JP2000269924A - Orthogonal frequency division multiplex modulation transmission equipment - Google Patents

Abstract

(57) [PROBLEMS] To transmit an OFDM signal, reduce the interference of an OFDM transmission signal on an adjacent channel due to a sweep symbol, and perform synchronization on a receiving device side without any problem. SOLUTION: In an OFDM transmission apparatus, when inserting a plurality of predetermined synchronization data at a predetermined period into information data to be transmitted on a transmission apparatus side, an amplitude value of a sweep symbol data among the synchronization data is changed to the sweep value. The amplitude value decreases as the frequency increases from the center frequency of the sweep symbol waveform generated within the symbol period.
Since the amplitude value of the sweep symbol having a frequency close to the frequency band of the adjacent channel where the influence of the interference on the adjacent channel is large is reduced, the synchronization processing on the receiving device side can be performed without any trouble, and Since the interfering fixed pattern noise is reduced, the OFDM
The interference of the transmission channel with the adjacent channel can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to orthogonal frequency division multiplexing (OFDM).
The present invention relates to a synchronization generation circuit of a transmission device of the lexing type.

[0002]

2. Description of the Related Art For terrestrial transmission of moving image signals, FPU (F
2. Description of the Related Art A communication device (hereinafter, abbreviated as FPU) is widely used. Signal transmission using mobile radio or semi-fixed radio such as FPU is a system in which a signal is transmitted from a mobile station such as a camera and received by a base station such as a broadcast center. An overview of a signal transmission system using a conventional FPU is shown in FIG. 4 and will be described below. This system includes a transmission system having a transmission control unit 19, a transmission high-frequency unit 20, a transmission antenna 21 on the transmission side, and a reception antenna 22, a reception high-frequency unit 23, and a reception control unit 24 on the reception side. On the transmission side, _ID of the transmission control unit 19
The data input to the terminal is modulated by digital modulation, that is, orthogonal frequency division multiplexing (OFDM), and then modulated into an IF signal having a frequency determined by the local oscillator LO OSC and output. Note that the transmission data rate of the transmission control unit 19 is determined by the clock oscillator CK OSC.
The transmission high-frequency unit 20 converts the IF signal from the transmission control unit 19 into a signal of a designated RF frequency. The converted signal is transmitted to the receiving side via the antenna 21. On the other hand, on the reception side, the reception high-frequency section 2
In 3, only the RF signal of the designated frequency is received via the antenna 22 and converted into an IF signal. The reception control section 24 demodulates the input reception IF signal with the frequency of the local voltage controlled oscillator LO VCO, converts the signal into a digital signal having a rate determined by the output of the clock voltage controlled oscillator CK VCO, and outputs the digital signal.

Next, the structure of the transmission signal shown in FIG. 5 will be described. The transmission signal has a frame structure and is composed of several types of synchronization symbol groups and data symbol groups for transmitting information codes. As an example of this synchronization symbol group, for example, a null symbol having a signal power intensity of 0 as a first symbol, an autocorrelation function having a sharp peak value as a second symbol, and indicating a specific time point on a time axis. There are sweep symbols and the like. Further, as a modulation scheme of these data symbol groups, a quadrature phase shift keying (QPSK),
Six-level quadrature amplitude modulation (16 QAM: 16 Quadrature Amplitu)
de Modulation) can be used, but it is difficult to adapt to an analog AM / FM method or the like, which is a modulation method not including a synchronization symbol and a synchronization header.
FIG. 6 shows an example of the configuration of the transmission side of the transmission signal shown in FIG. 5 and will be described. Digital data for mapping to the I axis and the Q axis is input to the f-axis mapping circuit 1.
The f-axis mapping circuit 1 maps the input digital data to the I and Q axes, and outputs each data to an inverse discrete Fourier transform (IFFT) circuit 2. The IFFT circuit 2 performs an inverse Fourier transform on each of the I-axis data and the Q-axis data.
A guard interval is added to each of the Q-axis data and supplied to the switching circuit 8.

As the above-mentioned synchronization data, I-axis synchronization data and Q-axis synchronization data are generated in a synchronization data generation circuit 25. At this time, null and sweep synchronization data are
Null data generation circuit 5, sweep data generation circuit 26,
It is generated by the synchronization data mixing circuit 7 in units of one symbol. The synchronization data generated by the synchronization data generation circuit 25 is
It is supplied to the switching circuit 8. In the switching circuit 8, I-axis data and Q-axis data from the guard interval adding circuit 3,
The I-axis synchronization data and the Q-axis synchronization data from the synchronization data generation circuit 25 are mixed and output. The output of each of the I-axis and the Q-axis of the switching circuit 8 is supplied to a D / A conversion circuit 9, where the output is digital-to-analog converted. The I-axis and Q-axis data that have been digital / analog converted by the D / A conversion circuit 9 are supplied to a quadrature modulator 10. The orthogonal modulator 10 orthogonally modulates the input I-axis and Q-axis data and outputs the result. The output of the quadrature modulator 10 is supplied to a frequency converter 11 and output as a transmission signal converted to a transmission band.

