JP2818151B2 - OFDM transmission system and OFDM transceiver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an OFDM transmission system and a transmission / reception apparatus thereof, and more particularly to a case where a plurality of transmission systems having different configurations (number of carriers, guard length) in a transmission frame of an OFDM modulated signal exist.

[0002]

2. Description of the Related Art In recent years, digital modulation systems have been actively developed for transmission of audio signals and video signals. Especially in digital terrestrial broadcasting, it is strong against multipath interference.
An OFDM system having features such as high frequency use efficiency has been attracting attention. For details of the OFDM method,
Document ITU-RS contribution (TG11 / 3) or the Institute of Television Engineers of Japan Vol.17. No.54. Pp7-12, BCS # 93-3
3 (Sep. 1993) and the like, and here, a conventional technique related to the present invention will be described.

In OFDM transmission, modulation and demodulation are performed by assigning data to a plurality of orthogonal carriers. This can be realized by performing IFFT processing on a plurality of symbol data on the transmission side and performing FFT processing on reception data on the reception side.

[0004] In this case, it is necessary for the OFDM receiver to perform demodulation in a mode setting corresponding to the transmission system. Therefore, when there are a plurality of transmission schemes having different configurations (the number of carriers and the guard length) in the transmission frame of the OFDM signal, it is necessary to switch the reception mode of the OFDM receiver according to the transmission scheme.

FIG. 16 is a diagram showing a configuration example of a conventional OFDM transmitting apparatus. First, in FIG. 16A, when an input signal as information to be transmitted is provided to an input terminal 201, this input signal is encoded by an error correction encoding unit 202, and is associated with a complex vector plane by a modulation circuit 203. .

[0006] Next, the signal complex-vectorized by the modulation circuit 203 is multiplexed with a mode symbol indicating a transmission parameter together with a null symbol and a synchronization symbol for reception synchronization by a multiplexing unit 204 and supplied to an inverse FFT unit 205. You.
The inverse FFT unit 205 converts a signal in the frequency domain into a signal in the time axis domain by performing a fast inverse Fourier transform on the input signal.

[0007] The output signal of the inverse FFT unit 205 is supplied to a quadrature modulation unit 207 after a guard period for suppressing interference is added by a guard addition unit 206, where it is orthogonally transformed by a predetermined frequency. You.

The quadrature modulation output is a D / A (digital
After being converted into an analog signal by the (Analog) converter 208, the signal is converted into a carrier frequency by the frequency signal from the local oscillator 212 by the frequency converter 209. Then, the power is amplified by the power amplifier 210 and transmitted from the antenna 211.

A clock and a timing signal required for the digital signal processing are generated based on a frame length by a timing generator 213 shown in FIG. 16B and output to each unit. As shown in FIG. 16C, the mode symbol multiplexed by the multiplexing section 204 is the mode set by the mode setting section 214 and the mode signal modulating section 21.
5 is a signal modulated. Here, the mode signal modulation unit 215 includes a carrier number setting unit 216 and a guard length setting unit 2
The modulation coefficient is switched based on each of the 17 setting values.

FIG. 17 is a diagram showing a configuration example of a conventional OFDM receiving apparatus. First, the transmission signal is received by the receiving antenna 301.
After passing through the high-frequency amplifier 302 and a tuner circuit 303, a channel is selected. This tuning is performed by inputting tuning information from the input terminal 310 and changing the frequency of the local oscillator 311. The output of the tuner 303 is converted into a digital signal by an A / D (analog / digital) converter 304,
After being orthogonally detected by the orthogonal detection unit 305, the FFT unit 306
Is converted from a time domain to a frequency domain signal.

The clock and timing signals used in the A / D conversion clock and other digital circuits are as follows:
The received signal (quadrature detection output) is reproduced by the synchronous reproduction unit 312 from itself.

The output of the FFT section 306 indicates the phase and amplitude of each carrier of the OFDM signal. These phases and amplitudes are a constellation (complex vector) of the multi-level QAM, and data assigned to each phase and amplitude of the multi-level QAM is determined by the demodulation circuit 307.
In the determined digital data, an error generated during transmission is corrected by an error correction unit 308, and the digital data is output as a demodulated signal to an output terminal 3.
09 is output.

The mode setting according to the transmission system is initially performed in the mode set by the initial mode setting unit 313,
After the mode signal is detected by the mode signal demodulation unit 315 and the mode decoding unit 316 from the output of the FT unit 306, the operation is performed with the detected mode signal. Switching between the initial state of the mode signal and after the detection is performed by the mode setting unit 314. The mode signal set here is output to a necessary digital processing circuit unit.

