JP2007088713A - Receiver, transmission system, and receiving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a receiver for receiving modulation signals adopting OFDM modulation system that detects the frame position of a received signal with high accuracy, using a simple configuration. <P>SOLUTION: A plurality of subcarriers of the modulation signal, adopting the OFDM modulation system, are modulated by the differential coding system by each subcarrier and formed to be a frame, comprising a data symbol part and a synchronization symbol part including two or more of the consecutively arranged same symbols. A differential detection means 11 applies differential detection on a received signal by each symbol and by each subcarrier; magnitude detection means 12, 13 apply arithmetic mean to each of I axis signals and Q axis signals, as a result of the differential detection by each symbol and by the subcarriers to detect the magnitudes of a result of the arithmetic mean; a timing detection means 17 detects the timing, when the magnitudes exceed a prescribed threshold; and a frame timing detection means 18 detects a frame timing on the basis of the timing. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a receiving apparatus that receives a signal modulated by, for example, an Orthogonal Frequency Division Multiplexing (OFDM) modulation scheme, and more particularly to a receiving apparatus that detects a frame position of a received signal with high accuracy with a simple configuration. It relates to devices.

In recent years, orthogonal frequency division multiplex modulation (OFDM modulation), which has the characteristics of being resistant to multipath fading and ghosting, has attracted attention as a modulation suitable for digital transmission for mobile and digital terrestrial television broadcasting. ing.
The OFDM modulation method is a kind of multi-carrier modulation method, and is a transmission method in which n (n is several tens to several thousands) carrier waves (carriers) orthogonal to each other are digitally modulated. A digital modulation of each carrier uses a modulation scheme such as DQPSK (Differential Quadrature Phase Shift Keying), and a waveform obtained by combining modulation signals of a plurality of carriers becomes an OFDM modulated wave.

Here, FIG. 4 shows a configuration example of symbols of the OFDM modulation signal, and FIG. 5A shows a configuration example of frames of the OFDM modulation signal and a configuration example of synchronization symbols included in the frames. FIG. 2 shows a configuration example of a transmission apparatus of a data transmission apparatus adopting the OFDM modulation method. These will be described in detail in the embodiments of the present invention described later.
FIG. 6 shows a configuration example of a receiving device of a data transmission device adopting the OFDM modulation method.
Here, the configuration of the receiving device of this example is different from the configuration of the receiving device shown in FIG. 3 according to an embodiment of the present invention described later, with respect to the frame detection circuit 51 and the demodulating circuit 52. And since it is the same about another component part, the code | symbol same as FIG. 3 is attached | subjected and detailed description is abbreviate | omitted here.

FIG. 7 shows a configuration example of the frame detection circuit 51.
The frame detection circuit 51 of this example includes a NULL end detector 61, a SWEEP pattern memory 62, a SWEEP correlator 63, and a frame counter 64. The clock signal CK from the timer circuit is input to the NULL end detector 61, the SWEEP correlator 63, and the frame counter 64.
The I-axis signal and Q-axis signal output from the quadrature demodulation circuit 44 are input to the frame detection circuit 51.
In the frame detection circuit 51, the input I-axis signal and Q-axis signal are input to the NULL end detector 61 and the SWEEP correlator 63.

The NULL end detector 61 detects a null symbol in a no-signal state in a synchronization symbol from a symbol group having a frame configuration as shown in FIG. 5A, and detects a rough position (timing) of the synchronization symbol. Then, the start time of the SWEEP symbol is estimated from the end time of the NULL symbol by the built-in timer circuit, and the SWEEP start position signal ST indicating the start position of the SWEEP symbol is output to the SWEEP correlator 63 and the frame counter 64.
The SWEEP pattern memory 62 stores a SWEEP symbol pattern in advance.

  The SWEEP correlator 63 refers to the SWEEP start position signal ST, estimates and captures the waveform existing after the second symbol as the waveform of the SWEEP symbol, and searches for the exact switching timing of each symbol. Specifically, the SWEEP symbol memory stored in the SWEEP pattern memory 62 is used to correlate the I-axis signal and Q-axis signal captured as the SWEEP symbol waveform with the pattern read from the SWEEP pattern memory 62. In order to adjust the reference clock signal CK on the receiving side so that the phase shift with the SWEEP symbol waveform estimated from the coincidence state of both signal patterns is calculated and the frame phase on the receiving side matches the transmission data A correction signal VC is output.

The frame counter 64 starts counting the clock signal CK based on the SWEEP start position signal ST, and every time this count reaches a value corresponding to the frame period (for example, 1072 × 900), the pulse FST (Frame (Start Timing) is output and the count value is returned to 0, and then the counting of the clock signal CK is started again. Accordingly, after that, the pulse FST is output at every fixed count, that is, at each frame start point, and the reception side passes this pulse FST to the demodulation circuit 52 to set the data demodulation timing.
The demodulation circuit 52 receives the calculation result obtained by the FFT calculation circuit 45 and the pulse FST detected by the frame detection circuit 51, deletes the synchronization symbol portion from the received symbol, and demodulates only the data symbol.

