JP2000115118A - Ofdm transmission line network - Google Patents

Abstract

PROBLEM TO BE SOLVED: To receive wide area information sent out from a transmitter A and area limited information sent out from the transmitter B1 as one channel and to perform a demodulation processing. SOLUTION: In the transmitter A, an optional hierarchy is determined as a blank hierarchy for not transmitting a sub carrier within a prescribed transmission channel band and OFDM signals to a wide area are transmitted by using the other hierarchies excluding the band of the blank hierarchy. Also, in the transmitters B1 and B2, the OFDM signals to a limited area are generated in the band of the blank hierarchy, synchronized with the OFDM signals to the wide area transmitted from the transmitter A, controlled so as to include the receivable range in the receivable range of the output of the transmitter A and sent out. In the transmitters B1 and B2, they are arranged separately from each other so as not to overlap the respective receivable ranges with each other or the respective output is controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to (orthogonal frequency division multiplexing)
In connection with terrestrial digital broadcasting technology using the OFDM transmission method,
In particular, the present invention relates to an OFDM transmission line network that performs so-called hierarchical transmission.

[0002]

2. Description of the Related Art As is well known, in OFDM transmission, resistance to multipath interference (so-called ghost) can be increased by adding a symbol length and a guard interval portion, and the occurrence of multipath interference by a building is increased. Suitable for terrestrial television broadcasting
It is expected to be an effective digital transmission system for terrestrial television broadcasting instead of analog television broadcasting using the F and UHF bands.

[0003] Further, according to the OFDM transmission, in a place where the broadcast waves of the same contents transmitted from a plurality of transmitting stations and having the same contents can be received in an overlapping manner, the arrival times of the respective broadcast waves are different. However, similarly to the reason that the ghost resistance is strong, the quality of the received signal is hardly reduced. Therefore, SFN (Single Frequency Network) that performs relay transmission by reception and retransmission in a single frequency band
k: single frequency network) is said to be feasible.

[0004] On the other hand, from the viewpoint of differentiation from satellite broadcasting which is suitable for simultaneous broadcasting of the same contents over a wide area, terrestrial broadcasting is a limited area of about several km square called so-called community broadcasting in units of municipalities. It is expected that limited area information will be distributed by broadcasting within the country.

However, limited area information is added to information having contents common to a wide area transmitted by SFN.
When adding new information or a program to an OFDM-modulated broadcast wave, the transport stream packet which encodes information to be added after OFDM demodulation and returns to a transport stream of MPEG2 Systems (hereinafter referred to as TS). (Hereinafter referred to as TSP) and OFDM modulation and transmission. Therefore, the size of the apparatus for that purpose becomes large, and the cost of the broadcasting equipment in a small service area such as community broadcasting becomes high, so that it becomes practically impossible to adopt it.

[0006] Also, due to the process of re-multiplexing and modulating limited area information, a difference occurs in broadcast contents in adjacent areas.
Since the waveforms of the OFDM signals broadcast in adjacent areas are different from each other, the other broadcast wave for one becomes an interference signal, and the SFN cannot be configured.

As another method, it is conceivable to multiplex all the information for each limited area in advance to the TS of MPEG2 Systems and transmit it, and control access for each area. Is unnecessary information, and transmission of such unnecessary information in large quantities
The efficiency of use of the transmission path for the receiver is significantly reduced.

[0008]

As described above, O
In the FDM transmission line network, information common to a wide area
In the case of adding limited area information, the process of remultiplexing and modulating limited area information is used, which increases the equipment scale and increases the cost of broadcasting equipment for small service areas such as community broadcasting. , Which makes it virtually impossible to adopt it.

Also, in SFN, the process of remultiplexing and modulating limited area information causes a difference in broadcast contents in adjacent areas, and the waveforms of OFDM signals broadcast in adjacent areas are different from each other. Therefore, the other broadcast wave for one becomes an interference signal, and the SFN cannot be configured.

The present invention has been made in view of the above circumstances, and an object of the present invention is to add limited area information to information having contents common to a wide area using a simple transmission device. Even if there is a difference in broadcast content in an adjacent area due to the addition of the limited area information, the other broadcast wave for one does not become an interfering signal, and thus, OFDM capable of realizing SFN can be transmitted. Transmission network and OFDM for transmitting limited area information in this OFDM transmission network
An object of the present invention is to provide a transmitter and a receiver for synchronous error detection suitable for use in synchronization processing of the OFDM transmitter.

