JP2006093760A - Ofdm wave delay profile measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an OFDM wave delay profile measuring device in which the length of maximum delay time capable of measuring a delay wave, the time resolution capable of measuring a delay wave, the level capable of measuring a delay wave, the precision of delay wave level, and the false pulse response in the delay profile measuring method can be eliminated. <P>SOLUTION: The OFDM wave delay profile measuring device 1 comprises a means 13 for measuring a delay profile including the delay time of OFDM delay wave and the DU ratio indicative of the intensity ratio between direct wave and delay wave of the OFDM wave. It is further provided with an OFDM wave receiving means 3, a direct wave estimating means 5, a frequency region converting means 7, a transfer function deriving means 9, a delay profile converting means 11, and a measurement decision/output means 15. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an OFDM wave delay profile measuring apparatus that measures a delay profile composed of a delay time of an OFDM wave delay wave and a DU ratio indicating a ratio of the intensity of the desired wave and the delay wave of the OFDM wave.

  Conventionally, when measuring a delay profile of an OFDM wave received in an SFN (Single Frequency Network) of digital terrestrial broadcasting using an OFDM (Orthogonal Frequency Division Multiplex) system, this delay profile An ideal measurement method is to obtain a transfer function of a propagation path using a direct wave as an input signal and a received wave as an output signal, and performing IFFT (Inverse Fast Fourier Transform) on the obtained transfer function. .

  Here, the direct wave is an OFDM wave directly propagated from the transmission side to the reception side, and does not include a delay wave (multipath delay wave). The received wave is an OFDM wave that is received while interfering waves and delay waves are mixed during propagation from the transmitting side to the receiving side. That is, if the received wave does not include a delayed wave (and an interference wave), it is the same as the direct wave.

  If the received wave does not include a delayed wave, the response obtained by IFFT of the transfer function of the propagation path is the time domain number “0” when the time axis is the horizontal axis and the level intensity is the vertical axis. An impulse corresponding to a direct wave appears at a location (time 0), and no impulse appears at a location corresponding to another time domain number.

  On the other hand, if the received wave includes a delayed wave, an impulse corresponding to the direct wave appears in the time domain number “0” in the response obtained by IFFT of the transfer function of the propagation path, which corresponds to the delay time. An impulse with a low intensity corresponding to a delayed wave appears at the position of the time domain number.

  That is, if the time domain number of the impulse corresponding to the delayed wave and the intensity of the level appear in the time domain number other than the time domain number “0” from the response obtained by IFFT of the transfer function of the propagation path, the time domain number is obtained. From the delay time and level intensity, the delay wave level can be estimated, that is, the delay profile can be measured.

  Note that the maximum value of the delay time that can be measured as a delay profile is half the window length for IFFT of the transfer function of the propagation path, and the resolution of the delay time is the reciprocal of the sample frequency.

  However, since it is difficult to realize a receiving means that receives only a direct wave that does not include a delayed wave at a receiving point that is in the SFN and receives a propagating OFDM wave, an output when obtaining a transfer function is obtained. It is necessary to estimate a direct wave as an input signal when obtaining the transfer function from a received wave as a signal. A method of obtaining a delay profile by obtaining a transfer function of the propagation path from the estimated direct wave and performing IFFT is employed.

Incidentally, some methods (existing delay profile measuring methods) for measuring a delay profile after estimating an input signal (direct wave) from an output signal (received wave) are disclosed.
For example, as an existing delay profile measurement method, paying attention to the fact that an SP signal (scattered pilot signal) having a known amplitude and phase is inserted into a demodulated carrier obtained by demodulating a received OFDM wave, There is a method using the extracted SP signal (hereinafter referred to as SP method).

  Further, as an existing delay profile measurement method, there is “OFDM wave delay profile measurement device” (refer to Patent Document 1) as a method of analyzing an amplitude frequency characteristic obtained by observing an OFDM wave with a spectrum analyzer by FFT (refer to Patent Document 1 below). Called the Sparena method).

  The input signal by the SP method has a value (direct wave) set in advance according to the signal standard. Further, the maximum delay time of the delay wave that can be measured by the SP method is up to one third of the effective symbol time length of the OFDM wave, which is insufficient as a delay profile measurement function in SFN (Single Frequency Network). is there. That is, in order to demodulate the SP signal, the window length must be the effective symbol time length (1008 μs for the mode 3 signal).