JP 2004-96290 A

  Here, regarding the receiving apparatus as shown in FIG. 6 and FIG. 7, transmission under poor transmission path conditions such as mobile transmission is considered. In such a transmission line, the main wave that is directly propagated from the transmission device to the reception device and the various reflected waves that are reflected and propagated to buildings, mountains, etc., each have a delay time corresponding to the transmission line. Accordingly, since the signal reaches the receiving device, the combined signal is received by the receiving device. In a situation where there is a reflected wave in addition to the main wave, a dip occurs in the frequency spectrum of the received signal, and fading occurs in which a certain frequency component is attenuated.

  Attention is paid to the CW symbol included in the synchronization symbol shown in FIG. Since the CW symbol has only one frequency component, if the frequency component of the CW symbol disappears due to the influence of fading as described above, there is no signal. When such a no-signal CW symbol is input to the frame detection circuit 51, it is erroneously detected as a NULL symbol signal up to the end position of the CW symbol (position t2) shown in FIG. Therefore, when the SWEEP start position is two symbols after the end of the NULL symbol, the start position of the first REF symbol (the position of t3) is erroneously detected as the start position of the SWEEP symbol, and decoding is performed. It becomes impossible.

6 and FIG. 7, after detecting the position of the NULL symbol, the position of the SWEEP symbol is estimated, and then the SWEEP symbol pattern data stored in the SWEEP pattern memory 62 and the reception are received. There is also a problem that the circuit scale becomes large because it is necessary to perform a correlation operation with the signal.
The present invention has been made in view of such a conventional situation, and an object of the present invention is to provide a receiving apparatus and the like that can detect the frame position of a received signal with a simple configuration and with high accuracy.

In order to achieve the above object, the receiving apparatus according to the present invention has the following configuration when receiving a signal modulated by the OFDM modulation scheme.
Here, the modulation signal by the OFDM modulation method is modulated by a differential encoding method for each subcarrier for a plurality of subcarriers. Also, the modulation signal by the OFDM modulation method is formed in a frame composed of a synchronization symbol portion including a sequence in which two or more identical symbols are continuously arranged and a data symbol portion.
Then, the receiving apparatus performs the following processing.
That is, the differential detection means differentially detects the received signal for each subcarrier for each symbol. The magnitude detection means adds (or adds and averages) each of the I-axis signal and the Q-axis signal as a result of differential detection by the differential detection means for each of the plurality of subcarriers for each symbol, and the addition result The size of (or the addition average result) is detected. The timing detection unit detects a timing at which the size detected by the size detection unit is equal to or greater than a predetermined threshold (or exceeds a predetermined threshold). The frame timing detection means detects the frame timing based on the timing detected by the timing detection means.
Therefore, the frame timing (frame position) of the received signal can be accurately detected with a simple configuration.

Here, various numbers may be used as the number of the plurality of subcarriers, and generally a large number is used.
Various methods may be used as the differential encoding method. For example, a DQPSK method that is a differential encoding 4-level PSK method and a DBPSK (Differential Binary) that is a differential encoding binary PSK method. For example, a phase shift keying method may be used.
Various frame configurations may be used.
Various configurations of the synchronization symbol portion may be used.
Various numbers may be used as the number of consecutive identical symbols included in the synchronization symbol portion. As an example, three consecutive REF symbols can be used.
Various configurations of the data symbol portion may be used. For example, a configuration in which a plurality of data symbols are arranged side by side is used.

For each symbol, as an aspect of adding or averaging the respective I-axis signals and Q-axis signals as a result of differential detection for a plurality of subcarriers, for example, an aspect of acquiring an addition result by addition It may be used, or a mode of obtaining an addition average result by adding and averaging may be used.
Further, as the magnitude of the addition result or the addition average result for the I-axis signal and the Q-axis signal, for example, an absolute value of a level of a complex signal composed of the I-axis signal and the Q-axis signal or a simple absolute value is used. be able to.
In addition, various values may be used as the predetermined threshold regarding the magnitude of the addition result or the addition average result. For example, a predetermined value may be set in advance, or based on the result of differential detection. A configuration in which a threshold value is generated may be used.

  For example, when a value such as an average distribution of a plurality of subcarriers is obtained as a value of an I-axis signal and a value of a Q-axis signal as a result of differential detection for a certain symbol, an addition result or an addition average While the magnitude of the result is zero or a small value close to zero, when the same value or an approximate value is obtained for a plurality of subcarriers, the magnitude of the addition result or the addition average result is non-zero or It will be a large value. For this reason, the magnitude of the addition result or the addition average result becomes non-zero when the same symbol continues and becomes a somewhat large value, and the magnitude of the addition result or the addition average result is zero or close to zero elsewhere. It can be set to a small value.

