JPH05252214A - Digital modulator - Google Patents

Abstract

PURPOSE:To flexibly set a carrier frequency by implementing independently sample designation to one bit data in a base band waveform generating section and sample designation to one period of a shifting wave in a base band frequency shifting section. CONSTITUTION:Input data are fetched by a base band waveform generating section 1-2, mapped by a signal point arrangement in response to the modulation system by a mapping means 1-4 to obtain I, Q channel data and a band limiting means 1-5 applies band limit to the data. The I, Q channel signals are fetched by a frequency shifting means 1-7, in which the I, Q channel signals subjected to frequency shift by a quantity corresponding to external carrier designation data are obtained. The signal is fetched by an orthogonal modulation section, in which a modulation wave is obtained by orthogonal modulation. The designation of a sampling point to the means 1-5 is implemented by a sampling point designation means 1-6 and the designation of a sampling point to the means 1-7 is implemented by a sampling point designation means 1-8 respectively and independently.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital modulator used for digital radio communication, and more particularly to a digital modulator using a quadrature modulator.

[0002]

2. Description of the Related Art In mobile communication or the like, a modulator for collectively modulating signals of a plurality of channels, such as a base station, or sequentially outputs modulated waves of a plurality of carriers (frequency hopping)
In such a modulator, it is necessary to generate signals of a plurality of carriers as shown in FIG. 9 simultaneously or sequentially. In FIG. 9, f _{1 to} f ₅ are center frequencies corresponding to the respective channels,
The dashed lines f ₂ and f ₅ indicate empty channels.

By the way, a digital modulation wave can be generated by inputting each of I-channel and Q-channel baseband signals to a quadrature modulator. As shown in FIG. 10, the carrier frequency of the modulated wave of a certain channel is Δfi from a certain reference frequency fc (= ωc / 2π) (reference carrier frequency).
It can be regarded as a frequency shifted by (= Δωi). At this time, the modulated wave signal s (t) whose instantaneous amplitude is A (t) and instantaneous phase angle is φi (t) in the signal space diagram of the baseband signal is S (t) = A (t) cos { .phi.i (t) + (. omega.c + .DELTA..omega.t)} ... (1), and the formula (1) can be transformed into the following formula.

S (t) = A (t) cos {φi (t) + Δωit} cos ωct-A (t) sin {φi (t) + Δωit} sin ωct (2) Therefore, the carrier frequency is To generate a modulated wave that is (ωc + Δωi), I channel, Q
The frequency of the channel signal is shifted by Δωi and then ωc
It can be seen that quadrature modulation at a frequency of 1 gives the same modulated wave.

Next, I which is frequency-shifted by this Δωi
Signals SI (t) and SQ (t) of the channel and Q channel are SI (t) = A (t) cos {φi (t) + Δωit} = {A (t) cos φi (t)} cos Δωit, respectively -{A (t) sin φi (t)} sin Δωit ・ ・ ・ (3) SQ (t) = A (t) sin {φi (t) + Δωit} = {A (t) sin φi (t)} It can be transformed into cos Δωit + {A (t) cos φi (t)} sin Δωit (4). Therefore, I channel, Q
It is possible to shift the frequency in the baseband by multiplying and adding the baseband signal of the channel and the sine wave of frequency Δωi.

Conventionally, the shift waveforms cosΔωit and sinΔ
ωit is generally generated by a read-only memory (ROM). As an example of a method for performing a multiplication operation for frequency shift, a method for performing an operation process by a digital multiplier will be described below.

FIG. 6 is a block diagram showing the configuration of a conventional quadrature modulation type modulator which performs an operation for frequency shift using a digital multiplier. In the figure, the input data to the baseband digital signal processing circuit 6-1 is the mapping circuit 6 in the baseband waveform generator 6-2.
In -8, the I channel is mapped according to the modulation method,
It is divided into Q channel data. The I-channel data and the Q-channel data are band-limited by the band limiting means 6-9, respectively. The band point limiting means 6-9 is provided with the sampling point designation information from the sampling point designation means 6-6.

