JP6580449B2 - Delay profile creation circuit and delay profile creation method - Google Patents

Description

  The present invention relates to a creation circuit for creating a delay profile used for measurement of a delay wave state based on a received digital signal using the OFDM method, and a creation method thereof.

  Conventionally, in the transmission / reception in the OFDM (Orthogonal Frequency Division Multiplex) method used in digital FPU (Field Pickup Unit), terrestrial digital TV broadcasting, etc., the state of radio wave delay caused by multipath on the receiving side is measured. Therefore, a delay profile has been created. As a method of creating this delay profile, the inverse Fourier transform (IFFT) is performed based on channel information obtained from a pilot signal whose phase, amplitude, insertion position, etc. are known. A technique that employs a process such as processing has been generally adopted.

  For example, as shown in FIG. 4, a conventional delay profile creation circuit 50 is composed of a general OFDM demodulation side and a delay profile creation (calculation) side. The transform unit 52 performs a Fourier transform on the received, synchronously reproduced / orthogonally demodulated OFDM signal to output a frequency domain signal, and further, a subcarrier determination unit 54 is output by the Fourier transform unit 52. Each subcarrier information is acquired from the frequency domain signal, and the type of the acquired subcarrier is determined.

  Subsequently, the subcarrier adjustment unit 56 extracts pilot information data from the subcarriers determined by the subcarrier determination unit 54 as pilot signals, and discards all data from other subcarriers. Process. Then, the data number adjustment unit 58 adjusts the number of data by inserting Null data (0 data) to both ends of the pilot information data extracted by the subcarrier adjustment unit 56, and the data is adjusted. The window function processing unit 60 performs window function processing, and a delay profile is created through subsequent processing (62, 64, 66) such as inverse Fourier transform processing.

  For example, in Patent Document 1, in an OFDM signal receiving apparatus that receives an OFDM signal and calculates a transmission path characteristic, the RF signal of the OFDM signal is converted into an IF signal, and the analog IF signal is converted into a digital IF signal. A radio unit for performing an orthogonal demodulation on the digital IF signal to generate an equivalent baseband signal, removing a GI from the equivalent baseband signal, and outputting an equivalent baseband signal in an effective symbol period; and the radio unit FFT of the equivalent baseband signal output by the above, and an FFT unit that outputs a frequency domain signal, and a pilot signal is extracted from the frequency domain signal output by the FFT unit to calculate the channel characteristics of the pilot carrier position A pilot signal extraction unit that performs transmission of the pilot carrier position calculated by the pilot signal extraction unit A phase correction unit that corrects the phase of the signal and aligns the phases between the OFDM symbols, and an interpolation processing unit that performs interpolation in the OFDM symbol direction on the signal in which the phase between the symbols is aligned by the phase correction unit And IFFT of the addition average processing unit that adds and averages a plurality of signals interpolated by the interpolation processing unit between OFDM symbols, and calculates the delay profile by performing IFFT on the addition averaged signal by the addition average processing unit There is disclosed an OFDM signal receiving apparatus comprising a delay profile calculation unit for performing the above-described operation.

  Patent Document 2 discloses FFT means for performing FFT processing on a digital baseband OFDM signal in which pilot signals for amplitude / phase equalization are arranged at predetermined carrier positions, and the pilot output from the FFT output of this means. Pilot signal extracting means for extracting a signal, specific estimation means for estimating the amplitude frequency characteristic and phase frequency characteristic of the input signal from the pilot signal extracted by this means, and IFFT processing of the characteristic value estimated by this means, There is disclosed a delay profile measuring device comprising IFFT means for detecting an amplitude value and a phase value.

JP2012-10179A JP 2000-115087 A

  However, according to the above-described conventional technique and the technique described in the patent document, for example, the delay profile is created based only on the information data obtained from the pilot signal. As shown in (b), since the frequency interval of subcarriers used for computation for creating a delay profile becomes wide, the delay profile can be estimated only for a short time, so that multipath and the like can be performed. It has been pointed out that a long-time delayed wave in which the frequency interval of the resulting transmission path distortion is shorter than the pilot signal insertion interval cannot be measured correctly.