[0014]

As described above, the conventional OFDM
The transmission method and the reception mode setting in the OFDM receiver have been described. Next, problems to be solved by the present invention will be described. For example, in digital broadcasting using the OFDM scheme, the receiving apparatus needs to perform a demodulation operation in a mode corresponding to each transmission scheme. In this case, if the transmission system mode is known in advance, the receiver may set the mode according to the transmission system, but if the transmission mode is unknown, the mode signal multiplexed into the OFDM signal By demodulating this, the mode setting of the receiving apparatus is performed.

However, when there are a plurality of transmission schemes having different configurations (the number of carriers and the guard length) in the transmission frame, if a mode corresponding to the transmission scheme is not known,
The demodulation of the mode signal multiplexed on the OFDM signal cannot be performed. Therefore, the mode setting of the receiving device cannot be performed, and the demodulation process cannot be performed.

Therefore, the present invention solves the above-mentioned problem, and demodulates the mode signal multiplexed on the OFDM signal on the receiving device side even when there are a plurality of transmission systems having different frame configurations (the number of carriers and the guard length). It is another object of the present invention to provide an OFDM transmission system and an OFDM transmission / reception apparatus capable of demodulating information symbols by performing mode setting.

[0017]

In order to solve the above problems, the present invention is configured as follows. (1) at least the number of carriers in the transmission frame with each other;
In an OFDM transmission method in which a plurality of transmission signals having different guard lengths are respectively transmitted by orthogonal frequency division multiplexing, the transmitting side determines a frame length according to the number of carriers and the guard length, performs OFDM modulation, and transmits the signal. The receiving side detects the frame length of the OFDM received signal, determines the number of carriers and the guard length, and sets the mode of the number of carriers and the guard length corresponding to the determination result to perform the OFDM demodulation.

(2) An OFDM transmitting apparatus used in the OFDM transmission method according to (1), wherein the multiplexing means multiplexes an information symbol, a null symbol, a synchronization symbol, and a mode symbol for transmitting mode information. An inverse Fourier transform unit that performs an inverse Fourier transform on the multiplexed signal obtained by this unit to convert the frequency domain to the time domain, a guard adding unit that adds a guard period to the output of this unit, and an output of this unit. Orthogonal modulation means for performing orthogonal modulation at a predetermined frequency, carrier setting means for setting the number of carriers for each transmission method, guard length setting means for setting a guard length for each transmission method, and the carrier setting means and guard length setting means Frame length determining means for determining a frame length according to the number of carriers and the guard length set in the step (c). Multiplexing frame length corresponding to the length, the inverse Fourier transform performs a guard addition and orthogonal modulation, and transmits outputs a frame length modulation signal corresponding to the set number of carriers and guard length.

(3) An OFDM receiving apparatus used in the OFDM transmission system described in (1), wherein the orthogonal detection means performs orthogonal detection of the OFDM transmission signal, and a fast Fourier transform of the orthogonal detection output obtained by the means. Fast Fourier transform means for converting from the time domain to the frequency domain, demodulating means for demodulating information transmitted from the Fourier transform result of this means, synchronous reproducing means for reproducing timing and clock from the quadrature detection output, Initial mode setting means for setting a mode when the mode of an OFDM transmission signal is unknown; frame length detecting means for detecting a frame length from the quadrature detection output; and the number of carriers and guard length based on the frame length detected by this means. From the output of the fast Fourier transform means.
A mode signal demodulating means for demodulating a mode signal multiplexed on the M signal, a mode decoding means for converting the mode signal demodulated by this means from serial to parallel, an initial mode setting means, a frame length decoding means, and a mode. And a mode setting means for selecting any one of the mode signals set by the decoding means and operating the receiving apparatus.

(4) In the OFDM receiver according to (3), the mode setting means detects a mode signal multiplexed on the OFDM transmission signal and performs a sequence until demodulation is performed in the detected mode. A first step of operating in a mode set by the initial mode setting means at power-on and a system reset; and when the frame length is detected by the frame length detection means during the operation of this step, Operate in the mode of the number of carriers and the guard length determined by the length detection result.
And a third step of operating in the mode set by the mode decoding means when the mode signal multiplexed on the OFDM transmission signal is detected and demodulated by the mode signal demodulation means during the operation of this step. It is characterized by having.

