JP2002232384A - Orthogonal frequency division multiplex signal transmitting method and orthogonal frequency division multiplex signal transmitter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an orthogonal frequency division multiplex signal transmitter for generating OFDM signals including a high quality pilot signals with little unwanted leakage components. SOLUTION: The orthogonal frequency division multiplex signal transmitter for generating signals to which a part of a plurality of generated carrier signals is added as a guard interval signal, comprises a means 21 for detecting carriers continuous in adjacent symbol periods and amplitude control means 14a, 14b, to 14n, 15a, 15b, to 15n for attenuating the amplitudes of signals near start points of the guard interval signals added to carrier signals detected as discontinuous carriers by the continuous carrier detecting means 21.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention reduces the unnecessary leakage spectrum of an orthogonal frequency division multiplex signal transmitted with a guard band and stabilizes a demodulation pilot signal component of the orthogonal frequency division multiplex signal. The present invention relates to a transmission method of an orthogonal frequency division multiplex signal to be transmitted, and an orthogonal frequency division multiplex signal transmission apparatus.

[0002]

2. Description of the Related Art OFDM (Orthogonal Frequency Divis)
ion Multiplexing (orthogonal frequency division multiplexing) signal
Since the constituent carriers are orthogonally arranged in the frequency domain, it is a modulation method that can transmit information signals with high efficiency using a large number of carriers arranged at narrow frequency intervals, and also uses a large number of carriers. The modulation signal frequency band for each carrier can be reduced, so that it is possible to configure a transmission and reception system that is less susceptible to multipath distortion while keeping the transmission efficiency from being reduced by providing a guard interval.

The OFDM transmission system having such characteristics is a digital modulation system adopted for digital terrestrial broadcasting in Japan and Europe.
The FDM method is used as a wireless LAN system as a wireless coupling means for a home network.
(Formation Technology) It is expected to be used in the future as an important technology for realizing the system.

At present, in order to realize a wireless LAN, a method of transmitting a modulated signal with low power using a spread spectrum technique is also used. However, more and more wireless terminals have been introduced toward the information society. When thinking about going,
Further, it is necessary to realize a wireless system with high frequency use efficiency.

[0005]

An OFDM signal is generated using an IFFT (Inverse fast Fourier transform), and a part of the generated signal is added to the generated signal as a guard interval signal. Transmitted.

[0006] The OFDM signal to which the guard interval signal is added can obtain stable reception performance without being affected by multipath distortion. The unnecessary leak signal component may interfere with communication of an adjacent frequency. For example, an OFDM signal in which the unnecessary leak signal component is reduced can be generated.
Realization of an FDM transmission device is desired.

OFDM from which unnecessary leakage signal components have been removed
Regarding the generation of the signal, Japanese Patent Application Laid-Open No.
An FDM modulator is disclosed in Japanese Patent Application Laid-Open Publication No. H11-157,197, in which a discontinuous component of a signal generated during a guard interval is reduced by periodically changing an amplitude value before and after the guard interval. OFDM modulator is realized.

[0008] The OFDM signal thus generated is attenuated before the guard interval, so that it has a minimum signal value at the start of the guard interval and returns to the original signal level at the end of the guard interval. However, such signal level control is
This is performed for all the carriers constituting the FDM.

The OFDM signal generated in this way is demodulated using an FFT (Fast Fourier Transform) circuit. The FFT circuit needs to be in synchronization with the IFFT of the transmitting apparatus, and The device generates and transmits a signal for synchronization of the receiver as a signal inherent in the OFDM signal.

The signal for synchronization is called a pilot signal, and the pilot signal defines a specific carrier constituting OFDM as a transmission carrier, and transmits a synchronization signal component by the carrier.

The transmission method of the pilot signal is disclosed in
Although it is disclosed in -32546 "Orthogonal frequency division multiplexing signal transmission / reception apparatus", a signal of a frequency such that an integer wavelength exists in a guard interval section is generally used for the pilot signal.

Accordingly, the present invention relates to an OFDM signal generated with a guard interval period provided therein, the OFDM signal having a small unnecessary leakage component and containing a high quality pilot signal and a high quality OFDM signal reference signal for decoding.
An object of the present invention is to provide a method of transmitting an orthogonal frequency division multiplexed signal and a configuration of an orthogonal frequency division multiplexed signal transmitting apparatus that enable generation of a DM signal.

