Pulse or digital communications – Transmitters – Antinoise or distortion
Reexamination Certificate
1998-07-15
2002-07-09
Ghayour, Mohammad H. (Department: 2734)
Pulse or digital communications
Transmitters
Antinoise or distortion
C375S254000
Reexamination Certificate
active
06418173
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a nonlinear distortion compensating technique in a transmission apparatus for digital radio communications.
BACKGROUND ART
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.
A description is given of a conventional transmission apparatus which compensates nonlinear distortions by using such a method.
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.
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
.
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.
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.
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.
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.
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.
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.
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
.
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
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.
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.
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.
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.
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.
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.
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.
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 c
Matsuoka Akihiko
Misaizu Kouei
Orihashi Masayuki
Sagawa Morikazu
Takahashi Ken'ichi
Greenblum & Bernstein P.L.C.
Matsushita Electric - Industrial Co., Ltd.
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