(5) In the OFDM receiving apparatus described in (3), the mode setting means is a mode signal set by the initial mode setting means at the time of power-on and system reset as a mode signal of the number of carriers and a guard length. A first switching means for selecting a signal, and selecting and outputting a mode signal of a carrier number and a guard length determined by the frame length decoding means when the frame length is detected by the frame length detection means; When the power is turned on, a mode signal set by the initial mode setting means is selected as a mode signal other than the guard length, and when the mode signal multiplexed with the OFDM transmission signal is detected by the mode signal demodulating means, the mode decoding is performed. Second switching means for selecting and outputting the mode signal output from the means. To.

(6) In the OFDM receiving apparatus described in (3), the frame length decoding means determines whether or not the frame length detected by the frame length detection means is within a permissible range of the frame length of any mode. And a decoding unit for converting the frame length determination result into a mode signal of the number of carriers and a guard length.

(7) In the OFDM receiver according to (3), the frame length detecting means detects a period length between null symbols multiplexed in the OFDM transmission signal.

(8) In the OFDM receiver described in (7), the frame length detecting means for detecting the period length between the null symbols includes an envelope detecting means for detecting an envelope from the quadrature detection output, and an envelope detecting means for detecting the envelope length. Moving average means for performing a moving average operation for a fixed period of time on the envelope detection signal, comparison means for comparing the result of the moving average means with a set comparison level, and comparison level setting means for setting the comparison level; A differential means for performing a differential operation of an output of the comparing means, and a frame length counter means for counting a frame length based on a result of the differential means.

(9) In the OFDM receiver according to (3), the frame length detecting means detects a period length between chirp symbols by sine sweep multiplexed in a reference symbol period of the OFDM transmission signal. It is characterized by.

(10) In the OFDM receiving apparatus according to (9), the frame length detecting means for detecting the period length between the chirp symbols includes a correlation calculation between the complex signal of the quadrature detection output and a reference signal of a sine sweep waveform. , A reference signal determining means for determining a reference signal generated based on a result of the correlation calculation by the means, a reference signal generating means for generating a reference signal determined by the means, Envelope detection means for detecting an envelope from the result, comparison means for comparing the detection result of the means with a set comparison level, comparison level setting means for setting the comparison level, and differentiation of the output of the comparison means Differentiating means for performing an operation, and frame length counter means for counting the length of the frame based on the result of the differentiating means. It is characterized in.

(11) In the OFDM receiving apparatus according to (9), the frame length detecting means for detecting the period length between the chirp symbols by the sine sweep may perform a plurality of different transmissions on the complex signal of the quadrature detection output. Correlation operation means for performing a correlation operation with a reference signal by a sine sweep corresponding to the number of carriers of a system, reference signal generation means for generating a reference signal for the number of carriers of the plurality of transmission systems, Maximum value detection means for detecting whether the result is maximum, switching means for selecting and outputting the correlation operation result which is maximum detected by this means, envelope detection means for detecting the envelope of the output of this means, Comparing means for comparing the detection result of this means with the set comparison level; and comparison level setting for setting the comparison level. Means, and differentiation means for performing a differential operation of the output of the comparing means, characterized in that it comprises a frame length counter means for counting the length of the frame based on the result of the differentiation means.

[0028]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a diagram showing an embodiment of an OFDM transmission system according to the present invention.
In digital transmission using OFDM, when there are a plurality of transmission schemes having different configurations (the number of carriers and the guard length) in the transmission frame of the OFDM modulated signal, the transmission device determines the number of carriers as shown in FIG. By determining and transmitting the frame length according to the guard length, the number of carriers and the guard length can be determined by detecting the frame length of the OFDM signal input by the receiving device.

FIG. 1B shows an example of the frame configuration shown in FIG.
(C) and (d). As evident from these figures,
In the transmission system according to the present invention, the frame length is different depending on the number of carriers and the guard length. FIG. 1E shows the structure of one symbol.

FIG. 2 is a block diagram showing a configuration of an embodiment of an OFDM transmission apparatus according to the OFDM transmission system in the present invention. For simplicity of explanation,
The same parts as those in the conventional example of FIG. 12 are denoted by the same reference numerals, and the description thereof will be omitted. Only different points will be described here.

The feature of this embodiment is shown in FIG.
The point is that a frame length determining unit 218 is provided as shown in FIG. This frame length determination unit 218 is, for example,
By storing table information indicating the relationship between the number of carriers, the guard length, and the frame length as shown in (a), fetching the setting values of the carrier number setting unit 216 and the guard length setting unit 217, and referring to the table information. , The corresponding frame length is determined.

The frame length determined and determined by the frame length determining unit 218 is determined by the multiplexing unit 204 shown in FIG.
Inverse FFT section 205, guard adding section 206, orthogonal transform section 2
07 and the timing generator 213 shown in FIG. Therefore, in the configuration of the present embodiment, signal processing is performed with a frame length corresponding to the number of carriers and the guard length.

