JPH0334654A - Orthogonal modulator - Google Patents

Abstract

PURPOSE:To prevent the generation of cross modulation and spuriousness by generating the signals of different center frequencies by applying digitally a frequency offset in a base band zone. CONSTITUTION:In a state that input data is brought to band limit and set to instantaneous frequency information by a base band digital signal processing part 1-4, data of an offset frequency corresponding to a center frequency of a channel is added, and signals of different center frequencies are generated in advance in a base band zone. Subsequently, they are added in the base band zone, and thereafter, modulated. In such a way, a multi-carrier frequency can be generated in one orthogonal modulator 1-13, and also, by varying the data of the offset frequency, the signals of different center frequencies can be generated, and since the synthesis in an RF zone is not executed, the generation of cross modulation and spuriousness is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a modulator suitable for digital wireless communication using a multicarrier system.

[Conventional technology]

The configuration of the digital FM modulator includes a voltage-controlled oscillator (Volt-age C) whose frequency changes according to the input voltage.
controlled 0scillator: V
There are two methods: one uses I and Q baseband signals, and the other uses two baseband signals, I and Q, to generate an upstream modulated wave in a quadrature modulator.

In wireless communication, for example, a transformer used in a transmitter that performs common amplification of multiple channel signals at a base station for a car phone, or a transmitter for multicarrier transmission in digital wireless communication, is shown in Figure 5. In some cases, a multi-channel signal as shown is generated.

In Figure 5, CHI to CH6 represent each channel, f and -fs represent the center frequency of each channel, and since not all channels are necessarily used, CH2 and CH5 are unused. An example of its use is shown.

A conventional method for generating RF multiplied signals of a plurality of channels using a single modulator will be described.

FIG. 6 shows a configuration for generating multiple channels of RF signals using a conventional CO.

The data of each channel input from each data input terminal 6-1 is band-controlled [filtered] in the baseband band.
(bandwidth-limiting LPF) Bandwidth-limited from 6-3S, V
FMll by converting voltage changes into frequency changes with CO6-4
! Obtain the tonal signal.

Since the oscillation frequency of the VCO 6-4 is set to the intermediate frequency band (IF), this modulation signal is generated in the IF band.

This FM modulation signal in the IF band is mixed by a mixer 6-5 with the output of a frequency synthesizer (also simply referred to as an "oscillator") 6-6 that oscillates at the center frequency f+ (i = 1 to n) of each channel. to obtain an RF modulated signal.

Then, each RF modulated signal is combined in the RF band by a combiner 6-7, and the RF signals of a plurality of channels are output from the output terminal 6-2.
You can get twice the signal.

Next, as another conventional example, a quadrature modulator is used to directly modulate the RF band, and the outputs are combined to generate multiple channels of RF
A conventional configuration for obtaining a doubled signal is shown in FIG.

Each data input from the input terminal 7-1 is processed through a ROM filter (ROM) using a read-only memory (ROM).
Bandwidth is limited by M LPF) 7-3.

This output is a frequency signal A(f), and this signal is integrated by an integrator 4 to obtain phase information φ.

φ=fA(f)dt And COS table 7-5, S which is composed of ROM
By subtracting the IN table 7-6, the baseband signals sinφ and eosφ of the 11Q channel are obtained, and D/
After being converted into an analog signal by A conversion @7-7, an RF band modulation signal is obtained by orthogonal conversion @1s7-13.

This orthogonal variable $11is7-13 has a known configuration, including a frequency synthesizer 7-8, a transfer n7-11 mixer 7-9
, an adder 7-10, and the modulated signals of each channel in the RF band are combined in the RF band by a combiner 7-12. t, be done.

[Problem to be solved by the invention]

The two conventional examples described above both perform signal synthesis in the RF band, and have the disadvantage that signal synthesis in the RF band tends to be accompanied by cross-modulation and spurious. *In addition, a frequency synthesizer, quadrature modulator, and D/A converter are required to specify the channel for each channel, and when the number of channels increases, the scale of the modulation circuit in the transmitter increases. there were.

SUMMARY OF THE INVENTION An object of the present invention is to provide a quadrature modulator that allows a baseband digital signal processing circuit to add modulated signals of each channel and to specify each channel.

(Means for solving !III) According to the present invention, the above-mentioned object is achieved by the means described in the claims.

That is, the present invention provides a low-pass filter (LPF) composed of a read-only memory (ROM), an adder for adding signal data band-limited by the LPF and data at an offset center frequency, and the adder. a plurality of digital FM modulators each comprising an integration circuit that integrates instantaneous frequency signals output from the FM modulators, and a ROM table that obtains the sine (SIN) component and cosine (COS) component of the integrated phase signal; This is a quadrature modulator that includes an adder that digitally adds I-channel output data and Q-channel output data of a digital FM modulator.