The receiving apparatus according to the present invention has the following configuration as one configuration example.
That is, the threshold generation unit generates the predetermined threshold based on the result of differential detection by the differential detection unit.
Further, the synchronization symbol part deleting means deletes the synchronization symbol part from the result of the differential detection by the differential detection means based on the frame timing detected by the frame timing detection means. The determination means determines a data symbol part that is a result of deleting the synchronization symbol part by the synchronization symbol part deletion means, and obtains a demodulation result.
Therefore, based on the detected timing of the frame, it is possible to determine the data symbol of the data symbol portion included in the frame and obtain the demodulation result.

The present invention can also provide a transmission system.
The transmission system according to the present invention has the following configuration when a signal modulated by the OFDM modulation scheme is transmitted from a transmission-side device (transmission device) to a reception-side device (reception device).
Here, the modulation signal by the OFDM modulation method is a signal in which a plurality of subcarriers are modulated by a differential encoding method for each subcarrier, and two or more identical symbols are continuously arranged. It is formed in a frame composed of a synchronization symbol portion and a data symbol portion.
The receiving apparatus performs the following processing.
That is, the differential detection means differentially detects the received signal for each subcarrier for each symbol. The magnitude detection means adds (or adds and averages) each of the I-axis signal and the Q-axis signal as a result of differential detection by the differential detection means for each of the plurality of subcarriers for each symbol, and the addition result The size of (or the addition average result) is detected. The timing detection unit detects a timing at which the size detected by the size detection unit is equal to or greater than a predetermined threshold (or exceeds a predetermined threshold). The frame timing detection means detects the frame timing based on the timing detected by the timing detection means.

The transmission system according to the present invention has the following configuration as a configuration example.
That is, in the reception-side apparatus, the threshold generation unit generates the predetermined threshold based on the result of differential detection by the differential detection unit.
Further, the synchronization symbol part deleting means deletes the synchronization symbol part from the result of the differential detection by the differential detection means based on the frame timing detected by the frame timing detection means. The determination means determines a data symbol part that is a result of deleting the synchronization symbol part by the synchronization symbol part deletion means, and obtains a demodulation result.

In the present invention, a receiving method can also be provided.
In the receiving method according to the present invention, the following processing is performed in a receiving apparatus that receives a signal modulated by the OFDM modulation method.
Here, the modulation signal by the OFDM modulation method is a signal in which a plurality of subcarriers are modulated by a differential encoding method for each subcarrier, and two or more identical symbols are continuously arranged. It is formed in a frame composed of a synchronization symbol portion and a data symbol portion.
Then, the receiving apparatus differentially detects the received signal for each subcarrier for each symbol, and the I-axis signal and the Q-axis signal as a result of the differential detection for each of the plurality of subcarriers for each symbol. Addition (or addition average), the magnitude of the addition result (or the addition average result) is detected, and the detected magnitude is greater than or equal to a predetermined threshold (or exceeds a predetermined threshold) And the timing of the frame is detected based on the detected timing.

  As described above, according to the receiving apparatus or the like according to the present invention, a plurality of subcarriers are modulated by the differential encoding method for each subcarrier, and two or more identical symbols are continuously arranged. When receiving a modulation signal based on the OFDM modulation method formed in a frame composed of a synchronization symbol portion and a data symbol portion, the received signal is differentially detected for each subcarrier for each symbol, and the differential detection is performed. Each of the resulting I-axis signal and Q-axis signal is added (or addition averaged) for a plurality of subcarriers for each symbol, and the magnitude of the addition result (or the addition average result) is detected. A timing at which the detected size is equal to or greater than a predetermined threshold (or exceeds a predetermined threshold) is detected, and a frame timing is determined based on the detected timing. For that to detect the timing, it is possible to accurately detect the timing of the frame of the received signal (position of the frame) with a simple configuration.

Embodiments according to the present invention will be described with reference to the drawings.
In this example, data transmission using the OFDM modulation method and the DQPSK method as the modulation method of each subcarrier will be described.
FIG. 1 shows a configuration example of a demodulation circuit 1 with a frame detection function according to an embodiment of the present invention.
FIG. 2 shows a configuration example of a transmission apparatus (transmitter) of a data transmission apparatus adopting the OFDM modulation scheme.
FIG. 3 shows a configuration example of a receiving device (receiver) of a data transmission device adopting the OFDM modulation method.

FIG. 4 shows a configuration example of symbols of the OFDM modulation signal.
FIG. 5A shows an example of a frame structure of an OFDM modulated signal and an example of a synchronization symbol included in the frame. FIG. 5B shows a frame structure whose timing is shifted by one symbol. An example is shown, and FIG. 5C shows the result of adding and averaging the phase difference for each symbol between these two frames.

