JPH08163191A - Quadrature modulator and its control method - Google Patents

Abstract

PURPOSE: To prevent the DC offset of a baseband signal generated in an analog signal processing part for quadrature modulation from occurring without performing adjustment. CONSTITUTION: Inputted transmission data is encoded by an encoder part 4, and converted to a coordinate position in the orthogonal coordinates of I, Q in a symbol mapping part 5 corresponding to a result of encoding, and the baseband signals of phases I, Q are outputted from I phase and Q phase signal generating parts 6, 7. The base-band signals of phases I, Q are frequency-offset by multiplying by a sine wave sinω1 t and a cosine wave cosω1 t in a frequency offset part 12. After that, they are inputted to a quadrature modulator 10 via capacitors 15a, 15b. Consequently, the fluctuation of the baseband signal due to a DC component can surely be prevented from occurring.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a QPSK (Quadrat-ure Phase) which is one of modulation methods in digital communication.
Shift keying) relates to a quadrature modulator used for modulation,
In particular, the present invention relates to a quadrature modulator which removes a DC offset component of a baseband signal and a control method thereof.

[0002]

2. Description of the Related Art Among digital modulation methods, QPSK modulation and 16Q are used as a relatively frequently used modulation method.
AM (Quadrature Amplitude Modulation) modulation is known. These modulation methods perform so-called quadrature modulation of a baseband signal and a carrier wave. FIG. 2 shows an example of the configuration of a quadrature modulation device that realizes such quadrature modulation, and a conventional device will be generally described below with reference to FIG.

This quadrature modulator is roughly divided into a baseband signal generator 1, a digital / analog converter 2, and a quadrature modulator 3. The baseband signal generation unit 1 is for outputting the input transmission data as I-phase and Q-phase baseband signals and outputting the baseband signals. The baseband signal generation unit 1 encodes the transmission data and an output signal of the encoder unit 4. A symbol mapping section 5 for arranging in the I-phase and Q-phase orthogonal coordinates, an I-phase signal generating section 6 for generating an I-phase signal, and a Q-phase signal generating section 7 for generating a Q-phase signal are provided. It will be.

The digital-analog converter 2 performs digital-analog conversion on the I-phase signal and the Q-phase signal, and two digital-analog converters (abbreviated as "D / A" in FIG. 2). 8a and 8b, and low-pass filters (abbreviated as "LPF" in FIG. 2) 9a and 9b for removing unnecessary high-frequency components.

The quadrature modulator 3 quadrature-modulates a carrier (cosωct) with an analog I-phase signal and a Q-phase signal, and includes a quadrature modulator 10 and a local signal oscillator 11 for transmission. It will be done.

[0006]

However, in the above-mentioned conventional quadrature modulator, the baseband signal generator 1 is
Since it is digital processing, there is essentially no room for DC offset other than quantization error.
Since the subsequent processing is analog processing, unnecessary DC components are generated due to so-called variations in the electrical characteristics of the individual components that make up the circuit. This DC component is superimposed on the baseband signal as it is, so-called DC offset occurs in which the DC level of the baseband signal is shifted by that amount.

On the other hand, in order to reproduce the data in the base band signal by demodulating the signal output from the quadrature modulator having the above-mentioned structure, the demodulated base band signal has a predetermined threshold value. There is a method of reproducing the data by judging the level of whether or not it has exceeded, but at this time, if the base band signal has the DC offset as described above, an erroneous judgment result will occur and accurate data will not be recorded. There arises a problem that reproduction becomes impossible.

Therefore, the quadrature modulator described above with reference to FIG. 2 is usually provided with an offset adjusting circuit for removing such a DC offset, but the offset adjusting circuit itself is an analog. Since it is a circuit, even if the DC offset can be temporarily removed, the DC offset will gradually increase due to the temporal change of the electrical characteristics of the circuit components, and the above-mentioned problems will eventually occur. become. In addition, since the magnitude of the DC offset varies among individual devices, even if an offset adjusting circuit is provided, each adjustment is required according to the magnitude of the DC offset, and there is a problem that usability is poor.

The present invention has been made in view of the above circumstances, and prevents the generation of a DC offset of a baseband signal in an analog signal processing portion, and does not require adjustment according to the magnitude of the DC offset. An object of the present invention is to provide a quadrature modulation device capable of removing a DC offset of a band signal and reliably preventing a fluctuation of a DC level of a baseband signal, and a control method thereof.

[0010]

According to a first aspect of the present invention for solving the problems of the conventional example, an input signal is coded, and I-phase and Q-phase signals are coded according to the result of the coding. In the quadrature modulator for quadrature modulating a carrier wave by the I-phase and Q-phase signals.
There are provided frequency position changing means for changing the positions of the phase signal and the Q phase signal in the frequency domain, and direct current component removing means for passing the signal components other than the direct current component of the output signal of the frequency position changing means. It is characterized in that the carrier wave is quadrature-modulated by the output signal of the component removing means.

According to a second aspect of the present invention for solving the problems of the conventional example, in the quadrature modulator according to the first aspect, the frequency position changing means includes a sine wave having a predetermined frequency, an I-phase signal, and A multiplier for multiplying with a Q-phase signal, a multiplier for multiplying a cosine wave having a predetermined frequency with an I-phase signal and a Q-phase signal, and a sine wave with a predetermined frequency and I
The result of multiplication with the phase signal, a cosine wave having a predetermined frequency, and Q
An adder for adding the multiplication result with the phase signal, the sign of the multiplication result of the cosine wave having a predetermined frequency and the I phase signal, and the multiplication result of the sine wave having the predetermined frequency and the Q phase signal It is characterized in that the direct current component removing means is a capacitor.

According to a third aspect of the present invention for solving the above-mentioned problems of the conventional example, in the control method of the quadrature modulation apparatus according to the first or second aspect, DC level fluctuation of a signal in quadrature modulation is prevented. A method of controlling a quadrature modulator, which encodes an input signal, generates an I-phase signal and a Q-phase signal according to a result of the encoding, and uses the generated I-phase signal and the Q-phase signal as a carrier wave. In the case of performing quadrature modulation with respect to, before converting the I-phase signal and the Q-phase signal into analog signals, the position of the I-phase signal and the Q-phase signal in the frequency domain is moved by the frequency position changing means, Then, when the I-phase signal and the Q-phase signal are converted into analog signals by performing analog signal conversion and then removing the DC component by the DC component removal means and then performing quadrature modulation on the carrier. It is characterized by preventing the fluctuation of cheating DC level.

[0013]

According to the first and second aspects of the present invention, the positions of the I-phase signal and the Q-phase signal in the frequency domain are changed by the frequency position changing means, so that conventionally, before performing quadrature modulation on the carrier wave. Generated DC component, I-phase signal and Q
Since the phase signal and the phase signal are separated in the frequency domain, and the DC component is removed by the DC component removing means, the I-phase signal and the Q-phase signal having no variation in the DC level are orthogonally modulated with the carrier. This makes it possible to prevent erroneous data reproduction on the receiving side, unlike the conventional case.

According to the third aspect of the present invention, by changing the positions of the frequency regions of the I-phase signal and the Q-phase signal before converting them into analog signals, a DC component generated in analog signal conversion can be obtained. The quadrature modulator control method according to claim 1, wherein the I-phase signal and the Q-phase signal are separated in the frequency domain, and only the DC component is removed before the quadrature modulation. The fluctuation of the DC level can be reliably prevented.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of a quadrature modulator according to the present invention will be described below with reference to FIG. Here, in FIG.
It is a block diagram which shows the structural example of the orthogonal modulation apparatus which concerns on this invention. The members, arrangements, and the like described below do not limit the present invention and can be variously modified within the scope of the gist of the present invention.

In the following description, the same components as those of the conventional apparatus shown in FIG. 2 are designated by the same reference numerals. This apparatus includes a baseband signal generation unit 1, a frequency offset unit 12 as a frequency position changing unit which is a characteristic part of the present embodiment, a digital / analog conversion unit 2, and a quadrature modulation unit 3 as a quadrature modulation unit. It is roughly divided into.

The baseband signal generator 1 has an I-phase and a Q-phase.
A phase baseband signal is generated, and its basic configuration is the same as that of the conventional device. That is, the baseband signal generation unit 1 includes an encoder unit 4 as a coding unit, a symbol mapping unit 5, and an I-phase signal generation unit 6.
And a Q-phase signal generator 7.

The encoder unit 4 encodes transmission data input from the outside, and more specifically, performs processing for converting serial data represented by a binary number into parallel data. Has become. The symbol mapping unit 5 converts the signal encoded by the encoder unit 4 into I
It is a circuit for arranging (symbol arranging) on the orthogonal coordinates of the phase and Q phase.

I-phase signal generator 6 and Q-phase signal generator 7
Is for generating an I-phase baseband signal or a Q-phase baseband signal according to the symbol arrangement by the symbol mapping unit 5. In this embodiment, the means for generating the quadrature signal is realized by the symbol mapping section 5, the I-phase signal generating section 6 and the Q-phase signal generating section 7.

The frequency offset unit 12 includes four multipliers 13a, 13b, 13c and 13d and two adders 14
and a and 14b. Multiplier 13
Output signals of the I-phase signal generator 6 are input to a and 13b, respectively, and one multiplier 13
The cosine wave cosω ₁ t is externally applied to a and the other multiplier 13
The sine wave sinω ₁ t is input to each of b.

The output signals of the Q-phase signal generator 7 are input to the multipliers 13c and 13d, respectively, and the sine wave s is applied to one of the multipliers 13c from the outside.
inω ₁ t is the cosine wave cosω ₁ t in the other multiplier 13d.
Are input respectively. Incidentally, the sine wave sin .omega ₁ t and cosine wave cos .omega ₁ t frequency f1 (= ω ₁
/ 2π) does not have to be as high as the carrier wave, and a so-called low frequency region is sufficient.

[0022] One of the adders 14a includes multipliers 13a of the output signal (the product of the I-phase signal and the cosine wave cos .omega ₁ t), the output signal of the multiplier 13c (Q-phase signal and the sine wave sin .omega ₁ t Product) and is added. The other adder 14b is
Output signal of multiplier 13b (I-phase signal and sine wave sinω ₁ t
And the output signal of the multiplier 13d (the product of the Q-phase signal and the cosine wave cosω ₁ t).

The digital-analog converter 2 converts the digital output signal of the frequency offset unit 12 into an analog signal. Two digital-analog converters ("D / A / D" in FIG. 1) for converting the digital signal into an analog signal are provided. A) and abbreviated as "D / A converter" hereinafter) 8a and 8b and two low-pass filters (see FIG. 1).
(Abbreviated as “LPF”) 9a, 9b, and two capacitors 15a, 15b as a DC component removing means.

The low-pass filters 9a and 9b are for removing unnecessary frequency components contained in the output signals of the D / A converters 8a and 8b. The low-pass filter 9
A bandpass filter may be used instead of a and 9b.
The two capacitors 15a and 15b are for removing the DC component contained in the output signals of the low pass filters 9a and 9b.

The quadrature modulator 3 comprises a quadrature modulator 10 and a transmitting local signal oscillator 11, and a carrier wave cos ωct generated by the transmitting local signal oscillator 11 is converted from digital to analog in the quadrature modulator 10. Quadrature modulation is performed by the output signal of the unit 2.

Next, the operation of this apparatus having the above-mentioned structure will be described. First, the externally input transmission data is separated and generated by the baseband signal generation unit 1 into an I-phase baseband signal and a Q-phase baseband signal. Here, for example, if the I-phase baseband signal output from the I-phase signal generation unit 6 is I (t) and the Q-phase baseband signal output from the Q-phase signal generation unit 7 is Q (t), These baseband signals are multiplied by the multipliers 13a to 13d.
Will be multiplied by the sine or cosine wave at.

That is, from the multiplier 13a, I (t) ×
cosω ₁ t is output from the multiplier 13b as I (t) × sinω
₁ t is the multiplier 13c _{is, Q (t) × sinω 1} t is from multiplier _{13d Q (t) × cosω 1} t is output Re Zorezo. The output signal of the multiplier 13c is the adder 14a.
At the time of addition in, the sign is inverted and added.

From the adder 14a, I (t) × c
_{osω 1 t-Q (t)} × sinω 1 t ( Equation 1) is, the adder 14
From b, I (t) × sin ω ₁ t + Q (t) × cos ω ₁ t (Equation 2) is output. This adder 1
The I-phase and Q-phase baseband signals output from 4a and 14b are multipliers 13a to 13d and adders 14a and 1
The phase of the conventional baseband signal without 4b is the angle ω
Corresponds to being offset by being shifted by ₁ t. Simply, I (t) × cosω ₁ t + Q (t) × si
In the case of synthesis such as nω ₁ t, both a phase lead and a lag occur around the base band, so two waves occur around the carrier ωc after quadrature modulation, and either one becomes unnecessary. However, in the case of combining as in (Equation 1) and Equation (2), only one phase lead or lag occurs with respect to the base band, so that one wave is generated around the carrier ωc after quadrature modulation. is there. The baseband signal generator 1 to which the transmission data is input to the output stage of the frequency offset unit 12 is digitally processed, so that the baseband signal does not include a DC offset component.

The baseband signal whose frequency is offset as described above is input to the low-pass filters 9a and 9b as analog signals via the D / A converters 8a and 8b, and unnecessary frequency components are removed so that the capacitor 15 is removed.
It is input to the quadrature modulator 10 through a and 15b.

Here, although a DC component is generated in the process of analog signal conversion by the D / A converters 8a and 8b and passing through the low-pass filters 9a and 9b, the capacitors 15a and 15b are used.
As a result, this DC component is removed, and only the frequency-offset baseband signal is input to the quadrature modulator 10 via the capacitors 15a and 15b.

Then, in the quadrature modulator 10, the carrier wave cos ωct generated by the local signal oscillator for transmission 11 is input to the signal {I (t) × c
_{osω 1 t-Q (t)} × sinω 1 as modulated by t}, the signal input through the capacitor 15b {I (t)
X sin ω ₁ t + Q (t) x cos ω ₁ t} is combined and output as a transmission signal.

As described above, in this embodiment, the baseband signal is multiplied / added by using the angular velocity ω _{1 in the} frequency domain to separate the direct current component as the offset component, and thereafter the direct current by the capacitor is used. Since the component is removed and input to the quadrature modulator 10, the offset component is not added to the baseband signal due to the DC component, unlike the conventional case.

Therefore, when demodulating on the receiving side and reproducing the data by performing level determination on the baseband signal, it is impossible to obtain an accurate level determination result due to the offset of the baseband signal due to the DC component. The conventional problems will be solved.

Moreover, since the DC component is removed after the baseband signal and the DC component are separated in the frequency domain, the influence of the DC component hardly remains on the baseband signal, which is different from the conventional one during use. There is no need for frequent adjustments, and the effect is that usability is improved.

[0035]

According to the first and second aspects of the present invention, the position of the I-phase signal and the Q-phase signal in the frequency domain is changed by the frequency position changing means, so that quadrature modulation is conventionally performed on the carrier. The DC component generated before and the I-phase signal and the Q-phase signal are separated in the frequency domain,
Further, since the DC component is removed by the DC component removing means, quadrature modulation with the carrier wave is performed by the I-phase signal and the Q-phase signal having no variation in the DC level. It has the effect of preventing the regeneration of.

According to the third aspect of the present invention, by changing the positions of the frequency regions of the I-phase signal and the Q-phase signal before converting them into analog signals, a DC component generated in analog signal conversion can be obtained. The quadrature modulator control method according to claim 1, wherein the I-phase signal and the Q-phase signal are separated in the frequency domain, and only the DC component is removed before the quadrature modulation. This has the effect of reliably preventing fluctuations in the DC level of.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a configuration in an embodiment of a quadrature modulation device according to the present invention.

FIG. 2 is a configuration diagram showing a configuration example of a conventional device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Baseband signal generation part, 2 ... Digital / analog conversion part, 3 ... Quadrature modulation part, 4 ... Encoder part,
5 ... Symbol mapping unit, 6 ... I phase signal generating unit,
7 ... Q-phase signal generator, 13a to 13d ... Multiplier,
14a, 14b ... Adder, 15a, 15b ... Capacitor

Claims (3)

[Claims] 1. An input signal is encoded and I-phase and Q-phase signals are generated according to the result of this encoding, and these I-phase signals are generated.
In a quadrature modulator that performs quadrature modulation on a carrier wave using phase and Q phase signals, frequency position changing means for changing the position of the I phase signal and Q phase signal in the frequency domain, and an output signal of the frequency position changing means. Among these, a quadrature modulator which is provided with a direct current component removing means for passing a signal component excluding a direct current component, and performs orthogonal modulation on a carrier wave by the output signal of the direct current component removing means. 2. The frequency position changing means comprises a multiplier for multiplying a sine wave having a predetermined frequency by an I-phase signal and a Q-phase signal, a cosine wave having a predetermined frequency, an I-phase signal and a Q-phase signal.
A multiplier for multiplying with a phase signal; an adder for adding a multiplication result of a sine wave having a predetermined frequency and an I-phase signal and a multiplication result of a cosine wave having a predetermined frequency and a Q-phase signal;
A direct current component; and an adder for adding a multiplication result of a cosine wave having a predetermined frequency and an I-phase signal and a sign-inverted result of a multiplication result of a sine wave having a predetermined frequency and a Q-phase signal. The quadrature modulator according to claim 1, wherein the removing means is a capacitor. 3. A method for controlling a quadrature modulation apparatus for preventing a DC level fluctuation of a signal in quadrature modulation, wherein an input signal is coded, and an I-phase signal and a Q-phase signal are generated according to a result of the coding. When the quadrature modulation is performed on the carrier wave generated by the generated I-phase signal and the Q-phase signal, the I-phase signal and the Q-phase signal are converted into analog signals by the frequency position changing means before being converted into analog signals. Phase signal and the Q
The I-phase signal and the Q-phase signal are obtained by moving the position of the phase signal in the frequency domain, converting it to an analog signal, then removing the DC component by the DC component removing means, and then performing quadrature modulation on the carrier. 3. A method for controlling a quadrature modulator according to claim 1 or 2, wherein fluctuations in a direct current level that occur when the signal is converted into an analog signal are prevented.