[0011]

Means for Solving the Problems To solve the above-mentioned problems, an OFDM transmission line network according to the present invention has the following characteristic configuration.

(1) A transmission path network constituted by a transmission apparatus for OFDM-modulating and transmitting digitally modulated data, wherein a plurality of subcarriers constituting the transmission channel band are defined by a set of a predetermined number of subcarriers (hereinafter referred to as a set of subcarriers). OF which performs so-called layered transmission in which the content of information included in each layer is completed in the layer.
In a DM transmission line network, an arbitrary layer is determined in advance as a blank layer that does not transmit subcarriers within a predetermined transmission channel band, and an OFDM signal for a wide area is transmitted using another layer excluding the band of the blank layer. First
And an OFDM signal for a limited area in the band of the blank layer, which is synchronized with the OFDM signal for a wide area transmitted from the first transmitting apparatus, and whose receivable range is the first transmitting apparatus. And one or more second transmitting devices that control and transmit so as to be included in the receivable range of the output. When the number of the second transmitting devices is plural, the respective receivable ranges overlap with each other. Not to be second
Or the output of each of the second transmitters is controlled.

(2) In the configuration of (1), the second transmitting device receives a wide-area OFDM signal transmitted from the first transmitting device, extracts synchronization information from the received signal, and OF for limited area based on synchronization information
A DM signal is synchronized with the wide-area OFDM signal.

(3) In the configuration of (1), furthermore, the transmission output of the second transmission device is provided at an arbitrary point within a receivable range, and O is transmitted from the first transmission device for a wide area.
FDM signal and O from the second transmitter for limited area
A synchronous error detection receiver for simultaneously receiving an FDM signal and detecting a synchronous error of a signal transmitted from the second transmitting apparatus with respect to a signal transmitted from the first transmitting apparatus, The device is configured to perform O for the limited area based on a synchronization error detection result obtained by the synchronization detection receiver.
An FDM signal is synchronized with an output of the first transmitting device.

(4) In the configuration of (1), the first transmitting device determines the number of carriers and the coding rate of the blank layer based on transmission data capacity information transmitted from the second transmitting device. A transmission data amount control unit that controls a transmission data capacity by changing included parameters is provided.

(5) In the configuration of (1), the first transmitting apparatus performs interleaving between layers other than the blank layer and transmits the result.

Further, the OFDM transmitting apparatus according to the present invention comprises:
It has the following characteristic configuration.

(6) A transmission path network constituted by a transmission apparatus for OFDM-modulating and transmitting digitally modulated data, wherein a plurality of subcarriers constituting the transmission channel band are divided into a set of a predetermined number of subcarriers (hereinafter referred to as a set of subcarriers). OF which performs so-called layered transmission in which the content of information included in each layer is completed in the layer.
Used in a DM transmission line network, a predetermined layer is predetermined as a blank layer that does not transmit subcarriers within a predetermined transmission channel band, and is used for a wide area by using another layer excluding the band of the blank layer. A OFDM signal generating means for generating a limited area OFDM signal in the band of the blank layer when the OFDM signal is transmitted, and synchronization for synchronizing the limited area OFDM signal with the wide area OFDM signal. Means, and transmitting means for controlling and transmitting the receivable range so as to be included in the receivable range of the output of the first transmitting apparatus.

(7) In the configuration of (6), the synchronizing means includes: a receiving unit for receiving the OFDM signal for wide area; a synchronizing information extracting unit for extracting synchronizing information from the received signal; A synchronization signal generation unit that generates a synchronization signal that synchronizes the OFDM signal for the limited area with the OFDM signal for the wide area, and the OFD for the limited area based on the synchronization signal generated by the synchronization signal generation unit.
It is characterized in that synchronization processing of the M signal is performed.

The synchronization error detecting receiver according to the present invention has the following characteristic configuration.