On the other hand, when the carrier designating data is given from the outside, the waveform pattern for generating the shift waveform corresponding to the designated carrier is the waveform pattern designating means 6-7.
The amplitude value of the shift waveform at the sample point selected by the sample point designating means 6-6 is stored in the ROM.
It is output from 6-12a to 6-12c. ROM here
The designated sample points to the band limiting means have the same value as the designated sample points to the band limiting means.

The respective ROM outputs are given by equations (3) and (4).
Of the band-limited I channel data and Q channel data so that the calculation result of
a to 6-10d, and adders 6-11a,
The addition by 6-11b is performed, and the I-channel and Q-channel data whose frequencies are shifted corresponding to the designated carrier are obtained.

The signals designated by the respective carriers in each baseband digital signal processing circuit are quadrature modulator 6
-4, the I-channel and the Q-channel are added by the adder 6-13, and the digital / analog converter (D / A) 6-14 and the low-pass filter (LPF) 6-
A quadrature modulator 6-5 performs quadrature modulation via 15 to obtain a composite modulation signal of a plurality of carriers.

[0011]

By the way, when a signal whose frequency is shifted with respect to a baseband signal is generated, if the shift waveform is discontinuous with respect to a continuous data bit string, unnecessary radiation occurs other than the modulated wave. , It becomes a problem as an interfering wave to a channel other than the designated channel. Therefore, the shift waveform must be continuous for continuous data bit strings.

When the shift frequency Δf is an integral multiple of the transmission baud rate fb, that is, Δf / fb = n (n: integer) (5), the shift waveform 1 cycle corresponds to the number of samples for 1 bit of data in the band limiting means. The amplitude value obtained by sampling the minutes may be prepared in the ROM or the like. As a specific example, FIG.
Shows the relationship between the data bit and the sampling of the shift waveform when Δf = fb. In the figure, the number of samples in the band limiting means for 1 bit of data is 4 and the shift waveform is a sine wave of Δf = fb.

From the figure, in order to make the shift waveform continuous for continuous data bits, the number of samples for one cycle of the shift waveform may be four samples. That is, the number of samples for one shift waveform period is equal to the number of samples for one bit of data in the band limiting means.

However, when there is a relationship of Δf / fb = h / k (irreducible, h, k: integer) (6) between the shift frequency Δf and the transmission baud rate fb, in the band limiting means. In the conventional method of performing the frequency shift calculation using the value of the sampling point for one bit of data, it is necessary to prepare k patterns for one shift frequency in order to make the shift waveform continuous.

That is, for one cycle of the shift waveform, the sampling point k for one bit of data in the band limiting means is k.
The amplitude value of the shift waveform sampled by double the number of samples is required, and the storage capacity of the ROM for generating the shift waveform is also required to be k times the shift frequency Δf when the transmission baud rate fb is an integral multiple.

For example, FIG. 8 shows Δf / in the conventional method.
The relationship between the data bit and the sampling of the shift waveform is shown for the example of fb = 4/5. From the figure, when the number of samples for 1-bit data for band limitation is 4, in order to make the shift waveforms in the relationship of Δf / fb = 4/5 continuous, five types of shift waveform patterns are prepared. It is understood that it is necessary to prepare, that is, it is necessary to prepare the amplitude value of the shift waveform with 20 samples for four periods of the shift waveform.

Accordingly, the storage capacity of the shift waveform generating ROM is required to be five times as large as that when the shift frequency Δf is an integral multiple of the transmission baud rate fb. As described above, in the conventional method, when the shift frequency Δf is not an integral multiple of the transmission baud rate fb, the storage capacity of the shift waveform generation ROM is greatly increased to make the shift waveform continuous, and thus the circuit scale is increased. There was a drawback that

An object of the present invention is to provide a digital modulator capable of flexibly setting a shift frequency (carrier frequency interval) while suppressing an increase in circuit scale.

[0019]

According to the invention, the above mentioned objects are achieved by the means recited in the patent claims.

