewed
coefficient updating signal 527 from the first updating signal 528
and the second updating signal 529 on the basis of the amplitude
comparison result 517 and renews the distortion compensation
coefficients of the first compensation table 504 or the second
compensation table 505. For example, in a case where the amplitude
comparison result 517 shows that the amplitude is smaller than the
threshold value, the write selecting section 513 selects the
renewed coefficient updating signal 527 from the first updating
signal 528 and renews a distortion compensation coefficient of the
first compensation table 504, and in a case where the amplitude
comparison result 517 shows that the amplitude is larger than the
threshold value, the write selecting section 513 selects the
renewed coefficient updating signal 527 from the second updating
signal 529, and renews the distortion compensation coefficient of
the second compensation table 505.
[0085] Therefore, in a prior nonlinear distortion compensation
technique, the maximum amplitude signal is assigned to the maximum
output value of an amplifier. However, since signals having the
maximum amplitude have a very low ratio of existence, they will not
exert any great influence as leak power even though the maximum
amplitude signals are slightly distorted. Therefore, the distortion
compensation coefficient is renewed so as to keep the linearity in
the first compensation table, and the distortion compensation
coefficient is renewed so as to adjust only the phase in the second
compensation table, wherein it is possible to cause signals of a
large amplitude to have a feature by which the signals are not
greatly distorted since the linearity is kept at the phase
components while the amplitude is properly limited by a lowering of
the gain of the amplifier.
[0086] Furthermore, since the amplitude of the maximum amplitude
signal is limited, the mean amplitude is relatively increased, and
it is possible to improve the amplification efficiency of an
amplifier.
[0087] Thus, according to the fifth embodiment, since it is
possible to control the distortion components with a simple
construction, it is possible to construct a more efficient
transmission apparatus than a conventional nonlinear distortion
compensation technique.
[0088] (Embodiment 6)
[0089] FIG. 6 is a main block diagram of a transmission apparatus
according to the sixth embodiment of the invention.
[0090] In FIG. 6, reference number 600 indicate a nonlinear
distortion compensating section, reference number 601 indicate a
transmission digital quadrature base band signal on I and Q
channels, reference number 602 indicate a power calculating
section, reference number 603 indicate an amplitude value
calculated in the power calculating section 602, reference number
604 indicate a compensation coefficient calculating section for
nonlinear distortion compensation, reference number 605 indicate
quadrature nonlinear distortion compensation data, reference number
606 indicate a distortion compensating section, reference number
607 indicate a quadrature base band signal for which nonlinear
distortion is compensated, reference number 608 indicate a D/A
converting section, reference number 609 indicate an analog
quadrature base band signal, reference number 610 indicate a low
band pass filter for limiting the band, reference number 611
indicate a band-limited analog quadrature base band signal,
reference number 612 indicate a quadrature modulator, reference
number 613 indicate a modulation signal, reference number 614
indicate a transmission system amplifier, and reference number 615
indicate an amplified transmission modulation signal.
[0091] Furthermore, the nonlinear distortion compensating section
600 is achievable by a surplus calculation performance of DSP (not
illustrated), which is a component of the transmission apparatus.
That is, calculation equations which are used by each power
calculating section 602, compensation coefficient calculating
section 604, and distortion compensating section 606 is
incorporated in programs of the DSP, and a coefficient which the
compensation coefficient calculating section 604 uses for
calculation is achievable by being stored in a data area in the
programs of the DSP.
[0092] A description is given of the actions of the transmission
apparatus thus constructed. Firstly, an amplitude value 603 of a
transmission signal is calculated by the power calculating section
602 on the basis of the transmission digital quadrature base band
signal 601. This is calculated as shown in the following equation
(1) where the amplitude value 603 is assumed to be "P".
P=I.sup.2+Q.sup.2 (1)
[0093] Next, using the calculated transmission signal amplitude
value 603 as an input value, nonlinear distortion compensation data
605, having an inversed characteristic of the transmission system
nonlinear distortion characteristics, in which the nonlinear
distortion compensation data is quadratured, is calculated by the
compensation coefficient calculation section 604. This is, for
example, an n-dimensional polynomial in which P is used as an
input, wherein the same phase component Ci and quadrature component
Cq are calculated as in the following equations (2) and (3).
