JPH07283806A - Orthogonal frequency division multiplex modulation signal transmission system - Google Patents

Abstract

PURPOSE:To send each OFDM modulation signal at a maximum bit rate per a transmission frequency band by allocating a transmission band in a form that an adjacent spectrum is in contact with spectrums of each OFDM modulation signal and locking a symbol clock phase. CONSTITUTION:At first frequency intervals DELTAf1, DELTAf2 of a carrier of 1st and 2nd OFDM modulation signals are set equal. An interval fbfa between a maximum carrier frequency fa of a 1st signal and a minimum carrier frequency fb of a 2nd signal is selected to be an integral multiple of DELTAf=DELTAf1=DELTAf2. A symbol clock phase of a 1st OFDM modulation signal and that of a 2nd OFDM modulation signal are locked to each other thereby making ideally symbol switching position of the both coincident with each other. Then the setting above is made to set a value N of NDELTAf=fb-fa to be an integer being one or over, then a DFT window applied discrete Fourier transformation to the 1st and 2nd OFDM modulation signals, then the relation of the 1st and 2nd OFDM modulation signals is set to be a relation as shown in figure. Thus, no interference disturbance is caused between them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to Orthogonal Frequency Division Multiplexing (OFDM) which is a modulation method suitable for terrestrial digital television broadcasting or digital audio broadcasting.
ency division multiplexing) digital modulation method, and more particularly to an orthogonal frequency division multiplex modulation signal transmission method used when transmitting a plurality of OFDM modulation signals using a certain transmission frequency band.

SUMMARY OF THE INVENTION The present invention is directed to orthogonal frequency division multiplexing (OFDM).
plexing) related to a transmission method of modulated signals, and when transmitting a plurality of OFDM modulated signals using a certain transmission frequency band, a guard band for preventing interference due to mutual interference between spectra of the OFDM modulated signals. Without setting, the transmission band of each OFDM modulated signal is allocated in such a manner that the spectra of adjacent OFDM modulated signals are in contact with each other,
Furthermore, by locking the symbol clock phase of each OFDM modulated signal, the maximum number of OFDM modulated signals can be allocated within a given transmission frequency band without causing interference between different OFDM modulated signals. Thus, data is transmitted at the maximum bit rate per transmission frequency bandwidth.

[0003]

2. Description of the Related Art Currently, OF is a modulation method suitable for terrestrial digital television broadcasting or digital audio broadcasting.
DM modulation schemes are under study.

This OFDM modulation system is one type of multi-carrier modulation system, and includes QPSK modulation system and 16QAM system.
This is a modulation method in which a number of digital modulated waves obtained by modulating each carrier wave by a multi-value modulation method such as a modulation method or a 32QAM modulation method is added to generate one transmission signal. Then, the signal obtained by this receiving operation is sampled 2 ⁿ times in the DFT window (discrete Fourier transform window), and the sample (input data) obtained by this sampling operation is subjected to discrete Fourier transform to obtain each digital modulated wave. The amplitude and phase of the signal are detected to reproduce the digital television signal or digital audio signal included in the transmitted wave.

In this case, when a plurality of OFDM modulation signals are transmitted using a certain transmission frequency band, a guard band of several tens times the carrier frequency interval of OFDM is provided between each OFDM modulation signal as shown in FIG. It is indispensable to prevent the interference due to the interference between the OFDM modulated signals by providing each of these guard bands.

[0006]

However, when such frequency allocation is performed, the band utilization efficiency is reduced by the bandwidth corresponding to each of these guard bands. In particular, when the transmission bandwidth of the OFDM-modulated signal is relatively narrow, for example, about several 100 kHz, the guard band causes the band utilization efficiency to be extremely low.

In view of the above circumstances, the present invention, when transmitting a plurality of OFDM modulation signals using a certain transmission frequency band, does not cause interference due to mutual interference between different OFDM modulation signals, and is provided with a given transmission frequency. In the band
Orthogonal frequency division multiplex modulation signal transmission that can allocate the maximum number of OFDM modulation signals as much as possible and can transmit digital television broadcast signals and digital audio signals at the maximum bit rate per transmission frequency bandwidth It is intended to provide a scheme.