That is, according to the present invention, a plurality of baseband digital signals which take in input data of a plurality of channels and output I channel data and Q channel data of a plurality of channels which are frequency-shifted by an amount corresponding to a carrier frequency of a designated channel, respectively. The output from the processing circuit and the plurality of baseband digital signal processing circuits is added for each I channel and each Q channel and fetched,
The baseband digital signal processing circuit includes a quadrature modulator that performs quadrature modulation, wherein the baseband digital signal processing circuit generates a baseband signal of I channel and Q channel subjected to mapping and band limitation, and the baseband waveform generating unit. The I-channel and Q-channel baseband signals output from the baseband frequency shifter for performing an operation for shifting the frequency corresponding to the carrier frequency of the designated channel are provided, and the baseband waveform is generated. A flexible shift frequency can be set by independently designating a sampling point for 1-bit data in the section and a sampling point for one cycle of the shift waveform in the baseband frequency shift section. To do.

[0021]

FIG. 1 is a block diagram showing the basic structure of the present invention. In the figure, the input data to the baseband digital signal processing circuit 1-1 is the baseband waveform generation unit 1
-2, and the mapping means 1-4 obtains I-channel data and Q-channel data subjected to mapping according to the signal point arrangement according to the serial-parallel conversion and the modulation method. The mapped I channel data and Q channel data are band-limited by the band limiting means 1-5.

Amplitude A (t) of band-limited I channel signal
cos φi (t), the amplitude A (t) sin φi (t) of the Q channel signal is
The I-channel signal and the Q-channel signal are taken into the frequency shift means in the baseband frequency shift unit 1-3 and frequency-shifted by an amount corresponding to the carrier designation data from the outside. The I-channel signal and the Q-channel signal, which are frequency-shifted corresponding to the designated carrier, are taken into the quadrature modulator and a modulated wave is obtained by quadrature modulation.

Here, the sampling points for the band limiting means 1-5 are designated by the sampling point designating means (A) 1-6, and the sampling points for the frequency shifting means 1-7 are designated by the sampling point designating means (B). 1 to 8 independently.

According to the structure of the present invention, between the shift frequency Δf and the transmission baud rate fb, Δf / fb = h / k
If there is a relationship of (irreducible, h, k: integer), the ratio of the number of samples S ₁ for 1 bit of data in the band limiting unit and the number of samples S ₂ for 1 cycle of the shift frequency in the frequency shift unit is S ₁ : S _2. = H: k (7), if the sampling points of the band limiting section and the frequency shifting section are designated independently, a ROM for generating the necessary shift waveform is obtained.
The shift frequency can be set without increasing the storage capacity of the.

As a specific example, FIG. 2 shows the relationship in sampling data bits and shift patterns for the case of Δf / fb = 4/5. From the figure, if the number of samples for 1 bit of data in the baseband waveform generation unit is 4 and the number of samples for 1 cycle of the shift pattern in the baseband frequency shift unit is 5, it is possible to specify each sample point independently. , It is understood that the frequency shift amount can be set to Δf = (4/5) fb.

As described above, according to the present invention, a plurality of types of waveform patterns for one shift frequency are prepared by independently designating the sampling points in the band limiting means and the sampling points in the frequency shifting means. None, that is, the shift frequency can be flexibly set without increasing the storage capacity of the shift waveform generation ROM.

[0027]

FIG. 3 is a block diagram showing a first embodiment of the present invention, in which a digital multiplier is used for frequency shifting.

In the figure, the input data to the baseband digital signal processing circuit 3-1 is mapped by the mapping circuit 3-4 in the baseband waveform generation section 3-2 according to the modulation method, and the I channel and Q channel are input. Divided into data. The data of I channel and Q channel are
The band is limited by the respective band limiting means 3-5.
The band limiting means 3-5 has a sampling point designating means (A) 3-
Sample point designation information is given from 6.

On the other hand, when the carrier designation data is given from the outside, the waveform pattern for shifting the frequency corresponding to the designated carrier is waveform pattern designating means 3-11.
Selected by the sampling point designating means (B) 6-
The amplitude values of the shift waveform at the sample points designated by 10 are output from the ROMs 3-9a to 3-9c.