That is, in the mode setting in the conventional transmission system, the frame length is determined completely independently of the number of carriers and the guard length, and the frame length is determined according to the mode set for each parameter (the number of carriers, the guard length, the modulation system, etc.). The operation was performed by setting the mode of each part.

On the other hand, in the present invention, the carrier number mode set by the carrier number setting section 216 and the guard length 21
The frame length is determined by the frame length determining unit 218 in accordance with the guard length mode set in step 7, and the transmission signal is subjected to the OFDM modulation processing with the determined frame length. For this reason, the receiving side has the same table as the above table, detects the frame length from the OFDM reception signal,
By referring to the above table, the carrier number mode and the guard length mode can be identified.

FIG. 3 is a block diagram showing the configuration of an embodiment of an OFDM receiving apparatus according to the OFDM transmission system in the present invention. Again, for simplicity of explanation,
In FIG. 3, the same portions as those in FIG. 13 are denoted by the same reference numerals, and the description thereof will be omitted. Only different points will be described here.

The features of this embodiment are as follows.
Frame length detector 317 and frame length decoder 31
8 is provided. The frame length detection unit 317 captures the OFDM reception signal obtained by the quadrature detection unit 305,
For example, a frame length is detected by counting between reference symbols. The frame length decoding unit 318 stores the same table as the table previously stored in the frame length determining unit on the transmission side, and identifies the number of carriers and the guard length by referring to the table for the input frame length.
The number of carriers and the guard length obtained by the frame length decoding unit 318 are supplied to the mode setting unit 314, and are used for a mode switching operation.

This mode setting section 314 is used when power is turned on.
A mode setting sequence is executed by mode switching control at system reset / frame length detection / mode signal detection.

The mode setting sequence from power-on of the OFDM receiver to demodulation is enabled in the mode set by the initial mode setting unit 313 when the power is turned on and when the system is reset. 317 and the number of carriers determined by the frame length decoding unit 318 and the guard length. After the number of carriers and the guard length corresponding to the transmission method are set in this way, it becomes possible to demodulate the mode signal multiplexed on the OFDM signal, so that the mode signal demodulator 315 and the mode decoder 31
6 operates on the demodulated mode signal.

FIG. 4 is a diagram for explaining the flow of the process of the mode setting sequence and the operation state of the mode setting. When the power is turned on (during system reset operation), the operation set in the initial mode is performed. After the frame length is detected, the operation is performed based on the number of carriers and guard length based on the frame length detection result. It operates with the changed mode signal.

FIG. 5 is a block diagram showing a specific configuration of the mode setting section 314 and a specific connection relationship of peripheral circuits. The initial mode setting unit 313 sets an initial mode to be used at the time of power-on and at the time of system reset. The number of carriers and the guard length to be used as the initial setting values are determined by the carrier number selector 404 and the guard length selector in the mode setting unit 314. 405, and the other mode signals to the carrier number selector 406 and guard length selector 407 in the mode setting unit 314.

On the other hand, the quadrature detection signal output from the quadrature detection section 305 through the input terminal 401 is supplied to the frame length detection section 317, and the frame length detection section 317 detects the frame length. The detected frame length is supplied to a frame length decoding unit 318, and it is determined which one detected frame length corresponds to which carrier number and the guard length. The determination result is output to the carrier number selector 404 and the guard length selector 405 in the mode setting unit 314 as a carrier signal and a guard length mode signal.

The carrier number selector 404 and the guard length selector 405 selectively output the number of carriers and the guard length set by the initial mode setting unit 313 until the frame length is detected. , The number of carriers and the guard length obtained by the frame length decoding unit 318, and output to the mode signal output terminal 408.

After the number of carriers and the guard length corresponding to the transmission system have been detected, the mode signal can be demodulated. Therefore, the output of the FFT unit 306 is supplied to the mode signal demodulation unit 315 via the input terminal 402, where the mode signal is demodulated and then supplied to the mode signal decoding unit 316. The mode signal decoding unit 316 converts the demodulated signal into a mode signal, and outputs the signal to the selectors 406 and 407 for modes other than the number of carriers and the guard length.

The selectors 406 and 407 for modes other than the number of carriers and the guard length selectively output the mode signal set by the initial mode setting unit 313 until the mode signal is detected. Is switched to a demodulated mode signal and output to the mode signal output terminal 408. Each mode signal output from the mode output terminal 408 is output to each unit in the OFDM receiver.