  The present invention is for solving the above-described problem, and it is accurate even for a long delay wave in which the frequency interval of transmission path distortion caused by multipath or the like is shorter than the insertion interval of the pilot signal. It is an object of the present invention to provide a delay profile creation circuit and a creation method thereof that enable measurement.

In order to cope with the above-described problems, the present invention takes the following technical means.
That is, the invention according to claim 1 performs Fourier transform on the received OFDM signal and outputs a frequency domain signal, and each subcarrier information from the frequency domain signal output by the Fourier transform means. Subcarrier determination means for determining the type of the acquired subcarrier and subcarriers determined to have increased in amplitude by the subcarrier determination means. An amplitude adjustment unit that sets the amplitude multiplied by the coefficient and sets the amplitude as the average value of the amplitudes of the subcarriers adjacent to the subcarrier for the subcarrier determined to be unmodulated by the amplitude adjustment unit. By taking the absolute value of the coordinate represented by the complex number of each adjusted subcarrier and converting it to a real number, the amplitude of each subcarrier can be calculated. Amplitude acquisition means, and amplitude characteristic data acquisition means for obtaining amplitude characteristic change data by taking a time average of the amplitude of each subcarrier acquired by the amplitude acquisition means and obtaining an average amplitude for each subcarrier, Null data is inserted into both ends of the amplitude characteristic change data acquired by the amplitude characteristic data acquisition means, and the data number adjustment means for adjusting the number of data, and the data adjusted by the data number adjustment means Window function processing means for performing window function processing, and data processed by the window function processing means, and inverse Fourier transform means for performing inverse Fourier transform with the imaginary part of the input value regarded as 0, Processing data extraction means for extracting only one side portion from the processing data obtained by the inverse Fourier transform means; and the processing data extraction means. A delay profile creation circuit comprising: data calculation means for calculating an absolute value and logarithm of extracted data; and delay profile creation means for creating a delay profile based on a numerical value calculated from the data calculation means It is.

  Next, the invention according to claim 2 is the delay profile creation circuit according to claim 1, wherein the data calculation means calculates an absolute value and a logarithm of the data extracted by the processing data extraction means, A feature of this is that normalization processing in the amplitude direction is performed.

  Furthermore, the invention according to claim 3 performs a Fourier transform on the received OFDM signal and outputs a frequency domain signal, and each subcarrier information from the frequency domain signal output by the Fourier transform step. And a subcarrier determination step for determining each of the acquired subcarrier types, and a subcarrier for which the amplitude is determined to be increased by the subcarrier determination step, a predetermined value is set for the amplitude. For the subcarrier determined to be non-modulated by multiplying the coefficient by the amplitude, an amplitude adjustment step in which the amplitude is the average value of the amplitudes of the subcarriers adjacent to the subcarrier, and the amplitude adjustment step By taking the absolute value of the coordinate represented by the complex number of each adjusted subcarrier and converting it to a real number, Amplitude acquisition step for obtaining each amplitude of the carrier, and amplitude for obtaining amplitude characteristic change data by taking the time average of the amplitude of each subcarrier acquired by the amplitude acquisition step and obtaining the average amplitude for each subcarrier Characteristic data acquisition step, Null data is inserted at both ends of the amplitude characteristic change data acquired by the amplitude characteristic data acquisition step, and the data number adjustment step for adjusting the number of data and the data number adjustment step for adjustment A window function processing step for performing window function processing on the received data, and data processed by the window function processing step are input, and an inverse Fourier transform is performed by regarding the imaginary part of the input value as 0 From the Fourier transform step and the processed data by the inverse Fourier transform step, one side thereof A processing data extraction step for extracting only the minutes, a data calculation step for calculating the absolute value and logarithm of the data extracted by the processing data extraction step, and a delay profile based on the numerical values calculated from the data calculation step A delay profile creating step comprising: a delay profile creating step.

  The invention according to claim 4 is the delay profile creation method according to claim 3, wherein the data calculation step calculates absolute values and logarithms of the data extracted by the processing data extraction step, and On the other hand, a normalization process in the amplitude direction is performed.

  According to the present invention, it is possible to create a delay profile that can be accurately measured even for a long-time delay wave in which the frequency interval of transmission path distortion caused by multipath or the like is shorter than the pilot signal insertion interval. It becomes possible.