(8) A transmission path network constituted by a transmission apparatus for OFDM-modulating and transmitting digitally modulated data, wherein a plurality of subcarriers constituting the transmission channel band are defined by a set of a predetermined number of subcarriers (hereinafter referred to as a set of subcarriers). OF which performs so-called layered transmission in which the content of information included in each layer is completed in the layer.
An OFDM signal for a wide area, which is used in a DM transmission line network and is transmitted from a first transmitting apparatus to another area other than a blank layer which does not transmit a predetermined subcarrier within a predetermined transmission channel band. Is transmitted from the second transmitting apparatus to the wide-area OFD in the band of the blank layer.
When the limited area OFDM signal synchronized with the M signal is transmitted within the receivable range of the wide area OFDM signal,
An OF for a wide area, which is provided at an arbitrary point within a range in which the output of the second transmitting device can be received, and is output from the first transmitting device.
DM signal and OF for limited area from second transmitting device
DM signals are simultaneously received, a synchronization error of a signal transmitted from the second transmission device with respect to a signal transmitted from the first transmission device is detected, and a result of the synchronization error detection is transmitted to the second transmission device. Transmitting the OFDM signal for the limited area in the second transmitting device to the OFD for the wide area
It is characterized in that it is used for synchronization processing to an M signal.

That is, in the OFDM transmission line network according to the present invention, a blank layer is provided in the transmission band of the first transmitter for broadcasting information for a wide area, and the period of the OFDM symbol and the period of the OFDM symbol are calculated based on the signal transmitted from the transmitter. Various synchronization information such as synchronization timing information, a period of an OFDM frame which is a set of a predetermined number of OFDM symbols, and synchronization timing information is extracted. By transmitting the OFDM-modulated signal to the blank band from the second transmitting device that transmits information, the receiver can handle the OFDM-modulated signal as an OFDM signal having a bandwidth of one channel.
Both the wide area / region limited information can be received by the same receiver.

As described above, the output of the second transmitting apparatus is set to have a smaller service area than that of the first transmitting apparatus for wide area broadcasting, for example, about several km square. It does not interfere with the reception of wide area information in the area.

The difference in arrival time at the receiving point due to the difference between the transmission positions of the wide area information and the area limitation information is at most a few km square, so the hierarchy broadcasted from the second transmitting device in the service area and the first layer are different. The difference between the phase shifts of the layers broadcast from the transmission device can be almost ignored.

Further, since the symbol itself of the OFDM signal has a guard interval, which is a redundant width of the FFT window width at the time of demodulation, demodulation is possible. Further, when the area to which the area limitation information is to be supplied exceeds this transmittable area, it can be dealt with by increasing the number of second transmitting apparatuses.

[0026]

Embodiments of the present invention will be described below in detail with reference to the drawings. However, for the OFDM transmission method, refer to the literature (Video Information Media Technical Report BCS '
97-17 "Multiplexing method and transmission characteristics of TMCC signal in terrestrial ISDB" Uehara et al.), And the description is omitted here.

(First Embodiment) FIG. 1 shows a configuration of an OFDM transmission line network according to a first embodiment. FIG.
In the transmission device A, the signal a other than the layer b portion in the channel bandwidth shown in FIG. 3 is transmitted with the transmission output having the wide reception service area 0 as the receivable range, and the layer b It is a blank layer that does not transmit.

On the other hand, the transmitting apparatuses B1 and B2 transmit the OFDM signal in the band of the blank layer b with the transmission output in which the reception service areas 1 and 2 in the specific area are receivable.

Here, the transmitting devices B1 and B2 have a configuration as shown in FIG.
The FDM demodulation circuit 11 demodulates the received signal, and the synchronization information detection circuit 1
In step 2, various synchronization information is extracted. Specific contents of the synchronization information include the period of the OFDM symbol and the synchronization timing information, and the OFDM symbol which is a set of a predetermined number of OFDM symbols.
This is frame timing and synchronization timing information. The synchronization signal generation timing of the synchronization signal generation circuit 13 is controlled using the extracted synchronization information. On the other hand, after the limited area information to be newly added is converted into a transport stream TS by the MPEG2 encoder 14, the OFDM modulator 15 performs OFDM modulation based on the synchronization signal from the synchronization signal generation circuit 13, and the transmitter 16 3 to the band of the blank layer b.

The operation of the above configuration will be described below.

First, when a broadcast is received at a point F in the reception area 1 shown in FIG. 1, the wide area information transmitted from the transmitting apparatus A and the area limitation information transmitted from the transmitting apparatus B1 are respectively shown in FIG. Since the spectrum is transmitted as shown in (a) and (b), it can be received as one channel and demodulated.

The received data includes the OFDM symbol frequency and the same symbol timing of the signal transmitted from the transmitting apparatus A, and the OFDM which is a set of a predetermined number of OFDM symbols.
Since it is synchronized with the DM frame, one FFT circuit and one demodulation circuit can collectively demodulate with another layer part.