When a system reset signal is supplied to the input terminal 403, the reset signal is supplied to an initial mode setting section 313, a frame length detection section 314, and a mode signal demodulation section 3.
15 and is returned to the same state as when the power was turned on, and the same processing is performed.

FIG. 6 is a block diagram showing a specific configuration of the frame length decoding section 318, and FIG. 7 is a diagram showing a state of frame length detection and determination of the number of carriers and guard length. First, in FIG. 6, the input terminal 601 is determined according to the number of carriers and the guard length in FIG.
The frame length detection outputs shown in (b) and (c) are input,
The frame length is supplied to the frame length determination unit 602. In this frame length determination unit 602, the detected frame length is set to X
1 <frame length <Y1, X2 <frame length <Y2, X3
A comparison such as <frame length <Y3,... Is performed to determine the range of frame length. The result of the determination is supplied to the mode decoding unit 603. This mode decoding unit 60
In 3, the number of carriers and the guard length corresponding to the frame length are decoded. The decoding result is output as a mode signal.

FIG. 8 is a block diagram showing a specific configuration of the frame length detecting section 317, and FIG. 9 is a view showing the output timing of each section. Here, an embodiment in which the frame length detection is performed using a null symbol is shown.

In FIG. 8, an input terminal 701 is
As shown in (a), an OFDM quadrature detection output (complex signal) having a frame configuration in which an information symbol is arranged after a null symbol and a reference symbol is input and supplied to an envelope detector 702. The envelope detection unit 702 detects the envelope of the quadrature detection output by converting a complex signal into an amplitude, and the detection output is supplied to a moving average unit 704. The moving average section 704 performs a moving average calculation of the envelope detection signal for a fixed period, and the calculation result is reduced in the null symbol period and supplied to the comparator 705 as shown in FIG. You. The comparator 705 compares the moving averaged envelope detection signal with the value set by the comparison level setting unit 703 (indicated by the middle dotted line in FIG. 9B), and the comparison result is shown in FIG. 9C. The waveform is shaped as shown in FIG.
06.

As shown in FIG. 9D, the differentiating circuit 706 detects a rising edge or a falling edge (falling edge in the figure) of the output of the comparator 705.
The edge detection result is supplied to a frame length counter 707. This frame length counter 707 is shown in FIG.
As shown in (1), the interval between the edge detection results of the differentiating circuit 706 determines the null symbol period length by counting the clock. Thus, the length of one frame can be detected, and the frame length detection signal can be output from the output terminal 708.

FIG. 10 is a block diagram showing another specific configuration of the frame length detecting section 317, and FIGS. 11 and 12 are diagrams showing output timings of each section. here,
9 shows an embodiment in which frame length detection is performed using a chirp (sine sweep) symbol set as a reference symbol.

In FIG. 10, the input terminal 801 is
1 (a), as shown in FIG. 12 (a), an OFDM quadrature detection output having a frame configuration in which an information symbol is arranged after a null symbol and a reference symbol is input, and a correlation operation unit 80
2 is supplied. The correlation calculator 802 converts the input quadrature detection signal and the reference signal generated by the reference signal generator 803 (the chirp signal based on the I and Q axis data waveforms shown in FIGS. (time-division output is performed at the timing shown in b)), and the calculation result is supplied to the envelope detection unit 804.

This envelope detector 804 detects the envelope of the quadrature detection correlation calculation output by converting the correlation calculation result into amplitude, and the correlation calculation amplitude signal obtained here is shown in FIG. Is supplied to the comparator 806 as shown in FIG. The comparator 806 compares the correlation operation amplitude signal with the value set by the comparison level setting unit 805, and the comparison result is supplied to a differentiating circuit 807.

Here, in the present configuration, a reference signal determination unit 810 is provided for the reference signal generation unit 803. As shown in FIG. 11B, the reference signal determination unit 810 causes the reference signal generation unit 803 to generate, in a time division manner, reference signals for the number of carriers of a plurality of different transmission systems at power-on and at system reset. , The maximum value is detected from the output of the envelope detection unit 804, and the reference signal generation unit 80
3 to determine the number of carriers generated. After the maximum value is detected and the reference signal is determined, the envelope detection signal becomes as shown in FIG. 12B, and the output of the comparator 806 becomes as shown in FIG. 12C.

The differentiating circuit 807 detects the rising edge or falling edge (falling edge in the figure) of the output of the comparator 807, as shown in FIG. 808. This frame length counter 808 is shown in FIG.
As shown in the figure, the interval between the edge detection results of the differentiating circuit 706 is used to determine the chirp (sine sweep) period length by counting clocks. Thereby, the length of one frame can be detected.

