JP2879030B2 - OFDM transmitting apparatus and receiving apparatus, and OFDM transmitting method and receiving method - 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 (Orthogonal Frequency Division Multiplexing) method for transmitting digital signals.
The present invention relates to an FDM transmission device and a reception device, and an OFDM transmission method and a reception method.

[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.
Attention has been paid to a transmission system based on orthogonal frequency division multiplexing (hereinafter, OFDM) having features such as high frequency use efficiency.

In OFDM transmission, generally, a plurality of O
A transmission frame is formed by the FDM symbols, and a reference symbol for reception synchronization is transmitted for each frame. FIG. 9 shows a transmission frame configuration of the conventionally proposed OFDM transmission system.

In this transmission frame configuration, two reference symbols A and B for reception synchronization are arranged at the head of the frame, and information symbols are arranged after three symbols. For example, a null symbol is used for the reference symbol A, and a chirp symbol is used for the reference symbol B, which is used for timing synchronization in the demodulation device. The chirp symbol is shown in FIG.
The frequency of a complex sine wave based on I-axis data and Q-axis data as shown in (a) and (b) is swept.

[0005] As indicated by hatching in Fig. 9, a mode control signal such as a transmission parameter is transmitted using a specific carrier. In other words, by reproducing the mode control signal in the demodulation device, it is possible to demodulate information with parameters matching the transmission signal.

[0006]

By the way, in the conventional OFDM transmission system as described above, mode information is transmitted by a specific carrier, and the receiving device first reproduces the mode information and transmits the mode information such as transmission parameters of a transmission signal. Mode information needs to be obtained. For this purpose, at least the FFT window parameter on the receiving device side must match the transmission signal.

However, when parameters such as a symbol length and a guard period that change the configuration of a transmission frame are transmitted as mode information, the receiving apparatus cannot obtain a normal FFT output signal. And cannot follow the change in the transmission frame configuration, and may be in a reception disabled state.

[0008] Accordingly, the present invention provides a method for reliably obtaining mode information on the receiving side even when a parameter that changes the configuration of a transmission frame is transmitted as mode information.
An object of the present invention is to provide an FDM transmitting apparatus and a receiving apparatus, and an OFDM transmitting method and a receiving method.

[0009]

To achieve the above object, an OFDM transmitting apparatus according to the present invention comprises: a reference symbol generator for generating a plurality of reference symbols for synchronous reproduction;
Multiplexing means for multiplexing a plurality of reference symbols and information symbols output from the reference symbol generation means in a prescribed number unit to form a transmission frame; and outputting the output of the multiplexing means from the frequency domain to the time domain by inverse discrete Fourier transform. An inverse discrete Fourier transform unit for converting the data into a domain to generate an OFDM signal; and an arrangement interval for the plurality of reference symbols in the transmission frame according to mode information indicating the configuration of the transmission frame. And mode-specific control means for selectively allocating and controlling.

This OFDM transmitting apparatus multiplexes a plurality of reference symbols and information symbols generated for synchronous reproduction in a prescribed number unit, and transforms the frequency domain to the time domain by inverse discrete Fourier transform to generate an OFDM signal. When transmitting, the OFDM transmission method is configured to selectively allocate and control the arrangement intervals of the plurality of reference symbols in the transmission frame in accordance with mode information indicating the configuration content of the transmission frame.

[0011] Further, an OFDM receiving apparatus according to the present invention comprises:
An information symbol and a plurality of reference symbols for synchronous reproduction are multiplexed in a prescribed number unit to form a transmission frame, and an OFDM signal having a different arrangement interval of the plurality of reference symbols according to a mode is received. An OFDM receiver for demodulating information symbol data from a signal, comprising: a quadrature detector for orthogonally detecting the OFDM received signal; and a discrete Fourier for converting an output of the orthogonal detector to a time domain from a time domain by a discrete Fourier transform. Conversion means, demodulation means for demodulating information transmitted from the Fourier transform result of the means, reference symbol detection means for detecting the plurality of reference symbols from the output of the quadrature detection means, and output of the reference symbol detection means Synchronous reproducing means for reproducing the timing and clock from the input signal, and the output of the reference symbol detecting means Detecting the arrangement interval of al the plurality of reference symbols, and comprises a mode detection means for detecting the mode information based on the detection result.