Also, as shown in FIG. 1, the transmission devices B1 and B2 do not overlap the broadcast service areas 1 and 2, respectively, and therefore do not interfere with each other even if they use the same frequency band at the same time.

Therefore, the OFDM transmission line network according to the above configuration effectively uses the amount of transmission information as compared with a case where all the local information and wide area information are multiplexed in the TS stage and then the number of recipients is limited by access control. it can. Also, SF
Even within N, broadcasting limited to an area can be realized, and reception by a normal receiver becomes possible.

(Second Embodiment) FIG. 4 shows the configuration of an OFDM transmission line network according to a second embodiment. However, in FIG. 4, the same parts as those in FIG. 1 are denoted by the same reference numerals. FIG. 4 is an enlarged view of the broadcast service area 1 in FIG. 1. In this OFDM transmission line network, the first
In addition to the configuration of the embodiment, a receiver C is provided at an arbitrary point F in the service area 1 so that the transmission output of the transmission device B1 and the output from the transmission device A are simultaneously received.

FIG. 5 shows a specific configuration of the transmitting device B1 and the receiver C. In FIG. 5, FIG.
The same parts as those described above are denoted by the same reference numerals, and different parts will be described here.

First, the receiver C extracts the b-layer removal filter 2 from the composite broadcast wave received from the transmitting devices A and B1.
FIG.
(A) and (b) are separated into layers a and b,
After the respective hierarchical signals are demodulated by the demodulation circuits 23 and 24, the respective OFDM signals are demodulated by the synchronization information detection circuits 25 and 26.
It detects synchronization information such as symbol frequency, OFDM symbol timing, frame frequency, and frame timing. Then, the phase comparator 27 compares the phase of the synchronization position of the layer a with the phase of the synchronization position of the layer b, thereby detecting a synchronization error. The synchronization error detection signal thus obtained is provided to the transmitting device B1.

The transmitting apparatus B1 is basically the same as that shown in FIG. 2, but here the synchronization signal generating circuit 13 and the O
A timing adjustment circuit 17 is added between the FDM modulator 16 and the synchronization error detection signal from the receiver C is fed back to the timing adjustment circuit 17 to adjust the timing of the synchronization signal. The transmission output is reliably synchronized with the transmission output of the transmission device A.

As a result, based on the synchronization information of the broadcast wave from the transmitting device A, a negative feedback control loop in which the synchronization signal of the transmitting device B1 is controlled is formed.
The frequency and the timing of each of the synchronization signals of the transmitting device A and the transmitting device A match with high accuracy at the receiving point F, and the change with time decreases.

Therefore, according to the configuration of this embodiment,
Wide-area information output from the transmitting device A and the transmitting device B
Where you actually receive the limited area information from
Since the receiver C is provided, the synchronization accuracy at the OFDM signal stage is improved, and the effect of being resistant to aging is obtained due to the negative feedback control.

(Third Embodiment) FIG. 6 shows a configuration of a transmitting apparatus A and a transmitting apparatus B (B1 or B2) in an OFDM transmission line network according to a third embodiment. 6, the same parts as those in FIG. 2 are denoted by the same reference numerals, and different parts will be described here.

The purpose of the present embodiment is to variably control the bandwidth of the blank layer set by the transmitting device A according to the amount of data transmitted from the transmitting device B, so that the band in the channel is used effectively. is there.

That is, in the transmitting apparatus A, after the wide area information is converted into the transport stream TS by the MPEG2 encoder 31, various parameters of multiplexing and layering are set by the multiplexing and layering integrated controller 32, OFDM modulator 33 based on OFDM modulation based on
Send from.

On the other hand, the transmitting apparatus B converts the new additional information such as the regional information into the transport stream TS by the MPEG2 encoder 14. At this time, the information amount data of the TS is transmitted to the transmitting device A. In the transmitting device A, the information amount data is received by the multiplexed hierarchical integration control device 32, and if the required information amount can be ensured, a blank layer is adaptively formed and transmitted, and the blank layer information is transmitted. Send it to transmitting device B. The transmitting apparatus B receives the blank layer information, puts the transport stream TS on the corresponding blank layer, performs OFDM modulation, and outputs the result.