FIG. 14 shows that the frame length detection section 317 performs chirp (sine sweep) for frame length detection.
FIG. 15 is a block diagram showing another specific configuration in the case of using symbols, and FIG. 15 is a diagram showing the output timing of each unit. In FIG. 14, the same parts as those in FIG. 10 are denoted by the same reference numerals, and only different parts will be described.

In this configuration, the correlation calculation units 8 for the number of carriers (here, n) of a plurality of transmission systems different from each other are used.
021-802n and reference signal generators 8031-803n
The maximum value detection unit 901 controls the correlation calculation units 80
The maximum value is detected from the calculation results of 21 to 802n, the signal of the carrier having the maximum correlation calculation result is extracted from the switching unit 904, and is output to the above-described envelope detection unit 804.

The reference signal generators 8031 to 803n transmit different reference signals (see FIG.
(A chirp signal based on the I and Q axis data waveforms shown in FIGS. 11A and 11B is output in a time division manner at the timing shown in FIG. 11B).

In the above configuration, reference signal generators 8031 to 803 are applied to input signals as shown in FIG.
When reference signals as shown in FIGS. 15 (b) and 15 (d) are generated from n (only 8031 and 803n are shown in the figure and the middle is omitted), as shown in FIGS. 15 (c) and (e). Then, when the correlation is obtained with the sine sweep in the reference symbol, the correlation calculation result becomes the maximum (the output of the correlation calculation unit 802n in FIG. 15). Therefore, the maximum value detection unit 901 detects a path where the correlation calculation result takes the maximum value, and derives the path to the envelope detection unit 804 through the switching unit 902. The operation after the envelope detection is the same as in FIG. As a result, the number of carriers is determined by detecting the maximum value of the correlation operation result, and the optimum mode can be set.

[0059]

As described above, according to the present invention, even when there are a plurality of transmission systems having different frame configurations (the number of carriers and the guard length), the receiving apparatus demodulates the mode signal multiplexed with the OFDM signal. In addition, it is possible to provide an OFDM transmission system and an OFDM transmission / reception device capable of demodulating information symbols by performing mode setting.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of an OFDM transmission system according to the present invention.

FIG. 2 is an OFDM transmission scheme according to the present invention.
FIG. 2 is a block diagram illustrating a configuration of a DM transmission device.

FIG. 3 is an OF related to an OFDM transmission system according to the present invention.
FIG. 2 is a block diagram illustrating a configuration of a DM receiver.

FIG. 4 is an exemplary view for explaining the sequence of a mode setting unit in FIG. 3;

FIG. 5 is a block diagram showing a specific configuration of a mode setting unit in FIG. 3;

FIG. 6 is a block circuit diagram showing a specific configuration of a frame length decoding unit in FIG. 3;

FIG. 7 is a diagram showing a state of frame length detection and determination of the number of carriers and guard length in FIG. 6;

FIG. 8 is a block diagram showing a specific configuration in a case where frame length detection is performed using a null symbol as the frame length detection unit in FIG. 3;

FIG. 9 is a diagram showing output timing of each unit in FIG. 8;

FIG. 10 is a block diagram showing a specific configuration when frame length detection is performed by chirp (sine sweep) as the frame length detection unit in FIG. 3;

FIG. 11 is a diagram showing output timing of each unit until the envelope is detected in FIG. 10;

FIG. 12 is a diagram showing output timing of each unit after the envelope detection of FIG. 10;

FIG. 13 is a waveform chart showing I and Q-axis data waveforms (chirp signals) of the reference signal generated by the reference signal generator of FIG.

FIG. 14 is a block diagram showing another specific configuration in a case where frame length detection is performed by chirp (sine sweep) as the frame length detection unit in FIG. 3;

FIG. 15 is a diagram showing output timings of the characteristic unit in FIG. 14;

FIG. 16 is a block diagram showing a configuration of a conventional OFDM transmission device.

FIG. 17 is a block diagram showing a configuration of a conventional OFDM receiver.

