Radio equipment

Radio equipment including a characteristic compensator for compensating for an orthogonality error of a mixer with low consumption power is disclosed. In radio equipment, an orthogonal detector converts a received real signal into a complex reception signal of an intermediate frequency. Further, when a complex reception signal converted into a digital signal by A/D converters includes a desired signal (quasi-desired signal), which includes an image signal of a non-desired signal, and a non-desired signal (preparatory desired signal), which includes an image signal of a desired signal, a frequency of the quasi-desired signal is frequency-converted to a signal closer to a direct current component by a frequency converter and a frequency of the preparatory desired signal is frequency-converted to a signal closer to a direct current component by a frequency converter. A decimator respectively performs a filtering and a down-sampling on the frequency-converted quasi-desired signal and preparatory desired signal. A characteristic compensator 7 suppresses the image signal of the non-desired signal included in an inputted quasi-desired signal by means of a complex codomain signal of an inputted preparatory desired signal.

PRIORITY

This application claims priority to an application entitled “Radio Equipment” filed in the Japanese Industrial Property Office on Aug. 7, 2002 and assigned Serial No. 2002-230517, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radio equipment, and more particularly to radio equipment including a compensator for compensating for an orthogonality error between a real-axis signal and an imaginary-axis signal of a signal expressed as a complex number.

2. Description of the Related Art

Japanese Laid-Open Patent Publication No. P10-56484 discloses a conventional receiver which employs a characteristic compensator for compensating for orthogonal/amplitude errors occurring in received signals owing to incompleteness of an apparatus.

In radio equipment including such a receiver as disclosed by the Japanese Publication, an orthogonality error of a complex signal caused by a dispersion or all characteristics of an analog processing section in mixers (frequency converters) which process RF (Radio Frequency) band of the radio equipment, such as an orthogonal modulator (a mixer having an input of a complex signal and an output of a real signal), an orthogonal detector (a mixer having an input of a real signal and an output of a complex signal), or a mixer having an input of a complex signal and an output of a complex signal, may appear as an image signal which does not exist in an ideal signal. Accordingly, in order to transceive signals without distortion, conventional radio equipment may employ a compensator for compensating for an orthogonality error of a complex signal.

However, in recent radio equipment, as the frequency of RF signal increases and system bands become wider, it is difficult to obtain a necessary degree of image suppression even if a mixer with a high image suppression effect is used. Further, since research for obtaining not only characteristic compensation of a mixer but also the necessary degree of image suppression by suppressing an image frequency signal in a RF filter, a high intermediate frequency has been necessary for a radio processing section.

Accordingly, as a conventional receiver shown inFIG. 17, when an output of an orthogonal detector2is sampled by ADCs (A/D converters)3and4, a characteristic compensation process of the orthogonal detector2is performed by a characteristic compensator50through a digital signal processing, the compensated signal is frequency-converted by a frequency converter51so that an immediate frequency can be low, the converted signal is converted to a signal with low sampling frequency by a decimator52, and the converted signal is demodulated by a detector8, processing a high IF frequency in the output of the orthogonal detector2implies that a high sampling frequency is necessary when a sampling is performed. Further, in order to perform the characteristic compensation process of the orthogonal detector2, the consumption power of characteristic compensator50becomes much greater.

Further, even in a case in which a characteristic compensation is performed by means of an analog circuit without conversion into a digital signal, it is difficult to secure sufficient accuracy in a passive circuit in order to perform a compensation with high accuracy in a higher frequency, and it is necessary to increase consumption power in an active circuit in order to maintain high frequency.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide radio equipment including a characteristic compensator for compensating for an orthogonality error of mixers, such as an orthogonal modulator, an orthogonal detector, or a complex signal input complex signal output mixer, with a low consumption power.

In order to accomplish these objects, according to the preferred embodiment of the present invention, there is provided a radio equipment comprising: an orthogonal detector for obtaining a complex intermediate frequency signal with respect to a real input signal; a first frequency converter for frequency-converting a target signal outputted from the orthogonal detector into a signal with lower frequency; a second frequency converter for frequency-converting a non-target signal outputted from the orthogonal detector into a signal of a frequency symmetrical to a signal outputted from the first frequency converter and a direct current component with a frequency of zero; and a characteristic compensator for compensating for an orthogonality error between a real-axis signal and an imaginary-axis signal occurring in the target signal owing to the orthogonal detector by means of an output signal of the second frequency converter, with respect to an output signal of the first frequency converter.

In the radio equipment with such construction, the target signal and non-target in an output of the orthogonal detector are frequency-converted to a signal closer to a direct current component with a frequency of zero by the first frequency converter and the second frequency converter, and the converted signals are inputted to the characteristic compensator for compensating for an orthogonality error, thereby compensating for an orthogonality error of the orthogonal detector by means of a characteristic compensator with low sampling frequency.

Preferably, one side of the first frequency converter or second frequency converter utilizes a complex codomain signal of a complex local signal used in other side of the first frequency converter or second frequency converter as own local signal. Accordingly, in the radio equipment, since the frequency converters use the local signal in common, a local oscillator in one side of the frequency converters can be omitted, thereby simplifying the circuit construction.

In order to accomplish these objects, according to the preferred embodiment of the present invention, there is provided a radio equipment further comprising: a first filter for employing a frequency band of the target signal in the output of the orthogonal detector as a pass band, and extracting the target signal from the output signal of the orthogonal detector; and a second filter for having a pass band characteristic symmetrical to a direct current component with a frequency of zero, employing a frequency band of the non-target signal in the output of the orthogonal detector as a pass band, and extracting the non-target signal from the output signal of the orthogonal detector. Accordingly, an output of the first filter is frequency-converted to a signal with lower frequency by the first frequency converter, and an output of the second filter is frequency-converted to a signal of a frequency symmetrical to the signal outputted from the first frequency converter and the direct current component with a frequency of zero by the second frequency converter.

In the radio equipment with such construction, since the target signal and the non-target signal are certainly separated and inputted to a characteristic compensator by the first/second filters, compensation operation in the characteristic compensator can be accurately performed. Furthermore, when adaptation signal processing is used in the characteristic compensator, the adaptation characteristic can be improved.

In order to accomplish these objects, according to the preferred embodiment of the present invention, there is provided a radio equipment further comprising: a first filter for employing a frequency band of the target signal in the output of the first frequency converter as a pass band, and extracting the target signal from the output signal of the first frequency converter; and a second filter for having a pass band characteristic symmetrical to a direct current component with a frequency of zero, employing a frequency band of the non-target signal in the output of the second frequency converter as a pass band, and extracting the non-target signal from the output signal of the second frequency converter. Accordingly, a characteristic compensator compensates for an orthogonality error between a real-axis signal and an imaginary-axis signal occurring in the target signal owing to the orthogonal detector by means of an output signal of the second filter, with respect to an output signal of the first filter.

In the radio equipment with such construction, since the target signal and the non-target signal are certainly separated and inputted to a characteristic compensator by the first and second filters, compensation operation in the characteristic compensator can be accurately performed. Furthermore, when adaptation signal processing is used in the characteristic compensator, the adaptation characteristic can be improved.

The first filter and the second filter according to the present invention are complex filters for receiving and outputting a complex signal, one side of the first filter or second filter inverts a sign of an imaginary-axis side of a complex filter coefficient prepared in other side of the first filter or second filter so that the first filter and the second filter realize a band characteristic symmetrical to a direct current component with a frequency of zero.

Accordingly, in the radio equipment, since the filter uses the complex filter coefficient in common, a complex filter coefficient memory in one side of filter can be omitted, thereby simplifying the circuit construction.

