JP3094940B2 - Quadrature modulated wave receiving method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiving device used for satellite communication and mobile communication devices, and more particularly, to a frequency converter for converting a radio frequency into an intermediate frequency, which provides a radio frequency to a frequency converter. Quadrature modulation, which is an integral multiple of the frequency step of the channel and is used in systems where the frequency component remains in the output signal of the quasi-synchronous quadrature detector, especially in systems where the influence of undesired waves due to adjacent waves is large. The present invention relates to a receiving device for receiving a modulated wave and extracting a signal.

[0002]

2. Description of the Related Art FIG. 3 is a block diagram of a conventional quadrature modulated wave receiving apparatus for receiving a quadrature modulated radio frequency band signal. The orthogonally modulated received signal is power-amplified by a low noise amplifier (LNA) 101 and mixed with an output frequency of a frequency synthesizer 103 in a frequency converter 102 to convert a radio frequency band (RF) signal to an intermediate frequency band (IF). The frequency is converted to a signal.

The frequency-converted IF signal is band-limited by a band-pass filter (BPF) 104, quasi-synchronous detected by a quasi-synchronous quadrature detector 105, and a quasi-synchronous quadrature signal is output. The quasi-synchronous quadrature signal subjected to quasi-synchronous detection is
After a harmonic component is removed by a low-pass filter (LPF) 107, the signal is converted into a digital signal by an A / D converter 108. The digitized quasi-synchronous quadrature signal is input to a synchronous detection or delay detection quadrature demodulator 109, and a received signal is demodulated.

Next, consider a case where the frequency step of a synthesizer that provides a radio frequency to a frequency converter that converts a radio frequency band (RF) to an intermediate frequency (IF) is an integral multiple of the frequency step of a reception channel.

In FIG. 4, a quadrature-modulated received signal is power-amplified by an LNA 110 and frequency-converted by a frequency converter 111 from an RF signal to an IF signal by mixing with an output frequency of a frequency synthesizer 112. The frequency-converted IF signal is a BPF1
The quasi-synchronous quadrature detector 114 performs quasi-synchronous detection, and outputs a quasi-synchronous quadrature signal. When the frequency step of the frequency synthesizer 112 is n times (n is an integer) the frequency step of the reception channel, the output signal of the quasi-synchronous detector is ± n / 2 × fsc (fs
c: a frequency step of the reception channel), a digital frequency shifter 118 for selecting a signal of a desired channel is inserted after the quasi-synchronous quadrature detection.

That is, the quasi-synchronous quadrature signal from which the harmonic component has been removed by the LPF 116 is converted into an A / D converter 117.
After being converted into a digital signal by the digital frequency shifter 118,
, And only the signal of the desired channel is converted to a baseband signal. The frequency-converted baseband signal is input to a synchronous detection or delay detection quadrature demodulator 121 via an LPF 120, and a desired received signal is demodulated.

[0007]

As described above, the frequency step of the frequency synthesizer for providing the radio frequency to the frequency converter for converting the radio frequency to the intermediate frequency is set to an integral multiple of the frequency step of the reception channel. The output signal of the quasi-synchronous quadrature detector is a quasi-synchronous quadrature signal containing a frequency component that is an integral multiple of the frequency step of the reception channel. If there is a large undesired wave in the residual frequency component, the image component of the undesired wave interferes with the desired wave at the output of the digital frequency shifter due to the amplitude error and phase error of the quasi-synchronous quadrature detector. Deterioration of characteristics occurs.

