JPH07321765A - Hierarchical modulation system and transmitter-receiver - Google Patents

Abstract

PURPOSE:To reduce crosstalk disturbance onto other services and to prevent disturbance from being concentrated on a specific layer even when a large effect is caused only to a specific frequency band in transmission bands due to multi-path disturbance by adopting the specific hierarchical modulation system so as to keep a power spectrum density of an OFDM signal flat in the transmission band. CONSTITUTION:The power to each carrier for each transmission symbol of a multi-carrier signal and the assignment of the modulation system are changed when hierarchical modulation is implemented by changing the power of each carrier and the modulation system for each carrier or each carrier block in the orthogonal frequency division multiplex modulation OFDM system. That is, the system is provided with a mapping memory circuit 3 and the content of correspondence between complex data and each carrier is set to the circuit 3 as a mapping pattern to be registered therein so as to set freely the power of each carrier and the modulation system. A data conversion assignment circuit 4 converts transmission data into complex data based on the mapping pattern of the circuit 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orthogonal frequency division multiplexing digital modulation system (Orth) which is a modulation system suitable for terrestrial digital television broadcasting or digital audio broadcasting.
TECHNICAL FIELD The present invention relates to a layered modulation method and a transmission / reception apparatus that use an optical frequency division multiplexing (OFDM).

SUMMARY OF THE INVENTION The present invention is an orthogonal frequency division multiplex digital modulation system (Orthogonal Frequency Divisio).
n Multiplexing (OFDM) layering. When layered modulation is performed, which carrier power is increased and which carrier power is decreased on the frequency axis for each transmission symbol included in the transmission frame. By changing the allocation pattern indicating whether or not the power spectrum density of the OFDM signal is kept close to white Gaussian noise in the transmission band even after layered modulation, interference with other services is prevented. It is an excellent feature of OFDM that its properties are almost the same as those of white Gaussian noise so that it is not damaged by layered modulation. Furthermore, when performing a hierarchical modulation by changing the modulation method of each carrier for each carrier or each carrier block,
By changing the allocation of the modulation method of a certain carrier for each OFDM transmission symbol, even if only a specific frequency band within the transmission band is significantly affected by multipath interference, the bit This makes it possible to minimize the deterioration of the error rate characteristic.

[0003]

2. Description of the Related Art Orthogonal frequency division multiplexing digital modulation system (Orthogonal Frequency) which is a modulation system suitable for terrestrial digital television broadcasting or digital audio broadcasting.
In a transmission / reception system that uses Division Multiplexing (OFDM), a transmitter transmits multiple signals to be transmitted (effective data) and amplitude / phase reference data (reference data) as complex number data on the frequency axis. Inverse Discrete Fourier Transform is performed on the data to convert it to a baseband time base waveform on the time base to generate an OFDM signal,
This is transmitted by radio frequency.

Then, the receiving apparatus receives the OFDM signal to reproduce the baseband time base waveform, and the baseband time base waveform is subjected to discrete Fourier transform. Based on the value of the reference data thus obtained, The value of the signal is determined and the received data included in the OFDM signal is reproduced.

[0005]

By the way, in such a digital modulation system, when the reception C / N ratio is lowered, compared to the analog modulation system at a certain C / N ratio,
There is a property that the reception quality deteriorates rapidly. As a method for alleviating this property and improving the reception quality so that the reception quality gradually deteriorates even if the reception C / N decreases, in a general digital modulation method, some of the bits transmitted are transmitted. , Hierarchical modulation schemes that are less error-prone than other bits and that have several steps in the strength of each bit against deterioration of transmission line characteristics are being considered.

As for the OFDM modulation method, such a layered modulation method can be considered.
At present, there is no technique for applying hierarchical modulation to such an OFDM modulation method.

Therefore, in the OFDM modulation method, as a method of performing hierarchical modulation, a method of changing the magnitude of power for each carrier, QPSK, 16QAM for each carrier,
Although a method of changing the modulation method such as 32QAM and a method of changing both the power changing method and the modulation method can be considered, it has been found that such a hierarchical modulation method has the following problems.

First, in the method of changing the magnitude of power for each carrier, if the frequency of the carrier giving a large power is made the same for all transmission symbols, the power spectrum density of the OFDM signal after layered modulation is transmitted. It may not be flat in the band, and co-channel interference to other services may become large.

