JPH1188286A - Multifrequency network system, its transmitter and repeater - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress an interference amount between carriers by Doppler shift to be low without sacrificing a transmitting rate by using every N (N is an integer of at least 1)-number of carriers as a carrier for transmitting information among plural carriers constituting an OFDM system at a transmitter and using the other carriers as null carriers. SOLUTION: At a transmitter at a transmitting station, a mapping circuit 1 uses every N (N is an integer of at lest 1)-number of carriers as a carrier for transmitting information among the plural carriers constituting the OFDM (orthogonal frequency dividing multiplexing) system corresponding to video/voice digital signals inputted as a broadcasting signal. On the other hand, the other carriers are used as the null carrier. An IFFT circuit 2 coverts signals being the output of the circuit 1 and disposed in a frequency axial direction to signals on a time axis. An orthogonal modulation circuit 3 orthogonally modulates IFFT output and a transmitter 4 power-amplifies it to send from an antenna 5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-frequency network system used for radio transmission of broadcasting or communication, and more particularly to a system for transmitting digital signals by an OFDM (Orthogonal Frequency Division Multiplexing) system, a transmission apparatus, and a relay. Related to the device.

[0002]

2. Description of the Related Art As a conventional multi-frequency network system, a system using a plurality of frequency bands alternately is known. As a specific technical document, "Digital Terrestrial Broadcasting with OFDM-Examination of Dual Frequency Broadcasting Wave Relay (DFN)-" (p. 277) Aiichiro Tsutake, Ichi Fukuchi)
There is. The outline of the two-frequency network system described in the above document will be described with reference to FIG.

In the system shown in FIG. 8, in consideration of application to television broadcasting in Japan, transmission is performed by using two frequency channels f1 and f2 alternately from a broadcasting station A for each of relay stations B, C,. I am trying to do it. in this way,
The study of the multi-frequency network system that has been conventionally performed is for fixed reception as in the case of the current analog terrestrial broadcasting. For this reason, it is assumed that one broadcast is performed using the current channel having a width of 6 MHz.

On the other hand, the OFDM system is a kind of multi-carrier system. For example, when transmitting a television signal, several hundred to several thousand carriers are used. As a result,
The transmission speed of each carrier becomes low, and even when a redundant section in the time axis direction called a guard interval is provided, it is possible to reduce the rate at which the transmission speed is reduced.

[0005] The guard interval provides resistance to a multipath ghost having a delay time difference. As a result, OFDM is considered to be an effective method in an environment where a multipath ghost exists. This makes it possible to configure a single frequency network that configures a broadcast network using a single frequency band, or a multi-frequency network that configures a broadcast network using a plurality of frequency bands. This can be said to be suitable for mobile transmission and reception in which many multipath ghosts exist. Therefore, mobile reception is also possible by digitalization of broadcasting.

The above-mentioned guard interval is a redundant section in the direction of the time axis. By making this period longer, it is possible to provide resistance to a multipath ghost having a long delay time. However, the information transmission speed is reduced. It is possible to secure a long guard interval period while suppressing a decrease in the information transmission rate by increasing the OFDM symbol length.

On the other hand, in the case of mobile body transmission / reception, since there is a Doppler shift accompanying the movement of the mobile body,
In the case of the multi-carrier system, inter-carrier interference occurs due to a frequency difference due to a Doppler shift between the direct wave and the reflected wave.

In order to reduce the influence of the inter-carrier interference, the inter-carrier interval may be increased.
If the carrier interval is widened, the effective symbol length becomes short. This means that when the time length of the guard interval is the same, the ratio of the guard interval, which is a redundant section, increases, and the transmission speed decreases.

Further, it is necessary to determine the transmission parameters of the OFDM signal in consideration of the transmission speed and the carrier interval. However, there may be a case where a value which cannot ignore the inter-carrier interference has to be adopted.

[0010]

As described above, in the conventional broadcasting or communication multi-frequency network system adopting the OFDM system as the wireless transmission system, when the reception of the mobile unit is taken into consideration, the movement of the mobile unit is accompanied. Although it is necessary to reduce the influence of carrier interference due to Doppler shift, if the carrier spacing is widened, the transmission speed is sacrificed. Further, there may be a case where the transmission parameter of the OFDM signal has to adopt a value in which the inter-carrier interference cannot be ignored.