  As shown in FIG. 4, one symbol of the OFDM modulated wave is composed of an effective symbol and a guard interval. The guard interval is a copy of the waveform of a part of the effective symbol, and an effect of reducing the influence of multipath can be obtained by adding it to the head of the effective symbol. One unit that combines the effective symbol and the guard interval is called a symbol. Further, for example, a total of 900 symbols including 894 symbols and 6 symbols as synchronization symbols constitutes a stream unit called a frame.

As shown in FIG. 5A, one frame according to the OFDM modulation scheme is composed of 6 symbols of synchronization symbols and 894 symbols of data (DATA) symbols. Further, for example, a plurality of frames having the same configuration are continuously transmitted.
The synchronization symbol includes a null symbol that is a no-signal part, a CW symbol that outputs the center frequency of the channel, and a SWEEP that sweeps continuously from the lowest carrier frequency to the highest carrier frequency on the RF spectrum. It is composed of a symbol and three REF symbols serving as a reference for differential decoding.

Here, a NULL symbol is a signal whose signal level is theoretically zero (0) if noise that actually exists is ignored.
A CW symbol is a signal composed only of the center frequency, and the signal level is constant. As an example, in the case of an OFDM modulation signal in which a subcarrier having a bandwidth of 4 KHz exists in each of 10 KHz, 20 KHz, 30 KHz, 40 KHz, and 50 KHz, 30 KHz is the center frequency.
In this example, a signal that continuously changes from the lowest frequency to the highest frequency in one symbol is used as the SWEEP symbol. However, as another example, the highest frequency to the lowest frequency in one symbol is used. It is also possible to use a signal that continuously changes to the highest frequency and further changes continuously from the lowest frequency to the highest frequency.

As the REF symbol, three identical symbols are arranged in succession, and a phase comparison between a symbol at a certain time point and a symbol at a previous time point is performed with respect to the first data (DATA) symbol that follows. This is the reference data for differential detection. As the REF symbol, fixed data (I component and Q component) is stored for each subcarrier, and the whole looks like a random waveform in the time domain.
As shown in FIG. 5A, in this example, one frame starts from a NULL symbol and the one frame ends with the last data symbol. Further, FIG. 5A shows time t0, t1, t2,..., Tm (for example, m is 900) equally spaced for each symbol, like the time interval between t0 and t1. A time interval adjacent to each other corresponds to a time length of one symbol, and a time interval between t0 and tm corresponds to a time length of one frame.

  As shown in FIG. 2, the transmission apparatus of this example includes an encoding unit 31, a mapping circuit 32, an inverse fast Fourier transform (IFFT) operation circuit 33, a guard addition circuit 34, a synchronization A symbol insertion unit 35, a quadrature modulation circuit 36, a D / A (Digital to Analog) conversion unit 37, an up converter 38, and an antenna 39 are provided.

An example of the processing operation of the transmission system performed by the transmission apparatus of this example is shown.
Data to be transmitted is input to the encoding unit 31. The encoding unit 31 performs signal processing such as error correction encoding using a convolutional code and time interleaving so that even if an error occurs in data during transmission. The mapping circuit 32 converts (maps) the signal output from the encoding unit 31 into information on a predetermined point on the IQ plane composed of the I axis and the Q axis by using, for example, the DQPSK method for each subcarrier. . The IFFT operation circuit 33 performs inverse Fourier transform on the I-axis and Q-axis signals output from the mapping circuit 32 to convert them into time-axis waveforms.

  The guard adding circuit 34 adds a guard interval part to a valid symbol for the signal output from the IFFT arithmetic circuit 33 to generate a data symbol. The synchronization symbol insertion unit 35 inserts a synchronization symbol for the signal output from the guard addition circuit 34 to form a frame stream. The quadrature modulation circuit 36 performs quadrature modulation on the signal output from the synchronization symbol insertion unit 35. The D / A converter 37 converts the signal of the quadrature modulation result output from the quadrature modulation circuit 36 from a digital signal to an analog signal. The up-converter 38 frequency-converts (up-converts) the signal output from the D / A conversion unit 37 into a signal with a higher radio frequency (RF). A signal output from the up-converter 38 is transmitted from the antenna 39 by radio.

  As shown in FIG. 3, the receiving apparatus of this example includes an antenna 41, a down converter 42, an A / D (Analog to Digital) conversion unit 43, an orthogonal demodulation circuit 44, and a fast Fourier transform (FFT: Fast). (Fourier Transformation) arithmetic circuit 45, demodulation circuit 1, and decoding unit 46.