[0008]

In order to achieve the above object, an orthogonal frequency division multiplex modulation signal transmission system according to the present invention is characterized in that, in claim 1, a plurality of orthogonal frequency division multiplexes are used by using a certain transmission frequency band. When transmitting an (OFDM) modulated signal, a frequency band from frequency f ₁ to frequency f ₂ within the transmission frequency band is assigned as a transmission band of _one OFDM modulated signal, and this is used as a first OFDM modulated signal, and As a transmission band of one OFDM modulated signal, the frequency band from the frequency f ₁ to the frequency f ₂ is adjacent to the frequency band from the frequency f ₂ to the frequency f ₃ in the transmission frequency band.
To the second OFDM modulated signal, and among the transmission parameters of the first OFDM modulated signal and the second OFDM modulated signal, the frequency interval Δf of each carrier, the effective symbol length t _s , the guard interval length t _G is set to the same value, and the first OFDM
The frequency of the highest carrier among the carriers forming the modulated signal is the maximum carrier frequency f _a, and the frequency of the lowest carrier among the plurality of carriers forming the second OFDM modulated signal is the minimum carrier frequency f _b. The value of the difference f _b −f _a between the maximum and minimum carrier frequencies f _a and f _b is set to an integral multiple of the frequency interval Δf, and on the transmission side, the symbol clock phase of the first OFDM modulated signal and the symbol clock of the second OFDM modulated signal. The phases are locked to each other, and further, the first OFD on the receiving side in the service area of the first OFDM modulated signal and the second OFDM modulated signal.
In order to minimize interference caused by mutual interference between the M-modulated signal and the second OFDM-modulated signal, the first OFDM
It is characterized in that the phase difference between the symbol clock phase of the modulated signal and the symbol clock phase of the second OFDM modulated signal is set.

According to a second aspect, in the orthogonal frequency division multiplexing modulation signal transmission system according to the first aspect, the second O
The minimum carrier frequency f _b of the FDM modulated signal and the first OF
The difference f _b −f _{a from} the maximum carrier frequency f _a of the DM modulated signal
Is set to be equal to the frequency interval Δf of each carrier wave forming the first OFDM modulated signal and the second OFDM modulated signal.

A third aspect of the present invention is characterized in that, in the orthogonal frequency division multiplex modulation signal transmission system according to the first or second aspect, three or more OFDM modulation signals are assigned to a certain transmission frequency band.

According to a fourth aspect, in the orthogonal frequency division multiplex modulation signal transmission system according to any one of the first, second and third aspects, a plurality of OFs transmitted in a certain transmission frequency band are transmitted.
Of the DM modulated signals, one OFDM modulated signal is used as the reference of the symbol clock phase, and this phase reference O
The FDM modulation signal is used as a reference OFDM modulation signal, the transmission station of this reference OFDM modulation signal is used as a reference transmission station, and from this reference transmission station to other transmission stations, either a wireless line or a wired line is used. Transmitting the reference OFDM modulated signal, transmitting stations other than the reference transmitting station, receiving the reference OFDM modulated signal, and setting the symbol clock phase of the OFDM modulated signal transmitted from each of these transmitting stations to the reference OFDM modulated signal. It is characterized in that it is locked to the symbol clock phase of the modulation signal.

According to a fifth aspect of the present invention, in the orthogonal frequency division multiplexing modulation signal transmission system according to the fourth aspect, as a radio line for distributing the reference OFDM modulation signal from the reference transmission station to each of the transmission stations, It is characterized in that a broadcast wave from the reference transmitting station is used.

According to a sixth aspect of the present invention, in the orthogonal frequency division multiplex modulation signal transmission system according to any of the first, second and third aspects, a reference signal for providing a symbol clock phase of each of the OFDM modulation signals is provided. A reference signal is transmitted from the reference signal generating station that generates the reference signal to each transmitting station using either a wireless line or a wired line. At each transmitting station, the reference signal is received and each of these broadcasting stations It is characterized in that the symbol clock phase of the OFDM modulated signal transmitted from the device is locked to the phase of the reference signal.