The operation of the above configuration will be described in detail below. From the MPEG2 encoder 14 of the transmitting device B, the information amount data is output after encoding the area limitation information. After encoding by the transmitting device B, the information amount data is input to the multiplexed hierarchical integration control device 32 of the transmitting device A.

The multiplexed hierarchical integration control device 32 calculates parameters related to the code amount and the bandwidth, such as the coding rate and modulation scheme of the layer output from the transmitting device A. According to the parameters calculated here, the multiplexed and layered data is input to the OFDM modulator 33 of the transmission device A, and the layer portion output from the transmission device B is regarded as no signal (blank layer). Output a signal.

At this time, it is more effective to provide a function for allocating mutual information between the transmitting device A and the transmitting device B in consideration of the priority of the information contents and the like.

Therefore, according to the configuration of the present embodiment,
Since the information transmitted from the transmission device B is not limited to the value unilaterally determined by the transmission device A, and is distributed according to the priority of each information, one channel band can be used effectively. Become like

In each of the above embodiments, even if interleaving is performed in layer a excluding blank layer b, transmitting apparatus A affects the OFDM signal for the limited area transmitted in blank layer b. Never. Of course,
In the transmitting device B, interleaving may be performed in the b-th layer.

[0050]

As described above, according to the present invention, compared to a case where all the local information and wide area information are multiplexed at the TS stage and the number of recipients is limited by access control thereafter, the amount of transmitted information is more effective. Available. In addition, even within a single frequency network, broadcasting limited to an area can be realized, and reception by an ordinary receiver becomes possible.

Further, a receiver for detecting a synchronization error is installed at an actual receiving location of the wide area information output from the first transmitting apparatus and the limited area information output from the second transmitting apparatus. Therefore, the synchronization accuracy at the OFDM signal stage is improved, and the negative feedback control is performed.

Further, the information transmitted from the second transmitting device is not limited to the value unilaterally determined by the first transmitting device, but is distributed according to the priority of each information. Bandwidth can be used effectively.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a broadcast service area of an OFDM transmission line network according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a transmission device B1 or B2 used in the first embodiment.

FIG. 3 shows a transmitting device A and a transmitting device B according to the first embodiment.
FIG. 1 is a diagram showing an example of frequency band allocation of signals transmitted from B1 and B2.

FIG. 4 is a partially enlarged view of FIG. 1 for explaining an OFDM transmission line network according to a second embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a transmitting device B1 and a receiver C used in the second embodiment.

FIG. 6 is a block diagram showing a configuration of a transmitting device A and a transmitting device B used in a third embodiment of the present invention.

[Explanation of symbols]

 0: Wide area broadcasting service area 1, 2 ... Area limited broadcasting service area A ... Wide area transmitting apparatus B ... Limited area transmitting apparatus C ... Synchronization error detection receiver 11 ... OFDM demodulation circuit 12 ... Synchronization information detection circuit 13 ... Synchronization Signal generation circuit 14 MPEG2 encoder 15 OFDM modulator 16 transmitter 17 timing adjustment circuit 21 b-layer removal filter 22 b-band bandpass filter 23, 24 demodulation circuit 25, 26 synchronization information detection circuit 27 Phase comparator 31 ... MPEG2 encoder 32 ... Multilayered integrated controller 33 ... OFDM modulator 34 ... Transmitter

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Shuichi Nakanishi 686-1 Nishioi, Oimachi, Ogari-gun, Ashigara-gun, Kanagawa F-term (reference) 5C063 AB20 CA11 5K022 DD01 DD13 DD23 DD33 DD42 5K047 AA11 AA15 BB01 CC08 GG12 GG41 MM03 MM11

Claims (8)