Accordingly, an object of the present invention is to provide a multi-frequency network system and a transmission apparatus which can suppress the amount of inter-carrier interference due to Doppler shift without sacrificing the transmission speed when configuring a multi-frequency network. An object of the present invention is to provide a relay device.

[0012]

A multi-frequency network system according to the present invention for solving the above-mentioned problems is configured as follows.

(1) A plurality of transmitting stations or relay stations use at least two or more different frequency carrier groups, and
A multi-frequency network system provided for a broadcasting system or a communication system for wirelessly transmitting information by an FDM (Orthogonal Frequency Division Multiplexing) system, wherein the transmitting device or the relay device of each of the plurality of transmitting stations or the relay stations uses the OFDM system. Out of a plurality of constituent carriers, every N (N is an integer of 1 or more) carriers are used as information transmission carriers, other carriers are used as null carriers, and M
(M is an integer of 2 or more) Each station transmits information using every Nth carrier including a case where a carrier allocated to another station in the same frequency band is used as an information transmission carrier.

(2) In the configuration of (1), in the relay station, the parent transmitting station uses N (N is an integer of 1 or more) carriers out of a plurality of carriers constituting the OFDM system. Receiving a signal to be transmitted as an information transmission carrier,
Retransmission is performed using a carrier of the same frequency as the transmitting station including the parent transmitting station transmitting the received signal, or every Nth carrier not used by other transmitting stations.

(3) In the configuration of (1), the broadcasting or communication system is a system for performing hierarchical transmission by frequency division multiplexing or time division multiplexing, wherein the plurality of transmitting stations or relay stations are configured to perform one of the hierarchical transmissions. In the case where information is transmitted by a multi-frequency network method using at least two or more different frequency carriers for only the above layers, the transmitting device or the relay device of each of the plurality of transmitting stations or relay stations requires Of a plurality of carriers constituting the OFDM system of a hierarchy in which a frequency network is constructed, N (N
Is an integer of 1 or more), every other carrier is an information transmission carrier, other carriers are null carriers, and M (M is 2
(Integer above) As the information transmission carrier for each station,
Every other N stations are used, including the case where other stations in the same frequency band use carriers allocated as information transmission carriers.

(4) In the configuration of (1), the transmitting device or the relay device of the transmitting station or the relay station transmits the same information between the stations using adjacent carriers.

The multi-frequency network transmitting apparatus according to the present invention is configured as follows.

(5) Of a plurality of carriers constituting the OFDM system, which are used for a transmitting station or a relay station of a broadcast or communication system for wirelessly transmitting information by the OFDM system,
A transmission signal is generated and transmitted by setting every other N (N is an integer of 1 or more) carriers as information transmission carriers and the other carriers as null carriers.

(6) In the configuration of (5), the broadcasting or communication system is a system for performing hierarchical transmission by frequency division multiplexing or time division multiplexing, wherein a plurality of transmitting stations or relay stations perform one or more of the hierarchical transmissions. When information is transmitted by the multi-frequency network method using at least two or more different frequency carriers for only the layer of the hierarchy, the information is transmitted among the plurality of carriers constituting the OFDM system of the layer in which the multi-frequency network is configured. , N (N is an integer equal to or greater than 1) every other carrier as an information transmission carrier and the other carriers as null carriers to generate and transmit transmission signals.

Further, the relay apparatus of the multi-frequency network system according to the present invention is configured as follows.

(7) Used for relaying broadcast or communication systems for wirelessly transmitting information by the OFDM method,
Among a plurality of carriers constituting the OFDM system, information is received by the OFDM system in which every N (N is an integer of 1 or more) carriers are used as information transmission carriers and the other carriers are null carriers, and the received signal is received. Resubmit.