Here, the designated sample points to the ROM have different values from the designated sample points to the band limiting means. The respective ROM outputs are multiplied by the band-limited I channel data and Q channel data by the multipliers 3-7a to 3-7d so as to obtain the calculation results of the equations (3) and (4), and Addition is performed by the adders 3-8a and 3-8b, and the I channel signal and the Q channel signal that are frequency-shifted corresponding to the designated carrier are obtained.

The I-channel signal and the Q-channel signal, which are frequency-shifted corresponding to the designated carrier, are taken into the quadrature modulator and a modulated wave is obtained by the quadrature modulation. Also, in FIG.
A second embodiment of the present invention is a block diagram showing an example of the configuration of a QPSK modulator, and here shows a method of calculating a frequency shift using a ROM.

In the figure, the input data is taken in by the baseband waveform generator 4-2 of the baseband digital signal processing circuit 4-1, serial-parallel converted by the mapping circuit 4-4, and converted into I-channel and Q-channel. Divided into data.

The data of the I channel and the Q channel are respectively transferred to the band limiting ROM 4 via the shift register 4-5.
It becomes the input address of -6a and 4-6b, and the counter 4-
Band-limited ROM 4-6a and 4-6b output band-limited I-channel and Q-channel baseband signals corresponding to the sample points designated by 7. The amplitude value data of the I-channel and Q-channel baseband signals output from the baseband waveform generation unit is stored in the ROMs 4-8a to 4-4 of the baseband frequency shift unit 4-3.
It becomes the input address of 8d.

On the other hand, when the carrier designation data is given from the outside, the phase step for generating the shift frequency corresponding to the carrier is the phase step setting circuit 4-.
It is output from 11. The obtained phase steps are cumulatively added by the phase accumulator 4-10 to obtain instantaneous phase data in the shift waveform, and the instantaneous phase data is supplied to the ROMs 4-8a to 4-8d in the baseband frequency shift unit 4-3.

Each R in the baseband frequency shift section
In OM4-8a to 4-8d, I channel signal,
The amplitude data and instantaneous phase data of the Q channel signal are used as input addresses, and the amplitude of the I channel signal A (t) icosφi (t)
And the amplitude of the Q channel signal A (t) isinφi (t) and the amplitude of the shift waveform corresponding to the instantaneous phase (cos Δωit or sin Δω
The result of multiplication with it) is output.

That is, in the ROM 4-8a, {Ai (t) cos
φi (t)} cos Δωit, {Ai (t) cosφ in ROM4-8b
i (t)} sin Δωit, in ROM4-8c- {Ai (t) sinφ
i (t)} sin Δωit, in ROM4-8d {Ai (t) sinφi
(t)} The amplitude value of cos Δωit is stored. Adder 4
In -9a, by adding the output data of ROM4-8a and ROM4-8c, the I channel amplitude data Ai (t) cos {φi (t) + Δωit} frequency-shifted by the designated amount is
In the adder 4-9b, the output data of the ROM 4-8b and the ROM 4-8d are added to each other, so that the Q channel amplitude data Ai (t) sin {φi (t) + Δω
it} is output.

The I-channel signal and the Q-channel signal, which are frequency-shifted corresponding to the designated carrier, are taken into the quadrature modulator and a modulated wave is obtained by the quadrature modulation. Also, FIG.
[FIG. 8] is a diagram showing a third embodiment of the present invention and is a block diagram showing an example of a configuration of a π / 4 shift QPSK modulator. In the figure, the input data is the baseband waveform generation unit 5-2 of the baseband digital signal processing circuit 5-1.
Is taken in by the mapping circuit 5-4, and the π / 4 shift Q is generated.
In order to generate a PSK modulation baseband signal,
It is divided into two I-channel data with different amplitudes and two Q-channel data with different amplitudes.