  Therefore, the present inventor proposes a “terrestrial digital SFN wave measuring device” (Japanese Patent Application No. 2004-73673), which is a measurement method in which there is no principle restriction on the long-distance delay time, which is the delay time of a delayed wave from a long distance. (Hereinafter referred to as the power spectrum method).

  This power spectrum method takes a longer window length (FFT window length) when the OFDM wave is converted into a frequency domain signal by FFT (Fast Fourier Transform) than the SP method, and squares the time domain signal. Then, the delay profile is obtained by converting the OFDM wave from the voltage dimension to the power dimension. In this power spectrum method, there is no constraint that the window length time length must be an effective symbol time length as in the SP method, and can be freely set. Therefore, the maximum delay time of the delay wave that can be measured There is a merit that there is no principle restriction.

  Moreover, the transfer function calculated | required by this power spectrum method means converting the complex number which is an output signal (received wave) of a frequency domain into the value of a real number, and as an input signal (direct wave), The values of all frequency domain numbers (numbers when the frequency is plotted on the horizontal axis and the intensity of each frequency level on the vertical axis) are constant values of “1”.

  Incidentally, in the power spectrum method, when a transfer function is obtained from an input signal (direct wave) and an output signal (received wave), and the obtained transfer function is subjected to IFFT (Inverse Fast Fourier Transform), the number of delay waves is one. There is no problem, but an impulse corresponding to the delayed wave appears, but when there are a plurality of delayed waves, a false impulse due to cross modulation due to interference between the delayed waves appears.

  Further, the estimated input signals (direct waves) are all approximated to “1” even though they are actually complex values. Therefore, the approximate value “1” and the input signal are approximated. An error (approximate error) with the actual value of (direct wave) may increase, and impulses with a lower level than the impulse corresponding to the delayed wave (error impulse) are used for the responses of all time domain numbers. ) Appears.

  This error impulse affects the lower identification limit of a small level impulse corresponding to a delayed wave. In other words, in all time domain numbers, an error impulse that appears almost uniformly and a small level impulse corresponding to a delayed wave cannot be separately identified. As a result, a small level impulse is generated from the input signal (direct wave). It becomes difficult to identify (recognize) whether it is caused by an approximation error with an actual value or a delayed wave.

Here, further, matters (evaluation items) for evaluating the superiority or inferiority of the measurement method from the examples of the two delay profile measurement methods of the SP method and the power spectrum method will be described.
The superiority and inferiority evaluation items of the delay profile measurement method include the maximum delay time that can measure the delay wave, the time resolution that can measure the delay wave, the level that can measure the delay wave, the accuracy of the delay wave level, and the false And the presence or absence of an impulse response.

  In the SP method, the maximum delay time in which the delay wave can be measured has a limit of 1/2 of the effective symbol time length, and in the power spectrum method, the window length (FFT window length) is increased to be a practical limit. Disappears.

  In the SP method, the time resolution capable of measuring the delayed wave is inserted only every 12 in the carrier demodulated by the SP signal, and the effective sample frequency is reduced to 1/12. The power spectrum method does not decrease because the effective sample frequency remains 8192 times the reciprocal of the effective symbol time length.

  In the SP method, there is no error in the input signal (direct wave) and no error response occurs in the response of all time domain signals in the SP method. Identification is possible. The level at which the delayed wave can be measured is theoretically very rough approximation that all input signals (direct waves) are “1” in the frequency domain number in the power spectrum method. Compared with the impulse corresponding to the delayed wave in the response of the number, an error impulse with a small level is generated in all frequency regions, and it becomes difficult to separate and distinguish from the impulse corresponding to the delayed wave with a low level. .

  The accuracy of the delay wave level is deteriorated because an error occurs in the measured delay wave level when both the SP method and the power spectrum method include a delay wave having a delay time exceeding the guard interval period. However, in the power spectrum method, if the ratio of the delay time exceeding the guard interval to the window length is small, the error of the delay wave level generated by the power spectrum method is smaller than the error of the delay wave level generated by the SP method. Thus, if the window length is increased, the error can be ignored in practice, and the accuracy of the delayed wave level can be maintained at a high level.