(8) In the configuration of (7), the broadcasting or communication system is a system for performing hierarchical transmission by frequency division multiplexing or time division multiplexing, wherein a plurality of transmitting stations or relay stations perform one or more of the hierarchical transmissions. When information is transmitted by the multi-frequency network method using at least two or more different frequency carriers for only the layer of the hierarchy, the information is transmitted among the plurality of carriers constituting the OFDM system of the layer in which the multi-frequency network is configured , N (N is an integer equal to or greater than 1) every other carrier as an information transmission carrier, and receives information according to the OFDM method using other carriers as null carriers,
Retransmit the received signal.

(9) In the configurations of (7) and (8), after the received signal is converted into a signal on the frequency axis by FFT (Fast Fourier Transform), IFFT (Inverse Fast Fourier Transform)
Is converted to a signal on the time axis again and transmitted.
When inputting the FFT output to the IFFT, the frequency of the null carrier is changed by setting the read address of the FFT and the write address of the IFFT to different addresses.

(10) In the configuration of (9), the FF
An equalizing circuit using a determination based on a threshold value is provided between T and the IFFT.

(11) In the configuration of (9), the IF
As an input of the FT, data of a frequency to be a null carrier is replaced with “0”.

That is, in the multi-frequency network system of the present invention,
Since it is possible to equivalently increase the carrier interval without changing the symbol length, it is possible to reduce the influence of inter-carrier interference due to Doppler shift.

[0027]

Embodiments of the present invention will now be described in detail with reference to the drawings.

FIG. 1 shows a preferred embodiment of the present invention. FIG. 1 (A) shows a configuration of a transmitting apparatus, and FIG. 1 (B) shows a specific example of a mapping circuit used in the transmitting apparatus of FIG. 1 (A). FIG. 1C shows an example of an output signal of the mapping circuit.

In the transmitting apparatus shown in FIG. 1A, a mapping circuit 1 associates a video and audio digital signal input as a broadcast signal with each carrier, and inserts a null carrier. Is sent to an IFFT (Inverse Fast Fourier Transform) circuit 2.

The IFFT circuit 2 includes a mapping circuit 1
A signal arranged in the direction of the frequency axis, which is the output of the above, is converted into a signal on the time axis. The orthogonal modulation circuit 3 orthogonally modulates the IFFT output. The modulated output is power-amplified by the transmitter 4 and transmitted from the antenna 5 toward the space.

Next, the operation of the embodiment of the present invention will be described in detail.

In the transmitting apparatus shown in FIG. 1A, video and audio digital signals are input to a mapping circuit 1. FIG. 1B shows a configuration example of the mapping circuit 1 and shows an example in which QPSK is adopted as a carrier modulation method.

In the case of QPSK, two bits of information can be transmitted per symbol per carrier, so that the signal is converted into a two-bit parallel signal by the serial / parallel converter 6. The output signal of the serial / parallel converter 6 is QPSK
It is mapped on the complex plane by the mapper 7. QP
The signals (real part data output signal, imaginary part data output signal) converted into data on each complex coordinate axis by the SK mapper 7 are output via the switch 8. This switch 8 is a circuit for inserting "0" between data on each complex axis, and generates a null carrier when both data on each complex axis become "0".

The output signal of the mapping circuit 1 is input to the IFFT circuit 2. The input signal of this IFFT circuit 2 is O
It corresponds to a carrier of each frequency constituting the FDM signal. FIG. 1C shows an output signal sequence of the mapping circuit 1.

In FIG. 1C, 1 or -1 shown in the real data output signal and the imaginary data output signal respectively indicate information to be transmitted, and 0 indicates a null carrier. FIG.
The horizontal direction in (C) indicates the address of the IFFT circuit 2 to which the output of the mapping circuit 1 is connected, and this address corresponds to the frequency of the carrier. In each output signal, the number of addresses of the IFFT circuit 2 is a power of 2,
Since there is a difference between the number of carriers required for transmission, both sides are filled with zeros.

The signal taken into the IFFT circuit 2 is converted into a signal on the time axis by inverse fast Fourier transform, and then quadrature-modulated by the quadrature modulation circuit 3 to become a high-frequency OFDM signal. This OFDM signal is frequency-converted and amplified by the transmitter 4 and transmitted from the antenna 5.

FIG. 2 shows OFDM of the transmitting apparatus having the above configuration.
It shows an arrangement of signal carriers. Here, an example in which a multi-frequency network is configured using two carrier groups is shown.