Next, the synchronization data generated by the synchronization data generation circuit 25 shown in FIG. 6 will be described. As described with reference to FIG. 5, the transmission signal has a frame structure, and is composed of several types of synchronization symbol groups and data symbol groups for transmitting information codes. As the synchronization symbol group,
As described above, the first symbol is a null symbol having a signal power intensity of 0, and the second symbol is a sweep symbol having a sharp peak value of an autocorrelation function and indicating a specific time point on a time axis. Hereafter, the null symbol,
The sweep symbol generation circuit will be described. FIG.
FIG. 8 shows a null symbol and a sweep symbol waveform.
7A shows an I-axis null symbol waveform, and FIG.
It is an axis null symbol waveform. The I-axis and Q-axis null symbol waveforms are one symbol of the transmission signal forming the frame structure, and have a signal power intensity of 0 as described above. 8A illustrates an I-axis sweep symbol waveform, and FIG. 8B illustrates a Q-axis sweep symbol waveform. The sweep waveforms shown in FIGS. 8A and 8B are signals having frequency components continuously from the minimum to the maximum of the transmission signal band.

First, the waveform of the I-axis sweep symbol shown in FIG. The frequency band of the sweep symbol waveform depends on the signal band of the transmission signal. That is,
Assuming that the signal band of the transmission signal is ≤ f (Hz), the frequency band of the sweep symbol waveform is also ≤ f (Hz). In FIG. 8A, the signal band of the transmission signal is set to 0 to f (Hz).
Then, the I-axis sweep symbol waveform is a waveform of the same amplitude of positive polarity having a frequency component continuously from 0 to f (Hz) in the positive direction on the time axis from the center of the symbol period,
It is composed of a waveform of the same amplitude of the opposite polarity having a frequency component continuously from 0 to f (Hz) in the negative direction on the time axis. Similarly, for the Q-axis sweep symbol waveform of FIG. 8B, a waveform of the same amplitude of positive polarity having a frequency component continuously from 0 to f (Hz) in the positive direction on the time axis from the center of the symbol period. And 0 to f in the negative direction on the time axis.
(Hz) and a waveform of the same amplitude of opposite polarity having a frequency component continuously up to (Hz). At this time, the I-axis sweep symbol waveform and the Q-axis sweep symbol waveform
0 degrees out of phase. That is, the OFDM transmission signal is composed of a frame structure of several kinds of synchronization symbol groups and data symbol groups for transmitting information codes as described above, and orthogonally modulates I-axis and Q-axis data and frequency-converts the data to a transmission band. Transmitted.

[0007] Next, interference with adjacent channels when transmitting an OFDM transmission signal will be described. FIG.
4 schematically shows a relationship between a DM transmission channel and an adjacent channel. Band of the OFDM transmission channel is f ₂ ~f _3, the band of the adjacent channel is assumed to be _{f 1 ~f 2, f 3 ~f} 4. Here, the OFDM transmission signal has a transmission band f ₂
If all exist ~f _3, adjacent channels (f ₁ ~f _2,
f _{3 to} f ₄ ) do not interfere. However, if the OFDM transmission signal has a transmission band f _1-
If they exist in f ₂ , f _{3 to} f ₄ , interference will occur in adjacent channels. The OFDM transmission signal is transmitted through a transmission band f ₂ to
quite difficult to be present all the f _3, it leaks inevitably to an adjacent channel. In FIG.
5 shows an example in which a DM transmission signal leaks to an adjacent channel. An actual OFDM transmission signal is as shown in FIG.
As can be seen from FIG. 10, OFDM transmission signal is leaked to the adjacent channels _{(f 1 ~f 2, f 3} ~f 4). That is,
The signal leaking into the transmission bands f _{1 to} f ₂ and f _{3 to} f ₄ of the adjacent channel is an adjacent channel interference signal.

As a factor of the OFDM transmission signal generating an adjacent channel interference signal, waveform distortion existing in the quadrature modulator 10 and the frequency converter 11 in FIG. 6 can be considered. Here, it is quite difficult to make the waveform distortion existing in the quadrature modulator 10 and the frequency converter 11 zero, and the waveform distortion always exists. Next, how the waveform distortion causes interference to an adjacent channel will be described. There are roughly two types of interference of waveform distortion on adjacent channels. One is the case where the interference to the adjacent channel is fixedly present, and the other is the case where it is randomly present. When the interference component to the adjacent channel exists fixedly, it always exists and causes interference such as fixed pattern noise. In addition, when the interference to the adjacent channel exists at random, interference such as random noise generated randomly occurs. In the interference to the adjacent channel, the dominant one is interference such as fixed pattern noise in which the interference to the adjacent channel is fixed.

[0009]

In the above prior art, O
When transmitting an FDM signal, interference occurs with analog transmission of a channel adjacent to the transmission channel of the OFDM transmission signal. The OFDM transmission signal has a frame structure of several types of synchronization symbol groups and data symbol groups for transmitting information codes as described above.
This data symbol group consists of multiple (several hundred) in the transmission band.
, And is transmitted. That is, the data symbol group of the OFDM transmission signal is
Because of frequency division multiplex transmission, interference to adjacent channels is close to random noise. Further, the influence of the interference increases as the frequency increases from the center of the own channel closer to the adjacent channel. In contrast, OFD
Several types of synchronization symbol groups of the M transmission signal are fixed value signals as shown in FIGS. Therefore, the interference to the adjacent channel is close to fixed pattern noise. However, among the synchronization symbols, the null symbol has a signal power strength of 0, and therefore does not interfere with the adjacent channel. That is, it is the sweep symbol that interferes with the adjacent channel. Therefore, in order to reduce the interference to the adjacent channel, the amplitude value of the sweep symbol may be reduced, but if the amplitude value of the sweep symbol is reduced,
There is a problem in that synchronization becomes difficult on the receiving device side. An object of the present invention is to eliminate these drawbacks and reduce the interference of an OFDM transmission signal on adjacent channels due to a sweep symbol when transmitting an OFDM signal, and to perform synchronization on a receiving device side without any problem. I do.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a transmission apparatus using an orthogonal frequency division multiplexing modulation method. When inserting the synchronization data, an orthogonal frequency division multiplexing modulation method having means for variably setting and inserting the amplitude value of the synchronization data for indicating a specific time point on the time axis in the synchronization data according to the frequency. Transmission device. Further, the predetermined synchronization data is used as sweep symbol data, and the amplitude value has a predetermined slope within the synchronization data period. Further, the amplitude value of the sweep symbol data is reduced as the frequency becomes higher from the center frequency of the sweep symbol waveform generated within the sweep symbol period. As a result, OFD
When transmitting the M signal, the amplitude value of the sweep symbol having a frequency close to the frequency band of the adjacent channel where the influence of the interference on the adjacent channel becomes large is reduced, so that the synchronization processing on the receiving device side is performed without any trouble. In addition, since the fixed pattern noise in which the sweep data symbol waveform of the OFDM transmission channel interferes with the adjacent channel is reduced, the interference of the OFDM transmission channel with the adjacent channel can be reduced.

[0011]

FIG. 1 shows the configuration of an embodiment of the present invention, which will be described in detail below. Digital data for mapping to the I axis and the Q axis is input to the f-axis mapping circuit 1. The f-axis mapping circuit 1 maps the input digital data to the I and Q axes,
Each data is output to the inverse discrete Fourier transform (IFFT) circuit 2. In the IFFT circuit 2, each of the I-axis data and the Q-axis data is subjected to an inverse Fourier transform. As the above-mentioned synchronization data, I-axis synchronization data and Q-axis synchronization data are generated by the synchronization data generation circuit 4. At this time, null and sweep synchronization data are generated in units of one symbol by a null data generation circuit 5, a sweep data amplitude variable generation circuit 6, and a synchronization data mixing circuit 7. The synchronization data generated by the synchronization data generation circuit 4 is supplied to the switching circuit 8. The switching circuit 8 mixes and outputs the I-axis data and the Q-axis data from the guard interval addition circuit 3 and the I-axis synchronization data and the Q-axis synchronization data from the synchronization data generation circuit 4. The output of each of the I axis and Q axis of the switching circuit 8 is
It is supplied to the D / A conversion circuit 9 and is subjected to digital / analog conversion. The I-axis and Q-axis data that have been digital / analog converted by the D / A conversion circuit 9 are supplied to a quadrature modulator 10. The orthogonal modulator 10 orthogonally modulates the input I-axis and Q-axis data and outputs the result. The output of the quadrature modulator 10 is supplied to a frequency converter 11 and output as a transmission signal converted to a transmission band.

Next, the synchronization data generated by the synchronization data generation circuit 4 of FIG. 1 will be described. As described with reference to FIG. 5, the transmission signal has a frame structure, and is composed of several types of synchronization symbol groups and data symbol groups for transmitting information codes. Synchronous data generation circuit 4 of FIG.
Is a circuit for generating several types of synchronization symbol groups. As described above, the synchronization symbol group includes a null symbol having a signal power intensity of 0 as a first symbol and an autocorrelation function having a sharp peak value as a second symbol to indicate a specific time point on a time axis. There is a sweep symbol. Hereinafter, the null data generation circuit and the sweep data amplitude variable generation circuit will be described. 7 and 3 show waveforms of a null symbol and a sweep symbol. FIG. 7A shows an I-axis null symbol waveform, and FIG. 7B shows a Q-axis null symbol waveform. The null symbol waveform is the same as in the conventional example. I
The axis and Q axis null symbol waveforms are one symbol of a transmission signal having a frame structure. As described above, the signal has a signal power intensity of 0. The I-axis and Q-axis null symbol waveforms are one symbol of the transmission signal forming the frame structure, and have a signal power intensity of 0 as described above.

FIG. 3A shows an I-axis sweep symbol waveform of the present invention, and FIG. 3B shows a Q-axis sweep symbol waveform of the present invention. The sweep symbol waveforms shown in FIGS. 3A and 3B are signals having frequency components continuously from the minimum to the maximum of the transmission signal band. First, FIG.
The (a) I-axis sweep symbol waveform will be described.
The frequency band of the sweep symbol waveform depends on the signal band of the transmission signal. That is, the signal band of the transmission signal is
If ≦ f (Hz), the frequency band of the sweep symbol waveform also becomes ≦ f (Hz). In FIG. 3A, if the signal band of the transmission signal is 0 to f (Hz), the I-axis sweep symbol waveform is 0 to f (Hz) in the positive direction on the time axis from the center of the symbol period. ) And a waveform having a different amplitude with a positive polarity having a frequency component continuously up to a waveform having a different polarity with a reverse polarity having a frequency component continuously from 0 to f (Hz) in a negative direction on the time axis. It is configured. FIG. 3 (b)
Similarly, a positive-polarity waveform having a frequency component continuously having a frequency component from 0 to f (Hz) in the positive direction on the time axis from the center of the symbol period, , In the negative direction, the waveforms have opposite polarity and different amplitudes having frequency components continuously from 0 to f (Hz). At this time, the I-axis sweep symbol waveform and Q
The phase is different from the axis sweep symbol waveform by 90 degrees.

Next, interference to an adjacent channel when transmitting an OFDM transmission signal will be described. As described above, it is the sweep symbol that interferes with the adjacent channel, and in order to reduce the amount of interference with the adjacent channel, the amplitude value of the sweep symbol may be reduced, but if the amplitude value of the sweep symbol is reduced. This makes it difficult for the receiving device to synchronize. In order to solve this problem, in the present invention, the sweep data amplitude variable generation circuit 6 in the synchronous data generation circuit 4 has a frequency band of 0 to f (Hz) as shown in FIGS. Sweep symbol waveform
The amplitude value is variably set according to the frequency and output. That is, as can be seen from FIGS. 3A and 3B, the I axis,
Both the Q-axis sweep data symbol waveforms are set so that the amplitude value gradually decreases as the frequency increases from a predetermined frequency. In other words, the amplitude value is set to be smaller as the frequency is closer to the frequency band of the adjacent channel where the influence of the interference on the adjacent channel increases. As described above, by reducing only the amplitude value of the sweep symbol having a frequency close to the frequency band of the adjacent channel in which the influence of the interference on the adjacent channel becomes large, the synchronization processing on the receiving device side can be performed without any trouble, and , OF
Since the fixed pattern noise in which the sweep data symbol waveform of the DM transmission channel interferes with the adjacent channel is reduced, it is possible to reduce the interference of the OFDM transmission channel with the adjacent channel.

Next, an example of the configuration of the sweep data amplitude variable generation circuit 6 of the present invention will be described with reference to FIGS. 2 (a) and 2 (b). First, FIG. 2A will be described. RO for generating I sweep data amplitude variable for generating I sweep data
An M12 and a Q sweep data amplitude variable ROM 13 are provided. ROM for generating variable I sweep data amplitude
In FIG. 12, as shown in FIG.
A (Hz) sweep data symbol waveform is variably set in amplitude value according to the frequency and output. This allows I
The amplitude value of the axis sweep data symbol waveform decreases as the frequency increases from a predetermined frequency. In the ROM 13 for generating the Q sweep data variable amplitude, FIG.
As shown in (1), the amplitude value of the sweep data symbol waveform in the frequency band 0 to f (Hz) is arbitrarily variably set according to the frequency and output. As a result, the amplitude value of the Q-axis sweep data symbol waveform decreases as the frequency increases from a predetermined frequency. In other words, using ROM,
A variable I-axis and Q-axis sweep data symbol waveform is generated. Next, FIG. 2B will be described.
The I sweep data generation circuit 14 generates I sweep data. In the variable I amplitude value generating circuit 15,
A waveform is generated in which the amplitude value is arbitrarily set according to the frequency. The outputs of the I sweep data generation circuit 14 and the variable I amplitude value generation circuit 15 are input to the multiplier 16,
A waveform as shown in FIG. The Q sweep data generation circuit 17 generates Q sweep data. Further, the variable Q amplitude value generating circuit 18 generates a waveform in which the amplitude value is variably set according to the frequency. Q sweep data generation circuit 17, Q amplitude value variable generation circuit 18
Is input to the multiplier 16 and outputs a waveform as shown in FIG.

[0016]

As described above, according to the present invention,
When transmitting an OFDM signal, by lowering the amplitude value of a sweep symbol having a frequency close to the frequency band of the adjacent channel where the influence of interference on the adjacent channel increases, synchronization processing on the receiving device side can be performed without any trouble. In addition, since the fixed pattern noise in which the sweep data symbol waveform of the OFDM transmission channel interferes with the adjacent channel is reduced, the interference of the OFDM transmission channel with the adjacent channel can be reduced.

[Brief description of the drawings]

FIG. 1 is a block diagram showing one embodiment of a transmission side configuration of an OFDM transmission system according to the present invention.

FIG. 2 is a block diagram showing an example of a sweep data amplitude variable generation circuit according to the present invention.

FIG. 3 is a waveform chart showing an example of I-axis and Q-axis sweep symbol data of the present invention.

FIG. 4 is a block diagram showing a schematic configuration of a signal transmission system using an FPU.

FIG. 5 is a schematic diagram showing a frame structure of an OFDM transmission signal.

FIG. 6 is a block diagram showing one embodiment of a transmission side configuration of a conventional OFDM transmission system.

FIG. 7 is a waveform chart showing an example of general I-axis and Q-axis null symbol data.

FIG. 8 is a waveform diagram showing an example of I-axis and Q-axis sweep symbol data according to the related art.

FIG. 9 is a schematic diagram illustrating a relationship between an OFDM transmission channel and an adjacent channel.

FIG. 10 is a schematic diagram illustrating a relationship between an OFDM transmission channel and an adjacent channel.

[Explanation of symbols]

1: f-axis mapping circuit, 2: IFFT circuit, 3: guard interval addition circuit, 4: synchronous data generation circuit,
5: Null data generation circuit, 6: Sweep data amplitude variable generation circuit, 7: Synchronous data mixing circuit, 8: Switching circuit,
9: D / A conversion circuit, 10: quadrature modulator, 11: frequency converter, 12: RO for generating I sweep data amplitude variable
M, 13: ROM for generating Q sweep data amplitude variable, 1
4: I sweep data generation circuit, 15: I amplitude value variable generation circuit, 16: multiplier, 17: Q sweep data generation circuit, 18: Q amplitude value variable generation circuit, 19: transmission control unit,
20: transmission high frequency unit, 21: transmission antenna, 22: reception antenna, 23: reception high frequency unit, 24: reception control unit.

Claims (3)

[Claims] In a transmission apparatus using an orthogonal frequency division multiplexing modulation method, when a plurality of predetermined synchronization data are inserted into information data to be transmitted at a predetermined cycle on the transmission apparatus side,
Transmission of the orthogonal frequency division multiplexing modulation method, comprising means for variably setting and inserting the amplitude value of the synchronization data for indicating a specific time point on the time axis in the synchronization data according to the frequency. apparatus. 2. The method according to claim 1, wherein the synchronization data for indicating the specific time point on the time axis is sweep symbol data, and the amplitude value has a predetermined slope during the synchronization data period. A transmission apparatus using an orthogonal frequency division multiplexing modulation method. 3. The sweep symbol data according to claim 2, wherein the amplitude value of the sweep symbol data gradually decreases as the frequency increases from the center frequency of the sweep symbol waveform generated within the sweep symbol period. A transmission device of an orthogonal frequency division multiplexing modulation method.