The principle that the image component of the undesired wave interferes with the desired wave at the output of the digital frequency shifter will be described below. FIG. 5 is a block diagram of a quasi-synchronous quadrature detection unit when it is assumed that an amplitude error α and a phase error θ exist in the quasi-synchronous quadrature detector. In this case, the frequency of the input signal and omega, and the frequency of the local oscillator 203 of the quasi-synchronous quadrature detector and omega _I, the output signal of the quasi-synchronous quadrature detector is, I '+ jQ' = ( Icosωt + Qsinωt) × {cosω I t + j (1 + α) sin (ω I t +
θ)｝. When the output of the LPF 206 is first-order approximated under the condition of α, θ << 1, I ″ + jQ ″ = (１ ／) [ (I + jQ) exp {−j (ω
_{-ω I) t} - (I} - jQ) exp {j (ω-ω I) t} · (jθ + α) / 2]
(Equation 0) . Thus, a _zero frequency of the desired wave ω _{D =} ω _{I +} ω at the input of the quasi-synchronous quadrature detector, X frequency omega _D =
When (I + jQ) / 2 becomes the signal is present, the complex conjugate of X as a ^{X *,} the omega _D in omega in the formula 0, the I + jQ
When 2X ^* is substituted for 2X and I-jQ, the output signal of the LPF 206 of the frequency ω _D component is I ″ + jQ ″ = Xexp (−jω ₀ t) −X ^* exp (jω
₀ t) · (jθ + α) / 2 (Equation 1). In addition, there is an undesired wave having a frequency ω _U = ω _I −ω _o at the input of the quasi-synchronous quadrature detector, and a frequency ω _U
When Y = (I + jQ) / 2 becomes the signal is present, the complex conjugate of Y as a ^{Y *,} the omega _U to omega in Formula 0, I +
By substituting 2Y for jQ and 2Y ^* for I-jQ, the output signal of the LPF of the frequency ω _U component is: I ″ + jQ ″ = Yexp (jω ₀ t) −Y ^* exp (−jω
₀ t) · (jθ + α) / 2 (Equation 2). When an undesired wave is present, the output signal of the digital frequency shifter is the sum of the right side of Equations 1 and 2. α = θ =
If 0, only X exists in the term of exp (-jω ₀ t), but if α or θ ≠ 0, −Y ^* (jθ + α) /
The two terms are added. When the level of the non-desired wave is sufficiently higher than the desired wave, that is, when Y >> X, -Y
^{* The term} (jθ + α) / 2 is a value that cannot be ignored. At this time, the digital frequency shifter operates as shown in FIG. 6, and the image component of the undesired wave interferes with the desired wave, thereby deteriorating the reception characteristics.

According to the present invention, the frequency step of the frequency synthesizer for providing the radio frequency to the frequency converter for converting the radio frequency to the intermediate frequency is an integer multiple of the frequency step of the reception channel, and the output signal of the quasi-synchronous quadrature detector is Since the frequency component remains, in the quadrature modulated wave receiving apparatus having a digital frequency shifter at the subsequent stage of the quasi-synchronous quadrature detector, the interference wave of the desired wave generated due to the amplitude error and the phase error of the quasi-synchronous quadrature detector It is an object of the present invention to prevent the reception characteristic from being deteriorated due to the image component of the undesired wave.

[0010]

A quadrature modulated wave receiving apparatus according to the present invention calculates an image component of an undesired wave in a frequency shifter, and calculates the image component when the level of the undesired wave exceeds a certain threshold value. The above object is achieved by subtracting the image component of the undesired wave from the output of the frequency shifter unit to extract only the desired wave and demodulating it.

More specifically, means for analog-to-digital conversion of the output signal of the quasi-synchronous quadrature detector, and conversion of the converted digital signal into a frequency f ₀ (where f ₀ is a frequency which is an integral multiple of the frequency step of the reception channel) ), And a first LPF for extracting a baseband signal of a desired wave from the signal frequency-converted at the frequency f _0.
When, a second frequency converter for frequency-converting the frequency (-f _0), a second LPF for extracting a baseband signal from the frequency-converted signal at a frequency (-f _0), the first
A first multiplier for multiplying the output signal of the second LPF by the output signal of the second LPF, a squarer for squaring the output signal of the second LPF, and an output of the first multiplier A first integrator for integrating the signal for a fixed number of samples, a second integrator for integrating the output signal of the squarer for a fixed number of samples, and an integrated signal of the first integrator for the second integrator A divider that divides by the integrated signal; a complex conjugate calculator that outputs a complex conjugate of the output signal of the second LPF; and a second multiplier that multiplies an output signal of the divider and an output signal of the complex conjugate calculator. A subtractor for subtracting the output signal of the second multiplier from the output signal of the first LPF; a discriminator for determining a level of the output signal of the second LPF;
It is constituted by a digital frequency shifter comprising a selector controlled by an output signal of the discriminator.

The digital signal processing technology makes it possible to easily remove an image component of an undesired wave and extract a desired wave without deterioration. The level of the undesired wave is determined by determining the level of the undesired wave and providing a means for controlling the means for reducing the calculated image component of the undesired wave according to the determination result. It is possible to remove the influence of the error in the calculated value of the image component of the undesired wave, which occurs when the frequency is low.

[0013]

FIG. 1 is a block diagram showing an embodiment of a quadrature modulated wave receiving apparatus according to the present invention, and FIG. 2 is a block diagram showing means for calculating an undesired wave image component used in the present invention. It is. The quadrature modulated wave receiving device has
It comprises an F section 30, an IF section 31, a digital frequency shifter section 32, and a synchronous detection or delay detection quadrature demodulator 25.

The RF section 30 includes a low noise amplifier (LNA) 1 for power-amplifying an input signal, a frequency converter 2 for converting a frequency from a radio frequency band (RF) signal to an intermediate frequency band (IF) signal, and a frequency converter. A frequency synthesizer 3 for providing a radio frequency signal for frequency conversion to the device 2 is provided. The frequency synthesizer 3 is characterized in that its output frequency step is an integral multiple of the frequency step of the receiving channel.

The IF unit 31 has a band limiting filter (BPF) 4 for band limiting the IF signal output from the RF unit 30.
A quasi-synchronous quadrature detector 5 that performs quasi-synchronous quadrature detection on the band-limited IF signal and outputs an in-phase component and a quadrature component; a local oscillator 6 that supplies the quasi-synchronous quadrature detector 5 with an IF signal; A low-pass filter (LPF) 7 for removing a harmonic component of the output signal of the device 5 and an A / D converter 8 for sampling the quasi-synchronous quadrature signal from which the harmonic component has been removed by the LPF 7 and converting the signal into a digital signal. And

The digital frequency shifter unit 32 includes an IF unit 3
A signal sampled at 1, a frequency converter 9 to frequency conversion by the frequency f ₀ of converting the integral multiple is an in and desired received channel signal of the frequency step of the reception channel into a baseband signal, oscillates at a frequency f ₀ an oscillator 10 to a low-pass filter for extracting only the frequency-converted signal Karabe band signal at the frequency f ₀ (LP
F) 13; a frequency converter 11 for frequency-converting the signal sampled by the IF unit 31 at a frequency (−f ₀ );
An oscillator 12 oscillating at a frequency (−f ₀ ) and a frequency (−f ₀ )
f ₀ ), a low-pass filter (LPF) 14 for extracting only a baseband signal from the signal subjected to frequency conversion,
A complex multiplier 15 for complexly multiplying the output signal of the F13 and the output signal of the LPF 14, an amplitude squarer 17 for squaring and outputting the amplitude of the input signal, and an integration for integrating the output signal of the complex multiplier 15 by a constant sample 16, an integrator 18 for integrating the output signal of the amplitude squarer 17 by a constant sample, a divider 19 for dividing the output signal of the integrator 16 by the output signal of the integrator 18, and a complex of the output signal of the LPF 14. A complex conjugate calculator 22 that outputs a conjugate; a multiplier 20 that multiplies an output signal of the divider 19 by an output signal of the complex conjugate calculator 22;
A subtracter 21 for subtracting an output signal of the multiplier 20 from an output signal of the PF 13; and a discriminator 2 for determining a level of an undesired wave
3 and a selector 2 controlled by the output signal of the discriminator
4 is provided. It should be noted that oscillates at a frequency (-f ₀₎
An oscillator 12, out of the oscillator 10 which oscillates at a frequency _{f 0}
Signal whose output is phase-rotated in the negative direction
This is an oscillator that outputs a signal. Therefore, the frequency f ₀
For controlling the phase rotation of the output of the oscillator oscillating in the negative direction.
This can be realized by providing a step.
When using digital signal processing technology for
For example, digital oscillator 10 which oscillates at a frequency _{f 0}
If the output (jω ₀ ) is output via a complex conjugate calculator,
Oscillation output complex conjugate digital signal (-jω ₀₎
That is , an oscillator that oscillates at a frequency (−f ₀ ).