FIG. 3 is a block diagram showing an embodiment of a delay profile creation circuit according to the present invention. 5 is a flowchart illustrating an embodiment of a delay profile creation method according to the present invention. BRIEF DESCRIPTION OF THE DRAWINGS It is the conceptual diagram regarding embodiment of the delay profile creation circuit and delay profile creation method concerning this invention, (a) is the graph which showed the subcarrier used for a calculation, (b) is the delay displayed on the graph based on the calculation result. An example of a profile is shown. It is the block diagram which showed embodiment of the conventional delay profile creation circuit. It is a conceptual diagram regarding a conventional delay profile creation circuit and a delay profile creation method, (a) is a graph showing subcarriers used for computation, (b) shows an example of a delay profile displayed in a graph based on the computation results. It is a thing.

  Embodiments of a delay profile creation circuit and a creation method thereof according to the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a delay profile creating circuit according to the present invention, and FIG. 2 is a flowchart showing an embodiment of a delay profile creating method according to the present invention. FIG. 3 is a conceptual diagram relating to an embodiment of the delay profile creation circuit and the delay profile creation method according to the present invention. FIG. 3A is a graph showing subcarriers used for computation, and FIG. 3B is based on the computation result. 8 shows an example of a delay profile displayed in a graph.

  As for codes, 10 is a delay profile creation circuit, 12 is an OFDM demodulation unit, 14 is a Fourier transform unit, 16 is a subcarrier determination unit, 18 is an amplitude adjustment unit, 20 is an amplitude acquisition unit, and 22 is amplitude characteristic data acquisition. , 24 is a data number adjustment unit, 26 is a window function processing unit, 28 is an inverse Fourier transform unit, 30 is a processing data extraction unit, 32 is a data calculation unit, and 34 is a delay profile creation unit.

  First, as shown in FIG. 1, the delay profile creation circuit 10 according to the present embodiment includes a general OFDM demodulation side and a delay profile creation (calculation) side. The delay profile creation circuit 10 includes a Fourier transform unit 14 that outputs a frequency domain signal by performing a Fourier transform on the OFDM signal received by the OFDM demodulator 12 and synchronously reproduced and orthogonally demodulated, and a Fourier transform A subcarrier determination unit 16 that acquires each subcarrier information from the frequency-domain signal output by the unit 14 and determines the type of the acquired subcarrier.

  Further, the delay profile creation circuit 10 multiplies the amplitude by a predetermined coefficient for the subcarrier whose amplitude is determined to be increased by the subcarrier determination unit 16 (in this embodiment, the coefficient For subcarriers determined to be unmodulated, and the amplitude is an average value of amplitudes of subcarriers on both sides of the corresponding subcarrier; An amplitude acquisition unit 20 is provided which obtains the respective amplitudes of the subcarriers by taking the absolute values of the coordinates represented by the complex numbers of the subcarriers adjusted by the amplitude adjustment unit 18 and converting them to real numbers.

  Furthermore, the delay profile creation circuit 10 takes the time average of the amplitudes of the subcarriers acquired by the amplitude acquisition unit 20 (in this embodiment, about 16 OFDM symbols), and obtains the average amplitude for each subcarrier. Thus, Null data (0 data) is inserted into both ends of the amplitude characteristic data acquisition unit 22 for obtaining amplitude characteristic change data and the amplitude characteristic change data acquired by the amplitude characteristic data acquisition unit 22, respectively. And a window function processing unit 26 for performing window function processing on the data adjusted by the data number adjusting unit 24.

  Subsequently, the delay profile creation circuit 10 receives the data processed by the window function processing unit 26, and also performs an inverse Fourier transform unit 28 that performs an inverse Fourier transform by regarding the imaginary part of the input value as 0, and an inverse Fourier transform. A processing data extraction unit 30 that extracts only one side portion from the processing data by the conversion unit 28, a data calculation unit 32 that calculates the absolute value and logarithm of the data extracted by the processing data extraction unit 30, and a data calculation unit 32 And a delay profile creating unit 34 for creating a delay profile based on the numerical value calculated from the above.

  Next, details of the delay profile creating circuit 10 in the present embodiment will be described with reference to a flowchart shown in FIG. 2 together with an embodiment of a delay profile creating method according to the present invention. First, the OFDM demodulator 12 performs synchronous reproduction / orthogonal demodulation processing on the received OFDM signal, and Fourier-transforms the signal by the Fourier transform unit 14 to output it as a frequency domain signal (step). 1).