  The presence or absence of a false impulse response does not occur in the SP method, but in the power spectrum method, a complex number that is an output signal (received wave) in the frequency domain is squared, and the output signal is a non-linear characteristic that has a square characteristic. Since this is equivalent to having a characteristic, a false impulse response that is not included in the original output signal is generated.

Japanese Patent Laid-Open No. 2001-23666 (paragraphs 0021 to 0023, FIG. 1)

  As described above, the maximum delay time that can measure the delay wave, the time resolution that can measure the delay wave, and the delay, which are the superiority and inferiority evaluation items of the two delay profile measurement methods of the SP method and the power spectrum method There is a problem that there is no method for measuring a delay profile that satisfies all of the level at which a wave can be measured, the accuracy of the delayed wave level, and the presence or absence of a false impulse response.

  However, with the expansion of SFN (single frequency network) of terrestrial digital broadcasting, a new measurement method that satisfies all superiority and inferiority evaluation items of the delay profile measurement method is desired.

  Therefore, in the present invention, the above-mentioned problems can be solved, and the delay profile measurement method can increase the maximum delay time in which the delay wave can be measured, and the time resolution in which the delay wave can be measured can be improved. An object of the present invention is to provide an OFDM wave delay profile measuring device that can reduce the level at which a delayed wave can be measured, improve the accuracy of the delayed wave level, and eliminate a false impulse response. .

  In order to solve the above-mentioned problem, the delay for measuring the delay profile comprising the delay time of the delay wave of the OFDM wave according to claim 1 and the DU ratio indicating the intensity ratio between the direct wave and the delay wave of the OFDM wave. In an OFDM wave delay profile measuring apparatus comprising a profile measuring means, an OFDM wave receiving means, a direct wave estimating means, a frequency domain converting means, a transfer function deriving means, a delay profile converting means, a measurement result determination output means, It was set as the structure provided with.

  According to such a configuration, the OFDM wave delay profile measuring apparatus receives the propagating OFDM wave by the OFDM wave receiving means, and determines the phase of the demodulated carrier obtained by demodulating the received OFDM wave by the direct wave estimating means. By substituting the phase reference point in the demodulated carrier, a direct wave that is an integral power of 2 (for example, 2, 4,... 32, 64, etc.) times the effective symbol length of the OFDM wave is estimated. Note that the effective symbol excess time length exceeding the effective symbol length time length is a window length longer than the effective symbol length time length in order to obtain an input signal (direct wave) with a small error necessary for obtaining a transfer function. Is the time length set to. The phase reference point in the demodulated carrier is, for example, when the modulation method (signal format) of the OFDM wave is 64QAM, the demodulated carrier demodulating the OFDM wave is within 64 squares in the signal point arrangement diagram. It points to the center point of this kite. In other words, the replacement with the phase reference point is to converge the phase of the demodulated carrier dispersed in the cage to the center point of the cage.

  Further, the OFDM wave delay profile measuring apparatus converts the direct wave estimated by the direct wave estimating means and the received OFDM wave (the OFDM wave after reception) into a signal (frequency domain signal) in the frequency domain by the frequency domain converting means. Convert. This frequency domain conversion means is configured to be able to execute FFT, for example. Then, the OFDM wave delay profile measuring device receives a direct wave frequency domain signal which is a signal in the frequency domain of the direct wave converted by the frequency domain conversion unit by the transfer function deriving unit, and is a signal in the frequency domain of the received OFDM wave. The transfer function is derived by complex division by the OFDM frequency domain signal. The transfer function is a propagation characteristic of a propagation path obtained by dividing an output signal (received wave) output from a certain propagation path by an input signal (direct wave) input to the propagation path.

  Then, the OFDM wave delay profile measuring device converts the transfer function into a new delay profile by the delay profile conversion means. This delay profile conversion means is configured to be able to execute IFFT, for example. After that, the OFDM wave delay profile measurement device uses the measurement result determination output unit to measure the measurement result based on the result of comparing the new delay profile converted by the delay profile conversion unit and the delay profile measured by the delay profile measurement unit. Is output.

  The OFDM wave delay profile measurement device according to claim 2 is the OFDM wave delay profile measurement device according to claim 1, wherein the direct wave estimation means includes time domain signal conversion means and unit symbol signal generation means. The configuration.