The first filter and the second filter according to the present invention are filters for suppressing unnecessary frequency component through a phase process utilizing Hilbert transform.

In the radio equipment with such construction, since the phase process is performed by means of Hilbert transform, a target signal including an image signal of a non-target signal and a non-target signal including an image signal of a target signal are certainly separated and inputted to a characteristic compensator. Further, when a filtering is performed by means of a complex filter coefficient, it is necessary to perform convolution process on both a real-axis and an imaginary-axis. However, in a filter utilizing Hilbert transform, a characteristic of one side is flat. Accordingly, a process of an axis with flat characteristic can be replaced with delay process. That is, in order to harmonize delay amount of the real-axis and imaginary-axis, delay process corresponding to delay time of Hilbert conversion filter inserted in an axis of one side is performed on the axis with flat characteristic, thereby reducing the amount of operation of the filter as much as ½. Accordingly, the circuit construction can be simplified.

In order to accomplish these objects, according to the preferred embodiment of the present invention, there is provided a radio equipment comprising: a modulator for modulating a complex immediate frequency signal to transmission data; a characteristic compensator for compensating for an orthogonality error between a real-axis signal and an imaginary-axis signal occurring after a corresponding modulator with respect to the modulated complex immediate frequency signal outputted from the modulator; a first frequency converter for frequency-converting a target signal outputted from the characteristic compensator into a signal with higher frequency; a second frequency converter for frequency-converting a non-target signal outputted from the characteristic compensator into a signal of a frequency symmetrical to a signal outputted from the first frequency converter and a direct current component with a frequency of zero; an adder for adding a real-axis signal of a complex signal outputted from the first frequency converter to a real-axis signal of a complex signal outputted from the second frequency converter, and adding an imaginary-axis signal of a complex signal outputted from the first frequency converter to an imaginary-axis signal of a complex signal outputted from the second frequency converter; and an orthogonal modulator for obtaining a real output signal with respect to a complex signal outputted from the adder.

In the radio equipment with such construction, the target signal and non-target signal in an output of the modulator are generated as signals of a frequency symmetrical to a corresponding direct current component and close to a direct current component with a frequency of zero, and the generated signals are inputted to the characteristic compensator for compensating for an orthogonality error. Simultaneously, a frequency of the target signal and non-target signal in the output of the characteristic compensator is converted into a signal of transmission frequency, thereby compensating for an orthogonality error of the orthogonal detector by means of a characteristic compensator with low sampling frequency.

Preferably, one side of the first frequency converter or second frequency converter utilizes a complex codomain signal of a complex local signal used in other side of the first frequency converter or second frequency converter as own local signal.

Accordingly, in the radio equipment, since the frequency converter uses the local signal in common, a local oscillator in one side of frequency converter can be omitted, thereby simplifying the circuit construction.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, according to preferred embodiments of the present invention will be described with reference to the accompanying drawings. The same reference numerals are used to designate the same elements as those shown in other drawings. In the description below, many particular items, such as detailed elements of circuit, are shown, but these are provided for helping the general understanding of the present invention, it will be understood by those skilled in the art that the present invention can be embodied without the particular items. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention rather unclear.

A First Embodiment

FIG. 1is a block diagram showing a construction of a receiver realized in a radio equipment according to a first embodiment of the present invention.

The receiver according to the first embodiment of the present invention is described with reference toFIG. 1. In the receiver, a signal is received through an antenna1, and the received real signal is converted into a complex reception signal S1of an intermediate frequency (IF frequency) by an orthogonal detector2.

Next, when the received signal has been converted into the complex reception signal S1of the intermediate frequency, a real-axis signal and an imaginary-axis signal of the complex reception signal S1converted into the complex signal by an orthogonal detector2are respectively converted into digital signals by means of ADCs (A/D converters)3and4for quantizing an inputted signal with a predetermined sampling frequency according to a sampling theorem.

Further, in an output of the orthogonal detector2, an orthogonality error of a complex signal caused by a dispersion or all characteristics of the processing section appears as an image signal which does not exist in an ideal signal.

Herein, in an input of the orthogonal detector2, when an undesired signal exists in an image frequency of a desired signal in the output of the orthogonal detector2, an image signal of a corresponding undesired signal appears in the desired signal, or an image signal of a corresponding desired signal appears in the undesired signal.

Hereinafter, the desired signal including the image signal of the undesired signal is referred to as a quasi-desired signal, and the undesired signal including the image signal of the desired signal is referred to as a preparatory desired signal. Further, the quasi-desired signal and the preparatory desired signal are described by means of equations. When a desired signal D=cos(ω1+t) is inputted to the orthogonal detector2which employs a local signal as lo(ωct)=A cos(ωc1t)−jB sin(ωc1t), the output fd of the orthogonal detector2is shown in the following equation 1.
fd(ωt)=cos(ω1t)lo(ωc1t)=cos(ω1t)(Acos(ωc1t)−jBsin(ωc1t))

wherein, when d is A−B,

When an undesired signal U=cos(ωc2t) is inputted to the orthogonal detector2, the output fu of the orthogonal detector2is shown in the following equation 2.
fu(ωt)=cos(ω2t)lo(ωc1t)=cos(ω2t)=cos(ω2t)(ACOS(ωc1)−jBsin(ωc1t))

wherein, when d is A−B,

In equation 1 and 2, a first term is an original output and a second term is an image signal.

Accordingly, since the output fu of the orthogonal detector2is a signal obtained by adding equation 1 to equation 2, a quasi-desired signal fd′ obtained by adding the first term of equation 1 to the second term of equation 2 is shown in equation 3.

Further, a preparatory desired signal fu′ obtained by adding the second term of equation 1 to the first term of equation 2 is shown in equation 4.

Further, an amplitude ratio of the desired signal existing in the quasi-desired signal fd′ with respect to the image signal of the preparatory desired signal is shown inFIG. 5.

In the conventional receiver, in order to delete the second term of the equation 3, a complex codomain signal of equation 4 is multiplied by a reciprocal of the equation 5, and then the result is subtracted from equation 3. However, since a frequency of a signal is high, the quasi-desired signal fd′ and the preparatory desired signal fu′ are respectively frequency-converted to signals close to a direct current component with a frequency of zero, and then the converted signals are processed in a receiver of an embodiment of the present invention.

Herein, when the frequency-converted amount is ωc2, a quasi-desired signal fd″ shown in equation. 6 and a preparatory desired signal fu″ shown in equation. 7 are respectively obtained from the quasi-desired signal fd′ and the preparatory desired signal fu′.

Accordingly, in the receiver of an embodiment of the present invention, in order to delete the second term of the equation 6, a complex codomain signal of equation 7 is multiplied by the reciprocal of the equation 5, and then the result is subtracted from equation 6, thereby canceling the image signal of the undesired signal cos(ωc2t) existing in the quasi-desired signal.

By means of a frequency converter5, the frequency of the quasi-desired signal is frequency-converted (movement in a minus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero, and then a quasi-desired signal S2is obtained. Likewise, the frequency of the preparatory desired signal is frequency-converted (movement in a plus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero, and then a preparatory desired signal S4is obtained.

Next, the quasi-desired signal S2and preparatory desired signal S4frequency-converted to the signal closer to the direct current component having the frequency of zero are respectively filtered and down-sampled by means of a decimator6.

Next, the down-sampled quasi-desired signal S3and preparatory desired signal S5are inputted to a characteristic compensator7. The characteristic compensator7suppresses the image signal of the undesired signal included in the quasi-desired signal inputted from the decimator6by means of the complex codomain signal of the preparatory desired signal inputted from the decimator6.