Further, in claim 7, claims 1, 2, 3,
In the orthogonal frequency division multiplexing modulation signal transmission system according to any one of 4, 5, and 6, at least one of a symbol clock phase, a sampling clock phase, a frame clock phase, and a carrier wave phase of each OFDM modulation signal is locked. It has a feature.

[0015]

In the above structure, according to claim 1, a plurality of orthogonal frequency division multiplex (OF) signals are used by using a certain transmission frequency band.
When a DM) modulated signal is transmitted, a frequency band from frequency f ₁ to frequency f ₂ within the transmission frequency band is assigned as a transmission band of a certain OFDM modulated signal, and this is used as a first OFDM modulated signal. As a transmission band of one OFDM modulated signal of, the frequency band from the frequency f ₂ to the frequency f ₃ within the transmission frequency band is allocated in the form of being adjacent to the frequency band from the frequency f ₁ to the frequency f _2. As the second OFDM modulated signal, and among the transmission parameters of the first OFDM modulated signal and the second OFDM modulated signal, the frequency interval Δf of each carrier, the effective symbol length t _s , and the guard interval length t _G , respectively,
The frequencies of the highest carrier among the respective carriers forming the first OFDM modulated signal are set to the same value and the maximum carrier frequency f
_{Let a} be the frequency of the lowest carrier among the plurality of carriers that make up the second OFDM modulated signal, and the minimum carrier frequency f _b.
And the difference f between these maximum and minimum carrier frequencies f _a and f _b
the value of _b -f _a and an integer multiple of the frequency interval Delta] f, and the symbol clock phase of the 1OFDM modulated signal at the transmitting side, is locked together with the symbol clock phase of the 2OFDM modulated signal, yet a 1OFDM modulated signal and the 2 Within the service area of the OFDM modulated signal,
The phase difference between the symbol clock phase of the first OFDM modulated signal and the symbol clock phase of the second OFDM modulated signal so as to minimize interference interference due to mutual interference between the first OFDM modulated signal and the second OFDM modulated signal on the receiving side. When a plurality of OFDM modulation signals are sent using a certain transmission frequency band by setting
In the given transmission frequency band, the maximum number of OFDM modulation signals are allocated as much as possible without causing interference due to mutual interference between the DM modulation signals, whereby the maximum bit rate per transmission frequency bandwidth is obtained. It transmits television broadcast signals and digital audio signals.

According to a second aspect, in the orthogonal frequency division multiplex modulation signal transmission system according to the first aspect, the second O
The minimum carrier frequency f _b of the FDM modulated signal and the first OF
The difference f _b −f _{a from} the maximum carrier frequency f _a of the DM modulated signal
When a plurality of OFDM modulation signals are sent using a certain transmission frequency band by setting the value of s to be equal to the frequency interval Δf of each carrier wave forming the first OFDM modulation signal and the second OFDM modulation signal. , Different OF
In a given transmission frequency band, the maximum number of OFDM modulation signals can be allocated as much as possible without causing interference due to mutual interference between the DM modulation signals, whereby the maximum bit rate per transmission frequency bandwidth can be obtained. It transmits television broadcast signals and digital audio signals.

According to a third aspect of the present invention, in the orthogonal frequency division multiplex modulation signal transmission method according to the first or second aspect, by allocating three or more OFDM modulation signals in a certain transmission frequency band, Similar to 2, when transmitting a plurality of OFDM modulation signals using a certain transmission frequency band, it is possible within a given transmission frequency band without causing interference due to mutual interference between different OFDM modulation signals. The maximum number of OFDM-modulated signals is allocated as much as possible, whereby a television broadcast signal, a digital audio signal, etc. are transmitted at the maximum bit rate per transmission frequency bandwidth.