An example of the processing operation of the receiving system performed by the receiving apparatus of this example is shown.
A signal transmitted by radio from the transmission device is received by the antenna 41. The down converter 42 performs frequency conversion (down conversion) of the radio frequency signal received by the antenna 41 into a lower intermediate frequency (IF) signal. The A / D converter 43 converts the signal output from the down converter 42 from an analog signal to a digital signal. The quadrature demodulation circuit 44 performs quadrature demodulation on the signal output from the A / D converter 43 to generate an I-axis signal and a Q-axis signal that are baseband signals.

  In the FFT operation circuit 45, the I-axis and Q-axis signals output from the quadrature demodulation circuit 44 are Fourier-transformed and converted into a frequency-axis waveform. In the demodulating circuit 1, the synchronization symbol portion is deleted from the signal output from the FFT computing circuit 45, and only the data symbol is demodulated. The decoding unit 46 performs signal processing such as deinterleaving and error correction on the demodulation result signal output from the demodulation circuit 1.

As shown in FIG. 1, the demodulation circuit 1 of this example includes a differential detection circuit 11, an addition averaging circuit 12, a simple absolute value circuit 13, a simple absolute value circuit 14, an addition averaging circuit 15, and a threshold value. A calculation circuit 16, a threshold comparison circuit 17, a protection circuit 18, a synchronization symbol part deletion circuit 19, and a determination circuit 20 are provided.
The averaging circuit 12 includes an adder 21 and a flip-flop (FF) 22 related to the I-axis signal, and an adder 23 and a flip-flop (FF) 24 related to the Q-axis signal.
The averaging circuit 15 includes an adder 25 and a flip-flop (FF) 26.

An example of the operation performed by the demodulation circuit 1 of this example is shown. It is assumed that each symbol is synchronized.
The differential detection circuit 11 receives the I-axis signal and the Q-axis signal of the quadrature demodulated signal Fourier-transformed by the FFT operation circuit 45.
In this example, the I-axis signal and the Q-axis signal are acquired for each frequency of each subcarrier of the OFDM modulation scheme by the FFT operation circuit 45. In the demodulation circuit 1, for example, a signal for each of these subcarriers is obtained by time division. Processing is performed and demodulation corresponding to the DQPSK system is performed for each subcarrier.

In the differential detection circuit 11, with respect to the complex signal (I-axis signal and Q-axis signal) input from the FFT operation circuit 45, data of the current symbol and data of the previous symbol for each subcarrier and for each symbol. The differential detection process for detecting the phase difference between them and the result is output to the averaging circuit 12, the simple absolute value circuit 14, and the synchronous symbol part deletion circuit 19. The result of differential detection is obtained by, for example, multiplying the IQ data of the current symbol by the complex conjugate of the IQ data one symbol before.
Here, for the plurality of subcarriers, when the current symbol data and the data one symbol before match, the differential detection result is zero in the phase rotation component and concentrated on one point on the I axis. To do. On the other hand, when the current symbol data and the data one symbol before differ for a plurality of subcarriers, the differential detection results are dispersed on the ± I axis and the ± Q axis, for example.

Specifically, in the frame configuration of this example shown in FIG. 5A, for the second REF symbol and the third REF symbol included in the synchronization symbol, one symbol before is the same REF symbol. Therefore, the result of the differential detection is concentrated on one point on the I axis.
On the other hand, the NULL symbol, CW symbol, SWEEP symbol, and first REF symbol included in the synchronization symbol are different symbols one symbol before, and the differential detection results are on the ± I axis and the ± Q axis. Disperse on average over. Since the data (DATA) symbol usually changes randomly according to the data to be transmitted, the differential detection result is dispersed on the ± I axis and the ± Q axis on average.

In the averaging circuit 12, the I-axis signal of the differential detection result input from the differential detection circuit 11 and the output signal from the flip-flop 22 are added by the adder 21, and the added signal is input to the flip-flop 22. As a result, the I-axis signals are cumulatively added. Further, in this example, the flip-flop 22 or the like divides and averages such cumulative addition results by the added number or the like to obtain an addition average result. In this example, a reset signal is input to the flip-flop 22 from the internal or external processing unit of the demodulation circuit 1 at a timing for each symbol, and the addition average result is reset to zero at the timing for each symbol. The addition average result of the I-axis signals for a plurality of subcarriers for each symbol is output from the flip-flop 22 to the simple absolute value circuit 13.
Similarly, the averaging circuit 12 uses the adder 23, the flip-flop 24, and the reset signal for each symbol to calculate the addition average result of the Q-axis signals for a plurality of subcarriers for each symbol, and the flip-flop 24. To the simple absolute value circuit 13.