In this OFDM receiving apparatus, a transmission frame is formed by multiplexing information symbols and a plurality of reference symbols for synchronous reproduction in a specified number unit, and the arrangement intervals of the plurality of reference symbols differ depending on the mode. Upon receiving an OFDM signal, performing orthogonal detection for orthogonal detection of the OFDM reception signal, converting the time domain to the frequency domain by discrete Fourier transform, and demodulating information transmitted from the result of the Fourier transform, the quadrature detection output From the reference symbol detection means, synchronously reproduces the timing and clock from the output of the reference symbol detection means, and detects the arrangement interval of the plurality of reference symbols from the reference symbol detection output, based on the detection result. This is based on an OFDM receiving method characterized in that the mode information is detected by using the OFDM receiving method.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS.

FIG. 1 shows a transmission frame structure of an OFDM signal used in an OFDM transmitting apparatus and an OFDM receiving apparatus according to the present invention. A and B are reference symbols for synchronous reproduction, and the other parts are information. Symbol. For example, reference symbol A is a null symbol, reference symbol B
Is a chirp symbol.

In FIGS. 1A, 1B and 1C, a reference symbol A is arranged at the beginning of a transmission frame, and a reference symbol B is assigned according to modes (1), (2) and (3). The transmission frame configuration arranged at different positions in the transmission frame is shown.

If the transmission frame is formed by changing the reference symbol position according to the mode as described above, the receiver can obtain the mode information by detecting the arrangement of these reference symbols. In particular, since FFT processing is not required for this mode information detection, detection can be performed even when parameters such as a symbol length and a guard period change.

FIG. 2 is a block diagram showing an embodiment of the OFDM transmitting apparatus for transmitting the OFDM signal shown in FIG. In FIG. 2, complex-format information data I and Q are supplied to input terminals 11 and 12. The reference symbol A generation circuit 13 generates 0 data for generating a null symbol, and the reference symbol B generation circuit 14 generates complex data for generating a chirp symbol.

On the other hand, a mode control signal indicating a transmission frame configuration such as a symbol length and a guard period is supplied to the input terminal 15. This mode control signal is supplied to the timing generation circuit 16, where a clock and a timing signal according to the transmission frame configuration are generated.

The information data (information symbols) I, Q,
The reference symbols A and B are supplied to the multiplexing circuit 17 together with the mode-specific timing signals generated by the timing generating circuit 16. The multiplexing circuit 17 determines the position of the reference symbol B based on the timing signal for each mode, and multiplexes the input symbols according to the transmission frame configuration specified by the mode control signal. As described above, a transmission frame configuration as shown in FIG. 1 is generated.

The output of the multiplexing circuit 17 is supplied to an IFFT (Inverse Discrete Fourier Transform) circuit 18 and is converted into a real number I and an imaginary number Q of a baseband OFDM modulated wave by an IFFT operation. The output of the IFFT circuit 18 is supplied to a guard period adding circuit 19, and the latter half of the OFDM symbol is copied before the symbol as a guard period. The output of this guard period adding circuit 19 is
Is orthogonally modulated by a carrier of a predetermined frequency, and D / A
The signal is converted into an analog signal by a (digital / analog) conversion circuit 21. The output of the D / A conversion circuit 21 is frequency-converted into an RF signal by the frequency conversion circuit 22 and transmitted. The timing generation circuit 16 generates and outputs a clock and a timing signal to each circuit.

With the above configuration, an OFDM signal having the transmission frame structure shown in FIG. 1 can be transmitted.

FIG. 3 is a block diagram showing one embodiment of the OFDM receiving apparatus for receiving the OFDM signal shown in FIG. In FIG. 3, a received signal input from an input terminal 31 is converted into a predetermined frequency by a frequency conversion circuit 32, and then converted into a digital signal by an A / D (analog / digital) conversion circuit 33, and is converted into a quadrature detection circuit 34 Supplied to

The quadrature detection circuit 34 performs quadrature detection on a digital signal from the A / D conversion circuit 33 using a reproduction carrier of a predetermined frequency supplied from an AFC circuit 35 described later, thereby obtaining a baseband OFDM modulated wave. Is what you get. The in-phase detection axis output (I signal) and the quadrature detection axis output (Q signal) of the OFDM modulated wave are the real part and the imaginary part of the OFDM modulated wave, respectively.

As described above, the O obtained by the quadrature detection circuit 34
After the FDM modulated wave is converted into frequency axis data by an FFT operation of an FFT (Fast Fourier Transform) circuit 36, the demodulation circuit 37 corrects the amplitude and phase of each carrier and demodulates the data. This demodulated data is supplied to the demultiplexer 3
8 where only the information symbols are separated and output.