According to a fourth aspect, in the orthogonal frequency division multiplex modulation signal transmission system according to any one of the first, second, and third aspects, a plurality of OFs transmitted in a certain transmission frequency band are transmitted.
Of the DM modulated signals, one OFDM modulated signal is used as the reference of the symbol clock phase, and this phase reference O
The FDM modulation signal is used as a reference OFDM modulation signal, the transmission station of this reference OFDM modulation signal is used as a reference transmission station, and from this reference transmission station to other transmission stations, either a wireless line or a wired line is used. Transmitting the reference OFDM modulated signal, transmitting stations other than the reference transmitting station, receiving the reference OFDM modulated signal, and setting the symbol clock phase of the OFDM modulated signal transmitted from each of these transmitting stations to the reference OFDM modulated signal. By locking to the symbol clock phase of the modulation signal, when transmitting a plurality of OFDM modulation signals using a certain transmission frequency band, interference interference due to mutual interference between different OFDM modulation signals, as in claims 1, 2, and 3. Assigning the maximum possible number of OFDM modulated signals in a given transmission frequency band without Therefore transmitting a television broadcast signal and a digital audio signal at the maximum bit rate per transmission frequency bandwidth.

According to a fifth aspect of the present invention, in the orthogonal frequency division multiplex modulation signal transmission system according to the fourth aspect, as a radio line for distributing the reference OFDM modulated signal from the reference transmitting station to each of the transmitting stations, When a plurality of OFDM modulation signals are transmitted using a certain transmission frequency band by using the broadcast radio wave from the reference transmission station, interference between the OFDM modulation signals due to mutual interference is generated. In the given transmission frequency band, the maximum number of OFDM modulation signals are allocated as much as possible, thereby transmitting a television broadcast signal or a digital audio signal at the maximum bit rate per transmission frequency bandwidth.

According to a sixth aspect of the present invention, in the orthogonal frequency division multiplex modulation signal transmission system according to any one of the first, second and third aspects, a reference signal for providing a symbol clock phase of each of the OFDM modulation signals is provided. A reference signal is transmitted from the reference signal generating station that generates the reference signal to each transmitting station using either a wireless line or a wired line. At each transmitting station, the reference signal is received and each of these broadcasting stations When a plurality of OFDM modulated signals are sent using a certain transmission frequency band by locking the symbol clock phase of the OFDM modulated signal transmitted from the same to the phase of the reference signal. , Without causing interference due to mutual interference between different OFDM modulated signals,
Within the given transmission frequency band, the maximum number of OFDM modulated signals are allocated as much as possible, whereby a television broadcast signal, a digital audio signal, etc. are transmitted at the maximum bit rate per transmission frequency bandwidth.

Further, in claim 7, claims 1, 2, 3 and
The orthogonal frequency division multiplex modulation signal transmission system according to any one of claims 4, 5, and 6, wherein at least one of a sampling clock phase, a frame clock phase, and a carrier wave phase of each OFDM modulation signal is locked. Similar to Nos. 2, 3, 4, 5, and 6, when a plurality of OFDM modulation signals are transmitted using a certain transmission frequency band, they are given without causing interference due to mutual interference between different OFDM modulation signals. In the transmission frequency band, the maximum number of OFDM modulation signals are assigned as much as possible, whereby the television broadcast signal and the digital audio signal are transmitted at the maximum bit rate per transmission frequency bandwidth.

[0022]

【Example】

<< Outline of OFDM Modulation Method >> First, an outline of the OFDM modulation method will be described before a detailed description of the orthogonal frequency division multiplexing modulation signal transmission method according to the present invention.

The OFDM modulation method is one type of multi-carrier modulation method, and a modulation method in which a large number of carriers are set in advance as shown in FIG. 8, for example, a QPSK modulation method, a 16QAM modulation method, a 32QAM modulation method, etc. The basic principle is to generate a OFDM transmission symbol by adding digital modulated waves obtained by modulating by a modulation method such as the multi-valued modulation method.

In this case, each transmission symbol of OFDM is effective symbol period t indicating the information to be transmitted.
_s and a period called a guard interval t _{G in} which the signal waveform of the effective symbol period t _s is cyclically repeated in order to reduce the influence of multipath.
The OFDM transmission signal waveform in the effective symbol period t _s of each transmission symbol is represented by the following equation.

[0025]

[Equation 1] However, X (t): the value c _k of the transmission signal waveform at time _{t: c k = a k +} ib k transmitted data represented by f _0: frequency f _k of the first carrier: expressed as f _k = k / t _s The frequency of the k-th carrier t _s : the length of the effective symbol period M-1: the value indicating the number of the final carrier k: the value indicating the number of the carrier Re [ω]: a notation symbol indicating the real part of the complex function ω Then, if this equation (1) is expanded, the following equation is obtained.