  Here, the averaging circuit 12 adds and averages the I-axis signal and the Q-axis signal for all subcarriers for each symbol period. In this case, for the second REF symbol and the third REF symbol included in the synchronization symbol, the results of differential detection for each subcarrier are concentrated on one point on the I axis. The addition average result is not zero (0) but a constant value or a relatively large value, and the addition average result for the Q-axis component is zero (0) or a value close to zero. On the other hand, for the NULL symbol, CW symbol, SWEEP symbol, first REF symbol, or data (DATA) symbol included in the synchronization symbol, the differential detection results for each subcarrier are on the ± I axis and the ± Q axis. Since the dispersion is averaged upward, for example, the addition average result for the I-axis component and the Q-axis component becomes zero (0) or a value close to zero.

The simple absolute value circuit 13 adds the absolute values of the addition average result I1 of the I-axis signal and the addition average result Q1 of the Q-axis signal input from the addition average circuit 12 (| I1 | + | Q1 | ) As a simple absolute value, and the simple absolute value is output to the threshold value comparison circuit 17.
In the simple absolute value circuit 14, a value obtained by adding the absolute values of the I-axis signal I2 and the Q-axis signal Q2 input from the differential detection circuit 11 (| I2 | + | Q2 |) is a simple absolute value. And the simple absolute value is output to the averaging circuit 15.
Here, in this example, as a simplified configuration example, the sum of the absolute values of the I-axis component I and the Q-axis component Q (| I | + |) by the simple absolute value circuit 13 and the simple absolute value circuit 14. Q |) has been obtained, but as another configuration example, a configuration for calculating the square root {sqrt (I ² + Q ² )} of the sum of the square value of the I-axis component I and the square value of the Q-axis component Q is provided. May be used.

In this example, the addition averaging circuit 15 performs the same process as the addition averaging process for the I-axis signal (the same applies to the Q-axis signal) by the addition averaging circuit 12, and more specifically, the adder 25 and the flip-flop 26 and the reset signal for each symbol are used to calculate the addition average result of the simple absolute value signals for a plurality of subcarriers for each symbol and output the result from the flip-flop 26 to the threshold value calculation circuit 16.
The threshold calculation circuit 16 multiplies the signal of the addition average result input from the addition average circuit 15 by, for example, (1/4), and outputs the multiplication result to the threshold comparison circuit 17 as a threshold signal.

Here, in the system of the simple absolute value circuit 14 and the addition averaging circuit 15, since the simple absolute value which is the magnitude of the signal is first obtained and then the averaging is performed, the present example shown in FIG. In the frame configuration, the addition average result is the same value or close value for all symbols. For this reason, the threshold value calculated by the threshold value calculation circuit 16 is the same value or close value for all symbols.
In this example, the value obtained by multiplying the value of the addition average result by (1/4) is determined as the threshold value. However, the threshold value is not necessarily limited to (1/4) times. Can be changed to (1/3) times or (1/5) times. As another configuration example, a configuration in which a predetermined threshold is set in advance may be used.

The threshold comparison circuit 17 compares the simple absolute value input from the simple absolute value circuit 13 and the threshold input from the threshold calculation circuit 16 for each symbol, and the simple absolute value exceeds the threshold. The result of determining whether or not is output to the protection circuit 18.
The protection circuit 18 detects the frame start point (for example, detectively) based on the determination result input from the threshold comparison circuit 17, generates a pulse FST indicating the frame start point, and deletes the synchronization symbol portion. Output to the circuit 19.

Here, the threshold value output from the threshold value calculation circuit 16 is about the same size for all symbols. On the other hand, the simple absolute value output from the simple absolute value circuit 13 is larger than the threshold for the second REF symbol and the third REF symbol included in the synchronization symbol, and is about zero (0) for the other symbols. The threshold is not exceeded. Therefore, the threshold comparison circuit 17 can detect a peak at the timing of these two REF symbols, and the protection circuit 18 determines the frame position based on the positions (timing) of these two REF symbols. Can be detected.
In FIG. 5C, the phase difference (result of differential detection) between each symbol shown in FIG. 5A and the symbol one symbol before shown in FIG. 5B is added and averaged. An example of the magnitude of the result is shown.

In this example, the protection circuit 18 detects the frame position. However, for example, the threshold comparison circuit 17 may have a function of detecting the frame position and generating and outputting the pulse FST. In this case, the protection circuit 18 can be omitted.
In this example, the position of the frame is detected based on the positions of the two REF symbols. However, as another configuration example, only one of these two REF symbols (the former or It is also possible to adopt a configuration in which the position of the frame is detected based on the later position.

  The protection circuit 18 ensures the reliability of the pulse FST indicating the frame position by performing the pre-stage protection process and the post-stage protection process. In the pre-stage protection process, when the frame position is not synchronized, a peak exceeding the threshold value is detected in the threshold comparison circuit 17 continuously for a predetermined number of times (for example, three frames). The pulse FST is output, and the pulse FST is not output when the synchronization acquisition does not continue for a predetermined number of times. In the post-protection processing, when the frames are synchronized, the threshold comparison circuit 17 does not detect a peak exceeding the threshold continuously for a predetermined number of times (for example, three frames). In this case, the output of the pulse FST is stopped, and if the loss of synchronization does not continue for a predetermined number of times, the pulse FST is continuously output periodically at the timing of the previously determined frame position.