Ci=a.sub.inP.sup.n+a.sub.in-1P.sup.n-1+ . . .
+a.sub.i1P.sup.1+a.sub.i0P.s- up.0 (2)
Cq=a.sub.qnP.sup.n+a.sub.qn-1P.sup.n-1+ . . .
+a.sub.q1P.sup.1+a.sub.q0P.s- up.0 (3)
[0094] The distortion compensating section 606 provides a complex
product of the transmission digital quadrature base band signal 601
and the quadratured nonlinear distortion compensation data 605 and
outputs a quadrature base band signal 607, the nonlinear distortion
of which is compensated. This is calculated as in the following
equations (4) and (5) where I and Q channel components of the
quadrature base band signal 607 are respectively I' and Q';
I'=IC.sub.i-QC.sub.q (4)
Q'=IC.sub.q+QC.sub.i (5)
[0095] The quadrature base band signal 607 in which the nonlinear
distortion is compensated is converted to analog signals by a D/A
converting section 608, and is band-limited by a low band pass
filter 610, wherein an analog quadrature base band signal 611 is
obtained. After quadrature modulation is carried out by a
quadrature modulator 612 and a modulated signal 613 is obtained, it
is amplified to a necessary size by a transmission system amplifier
614, wherein a transmission modulation signal 615 is outputted.
[0096] Furthermore, a quadrature modulator 612 is replaced for such
a type as is able to carry out quadrature modulation of digital
quadrature base band signals, and a D/A converter and a low band
pass filter may be connected between the quadrature modulator and
amplifier 614.
[0097] This, according to the sixth embodiment, the nonlinear
distortion compensating section 600 is constructed so that signal
power is obtained from the inputted quadrature base band signal, a
distortion compensation coefficient is calculated by an
approximation equation for distortion compensation, in which the
value is used as a parameter, nonlinear distortion compensation is
carried out using the distortion compensation coefficient, and
simultaneously the coefficient of the approximation equation is
renewed using an error between the quadrature signal obtained by
demodulating the output to which the modulation output is shared,
and the quadrature base band signal. Therefore, nonlinear
distortion compensating section 600 for compensating nonlinear
distortions generated in the transmission system amplifier 614 can
be constructed to be small-sized without use of memory tables
achieved by a RAM or a ROM, etc.
[0098] (Embodiment 7)
[0099] FIG. 7 is a main block diagram of a transmission apparatus
of a seventh embodiment of the invention. However, parts of the
seventh embodiment, shown in FIG. 7, which correspond to those of
the sixth embodiment shown in FIG. 6 are given the same reference
numbers, and the description thereof is omitted.
[0100] In FIG. 7, reference number 700 indicate a nonlinear
distortion compensating section, reference number 704 indicate a
compensation coefficient calculating section for amplitude
distortion compensation, reference number 705 indicate amplitude
distortion compensation data, reference number 707 indicate an
analog quadrature base band signal, reference number 709 indicate a
band-limited analog quadrature base band signal, reference number
711 indicate a modulation signal, reference number 712 indicate a
gain controlling amplifier for amplitude distortion compensation,
and reference number 613 indicate a modulation signal, the
amplitude distortion of which is compensated. Furthermore, the
nonlinear distortion compensating section 700 is achievable by
surplus calculation performance of the DSP (not illustrated), which
is a component of the transmission apparatus.
[0101] A description is given of the actions of the transmission
apparatus thus constructed. First, amplitude value 603 of
transmission signal is calculated by the power calculating section
602 on the basis of transmission digital quadrature base band
signal 601. Next, the amplitude value 603 of the calculated
transmission signal is used as an input value, wherein amplitude
distortion compensation data 705 having an inversed characteristic
of the amplitude distortion characteristic of the transmission
system is calculated by the compensation coefficient calculating
section 704 using an approximation equation.