[0026]

[Equation 2] As is apparent from the equation (2), in the OFDM modulation method, two real numbers a _k and b _k can be transmitted on each carrier in each transmission symbol period. Then, the frequency interval Δf of each carrier is calculated as the reciprocal 1 / of the effective symbol period t _s.
By making it equal to t _s , the zero point of the spectrum of each digital modulated wave is made to coincide with the carrier frequency of the adjacent digital modulated wave as shown in FIG. 9, and this is subjected to discrete Fourier transform on the receiving side to obtain each carrier frequency component. It is possible to prevent mutual interference between the carriers when the amplitude and the phase of the are obtained.

Then, the above-described processing is performed for each transmission symbol, and as shown in FIG. 10, two to three synchronization / service identification symbols are added to several hundreds of information transmission symbols. One frame of OFDM is constructed by this and transmitted.

<< Outline of OFDM Demodulation Method >> On the other hand, the receiving side demodulates the OFDM and reproduces the digital television broadcast signal and the digital audio signal included in the OFDM by the procedure described below.

First, for each transmission symbol constituting the received OFDM, a DFT window is set at a position where the entire window is completely included in the transmission symbol period t _s + t _G. The length of the DFT window is equal to the effective symbol period t _s .

In this case, as shown in FIG. 11, the position and length of the DFT window are strictly set for each transmission symbol so that the symbol switching point does not enter the DFT window.

Next, in this DFT window, O
Normally, the time base waveform of the FDM is sampled 2 ⁿ times (n is a positive integer) to obtain input data for discrete Fourier transform, and discrete Fourier transform is performed on each of these input data to obtain each carrier frequency component. , And reproduces a digital television broadcast signal or digital audio signal composed of each transmission symbol.

<< Description of Embodiments >> Next, the above-mentioned OFDM
An embodiment of the orthogonal frequency division multiplexing modulation signal transmission system according to the present invention, which is based on the modulation system and the OFDM demodulation system, will be described in detail.

<Description of Each Carrier Frequency and DFT Window of Each OFDM Modulated Signal> First, when demodulating OFDM, only when the position and length of the DFT window satisfy the above conditions, the discrete Fourier transform is performed on the receiving side. In the subsequent OFDM spectrum, the zero point of the spectrum of each digital modulated wave coincides with the carrier frequency of the adjacent digital modulated wave as shown in FIG.

On the other hand, when at least one of the position and the length of the DFT window does not satisfy the above condition, the spectrum of the other carrier does not become zero at each carrier frequency, and the carrier between the carriers does not become zero. Interference occurs.

Similarly, when two or more OFDM modulated signals are arranged adjacent to each other on the frequency axis, different OFDs are used.
It is necessary to set the same conditions as the above-mentioned conditions so that interference interference due to mutual interference does not occur between the carriers of the M-modulated signal.

Therefore, in the present invention, when arranging a plurality of OFDM modulation signal spectra in a certain transmission frequency band, the zero point of the spectrum of one digital modulation wave between adjacent OFDM modulation signals is different.
In order to match the carrier frequencies of other carriers, and to prevent the symbol switching points of adjacent OFDM modulated signals from entering the DFT window of one OFDM modulated signal, the following procedure is performed. Each OFDM
The transmission band of the modulated signal is determined and the phase relationship is set.

(A) First, any two adjacent OFDs
When the M modulation signal is referred to as the first OFDM modulation signal and the second OFDM modulation signal from the low frequency side, respectively,
Frequency interval Δf of a plurality of carrier waves forming the modulated signal
₁ and the frequency interval Δf ₂ of a plurality of carriers forming the second OFDM modulated signal are set to the same value.

[0038] (B) and the maximum carrier frequency f _a of the 1OFDM modulated signal, the distance f _b -f _a and the minimum carrier frequency f _b of the 2OFDM modulated signal, constitute the first 1OFDM modulated signal and a 2OFDM modulated signal It is assumed that the frequency interval of a plurality of carrier waves is an integral multiple of Δf = Δf ₁ = Δf ₂ . That is, the _{N · Δf = f b -f a} (N is an integer).