The output of the characteristic compensator7is demodulated by a detector8, and then converted into data of a digital signal row.

Next, the orthogonal detector2is described. The orthogonal detector2includes an orthogonal carrier oscillator1afor outputting a complex local signal of a first frequency same as a carrier frequency of a received signal received by an antenna1, a multiplier1band1cfor respectively multiplying the real reception signal received through the antenna1by a real-axis signal “cos” of the local signal of the first frequency outputted from the orthogonal carrier oscillator1aand an imaginary-axis signal “−sin” of which phase has moved by 90° in relation to the real-axis signal. Further, the received real reception signal is orthogonal-transformed by the orthogonal detector2, and then the complex reception signal S1is obtained.

Next, the frequency converter5is described. As shown inFIG. 2, in order to convert the frequency of the quasi-desired signal into a signal closer to a direct current component with a frequency of zero, the frequency converter5includes an orthogonal carrier oscillator2afor outputting a complex local signal of a second frequency by a predetermined value lower than the frequency of the quasi-desired signal, a multiplier2bfor multiplying a real-axis signal S1.1of the complex reception signal S1inputted from a terminal S1.1by a real-axis signal “cos” of the local signal of the second frequency outputted from the orthogonal carrier oscillator2a, a multiplier2cfor multiplying an imaginary-axis signal S1.Q of the complex reception signal S1inputted from a terminal S1.Q by an imaginary-axis signal “−sin” of which phase has moved by 90° in relation to the real-axis signal, and a subtracter2dfor subtracting the output of the multiplier2cfrom the output of the multiplier2b, and then employing the result as a signal output T1.1of a real-axis signal.

Further, the frequency converter5includes a multiplier2efor multiplying the real-axis signal S1.1of the complex reception signal S1inputted from the terminal S1.1by the imaginary-axis signal “−sin” of the local signal of the second frequency outputted from the orthogonal carrier oscillator2a, a multiplier2ffor multiplying the imaginary-axis signal S1.Q of the complex reception signal S1inputted from the terminal S1.Q by the real-axis signal “cos” of the local signal of the second frequency outputted from the orthogonal carrier oscillator2a, and an adder2gfor adding the output of the multiplier2eto the output of the multiplier2f, and then employing the result as an imaginary-axis signal output T1.Q.

Further, in order to convert the preparatory desired signal into a signal closer to a direct current component with a frequency of zero, the frequency converter5includes a sign inverter3afor inverting a sign of the imaginary-axis signal outputted from the orthogonal carrier oscillator2a, and then obtaining a complex codomain signal of a local signal of the second frequency, a multiplier3bfor multiplying the real-axis signal S2.1of the complex reception signal S1inputted from a terminal S2.1by a real-axis signal “cos” of a local signal of a third frequency generated as the complex codomain signal of the local signal of the second frequency outputted from the orthogonal carrier oscillator2a, a multiplier3cfor multiplying the imaginary-axis signal S2.Q of the complex reception signal S1inputted from the terminal S2.Q by an imaginary-axis signal “−sin”, of which phase has delayed by 90° in relation to the real-axis signal, of the local signal of the third frequency generated as the complex codomain signal of the local signal of the second frequency outputted from the orthogonal carrier oscillator2a, and a subtracter3dfor subtracting the output of the multiplier3cfrom the output of the multiplier3b, and then employing the result as a real-axis signal output T2.1.

Further, the frequency converter5includes a multiplier3efor multiplying the real-axis signal S2.1of the complex reception signal S1inputted from the terminal S2.1by the imaginary-axis signal “−sin” of the local signal of the third frequency generated as the complex codomain signal of the local signal of the second frequency outputted from the orthogonal carrier oscillator2a, a multiplier3ffor multiplying the imaginary-axis signal S1.Q of the complex reception signal S1inputted from the terminal S1.Q by the real-axis signal “cos” of the local signal of the third frequency generated as the complex codomain signal of the local signal of the second frequency outputted from the orthogonal carrier oscillator2a, and an adder3gfor adding the output of the multiplier3eto the output of the multiplier3f, and then employing the result as an imaginary-axis signal output T2.Q.

Further, in stead of the orthogonal carrier oscillator2a, in order to convert the preparatory desired signal into a signal closer to a direct current component with a frequency of zero, an orthogonal carrier oscillator for outputting a complex local signal may be employed.

A complex codomain signal of a complex local signal outputted from a corresponding orthogonal carrier oscillator may be used as a complex local signal for frequency-converting the frequency of the quasi-desired signal into a signal closer to a direct current component with a frequency of zero.

Next, the decimator6will be described hereinafter. As shown inFIG. 3, the decimator6includes a band pass filter4a, which extracts the quasi-desired signal by utilizing a frequency band of the quasi-desired signal outputted from the frequency converter5as a pass band, and a down sampler4b, which select data from an output signal of the band pass filter4a. Therefore, the decimator6can separate a quasi-desired signal and a preparatory desired signal from each other, as well as removing signals of a frequency band in which an aliasing occurs, when a sampling frequency of signals inputted from terminals J1.1and J1.Q is lowered.

Further, the decimator6has pass band characteristic symmetrical to the band pass filter4aand direct current component with a frequency of zero, and includes a band pass filter4c, which extracts the preparatory desired signal by utilizing a frequency band of the preparatory desired signal outputted from the frequency converter5as a pass band, and a down sampler4d, which selects data from an output signal of the band pass filter4c. Therefore, the decimator6can separate a quasi-desired signal and a preparatory desired signal from each other, as well as removing signals of a frequency band in which an aliasing occurs, when a sampling frequency of signals inputted from terminals J2.1and J2.Q is lowered.

Further, in filter coefficients of the band pass filter4aand band pass filter4c, one side of the band pass filter4aand band pass filter4cinverts a sign of an imaginary-axis side of a complex filter coefficient prepared in other side of the band pass filter4aand band pass filter4cso that the band pass filter4aand band pass filter4crealize a band characteristic symmetrical to a direct current component with a frequency of zero.

Next, a characteristic compensator7is described. As shown inFIG. 4, the basic circuit of the characteristic compensator7includes a multiplier5afor multiplying an imaginary-axis signal X2.Q of a preparatory desired signal inputted from terminals X2.1/X2.Q by “−1” and generating a complex codomain signal S6of the preparatory desired signal S5, a multiplier5b/5cfor respectively multiplying a real-axis signal X2.1and imaginary-axis signal −X2.Q of the generated complex codomain signal X2.1/−X2.Q by a coefficient “a” and obtaining an image frequency interference cancellation signal aS6, and a subtractor5d/5efor subtracting the image frequency interference cancellation signal aS6from a quasi-desired signal S3inputted in terminals X1.1/X1.Q.

In the basic circuit of the characteristic compensator7utilized in the embodiment of the present invention, the value of the coefficient “a” may be adjusted so that the level of the quasi-desired signal can be minimized, or the value of the coefficient “a” may be adjusted so that the level of the preparatory desired signal can be minimized by means of a spectrum analyzer, etc., thereby obtaining the object of the present invention. As described above, the adjusting method is very simple in comparison to the conventional method requiring an adjustment of both a phase and an amplitude, and the object of the present invention can be obtained through the simple method. Further, when an inputted signal is intercepted and a calibration signal is inputted, the object of the present invention can be obtained through a simple method which can minimize a level of an output signal.

Further, in the above-described basic circuit, the multiplier5amay be omitted by employing a coefficient which is inputted to the multiplier5bas “a” and employing a coefficient which is inputted to the multiplier5cas “−a”.

