JPH0335640A - Orthogonal modulator - Google Patents

Abstract

PURPOSE:To control cross modulation and spurious by generating signals different in center frequencies by means of digital offsetting of the frequencies in a base band. CONSTITUTION:A base band digital signal processing part 1-5 restricts the band of input data, multiplies data of offsetting frequencies and generates the signals different in the center frequencies in the base band. Since the offsetting of the frequencies is digitally executed, the stable signals ca be generated. The signals different in the center frequencies can be generated by changing data of the offsetting frequencies. Consequently, respective channels are accessed in the base band.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a modulator in digital communications.

[Conventional technology]

The digital phase modulator has two channels: ■ channel and Q channel.
can be generated by a quadrature modulator using two baseband signals.

In phase modulation, the frequency of the reference carrier wave is fc, and the period of the data signal to be modulated, that is, one code period is T, and a constant phase φ9 is taken for each darkness t=iT (where i is an integer). The modulated wave is expressed as follows.

S (t) = Acos (2πfct + φ1)...
(1) Equation (1) can be transformed as follows: (t)=Acos φ1 (2yfct) −A sin φ + 5in (2πfct) (2).

Therefore, a modulated wave can be obtained using a quadrature modulator as shown in Figure WIJ4.

That is, FIG. 4 shows a diagram explaining phase modulation by a quadrature modulator, where 4-1 is a channel data input terminal, 4-2 is a Q-channel data input terminal, 4-3 is a modulation signal output terminal, 4-4 is a mixer, 4-5 is an adder,
4-6 represents a phase shifter, and 4-7 represents a frequency synthesizer.

■Data input from the channel data input terminal 4-1 and the Q channel data input terminal 4-2 are transmitted to the frequency synthesizer 4-7, the phase shifter 4-6, the mixer 4-4, and the adder 4-4.
5.

Further, a conventional base station transmitter for analog signals of a car telephone is shown in FIG. That is, FIG. 5 is a diagram showing the configuration of a base station transmitter, in which 5-1 is a data input terminal;
-2 is a channel switching input terminal, 5-3 is an RFi signal output terminal -4 is a modulator, 5-5 mixer, 5-6 high output amplifier (power amplifier), 5-7 is a filter, 5-8 is a frequency It represents a synthesizer (common numbers are assigned to multiple items with the same function in the figure).

As shown in Figure f55, the base station transmitter is composed of a modulator 5-4, a mixer 5-5, a power amplifier 5-6, and a filter 5-7 for each channel.
The F-fold signals are combined and transmitted from the base station antenna.

In digital phase modulation, it is necessary to generate signals for multiple channels as shown in Figure 6 in a base station transmitter, a transmitter that performs common amplification of the base station, and a modulator that performs multicarrier transmission. (In the figure, 6-1 to 6
-5 is the signal spectrum, f, ~f is the center frequency of each channel).

Regarding the conventional method in this case, spectrum 7-2 and mer 5 among spectra 7-1 to 7-6 as shown in FIG.
We will also discuss the case where the spectrum is empty and the spectrum is not continuous.

QPSK conversion of multiple channels using conventional quadrature modulator
I! The configuration for generating the signal is shown in tIS8.

In the figure, 8-1 is an I channel data input terminal;
-2 is Q channel data input terminal, 8-3 is ROM filter, 8-4 is D/A converter (D/A), 8-5 is mixer, 8-6 is analog adder, 8-7 is phase vessel (π/
2), 8-8 represents a frequency synthesizer, 8-9 represents a quadrature modulator, 8-10 represents a combiner, and 8-11 represents an RF signal output terminal (for the same type of 8! functions in the figure, , assigning a common number to multiple items).

The baseband signal of 1 channel and Q channel of each data is filtered using a ROM (ROM filter) 8-
3 and converted into analog signals by a D/A converter 8-4, and then an RF band modulated signal is obtained by a quadrature modulator 8-9.

The modulated signals of each channel in the RF band are combined by RFW, but combining signals in the RF band easily causes cross-modulation and spurious.

Further, a frequency synthesizer, a quadrature modulator, and a D/A converter are required for specifying a channel for each channel, and as the number of channels increases, the circuit scale of the transmission ff1fi increases.

[Problem to be solved by the invention]

Conventionally, when generating RF multiplied signals of multiple channels using a modulator or a multicarrier modulator of a base station transmitter, there has been a drawback that cross-modulation and spurious signals are likely to occur when the signals are combined in the RF band.

In addition, conventionally, a frequency synthesizer converts the frequency into a signal with a center frequency determined by the channel, but this requires a frequency synthesizer and quadrature modulator to specify the channel for each channel. had the disadvantage that the scale of the modulation circuit inside the transmitter was large.

The main feature of the present invention is that each channel of data is specified by a baseband gain signal processing circuit, and as a result, cross-modulation and spurious generation can be suppressed.
It is an object of the present invention to provide a quadrature modulator that can reduce the size of modulator equipment because there is no need to add quadrature modulators even when the number of channels increases.

[Means to solve the problem]

According to the invention, the above-mentioned objects are remotely related by the measures defined in the claims.

That is, the present invention provides read-only memory (ROM)
A low pass filter (LPF) consisting of
A plurality of dinotal phase modulators constituted by multipliers that receive signal data band-limited by F and offset frequency data, and channel output data and Q channel output data of the plurality of dinotal phase modulators. This is a quadrature modulator that has an adder that digitally adds the .

[For production]

In the baseband digital signal processing circuit, the baseband digital signal processing circuit band-limits the input data and calculates the data of the offset frequency, and Generate signals with different center frequencies in different bands.

At this time, since the frequency offset is performed digitally, a stable signal can be generated.

Also, by changing the offset frequency data, signals with different center frequencies can be generated, and therefore,
Each channel can be accessed in the baseband band.

Hereinafter, a more specific example will be explained based on the drawings.

FIG. 1 is a diagram showing a digital processing multi-access di-notal phase modulator using the present invention, where 1-1 is a data input terminal, 1-2 is an offset frequency data input terminal, and 1-3 is an RF signal output. Terminals 1-4 are A/D converters (
A/D), 1-5 is a baseband digital signal processing unit, 1-6 is a D/A converter (D/A), 1-7 is an analog filter, 1-8 is a mixer, and 1-9 is an analog An adder, 1-10 a phase shifter, and 1-11 a frequency synthesizer.

In addition, in the figure, a common number is given to a plurality of items having the same function.

The data of each channel is band-limited by the baseband differential signal processing unit 1-5 for each I and Q channel, and is specified to each channel in the baseband band. Signals designated for each channel are digitally added by an adder for each channel (1) and Q channel. The I channel and Q channel signals of multiple channels are transmitted to D/A converters 1-6, respectively.
is converted to an analog signal by analog filter 1-71.
``After harmonic components are removed, the signal is converted to RF times by a quadrature modulator.Baseband differential signal processing unit 1-5
Then, the input signal is passed through the filter (L
PF)-C' band is limited, but various band restrictions can be easily realized by rewriting the data in the ROM. The band-limited data is converted to A/D converted data of an offset frequency input from the input terminal 1-2, and then added to the adder for each of the I and Q channels.

〔Example〕

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

fltJ21 is a diagram showing a baseband processing multi-access QPSK modulator using the present invention, 2-1 is an I channel data input terminal, 2-2 is a Q channel data input terminal, and 2-3 offset frequency data input terminals. , 2-
4 is an input terminal, 2-5 is a shift reno star, 2-
6 is a ROM filter, 2-7 is a multiplier, 2-81.1A
/D converter (A/D), 2-9 is an addition W, device, 2-10
is a D/A converter (D/A), 2-11 is an analog filter, 2-12 is a counter, 2-13 is a mixer, 2-1
Reference numeral 4 represents an analog adder, 2-15 a phase shifter, 2-16 a frequency synthesizer, and 2-j7 an RF signal output terminal.

In addition, in the figure, a common number is given to a plurality of items having the same function.

The data of each channel enters the dinotal signal processing circuit for each ISQ channel. In the baseband digital signal processing section, the input signal is band-limited by a ROM filter (LPF) 2-6 composed of a ROM. The band-limited data has offset frequency data as shown in Figure 2-7.
is specified for each channel in the baseband band by multiplying by The signals designated for each channel are digitally added by addition W52-9 for each channel (1) and Q channel.

FIG. 3 shows waveforms of various parts for explaining one series of operations.

In the figure, (a) is the input data, (b) is the output waveform of the ROM filter 2-6, (C) is the offset frequency waveform, and (d) is the waveform obtained by D/A converting the output waveform of the multiplier 2-7. It shows.

(a) is, for example, normal NRZ format binary data. Since the ROM filter 2-6 operates digitally,
The output (b) lacks smoothness in its waveform. (c) shows an offset frequency, and what is input to the multiplier 2-7 is data obtained by A/D converting this.

When the offset frequency changes, the frequency of this signal changes.

Since multiplication is performed digitally in the multiplier 2-7, its output is in digital format, but (d) shows it as an image obtained by D/A conversion.

Therefore, the multiplier output can be aligned with the signal whose data is frequency-converted using the offset frequency, so if the offset frequency is shifted for each series, the outputs of each multiplier 2-7 can be added by the adder 2-9. Both in-phase and orthogonal signals can be multiplexed into one series.

The number of channels that can be processed at once is determined by the speed of the D/A converter.

For example, when using a commercially available 16-bit high-speed D/A converter and assuming that leakage power to adjacent channels is 60 dB or less, 64 channels can access the 2 MHz frequency band.

〔Effect of the invention〕

As explained above, according to the present invention, signals with different center frequencies are generated by digitally applying a frequency offset in the baseband band, so by using a lock signal with high stability and high accuracy, Channel specification can be performed without depending on the accuracy of the frequency synthesizer.

Furthermore, even if the number of channels increases, the number of orthogonal modulators can be significantly reduced, making it possible to downsize the modulator equipment.

Furthermore, since multi-channel signals are digitally added, cross-modulation and spurious signals do not occur, unlike when combining signals in the RF band.

4,

[Brief explanation of drawings]

FIG. 1 is a diagram showing a dinotal processing multi-access dinotal phase modulator using the present invention, FIG. 2 is a diagram showing a baseband processing multi-access QPSK modulator using the present invention, and FIG. 3 is a diagram showing a series of Figure #4 is a diagram showing the waveforms of each part to explain the operation, Figure #4 is a diagram explaining phase modulation by the orthogonal modulator, Figure @5 is a diagram showing the configuration of the base station transmitter, Figure #6 is a diagram showing the configuration of the base station transmitter,
The figure shows the spectrum of a plurality of channels in the RF band, FIG. 7 shows the spectrum of each channel in the RF band, and FIG. 8 shows the configuration of a conventional multi-access QPSK modulator. 1-1...Data input terminal, 1-2.
...Offset frequency data input terminal, 1-3.
... RF signal output terminal, 1-4 ...
...A/D converter (A/D), 1-5...
...Baseband dinotal signal processing section, 1-6
...D/A converter (D/A), 1-7 ...
... Analog filter, 1-8...
・ Mixer, 1-9 ... Analog adder, 1-10 ... Phaser (π/2), 1-1
1... Frequency synthesizer, 2-1...
... ■Channel data input terminal, 2-2 ...
... Q channel data input terminal, 2-3 ...
・・Offcent frequency data input terminal, 2-4 ・・
... Clock input terminal, 2-5...
・・・ Shift Reno Star, 2-6 ・・・・・・
ROM filter, 2-7... Multiplier, 2-8... A/D converter (A/D)
, 2-9 ......-addition, vessel, 2-1
0...D/A converter (D/A), 2
-11...Analog filter, 2
-12 ... Counter, 2-1
3... Mixer, 2-14... Analog adder, 2-15... Phase shifter,
2-16 ...Frequency synthesizer
2-17 ...... RF signal output terminal 4-1 ...... ■Channel data input terminal, 4
-2...Q channel data input terminal, 4-3
...Modulation signal output terminal, 4-4...
...Mixer, 4-5 ...Adder, 4-6 ...Phase shifter, 4-7
...Frequency synthesizer, 5-1
・・・・・・Data input terminal, 5-2 ・
... Channel switching input terminal, 5-3
...... RF signal output terminal, 5-
4...Modulator, 5-5...Mixer, 5-6...High output amplifier (
power amplifier), 5-7... Filter 5-8... Frequency synthesizer 6-1 to 6-5... Signal spectra of multiple channels 7-1 to 7- 6...
...Signal spectrum of multiple channels, 8
-1 ・・・・・・ I channel data input terminal,
8-2...Q channel data input terminal,
8-3 ROM filter,
8-4... D/A converter,
8-5... Mixa, 8-6...
... Analog adder, 8-7...
...Phase shifter, 8-8 ...Frequency synthesizer, 8-9 ....Quadrature modulator, -Synthesizer, -1 RFM power terminal charger

Claims (1)

[Claims] A plurality of digital filters comprising a low-pass filter (LPF) comprising a read-only memory (ROM) and a multiplier that multiplies signal data band-limited by the LPF by offset frequency data. A quadrature modulator comprising: a phase modulator; and an adder that digitally adds I-channel output data and Q-channel output data of the plurality of digital phase modulators.