  According to such a configuration, the OFDM wave delay profile measuring apparatus uses the time domain signal conversion unit to demodulate the demodulated carrier obtained by demodulating the OFDM wave in units of OFDM wave symbols, in the time domain that is a signal in the time domain of the effective symbol length. Convert to signal. The time domain signal is a signal having the time axis on the horizontal axis and the level intensity on the vertical axis. Subsequently, the OFDM wave delay profile measuring apparatus replicates the guard interval period portion from the time domain signal converted by the time domain signal conversion means by the unit symbol signal generation means, and also adds the unit symbol signal added to the time domain signal. Generate. That is, each unit symbol signal is formed by an effective symbol length (effective symbol period) and a guard interval period (guard period).

  The OFDM wave delay profile measuring device according to claim 3 is the OFDM wave delay profile measuring device according to claim 2, wherein the direct wave estimating means includes a multi-symbol signal generating means.

  According to such a configuration, the OFDM wave delay profile measuring apparatus generates unit symbol signals for a plurality of symbols by the multiple symbol signal generation means, and generates multiple symbol signals by connecting the generated symbol signals in symbol order. To do. Symbol order is the order in which unit symbol signals are generated.

  The OFDM wave delay profile measuring device according to claim 4 is the OFDM wave delay profile measuring device according to any one of claims 1 to 3, wherein the measurement result determination output means includes automatic logic determination selection means. It was set as the structure provided.

  According to such a configuration, the OFDM wave delay profile measuring apparatus measures the new delay profile converted by the delay profile converting means and the delay profile measuring means (conventional power spectrum method) by the automatic logic determination / selection means. For the delay wave level that exists in common in both delay profiles, the measurement results included in the delay profile measured by the delay profile measuring means are selected and converted by the delay profile converting means. A delayed wave measured only with a new delay profile is directly selected as a measurement result.

  According to the first aspect of the present invention, the phase of the demodulated carrier obtained by demodulating the OFDM wave is replaced with the phase reference point of the demodulated carrier for the direct wave having an excess time length exceeding the effective symbol length of the received OFDM wave. Since the transfer function is obtained using this estimated direct wave, an accurate delay profile can be obtained, and in the delay profile measurement method, the maximum delay time that can measure the delayed wave is increased. Can improve the time resolution that can measure the delayed wave, can lower the level that can measure the delayed wave, can improve the accuracy of the delayed wave level, and fake impulse response Can be eliminated.

  According to the second aspect of the present invention, a demodulation carrier obtained by demodulating the OFDM wave is converted into a time domain signal for each OFDM wave symbol, and a guard interval period portion is duplicated from the time domain signal. Since the direct wave is estimated by generating a unit symbol signal added to the region signal, an accurate transfer function is obtained by this estimated direct wave. As a result, compared to the conventional method (power spectrum method), A more accurate delay profile can be obtained.

  According to the third aspect of the present invention, generation of unit symbol signals is performed for a plurality of symbols, a multi-symbol signal is generated by connecting the generated symbol signals in the order of symbols, and the multi-symbol signal is used as a direct wave. Since the estimation is performed, an accurate transfer function is obtained by the estimated direct wave, and as a result, a more accurate delay profile can be obtained as compared with the conventional method (power spectrum method).

  According to the fourth aspect of the present invention, both of the new delay profile converted by the delay profile conversion unit and the delay profile measured by the delay profile measurement unit (conventional power spectrum method) are included in the delay profiles. The delay wave level that exists in common is measured using only the new delay profile converted by the delay profile conversion means by selecting the measurement result included in the delay profile measured by the delay profile measurement means. Since the delayed wave is selected as a measurement result as it is, an accurate delay profile can be obtained, and in particular, a false impulse response can be eliminated.

Next, embodiments of the present invention will be described in detail with reference to the drawings as appropriate.
<Configuration of OFDM wave delay profile measurement device>
FIG. 1 is a block diagram of an OFDM wave delay profile measuring apparatus. As shown in FIG. 1, an OFDM wave delay profile measuring apparatus 1 measures an OFDM wave delay profile in an SFN (single frequency network), and includes an OFDM wave receiving means 3, a direct wave estimating means 5, The frequency domain conversion means 7, the transfer function derivation means 9, the delay profile conversion means 11, the delay profile measurement means 13, and the measurement result determination output means 15 are provided.