Next, a suppression operation of an image signal performed by a receiver according to an embodiment of the present invention is described with reference toFIG. 5.

First, as shown inFIG. 5a, in an output of the orthogonal detector2inFIG. 1, the complex reception signal S1exists as either a quasi-desired signal, which includes a desired signal D and an image signal U′ of an undesired signal U integrated with each other, or a preparatory desired signal, which includes an undesired signal U and an image signal D′ of desired signal D integrated with each other.

Next, as shown inFIG. 5b, a frequency of the desired signal D (quasi-desired signal) is frequency-converted to a signal closer to a direct current component with a frequency of zero by the frequency converter5, and then the signal S2is generated. The signal S2is filtered by the band pass filter4ain the decimator6, that is, as shown inFIG. 5c, a return of a received signal repeating in each sampling frequency and the preparatory desired signal are simultaneously removed. Next, data is culled by the down sampler4bin the decimator6, and then the quasi-desired signal S3, which has a low sampling rate, including the image signal U′ in the undesired signal U is extracted.

Likewise, as shown inFIG. 5d, a frequency of the undesired signal U (preparatory desired signal) is frequency-converted to a signal closer to a direct current component with a frequency of zero by the frequency converter5, and then the signal S4is generated. The signal S4is filtered by the band pass filter4cin the decimator6, that is, as shown inFIG. 5e, a return of a received signal repeating in each sampling frequency and the quasi-desired signal are simultaneously removed. Next, data is culled by the down sampler4din the decimator6, and then the preparatory desired signal S5, which has a low sampling rate, including the image signal D′ in the desired signal D is extracted.

The extracted quasi-desired signal S3and preparatory desired signal S5are inputted to the characteristic compensator7. In the characteristic compensator7, a sign of an imaginary-axis signal in the preparatory desired signal S5is inverted by the multiplier5a, and then a complex codomain signal S6is generated. Simultaneously, the level of the complex codomain signal S6is adjusted by the multiplier5band5cby means of the coefficient “a”, thereby generating the image frequency interference cancellation signal aS6.

Further, when the image frequency interference cancellation signal aS6is subtracted from the quasi-desired signal S3, since the image signal U′ of the undesired signal U existing in the quasi-desired signal S3is cancelled, the desired signal D can be extracted.

As described above, according to the receiver of the first embodiment, in the output of the orthogonal detector2, when the image signal of the undesired signal existing in the quasi-desired signal is compensated for by means of a replica of the image signal in the undesired signal generated from the preparatory desired signal in the characteristic compensator7, the quasi-desired signal and preparatory desired signal outputted from the orthogonal detector2are frequency-converted to a signal closer to a direct current component with a frequency of zero by the frequency converter5, and then the converted signals converted into a signal with a low sampling rate by the decimator6, thereby reducing the amount of operation in the characteristic compensator7.

A Second Embodiment

A second embodiment of the present invention is described.

FIG. 6is a block diagram showing a construction of a receiver realized in a radio equipment according to a second embodiment of the present invention.

The receiver according to the second embodiment of the present invention has a characteristic in which a connection sequence between the frequency converter5and the band pass filters4a/4cincluded in the frequency converter5and the decimator6in the receiver according to the above-described first embodiment has changed.

The receiver according to the second embodiment of the present invention is described with reference toFIG. 6. In the receiver, a signal is received through an antenna1, and the received real signal is converted into a complex reception signal S1of an intermediate frequency (IF frequency) by an orthogonal detector2.

Next, when the received signal has been converted into the complex reception signal S1of the intermediate frequency, a real-axis signal and an imaginary-axis signal of the complex reception signal S1converted into the complex signal by an orthogonal detector2are respectively converted into digital signals by means of ADCs (A/D converters)3and4for quantizing an inputted signal with a predetermined sampling frequency according to a sampling theorem.

Next, in an output of the ADCs3and4, in order to remove a return of a received signal repeating in each sampling frequency and separate a quasi-desired signal and a preparatory desired signal included in the output of the ADCs3and4, the quasi-desired signal is extracted by a band pass filter9employing a frequency band of the quasi-desired signal outputted from the ADCs3and4as a pass band.

Likewise, in order to remove a return of a received signal repeating in each sampling frequency and separate a quasi-desired signal and a preparatory desired signal included in the output of the ADCs3and4, the preparatory desired signal is extracted by a band pass filter10, which has a pass band characteristic symmetrical to the band pass filter9and direct current component with a frequency of zero, employing a frequency band of the preparatory desired signal outputted from the ADCs3and4as a pass band.

Further, in filter coefficients of the the band pass filter9and band pass filter10, one side of the band pass filter9and band pass filter10inverts a sign of an imaginary-axis side of a complex filter coefficient prepared in other side of the band pass filter9and band pass filter10so that the band pass filter9and band pass filter10can realize a band characteristic symmetrical to a direct current component with a frequency of zero.

When the quasi-desired signal and the preparatory desired signal can be separated from each other, the frequency of the quasi-desired signal is frequency-converted (movement in a minus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero by the frequency converter5. Likewise, the frequency of the preparatory desired signal is frequency-converted (movement in a plus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero by the frequency converter5.

The quasi-desired signal and preparatory desired signal outputted from the frequency converter5are each converted into signals with a low sampling rate by a down sampler11, which converts a sampling rate of the quasi-desired signal outputted from the frequency converter5and employs the converted signal as a signal with a low sampling rate, and a down sampler12, which converts a sampling rate of the preparatory desired signal outputted from the frequency converter5and employs the converted signal as a signal with a low sampling rate.

Next, the down-sampled quasi-desired signal and preparatory desired signal are inputted to a characteristic compensator7. The characteristic compensator7suppresses an image signal of an undesired signal included in the quasi-desired signal inputted from the down sampler11by means of a complex codomain signal of the preparatory desired signal inputted from the down sampler12.

The output of the characteristic compensator7is demodulated by a detector8, and then converted into data of a digital signal row.

Since a detailed description for the orthogonal detector2and frequency converter5is the same as that of the first embodiment, the description is omitted.

As described above, according to the receiver of the second embodiment, in the output of the orthogonal detector2, when the image signal of the undesired signal existing in the quasi-desired signal is compensated by means of a replica of the image signal in the undesired signal generated from the preparatory desired signal in the characteristic compensator7, the quasi-desired signal and preparatory desired signal outputted from the orthogonal detector2are respectively separated into a quasi-desired signal and a preparatory desired signal, and the separated signals are frequency-converted to signals more close to a direct current component with a frequency of zero by the frequency converter5, and then the converted signals converted into a signal with a low sampling rate by the down sampler11and12, thereby reducing the amount of operation in the characteristic compensator7.

A Third Embodiment

A third embodiment of the present invention is described.

In a receiver realized in a radio equipment according to the third embodiment of the present invention, a quasi-desired signal and a preparatory desired signal can be separated by a filter for suppressing an unnecessary frequency component through a phase process utilizing the Hilbert transform, in stead of the decimator6in the receiver of the above-described first embodiment.

The receiver according to the third embodiment of the present invention is described with reference toFIG. 7. In the receiver, a signal is received through an antenna1, and the received real signal is converted into a complex reception signal S1of an intermediate frequency (IF frequency) by an orthogonal detector2.

Next, when the received signal has been converted into the complex reception signal S1of the intermediate frequency, a real-axis signal and an imaginary-axis signal of the complex reception signal S1converted into the complex signal by an orthogonal detector2are respectively converted into digital signals by means of ADCs (A/D converters)3and4for quantizing an inputted signal with a predetermined sampling frequency according to a sampling theorem.