[Explanation of symbols]

201: input terminal, 202: error correction encoder, 203
... a modulation circuit, 204 ... a multiplexing unit, 205 ... an inverse FFT unit,
206: guard addition section, 207: quadrature modulation section, 208 ...
D / A (digital / analog) converter, 209: frequency converter, 210: power amplifier, 211: antenna, 21
2 local oscillator, 213 timing generator, 214
Mode setting section, 215 mode signal modulation section, 216 carrier number setting section, 217 guard length setting section, 218 frame length determination section, 301 receiving antenna, 302 high frequency amplifier, 303 tuner circuit, 304 A / D (analog / digital) converter, 305 ... quadrature detector, 30
6 FFT section, 307 demodulation circuit, 308 error correction section, 309 demodulated signal output terminal, 310 channel selection information input terminal, 311 local oscillator, 312 synchronous reproduction section, 31
3: Initial mode setting unit, 314: Mode setting unit, 315
... Mode signal demodulator, 316 ... Mode decoder, 31
7: frame length detection unit, 318: frame length decoding unit, 401: orthogonal polarization signal input terminal, 402: FFT output signal input terminal, 403: system reset signal input terminal, 404: carrier number selector, 405: guard length selector , 406, 407 selector, 408 mode signal output terminal, 601 frame length detection signal input terminal, 6
02: frame length determining unit, 603: mode decoding unit,
701: quadrature detection signal input terminal, 702: envelope detector, 703: comparison level setting unit, 704: moving average unit, 705: comparator, 706: differentiating circuit, 707: frame length counter, 708: frame length detection signal output Terminal, 801... Quadrature detection signal input terminal, 802, 8021
.About.802n... Correlation calculator, 803, 8031 to 803n
... Reference signal generator, 804 Envelope detector, 80
5: comparison level setting unit, 806: comparator, 807: differentiation circuit, 808: frame length counter, 809: frame length detection signal output terminal, 901: maximum value detection unit, 902 ...
Switching unit.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takafumi Seki 5-28-8 Akasaka, Minato-ku, Tokyo Inside the Next Generation Digital Television Broadcasting System Research Laboratories (72) Inventor Noboru Taga Isogo, Yokohama-shi, Kanagawa Prefecture 8 Shinsugita-cho, Toku-ku, Japan Toshiba Multimedia Technology Research Institute, Inc. (72) Inventor Yuji Ohashi 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa, Japan Toshiba Multimedia Technology Research Institute Inc. (56) References 254915 (JP, A) JP-A-8-88617 (JP, A) JP-A-10-22973 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04J 11/00 H04L 27 / 34 H04N 7/08

Claims (11)