[Claims] An orthogonal frequency division multiplexing (OFDM) system for digitally modulated data.
This is a transmission network constituted by a transmitting apparatus that modulates and transmits the plurality of subcarriers that constitute a transmission channel band into a set of a predetermined number of subcarriers (hereinafter, referred to as a hierarchy). In an OFDM transmission line network that performs so-called layered transmission in which the content of information included in each layer is completed in the layer, subcarriers are not transmitted in an arbitrary layer in advance within a predetermined transmission channel band. A first transmitting device that determines a blank layer and transmits an OFDM signal for a wide area using another layer except for the band of the blank layer, and generates an OFDM signal for a limited area in the band of the blank layer; Wide-area O transmitted from the first transmitting device
And one or more second transmitting devices that synchronize with an FDM signal and control and transmit so that the receivable range is included in the receivable range of the output of the first transmitting device; In the case where there are a plurality of transmitting devices, the second transmitting devices are arranged separately or the output of each second transmitting device is controlled so that the receivable ranges do not overlap each other. OFDM transmission line network. 2. The second transmitting apparatus receives a wide-area OFDM signal transmitted from the first transmitting apparatus, extracts synchronization information from the received signal, and extracts the synchronization information from the reception signal. OFDM signal for the wide area
2. An O signal according to claim 1, wherein the signal is synchronized with an M signal.
FDM transmission network. 3. A wide-range OFDM signal from the first transmitting device and an OFDM signal from the second transmitting device are provided at an arbitrary point within a receivable range where the transmission output of the second transmitting device can be received. Simultaneously receiving an OFDM signal for a limited area and the second signal for the signal transmitted from the first transmitting device.
A synchronization error detection receiver for detecting a synchronization error of a signal transmitted from the transmission device, wherein the second transmission device is configured to detect the synchronization error based on a synchronization error detection result obtained by the synchronization detection receiver. OFD for
2. The OFDM transmission line network according to claim 1, wherein the M signal is synchronized with an output of the first transmitting device. 4. The transmission apparatus according to claim 1, wherein the first transmission device variably changes parameters including the number of carriers and a coding rate of the blank layer based on transmission data capacity information transmitted from the second transmission device. 2. The OFDM transmission line network according to claim 1, further comprising a transmission data amount control unit for controlling a capacity. 5. The OFDM transmission network according to claim 1, wherein said first transmitting apparatus performs interleaving between layers other than said blank layer and transmits the result. 6. An orthogonal frequency division multiplexing (OFDM) method for digitally modulated data.
This is a transmission network constituted by a transmitting apparatus that modulates and transmits the plurality of subcarriers that constitute a transmission channel band into a set of a predetermined number of subcarriers (hereinafter, referred to as a hierarchy). Is used in an OFDM transmission line network that performs so-called layered transmission in which the content of information included in each layer is completed in the layer, and a predetermined layer previously stores subcarriers in a predetermined transmission channel band. When an OFDM signal for a wide area is transmitted using a layer other than the band of the blank layer and is defined as a blank layer not to be transmitted, an OFDM signal for a limited area is generated in the band of the blank layer. Means for generating an OFDM signal for a limited area, and an OFDM signal for the limited area
An OFDM transmitting apparatus comprising: a synchronizing means for synchronizing with a signal; and a transmitting means for controlling and transmitting so that the receivable range is included in the receivable range of the output of the first transmitting apparatus. 7. The wide-area OFDM system according to claim 1, wherein:
A receiver for receiving a signal, a synchronization information extractor for extracting synchronization information from the received signal, and a synchronization signal generator for generating a synchronization signal for synchronizing the limited-area OFDM signal with the wide-area OFDM signal from the synchronization information Department and
The OFDM transmission apparatus according to claim 6, wherein synchronization processing of the limited area OFDM signal is performed based on a synchronization signal generated by the synchronization signal generation unit. 8. An orthogonal frequency division multiplexing (OFDM) system for digitally modulated data.
This is a transmission network constituted by a transmitting apparatus that modulates and transmits the plurality of subcarriers that constitute a transmission channel band into a set of a predetermined number of subcarriers (hereinafter, referred to as a hierarchy). Is used in an OFDM transmission line network that performs so-called layered transmission in which the content of information included in each layer is completed in the layer, and from the first transmission device, within a predetermined transmission channel band,
An OFDM signal for a wide area is transmitted using another layer excluding a band of a blank layer that does not transmit a predetermined subcarrier, and the second transmitting apparatus transmits the OFDM signal for the wide area to the blank layer band. When the synchronized limited-area OFDM signal is transmitted within the receivable range of the wide-area OFDM signal, the first transmission is provided at an arbitrary point in a receivable range of the output of the second transmission device. Wide area OF from equipment
DM signal and OF for limited area from second transmitting device
DM signals are simultaneously received, a synchronization error of a signal transmitted from the second transmission device with respect to a signal transmitted from the first transmission device is detected, and a result of the synchronization error detection is transmitted to the second transmission device. Transmitting the OFDM signal for the limited area in the second transmitting apparatus to the OFD for the wide area
A receiver for detecting a synchronization error, wherein the receiver is used for synchronization processing to an M signal.