Next, by means of the frequency converter5, the frequency of the quasi-desired signal is frequency-converted (movement in a minus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero, and likewise, the frequency of the preparatory desired signal is frequency-converted (movement in a plus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero.

Since two positive/negative separation filters, which suppress an unnecessary frequency component through a phase process utilizing the Hilbert transform, separate an inputted signal into two outputs with a pass band characteristic symmetrical to a direct current component with a frequency of zero, and then output the two outputs, are utilized, a frequency band of the quasi-desired signal and a frequency band of the preparatory desired signal are separated from an output of the frequency converter5and then the separated bands are extracted. In more detail, the quasi-desired signal is extracted to terminals P1.1and P1.Q of the positive/negative separation filter13aconnected to terminals T1.1and T1.Q of the frequency converter5. Then, the preparatory desired signal is extracted to terminals P2.1and P2.Q of the positive/negative separation filter13bconnected to terminals T2.1and T2.Q of the frequency converter5.

Next, the extracted quasi-desired signal and preparatory desired signal are inputted to a characteristic compensator7. The characteristic compensator7suppresses an image signal of an undesired signal included in the inputted quasi-desired signal by means of a complex codomain signal of the preparatory desired signal inputted in same way.

The output of the characteristic compensator7is demodulated by a detector8, and then converted into data of a digital signal row.

Since a detailed description for the orthogonal detector2and frequency converter5is the same as that of the first embodiment, the description is omitted.

As shown inFIG. 8, the positive/negative separation filter13aand13brespectively includes Hilbert transformers6band6e, and delayers6aand6dfor compensating for delay amount of the Hilbert transformers6band6e.

A signal after Hilbert-transforming an imaginary-axis signal O.Q inputted from terminals O.1and O.Q is subtracted from a delayed signal of a real-axis signal O.1inputted from terminals O.1and O.Q by a subtractor6c, and the signal obtained from the subtraction result is employed as a real-axis signal P1.1of a positive frequency component of a band pass characteristic symmetrical to a direct current component with a frequency of zero. A signal after Hilbert-transforming a real-axis signal O.1is added to a delayed signal of the imaginary-axis signal O.Q by an adder6f, and the signal obtained from the added result is outputted to terminals P1.1and P1.Q as an imaginary-axis signal P1.Q of a positive frequency component of a band pass characteristic symmetrical to a direct current component with a frequency of zero.

Further, a signal after Hilbert-transforming the imaginary-axis signal O.Q is added to the delayed signal of the real-axis signal O.1inputted from terminals O.1and O.Q by an adder6g, and the signal obtained from the added result is employed as a real-axis signal P2.1of a negative frequency component of a band pass characteristic symmetrical to a direct current component with a frequency of zero. The delayed signal of the imaginary-axis signal O.Q is subtracted from the signal after Hilbert-transforming the real-axis signal O.1by a subtractor6h, and the signal obtained from the subtraction result is outputted to terminals P2.1and P2.Q as an imaginary-axis signal P2.Q of a positive frequency component of a band pass characteristic symmetrical to a direct current component with a frequency of zero.

Not only a FIR filter but also an IIR filter may be utilized as the Hilbert transformers6band6e, thereby realizing good characteristic even with small amount of operation.

As described above, according to the receiver of the third embodiment, in the output of the orthogonal detector2, when the image signal of the undesired signal existing in the quasi-desired signal is compensated by means of a replica of the image signal in the undesired signal generated from the preparatory desired signal in the characteristic compensator7, the quasi-desired signal and preparatory desired signal outputted from the orthogonal detector2are respectively frequency-converted to signals more close to a direct current component with a frequency of zero by the frequency converter5, the converted signals are separated into a quasi-desired signal and a preparatory desired signal by means of the positive/negative separation filter13aand13bfor suppressing an unnecessary frequency component through a phase process utilizing the Hilbert transform, and the a quasi-desired signal and the preparatory desired signal are certainly separated and inputted to the characteristic compensator7, thereby excellently compensating for an orthogonal error.

A Fourth Embodiment

A fourth embodiment of the present invention is described.

In a receiver realized in a radio equipment according to the fourth embodiment of the present invention, a quasi-desired signal and a preparatory desired signal can be separated by a filter for suppressing an unnecessary frequency component through a phase process utilizing the Hilbert transform, in stead of the band pass filter9and10in the receiver of the above-described second embodiment.

The receiver according to the third embodiment of the present invention is described with reference toFIG. 9. In the receiver, a signal is received through an antenna1, and the received real signal is converted into a complex reception signal S1of an intermediate frequency (IF frequency) by an orthogonal detector2.

Next, when the received signal has been converted into the complex reception signal S1of the intermediate frequency, a real-axis signal and an imaginary-axis signal of the complex reception signal S1converted into the complex signal by an orthogonal detector2are respectively converted into digital signals by means of ADCs (A/D converters)3and4for quantizing an inputted signal with a predetermined sampling frequency according to a sampling theorem.

Next, by means of a positive/negative separation filter13a, which suppresses an unnecessary frequency component through a phase process utilizing the Hilbert transform, separates an inputted signal into two outputs with a pass band characteristic symmetrical to a direct current component with a frequency of zero, and then outputs the two outputs, a frequency band of the quasi-desired signal and a frequency band of the preparatory desired signal are separated in an ADCs3and4.

When a quasi-desired signal and a preparatory desired signal can be separated from each other, the frequency of the quasi-desired signal is frequency-converted (movement in a minus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero by the frequency converter5. Likewise, the frequency of the preparatory desired signal is frequency-converted (movement in a plus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero by the frequency converter5.

Next, the frequency-converted quasi-desired signal and preparatory desired signal are inputted to a characteristic compensator7. The characteristic compensator7suppresses an image signal of an undesired signal included in the quasi-desired signal inputted from the frequency converter5by means of a complex codomain signal of the preparatory desired signal inputted from the frequency converter5.

The output of the characteristic compensator7is demodulated by a detector8, and then converted into data of a digital signal row.

Since a detailed description for the orthogonal detector2and frequency converter5is the same as that of the first embodiment, the description is omitted. Further, a detailed description for the positive/negative separation filter13ais the same as that of the positive/negative separation filter13aor positive/negative separation filter13bdescribed in the third embodiment, the description is omitted.

As described above, according to the receiver of the fourth embodiment, in the output of the orthogonal detector2, when the image signal of the undesired signal existing in the quasi-desired signal is compensated for by means of a replica of the image signal in the undesired signal generated from the preparatory desired signal in the characteristic compensator7, the quasi-desired signal and preparatory desired signal outputted from the orthogonal detector2are respectively separated into a quasi-desired signal and a preparatory desired signal by means of the positive/negative separation filter13afor suppressing an unnecessary frequency component through a phase process utilizing the Hilbert transform, the separated signals are respectively frequency-converted to signals more close to a direct current component with a frequency of zero by the frequency converter5, and the a quasi-desired signal and the preparatory desired signal are certainly separated with a small size of circuit and inputted to the characteristic compensator7, thereby excellently compensating for an orthogonal error.

A Fifth Embodiment

A fifth embodiment of the present invention is described.

A receiver realized in a radio equipment according to the fifth embodiment of the present invention has a characteristic in which a characteristic compensator with two complex signal inputs and one complex signal output can be included, instead of the characteristic compensator7with two complex signal inputs and one complex signal output in the receiver of the above-described first embodiment.

The receiver according to the third embodiment of the present invention is described with reference toFIG. 10. In the receiver, a signal is received through an antenna1, and the received real signal is converted into a complex reception signal S1of an intermediate frequency (IF frequency) by an orthogonal detector2.