In both the method of changing the magnitude of power and the method of changing the modulation method for each carrier wave, the position of the carrier wave for sending a bit resistant to the deterioration of the transmission line characteristics is set to the whole transmission position. If the same symbols are used, if only a specific frequency band within the transmission band is significantly affected by multipath interference (interference due to multiple reflected waves), only a specific layer among multiple layers will be degraded intensively. In addition, when the layer that is intensively disturbed is the layer that transmits the most important bit, the entire transmission signal may be fatally damaged.

In view of the above situation, the present invention can keep the power spectrum density of the OFDM signal flat within the transmission band even after the layered modulation, reduce interference with other services, and reduce Even if only a specific frequency band in the transmission band is significantly affected by the path interference, it is possible to prevent the interference from being concentrated in a specific layer,
An object of the present invention is to provide a layered modulation system and a transmission / reception device that can improve the reliability of transmission.

[0011]

In order to achieve the above object, the present invention is a hierarchical modulation system according to claim 1, wherein after a plurality of transmission data to be transmitted is expanded on a frequency axis,
In the orthogonal frequency division multiplex modulation method that expands on the time axis to generate a multicarrier signal, when performing hierarchical modulation by changing the power and modulation method of each carrier for each carrier or each carrier block, It is characterized in that the magnitude of power and the allocation of the modulation method to each carrier are changed for each transmission symbol.

[0012] According to a second aspect of the present invention, in the layered modulation system according to the first aspect, a transmission frame of a multi-carrier signal composed of a plurality of transmission symbols is defined, and power and modulation of each carrier wave are performed for each transmission symbol. The method is characterized in that the process of changing the method allocation is performed in units of the transmission frame, and a fixed pattern is repeated for each transmission frame with respect to the allocation pattern in each transmission frame.

According to a third aspect of the present invention, in the layered modulation method according to the second aspect, an assignment is made as to which value the magnitude of the electric power of each carrier is set and which modulation method is used for each carrier. A feature is that a certain fixed pattern is defined as a pattern, and this fixed allocation pattern is cyclically shifted on the frequency axis to define the allocation pattern for each transmission symbol.

According to a fourth aspect, in the layered modulation system according to the second aspect, an assignment is made as to which value the magnitude of the power of each carrier is to be set and which modulation system is to be used for each carrier. The pattern is characterized by defining a pseudo-random allocation pattern for each transmission symbol.

Further, in claim 5, claim 1, 2, 3,
In the layered modulation method according to any one of 4 and 5, an OFDM signal is used as the multicarrier signal.

Further, the transmitting and receiving apparatus according to claim 6 is characterized in that the transmission processing or the reception processing is performed by using the layered modulation method according to any one of claims 1, 2, 3, 4, and 5. There is.

[0017]

In the above structure, in the layered modulation system according to claim 1, an orthogonal frequency for generating a multi-carrier signal by expanding a plurality of transmission data to be transmitted on a frequency axis and then expanding it on a time axis. In the division multiplex modulation method, when performing the hierarchical modulation by changing the power and modulation method of each carrier for each carrier or each carrier block, the magnitude of the power and the modulation method for each carrier for each transmission symbol of the multicarrier signal By changing the allocation of, the power spectrum density of the OFDM signal is kept flat in the transmission band even after the layered modulation, interference with other services is reduced, and multipath interference causes Even when only a specific frequency band is significantly affected, interference is prevented from concentrating on a specific layer and transmission reliability is improved. Improve.

According to a second aspect of the present invention, in the layered modulation system according to the first aspect, a transmission frame of a multi-carrier signal composed of a plurality of transmission symbols is defined, and the power and modulation of each carrier are transmitted for each transmission symbol. The power spectrum density of the OFDM signal is changed even after the hierarchical modulation by performing a process of changing the allocation of the method in units of the transmission frame and repeating a fixed pattern for each transmission frame with respect to the allocation pattern in each transmission frame. Is kept flat within the transmission band to reduce interference with other services, and even if a specific frequency band within the transmission band is significantly affected by multipath interference, the interference is concentrated in a specific layer. To improve the reliability of transmission.

According to a third aspect of the present invention, in the layered modulation system according to the second aspect, an assignment is made as to which value the magnitude of the power of each carrier is set and which modulation system is used for each carrier. As a pattern, a certain fixed pattern is defined, and this fixed allocation pattern is cyclically shifted on the frequency axis to define an allocation pattern for each transmission symbol. It keeps the power spectral density flat within the transmission band to reduce interference with other services, and even when a specific frequency band within the transmission band is significantly affected by multipath interference, it does not affect the specific layer. Prevents interference from concentrating and improves transmission reliability.