(C) The symbol clock phase of the first OFDM modulated signal and the symbol clock phase of the second OFDM modulated signal are locked to each other, and ideally, the symbol switching positions of both are made coincident with each other.

Then, by making the settings shown in (A) and (B) and setting N shown in (C) to an integer of 1 or more, for example, "3", in the above-mentioned DFT window, the first OFDM When the modulation signal and the second OFDM modulation signal are subjected to the discrete Fourier transform, the spectrum of the first OFDM modulation signal and the spectrum of the second OFDM modulation signal can be made to have the relationship shown in FIG. 1, whereby interference between them can be prevented. Can be prevented.

In this case, even when the symbol clock phase of the first OFDM modulated signal and the symbol clock phase of the second OFDM modulated signal do not completely match, the symbol clock phases are locked to each other and the phase shift value on the receiving side is set. If it is smaller than the guard interval length,
According to the symbol clock phase shift value tD as shown in
By setting the DFT window to an appropriate position,
It is possible to prevent interference from occurring between the first and second OFDM modulated signals.

At this time, if the symbol clock phase of the first OFDM modulated signal and the symbol clock phase of the second OFDM modulated signal are not locked, or the symbol clock phase shift value t _D becomes large as shown in FIG. Of the first and second OFDM modulated signals, for example, in the DFT window of the first OFDM modulated signal, the second O
When the symbol switching point of the FDM modulated signal is invading, the spectral relationships shown in FIG. 1 are not established, so that the side lobes of the respective spectra interfere with each other, resulting in interference.

That is, on the receiving side, it is necessary to suppress the phase shift value t _D between the symbol clock phase of the first OFDM modulated signal and the symbol clock phase of the second OFDM modulated signal within a predetermined value, for example, guard interval t _G. Becomes

Similarly, when arranging three or more OFDM modulated signals in a certain transmission frequency band, it is possible to prevent interference of each OFDM modulated signal by satisfying the above condition.

In this embodiment, when a plurality of OFDM modulation signals are assigned to a certain transmission frequency band,
In the setting of (C), by setting the value of the integer N to N = 1, the spectrum of each OFDM modulated signal can be made completely continuous without causing interference due to mutual interference as shown in FIG. You can

<Locking Method of Symbol Clock Phases of OFDM Modulated Signals> Further, in order to lock the symbol clock phases of different OFDM modulated signals,
Since it is necessary to share the phase reference signal among the OFDM transmitting stations, in this embodiment, the symbol clock phases of different OFDM modulated signals are set to each other by using one of the following two methods. It's locked.

The first phase locking method is a method of using one of a plurality of OFDM modulated signals as a phase reference signal, and as shown in FIG. 5, one of the OFDM transmitting stations, for example, the first OFDM transmitting station. The first OFDM modulated signal (reference OFDM modulated signal) transmitted from the above is used as a phase reference, and the other second OFDM transmitting station to the nth OFDM transmitting station receive the first signal.
The OFDM modulated signal is received, and the symbol clock phase of the second OFDM transmission signal to the nth OFDM modulation signal transmitted from the second OFDM transmission station to the nth OFDM transmission station is locked with the symbol clock phase of the first OFDM modulation signal as a reference phase. Let

The second phase-locking method is such that when the symbol clock phase is locked as shown in FIG.
This is a method of using a phase reference signal other than the modulated signal, as shown in FIG. 7, one of the first OFDM transmission station to the nth OFDM transmission station, or these first OFDM transmission station to the nth OF.
The reference signal transmitting station installed independently of the DM transmitting station modulates the 1st OFDM modulated signal transmitted from the 1st OFDM transmitting station to the nth OFDM transmitting station by the QPSK modulation method having the same symbol rate as the nth OFDM modulated signal. A single carrier digital modulation signal is generated, this is transmitted as a phase reference signal, and the phase reference signal is received by each of the first OFDM transmitter station to the nth OFDM transmitter station, and the symbol clock phase of this phase reference signal is used as the reference phase. As the first OFDM transmitting station to the nth
First OFDM modulated signal transmitted from OFDM transmitting station
Lock the symbol clock phase of the n-th OFDM modulated signal.