Next, when the received signal has been converted into the complex reception signal S1of the intermediate frequency, a real-axis signal and an imaginary-axis signal of the complex reception signal S1converted into the complex signal by an orthogonal detector2are respectively converted into digital signals by means of ADCs (A/D converters)3and4for quantizing an inputted signal with a predetermined sampling frequency according to a sampling theorem.

Next, by means of a positive/negative separation filter13a, which suppresses an unnecessary frequency component through a phase process utilizing the Hilbert transform, separates an inputted signal into two outputs with a pass band characteristic symmetrical to a direct current component with a frequency of zero, and then outputs the two outputs, a frequency band of the quasi-desired signal and a frequency band of the preparatory desired signal are separated in an ADCs3and4.

When a quasi-desired signal and a preparatory desired signal can be separated from each other, the frequency of the quasi-desired signal is frequency-converted (movement in a minus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero by the frequency converter5. Likewise, the frequency of the preparatory desired signal is frequency-converted (movement in a plus direction on a frequency axis) to a signal closer to a direct current component with a frequency of zero by the frequency converter5.

Next, a real-axis signal of the frequency-converted quasi-desired signal is added to and synthesized with a real-axis signal of preparatory desired signal by an adder14, and an imaginary-axis signal of the frequency-converted quasi-desired signal is added to and synthesized with an imaginary-axis signal of preparatory desired signal by an adder15.

Further, the synthesized signal is inputted to a decimator16, and then a filtering and a down-sampling are performed.

Next, the down-sampled synthesis signal is inputted to a characteristic compensator17, and the characteristic compensator17compensates for an orthogonal error and an amplitude error.

The output of the characteristic compensator17is demodulated by a detector8, and then converted into data of a digital signal row.

The characteristic compensator17is described.FIG. 11is an example of a case in which the characteristic compensator17is realized by means of an adaptive signal processing. With respect to a real-axis signal X.1and an imaginary-axis signal X.Q inputted from terminals X.1and X.Q, the real axis signal Y.1and the imaginary-axis signal Y.Q, in which an orthogonal error and an amplitude error have been compensated for, are obtained through equations,
(Y.1)=h3×(X.1)
(Y.Q)=h1×(X.Q)+h2×(X.1)

in which h1, h2, h3are responsively renewed by update equations of a coefficient,
h1,k=h1,k−1+μ×(Y.Q)×(X.Q)×e
h2,k=h2,k−1+μ×(Y.1)×(X.Q)×e
h3,k=h3,k−1+μ×(Y.1)×(X.1)×e

(herein, σ represents a desired signal amplitude value and e=σ2−((Y.1)2+(Y.Q)2)).

Further, a multiplier9amultiplies a real-axis signal X.1inputted from terminals X.1and X.Q by a coefficient h3, and employs the signal obtained from the multiplication result as a real-axis signal Y.1inputted from terminals Y.1and Y.Q. A multiplier9bmultiplies a real-axis signal X.1inputted from terminals X.1and X.Q by a coefficient h2, and a multiplier9cmultiplies an imaginary-axis signal X.Q inputted from terminals X.1and X.Q by a coefficient h1. Further, the output of the multiplier9bis added to the output of the multiplier9c, the signal obtained from the added result is employed as an imaginary-axis signal Y.Q inputted from terminals Y.1and Y.Q.

Since a detailed description for the orthogonal detector2, the frequency converter5and the positive/negative separation filter13ais the same as that of the fourth embodiment, the description is omitted. Further, in order to remove a return of a quasi-desired signal or preparatory desired signal, the decimator16employs a frequency band of a signal synthesized by adders14and15as a pass band, and includes a low pass filter of a real coefficient for extracting the signal, and a down sampler for converting a sampling rate of an output signal in the low pass filter and employing the converted signal as a signal with a low sampling rate. Herein, the low pass filter and the down sampler are provided for a real-axis signal processing as well as an imaginary-axis signal processing.

Further, the decimator16performs a filtering and a down sampling on each real-axis signal and each imaginary-axis signal of the synthesized signal.

As described above, according to the receiver of the fourth embodiment, the quasi-desired signal and preparatory desired signal outputted from the orthogonal detector2are respectively frequency-converted to signals more close to a direct current component with a frequency of zero by the frequency converter5, the converted signals are converted into signals with a low sampling rate by the decimator16, thereby reducing the amount of operation in the characteristic compensator. Further, the characteristic compensator15with a simple construction is utilized as a characteristic compensator, thereby excellently compensating for an orthogonal error with the small amount of operation and small size of circuit.

A Sixth Embodiment

A sixth embodiment of the present invention is described.

A receiver realized in a radio equipment according to the sixth embodiment of the present invention has a characteristic in which a circuit can be simplified by using in common the multipliers included in the frequency converter5described with reference toFIG. 2in the receiver of the above-described first embodiment.

A synthesis complex mixer used as the frequency converter5in a receiver according to an embodiment of the present invention is described with reference toFIG. 12.FIG. 12is a block diagram showing a construction of the synthesis complex mixer for use in common multipliers of a complex mixer, which includes a multiplier2b, a multiplier2c, amultiplier2eand a multiplier2f, and a complex mixer, which includes a multiplier3b, amultiplier3c, a multiplier3eand a multiplier3f, in the frequency converter5described with reference toFIG. 2in the first embodiment. The synthesis complex mixer includes a multiplier7bfor multiplying a real-axis signal S1.1of a complex reception signal S1inputted from terminals S.1and S.Q by a real-axis signal “cos” of a local signal in a second frequency generated from an orthogonal carrier oscillator7a, and a multiplier7cfor multiplying an imaginary-axis signal S1.Q of a complex reception signal S1inputted from terminals S.1and S.Q by an imaginary-axis signal “−sin”, of which phase has moved by 90° in relation to the real-axis signal, of a local signal in a second frequency generated from an orthogonal carrier oscillator7a. In the synthesis complex mixer, an output sign of the multiplier7cis inverted by a sign inverter7d. Simultaneously, the inverted output is added to an output of the multiplier7bby means of an adder7eand employed as a real-axis signal output T1.1of the two real-axis signal outputs.

The synthesis complex mixer includes a multiplier7ffor multiplying a real-axis signal S1.1of a complex reception signal S1inputted from terminals S.1and S.Q by the imaginary-axis signal “−sin” of a local signal in a second frequency generated from an orthogonal carrier oscillator7aconnected to an outside, and a multiplier7gfor multiplying an imaginary-axis signal S1.Q of a complex reception signal S1inputted from terminals S.1and S.Q by the real-axis signal “cos” of a local signal in a second frequency generated from an orthogonal carrier oscillator7a. In the synthesis complex mixer, the output of the multiplier7gis added to an output of the multiplier7fby means of an adder7eand employed as an imaginary-axis signal output T1.Q of the two imaginary-axis signal outputs.

In the synthesis complex mixer, the output of the multiplier7cis added to an output of the multiplier7bby means of an adder7i, and the output obtained from the added result is employed as a real-axis signal output T2.1in two real-axis signal outputs. An output sign of the multiplier7fis inverted by a sign inverter7j. Simultaneously, the inverted output is added to an output of the multiplier7gby means of an adder7k, and the output obtained from the added result is employed as an imaginary-axis signal output T2.Q in two imaginary-axis signal outputs.

Since elements excepting for the inside construction of the frequency converter5are the same as those of the above-described first embodiment, a description for the elements excepting for the frequency converter5is omitted.