According to a fourth aspect, in the layered modulation system according to the second aspect, which value is set for the magnitude of the power of each carrier, and which system is used for the modulation system of each carrier is assigned. By defining a pseudo-random allocation pattern for each transmission symbol as a pattern, the power spectrum density of the OFDM signal is kept flat within the transmission band even after hierarchical modulation, reducing interference with other services. In addition, even when only a specific frequency band within the transmission band is significantly affected by the multipath interference, interference is prevented from concentrating on a specific layer, and transmission reliability is improved.

Further, in claim 5, claims 1, 2, 3,
In the layered modulation method according to any one of 4 and 5, by using an OFDM signal as the multicarrier signal, the power spectrum density of the OFDM signal is kept flat within the transmission band even after layered modulation. In addition to reducing interference with other services, even when only a specific frequency band within the transmission band is significantly affected by multipath interference, interference is prevented from concentrating on a specific layer and transmission is performed. Improve the reliability of.

According to a sixth aspect of the present invention, there is provided a transmission / reception apparatus that performs a transmission process or a reception process by using the layered modulation method according to any one of the first, second, third, fourth, and fifth aspects. Even after modulated modulation, the power spectrum density of the OFDM signal is kept flat within the transmission band to reduce interference with other services, and multipath interference has a significant effect only on a specific frequency band within the transmission band. Even if it is received, the interference is prevented from concentrating on a specific layer to improve the reliability of transmission.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an embodiment of a transmission apparatus to which the layered modulation method according to the present invention is applied will be described with reference to the block diagram shown in FIG.

The transmitting apparatus 1 shown in FIG. 1 comprises a clock generating circuit 2, a mapping memory circuit 3, a data converting / allocating circuit 4, an OFDM modulating circuit 5 and a frequency converting circuit 6, and is a transmission target. The transmission data of each layer is acquired, and the transmission data is OFDM while cyclically changing the power and the modulation scheme for each transmission data for each transmission symbol based on a preset mapping pattern. It is converted into a signal and transmitted to the receiving device side.

The clock generation circuit 2 oscillates at a preset frequency to generate a frame synchronization signal, a symbol synchronization signal, a clock signal, etc. necessary for generating an OFDM signal, and these are generated in the mapping memory circuit 3 To the data conversion / allocation circuit 4 and the OFDM modulation circuit 5.

The mapping memory circuit 3 is registered with a mapping pattern for associating the transmission data of each layer to be transmitted with each carrier wave, and the frame synchronization signal, the symbol synchronization signal and the clock output from the clock generation circuit are registered. The contents of a preset mapping pattern are read out based on a signal or the like and supplied to the data conversion / allocation circuit 4.

The data conversion / allocation circuit 4 converts the transmission data (binary data) of each layer into complex number data based on the mapping pattern contents output from the mapping memory circuit 3, and also converts each of these complex number data. It is assigned to each carrier wave of OFDM and each processed complex number data is supplied to the OFDM modulation circuit 5.

In this case, the mapping memory circuit 3
By setting the value of each complex number data and the corresponding content with each carrier as the mapping pattern registered in, the power and modulation method of each carrier can be freely set.

The OFDM modulation circuit 5 takes in complex number data for each carrier wave output from the data conversion / allocation circuit 4 and converts it into a frame synchronization signal, a symbol synchronization signal or a clock signal output from the clock generation circuit 2. Based on this, inverse discrete Fourier transform (IFFT) is performed to convert the complex number data on the frequency axis into a baseband time axis waveform on the time axis, and this is supplied to the frequency conversion circuit 6.

The frequency conversion circuit 6 takes in the baseband time base waveform output from the OFDM modulation circuit 5, converts it into a radio frequency or an intermediate frequency, generates an OFDM signal as a transmission signal, and outputs it. .

Next, the signal processing in the OFDM modulation circuit 5 will be described in detail with reference to the schematic diagram shown in FIG. 2 and the schematic diagram shown in FIG.

First, an outline of general signal processing in the OFDM system is given in a known document, for example, "Le Floch et al.
"Digital Sound Broadcasting to Mobile Receivers",
IEEE Transactions on Consumer Electronics, Vol.35, N
o.3, August 1989, pp.493-503 ”.

Then, as is clear from this document,
In the OFDM method, a plurality of effective data to be transmitted is converted into a plurality of complex number data, which are expanded on a frequency axis and subjected to an inverse discrete Fourier transform (IFFT) to obtain a baseband time axis on the time axis. The waveform is converted into an OFDM signal to be transmitted.