  This OFDM wave delay profile measuring apparatus 1 measures a direct wave and a delayed wave of a transmission signal (OFDM wave at the time of transmission) transmitted from a plurality of transmission stations (basic broadcasting station, relay broadcasting station, etc.) constituting the SFN. Thus, a delay profile is generated.

The delay profile includes a delay time of an OFDM wave delay wave (including a multipath delay wave) and a DU ratio indicating an intensity ratio between the direct wave (desired wave, desired OFDM wave) and the delay wave. For example, when there are a plurality of delayed waves, the DU ratio indicating the intensity ratio between the delayed wave and the desired wave and the delay time of the delayed wave are included for each delayed wave.
Note that there are QPSK, 16QAM, 64QAM, DQPSK, and the like as modulation methods (signal formats) of OFDM waves. In this embodiment, a case where 64QAM is used will be described.

  The OFDM wave receiving means 3 receives an OFDM wave, which is input from a reception antenna (not shown) and propagates in an SFN (single frequency network), as an OFDM wave. In this OFDM wave, a direct wave (desired wave, desired OFDM wave) and a delayed wave (including a multipath delayed wave) are mixed.

  The OFDM wave receiving means 3 outputs the received OFDM wave to the direct wave estimating means 5, the frequency domain converting means 7 and the delay profile measuring means 13.

  The direct wave estimating means 5 estimates a direct wave having an effective symbol length excess time length that is a time length exceeding the effective symbol length time length from the OFDM wave output from the OFDM wave receiving means 3, and frequency domain transforming means 7 includes a time-domain signal conversion means 5a, unit symbol signal generation means 5b, and multiple symbol signal generation means 5c.

  First, the direct wave estimating means 5 performs OFDM demodulation on the OFDM wave output from the OFDM wave receiving means 3, and obtains a frequency domain signal (demodulated carrier) in symbol units by this OFDM demodulation. This symbol-unit frequency domain signal (demodulation carrier) is a complex number, which is composed of a real part and an imaginary part. When the real part is displayed on a plane with the horizontal axis and the imaginary part on the vertical axis, As shown in 2.

  When the modulation method (signal format) of the OFDM wave is 64QAM, there are 5617 demodulated carriers for one symbol, and a large number of these demodulated carriers are provided for every 64 cells as shown in FIG. , Forming a group with spread. The number of ridges varies depending on the signal format of the OFDM wave. In this embodiment, since the signal format of the OFDM wave is 64QAM, the number of traps that can accommodate the grouped demodulated carriers is 64. Further, for example, when the modulation method (signal format) of the OFDM wave is 16QAM, the number of traps in which the grouped demodulated carriers are accommodated is 16.

  The reason why the demodulated carrier becomes wider in each cage is that Gaussian noise and delayed waves are added directly to the waves. FIG. 2 (b) shows a transmission signal (OFDM wave at the time of transmission) transmitted from a transmitting station (basic transmitting station, relay transmitting station, etc.) constituting an SFN (single frequency network). Since the transmission signal is transmitted at the center value of each ridge, the center point of each ridge is referred to as a phase reference point.

  Then, the direct wave estimating means 5 quantizes each of the demodulated carriers having the spread shown in FIG. 2A, that is, the value of the horizontal axis component and the value of the vertical axis component with 3 bits (AD). And the phase reference point which is the center point of each ridge shown in FIG. The demodulated carrier replaced with the phase reference point that is the center point of each ridge shown in FIG. 2 (b) has a spread of the demodulation carrier having the spread shown in FIG. Since the transmission signal is equal to the carrier (modulation carrier) of the transmission signal in the ideal state, the transmission signal, that is, the frequency domain signal of the direct wave having one effective symbol length is obtained from the demodulation carrier.

Returning to FIG. 1, the description of the configuration of the OFDM wave delay profile measuring apparatus 1 will be continued.
The time domain signal converting means 5a performs IFFT (Inverse Fast Fourier Transform) on the frequency domain signal of the direct wave having one effective symbol length obtained from the demodulated carrier, and converts it into a time domain signal. The time domain signal is a signal in an effective symbol period when the horizontal axis is the time axis and the vertical axis is the level intensity.