The operation of the present invention will be described with reference to FIG.
In FIG. 1, the input RF signal of the quadrature modulated wave receiving device is
The power is amplified by the LNA 1, input to the frequency converter 2, and converted into an IF signal. The converted IF signal is B
The band is limited by the PF 4, quasi-synchronous detection is performed by the quasi-synchronous quadrature detector 5, and the quasi-synchronous quadrature signal is output. Where R
Since the frequency step of the frequency synthesizer 3 of the F unit 30 is n times (n is an integer) the frequency step of the reception channel, the output signal of the quasi-synchronous detector 5 is m × fsc (−n
/ 2 <m <n / 2, where m and n are integers, and fsc: a frequency step of the reception channel). The quasi-synchronous quadrature signal from which the harmonic components have been removed by the LPF 7 is converted into a digital signal by the A / D converter 8, and the converted digital signal is input to the digital frequency shifter 32. Here, the method of calculating the undesired wave image component of the digital frequency shifter unit 32 is shown in FIG.
This will be described with reference to FIG.

The output of the A / D converter 8 is defined as the sum of the right sides of the equations (1) and (2). Here, ω ₀ = 2πf ₀ , f ₀ = m × fsc, X is a signal existing at the frequency of the desired wave, and Y is a signal existing at the frequency of the undesired wave. The frequency converter 9 is +
The frequency shifts to f ₀ , and the frequency converter 11 shifts the frequency to −f ₀ . Therefore, the output signal of the LPF 13 is X ′,
Assuming that the output signal of the LPF 14 is Y ′, if Y >> X, X ′ = XY ^* (jθ + α) / 2 Y′'Y (Equation 3). Therefore, A and B in FIG. 2 are as follows: A = ΣXY− (jθ + α) / 2ΣYY ^* B = ΣYY ^*

Under the condition of Y >> X, ΣXY / ΣYY ^*
<< − (jθ + α) / 2, so A / B is A / B = − (jθ + α) / 2. Therefore, if A / B is multiplied by Y ^* and subtracted from X ′, the output of the subtractor 21 becomes X, and a signal existing at the frequency of the desired wave is extracted.

However, when the undesired wave level is small, that is, when the value of Y is small, the error of the approximate expression increases.
It is necessary to provide a function of controlling the output signal of the digital frequency shifter unit 32 according to the magnitude of the value. The function of controlling the output signal of the digital frequency shifter 32 will be described again with reference to FIG.

Since the output of the LPF 14 is Y from Equation 3, the output signal of the LPF 14 is input to the level discriminator 23. In the level discriminator 23, when the input signal is larger than a certain threshold, the selector 24 selects and outputs the output of the subtracter 21, and when the input signal is smaller than a certain threshold, the selector 24 selects the output. Selects the output of the LPF 13 and outputs it. The output signal of the selector 24 is input to the synchronous detection or delay detection quadrature demodulation circuit 25, and the received signal is demodulated.

[0022]

According to the present invention, an image component of an undesired wave serving as an interference wave of a desired wave is calculated from the output signal of the quasi-synchronous quadrature detector by digital signal processing. When the digital frequency shift is larger than the threshold value, an image component of an undesired wave serving as an interference wave is removed, so that a frequency synthesizer that provides a radio frequency to a frequency converter that converts a radio frequency to an intermediate frequency is used. Since the frequency step is set to be an integral multiple of the frequency step of the reception channel, a frequency shifter for selecting a desired reception channel from a plurality of frequency components remaining in the output signal of the quasi-synchronous quadrature detector is provided. In the quadrature modulated wave receiver, the amplitude error of the quasi-synchronous quadrature detector,
In addition, it is possible to prevent reception characteristics from deteriorating due to an image component of a non-desired wave that becomes an interference wave of a desired wave, which is caused by a phase error.

[0023]

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a unit for calculating an undesired wave image component according to the present invention.

FIG. 3 is a block diagram of a conventional quadrature modulation wave demodulator.

FIG. 4 is a block diagram of a quadrature modulation wave demodulator having a digital frequency shifter.