In this case, for example, as shown in FIG.
The number of carrier waves is "600" and the number of IFFT points is "102".
If it is 4 ″, each effective data and reference data are input to the OFDM modulation circuit 5 in the form of complex number data expanded on the frequency axis, and as shown in FIG. 2B by the IFFT processing of this OFDM modulation circuit 5. 2A, the carrier numbers “1” to “300” are converted to IFFT point numbers “2” to.
In "301", set carrier numbers "301" to "600" to I
It is assigned to the FFT point numbers “725” to “1024”.

Then, the above-described processing is performed for each symbol, and as shown in FIG. 3, an OFDM signal having a frame structure composed of one synchronization symbol and 100 transmission symbols following the synchronization symbol. To generate.

Next, with reference to the schematic diagram shown in FIG. 4 and the schematic diagram shown in FIG. 5, the layered modulation method according to the present invention will be described.

First, in the layered modulation method according to the present invention,
As in the example shown in FIG. 4, the mapping pattern of the first transmission symbol is cyclically shifted on the frequency axis to be the mapping pattern of the other transmission symbols after the second transmission symbol, which is used as the mapping memory circuit. 3 and the data conversion / allocation circuit 4 changes the modulation method of each carrier for each transmission symbol. Therefore, when the OFDM signals are averaged on the time axis, the OFDM signal is transmitted within the transmission band. The power spectral density of the signal can be flattened.

On the other hand, in the conventional OFDM modulation system, the power and modulation system of each carrier are fixed for each transmission symbol as shown in FIG.
When the M signals are averaged, the power spectrum density of the OFDM signal cannot be flattened within the transmission band.

As is clear from these results, in the layered modulation system according to the present invention, the power value for each carrier and the modulation system are cyclically switched for each transmission symbol to perform the layered modulation. Because it is set to O
When the power spectrum density of the FDM signal can be kept flat within the transmission band to reduce interference with other services, and only a specific frequency band within the transmission band is significantly affected by multipath interference. However, it is possible to prevent the interference from being concentrated on a specific layer and improve the reliability of transmission.

In addition to such a mapping pattern, it is also possible to define a pseudo-random mapping pattern for each transmission symbol, for example.

Next, with reference to the block diagram shown in FIG. 6, an embodiment of a receiving apparatus to which the hierarchical modulation method according to the present invention is applied will be described.

The receiving apparatus 11 shown in FIG. 6 is provided with a frequency conversion circuit 12, a synchronous reproduction circuit 13, a mapping memory circuit 14, an OFDM demodulation circuit 15, and a received data judgment / conversion circuit 16, and transmits A radio frequency OFDM signal (received signal) transmitted from the device 1 is taken in, frequency-converted into a baseband time-axis waveform, and this baseband time-axis waveform is OFDM demodulated into a plurality of complex number data. At the same time, based on the same mapping pattern as on the transmitter 1 side, the received data of each layer corresponding to each complex number data is reproduced while cyclically switching the demodulation method for each complex number data for each transmission symbol.

The frequency conversion circuit 12 takes in an OFDM signal in the form of a radio frequency signal (or an intermediate frequency signal) transmitted from the transmitter 1, converts it into a baseband time-axis waveform, and outputs this baseband time-axis waveform. Is supplied to the synchronous reproduction circuit 13 and the OFDM demodulation circuit 15.

The synchronous reproduction circuit 13 is the frequency conversion circuit 1 described above.
The baseband time-axis waveform output from 2 is taken in, the frame synchronization signal, the symbol synchronization signal, the clock signal, etc. included in this baseband time-axis waveform are reproduced, and these are reproduced by the mapping memory circuit 14 and the OFDM. The data is supplied to the demodulation circuit 15 and the received data determination / conversion circuit 16.

The same mapping pattern as the mapping pattern registered in the mapping memory circuit 3 of the transmitter 1 is registered in the mapping memory circuit 14, and the frame sync signal output from the synchronous reproduction circuit 13 is registered. , The content of the mapping pattern registered in advance is read based on the symbol synchronization signal, the clock signal, etc., and this is read by the received data determination / conversion circuit 16
Supply to.

The OFDM demodulation circuit 15 takes in the baseband time base waveform on the time base output from the frequency conversion circuit 12, and also outputs the frame sync signal, the symbol sync signal and the clock signal output from the sync reproduction circuit 13. Based on the above, a discrete Fourier transform (FFT) is performed to convert the baseband time base waveform on the time base into the complex number data on the frequency base, and this is supplied to the reception data determination / conversion circuit 16.