  Then, the subcarrier determination unit 16 acquires information on each subcarrier from the signal output from the Fourier transform unit 14, and determines the type of each subcarrier based on the acquired information (step 2). ). Subsequently, the amplitude adjusting unit 18 multiplies the amplitude by a predetermined coefficient for the subcarrier determined by the subcarrier determining unit 16 as having increased amplitude (in this embodiment, the coefficient For subcarriers determined to be non-modulated, the amplitude is adjusted so that the amplitude is the average value of the amplitudes of the subcarriers adjacent to the corresponding subcarrier. Note that special processing is not performed for other subcarriers determined to be general (step 3).

  This is because the average amplitude for each subcarrier is not constant for an OFDM signal used in a digital FPU or terrestrial digital TV broadcast. For example, the amplitude of a pilot signal or a subcarrier of TMCC (Transmission and Multiplexing Configuration Control) The subcarrier corresponding to the center of the band and the subcarrier for AC when the AC (Auxiliary Channel) is not used are unmodulated. Therefore, amplitude adjustment is performed to estimate the amplitude characteristics of the entire band. Because is important.

  Then, the amplitude acquisition unit 20 acquires the amplitude of each subcarrier adjusted by the amplitude adjustment unit 18 (step 4). The amplitude and phase of each subcarrier are represented by complex numbers. The absolute value of this coordinate is taken and converted into a real number to acquire the amplitude of each subcarrier. Note that the phase information is discarded here.

  Next, the amplitude characteristic data acquisition unit 22 takes the time average of the amplitude of each subcarrier acquired by the amplitude acquisition unit 20, obtains the average amplitude for each subcarrier, and acquires amplitude characteristic change data due to transmission path distortion. (Step 5). In the present embodiment, in the computer simulation, time averaging over about 16 OFDM symbols is performed, but the number is appropriately increased or decreased in consideration of the calculation speed and the circuit scale.

  Subsequently, in a subsequent process, in order to perform inverse Fourier transform on the amplitude characteristic data acquired by the amplitude characteristic data acquisition unit 22, the data number adjustment unit 24 sets the data number of the amplitude characteristic data in units of 2 ^ n. Accordingly, processing for adding Null data to both sides is performed (step 6). The window function processing unit 26 performs window function processing on the data with Null data added on both sides (step 7). In the present embodiment, the Blackman window function is used in the computer simulation, but other window functions may be used as appropriate.

  Next, the inverse Fourier transform unit 28 performs inverse Fourier transform on the input of the data subjected to the window function processing by the window function processing unit 26 while regarding the imaginary part of the input value as 0 (step 8). Furthermore, the processing data extraction unit 30 extracts (2 ^ (n-1) point) only from one side of the processing data (2 ^ n) point by the inverse Fourier transform unit 28 (step 9). This is because the calculation result is symmetrical in the time direction because it is a real number IFFT. This process corresponds to a process in which a delayed wave caused by transmission path distortion is regarded as only delayed in time from the main wave.

  And the data calculation part 32 calculates the absolute value and logarithm of the extracted data (step 10). This is a process necessary to display the calculated delay profile in a graph in order to display the vertical axis in dB units. Normally, since AGC (automatic gain control) is used in the process before the calculation of the delay profile, it is not necessary to perform normalization processing, but the main wave intensity is always set to 0 dB (reference intensity). Therefore, the data calculation unit 32 may be configured to perform normalization processing in the amplitude direction.

  Then, the delay profile creation unit 34 creates a delay profile based on the numerical value calculated by the data calculation unit 32 (step 11). Since the delay profile creation processing is performed with the configuration as described above, as shown in FIG. 3A, the frequency interval of subcarriers used for computation for delay profile creation is narrow, which is caused by multipath or the like. As shown in (b), it is possible to correctly measure a long-time delayed wave whose transmission path distortion frequency interval is shorter than the pilot signal insertion interval.