(57) [Claims] 1. An effective symbol period and the effective symbol period
Between the transmission system and the guard period of the waveform
Combination of synchronization symbols based on symbols and multiple information symbols
The transmission signal that constitutes the transmission frame
Multiple carriers that are generated in the region and are orthogonal to each other
In an OFDM transmission system for performing orthogonal frequency division multiplexing (hereinafter, referred to as OFDM) modulation and transmission using the same, the sampling frequency of the information symbol is constant and transmission is performed.
Under the condition that the transmission bandwidth is constant, the transmission frame
Effective symbol period determined by at least the number of carriers
Guard determined by a fixed ratio to the effective symbol period
If there are multiple transmission modes with different periods
The transmitting side determines the transmission frame length according to the number of carriers and the guard length for each transmission mode , performs OFDM modulation, and transmits the data. The receiving side detects the frame length of the OFDM reception signal and detects the number of carriers and guards. The length is determined, the number of carriers corresponding to the determination result is set, and the guard length mode is set.
An OFDM transmission method characterized by performing DM demodulation. 2. An OFDM transmission apparatus used in the OFDM transmission system according to claim 1, wherein the multiplexing means multiplexes an information symbol, a null symbol, a synchronization symbol, and a mode symbol for transmitting mode information. An inverse Fourier transform unit for performing an inverse Fourier transform on the multiplexed signal obtained by this unit to convert from the frequency domain to the time domain; a guard adding unit for adding a guard period to the output of this unit; Orthogonal modulation means for orthogonally modulating at the frequency of: carrier setting means for setting the number of carriers for each transmission method; guard length setting means for setting a guard length for each transmission method; and the carrier setting means and guard length setting means. Frame length determining means for determining a frame length according to the set number of carriers and the guard length, wherein the set number of carriers and Multiplexing in de frame length corresponding to the length, the inverse Fourier transform performs a guard addition and quadrature modulation, OFDM transmitting apparatus and transmits outputs a modulated signal of a frame length corresponding to the number set carrier and guard length. 3. An OFDM receiving apparatus used in the OFDM transmission system according to claim 1, comprising: a quadrature detection means for quadrature detecting an OFDM transmission signal; and a quadrature detection output obtained by this means by fast Fourier transform. Fast Fourier transform means for transforming from the time domain to the frequency domain; demodulating means for demodulating information transmitted from the Fourier transform result of the means; synchronous reproducing means for reproducing timing and clock from the quadrature detection output; Initial mode setting means for setting a mode when the mode of the transmission signal is unknown; frame length detecting means for detecting a frame length from the quadrature detection output; and a carrier number and a guard length based on the frame length detected by this means. Frame length decoding means for determining, and multiplexing from an output of the fast Fourier transform means into an OFDM signal Mode signal demodulating means for demodulating a mode signal being transmitted, mode decoding means for converting the mode signal demodulated by this means from serial to parallel, and setting by the initial mode setting means, frame length decoding means and mode decoding means. And a mode setting unit for selecting one of the mode signals and operating the receiving apparatus. 4. The mode setting means detects a mode signal multiplexed on the OFDM transmission signal, and sets the initial mode upon power-on and system reset as a sequence until demodulation is performed in the detected mode. A first step of operating in the mode set by the setting means, and, when the frame length is detected by the frame length detecting means during the operation of this step, the number of carriers and the guard length determined by the frame length detection result A second step of operating in the mode described above, and when a mode signal multiplexed on the OFDM transmission signal is detected and demodulated by the mode signal demodulating means during the operation of this step, the mode set by the mode decoding means is used. The OFDM receiver according to claim 3, further comprising a third step of operating. 5. The mode setting means selects a mode signal set by the initial mode setting means at power-on and at a system reset, as a mode signal of the number of carriers and a guard length. First switching means for selecting and outputting a mode signal of the number of carriers and a guard length determined by the frame length decoding means when the length is detected, and a mode signal other than the number of carriers and the guard length when power is turned on. A mode signal set by the initial mode setting means is selected, and when a mode signal multiplexed on the OFDM transmission signal is detected by the mode signal demodulating means, a mode signal output from the mode decoding means is selected and output. The OFDM receiver according to claim 3, further comprising a second switching unit. 6. The frame length decoding means, comprising: a frame length determination means for determining whether a frame length detected by the frame length detection means is within a permissible range of a frame length in any mode; 4. The OFDM receiving apparatus according to claim 3, further comprising: decoding means for converting the signal into a mode signal of the number of carriers and the guard length. 7. The OFDM frame length detecting means according to claim 1, wherein:
The OFDM receiving apparatus according to claim 3, wherein a period length between null symbols multiplexed in the transmission signal is detected. 8. A frame length detecting means for detecting a period length between null symbols, an envelope detecting means for detecting an envelope from the quadrature detection output, and a moving average calculation for a fixed period for an envelope detection signal of the means. Moving average means; comparing means for comparing the result of the moving average means with a set comparison level; comparison level setting means for setting the comparison level; and differentiating means for differentiating the output of the comparison means. The OFDM receiving apparatus according to claim 7, further comprising: frame length counter means for counting a frame length based on a result of the differentiating means. 9. The OFDM frame length detecting means according to claim 1, wherein:
4. The OFDM receiving apparatus according to claim 3, wherein a period length between chirp symbols by sine sweep multiplexed in a reference symbol period of the transmission signal is detected. 10. A frame length detecting means for detecting a period length between chirp symbols, a correlation calculating means for performing a correlation calculation between the complex signal of the quadrature detection output and a reference signal of a sine sweep waveform, and a correlation calculation of the means. Reference signal determination means for determining a reference signal generated based on the result; reference signal generation means for generating a reference signal determined by the means; envelope detection means for detecting an envelope from the result of the correlation operation means; Comparison means for comparing the detection result of the means with the set comparison level; comparison level setting means for setting the comparison level; differentiation means for performing a differential operation on the output of the comparison means; 10. The OFD according to claim 9, further comprising: frame length counter means for counting the length of the frame on the basis of: The receiving device. 11. A frame length detecting means for detecting a period length between chirp symbols by the sine sweep, wherein the complex signal of the quadrature detection output includes a reference signal by a sine sweep corresponding to the number of carriers of a plurality of transmission systems different from each other. Correlation calculation means for performing a correlation calculation; reference signal generation means for generating reference signals for the number of carriers in the plurality of transmission schemes; and maximum value detection for detecting which correlation calculation result is maximum in the correlation calculation means Means, a switching means for selecting and outputting the maximum correlation operation result detected by this means, an envelope detection means for detecting the envelope of the output of this means, and a comparison between the detection result of this means and the set comparison level. Comparison means for performing comparison; comparison level setting means for setting the comparison level; and differential operation of the output of the comparison means. A differential means Utame, OFDM receiving apparatus according to claim 9, characterized in that it comprises a frame length counter means for counting the length of the frame based on the result of the differentiation means.