By these first and second phase locking methods, not only the symbol clock phase but also the first OF
The sampling clock phase, frame clock phase, carrier wave phase, etc. of the DM transmitting station to the nth OFDM transmitting station may be locked.

<Effects of Embodiment> As described above, in this embodiment, the transmission bands of the respective OFDM modulation signals are allocated so that the spectra of the adjacent OFDM modulation signals are in contact with each other.
Further, by locking the symbol clock phase of each OFDM modulated signal, the maximum number of OFDM modulated signals can be allocated within a given transmission frequency band without causing interference between different OFDM modulated signals. be able to.

For example, assuming that the transmission bandwidth of each OFDM modulated signal is 200 kHz, the conventional OFD shown in FIG.
In the M modulation signal transmission method, the band utilization efficiency is approximately doubled in the OFDM modulation signal transmission method according to the present invention shown in FIG. 4, as compared with the case where a guard band of 200 kHz is set between each OFDM modulation signal spectrum. be able to.

[0052]

As described above, according to the present invention, in claims 1 to 7, a plurality of O's are used by using a certain transmission frequency band.
When sending an FDM modulated signal, the maximum number of OFs possible in a given transmission frequency band without causing interference due to mutual interference between different OFDM modulated signals.
A DM modulated signal can be assigned, whereby a digital television broadcast signal, a digital audio signal, etc. can be transmitted at the maximum bit rate per transmission frequency bandwidth.

[Brief description of drawings]

FIG. 1 is a diagram showing a spectral relationship between adjacent OFDM modulated signals when a transmission band of each OFDM modulated signal is set and a phase relationship is set in one embodiment of the present invention.

FIG. 2 is a diagram illustrating a first OF in a receiving side according to an embodiment of the present invention.
DF when the phase shift value t _D between the DM modulation signal and the second OFDM modulation signal is smaller than the guard interval length t _G
It is a figure which shows a T window setting example.

FIG. 3 is a diagram showing an example of a phase relationship when a symbol switching position of a second OFDM modulation signal enters a DFT window of a first OFDM modulation signal.

FIG. 4 is a diagram showing a frequency spectrum when a plurality of OFDM modulation signals are assigned to an arbitrary transmission frequency band as one embodiment of the present invention.

FIG. 6 shows a plurality of O's according to an embodiment of the present invention.
It is a figure which shows the example of an OFDM transmission station in the case of using arbitrary one among FDM modulation signals as a reference OFDM modulation signal.

FIG. 6 is a diagram showing an example of spectrum arrangement when a phase reference signal other than an OFDM modulated signal is used as an embodiment of the present invention.

FIG. 7 is a diagram showing a configuration example of an OFDM transmission station when a phase reference signal other than an OFDM modulated signal is used as an embodiment of the present invention.

FIG. 8 is a diagram showing an example of an OFDM signal waveform generated by the OFDM modulation method.

FIG. 9 is a diagram showing an example of an OFDM spectrum generated by the OFDM modulation method.

[Fig. 10] Fig. 10 is a diagram illustrating an example of an OFDM frame structure generated by the OFDM modulation method.

FIG. 11 is a diagram showing an example of setting positions of a DFT window used in the OFDM demodulation method.

FIG. 12 is a diagram showing an example of a spectrum when a guard band is provided between a plurality of OFDM modulated signal spectra and a transmission band is allocated by the conventional method.

[Explanation of symbols]

t _s Length of effective symbol period t _G Length of guard interval t _D Deviation value of symbol clock phase of each OFDM modulated signal

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masayuki Takada 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the Broadcasting Technology Laboratories, Japan Broadcasting Corporation (72) Shunji Nakahara 1-10-11 Kinuta, Setagaya-ku, Tokyo Broadcasting Technology Institute of Japan Broadcasting Corporation (72) Kenichi Tsuchida 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside Broadcasting Technology Laboratory of Japan Broadcasting Association (72) Makoto Sasaki 1-10 Kinuta, Setagaya-ku, Tokyo No. 11 Broadcasting Technology Institute of Japan Broadcasting Corporation (72) Inventor Satoshi Yamada 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside Broadcasting Technology Laboratory of Japan Broadcasting Corporation