[0102] On the other hand, transmission digital quadrature base band
signal 601 is converted to analog signals by D/A conversion section
608, and the band is limited by a low band pass filter 610, wherein
an analog quadrature base band signal 709 is obtained. After
quadrature modulation is carried out by a quadrature modulator 612
to obtain a modulation signal 711, amplitude distortion
compensation is carried out by a gain controlling amplifier 712 for
compensating the amplitude distortion on the basis of amplitude
distortion compensation data 705, thereby causing a modulation
signal 613 to be obtained, the amplitude distortion of which is
compensated. Finally, the signal is amplified to a size necessary
for the amplifier 614, and a transmission modulation signal 615 is
outputted.
[0103] Furthermore, it may be constructed that the quadrature
modulator 612 is replaced for such a type that modulates the
digital quadrature base band signals for quadrature, and a D/A
converting section and a low band pass filter are connected between
the quadrature modulator and gain controlling amplifier 712.
[0104] Thus, according to the seventh embodiment, since the
nonlinear distortion compensating section 700 is constructed so
that signal power is obtained from the quadrature base band signal
inputted, the amplitude distortion compensation coefficient is
calculated by an approximation equation for compensating the
distortion, in which the value is used as a parameter, the
amplitude distortion of the quadrature modulation signal is
compensated on the basis of the amplitude distortion compensating
coefficient using the same coefficient, and a modulation signal is
obtained, the amplitude distortion of which is compensated. Thus,
the nonlinear distortion compensating section 700 can be
constructed to be small-sized without use of a memory table which
is achieved by a RAM or ROM, etc.
[0105] (Embodiment 8)
[0106] FIG. 8 is a main block diagram of a transmission apparatus
according to an eighth embodiment of the invention. However, parts
of the eighth embodiment, shown in FIG. 8, which correspond to
those of the sixth and seventh embodiments shown in FIG. 6 and FIG.
7 are given the same reference numbers, and the description thereof
is omitted.
[0107] In FIG. 8, reference number 800 indicate a nonlinear
distortion compensating section, reference number 816 indicate a
directivity coupler, reference number 817 indicate a transmission
modulation signal shared, reference number 818 indicate a
quadrature demodulator, reference number 819 indicate a quadrature
base band signal, the quadrature of which is detected, reference
number 820 indicate a low band pass filter for limiting the band,
reference number 821 indicate a quadrature base band signal, the
band of which is limited, reference number 822 indicate an A/D
converter section, reference number 823 indicate digital quadrature
base band signal, reference number 824 indicate a coefficient
renewing section. Reference number 825 indicate coefficient data of
an approximation equation for calculation of a compensation
coefficient.
[0108] Furthermore, the power calculating section 602, compensation
coefficient calculating section 704 and coefficient renewing
section 824 of the nonlinear distortion compensating section 800
are achievable through the surplus calculation performance of the
DSP (not illustrated), which is a component of the transmission
apparatus.
[0109] A description is given of the actions of the transmission
apparatus thus constructed. Firstly, the amplitude value 603 of
transmission signal is calculated by the power calculating section
602 on the basis of transmission digital quadrature base band
signal 601. Next, the calculated amplitude value 603 of the
transmission signal is used as an input value, wherein amplitude
distortion compensation data 705 having an inversed characteristic
of the amplitude distortion characteristics of transmission system
is calculated by the compensation coefficient calculating section
704 using an approximation equation.
[0110] On the other hand, the transmission digital quadrature base
band signal 601 is converted to analog signals by the D/A
converting section 606, and the band is limited by a low band pass
filter 610, thereby causing an analog quadrature base band signal
709 to be obtained. After quadrature modulation is carried out by
quadrature modulator 612 to obtain modulation signals 711, the
amplitude distortion compensation is carried out by a gain
controlling amplifier 712 for compensating the amplitude distortion
on the basis of the amplitude distortion compensation data 705,
thereby causing modulation signals 713 to be obtained, the
amplitude distortion of which is compensated. The signals are
amplified to a necessary size by an amplifier 614, and transmission
modulation signals 615 are outputted. At this time, the
transmission modulation signals 615 are shared by a directivity
coupler 816.