[For production]

In the present invention, after band-limiting the input data to instantaneous frequency information in the baseband digital signal processing unit, data at an offset frequency corresponding to the center frequency of the channel is added to generate signals with different center frequencies in the baseband band. are generated, added in the baseband band, and then modulated. Therefore, according to the present invention, multicarrier frequencies can be generated with one orthogonal transformer.

Furthermore, by changing the offset frequency data, signals with different center frequencies can be generated, and R
Since no synthesis is performed in the F band, there is an advantage that cross-modulation does not occur.

〔Example〕

An example of the configuration of a transmitter using the 'li shoulder device of the present invention is shown in FIG.

That is, Figure w&1 is a diagram showing a digital processing multi-access dinotal FMtll device using the present invention, where 1-1 is a data input terminal, 1-2 is a channel designation data input terminal, and 1-3 is an RF signal output terminal. , 1-4 is a baseband signal processing section, 1-5 is a D/A converter (D/A)
, 1-6 is an analog filter, 1-7 is a mixer, 1-
8 is an analog adder W, 1-9 is a phase shifter, 1-10 is a frequency synthesizer (also simply called an "oscillator"), 1-1
3 represents an orthogonal ta device.

In addition, in the diagram, a common number is assigned to multiple items with the same function, and the numbers in parentheses () added to the signal name “data” indicate that the data corresponds to each channel. This indicates that the data is from one of channels "1 to n".

The data of each channel input from input terminal 1-1 is
Baseband signal processing unit 1- which is a digital signal processing unit
4, the frequency information is converted into phase information, and by the channel designation signal from the input terminal 1-2,
A ttIIS signal is generated for each channel in the baseband band.

Signals corresponding to each channel are digitally added for each channel (1) and Q channel to generate a waveform of a multicarrier baseband signal.

These signals are transmitted to the D/A converters 1-5, respectively.
? converted to an analog signal. This output signal becomes a signal as shown in FIG. However, the frequency is the baseband band.

After removing harmonic components from this signal using an analog filter 1-6, the signal is subjected to RF signal frequency conversion using a quadrature modulator 1-13.

The configuration of the quadrature modulator 1-13 is the same as that of the conventional example.

The operation of this circuit can be simply expressed mathematically as follows.

If the angular frequency of the oscillator 1-10 is ωC and the channel interval is Δω, then the RF multiplied signal of the output is expressed by the following equation.

Σcos((ωc+nΔω)t+φn(t))(1) The symbol Σ is It is a multi-carrier signal. represent.

Formula (1) is as follows.

eos (ωC t) Σcos (nΔω to 1φn(t)) −5in(ωC t)Σ5in(nΔω t+φn(t)) ・・・・・・・・・・・・・・・・・・・・・ (2) In this method, Σcos [nΔ(alt+φn(t))t Σs
in [nΔωt+φn(t)]...
...... (3) Generate components.

FIG. 2 shows an example of the configuration of the baseband digital signal processing section which is the gist of the present invention.

That is, FIG. 2 is a diagram showing an example of the configuration of the baseband signal processing section of the multi-access digital FM modulator of the present invention, in which 2-1 is a data input terminal, 2-2 is a channel designation data input terminal, and 2- 3 is a data output terminal, 2-4 is a ROM filter (ROM LPF), 2-5 is an adder,
2-6 is an integrator, 2-7 is a CO8ROM table (R
OM C08), 2-8 is the SlNROM table (RO
M5IN), 2-9 represent adders.

In addition, in the diagram, common numbers are assigned to multiple items with the same function, and numbers in parentheses added to signal names and block names are
It is shown that this part is used corresponding to any one of the channels "1 to n".

However, the adder (1) indicated by the numbers 2-9 corresponds to the I channel, and the adder (2) corresponds to the Q channel.

A signal input from the data input terminal 2-1 is band-limited by a filter (ROM LPF) 2-4 composed of a ROM. By changing the IF of the ROM data in the ROM filter 2-4, various band restrictions can be easily realized. The band-limited instantaneous frequency data is digitally added by an adder 2-5 to data representing an offset frequency, which is a channel designation signal input from an input terminal 2-2, and then integrated by an integrator 2-6. becomes phase information.

The phase information is CO8ROM table (ROMCO3)2
- MA and SIN ROM table (ROM 5I
N) Converted to cos, srN data by 2-8,
The CO6% SIN data for each channel is
Adders 2-9 add the signals as channel signals.