FIGS. 2A and 2B show carrier arrangements of signals transmitted from different transmitters. In FIG. 2, a solid line indicates a carrier for transmitting information, and a broken line indicates a null carrier to which no radio wave is transmitted. As is clear from FIG. 2, the carrier interval between the signals (A) and (B) is twice as long as the case where no null carrier is inserted.

FIG. 3 shows how the insertion of a null carrier enhances the resistance to Doppler shift. 3A shows a case of an OFDM signal with a null carrier inserted, and FIG. 3B shows a case of a normal OFDM signal. In FIG. 3, a solid line indicates a signal which has not undergone Doppler shift, and a broken line indicates a case where signals which have undergone Doppler shift are received at the same intensity.

In the case of FIG. 3A, only the inter-carrier interference due to the side lobe of the adjacent carrier is generated.
In the case of FIG. 3B, inter-carrier interference is also caused by the main lobe of the adjacent carrier. By comparing FIGS. 3A and 3B, it is understood that the OFDM signal into which the null carrier according to the present invention is inserted has less influence of the inter-carrier interference.

FIG. 4 shows an example of carrier arrangement when a multi-frequency network is constructed using three carrier groups. FIGS. 4A, 4B, and 4C show different transmission apparatuses. Sent from It is also possible to configure a multi-frequency network using four or more carrier groups.

FIG. 5 is a diagram showing an embodiment of the relay device according to the present invention. In FIG. 5A, a signal received by the antenna 10 is amplified by a high-frequency amplifier circuit 11 and then subjected to frequency conversion by a mixing circuit 12 to become an intermediate frequency band signal. At this time, a local oscillation signal for frequency conversion is generated in local oscillation circuit 13 with reference to the frequency of reference oscillation circuit 14.

The intermediate frequency signal output from the mixing circuit 12 is amplified by the intermediate frequency
The frequency is converted by the mixing circuit 16 and becomes a high frequency band signal again. At this time, a local oscillation signal for frequency conversion is generated in local oscillation circuit 17 based on the frequency of reference oscillation circuit 14.

The output signal of the mixer 16 is amplified by the power amplifier 18 and transmitted from the antenna 19.
The local oscillation signals input to the mixing circuits 12 and 16 have a frequency difference of zero or a positive integer multiple of half the carrier interval of the received signal. Also, the mixing circuit 12,
Since the local oscillation circuits 13 and 17 that generate the local oscillation signals respectively input to the reference 16 are based on the output signal of the same reference oscillation circuit 14, the oscillation frequency accuracy of the reference oscillation circuit 14 is the frequency deviation of the transmission frequency. Has little effect on

FIG. 5B is a diagram showing the frequency relationship between the received signal and the transmitted signal in the above-mentioned relay apparatus. The carrier is changed when the frequency is changed by a half of the carrier interval of the received signal. The frequency relationship is shown. The arrows in the figure indicate the relationship between carriers for transmitting the same information. As a result, when transmitting signals from the parent transmitting station and the relay station are received simultaneously, a signal in which the same information is transmitted on adjacent carriers is received.

FIG. 6 is a diagram showing a second embodiment of the relay apparatus according to the present invention. In FIG. 6A, the antenna 1
The signal received at 0 is amplified by the high-frequency amplifier circuit 11 and then frequency-converted by the mixing circuit 12 to become an intermediate frequency band signal. At this time, a signal generated in the local oscillation circuit 13 is used as a local oscillation signal for frequency conversion.

The intermediate frequency signal output from the mixing circuit 12 is amplified by the intermediate frequency amplification circuit 15 and then quadrature demodulated by the quadrature demodulation circuit 20. Quadrature demodulation circuit 20
Is a complex OFDM signal on the time axis. This signal is converted by the FFT circuit 21 into a signal on the frequency axis corresponding to each carrier. The signal on the frequency axis is a signal that can be demodulated using a threshold value, like multi-value QAM or QPSK using ordinary single carriers. Therefore, it is a signal that can compensate for a deviation from a position on an original complex coordinate caused by a transmission path or the like by a determination based on a threshold value.