  The time range of the time domain signal obtained by the time domain signal conversion means 5a is an effective symbol period. The reason for this effective symbol period is that the direct wave estimation means 5 sets the length and position of the FFT window to the effective symbol period (so that only effective symbols are extracted from continuous OFDM waves to obtain a demodulated carrier. This is because the effective symbol length is an excess time length exceeding (effective symbol length).

  That is, by applying IFFT (Inverse Fast Fourier Transform) to the frequency domain signal of the direct wave having one effective symbol length by the time domain signal conversion means 5a, the FFT is performed as a normal demodulation operation before obtaining the demodulated carrier. Since the reverse is performed, the time domain range returns to the original effective symbol period.

  The time-domain signal is obtained by removing the Gaussian noise and delayed wave components contained in the demodulated carrier by the operation of converting the OFDM wave into the frequency-domain signal by the direct wave estimating means 5 and replacing it with the phase reference point. Only direct wave components.

  The unit symbol signal generation means 5b replicates the time domain signal that is a part corresponding to the guard interval period (guard period) from the time domain signal (signal in the effective symbol period) converted by the time domain signal conversion means 5a. A unit symbol signal added to the original time domain signal (signal in an effective symbol period) is generated. That is, this unit symbol signal is a combination of the signal in the effective symbol period and the signal in the guard interval period (guard period).

  In addition, the time domain signal that is a part corresponding to the guard interval period (guard period) is obtained by duplicating the end of the time domain signal (signal in the effective symbol period) by the time length of the guard interval period (guard period). is there.

  The multi-symbol signal generating means 5c generates a multi-symbol signal obtained by connecting (concatenating) the generated unit symbol signals in a necessary number of symbols in order (generated order). Here, the number of unit symbol signals to be connected (the number of necessary symbols), that is, the window length is determined in consideration of the fact that no measurable delay time and DU ratio error occur. Incidentally, the measurable delay time is ½ of the window length in principle, and the ratio between the delay time and the window length determines the error of the DU ratio. The longer the window length, the smaller the error. . The error of the DU ratio is very small and practically negligible if the window length is 16 times or more the delay time.

  Here, the unit symbol signal generated by the unit symbol signal generation unit 5b is connected to the unit symbol signal by the unit symbol signal generation unit 5c. FIG.

  As shown in FIG. 3, the multi-symbol signal is a series of a large number of unit symbol signals (3). The unit symbol signal (3) includes an effective symbol period (1), a guard period (2), and the like. It is constituted by. As shown in FIG. 3, a multi-symbol signal in which unit symbol signals are continuous is transmitted from a transmitting station (not shown). The multiple symbol signal generation means 5 c outputs the multiple symbol signal as a direct wave to the frequency domain conversion means 7.

Returning to FIG. 1, the description of the configuration of the OFDM wave delay profile measuring apparatus 1 will be continued.
The frequency domain transforming means 7 performs FFT (Fast Fourier Transform) on each of the OFDM wave output from the OFDM wave receiving means 3 and the direct wave (multi-symbol signal) estimated by the direct wave estimating means 5. The frequency domain signal is converted. The FFT window length applied by the frequency domain transform means 7 is a power of 2 and the delay time during which the delayed wave can be measured is set to a length that does not cause an error in the DU ratio. Specifically, if the maximum delay time that can be measured for the delayed wave is in principle half of 1008 μs (measurable target value) (504 μs) and converted to the propagation distance, it is about 150 km, the FFT window length Is 1008 μs × 16 or more (16128 μs or more).

  The frequency domain signal (OFDM frequency domain signal and direct wave frequency domain signal) converted by the frequency domain converting means 7 is a complex spectrum having a real part and an imaginary part.

  The transfer function deriving means 9 uses the direct wave frequency domain signal (complex spectrum of the direct wave), which is the estimated frequency domain signal of the direct wave converted by the frequency domain transforming means 7, as a numerator, The division function (complex number division) is performed using the OFDM wave frequency domain signal (the spectrum of the complex number of the OFDM wave) that is an OFDM wave frequency domain signal including the denominator to derive a transfer function.

  In the SFN (single frequency network), this transfer function is an OFDM signal of the OFDM wave delay profile measuring apparatus 1 that is a receiving point of a propagating OFDM wave with a transmitting antenna of a transmitting station (not shown) as an input end. When a receiving antenna (not shown) connected to the wave receiving means 3 is used as an output end, it means a complex frequency characteristic of the transmission path.

  The delay profile conversion unit 11 performs IFFT (Inverse Fast Fourier Transform) on the transfer function (complex frequency characteristic) derived by the transfer function deriving unit 9, and converts the transfer function into a delay profile (a new one indicated in the claims). The delay profile). The delay profile is data in which the delay time and the numerical value (DU ratio) indicating the level are combined into one set for the delayed wave.

  In other words, if the transfer function (complex frequency characteristic) is IFFT, an impulse appears at the position of the time axis corresponding to the delay time of the delayed wave, and the level of this impulse corresponds to the intensity of the delayed wave. This is a delay profile including the delay time of the delay wave and the DU ratio indicating the intensity ratio between the direct wave (desired wave, desired OFDM wave) and the delayed wave. In other words, the IFFT that converts the transfer function in the frequency domain into the time domain gives the delay time of the delayed wave corresponding to the response in the time domain and the impulse indicating the level of the delayed wave, and these are the delay profile and Become.

  FIG. 4 shows the relationship between the transfer function and the delay profile. A function (transfer function) in the frequency domain as shown in FIG. 4A is subjected to IFFT by the delay profile conversion means 11 to obtain a function (delay profile) in the time domain as shown in FIG. It has been converted. In addition, the vertical axis | shaft of Fig.4 (a) has shown the value of the transfer function, and the unit of the vertical axis | shaft of FIG.4 (b) has shown DU ratio.

  In FIG. 4A, the transfer function has a continuous sinusoidal waveform, whereas in FIG. 4B, the delay profile has two triangular waveforms. That is, this delay profile indicates that a direct wave and one delayed wave are included, and the delay time of the delayed wave is indicated by the length of the second triangle up to the apex of the triangle (4 memories). And the level of the delayed wave is indicated by the height of the triangle.

Returning to FIG. 1, the description of the configuration of the OFDM wave delay profile measuring apparatus 1 will be continued.
The delay profile measuring means 13 measures the delay profile by the power spectrum method. In this power spectrum method, a window length (FFT window length) when an OFDM wave is converted to a frequency domain signal by FFT (Fast Fourier Transform) is longer than that of the SP method, and a time domain signal is squared. Then, the delay profile is obtained by converting the OFDM wave from the voltage dimension to the power dimension.

  The delay profile measured by the delay profile measuring unit 13 is referred to as a delay profile by the power spectrum method, and the new delay profile converted by the delay profile conversion unit 11 is referred to as a delay profile by the transfer function method. .

  The measurement result determination output means 15 compares the delay profile based on the transfer function method converted by the delay profile conversion means 11 with the delay profile based on the power spectrum method measured by the delay profile measurement means 13, and compares the result. Based on this, the measurement result as the OFDM wave delay profile measuring device 1 is output, and includes an automatic logic determination / selection means 15a.

  The automatic logic determination / selection unit 15a uses the power level of the delay wave that exists in common between the delay profile converted by the delay profile conversion unit 11 and the delay profile measured by the delay profile measurement unit 13. The measurement result included in the delay profile by the spectrum method is selected, and the delay wave measured only by the delay profile by the transfer function method is directly selected as the measurement result.

  The automatic logic determination / selection means 15a removes impulses of delayed waves that exist in the delay profile by the power spectrum method and do not exist in the delay profile by the transfer function method as false impulse responses. is there.

  According to this OFDM wave delay profile measuring apparatus 1, the constraint condition that the maximum delay time that can be measured for a delay wave is one half of 1008 μs in principle and about 150 km in terms of the propagation distance is overcome. It is possible to measure the delay time of the delayed wave of the OFDM wave from a long distance without any.

  Further, according to the OFDM wave delay profile measuring apparatus 1, the direct wave estimating means 5 replaces the phase of the demodulated carrier obtained by demodulating the OFDM wave with the phase reference point in the demodulated carrier, thereby enabling the effective symbol of the OFDM wave. A direct wave with an overtime length exceeding the length is estimated. Since the transfer function is obtained by the transfer function deriving means 9 using the estimated direct wave, a more accurate delay profile can be obtained by the delay profile converting means 11, and in the delay profile measuring method, Satisfy all superiority and inferiority evaluation items, that is, the maximum delay time that can measure the delay wave can be lengthened, the time resolution that can measure the delay wave can be improved, and the level at which the delay wave can be measured The delay level can be improved, and the false impulse response can be eliminated.