The respective I-channel and Q-channel data are input to the band limiting ROMs 5-6a to 5-6d via the shift register 5-5 and band-limited. The adder 5-7a includes band limiting ROMs 5-6a and 5-
The output of 6b is added to generate the I channel signal of the baseband signal in the π / 4 shift QPSK modulation system, and the adder 5-7b adds the outputs of the band limiting ROMs 5-6c and 5-6d to generate the same Q signal. Generate a channel signal.

As described above, in the π / 4 shift QPSK modulation system, two band limiting ROM outputs having different amplitudes are added to each other to obtain the I channel and Q channel baseband signals.

Each of the I-channel and Q-channel baseband signals generated by the baseband waveform generator is taken into the baseband frequency shifter 5-3 and frequency-shifted by a designated amount from the outside. The subsequent steps are the same as those of the above-described embodiment of the QPSK modulation method of the present invention.

[0041]

According to the present invention, it is possible to flexibly set the carrier frequency by the baseband signal processing regardless of the relationship between the carrier frequency interval and the transmission baud rate, and further, to suppress the increase in the circuit scale. There is an advantage that can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing a relationship between a data bit of Δf / fb = 4/5 and a shift waveform in the configuration of the present invention.

FIG. 3 is a block diagram showing a first embodiment of the present invention.

FIG. 4 is a block diagram showing a second embodiment of the present invention.

FIG. 5 is a block diagram showing a third embodiment of the present invention.

FIG. 6 is a block diagram showing an example of a conventional configuration.

FIG. 7 is a diagram showing a relationship between a data bit and a shift waveform when Δf = fb.

FIG. 8 is a diagram showing a relationship between data bits and a shift waveform when Δf / fb = 4/5 in the conventional configuration.

FIG. 9 is a diagram showing modulated wave spectra of a plurality of carriers in an RF band.

FIG. 10 is a diagram showing spectrums of modulated waves of a plurality of carriers that are frequency-shifted in the baseband.

[Explanation of symbols]

1-1,3-1,4-1,5-1,6-1 Baseband Digital Signal Processing Circuit 1-2, 3-2, 4-2, 5-2, 6-2 Baseband Waveform Generator 1 -3, 3-3, 4-3, 5-3, 6-3 Baseband frequency shift section 1-4 Mapping means 3-4, 4-4, 5-4, 6-8 Mapping circuit 1-5, 3 -5, 6-9 Band limiting means 1-6, 1-8, 3-6, 3-10, 6-6 Sample point designating means 1-7 Frequency shifting means 3-7, 6-10 Digital multiplier 3- 8, 4-9, 5-7, 5-10, 6-11, 6-1
3 Digital Adder 3-9, 6-12 Shift Waveform Generation ROM 3-11, 6-7 Waveform Pattern Designating Means 4-5, 5-5 Shift Register 4-6, 5-6 Band Limiting ROM 4-7 , 5-8 Counter 4-8, 5-9 ROM for shift waveform multiplication 4-10, 5-11 Phase accumulator 4-11, 5-12 Phase step setting circuit 6-4 Quadrature modulator 6-5 Quadrature modulator 6 -14 D / A converter 6-15 LPF 6-16 Mixer 6-17 Analog adder 6-18 Frequency synthesizer 6-19 π / 2 phaser

Claims (1)

[Claims] 1. Input data of a plurality of channels,
A plurality of baseband digital signal processing circuits that respectively output I-channel and Q-channel signals that are frequency-shifted by an amount corresponding to the carrier frequency of the designated channel, and outputs from the plurality of baseband digital signal processing circuits for each I-channel. , And a quadrature modulator that adds and takes in each Q channel and performs quadrature modulation, wherein the baseband digital signal processing circuit includes mapping and band-limited I and Q channels. A baseband waveform generation unit that generates a baseband signal, and a frequency shift operation is performed on the I-channel and Q-channel baseband signals output from the baseband waveform generation unit to correspond to the carrier frequency of the specified channel. And frequency-shifted I A baseband frequency shift section for outputting channel and Q channel baseband signals, designating a sampling point for 1-bit data in the baseband waveform generation section, and a shift waveform of 1 in the baseband frequency shift section. A digital modulator characterized in that a shift frequency is set by independently specifying a sampling point for a period.