The output of the FFT circuit 21 is input to the equalization circuit 22, and the equalization circuit 22 compensates for a deviation from the original position on the IQ coordinates. Incidentally, in QPSK and DQPSK in which information is not transmitted due to a level difference in the amplitude direction,
Equalization based on the presence or absence of a signal can be performed by the determination based on the threshold value. The output of the equalizing circuit 22 is input to the IFFT circuit 24 via the switch 23.

Here, the switch 23 replaces the signal corresponding to the frequency at which the null carrier is transmitted with “0”,
An unnecessary signal is prevented from being transmitted at a frequency used as a null carrier in the relay device.

It should be noted that this function can be included in the equalizer circuit, and a relay device can be constructed without using the equalizer circuit 22. It is replaced by "0" by the switch 23. Further, when unnecessary signals are allowed to be transmitted at the frequency used as the null carrier in the relay device, the switch 23 is unnecessary.

The signal on the frequency axis input to the IFFT circuit 24 is returned to the signal on the time axis again, but the FFT signal when the output signal of the FFT circuit 21 is input to the IFFT circuit 24 is output.
It is assumed that the addresses of the FT circuit 21 and the IFFT circuit 24 are different.

FIG. 6B shows this state. In FIG. 6B, the data sequence corresponding to each address of the FFT output is shifted by one address when input to the IFFT, as indicated by the arrow in the figure. As a result, a carrier to be transmitted is assigned to a frequency that was a null carrier in the received signal. Also, a null carrier is assigned to a frequency that was a carrier for transmitting information in a received signal.

In FIG. 6A, the output signal of the IFFT circuit 24 in which the frequency of the carrier for transmitting information is changed is converted into an intermediate frequency signal of an OFDM signal by a quadrature modulation circuit 25, and a required signal is output by a mixing circuit 16. After being converted to the transmission frequency, the signal is amplified by the power amplifier circuit 18 and transmitted from the antenna 19.

The local oscillation signal used in the frequency conversion by the mixing circuit 16 is a signal generated in the local oscillation circuit 13 and is the same as the signal used in the receiving-system mixing circuit 12. Therefore, even when the frequency of the local oscillation circuit 13 deviates from the required frequency,
The effect does not appear on the transmission frequency of the relay device.

FIG. 7 is a diagram showing an embodiment of a relay device in the case of hierarchical transmission by frequency division multiplexing. Note that, in FIG. 7A, the same parts as those in FIG. 6A are denoted by the same reference numerals, and redundant description is omitted here.

The feature of the embodiment shown in FIG. 7A is that an address control unit 26 is added, as is apparent from comparison with the embodiment shown in FIG. 6A. .

Since the OFDM system is one of the multi-carrier systems, it is possible to perform hierarchical transmission by dividing the carrier to be used into a plurality of bands and changing the modulation system and the strength of the error correction code.

As a specific example, for fixed transmission, a high transmission rate is secured by using multi-level QAM and an error correction code having a low error correction capability, and the reception environment is inferior to that of fixed reception. In some cases, a service area may be secured for a mobile object using QPSK and an error correction code having high error correction capability. Since the Doppler shift occurs only in the transmission / reception of the mobile unit, in this case, it is not necessary to insert a null carrier in the fixed band, and it is sufficient to insert a null carrier only in the mobile band.

In this case, in the relay device, an application in which the position of the carrier is changed only in the band for the mobile body is considered. FIG.
The embodiment shown in (A) corresponds to this.

FIG. 7B shows how the position of the carrier is changed in the embodiment shown in FIG. 7A. In the figure, the horizontal axis represents the FFT / IFFT address, that is, the array of carriers on the frequency axis.

In FIG. 7B, a null carrier is not inserted in the band indicated as fixed, but a null carrier is inserted only in the band indicated as mobile. The relay apparatus changes the frequency of the carrier that transmits information only for the band indicated as intended for the mobile, and retransmits the information. FIG.
In (B), when retransmitting, only the band for mobile
For example, a state in which the frequency is shifted in a direction higher by one carrier interval is shown. In FIG. 7A, FF
The signal converted to a signal on the frequency axis by the T circuit 21 is again converted to a signal on the time axis by the IFFT circuit 24. When the output of the FFT circuit 21 is input to the IFFT circuit 24, the address control circuit 26 Thus, the address change shown in FIG. 7B is performed.