[0013]

The present invention comprises the following means 1) to 6) to solve the above-mentioned problems. That is,

1) A plurality of signal points are defined on a two-dimensional plane constituted by a real axis and an imaginary axis, and information signals supplied to the defined signal points are allocated and modulated for each effective symbol period. A plurality of carrier signals are obtained, and a part of the signal of the effective symbol period is added to the obtained carrier signal as a guard interval signal to obtain a carrier signal for each symbol period, and the obtained carrier signal is obtained. For transmitting an orthogonal frequency division multiplexed signal to a spatial transmission path, comprising: detecting a carrier signal that is discontinuous in an adjacent symbol period among a plurality of carrier signals for each symbol period. (21), and a carrier signal detected as a discontinuous carrier signal in the first step , 14n, 1n, attenuating the amplitude of the carrier signal near the start point of the guard interval signal
5a, 15b,..., 15n) and a third step (16) of obtaining the orthogonal frequency division multiplexed signal by combining a plurality of carrier signals obtained in the second step. Characteristic orthogonal frequency division multiplexing signal transmission method.

2) A plurality of signal points are defined on a two-dimensional plane constituted by a real axis and an imaginary axis, and information signals supplied to the defined signal points are assigned to the first and first signal points. Next, a plurality of carrier signals modulated for each second effective symbol period to be arranged are obtained, and a carrier signal modulated for each of the first or second effective symbol periods is added to the obtained plurality of carrier signals. Is added as a guard interval signal before the first effective symbol period to obtain a carrier signal for each symbol period,
A method for transmitting an orthogonal frequency division multiplexed signal for transmitting the obtained carrier signal to a spatial transmission path, wherein a carrier discontinued in an adjacent symbol period among a plurality of carrier signals for each symbol period. A first step (21) of detecting a signal, and a carrier in a second effective symbol period before a guard interval signal added to a carrier signal detected as a discontinuous signal in the first step. The second step of attenuating the signal amplitude (14a, 14b,..., 14)
, 15a, 15b,..., 15n) and a third step (16) of obtaining the orthogonal frequency division multiplexed signal by combining the plurality of carrier signals obtained in the second step. A method for transmitting an orthogonal frequency division multiplexed signal.

3) In the detection of the discontinuous carrier signal in the first step, a carrier signal defined as a reference signal among the plurality of carrier signals is not detected as a discontinuous carrier signal. The method for transmitting an orthogonal frequency division multiplexed signal according to the above item 1) or 2).

4) The detection of the discontinuous carrier signal in the first step is performed by detecting a carrier signal defined as a receiver synchronization signal among the plurality of carrier signals as a discontinuous carrier signal. The method for transmitting an orthogonal frequency division multiplexed signal according to the item 1) or 2), wherein the signal is not detected.

5) A plurality of signal points are defined on a two-dimensional plane composed of a real axis and an imaginary axis, and information signals supplied to the defined signal points are allocated and modulated for each effective symbol period. A plurality of carrier signals are obtained, and a part of the signal of the effective symbol period is added to the obtained carrier signal as a guard interval signal to obtain a carrier signal for each symbol period, and the obtained carrier signal is obtained. Frequency division multiplexing signal transmitting apparatus for transmitting a signal to a spatial transmission path, wherein a discontinuous carrier for detecting a carrier signal that is discontinuous in an adjacent symbol period among a plurality of carrier signals for each symbol period. Detecting means (21) for detecting a carrier signal detected as a discontinuous carrier signal by the discontinuous carrier detecting means; Amplitude control means (14a, 14b,...) For attenuating the amplitude of the carrier signal in the vicinity of the start point of the guard interval signal to be added
, 14n, 15a, 15b,..., 15n) and signal combining means (16) for obtaining the orthogonal frequency division multiplexed signal by combining a plurality of carrier signals obtained by the amplitude control means. An orthogonal frequency division multiplexing signal transmission device characterized by being performed.

6) A plurality of signal points are defined on a two-dimensional plane constituted by a real axis and an imaginary axis, and information signals supplied to the defined signal points are assigned to the first and first signal points. Next, a plurality of carrier signals modulated for each second effective symbol period to be arranged are obtained, and a carrier signal modulated for each of the first or second effective symbol periods is added to the obtained plurality of carrier signals. Is added as a guard interval signal before the first effective symbol period to obtain a carrier signal for each symbol period,
An orthogonal frequency division multiplexing signal transmitting device for transmitting the obtained carrier signal to a spatial transmission path, wherein a carrier signal that is discontinuous in an adjacent symbol period among a plurality of carrier signals for each symbol period And a discontinuous carrier detecting means (21) for detecting a carrier signal detected in the second effective symbol period before a guard interval signal added to a carrier signal detected as a discontinuous carrier signal by the discontinuous carrier detecting means. Amplitude control means (14a, 1a) for attenuating the amplitude of the carrier signal
4b, ..., 14n, 15a, 15b, ..., 15
n) and signal combining means (16) for combining the plurality of carrier signals obtained by the amplitude control means to obtain the orthogonal frequency division multiplex signal. Transmission device.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of a method for transmitting an orthogonal frequency division multiplexed signal and an apparatus for transmitting an orthogonal frequency division multiplexed signal according to the present invention will be described below. FIG. 1 shows a configuration of an orthogonal frequency division multiplex signal transmitting apparatus according to the embodiment, which will be described below with reference to the drawings.

The orthogonal frequency division multiplex signal transmitting apparatus shown in FIG. 1 includes an S / P mapping circuit 11, an IFFT 12, a guard interval adding circuit 13, an amplitude limiting circuit 14a,
14b,..., 14n, switches 15a, 15b,
.., 15n, a P / S / D / A circuit 16, a quadrature modulation circuit 17, a discontinuous data detection circuit 21, and an amplitude limit control circuit 22.

Next, the operation of the orthogonal frequency division multiplexed signal transmitting apparatus configured as described above will be described. First, a digital information signal transmitted in a serial data format transmitted by the transmission device is connected to a discontinuous data detection circuit 21 described later.
And is supplied to the S / P mapping circuit 11, where the serial data (S) is converted into parallel (P) format data.

The data converted into the parallel format is multi-level QAM (Quadrature Amplitude Modulatio) by each carrier constituting the orthogonal frequency division multiplexed signal.
n) Modulation is performed. In accordance with the value of the supplied parallel data, mapping is performed at a signal point position on an IQ plane defined by a real axis and an imaginary axis for performing multi-level QAM modulation, and the mapping is performed. I (In-phase) axis according to position,
And an IQ signal corresponding to the Q (quadrature) axis.

The IQ signal generated for each of a plurality of carriers constituting OFDM is an IFFT (Inverse fast Fou
carrier transform (inverse Fourier transform) circuit 12, where each of the plurality of carriers is QAM-modulated OFDM based on the supplied plurality of IQ signals.
Modulated carrier signals constituting the signal are generated, and the generated modulated carrier signals are supplied to the guard interval adding circuit 13.

The signal supplied to the guard interval circuit 13 is a signal in an effective symbol period corresponding to a window period during which the IFFT circuit operates, and a signal at the rear end corresponding to the guard interval in the effective symbol period is copied. , And the obtained signals are arranged before the effective symbol period to obtain modulated carrier signals to which a guard interval is added. The obtained carrier signals, that is, carrier 0 (IQ), Carrier 1
,..., 15n and an amplitude limiting circuit 14a provided for each carrier.
, 14b,..., 14n.

The amplitude limiting circuits 14a, 14b,.
.., 14n limit the amplitude of each of the supplied carrier signals by a method described later, and each of the carrier signals subjected to the amplitude limitation is switched by a switch 15a,
, 15n, and the switching units 15a, 15b,..., 15n generate the amplitude limit control circuit 22 based on the discontinuous data detected by the discontinuous data detection circuit 21. One of the two supplied signals is switched under the control of a control signal for each carrier, and a signal obtained by the switching is supplied to a plurality of input terminals of the P / SD / A circuit 16.

In the P / S / D / A circuit 16, the parallel signals (P) supplied from the plurality of switches 15a, 15b,..., 15n are rearranged for each of the I signal and the Q signal. Each of the converted digital signals is converted to an analog I signal and Q signal by a D / A converter, and the converted signal is supplied to a quadrature modulator 17. You.

In the quadrature modulator 17, the supplied I signal and Q signal are subjected to quadrature modulation according to the existing technology on the carrier, and the quadrature frequency division multiplexed signal obtained by the quadrature modulation is not shown. It is adapted to be supplied to a spatial transmission path.

The supplied orthogonal frequency division multiplex signal is received by an orthogonal frequency division multiplex signal receiving device (not shown). The receiving device is configured to be complementary to the transmitting device and receives the signal. A plurality of carrier signals composed of an I signal and a Q signal from an orthogonal frequency division multiplex signal, that is, carrier 0 (IQ) and carrier 1 (I
,..., And each of the I signal and the Q signal of the carrier n (IQ) are added and synthesized for each of the signals, and the added and synthesized signal is not shown in the FFT (Fast Fourier).
Transform: Fast Fourier Transform), where the carrier signal subjected to Fast Fourier Transform and subjected to each multi-level QAM modulation is converted into an I (In-phase) axis and a Q (quadrature) corresponding to each mapping position. ) Demodulated as an IQ signal for each carrier corresponding to the axis.

The signal point and the information signal are decoded based on the IQ signal for each carrier obtained by demodulation in this way, and the transmitted information signal is obtained. The operation of the FFT circuit on the receiver side needs to be in synchronization with the IFFT circuit on the transmitter side.

In order to maintain the synchronization relationship, a predetermined carrier among a plurality of carriers constituting the OFDM is defined as a synchronization carrier signal for a receiving device. "A clock signal for operating the FFT by the defined synchronization carrier signal is used. Is transmitted.

The synchronizing signal generates the same signal in a plurality of effective symbol periods, and the receiving apparatus drives a demodulation circuit such as an FFT based on the same signal in the plurality of effective symbol periods. Generated as a clock signal for

FIG. 2 shows an example of the waveform of the synchronization signal. The signal shown in the figure is an example of a case where a signal having three cycles in an effective symbol period is used as a synchronization signal.

In this case, 1/1 of the effective symbol period
Period 3 is set as a guard interval,
The signal waveform of 1/3 on the right side of the effective symbol period in the figure is obtained by copying, and is inserted on the left side of the effective symbol period.

The guard interval signal thus inserted is continuous on the right side due to the nature of FFT, but may be continuous or discontinuous on the left side.

In this example, since the same signal exists for each effective symbol period, and the wavelength of the signal existing in the guard interval is an integer wavelength, the signal waveform becomes continuous even on the left side of the guard interval. Therefore, such a signal having a continuous waveform is a desirable signal for generating a stable synchronization signal.

In this manner, the IFFT circuit 12 and the FFT circuit in the receiving apparatus can be easily synchronized by using the modulated signal having an integer wavelength within the guard interval period as the pilot signal for synchronizing the receiving apparatus. And information signals can be transmitted and received.

However, in the case of a modulated carrier signal used for transmitting an information signal, the wavelength in the guard interval is not an integer wavelength, and the information signal transmitted in each effective symbol period is different. A discontinuous signal is generated in the signal portion in front.

FIG. 3 shows an example of a carrier signal that becomes discontinuous before such a guard interval. The figure shows
This shows a case where a signal of one cycle exists in an effective symbol period, and a signal of a predetermined period of the effective symbol period is inserted into a guard interval as a guard interval signal.

As exemplified above, a normal carrier signal is a signal of the immediately preceding effective symbol period,
A discontinuous signal is generated between the next guard interval and the discontinuous signal causes unnecessary leakage components to adjacent frequency bands.

Therefore, the level of the carrier signal is reduced before and after the discontinuous portion to reduce the unnecessary leakage signal component. FIG. 4 shows a waveform of the modulated signal in which the level of the modulated signal is reduced in the discontinuous signal portion.

In the figure, the modulated signal of the signal portion shown by the dotted line is attenuated from the last portion of the immediately preceding effective symbol period, the maximum amount of attenuation is given in the discontinuous signal portion, and then the guard interval The signal obtained when the attenuation is reduced near the center is shown by a solid line.

In this way, a discontinuous signal is converted into a continuous signal. FIG. 5 illustrates a frequency spectrum of the OFDM signal thus obtained. In the figure, the horizontal axis represents the frequency with respect to the center carrier frequency, and the vertical axis represents the level of the signal spectrum.

The curve shown in (a) is the spectrum of an OFDM signal to which a guard interval has been added.
Unnecessary leakage signal components exist on the left and right sides of the signal portion shown flat in the center.

The unnecessary leak signal component outside such a band is
This will cause interference with other communication parties performed in the adjacent band. There is a method to set the frequency band used by other communication parties to a position of a distant frequency in order to avoid the interference, but such a setting of the frequency will use a wide band for communication. .

In OFDM, the frequency spectrum used for communication can be made rectangular, and although it is a communication system having high frequency use efficiency, it is not preferable to lower such frequency use efficiency, and it is necessary to prevent such reduction.

The curve shown in FIG.
As shown in (1), the characteristic is obtained by lowering the level of the carrier signal near the start point of the guard interval to reduce unnecessary leakage signal components.

By limiting the amplitude value in the vicinity of the start point of the guard interval in this manner, unnecessary leakage frequency components can be reduced. Next, a circuit for that purpose will be described.

FIG. 6 shows an example of an orthogonal frequency division multiplex signal transmitting apparatus for limiting the amplitude value near the start point of the guard interval. The apparatus shown in this figure has the same configuration as that of the orthogonal frequency division multiplexing signal transmitting apparatus shown in FIG. 1, and the same reference numerals are given to the blocks having the same functions.

That is, the frequency division multiplexed signal transmitting apparatus shown in the figure has an S / P mapping circuit 11, an IFFT 12, a guard interval adding circuit 13, an amplitude limiting circuit 14,
/ S / D / A circuit 16 and quadrature modulation circuit 17.

In the apparatus shown in FIG.
A guard interval signal is added to all the carrier signals of the OFDM signal generated by the guard interval adding circuit 13, and all the carrier signals to which the guard interval signal is added are supplied to the amplitude limiting circuit 14.

The amplitude limiting circuit 14 limits the amplitude values of all carrier signals supplied to all the supplied carrier signals by the same operation as that shown in FIG. 4 described above. Such a carrier signal with reduced leakage signal power is obtained.

In this way, an OFDM signal with reduced leakage signal power is obtained by limiting the amplitude in the vicinity of the start point of the guard interval, which is a discontinuous signal generated at the start point of the guard interval. It is obtained by attenuating the components.

When the signal in the guard interval is continuous as shown in FIG. 2, the signal does not increase the leakage signal power. There is no need to limit the amplitude.

Further, the spectrum of a continuous signal without amplitude limitation is a single-frequency line spectrum,
The signal of the line spectrum can be obtained as a synchronization signal for OFDM signal demodulation with high accuracy and a stable frequency synchronization signal having a small phase error.

Further, OFFT 12 is used for the
In transmitting and receiving a signal that generates a DM signal and demodulates the OFDM signal using an FFT (not shown) in the receiver, the IFFT and the FFT need to be in a synchronized state.

In order to obtain the synchronization state, a specific carrier of the OFDM signal is defined as a pilot signal, and the operation timing of IFFT is transmitted from the transmitting apparatus to the receiving apparatus using the pilot signal. A clock signal with high frequency accuracy for driving the FFT is generated, and the generated clock signal is used to generate an FF.
T is driven to demodulate the OFDM signal.

As described above, the pilot signal for generating the clock signal needs to be supplied to the receiver as a signal with high frequency accuracy, the pilot signal also has a guard interval period, and has a guard interval. Is preferably not imposed at the starting point of.

Therefore, the transmitting apparatus detects signal continuity / discontinuity at the start point of the guard interval,
When the interval is continuous, the amplitude is not limited at the guard interval start point, and when the interval is discontinuous, the amplitude is limited.

The amplitude limiting circuit 14a in FIG.
14b,..., 14n, switches 15a, 15b,
.., 15n, the P / S / D / A circuit 16, the quadrature modulation circuit 17, the discontinuous data detection circuit 21, and the amplitude limit control circuit 22 are circuits for performing the operations. Will be described.

That is, a part of the digital signal supplied to the orthogonal frequency division multiplex signal transmission device is supplied to the discontinuous data detection circuit 21. Here, the phase of the modulation signal at the rear end of the symbol period generated based on the signal point given by the digital data supplied in the previous symbol period and the guard generated by the currently supplied signal. If the phase at the start point of the interval is the same, it is detected as continuous data.

In the simplest example, for a carrier that provides a modulation frequency such that the signal generated by the IFFT has an integer wavelength in the guard interval, data is supplied from the same signal point immediately before and now. At that time, the signal is continuous at the start point of the guard interval.

As another example, when the signal generated by the IFFT is a carrier that provides a modulation frequency that exists in the guard interval at an odd multiple of half a wavelength, the signal is point-symmetrical between the immediately preceding symbol period and the current symbol period. When data at a certain signal point is supplied, the signal is continuous at the start point of the guard interval.

In this way, the discontinuous data detection circuit 21 detects a continuous signal and a discontinuous signal at the start point of the guard interval, and supplies the detected signal to the amplitude limit control circuit 22.

The amplitude limit control circuit 22 switches the switches 15a, 15b,..., 15n in accordance with the detection result detected by the discontinuous data detection circuit 21 by the amplitude limit circuits 14a, 14b,. , A switching control signal for a signal supplied via the amplitude limiting circuit and a switching control signal for each signal supplied without the signal, and switches the generated signals to the switches 15a, 15b,.
n.

Therefore, the switches 15a, 15b,...
.., 15n indicate the signal that does not pass through the amplitude limiting circuit for a signal that is continuous at the first position of the guard interval, and the signal that does not pass through the amplitude limiting circuit for a signal that is considered not to be continuous. It operates to supply the signal to the P / SD / A converter.

In this manner, OFD is performed based on the carrier signal obtained through or not through the amplitude limiting circuit.
An M signal is generated, and the generated OFDM signal is converted to a transmission frequency band by a high-frequency circuit (not shown).
The signal is amplified by a high-frequency amplifier circuit (not shown) and radiated to a space transmission line by an antenna (not shown).

In the above description, the OFDM signal generated by providing one guard interval for each information symbol has been described. Next, the same information signal is transmitted by two adjacent information symbols and the first information symbol is transmitted. An example of an OFDM signal generated by adding a guard interval to an information symbol will be described.

FIG. 7 shows an OFDM signal when the same information signal is transmitted by the two information symbols.
In the figure, the horizontal axis represents time, the vertical axis represents signal level, and the depth direction represents frequency, and the signal levels of carrier 0, carrier 1, and carrier n from the back are shown.

In the signal shown here, a first information symbol and a second information symbol are arranged following a guard interval, and the same digital signal is transmitted in the first and second information symbols. In addition, a signal at the rear of the first or second information symbol is copied and added to the guard interval immediately before the first information symbol.

The amplitude limitation is performed for the period of the second information symbol arranged before the start of the guard interval. In this case, since the information signal of the same content is transmitted in the first and second information, the frequency utilization rate for the information is reduced, but the signals obtained by demodulating the first and second information signals must be compared. Thus, the protection characteristics against data errors can be improved.

Further, since the operating speed of the amplitude limiting circuit may be lower than that of the example having one symbol period as described above, it is suitable for configuring a transmitting / receiving device for transmitting a high frequency signal. I have.

However, since the carrier is attenuated by the amplitude limiting circuit for a long time, it is not suitable for transmitting the synchronous clock pilot signal.

Therefore, a continuous carrier signal is used as the pilot signal and the reference signal used for decoding the OFDM signal, and the amplitude limitation is not performed on the continuous carrier signal, so that a high quality signal is obtained. A synchronization pilot signal and a reference signal are transmitted.

FIG. 8 shows a change in carrier signal level when amplitude limitation is not performed on continuous signals. In the figure, the portions indicated by thin halftone dots are portions where the carrier signal is continuous, and indicate the portion of the carrier that is not subjected to amplitude limitation, and a carrier signal without such amplitude limitation is generated. The data is transmitted by the same circuit block as described above.

As described above, two examples have been shown, namely, a case where one information symbol is used for an information signal to be transmitted and a case where transmission is performed by using two information symbols. signal,
In addition, the transmission quality of the reference signal can be improved, and an orthogonal frequency division multiplexing transmission device having a stable quality can be configured.

The multi-level QAM modulation is 16 QA
M, and a digital modulation system that defines and defines integer signal points such as 16, 64 given by 64QAM modulation,
If the multivalued value is 4, QPSK (quadrature p
hase shift keying) modulation method, and if the modulation method is 2, PSK (phase shift keying) and FSK (frequenc
y shift keying) digital modulation method.

The multi-level QAM digitally modulated carrier signal is generated by IFFT. The above-mentioned IFFT outputs digitally modulated carriers individually. It is different from IFFT which supplies as an output signal.

Accordingly, the IFFT may be an oscillator capable of supplying a plurality of carrier signal outputs corresponding to the supplied signal points. For example, the oscillator stores the waveform of the carrier signal to be generated in a storage element such as a ROM. Aside
It is configured such that the readout position is varied according to the defined signal point to provide phase modulation, and the readout value is multiplied by a constant to provide amplitude modulation. Is also good.