The synchronous symbol part deletion circuit 19 is synchronized with the complex signal (I-axis signal and Q-axis signal) of the differential detection result input from the differential detection circuit 11 based on the timing of the pulse FST input from the protection circuit 18. The symbol portion is deleted, and the signal of the data portion thus obtained (signal of only the data symbol) is output to the determination circuit 20.
In the determination circuit 20, for the data symbol signal input from the synchronization symbol partial deletion circuit 19, a bit consisting of 0 or 1 corresponding to the phase difference between the current symbol and the previous symbol, for example, according to the DQPSK system The obtained data is output to the decoding unit 46 as a demodulation result. Such a determination is performed for each subcarrier and each symbol, for example, by time division.

  As described above, the receiving apparatus of the present example receives a signal of a frame composed of several types of synchronization symbols and a plurality of data symbols modulated by the DQPSK method for each subcarrier by the OFDM modulation method. In the processing, the synchronous symbol portion is differentially detected, and the position of the frame is detected based on the result of averaging the differential detection results. Specifically, differential detection is performed, the result of the differential detection is added and averaged, and a threshold is calculated based on the result of the differential detection, and the result of the addition of the differential detection and the threshold are calculated. The position of the peak is detected based on, and the position of the frame is detected based on the position of the peak.

  Therefore, in the receiving apparatus of this example, the synchronous symbol portion is differentially detected and added and averaged, and a large peak is detected only at the positions of a plurality of REF symbols where the same signal (same data) is repeated. By detecting the position of the frame based on the peak position, the position of the frame can be detected with high accuracy. Further, in the configuration of this example, compared with the configuration of the frame detection circuit 51 as shown in FIG. 7, for example, the SWEEP pattern memory 62 for storing the SWEEP symbol pattern and the SWEEP correlator 63 for performing the correlation calculation are used. Therefore, the circuit scale can be greatly reduced, and simplification and cost reduction of the apparatus can be realized.

Here, in this example, the demodulation circuit 1 is provided with a frame detection function for detecting the position of the frame and a demodulation function for demodulating the data symbols. However, as another configuration example, the frame detection function and the demodulation function are separately provided. It is also possible to arrange for the processing unit.
Further, in this example, a description has been given by taking as an example a standard in which three REF symbols, which are the same symbol, are arranged in the synchronization symbol portion included in the frame, but for example, two or more identical symbols are arranged in succession. In this case, since the threshold value comparison circuit 17 detects one or more peaks, the same configuration as in this example can be applied.

In this example, the DQPSK method is used as the differential encoding method, and the REF symbol is used as the same symbol that is consecutively arranged in the synchronization symbol portion.
Further, in the demodulation circuit 1 provided in the receiving apparatus of this example, the differential detection means is configured by the function of the differential detection circuit 11, and is larger by the function of the averaging circuit 12 and the function of the simple absolute value circuit 13. The threshold value generating means is configured by the function of the simple absolute value circuit 14, the function of the addition averaging circuit 15, and the function of the threshold value calculating circuit 16, and the function of the threshold value comparing circuit 17 is used for timing detection means. The frame timing detection means is constituted by the function of the protection circuit 18, the synchronization symbol part deletion means is constituted by the function of the synchronization symbol part deletion circuit 19, and the judgment means is constituted by the function of the judgment circuit 20. Is configured.

Here, the configuration of the system and apparatus according to the present invention is not necessarily limited to the configuration described above, and various configurations may be used. The present invention can also be provided as, for example, a method or method for executing the processing according to the present invention, a program for realizing such a method or method, or a recording medium for recording the program. It is also possible to provide various devices and systems.
The application field of the present invention is not necessarily limited to the above-described fields, and the present invention can be applied to various fields.
In addition, as various processes performed in the system and apparatus according to the present invention, for example, the processor executes a control program stored in a ROM (Read Only Memory) in hardware resources including a processor and a memory. A controlled configuration may be used, and for example, each functional unit for executing the processing may be configured as an independent hardware circuit.
The present invention can also be understood as a computer-readable recording medium such as a floppy (registered trademark) disk or a CD (Compact Disc) -ROM storing the control program, and the program (itself). The processing according to the present invention can be performed by inputting the program from the recording medium to the computer and causing the processor to execute the program.

It is a figure which shows the structural example of the demodulation circuit which concerns on one Example of this invention. It is a figure which shows the structural example of the transmitter which concerns on one Example of this invention. It is a figure which shows the structural example of the receiver which concerns on one Example of this invention. It is a figure which shows the structural example of the symbol of an OFDM modulation signal. It is a figure which shows the structural example of a flame | frame, and the structural example of a synchronization symbol. It is a figure which shows the structural example of a receiver. It is a figure which shows the structural example of a flame | frame detection circuit.