In the embodiment shown in FIG. 7, a case where hierarchical transmission is realized by frequency division multiplexing has been described.
It is known that hierarchical transmission can also be realized by time division multiplexing. Even in the case of realizing hierarchical transmission by dividing in the time direction, by changing the address by the address control circuit only during the period when the signal for mobile is transmitted,
Obviously, a relay device can be realized in the same manner as in the case of performing hierarchical transmission by dividing in the frequency direction.

As is apparent from the above embodiment, by applying the present invention, a plurality of transmitting apparatuses alternately arrange carriers used for information transmission and null carriers, thereby equivalently providing carrier spacing. And the effect of inter-carrier interference caused by Doppler shift during mobile reception can be reduced.

[0064]

As described above, according to the present invention, when configuring a multi-frequency network, without sacrificing the transmission speed,
It is possible to provide a multi-frequency network system, a transmission device, and a relay device that can suppress the amount of inter-carrier interference due to Doppler shift.

[Brief description of the drawings]

FIG. 1 shows one embodiment of a transmission device according to the present invention.
3A and 3B are a block circuit diagram illustrating an entire configuration, a configuration of a mapping circuit, and an example of an output signal of the mapping circuit, and a diagram illustrating an example of a data array.

FIG. 2 is a diagram illustrating an example of a carrier arrangement of a transmission device or a relay device according to the present invention.

FIG. 3 is a diagram illustrating an example of inter-carrier interference.

FIG. 4 is a diagram illustrating an example of a carrier arrangement of a transmission device or a relay device according to the present invention.

FIG. 5 shows an embodiment of the relay device according to the present invention.
It is the block diagram which shows the whole constitution, the example of the reception signal and the transmission signal and the figure which shows the carrier arrangement example.

FIG. 6 shows one embodiment of the relay device according to the present invention.
FIG. 3 is a block circuit diagram showing an overall configuration thereof, an example of output signals of FFT and IFFT, and a diagram showing an example of data arrangement.

FIG. 7 shows an embodiment of a relay device according to the present invention.
FIG. 3 is a block circuit diagram showing an overall configuration thereof, an example of output signals of FFT and IFFT, and a diagram showing an example of data arrangement.

FIG. 8 is a schematic diagram showing an example of a multi-frequency network system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Mapping circuit 2 ... IFFT circuit 3 ... Quadrature modulation circuit 4 ... Transmitter 5 ... Antenna 6 ... Serial parallel conversion circuit 7 ... QPSK mapper 8 ... Switch 10 ... Antenna 11 ... High frequency amplifier circuit 12 ... Mixing circuit 13 ... Local oscillation circuit DESCRIPTION OF SYMBOLS 14 ... Reference oscillation circuit 15 ... Intermediate frequency amplification circuit 16 ... Mixing circuit 17 ... Local oscillation circuit 18 ... Power amplification circuit 19 ... Antenna 20 ... Quadrature demodulation circuit 21 ... FFT circuit 22 ... Equalization circuit 23 ... Switch 24 ... IFFT circuit 25 ... Quadrature modulation circuit 26 ... Address control circuit

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroo Takeda 1-10 Nisshinmachi, Fuchu-shi, Tokyo Inside the Fuchu Office of NEC Corporation

Claims (11)