The orthogonal frequency division multiplexing signal transmitting apparatus or orthogonal frequency division multiplexing signal transmission method configured as described above uses a real axis for modulating each carrier constituting OFDM with a multilevel QAM signal. And a plurality of signal points are defined on a two-dimensional plane composed of
A plurality of carrier signals modulated by allocating information signals supplied to the defined signal points for each effective symbol period are obtained, and a part of the carrier signal is added to the obtained plurality of carrier signals by a guard interval. By adding the signal as a signal, the carrier signal is obtained as a carrier signal for each symbol period. When the obtained carrier signal is transmitted to the spatial transmission path, among a plurality of carrier signals for each symbol period,
A continuous carrier is detected in an adjacent symbol period, and when the continuous carrier is detected, the amplitude is set so as to attenuate the amplitude of the carrier signal near a start point of a guard interval signal added to the carrier signal. Since the orthogonal frequency division multiplexing signal is obtained based on a plurality of carrier signals obtained by performing the control, it is possible to reduce the generation of the unnecessary leakage spectrum based on the discontinuous signal at the start point of the guard interval signal. A pilot signal related to synchronization for an OFDM demodulator or an OFDM demodulator can be used to transmit a continuous signal at the start point of a guard interval signal as a continuous carrier without controlling the carrier amplitude. The reference signal related to the reference level information during signal demodulation is a key. Low levels of unwanted leakage spectrum because you have to transmit high quality without rear reduction, and stable, it is possible to configure the transmission apparatus for an orthogonal frequency division multiplex signal transmission with a transmission characteristic.

Then, in a transmitting apparatus which modulates the same information signal in the first and second symbol periods to generate and transmit an orthogonal frequency division multiplexed signal, in the guard interval in the second symbol period Even in the case where the amplitude is limited for a signal having no continuous signal, it is possible to configure a transmitting apparatus for orthogonal frequency division multiplex signal transmission having the same effect as described above.

[0082]

According to the first aspect of the present invention, it is possible to provide a transmission method for transmitting an orthogonal frequency division multiplex signal having a low level of unnecessary leak spectrum and having stable transmission characteristics.

According to the second aspect of the present invention, when transmitting the first and second effective symbol periods with the same digital information, the orthogonal frequency division having a low unnecessary leak spectrum level and stable transmission characteristics. There is an effect that a transmission method for multiplex signal transmission can be provided.

According to the third aspect of the present invention, in addition to the effects of the first and second aspects, in particular, a reference signal for decoding a received signal can be stably transmitted with high quality. There is an effect that it is possible to provide a transmission method for orthogonal frequency division multiplex signal transmission having a low level of unnecessary leak spectrum and having stable transmission characteristics.

According to the fourth aspect of the present invention, in addition to the effects of the first and second aspects, in particular, since a pilot signal for reception synchronization can be transmitted stably and with high quality, it is unnecessary. There is an effect that it is possible to provide a transmission method for orthogonal frequency division multiplex signal transmission having a low level of leakage spectrum and having stable transmission characteristics.

According to the fifth aspect of the invention, there is an effect that a configuration of an orthogonal frequency division multiplex signal transmitting apparatus having a low level of unnecessary leak spectrum and having stable transmission characteristics can be provided.

According to the sixth aspect of the present invention, when transmitting the first and second effective symbol periods using the same digital information, the orthogonal frequency division having a low unnecessary leak spectrum level and a stable transmission characteristic. There is an effect that the configuration of the multiplex signal transmitting device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram of an orthogonal frequency division multiplex signal transmitting apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating a relationship between an effective symbol period and a signal of a guard interval according to an embodiment of the present invention.

FIG. 3 is a diagram illustrating a relationship between an effective symbol period and a signal that is discontinuous in a guard interval according to an embodiment of the present invention.

FIG. 4 is a diagram for explaining reduction of unnecessary leak spectrum caused by addition of a guard interval according to the embodiment of the present invention.

FIG. 5 is a diagram for explaining an unnecessary leak spectrum caused by adding a guard interval according to the embodiment of the present invention.

FIG. 6 is a block diagram of an orthogonal frequency division multiplex signal transmitting apparatus according to an embodiment of the present invention.

FIG. 7 is a diagram showing a spectrum of an orthogonal frequency division multiplexed signal for explaining an embodiment of the present invention.