The received data judging / converting circuit 16 is based on the frame synchronizing signal, the symbol synchronizing signal and the clock signal outputted from the synchronizing reproducing circuit 13 and the mapping pattern contents outputted from the mapping memory circuit 14, and The complex number data of each carrier output from the OFDM demodulation circuit 15 is taken in, the value of the received data is determined for each carrier, and the received data (binary data) obtained by this is output for each layer.

As described above, in this embodiment, the transmitter 1 side cyclically switches the power and the modulation method for the transmission data of each layer to be transmitted for each transmission symbol to generate an OFDM signal, On the side of the receiving device 11, since each complex number data obtained by OFDM demodulating the received signal by the demodulation method designated for each transmission symbol is converted into the received data of each layer for each carrier, layering is performed. Even after modulation, the OFD is kept within the transmission band.
The power spectral density of the M signal can be kept flat,
This can reduce interference with other services, and prevent interference from being concentrated in a specific layer even if only a specific frequency band within the transmission band is significantly affected by multipath interference. In addition, the reliability of transmission can be improved.

[0049]

As described above, according to the present invention, in claims 1 to 6, even after the hierarchical modulation, the power spectrum density of the OFDM signal is kept flat within the transmission band and other services are provided. Interference can be reduced, and even if only a specific frequency band within the transmission band is significantly affected by multipath interference, the interference is prevented from concentrating on a specific layer and the transmission reliability is improved. Can be improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing an example of a transmission apparatus to which an embodiment of a layered modulation method according to the present invention is applied.

FIG. 2 is a schematic diagram showing an example of an inverse Fourier transform operation of the OFDM modulation circuit shown in FIG.

3 is a schematic diagram showing a schematic format example of a transmission frame configuration of an OFDM signal transmitted from the transmission device shown in FIG.

FIG. 4 is a data conversion / allocation circuit and O shown in FIG.
It is a schematic diagram which shows the allocation pattern example of the electric power and the modulation system in an FDM modulation circuit.

FIG. 5 is a schematic diagram showing an example of a power and modulation scheme allocation pattern in a conventional OFDM modulation scheme.

FIG. 6 is a block diagram showing an example of a receiver to which an embodiment of the layered modulation method according to the present invention is applied.

[Explanation of symbols]

 1 transmitter (transceiver) 2 clock generator 3 mapping memory circuit 4 data converter / assigner 5 OFDM modulator 6 frequency converter 11 receiver (transmitter / receiver) 12 frequency converter 13 sync replay circuit 14 mapping memory circuit 15 OFDM demodulation circuit 16 Received data determination / conversion circuit

Front page continuation (72) Kenichi Tsuchida 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside the Japan Broadcasting Corporation Broadcasting Technology Laboratory (72) Inventor Makoto Sasaki 1-10-11 Kinuta, Setagaya-ku, Tokyo Japan (72) Inventor, Satoshi Yamada 1-10-11 Kinuta, Setagaya-ku, Tokyo Inside Broadcasting Technology Institute, Japan Broadcasting Corporation

Claims (6)

[Claims] 1. An orthogonal frequency division multiplex modulation system in which a plurality of transmission data to be transmitted are expanded on a frequency axis and then expanded on a time axis to generate a multicarrier signal, in each carrier or each carrier block. When performing hierarchical modulation by changing the power and modulation method of each carrier, the magnitude of power and the allocation of the modulation method to each carrier are changed for each transmission symbol of the multicarrier signal. Modulation method. 2. The layered modulation system according to claim 1, wherein a transmission frame of a multi-carrier signal composed of a plurality of transmission symbols is defined, and power of each carrier and allocation of a modulation system are changed for each transmission symbol. The layered modulation method, wherein the processing is performed in units of the transmission frames, and a fixed pattern is repeated for each transmission frame with respect to an allocation pattern in each transmission frame. 3. The layered modulation system according to claim 2, wherein a certain fixed pattern is used as an allocation pattern for setting the magnitude of the power of each carrier to which value and the modulation system of each carrier. The layered modulation method is characterized in that the allocation pattern is defined for each transmission symbol by cyclically shifting this fixed allocation pattern on the frequency axis. 4. The layered modulation method according to claim 2, wherein each transmission is performed as an allocation pattern of which value the magnitude of the power of each carrier is set and which modulation method is used for each carrier. A layered modulation method characterized by defining a pseudo-random allocation pattern for each symbol. 5. The layered modulation system according to claim 1, wherein an OFDM signal is used as the multi-carrier signal. 6. A transmission / reception device, which performs transmission processing or reception processing using the layered modulation method according to claim 1. Description: