JP3331978B2 - Modulation circuit for digital wireless communication device and modulation method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation circuit of a digital radio communication apparatus and a modulation method thereof, and more particularly, to a digital radio communication using a multilevel quadrature amplitude modulation (QAM) system, the S / N value of an output spectrum. The present invention relates to a modulation circuit and a modulation method for improving the modulation.

[0002]

2. Description of the Related Art As a modulation circuit of a digital radio communication apparatus, for example, a modulation circuit as shown in FIG. 8 is known. This circuit is based on the p. Of "Modulation and Demodulation of Digital Radio Communication" (published by IEICE).
121 is a 16QAM modulator.

As shown in FIG. 8 (a), signals inputted from I and Q are shaped by filters H (f), and are multiplied by carrier waves fc by multipliers 6 and 6 '. Where Q
Is shifted by π / 2 with respect to I, and both outputs are combined by the combiner 7. As a result, as shown in FIG.
The modulated wave signal having the amplitude and phase information of the point is output.

FIG. 9 shows a modulation device which is generalized based on the above configuration. The data to be modulated is input from the input terminal 101 to the mapping circuit 1. The mapping circuit 1 is a circuit for arranging data based on a control signal "QAM CONT" from a control terminal 102 so as to output a modulated wave suitable for a required system.

From the input terminal 101, the transmission rate fs (bp
s) from the data signal and clock input terminal 103 to fs
(Hz) clock signal is input.
From 02, information on the modulation scheme is input. Based on the information on the modulation scheme, for example, if the modulation scheme is 64Q
At the time of AM, the mapping circuit 1 converts the data input from the input terminal 101 into six columns (2 ⁶ = 64) and inputs the data to the roll-off filters FIR2, 2 ′. that time,
The mapped DATA is divided into three columns each for I-ch and Q-ch, and the transmission rate per column is fs / 6.
(Bps).

After being shaped into required filter waveforms by digital filters FIR2 and FIR, they are input to digital-analog converters (D / A) 4, 4 '. The digital-to-analog converters 4 and 4 'convert the analog signals into analog signals at the sampling rate of M times the transmission rate, and attenuate the harmonic components by low-pass filters 5 and 5'.
At 6 ', it is multiplied by the carrier f0.

In the multiplier 6 ', when multiplying the carrier wave f0, the carrier wave is multiplied by a phase shifted by π / 2. As a result, a modulation wave signal having the carrier f0 as the center frequency is output from the modulation output terminal 104. In addition, FIR
The number of columns between 2, 2 'and the digital-analog converters 4, 4' is determined by the required S / N value of the spectrum waveform output from the digital-analog converters 4, 4 '. Generally, a digital-to-analog converter with a multi-bit input has a S /
Although the N ratio is improved, it also affects the performance of the digital-to-analog converter, and some have a low S / N ratio even with a large number of columns.

Also, the choice of a digital-to-analog converter affects the cost, and in particular, tends to be more expensive with multi-bit and higher speed. Therefore, it is important to select a digital-analog converter that satisfies a predetermined standard. The above-described general-purpose modulator includes a transmission rate input from an input terminal 101 and a clock input terminal 103 and a control terminal 1.
The bandwidth of the modulated wave spectrum output from the modulation output terminal changes according to the information input from 02. Further, a modulation method and a roll-off rate of a roll-off filter FIR are set and used according to a transmission rate and a required band transmitted in each system.

However, the above-described modulator has the following problems. (1) In particular, in a system such as 32,128 QAM, the S / N ratio of the spectrum of the modulator output deteriorates as compared with 64,256 QAM, and as a result, a required standard may not be satisfied. The reason is that the S / N of the modulator output is determined by the performance of the digital-analog converter.
The reason is that the output level of 32,128 QAM decreases as the number of signal points decreases, and as a result, the signal level of the digital-analog converter decreases.

(2) To solve the above problems, there is a method of increasing the number of bits of the digital-analog converter.
In that case, there is a problem that the cost of the digital-analog converter is increased.

[0011]

SUMMARY OF THE INVENTION It is an object of the present invention to remedy the above-mentioned disadvantages of the prior art, and in particular to a 32,128 QA
In systems such as M, the S / N of the modulated wave output due to the signal level being lower than 64, 256 QAM
It is an object of the present invention to provide a novel modulation circuit for a digital radio communication device and a modulation method for preventing the deterioration of the ratio.

[0012]

SUMMARY OF THE INVENTION The present invention basically employs the following technical configuration to achieve the above object. That is, a first aspect of the modulation circuit of the digital wireless communication apparatus according to the present invention is provided at a stage subsequent to the mapping circuit for performing mapping corresponding to a predetermined QAM modulation method on transmission data based on modulation instruction information. A digital radio comprising a roll-off filter for waveform shaping and a digital-analog converter for converting an output of the roll-off filter into an analog value, wherein the transmission data can be selectively modulated by at least two different modulation schemes. In the modulation circuit of the communication device, a digital multiplier is provided between the mapping circuit and the digital-analog converter, and the digital multiplier multiplies the transmission data by a predetermined coefficient, and calculates a result of the multiplication. Characterized in that it is input to a digital-analog converter, and 2 embodiment, the multiplier is characterized in that provided between the mapping circuit and the roll-off filter,
In a third aspect, the multiplier is provided between the roll-off filter and a digital-analog converter, and in a fourth aspect, the modulation instruction information is: The coefficient is given in synchronization with the mapping circuit and the multiplier. In a fifth aspect, the coefficient is such that the input level of the digital-analog converter is the dynamic level of the digital-analog converter. It is characterized by being set to be equal to or less than the range. Also, an aspect of the modulation method of the modulation circuit of the digital wireless communication apparatus according to the present invention is a mapping circuit that performs mapping of transmission data according to a predetermined QAM modulation scheme based on modulation instruction information, and a mapping circuit provided at a subsequent stage of the mapping circuit. A digital-to-analog converter for converting the output of the roll-off filter into an analog value, wherein the transmission data can be selectively modulated by at least two different modulation schemes. In a modulation method of a modulation circuit of a wireless communication device,
A digital multiplier is provided between the mapping circuit and the digital-analog converter. Data transmitted by the digital multiplier is multiplied by a predetermined coefficient, and the multiplied signal is guided to the digital-analog converter. It is characterized by modulation.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A modulation circuit of a digital radio communication apparatus according to the present invention is provided at a subsequent stage of a mapping circuit for mapping transmission data according to a predetermined QAM modulation method based on modulation instruction information. A digital-to-analog converter for converting the output of the roll-off filter into an analog value, wherein the transmission data can be selectively modulated by at least two different modulation schemes. In the modulation circuit of the wireless communication device, a digital multiplier is provided between the mapping circuit and the digital-analog converter, and the digital multiplier multiplies the transmission data by a predetermined coefficient, and a result of the multiplication. Is input to the digital-analog converter.

The input level of the digital-analog converter can be increased by multiplying the data to be transmitted by a predetermined coefficient. As a result, it has become possible to improve the S / N ratio of the spectrum of the modulator output.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A specific example of a modulation circuit and a modulation method of a digital radio communication apparatus according to the present invention will be described below in detail with reference to the drawings. FIG. 1 is a block diagram of a modulation circuit of a digital wireless communication apparatus according to the present invention. FIG. 1 shows a mapping for performing transmission mapping corresponding to a predetermined QAM modulation method on the basis of modulation instruction information "QAM CONT". A circuit 1 and a waveform shaping roll-off filter 3, 3 ′ provided at a subsequent stage of the mapping circuit 1.
And digital-to-analog converters (4, 4 ') for converting the outputs of the roll-off filters (3, 3') to analog values, wherein the transmission data can be selectively modulated by at least two different modulation schemes. In a modulation circuit of a wireless communication device, a digital multiplier 2 is connected between the mapping circuit 1 and digital-analog converters 4 and 4 '.
2 ', the digital multipliers 2 and 2' multiply the transmission data by a predetermined coefficient and input the multiplication result to the digital-analog converters 4 and 4 '. A modulation circuit is shown,
Further, the multipliers 2 and 2 ′ are modulation circuits of the digital wireless communication device provided between the mapping circuit 1 and the roll-off filters 3 and 3 ′, and further include the modulation instruction information “QAM CONT”. 1 shows a modulation circuit of a digital radio communication device which is provided in synchronization with the mapping circuit 1 and the multipliers 2 and 2 '.

Hereinafter, the present invention will be described in more detail. A signal of a transmission rate fs (bps) is input from an input terminal 101, a clock signal of fs (Hz) is input from a clock input terminal 103, and information on a modulation method is input from a control terminal 102. The output of the mapping circuit 1 is input to the multipliers 2 and 2 'at the data of the number of columns corresponding to the modulation method and the transmission rate per column. The multipliers 2 and 2 ′ multiply the input data by a coefficient set in advance based on the modulation method input from the control terminal 102, and perform a roll-off filter FI
Output to R3, 3 '. Roll-off filter FIR3,
After being shaped into a required filter waveform at 3 ', it is inputted to digital-analog converters 4, 4', and analog-converted by the digital-analog converters 4, 4 'by sampling M times the transmission rate. The signal is attenuated by the low-pass filters 5 and 5 'to a higher harmonic component,
At 6 ', it is multiplied by the carrier f0.

When the multiplier 5 'multiplies the carrier f0 by a phase shifted by π / 2, the modulation output terminal 104 outputs a modulated wave signal of the carrier f0 in which the I and Q data are orthogonal. You. Note that multipliers 2 and 2 ′
The condition of the coefficient of
The setting may be within the input range of the analog converters 4 and 4 '(a range that does not cause an overrange).
In the case of 4,256 QAM, similarly, if the signal is within the range of the digital-analog converter, the S / N ratio can be improved by adding and multiplying the coefficient.

Next, the operation of the modulation circuit of the digital radio communication apparatus thus configured will be described with reference to FIGS. The multipliers 2 and 2 'for 32QAM have coefficients of 6Q
Constellation and D with the same coefficient as AM
/ A output waveforms are shown in FIGS. Mapping circuit 1
Output is DAT of I and Q each of 3 columns for both 64 and 32 QAM.
A (D0, D1, D2) can be expressed as “0” and “1” data, and when this is indicated by the modulation output terminal 104, 6
4QAM constellation is shown in Fig. 2 (a), 32QAM
The constellation is as shown in FIG. When the signal arrangements are compared, the 32QAM is an arrangement in which there are no signals at the periphery and at the four corners indicated by white circles in FIG. 2 (b) and 3 (b) show the output spectrum waveforms of the digital-analog converters 4 and 4 'in the above state. In 32QAM, only the part without signal points
The input signal level of the digital-analog converter decreases. However, the thermal noise level of the digital-analog converter is a constant value, and as a result, the S / N ratio becomes A ′ dB as shown in FIG.
Compared with 64QAM (FIG. 2B), the S / N ratio is △ ad
B will be worse.

Although low-pass filters 5, 5 'and low-pass filter (or band-pass filter) 9 are provided, since these filters are for removing harmonics, noise near 2xfs of the spectrum waveform is reduced. It does not attenuate, and therefore, the deterioration of the S / N ratio by △ adB directly affects the S / N of the transmitter output. As a result, a case where the mask value specified by the wireless device is not satisfied may be considered.

FIGS. 4 and 5 show examples in which multipliers 2 and 2 'multiply coefficients by 8/6 times in the 32QAM system. FIG. 4A shows data and a constellation when input to the multipliers 2 and 2 ′, and FIG. 4B shows data and a constellation of the outputs of the multipliers 2 and 2 ′. Unused signal points indicated by white circles in the constellation before multiplication are out of the input range of the digital-analog converters 4 and 4 'at the outputs of the multipliers 2 and 2'. However, since the signals shown by white circles are not used as actual signals, there is no operational problem.

FIG. 5B shows the spectrum of the output of the digital-analog converters 4 and 4 '. 4 and 5
As shown in (a), by providing the multipliers 2 and 2 ', the reduction of the input level of the digital-analog converters 4 and 4' is improved, and as a result, the S / N ratio is equivalent to 64 QAM. The ratio is obtained.

In FIG. 6, the selector "SEL" determines that the multipliers 2 and 2 'are based on the modulation control signal "QAM CONT".
The figure shows a state in which the coefficient of is multiplied by the data to be transmitted. Next, another specific example of the present invention will be described. In the configuration shown in FIG. 7, the arrangement of the roll-off filters FIR3, 3 'and the multipliers 2, 2' is interchanged. Although the number of bits of the roll-off filter FIR input is the same as the conventional number of bits, the multipliers 2 and 2 'need to operate at the oversampling frequency. Roll-off filter F
In a system with a large number of IR taps and a low oversampling frequency, the roll-off filter FI
It is considered that this is suitable in that the scale of R is not increased and the effect of speed is small, and the same effect as the configuration of FIG. 1 can be obtained.