The output of the quadrature detection circuit 34 is branched and supplied to an AFC (automatic frequency control) circuit 35. The AFC circuit 35 detects a frequency error of ± １ ／ of the carrier interval, generates a signal for correcting the error, and further inputs a signal for correcting the frequency error per carrier interval from the demodulation circuit 37. The result of addition to the above correction signal is supplied to the quadrature detection circuit 34. The orthogonal detection circuit 34 corrects the frequency error of the reproduced carrier based on the correction signal. Thereby, frequency synchronization of the reproduction carrier is achieved.

The output of the quadrature detection circuit 34 is supplied to a reference symbol A detection circuit 39 and a reference symbol B detection circuit 4.
0 is supplied. The reference symbol A detection circuit 39 detects a null symbol and outputs a null detection timing signal.
The reference symbol B detection circuit 40 detects a chirp symbol and outputs a chirp detection timing signal. The respective detection timing signals are supplied to the timing recovery circuit 41. This timing reproduction circuit 41
A clock is reproduced based on null and chirp detection timing, and a timing signal synchronized with a frame is generated.

The respective detection timing signals are also supplied to a mode detection circuit 42. The mode detection circuit 42 determines the arrangement of the null and the chirp from the detection timing of the null and the chirp, detects the mode information from the determination result, and supplies a mode control signal to each circuit.

With the above configuration, mode information can be detected from an OFDM modulated wave having the transmission frame structure shown in FIG.

The specific circuit configuration of the main part of the OFDM receiver will be described below.

FIG. 4 is a block diagram showing a specific configuration of the reference symbol A detection circuit 39. 4, the I and Q outputs of the quadrature detection circuit 34 are supplied to input terminals 391 and 392, respectively, and the envelope is detected by an envelope detection circuit 393. The detection result is sufficiently smoothed in a low-pass filter (LPF) 394 and supplied to a comparator 395. On the other hand, the null symbol detection slice level is input to the comparator 395 from the threshold value setting circuit 396, where it is compared with the envelope detection result. The output of the comparator 395 is converted to a null detection timing signal in a timing detection circuit 397, and the output terminal 3
98.

FIG. 5 is a block diagram showing a specific configuration of the reference symbol B detection circuit 40. In FIG. 5, the I and Q outputs of the quadrature detection circuit 34 are supplied to the correlation operation circuit 403 from input terminals 401 and 402. The correlation operation circuit 403 receives the reference signal (chirp symbol) generated by the reference signal generation circuit 404, performs a correlation operation between the reference signal and the quadrature detection signals I and Q, and outputs an envelope signal. The maximum value of the envelope signal is detected by a maximum value detection circuit 405, and a detection timing pulse is generated and output by a timing detection circuit 406.

FIG. 6 is a block diagram showing a specific configuration of the mode detection circuit 42. In FIG. 6, input terminal 4
Null detection timing signal is input from 21, and chirp detection timing signal is input from the input terminal 422, and both are supplied to the timing comparison circuit 423. This timing comparison circuit 423 counts the time from the null detection timing to the chirp detection timing, and outputs the count value to the mode determination circuit 424. The mode determination circuit 424 determines the mode information from the above count value and outputs a mode control signal.

FIG. 7 is a block diagram showing another example of the configuration of the reference symbol B detection circuit. In FIG. 7, the I and Q outputs of the quadrature detection circuit 34 are supplied from input terminals 40a and 40b to a correlation operation circuit 40c and a correlation operation circuit 40d.

The reference signal is supplied to the correlation operation circuit 40c from the reference signal generation circuit 40e, and the correlation operation with the input signal is performed. Further, the reference signal is supplied to the correlation operation circuit 40d from the reference signal generation circuit 40f, and the correlation operation is performed on the input signal. Here, the correlation operation circuit 40c performs a correlation operation for performing high-precision timing detection, and the correlation operation circuit 40d only needs to be able to determine the mode information, and performs a coarse-accuracy correlation operation.

In general, the circuit size of the correlation operation processing increases, and there is a method of performing non-real-time processing in order to avoid this. In this case, the range detectable within a predetermined time depends on the detection accuracy. . Therefore, in the present embodiment, separate correlation calculations are performed for timing reproduction that requires high accuracy and mode detection that requires a wide detection range within a short time.

An envelope output of a highly accurate correlation operation result is supplied from the correlation operation circuit 40c to a maximum value detection circuit 40g. The maximum value detection circuit 40g detects the maximum value of the envelope output, and the timing detection circuit 40h outputs the detected timing pulse from the output terminal 40i to the timing reproduction circuit 41.

Further, the envelope output of the coarse correlation operation result is supplied from the correlation operation circuit 40d to the maximum value detection circuit 40j. The maximum value detection circuit 40j detects the maximum value of the envelope output, and the timing detection circuit 40k outputs the detected timing pulse from the output terminal 401 to the mode detection circuit 42.