FIG. 8 is a diagram showing how the amplitude of each carrier of an orthogonal frequency division multiplex signal is limited according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 11 S / P mapping circuit 12 IFFT 13 Guard interval adding circuit 14 Amplitude limiting circuit 14a, 14b,..., 14n Amplitude limiting circuit 15a, 15b,. 17 Quadrature modulation circuit 21 Discontinuous data detection circuit 22 and amplitude limit control circuit

Claims (6)

[Claims] A plurality of signal points are defined on a two-dimensional plane composed of a real number axis and an imaginary number axis, and information signals to be supplied to the defined signal points are allocated and modulated for each effective symbol period. A plurality of carrier signals are obtained, and a part of the signal of the effective symbol period is added to the obtained carrier signal as a guard interval signal to obtain a carrier signal for each symbol period, and the obtained carrier signal is obtained. For transmitting an orthogonal frequency division multiplexed signal to a spatial transmission path, comprising: detecting a carrier signal that is discontinuous in an adjacent symbol period among a plurality of carrier signals for each symbol period. And a guard added to the carrier signal detected as a discontinuous carrier signal in the first step. A second step of attenuating the amplitude of the carrier signal in the vicinity of the start point of the Tarval signal; and a third step of combining the plurality of carrier signals obtained in the second step to obtain the orthogonal frequency division multiplexed signal. A method for transmitting an orthogonal frequency division multiplexed signal, comprising the steps of: 2. A method according to claim 1, wherein a plurality of signal points are defined on a two-dimensional plane constituted by a real axis and an imaginary axis, and information signals supplied to the defined signal points are allocated. Next, a plurality of carrier signals modulated for each second effective symbol period to be arranged are obtained, and a carrier signal modulated for each of the first or second effective symbol periods is added to the obtained plurality of carrier signals. Is added as a guard interval signal before the first effective symbol period to obtain a carrier signal for each symbol period, and an orthogonal frequency division multiplexed signal for transmitting the obtained carrier signal to a spatial transmission path. A first step of detecting a carrier signal that is discontinuous in an adjacent symbol period among a plurality of carrier signals for each symbol period, Attenuating the amplitude of the carrier signal in the second effective symbol period before the guard interval signal added to the carrier signal detected as a discontinuous carrier signal in the first step of And transmitting the orthogonal frequency division multiplexed signal by combining the plurality of carrier signals obtained in the second step. 3. The method of detecting a discontinuous carrier signal in the first step does not detect a carrier signal defined as a reference signal among the plurality of carrier signals as a discontinuous carrier signal. The method for transmitting an orthogonal frequency division multiplexed signal according to claim 1 or 2, wherein: 4. The method according to claim 1, wherein the detecting of the discontinuous carrier signal in the first step includes detecting a carrier signal defined as a receiver synchronization signal among the plurality of carrier signals as a discontinuous carrier signal. 3. The method of transmitting an orthogonal frequency division multiplexed signal according to claim 1, wherein the signal is not detected. 5. A plurality of signal points are defined on a two-dimensional plane constituted by a real axis and an imaginary axis, and information signals supplied to the defined signal points are allocated to each of the effective symbol periods and modulated. A plurality of carrier signals are obtained, and a part of the signal of the effective symbol period is added to the obtained carrier signal as a guard interval signal to obtain a carrier signal for each symbol period, and the obtained carrier signal is obtained. For transmitting a signal to a spatial transmission path, wherein a discontinuous carrier for detecting a carrier signal that is discontinuous in an adjacent symbol period among a plurality of carrier signals for each symbol period. Detection means, and a carrier signal detected as a discontinuous carrier signal by the discontinuous carrier detection means. Amplitude control means for attenuating the amplitude of the carrier signal in the vicinity of the start point of the guard interval signal, and signal combining for obtaining the orthogonal frequency division multiplexed signal by combining a plurality of carrier signals obtained by the amplitude control means. Means for transmitting an orthogonal frequency division multiplexed signal. 6. A method according to claim 1, wherein a plurality of signal points are defined on a two-dimensional plane formed by a real axis and an imaginary axis, and information signals supplied to the defined signal points are allocated. Next, a plurality of carrier signals modulated for each second effective symbol period to be arranged are obtained, and a carrier signal modulated for each of the first or second effective symbol periods is added to the obtained plurality of carrier signals. Is added as a guard interval signal before the first effective symbol period to obtain a carrier signal for each symbol period, and an orthogonal frequency division multiplexed signal for transmitting the obtained carrier signal to a spatial transmission path. A transmission device, comprising: a discontinuous carrier detection unit that detects a carrier signal that is discontinuous in an adjacent symbol period among a plurality of carrier signals for each symbol period. Amplitude control means for attenuating the amplitude of the carrier signal in a second effective symbol period before a guard interval signal added to the carrier signal detected as a discontinuous carrier signal by the discontinuous carrier detection means An orthogonal frequency division multiplex signal transmitting apparatus, comprising: a signal synthesizing means for obtaining the orthogonal frequency division multiplex signal by synthesizing a plurality of carrier signals obtained by the amplitude control means.