As described above, according to the receiver of the sixth embodiment, in the output of the orthogonal detector2, when the image signal of the undesired signal existing in the quasi-desired signal is compensated by means of a replica of the image signal in the undesired signal generated from the preparatory desired signal in the characteristic compensator7, only four multipliers are utilized after using the eight multipliers in the frequency converter5used in the first embodiment in common, the a quasi-desired signal and the preparatory desired signal are separated with a small size of circuit and inputted to the characteristic compensator7, thereby excellently compensating for an orthogonal error.

Even in the above-described third embodiment, the synthesis complex mixer described with reference toFIG. 12in the sixth embodiment may be utilized. Accordingly, like the sixth embodiment, the a quasi-desired signal and the preparatory desired signal can be separated with a small size of circuit can be inputted to the characteristic compensator7, thereby excellently compensating for an orthogonal error.

A Seventh Embodiment

A seventh embodiment of the present invention is described.

A receiver realized in a radio equipment according to the seventh embodiment of the present invention has a characteristic in which an adaptation process is introduced in the characteristic compensator7described with reference toFIG. 4in the receiver of the above-described first embodiment.

A characteristic compensator, which has introduced the adaptation process, utilized as the characteristic compensator7in the receiver according to the seventh embodiment is described with reference toFIG. 13.FIG. 13is a block diagram showing a construction of the characteristic compensator7, which has introduced the adaptation process, described with reference toFIG. 4in the first embodiment. The characteristic compensator, which has introduced the adaptation process, includes a multiplier8afor multiplying an imaginary-axis signal X2.Q of a preparatory desired signal inputted from terminals X2.1and X2.Q by “−1” and generating a complex codomain signal of the inputted preparatory desired signal by inverting the sign of the imaginary-axis signal X2.Q, and a LMS core8b, which is a central pate of an adaptation filter, for controlling a filter coefficient after employing output signals Y.1and Y.Q of the characteristic compensator7as error signals, and employing the generated complex codomain signal as a reference signal.

The characteristic compensator, which has introduced the adaptation process, includes an ATT8c(signal attenuator) of a real-axis side for adjusting a signal level of an output (image frequency interference cancellation signal) of the LMS core8b, an ATT8d(signal attenuator) of an imaginary-axis side for adjusting a signal level of an output (image frequency interference cancellation signal) of the LMS core8b, a subtractor8eof a real-axis side for synthesizing the image frequency interference cancellation signal adjusted by the ATT8cto a quasi-desired signal inputted from a terminal X1.1, and a subtractor8fof an imaginary-axis side for synthesizing the image frequency interference cancellation signal adjusted by the ATT8dto a quasi-desired signal inputted from a terminal X1.Q.

The LMS core8bemploys the complex codomain signal generated from the preparatory desired signal inputted to the terminals X2.1and X2.Q as a reference signal S. The LMS core8boperates so that an error between the reference signal S and an image signal of undesired signal, which has generated from the orthogonal detector2existing in a quasi-desired signal inputted to the terminals X1.1and X1.Q, can be minimized. When there is no error, since the image signal of undesired signal is completely suppressed, a suppression characteristic of the image signal can be improved up to an adaptation accuracy limitation of the characteristic compensator7.

When the adaptation process is performed, a calibration signal may be inputted to the characteristic compensator7, and then a coefficient of the adaptation filter may be obtained.

The ATT8cof the real-axis side for adjusting a signal level of an output of the LMS core8band the ATT8dof the imaginary-axis side for adjusting a signal level of an output of the LMS core8bare inserted so that a filter coefficient word length of the LMS core8bcan be operated at a minimum coefficient word length. This insertion is performed because the image signal of undesired signal has a very low signal level in comparison to the complex codomain signal, which is inputted to the adaptation filter as the reference signal, generated from the preparatory desired signal inputted to the terminals X2.1and X2.Q. When the attenuator is not used, the LMS core8bvaries a signal level of an image frequency interference cancellation signal, which is an output, to a signal level of the image signal of undesired signal by varying the size of the coefficient value. However, when the coefficient value must be small, the variation operation causes an adaptation accuracy to lower as the filter coefficient word length is shortened. Accordingly, the variation operation is not preferable.

Since a characteristic variation of an analog section does not occur in a short time, it is not always necessary to perform the adaptation process when the image signal of undesired signal slowly varies on the time-axis. Accordingly, except for a necessary case, signals can be processed when an adaptation operation of the adaptation filter is stopped. Specially,

ON/OFF (operation/stop) of the adaptation process of the LMS core8bin the characteristic compensator7is controlled, and then the adaptation process is performed during a predetermined time. During the rest time, the adaptation filter of the LMS core8bis operated as an equalizer by means of an obtained coefficient (a final coefficient maintained when the adaptation process is stopped) or a fixed coefficient. The object of the present invention can be obtained by repeating the operation.

As described above, according to the receiver of the sixth embodiment, in the output of the orthogonal detector2, when the image signal of the undesired signal existing in the quasi-desired signal is compensated by means of a replica of the image signal in the undesired signal generated from the preparatory desired signal, the adaptation process is introduced in the characteristic compensator7used in the first embodiment, thereby excellently compensating for an orthogonal error according to a characteristic variation of the orthogonal detector2.

Further, the above-described second, fourth and sixth embodiment may employ the characteristic compensator, which has introduced the adaptation process, described with reference toFIG. 13in the seventh embodiment as the characteristic compensator7, thereby excellently compensating for an orthogonal error according to a characteristic variation of the orthogonal detector2, like the seventh embodiment.

An Eighth Embodiment

A eighth embodiment of the present invention is described.

FIG. 14is a block diagram showing a construction of a transmitter realized in a radio equipment according to the eighth embodiment of the present invention.

The transmitter according to the eighth embodiment of the present invention is described with reference toFIG. 14. In the transmitter, a modulator21prepares a complex carrier signal of a perpendicular intersecting intermediate frequency (IF frequency), and then generates a transmission signal by modulating the complex carrier signal to transmission data.

In a characteristic compensator22, an orthogonality error between a real-axis signal and an imaginary-axis signal occurring after the modulator21is compensated, and then a reverse characteristic of the orthogonality error is added in advance, thereby generating a synthesis transmission signal between the original complex carrier signal and a complex codomain signal of a corresponding complex carrier signal.

In an interpolator23, a positive/negative frequency component of the synthesis transmission signal is separated by a filtering, and then the separated signal is separated into the original complex carrier signal and the complex codomain signal of the corresponding complex carrier signal. Simultaneously, an upsampling is performed so that a conversion to an analog signal can be easily performed.

A frequency of the separated original complex carrier signal is frequency-converted to complex codomain frequency of an input frequency of an orthogonal modulator29by a frequency converter24. A frequency of the separated the complex codomain signal of the corresponding complex carrier signal is frequency-converted to a complex codomain frequency of a corresponding input frequency by the frequency converter24.

A real-axis signal is synthesized to a real-axis signal by an adder25, and an imaginary-axis signal is synthesized to an imaginary-axis signal by an adder26, and the real-axis signal and the imaginary-axis signal are converted into analog signals by DAC (D/A converter)27and28. The converted signals are inputted to the orthogonal modulator29

In the orthogonal modulator29, the inputted complex signal is frequency-converted to a transmission frequency, and simultaneously only a real-axis signal of the frequency-converted signal is outputted to an antenna30.

The interpolator23is described. As shown inFIG. 15, the interpolator23includes an upsampler12afor interpolating data of signals inputted from terminals M.1, M.Q, and a band pass filter12bfor employing a frequency band of the original complex carrier signal in the output of the characteristic compensator22as a pass band, and for extracting the original complex carrier signal, in order to remove a return of the original complex carrier signal and separate the original complex carrier signal and the complex codomain signal in the output of the upsampler12a.