According to the above configuration, mode information can be detected by detecting a plurality of reference symbol arrangements in a transmission frame.

Here, the mode detection may be performed in the initial reception state, and after the detection, the chirp can be detected by the conventional correlation calculation. Therefore, in the above embodiment, the reference signal generation circuit 40e is made variable, and in the initial state, the reference signal frequency of the reference signal generation circuit 40e is controlled so that the mode can be detected in a short time. Let it run. After the mode detection is completed from the chirp detection timing signal obtained through the maximum value detection circuit 40g and the timing detection circuit 40h, the reference signal frequency of the reference signal generation circuit 40e is controlled according to the mode detection result, The correlation calculation circuit 40c executes a highly accurate correlation calculation.

According to this configuration, the correlation operation circuit 40c,
Since the coarse correlation operation and the high-precision correlation operation can be switched and executed as needed only by the reference signal generation circuit 40e, the correlation operation circuit 40d, the reference signal generation circuit 40f, the maximum value detection circuit 40j, and the timing detection circuit 40k are unnecessary. Thus, the configuration can be simplified.

In the above description, a case has been described where a null symbol is used as the reference symbol A and a chirp symbol is used as the reference symbol B. However, the present invention is not limited to this. It is clear that the effect is obtained. For example, a reference symbol for frequency synchronization as shown in FIG. 8 can be handled similarly. The reference symbol for frequency synchronization transmits a predetermined data sequence depending on the presence or absence of a carrier. The envelope of the quadrature detection output signal is smaller than other information symbols, and can be determined in the same manner as a null symbol.

[0042]

As described above, according to the present invention, the mode information is transmitted by the arrangement of a plurality of reference symbols in the transmission frame. It is possible to provide an OFDM transmitting apparatus and a receiving apparatus, and an OFDM transmitting method and a receiving method that can reliably obtain mode information on the receiving side even when transmitting.

[Brief description of the drawings]

FIG. 1 is an OFDM transmission apparatus and OFDM according to the present invention.
FIG. 2 is a diagram illustrating an embodiment of a transmission frame configuration of an OFDM transmission scheme used in a receiving device.

FIG. 2 is a block diagram showing an embodiment of an OFDM transmission apparatus according to the present invention.

FIG. 3 is a block diagram showing an embodiment of an OFDM receiving apparatus according to the present invention.

FIG. 4 is a block diagram showing a specific configuration of a reference symbol A detection circuit of the OFDM receiver according to the present invention.

FIG. 5 is a block diagram showing a specific configuration of a reference symbol B detection circuit of the OFDM receiver according to the present invention.

FIG. 6 is a block diagram showing a specific configuration of a mode detection circuit of the OFDM receiver according to the present invention.

FIG. 7 is a block diagram showing another configuration of the reference symbol B detection circuit of the OFDM receiver according to the present invention.

FIG. 8 is a view for explaining a reference symbol for frequency synchronization in an OFDM transmission system to which the present invention can be applied.

FIG. 9 is a diagram showing a configuration of a transmission frame of a conventional OFDM transmission system.

FIG. 10 is a diagram illustrating a chirp symbol conventionally used as a reference symbol.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 13 ... Reference symbol A generation circuit 14 ... Reference symbol B generation circuit 16 ... Timing generation circuit 17 ... Multiplexing circuit 18 ... Inverse discrete Fourier transform circuit 19 ... Guard period addition circuit 20 ... Quadrature modulation circuit 21 ... D / A conversion circuit 22 ... frequency conversion circuit 32 ... frequency conversion circuit 33 ... A / D conversion circuit 34 ... quadrature detection circuit 35 ... AFC circuit 36 ... discrete Fourier conversion circuit 37 ... demodulation circuit 38 ... demultiplexer 39 ... reference symbol A detection circuit 393 ... envelope detection Circuit 394 LPF 395 Comparator 396 Threshold value 397 Timing detection circuit 40 Reference symbol B detection circuit 403, 40c, 40d Correlation operation circuit 404, 40e, 40f Reference signal generation circuits 405, 40g, 40j Maximum value detection circuit 406, 40h, 40k ... Timing detection Road 41 ... timing recovery circuit 42 ... mode detecting circuit 423 ... timing comparison circuit 424 ... mode decision circuit

Continued on the front page (72) Inventor Takafumi Seki 5-2-2 Akasaka, Minato-ku, Tokyo Inside the Next Generation Digital Television Broadcasting System Research Laboratories (72) Inventor Makoto Sato Shinsugita-machi, Isogo-ku, Yokohama-shi, Kanagawa No. 8 Toshiba Multimedia Technical Research Institute, Inc. (72) Inventor Yuji Ohashi 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Toshiba Multimedia Technical Research Institute, Inc. (56) References JP-A-10-173625 (JP) , A) JP-A-9-312582 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H04J 11/00