In the description of the present invention, a digital-analog converter is provided for each of I and Q, and the carrier f0 is multiplied by analog. However, the same applies to the case where the synthesizer 7 is configured digitally. In this case, the synthesizer 7 is used as an adder, and a digital-analog converter is added after that, and the same effect as described above can be obtained.

[0024]

The modulation circuit and the modulation method of the digital radio communication apparatus according to the present invention have the following effects because they are configured as described above. (1) By amplifying transmission data of 32, 128 QAM by a multiplier within a range not exceeding the range of the digital-analog converter, it is possible to prevent S / N deterioration of the modulator output. Therefore, especially in a system such as 32,128 QAM, by multiplying by a preset coefficient, 6
A modulator output spectrum equivalent to that of 4,256 QAM can be obtained, and the S / N ratio can be improved.

(2) To solve the above problems, digital-
There is no need to increase the number of bits of the analog converter, and there is no need to increase the cost of the digital-analog converter. The reason is that the 32,128 QAM amplifies the portion with few signal points at the input side of the digital-analog converter,
This is because an S / N ratio equivalent to 64, 256 QAM can be obtained by increasing the output signal level to 64, 256 QAM.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of a modulation circuit of a digital wireless communication apparatus according to the present invention.

2A is a diagram illustrating a constellation of a 64QAM modulation scheme, and FIG. 2B is a graph illustrating an output spectrum of a digital-analog converter.

FIG. 3 is a diagram showing the effect of the present invention.

FIG. 4 is a diagram illustrating the operation of the present invention.

FIG. 5 is a diagram showing the effect of the present invention.

FIG. 6 is a diagram showing a state in which a coefficient of a multiplier for each system is selected by a control signal “QAM CONT” of the present invention, and this coefficient is multiplied by data to be transmitted.

FIG. 7 is a block diagram showing another specific example of the present invention.

FIG. 8 is a principle diagram of a modulation circuit of a digital wireless communication device according to a conventional technique.

FIG. 9 is a block diagram of a conventional modulation circuit based on FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mapping circuit 2, 2 ', 6, 6' Multiplier 3, 3 'Roll-off filter (FIR) 4, 4' Digital-analog converter (D / A) 5, 5 'High-pass filter (LPF) 7 Combiner (HUB) 8, 10 Amplifier 9 Filter (LPF / BPF) 11 Multiplier 12 Oscillator (f0) 13 90 ° shifter (π / 2) 101 Data input terminal 102 Control terminal 103 Clock input terminal 104 Modulation output terminal QAM CONT Control signal

Claims (6)

(57) [Claims] 1. A mapping circuit for mapping transmission data according to a predetermined QAM modulation scheme based on modulation instruction information, a waveform shaping roll-off filter provided at a subsequent stage of the mapping circuit, and a roll-off filter. A digital-to-analog converter for converting an output into an analog value, wherein the transmission data is selectively modulatable by at least two different modulation schemes. A digital multiplier is provided between the digital-to-analog converter and a digital multiplier, wherein the digital multiplier multiplies the transmission data by a predetermined coefficient and inputs the multiplied result to the digital-analog converter. Modulation circuit of wireless communication device. 2. The modulation circuit according to claim 1, wherein the multiplier is provided between the mapping circuit and a roll-off filter. 3. The modulation circuit according to claim 1, wherein the multiplier is provided between the roll-off filter and a digital-to-analog converter. 4. The modulation circuit according to claim 1, wherein the modulation instruction information is given to the mapping circuit and a multiplier in synchronization with each other. 5. The apparatus according to claim 1, wherein the coefficient is set such that an input level of the digital-analog converter is equal to or less than a dynamic range of the digital-analog converter. A modulation circuit of the digital wireless communication device according to the above. 6. A mapping circuit for mapping transmission data according to a predetermined QAM modulation scheme based on modulation instruction information, a waveform shaping roll-off filter provided at a subsequent stage of the mapping circuit, and a roll-off filter. A digital-analog converter for converting an output to an analog value, wherein the modulation method of a modulation circuit of a digital wireless communication apparatus in which the transmission data can be selectively modulated by at least two different modulation methods, A digital multiplier is provided between the digital-analog converter and the data transmitted by the digital multiplier is multiplied by a predetermined coefficient, and the multiplied signal is guided to the digital-analog converter for modulation. A method for modulating a modulation circuit of a digital wireless communication device.