[0111] The shared transmission modulation signals 817 are detected
by a quadrature demodulator 818. After they pass through a low band
pass filter 820 for limiting the band, they are converted to
digital signals by an A/D converting section 822, thereby causing
digital quadrature base band signals 823 to be obtained. The
coefficient data 825 of the approximation equation is renewed by
the coefficient renewing section 824 so that the difference between
the amplitude of digital quadrature base band signal 823 and the
amplitude value 603 of the transmission signal is minimized.
[0112] Thus, according to the eighth embodiment, the nonlinear
distortion compensating section 800 is constructed so that signal
power is obtained on the basis of the inputted quadrature base band
signals, the amplitude distortion compensation coefficient is
calculated by an approximation equation for compensating the
distortion, in which the value of signal power is used as a
parameter, an amplitude distortion of the quadrature modulation
signal is compensated on the basis of the amplitude distortion
compensation coefficient using the coefficient, the modulation
signals, the amplitude distortion of which is compensated, is
shared, and the amplitude compensation coefficient is renewed so
that the difference between the detected signal (output signal) and
the input signal having power obtained beforehand is minimized
after the shared modulation signals are detected for quadrature.
Therefore, the nonlinear distortion compensating section 800 can be
constructed to be small-sized without use of a memory table
achievable by a RAM or ROM, etc., and at the same time it is
possible to compensate distortion changes due to environmental
changes such as in temperature, etc.
[0113] (Embodiment 9)
[0114] FIG. 9 is a main block diagram of the transmission apparatus
of a ninth embodiment of the invention. However, parts of the ninth
embodiment shown in FIG. 9, which correspond to those of the sixth
and eighth embodiments shown FIG. 6 and FIG. 8 are given the same
reference numbers, and the description thereof is omitted.
[0115] In FIG. 9, reference number 900 indicate a nonlinear
distortion compensating section, reference number 904 indicate a
fixed coefficient reference section by ROM, which refers to a fixed
compensation coefficient for compensating nonlinear distortions
using the amplitude value 603, reference number 905 indicate a
quadratured fixed nonlinear distortion compensation coefficient,
reference number 908 indicate a distortion compensating section,
reference number 926 indicate a coefficient renewing section, and
reference number 927 indicate coefficient data of an approximation
equation for calculation of compensation coefficients.
[0116] Furthermore, the power calculating section 602, compensation
coefficient calculating section 604 and coefficient renewing
section 926 of the nonlinear distortion compensating section 900
are achievable by surplus calculation performance of the DSP (not
illustrated), which is a component of the transmission section.
[0117] A description is given of the actions of a transmission
section thus constructed. First, the amplitude value 603 of
transmission signals is calculated by the power calculating section
602 on the basis of the transmission digital quadrature base band
signal 601 as in the abovementioned equation (1). Next, with
reference to the fixed coefficient reference section 904 as using
the amplitude value 603 of the calculated transmission signal as an
address, the nonlinear distortion compensation data having an
inversed characteristic of the nonlinear distortion characteristics
of the transmission system calculated in advance is obtained as a
quadratured nonlinear distortion compensation coefficient 905.
[0118] Herein, it is assumed that wherein the amplitude value 603
is P as shown in the equation (1), a nonlinear distortion
compensation coefficient 905 corresponding to P is (di, dq).
[0119] Simultaneously, the amplitude value 603 of the transmission
signal calculated is used as an input value, wherein a correcting
coefficient 605 for correcting the nonlinear distortion
compensation coefficient 905 is -calculated by the correcting
coefficient calculating section 604 using the abovementioned
approximation equations (2) and (3).
[0120] The distortion compensating section 908 carries out a
complex product of a transmission digital quadrature base band
signal 601, a quadratured nonlinear distortion compensation data
905 and correcting coefficient 605, and outputs a quadrature base
band signal 607, the nonlinear distortion of which is
compensated.