Claims (7)

(57) [Claims] 1. A synchronous and reference symbol generating means for generating a plurality of kinds of reference symbols for reproduction, inserted provisions a plurality of types of reference symbols output from the reference symbol generating unit between the respective object transmission information symbols <br Multiplexing means for multiplexing a fixed number of units to form a transmission frame, and a plurality of keys which are orthogonal to each other and output from the multiplexing means.
4 shows an inverse discrete Fourier transform means for transforming from the frequency domain to the time domain by generating an OFDM (orthogonal frequency division multiplexing) signal by assigning to the carrier and performing an inverse discrete Fourier transform, and a predetermined configuration of the transmission frame. Multiple
Enter the mode information to specify one of the modes
And, according to the input mode information,
Of the plurality of types of reference symbols in the transmission frame.
An OFDM transmission apparatus comprising: a mode-specific control unit that selectively controls an arrangement time length . 2. A plurality of transmission frames, each of which indicates a configuration content of a transmission frame in advance.
The mode is determined, and any one of the modes
Multiple time allocation lengths corresponding to the mode information that specifies
Types of reference symbols are inserted between transmitted information symbols.
Are multiplexed in specified units to form a transmission frame.
Multiplexed outputs whose orthogonality is
Rearranged and inverse discrete Fourier transformed
Receives tuned OFDM (orthogonal frequency division multiplex) signal
And, an OFDM receiver for demodulating the data information symbols from the OFDM reception signal, and quadrature detection means for quadrature detection the OFDM received signal, the frequency domain from the time domain by the discrete Fourier transform output of said orthogonal detection means Discrete Fourier transform means for converting to an information symbol transmitted from the Fourier transform result of the means
Demodulation means for demodulating the data of the reference symbol, reference symbol detection means for detecting the plurality of types of reference symbols from the output of the quadrature detection means, and synchronous reproduction means for reproducing the timing and clock from the output of the reference symbol detection means. detects the placement time length of the plurality of types of reference symbols from the output of the reference symbol detection unit, before the result of the detection
A mode showing the configuration of the transmission frame of the OFDM reception signal.
An OFDM receiver comprising a mode determining means for determining a mode. 3. The OFDM transmitting apparatus or OFDM receiving apparatus according to claim 1, wherein at least one of the plurality of types of reference symbols for synchronous reproduction is a null symbol. 4. The OFDM transmitting apparatus or OFDM receiving apparatus according to claim 1, wherein at least one of the plurality of types of reference symbols for synchronous reproduction is a chirp symbol. 5. The OFDM transmission apparatus or OFDM according to claim 1, wherein at least one of the plurality of types of reference symbols for synchronous reproduction transmits a predetermined data sequence depending on the presence or absence of a carrier. Receiver. 6. A plurality of transmission frames indicating the contents of a transmission frame in advance.
The mode is determined, and any one of the modes
Synchronize with the deployment time length corresponding to the mode information that specifies
Multiple types of reference symbols generated for reproduction
Inserted between broadcast symbols and multiplexed in specified number units for transmission
A plurality of carriers that form a frame and are orthogonal to each other
Convert from the frequency domain to the time domain by inverse discrete Fourier transform assigned to A OFDM (orthogonal frequency content
OFDM transmission method is characterized in that so as to deliver it generates division multiplexing) signal. 7. A plurality of transmission frames, each of which indicates a configuration content of a transmission frame in advance.
The mode is determined, and any one of the modes
Synchronize with the deployment time length corresponding to the mode information that specifies
Multiple types of reference symbols generated for reproduction are transmitted
And multiplexed by the specified number unit.
A transmission frame is formed and a plurality of
Assigned to carriers and subjected to inverse discrete Fourier transform
OFDM transformed from frequency domain to time domain by
(Orthogonal frequency division multiplexing) A signal is received, the orthogonal detection is performed by orthogonal detection of the OFDM reception signal, the time domain is converted to the frequency domain by the discrete Fourier transform , and the data of the information symbol transmitted from the result of the Fourier transform is demodulated. When detecting, the plurality of types of reference symbols are detected from the quadrature detection output, the timing and clock are synchronously reproduced from the output of the reference symbol detection means, and the plurality of types of reference symbols are arranged from the reference symbol detection output.
A time length is detected, and the OFDM reception signal is detected from the detection result.
OFDM receiving method characterized by the this <br/> to determine the mode showing the configuration contents of the transmission frame No..