Claims (7)

[Claims] 1. When transmitting a plurality of orthogonal frequency division multiplexing (OFDM) modulated signals using a certain transmission frequency band,
A frequency band from frequency f ₁ to frequency f ₂ within the transmission frequency band is allocated as a transmission band of a certain OFDM modulated signal, and this is used as a first OFDM modulated signal,
As another transmission band of one OFDM modulated signal, in a form adjacent to the frequency band from frequency f ₁ to frequency f ₂ ,
A frequency band from frequency f ₂ to frequency f ₃ in the transmission frequency band is assigned to be a second OFDM modulated signal, and the frequency of each carrier is selected from the transmission parameters of the first OFDM modulated signal and the second OFDM modulated signal. Interval Δ
f, the effective symbol length t _s , and the guard interval length t _G are equal to each other, the highest carrier frequency among the carriers forming the first OFDM modulated signal is the maximum carrier frequency f _a , and the second OFDM modulated signal is the lowest carrier frequency among the plurality of carriers constituting the minimum carrier frequency f _b, the maximum of these minimum carrier frequency f _a, f _b
Value of the difference f _b −f _a is an integer multiple of the frequency interval Δf, and the symbol clock phase of the first OFDM modulated signal and the symbol clock phase of the second OFDM modulated signal are locked to each other on the transmitting side, Within the service area of the modulated signal and the second OFDM modulated signal, the first O
In order to minimize interference caused by mutual interference between the FDM modulated signal and the second OFDM modulated signal, the first OF
An orthogonal frequency division multiplex modulation signal transmission system, wherein a phase difference between the symbol clock phase of the DM modulation signal and the symbol clock phase of the second OFDM modulation signal is set. 2. The value of the difference f _b −f _a between the minimum carrier frequency f _b of the second OFDM modulated signal and the maximum carrier frequency f _a of the first OFDM modulated signal constitutes the first OFDM modulated signal and the second OFDM modulated signal. The orthogonal frequency division multiplex modulation signal transmission system according to claim 1, wherein the frequency interval Δf of each carrier wave is set to be equal. 3. Three or more O's in a transmission frequency band
The orthogonal frequency division multiplex modulation signal transmission system according to claim 1 or 2, wherein an FDM modulation signal is allocated. 4. One of a plurality of OFDM modulated signals transmitted in a certain transmission frequency band is used as a reference of a symbol clock phase, and the OFDM modulated signal serving as the phase reference is referred to as a reference OFDM modulated signal. In addition, the transmission station of this reference OFDM modulated signal is set as the reference transmission station,
From this reference transmitting station to the other transmitting stations, wireless line,
The reference OFDM modulated signal is transmitted using any of the wired lines, and the reference OF is transmitted to a transmission station other than the reference transmission station.
The DM modulated signal is received, and the symbol clock phase of the OFDM modulated signal transmitted from each of these transmitting stations is locked to the symbol clock phase of the reference OFDM modulated signal. An orthogonal frequency division multiplex modulation signal transmission system according to any one of 1. 5. The broadcast radio wave from the reference transmission station is used as a wireless line for distributing the reference OFDM modulated signal from the reference transmission station to each of the transmission stations. Orthogonal Frequency Division Multiplexing Modulation Signal Transmission System. 6. A reference signal for providing a symbol clock phase of each of the OFDM modulated signals is provided, and a reference signal is generated from the reference signal generating station for generating the reference signal to each transmitting station by using either a wireless line or a wired line. Is transmitted, each of the transmitting stations receives the reference signal, and the symbol clock phase of the OFDM modulated signal transmitted from each of these broadcasting stations is locked to the phase of the reference signal. 4. An orthogonal frequency division multiplex modulation signal transmission system according to any one of items 1, 2 and 3. 7. The method according to claim 1, wherein at least one of a sampling clock phase, a frame clock phase, and a carrier wave phase of each of the OFDM modulated signals is locked. Orthogonal frequency division multiplex modulation signal transmission system according to.