FIG. 5 is a block diagram illustrating a quasi-synchronous quadrature detection unit.

FIG. 6 is a diagram illustrating the operation of the digital frequency shifter.

[Explanation of symbols]

1,101,110 Low noise amplifier (LNA) 2,9,11,102,111 Frequency converter 3,103,112 Frequency synthesizer 4,104,113 Bandpass filter (BPF) 5,105,114 Quasi-synchronous quadrature detection Unit 6 Local oscillator 7, 13, 14, 107, 116, 120 Low-pass filter (LPF) 8, 108, 117 A / D converter 10, 12, 106, 115 Oscillator 15, 20 Complex multiplier 16, 18 Integration Unit 17 amplitude squarer 19 divider 21 subtracter 22 complex conjugate calculator 23 level discriminator 24 selector 25, 109, 118, 121 synchronous detection or delay detection quadrature demodulator 30 RF unit 31 IF unit 32 digital frequency shifter unit

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H04L 27/00-27/38 H04B 1/10

Claims (5)

(57) [Claims] A frequency synthesizer for providing a radio frequency to a frequency converter for converting a radio frequency to an intermediate frequency has a frequency step of an integer multiple of the frequency step of a reception channel, and includes a quasi-synchronous quadrature including frequency components of a plurality of reception channels. A quadrature modulated wave receiving method in a receiving apparatus including a frequency shifter for extracting a baseband signal of a desired reception channel from a detection output signal, wherein an undesired wave generated by an amplitude error and a phase error of the quasi-synchronous quadrature detection output signal When the level of the undesired wave is equal to or higher than a predetermined value, a signal obtained by subtracting the image component of the undesired wave is used as an output signal of the frequency shifter, thereby obtaining the image component of the undesired wave. And a quadrature modulated wave receiving method. 2. A frequency synthesizer for providing a radio frequency to a frequency converter for converting a radio frequency to an intermediate frequency, wherein the frequency step of the frequency synthesizer is an integral multiple of the frequency step of the reception channel, and a desired reception is performed from an output signal of the quasi-synchronous quadrature detector. In a receiving apparatus provided with a frequency shifter for extracting a baseband signal of a channel, the frequency shifter calculates an image component of an undesired wave generated by an amplitude error and a phase error of an output signal of the quasi-synchronous quadrature detector. And a means for removing an image component of the undesired wave controlled by a level of the undesired wave. Wherein the frequency shifter, the sampled signal frequency f ₀ (where, f ₀ is an integer multiple of the frequency steps of the received channel frequency) and a first frequency converter for frequency conversion, the frequency f _A first LPF for extracting a baseband signal of a desired wave from a signal frequency-converted by ₀
If, frequency and the second frequency converter for frequency conversion (-f _0), a second LPF for extracting a baseband signal from the frequency-converted signal at said frequency (-f _0), the first A first multiplier for multiplying an output signal of the LPF by an output signal of the second LPF, a squarer for squaring the output signal of the second LPF and outputting the output signal, and an output signal of the first multiplier , A second integrator for integrating the output signal of the squarer for a fixed sample, and an integration of the integrated signal of the first integrator by the second integrator. A divider for dividing by a signal, a complex conjugate calculator for outputting a complex conjugate of the output signal of the second LPF, and a second for multiplying an output signal of the divider and an output signal of the complex conjugate calculator. A multiplier, the second multiplication from the output signal of the first LPF, 3. A subtractor for subtracting the output signal of the second LPF, a discriminator for judging the level of the output signal of the second LPF, and a selector controlled by the output signal of the discriminator. The quadrature modulated wave receiving device according to the above. 4. The selector selects the output of the subtractor when the output signal of the second LPF is larger than a certain threshold, and selects the output of the second LPF when the output signal of the second LPF is larger than a certain threshold. 4. The quadrature modulated wave receiving apparatus according to claim 2, wherein when the value of the first LPF is smaller, the output signal of the first LPF is controlled to be selected and output. 5. The quadrature modulated wave receiving apparatus according to claim 2, wherein said quadrature modulated wave receiving apparatus is used as a receiving apparatus for satellite communication or mobile communication.