[0121] This is calculated by the following equations (6) and (7),
first using (di, dq) of the nonlinear distortion compensation
coefficient where the I and Q channel components of the quadrature
base band signal 607 are respectively I" and Q".
I'=Idi-Qdq (6)
Q'=Idq+Qdi (7)
[0122] Next, (Ci, Cq) of the correcting coefficient 605 is used
with respect to the result of the abovementioned equations (6) and
(7), and calculation is made as in the following equations (8) and
(9).
I"=I'Ci-Q'Cq (8)
Q"=I'Cq+Q'Ci (9)
[0123] The quadrature base band signals 607 for which the nonlinear
distortion is thus compensated are converted to analog signals by a
D/A conversion section 608 and the band thereof is limited by a low
band pass filter 610, thereby causing analog quadrature base band
signals 611 to be obtained. After the signals are
quadrature-modulated by a quadrature modulator 612 to obtain
modulation signals 613, they are amplified by an amplifier 614 of
the transmission system to a necessary size, and transmission
modulation signals 615 are outputted. At this time, the
transmission modulation signals 615 are shared by a directivity
coupler 816.
[0124] The shared transmission modulation signals 817 are detected
by a quadrature demodulator 818, and pass through a low band pass
filter 820 for limiting the band. Thereafter, the signals are
converted to digital signals by an A/D converting section 822 to
obtain digital quadrature base band signals 823. The coefficient
data 927 of approximation equations for calculating the correcting
coefficients are renewed by a coefficient renewing section 926 so
that the difference between the quadrature base band signals 601
and 823 is minimized.
[0125] Thus, according to the ninth embodiment, the nonlinear
distortion compensating section 900 is constructed so that signal
power is obtained from the quadrature base band signals inputted,
nonlinear distortion compensation coefficients are obtained using
the value of signal power as a parameter, compensation coefficients
are calculated by approximation equations for compensating
distortions to carry out distortion compensations using the
coefficients, modulation signals in which the distortion
compensation signals are modulated for quadrature are shared, and
the compensation coefficients of approximation equations are
renewed so that the difference between the detection signals
(output signals) and input signals for which power is obtained in
advance is minimized after the shared modulation signals are
detected for quadrature. Therefore, the nonlinear distortion
compensating section 900 can be constructed so as to achieve high
accuracy and compensate the distortions changing in line with
changes of the environments due to temperature changes, etc.
[0126] Furthermore, the respective nonlinear distortion
compensating sections 600, 700, 800, and 900 described above
according to embodiments 6 through 9 shown in FIGS. 6 through 9 may
be replaced for any one of the nonlinear distortion compensating
sections 104, 201, 501 shown in FIGS. 1 through 5. However, when
replacing nonlinear distortion compensation sections, it is
necessary that a matching is secured with respect to the type of
quadrature modulators, positions of the D/A converting section and
low band pass filter, and position of gain controlling amplifier
712 on the basis of the description made with respect to the first
through the ninth embodiments.
[0127] Furthermore, each of the nonlinear distortion compensating
sections 600, 900 may be composed of integrated circuits by a
hardware configuration using logic circuits, etc. individually, or
with its transmission apparatus included in a DSP (not
illustrated), which is a component.
[0128] Still furthermore, three elements, that is, amplitude
calculating section 101, limiting coefficient calculating section
301 and amplitude limiting section 103 shown in FIG. 3 and FIG. 4
may be composed of integrated circuits by a hardware configuration
combination with any one of the respective nonlinear distortion
compensating sections 600, 900, or they may be composed of
integrated circuits by a hardware configuration combined with any
one of the respective nonlinear distortion compensating sections
600, 900, and included in the DSP.
[0129] In a case where they are composed of integrated circuits,
the nonlinear distortion compensation can be carried out at a high
speed.
INDUSTRIAL APPLICABILITY
[0130] As described above, a transmission apparatus according to
the invention is very useful as a transmission apparatus of radio
communication systems and is suitable for compensation of nonlinear
distortions generated in the transmission system.
* * * * *