  The delay profile creation circuit and the creation method according to the present invention provide an accurate delay profile even for a long delay wave in which the frequency interval of transmission path distortion due to multipath or the like is shorter than the pilot signal insertion interval. Can be suitably used in situations where it is necessary to create

DESCRIPTION OF SYMBOLS 10 Delay profile creation circuit 12 OFDM demodulation part 14 Fourier transform part 16 Subcarrier determination part 18 Amplitude adjustment part 20 Amplitude acquisition part 22 Amplitude characteristic data acquisition part 24 Data number adjustment part 26 Window function process part 28 Inverse Fourier transform part 30 Process data Extraction unit 32 Data calculation unit 34 Delay profile creation unit

Claims (4)

Fourier transform means for performing a Fourier transform on the received OFDM signal and outputting a frequency domain signal;
Subcarrier determination means for acquiring each subcarrier information from the frequency domain signal output by the Fourier transform means and determining the type of the acquired subcarrier,
For subcarriers determined by the subcarrier determination means to be increased in amplitude, the amplitude is obtained by multiplying the amplitude by a predetermined coefficient, and for subcarriers determined as unmodulated. , An amplitude adjusting means that sets the amplitude as the average value of the amplitudes of the subcarriers adjacent to the subcarrier;
Amplitude acquisition means for obtaining the amplitude of each subcarrier by taking the absolute value of the coordinates represented by the complex number of each subcarrier adjusted by the amplitude adjustment means and making it a real number;
Amplitude characteristic data acquisition means for obtaining amplitude characteristic change data by taking a time average of the amplitude of each subcarrier acquired by the amplitude acquisition means and obtaining an average amplitude for each subcarrier;
Data number adjusting means for inserting Null data at both ends of the amplitude characteristic change data acquired by the amplitude characteristic data acquiring means and adjusting the number of data;
Window function processing means for performing window function processing on the data adjusted by the data number adjusting means;
The data processed by the window function processing means is input, and the inverse Fourier transform means for performing the inverse Fourier transform by regarding the imaginary part of the input value as 0,
Processing data extracting means for extracting only one side portion from the processing data by the inverse Fourier transform means;
Data calculating means for calculating the absolute value and logarithm of the data extracted by the processing data extracting means;
A delay profile creating means for creating a delay profile based on the numerical value calculated from the data calculating means;
A delay profile creation circuit comprising:   2. The delay according to claim 1, wherein the data calculation unit calculates an absolute value and a logarithm of the data extracted by the processing data extraction unit, and performs normalization processing in an amplitude direction on the absolute value and logarithm. Profile creation circuit. A Fourier transform step for performing a Fourier transform on the received OFDM signal and outputting a frequency domain signal;
Subcarrier determination step of acquiring each subcarrier information from the frequency domain signal output by the Fourier transform step and determining the type of the acquired subcarrier,
For subcarriers determined to have increased in amplitude by the subcarrier determination step, the amplitude is obtained by multiplying the amplitude by a predetermined coefficient, and for subcarriers determined to be unmodulated. An amplitude adjustment step in which the amplitude is an average value of the amplitudes of the subcarriers adjacent to the subcarrier;
Taking the absolute value of the coordinates represented by the complex number of each subcarrier adjusted by the amplitude adjustment step, and converting it to a real number, an amplitude acquisition step for obtaining each amplitude of each subcarrier;
Amplitude characteristic data acquisition step of obtaining amplitude characteristic change data by taking a time average of the amplitude of each subcarrier acquired by the amplitude acquisition step and obtaining an average amplitude for each subcarrier;
A data number adjusting step of inserting Null data at both ends of the amplitude characteristic change data acquired by the amplitude characteristic data acquiring step and adjusting the number of data;
A window function processing step for performing window function processing on the data adjusted in the data number adjustment step;
The data processed by the window function processing step is input, and the inverse Fourier transform step for performing the inverse Fourier transform with the imaginary part of the input value regarded as 0,
A processing data extraction step for extracting only one side portion from the processing data by the inverse Fourier transform step;
A data calculation step for calculating the absolute value and logarithm of the data extracted by the processing data extraction step;
A delay profile creating step for creating a delay profile based on the numerical value calculated from the data calculating step;
A delay profile creation method comprising:   4. The delay according to claim 3, wherein the data calculation step calculates an absolute value and a logarithm of the data extracted by the processing data extraction step, and performs normalization processing in an amplitude direction on the absolute value and logarithm. Profile creation method.