Explanation of symbols

  1, 52 .. Demodulation circuit 11.. Differential detection circuit 12, 15 .. Addition averaging circuit 13, 14... Simple absolute value circuit 16... Threshold calculation circuit 17. ..Protection circuit 19 ..Synchronization symbol part deletion circuit 20 ..Judgment circuit 21, 23, 25 ..Adder 22, 24, 26 ..Flip flop 31 ..Encoding unit 32. Mapping unit 33.. IFFT arithmetic circuit 34.. Guard addition circuit 35.. Synchronization symbol insertion unit 36.. Quadrature modulation circuit 37.. D / A conversion unit 38. ..Antenna, 42 ... Down converter, 43 ... A / D converter, 44 ... Orthogonal demodulator, 45 ... FFT arithmetic circuit, 46 ... Decoder, 51 ... Frame detection circuit, 61 ... NULL end detector 62 ... SWEEP pattern memory 63 ... SWEEP correlator 64 ... Frame counter

Claims (5)

In a receiving apparatus that receives a signal modulated by an OFDM modulation scheme,
The modulation signal according to the OFDM modulation scheme is modulated by a differential encoding scheme for each subcarrier for a plurality of subcarriers, and includes a synchronization symbol portion including two or more consecutive identical symbols. It is formed in a frame composed of data symbol parts,
The receiving apparatus includes differential detection means for differentially detecting the received signal for each subcarrier for each symbol;
Each of the I-axis signal and the Q-axis signal as a result of differential detection by the differential detection means is added or averaged for each of the plurality of subcarriers for each symbol, and the magnitude of the addition result or the addition average result is obtained. A size detecting means for detecting;
Timing detection means for detecting timing at which the size detected by the size detection means is equal to or greater than a predetermined threshold or exceeds a predetermined threshold;
Frame timing detection means for detecting the timing of the frame based on the timing detected by the timing detection means,
A receiving apparatus. The receiving device according to claim 1,
Threshold generation means for generating the predetermined threshold based on the result of differential detection by the differential detection means;
Synchronization symbol part deleting means for deleting the synchronization symbol part from the result of differential detection by the differential detection means based on the timing of the frame detected by the frame timing detection means;
A determination unit that determines a data symbol part that is a result of deletion of the synchronization symbol part by the synchronization symbol part deletion unit and sets it as a demodulation result;
A receiving apparatus comprising: In a transmission system for transmitting a signal modulated by an OFDM modulation method from a transmission-side device to a reception-side device,
The modulation signal according to the OFDM modulation scheme is modulated by a differential encoding scheme for each subcarrier for a plurality of subcarriers, and includes a synchronization symbol portion including two or more consecutive identical symbols. It is formed in a frame composed of data symbol parts,
The reception-side device includes differential detection means for differentially detecting the received signal for each subcarrier for each symbol;
Each of the I-axis signal and the Q-axis signal as a result of differential detection by the differential detection means is added or averaged for each of the plurality of subcarriers for each symbol, and the magnitude of the addition result or the addition average result is obtained. A size detecting means for detecting;
Timing detection means for detecting timing at which the size detected by the size detection means is equal to or greater than a predetermined threshold or exceeds a predetermined threshold;
Frame timing detection means for detecting the timing of the frame based on the timing detected by the timing detection means,
A transmission system characterized by that. The transmission system according to claim 3,
The reception-side device includes threshold generation means for generating the predetermined threshold based on a result of differential detection by the differential detection means;
Synchronization symbol part deleting means for deleting the synchronization symbol part from the result of differential detection by the differential detection means based on the timing of the frame detected by the frame timing detection means;
A determination unit that determines a data symbol part that is a result of deletion of the synchronization symbol part by the synchronization symbol part deletion unit and sets it as a demodulation result;
A transmission system characterized by that. In a receiving method in a receiving apparatus that receives a signal modulated by an OFDM modulation method,
The modulation signal according to the OFDM modulation scheme is modulated by a differential encoding scheme for each subcarrier for a plurality of subcarriers, and includes a synchronization symbol portion including two or more consecutive identical symbols. It is formed in a frame composed of data symbol parts,
The receiving apparatus differentially detects the received signal for each subcarrier for each symbol, and adds each of the I-axis signal and the Q-axis signal as a result of the differential detection for each of the plurality of subcarriers for each symbol. Addition averaging is performed to detect the addition result or the magnitude of the addition average result, detect a timing at which the detected magnitude is equal to or greater than a predetermined threshold or exceeds a predetermined threshold, and based on the detected timing Detect frame timing,
And a receiving method.

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