This ROM filter 2-4, adder 2-5, integrator 2-
6. ROM tables 2-7 and 2-8 are well-known, but the present invention adds a channel designation signal to the adder 2-5, and adds the I%Q signal from each channel to the adder 2-5. The feature is that it is added digitally at step 9.

One of the adders 2-9 adds data of the engineering signals of each channel. This method can be used, for example, in ROMCO3(1)2-7
Assuming that the output signal of ROM CO3 (2) is 8 bits and the output signal of ROM CO3 (2) is also 8 bits, the sum consists of 9 bits.

Therefore, if the number of channels n is expressed as 2, each R
If the number of output bits of the OM CO3(n) circuit is equal to bits, then the adder output will be (m+k) bits.

When n cannot be expressed as 2, the number of bits is increased by an exponent m of a number larger than the value n and that can be expressed as 2''.

For example, when adding signals of n=36 channels, 2
Since '<36<2'', the number of output bits of the adder is 6.
Bits increase.

The Q signal adder operates similarly. Also, addition n2-5
For ROM filter (ROM LPF) 2-
Since the number of output bits of 4 and that of the channel designation signal do not necessarily match, the number of output bits of addition n2-5 is the larger number of bits.

Output signals I (t), Q from terminals 2-3 of this circuit
(t) is a digital signal, which can be converted to D/
When A-converted, a signal like the one shown in FIG. 5 is obtained.

An embodiment in which a GMSK modulator is configured according to the present invention will be shown below.

! ! 1I13 is a diagram showing a configuration example of a baseband signal processing section of a GMSK modulator which is an application example of the present invention, and 3
-1 is a data input terminal, 3-2 is a channel specification data input terminal, 3-3 is a data output terminal, 3-4 is a Gauss-type ROM filter (Gauss ROM LPF),
3-5 is an adder, 3-6 is an integrator, 3-7 is a CO8RO
M table (ROM C03), 3-8 is SlNRO
M table (ROM 5IN), 3-9 represents an adder.

In addition, in the diagram, a common number is assigned to multiple items with the same function, and numbers in parentheses added to signal names and block names refer to each channel. It shows that it is used corresponding to any one of "1 to n".

However, the adder (1) indicated by the numbers 3-9 corresponds to the E channel, and the adder 5 (2) corresponds to the Q channel.

In this embodiment, a large R
OM filter (Gauss ROM LPF) is used, and the Gaussian ROM filter (hereinafter simply referred to as rR
L is the number of quantization bits of data (also called OMLPFJ).
B), the number of quantization bits of the adder 3-5 that adds the ROM LPF 3-4 and the frequency offset data is M bits, and the number of quantization bits of the CO3 ROM table 3-7 and the SlNROM table 3-8 is P bits. If the data transmission speed is f and the number of sampling bits of the ROM LPF 3-4 is S bits, then the sampling clock frequency is 2'fb.

The minimum amount of frequency offset Δf win is Δf a+i
n=45/2" (4).

frequency offset The maximum 1Δf mackerel ax of Δfma = (2M-L -1) Δf sin - f d wax (5) becomes.

here fd is the maximum frequency of FMqi harmonics It is the wavenumber shift.

In the case of MSK with 111 losses and 0.5, Δfd・RX
= f11 /4 (6) Therefore, the maximum value of the offset frequency is determined by Δf wax = (February - 1) f b / 2''''' - f b / 4 (7) (8).

-For example, if the signal transmission speed is 16 kbps and the channel spacing is 25 kHz, and if the leakage power to adjacent channels is 60 dB or less, CO3ROM%Sl
The number of output bits of the NROM may be 8 bits.

Therefore, if a 12-bit D/A converter is used, 16
Channels can be collectively modulated and channels in the 20 MHz frequency band can be accessed.

In the above example, the signal input from the data input terminal is a digital signal, but the case where it is an analog signal will be described below.

FIG. 4 is a diagram showing another configuration example of the baseband signal processing section of the multi-access digital F, M modulator of the present invention, and the difference from the previous example shown in FIG. 2 is the input part. Yes, A/D* converter 2-11 is added,
The input signal is converted into a digital 1 by an A/D converter 2-11. This instantaneous frequency data is band-limited by a ROM filter 2-4, which is ROM-C'*.

The band-limited instantaneous frequency data is integrated by an integrator 2-6 to obtain phase information after data representing an offset frequency is added thereto.

The phase data is according to ROM table 2-7.2-81)
CO8, converted to SIN data, CO8 of each channel
1SIN ROM output data is added for 1s each
Added 2-9 j1. be done.

If the frequency deviation of X kHz is represented by Y bit data, the minimum frequency offset 1Δfwin is Δf magazine 1n-X/2” ・・・・・・・・・・・・・・・
...... It is expressed as (9).

On the other hand, the number of quantization bits of addition n2-5 that adds ROM LPF2-4 and frequency offset data is M bits,
When the number of quantization bits of CO3ROM table 2-7 and SIN ROM table 2-8 is P bits, and the sampling clock frequency of the digital signal processing section is fs, the minimum amount of frequency offset Δf win is Δf
5in = (s/2P (10)) The circuit constants are determined so that the equation (9) and the equation (10) match.

Furthermore, the maximum amount of frequency off-certification Δf wax is Δf wax = (2”-' -1) Δf m1
n-f d a+ax・・・・・・・・・・・・・・・
... (11), where (dmax is the maximum frequency deviation).

As an example, if the average frequency deviation of the modulation signal is 3°5kHz
Assuming that the channel spacing is 25kHz and the leakage power to adjacent channels is 60dB or less, CO8ROM,
The number of output bits of the SIN ROM may be 8 bits.

Therefore, when using a 12-bit D/A @ converter, 1
It is possible to modulate six channels at once and access channels within a frequency range of 20 MHz.

〔Effect of the invention〕

By digitally applying a frequency offset in the baseband band, signals with different center frequencies are generated, resulting in high stability and precision, and by using a lock signal,
Channel specification can be performed without depending on the accuracy of the frequency synthesizer.

In addition, even if the number of channels increases, the number of frequency synthesizers and quadrature modulators can be significantly reduced, making it possible to downsize the modulator equipment.6 Since multi-channel signals are digitally added, R
Unlike when combining signals in the F band, cross-modulation and spurious signals do not occur.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example of the configuration of a digital processing multi-access digital FM modulator using the present invention, and FIG. 2 is a diagram showing an example of the configuration of the baseband signal processing section of the multi-access digital FM modulator of the present invention. , FIG. 3 is a diagram showing a configuration example of a baseband signal processing section of a GMSK modulator which is an application example of the present invention, and FIG. 4 is a diagram showing a configuration example of a baseband signal processing section of a GMSK modulator which is an application example of the present invention. Fig. 5 shows the spectrum of each channel in the RF band; Fig. 6 shows a multi-access digital FM modulator using a conventional VCO. Figure, 7th
The figure shows a conventional multi-access digital FM modulator 1IIn using a quadrature modulator. 1-1...Data input terminal, 1-2.
...Channel specification data input terminal, 1-3.
...RF signal output terminal, 1-4 ・
...Baseband signal processing section, 1-5
...D/A converter (D/A), 1-6
...Analog filter 1-7...
...Mixer, 1-8 ...Analog adder, 1-9 ...Phase shifter, 1-
10... Frequency synthesizer, 1-1
3... Quadrature modulator, 2-1... Data input terminal, 2-2... Channel designation data input terminal, 2-3... Data output Terminal, 2-4...ROM filter, 2-5...Adder,
2-6...Integrator, 2-7...
...CO8ROM table, 2-8...
... SlNROM table, 2-9...
...Adder, 2-11 ...A
/D converter, 3-1... Data input terminal, 3-2... Channel specification data input terminal, 3-3... Data output terminal, 3
-4...... Mouth-shaped ROM filter, 3-5.
...Adder, 3-6 ...Integrator, 3-7 ...CO3ROM table, 3-
8... SrNROM table, 3-9 ・
...Adder, 6-1 ...Data input terminal, 6-2 ...RF signal output terminal, 6-3 ...Band limit filter, 6 -4 ・・・・・・ VCo,
6-5... mixer, 6-6...
...Frequency synthesizer (oscillator), 6-
7...Synthesizer, 7-1...
...Data output terminal, 7-2...RF signal output terminal, 7-3...ROM filter, 7-4...Integrator, 7-
5...CO8ROM table, 7-
6... SIN ROM table,
7-7...D/A converter, 7-8...
・・Frequency synthesizer, 7-9 ・・・・・・
Mixa, ? -10... Analog adder, 7-11... Phase shifter, 7-12
・・・・・・Synthesizer, 7-13 ・・・・・・Quadrature modulator

Claims (1)

[Claims] A low-pass filter (LPF) composed of a read-only memory (ROM), an adder that adds signal data band-limited by the LPF and offset center frequency data, and an instantaneous signal output from the adder. A plurality of digital FM modulators each comprising an integration circuit that integrates frequency signals and a ROM table that obtains the sine (SIN) component and cosine (COS) component of the integrated phase signal; A quadrature modulator comprising an adder that digitally adds I-channel output data and Q-channel output data, respectively.