The interpolator23includes a band pass filter12cfor employing a frequency band of the complex codomain signal of the original complex carrier signal in the output of the characteristic compensator22as a pass band, and for extracting the complex codomain signal of the original complex carrier signal, in order to remove a return of the original complex carrier signal and separate the original complex carrier signal and the complex codomain signal in the output of the upsampler12a.

In filter coefficients of the band pass filter12band band pass filter12c, one side of the band pass filter12band band pass filter12cinverts a sign of an imaginary-axis side of a complex filter coefficient prepared in other side of the band pass filter12band band pass filter12cso that the band pass filter12band band pass filter12ccan realize a band characteristic symmetrical to a direct current component with a frequency of zero.

A characteristic compensator, which is equal to the characteristic compensator17described with reference toFIG. 11in the fifth embodiment, is utilized as the characteristic compensator22.

The frequency converter24is described. As shown inFIG. 16, in order to convert the frequency of original complex carrier signal into the input frequency of the orthogonal modulator29, the frequency converter24includes an orthogonal carrier oscillator10afor outputting a complex local signal of a fourth frequency by a predetermined value lower than the frequency of original complex carrier signal, a multiplier10bfor multiplying a real-axis signal V1.1of the complex reception signal S1inputted from a terminal V1.1by a real-axis signal “cos” of the local signal of the fourth frequency outputted from the orthogonal carrier oscillator10a, a multiplier10cfor multiplying an imaginary-axis signal V1.Q of the complex reception signal S1inputted from a terminal V1.Q by an imaginary-axis signal “−sin”, of which phase has moved by 90° in relation to the real-axis signal, of the local signal of the fourth frequency outputted from the orthogonal carrier oscillator10a, and a subtracter10dfor subtracting the output of the multiplier10cfrom the output of the multiplier10b, and then employing the subtraction result as a real-axis signal output W1.1.

The frequency converter24includes a multiplier10efor multiplying the real-axis signal V1.1of the complex reception signal S1inputted from the terminal V1.1by the imaginary-axis signal “sin” of the local signal of the fourth frequency outputted from the orthogonal carrier oscillator10a, a multiplier10ffor multiplying the imaginary-axis signal V1.Q of the complex reception signal S1inputted from the terminal V1.Q by the real-axis signal “cos” of the local signal of the fourth frequency outputted from the orthogonal carrier oscillator10a, and an adder10gfor adding the output of the multiplier10eto the output of the multiplier10f, and then employing the result as a imaginary-axis signal output W1.Q.

In order to convert the frequency of the complex codomain signal of the original complex carrier signal into a complex codomain frequency of the input frequency of the orthogonal modulator29, the frequency converter24includes a sign inverter11afor inverting a sign of the imaginary-axis signal outputted from the orthogonal carrier oscillator10a, and then obtaining complex codomain signal of local signal of the fourth frequency, a multiplier11bfor multiplying the real-axis signal V2.1of the complex reception signal S1inputted from a terminal V2.1by a real-axis signal “cos” of a local signal of a fifth frequency generated as the complex codomain signal of the local signal of the fourth frequency outputted from the orthogonal carrier oscillator10a, a multiplier11cfor multiplying the imaginary-axis signal V2.Q of the complex reception signal S1inputted from the terminal V2.Q by an imaginary-axis signal “−sin”, of which phase has moved by 90° in relation to the real-axis signal, of the local signal of the fifth frequency generated as the complex codomain signal of the local signal of the fourth frequency outputted from the orthogonal carrier oscillator10a, and a subtracter11dfor subtracting the output of the multiplier11cfrom the output of the multiplier11b, and then employing the subtraction result as a real-axis signal output W2.1.

The frequency converter24includes a multiplier1efor multiplying the real-axis signal v2.1of the complex reception signal S1inputted from the terminal V2.1by the imaginary-axis signal “−sin” of the local signal of the fifth frequency generated as the complex codomain signal of the local signal of the fourth frequency outputted from the orthogonal carrier oscillator10a, a multiplier11ffor multiplying the imaginary-axis signal V2.Q of the complex reception signal S1inputted from the terminal V2.Q by the real-axis signal “cos” of the local signal of the fifth frequency generated as the complex codomain signal of the local signal of the fourth frequency outputted from the orthogonal carrier oscillator10a, and an adder11gfor adding the output of the multiplier11eto the output of the multiplier11f, and then employing the result as a signal output W2.Q of a imaginary-axis signal.

Instead of the orthogonal carrier oscillator10a, an orthogonal carrier oscillator, which outputs a complex local signal for converting the frequency of complex codomain signal of original complex carrier signal into a complex codomain frequency of the input frequency of the orthogonal modulator29, may be utilized. A complex codomain signal of a complex local signal outputted from a corresponding orthogonal carrier oscillator may be utilized as the complex local signal for frequency-converting the frequency of original complex carrier signal into the input frequency of the orthogonal modulator29.

In the transmitter according to the above-described eighth embodiment, the same effect can be obtained even if the frequency converter24is located in front of the band pass filter12b/12cincluded in the interpolater23. However, the pass frequency band of the band pass filter12band12cmust match with a frequency band of the original complex carrier signal and a frequency band of the complex codomain signal of the original complex carrier signal in the output of the frequency converter24.

As described above, according to the transmitter of the eighth embodiment, with respect to a signal with low immediate frequency, the characteristic compensator22performs a compensation process of an orthogonality error with the low sampling frequency intact. In the compensated signal, a sampling frequency and a transmission frequency are adjusted by the interpolator23and the frequency converter24, thereby reducing the amount of operation in the characteristic compensator22.

In the above-described first to eighth embodiment, the characteristic compensator7, the characteristic compensator17and the characteristic compensator22are digital circuits, and the characteristic compensation process of the orthogonality error in the complex signal is performed by a digital signal processing. However, as the first to eighth embodiment, without an A/D conversion or a D/A conversion, the characteristic compensation process of orthogonal error in the complex signal may be performed by the characteristic compensators of analog circuits in a state in which signals are maintained as analog signals.

In this case, even in the characteristic compensation process by means of an analog circuit, since the compensation process is performed in low frequency below a RF frequency or a IF frequency, the compensation having high accuracy can be performed even if a passive circuit is used. Accordingly, it is always unnecessary to use an active circuit with a high consumption power in an operation state, thereby reducing the consumption power.

According to the present invention, in a state in which a target signal and a non-target signal in an output of orthogonal detector are kept as signals of a frequency symmetrical to a direct current component with a frequency of zero, the target signal and the non-target signal are converted into signals of a frequency more close to a direct current component, and then the converted signals are inputted to a characteristic compensator for compensating for an orthogonality error of the orthogonal detector, thereby compensating for the orthogonality error of the orthogonal detector by means of a characteristic compensator with a low sampling frequency. Accordingly, the consumption power in the characteristic compensator for compensating for an orthogonality error of a complex signal can be reduced, thereby realizing a radio equipment capable of transceiving signals with no distortion.

A target signal and a non-target signal in an output of modulator are close to a direct current component with a frequency of zero, and the target signal and the non-target signal are simultaneously generated as signals of a frequency symmetrical to a corresponding direct current component. Simultaneously, a frequency of a target signal and a non-target signal in an output of a characteristic compensator is converted into a signal of transmission frequency, thereby compensating for the orthogonality error of the orthogonal modulator by means of a characteristic compensator with a low sampling frequency. Accordingly, the consumption power in the characteristic compensator for compensating for an orthogonality error of a complex signal can be reduced, thereby realizing a radio equipment capable of transceiving signals with no distortion.