[Claims] 1. A method according to claim 1, wherein the plurality of transmitting stations or relay stations have at least two stations.
Using the above-mentioned carrier groups of different frequencies, OFDM
A multi-frequency network system provided for a broadcasting system or a communication system for wirelessly transmitting information by an (orthogonal frequency division multiplexing) system, wherein an OFDM system is configured in each of the plurality of transmitting stations or relay stations. Out of a plurality of carriers, N (N is an integer of 1 or more) carriers are used as information transmission carriers, other carriers are used as null carriers, and M (M is an integer of 2 or more) stations Each includes a case where a carrier allocated to another station in the same frequency band as a carrier for information transmission is used.
A multi-frequency network system for transmitting information using every other carrier. 2. The relay station according to claim 1, wherein the parent transmitting station is an OFD.
Receives a signal transmitting every other N (N is an integer of 1 or more) carriers out of a plurality of carriers constituting the M system as an information transmission carrier, and includes a parent transmitting station transmitting the received signal. 2. The multi-frequency network system according to claim 1, wherein retransmission is performed using a carrier having the same frequency as the transmitting station or every Nth carrier not used by another transmitting station. 3. The system according to claim 1, wherein said broadcasting or communication system performs hierarchical transmission by frequency division multiplexing or time division multiplexing, wherein said plurality of transmitting stations or relay stations are at least two or more in only one or more layers of said hierarchical transmission. When information is transmitted by a multi-frequency network system using a carrier group of different frequencies, the transmitting device or the relay device of each of the plurality of transmitting stations or the relay stations has a layer O in which a multi-frequency network is formed.
Among a plurality of carriers constituting the FDM system, N (N is 1
(Integer above) every other carrier is the carrier for information transmission,
Other carriers may be null carriers, and M (M is an integer of 2 or more) stations may include a carrier to which another station in the same frequency band is assigned as a carrier for information transmission as an information transmission carrier. 2. The multi-frequency network system according to claim 1, wherein every other carrier is used. 4. The multi-frequency network system according to claim 1, wherein the transmitting device or the relay device of the transmitting station or the relay station transmits the same information between the stations using adjacent carriers. 5. A plurality of carriers which are used for a transmitting station or a relay station of a broadcast or communication system for wirelessly transmitting information according to the OFDM system and which constitute the OFDM system.
(N is an integer of 1 or more) A transmission apparatus of a multi-frequency network system, wherein a transmission signal is generated and transmitted using every other carrier as an information transmission carrier and another carrier as a null carrier. 6. A system in which the broadcast or communication system performs hierarchical transmission by frequency division multiplexing or time division multiplexing, wherein a plurality of transmitting stations or relay stations transmit at least two or more layers for at least one layer of the hierarchical transmission. When information is transmitted by a multi-frequency network system using a group of carriers of different frequencies, N (N is one or more) of a plurality of carriers constituting an OFDM system of a hierarchy in which the multi-frequency network is configured. 6. The multi-frequency network transmission apparatus according to claim 5, wherein a transmission signal is generated and transmitted with every other (integer) carrier being an information transmission carrier and other carriers being null carriers. 7. An OFD system for relaying a broadcast or communication system for wirelessly transmitting information according to the OFDM method.
Among a plurality of carriers constituting the M system, every other N (N is an integer of 1 or more) carriers are used as information transmission carriers,
A multi-frequency network type relay apparatus, which receives and retransmits information according to the OFDM method using another carrier as a null carrier. 8. A system in which the broadcast or communication system performs hierarchical transmission by frequency division multiplexing or time division multiplexing, wherein a plurality of transmitting stations or relay stations transmit at least two or more layers for at least one layer of the hierarchical transmission. When information is transmitted by a multi-frequency network system using a group of carriers of different frequencies, N (N is one or more) of a plurality of carriers constituting an OFDM system of a hierarchy in which the multi-frequency network is configured. 8. The multi-frequency network system according to claim 7, wherein information is received by an OFDM system in which every other carrier is an information transmission carrier and other carriers are null carriers, and the received signal is retransmitted. Relay device. 9. After converting the received signal into a signal on a frequency axis by FFT (Fast Fourier Transform), an IFFT
(Inverse Fast Fourier Transform), a relay device that converts the signal into a signal on the time axis and transmits the signal again. When the FFT output is input to the IFFT, a read address of the FFT and a write address of the IFFT are changed. 9. The multi-frequency network type relay apparatus according to claim 7, wherein a frequency of a carrier to be a null carrier is changed by setting a different address. 10. The multi-frequency network type relay apparatus according to claim 9, further comprising an equalizing circuit using a decision based on a threshold value between said FFT and said IFFT. 11. The multi-frequency network type relay apparatus according to claim 9, wherein at the input of said IFFT, data of a frequency to be a null carrier is replaced with "0".