  Further, according to this OFDM wave delay profile measuring apparatus 1, the time-domain signal conversion means 5a of the direct wave estimation means 5 converts a demodulated carrier obtained by demodulating the OFDM wave into a time-domain signal for each OFDM wave symbol. The unit symbol signal generation means 5b replicates the guard interval period portion from the time domain signal and generates a unit symbol signal added to the time domain signal to estimate the direct wave. For this reason, a unit symbol signal from which Gaussian noise and delayed waves have been removed can be obtained, and an accurate direct wave can be obtained. An accurate transfer function can be obtained by this estimated direct wave, and as a result, compared to the conventional power spectrum method. Thus, an accurate delay profile can be obtained.

  Furthermore, according to the OFDM wave delay profile measuring apparatus 1, the multiple symbol signal generating means 5c generates unit symbol signals for a plurality of symbols, and the generated symbol signals are connected in symbol order. And the multiple symbol signal is estimated as a direct wave. For this reason, since a multi-symbol signal in which unit symbol signals from which Gaussian noise and delayed waves have been removed are consecutive is estimated as a direct wave, an accurate transfer function is obtained by the estimated direct wave, and as a result, the conventional power Compared to the spectral method, an accurate delay profile can be obtained.

  In addition, according to the OFDM wave delay profile measuring apparatus 1, a new delay profile (delay profile by the transfer function method) converted by the delay profile converting unit 11 and a delay profile (delayed by the delay profile measuring unit 13) ( In both delay profiles with the power spectrum method), for the delay wave level that exists in common, select the measurement result included in the delay profile by the power spectrum method, and delay by the transfer function method Since the delay wave measured only by the profile is selected as a measurement result as it is, an accurate delay profile can be obtained. In particular, since the delay wave measured only by the delay profile by the transfer function method is selected as the measurement result, the false impulse response appearing in the delay profile by the power spectrum method can be eliminated.

<Operation of OFDM wave delay profile measurement device>
Next, the operation of the OFDM wave delay profile measuring apparatus 1 will be described with reference to the flowchart shown in FIG. 5 (see FIG. 1 as appropriate).
First, the OFDM wave delay profile measuring apparatus 1 receives an OFDM wave propagating in the SFN by the OFDM wave receiving means 3 as received OFDM (step S1).

  Subsequently, the OFDM wave delay profile measuring apparatus 1 performs OFDM demodulation on the OFDM wave by the direct wave estimation means 5 to obtain a demodulated carrier, performs IFFT in the time domain signal conversion means 5a, and performs time in an effective symbol period. Find the region signal. Then, the OFDM wave delay profile measuring apparatus 1 generates a unit symbol signal by the unit symbol signal generation unit 5b and the multiple symbol signal generation unit 5c of the direct wave estimation unit 5, and connects the unit symbol signal to the multiple symbol signal. And the multi-symbol signal is estimated as a direct wave (step S2).

  Then, the OFDM wave delay profile measuring apparatus 1 converts the OFDM wave received by the OFDM wave receiving means 3 and the direct wave estimated by the direct wave estimating means 5 by the frequency domain converting means 7 into an OFDM signal that is a frequency domain signal. It converts into a wave frequency domain signal and a direct wave frequency domain signal (step S3).

  Then, the OFDM wave delay profile measuring apparatus 1 uses the transfer function (complex frequency) to divide the direct wave frequency domain signal transformed by the frequency domain transforming means 7 by the transfer function deriving means 9 by the OFDM wave frequency domain signal. Characteristic) is derived (step S4). Then, the OFDM wave delay profile measuring apparatus 1 converts the transfer function derived by the transfer function deriving unit 9 into a delay profile by the delay profile converting unit 11 (step S5).

  Further, the OFDM wave delay profile measurement device 1 compares the new delay profile converted by the delay profile conversion unit 11 with the delay profile measured by the delay profile measurement unit 13 by the measurement result determination unit 15 and compares the delay profile. Based on the result, the measurement result as the OFDM wave delay profile measuring apparatus 1 is determined and output (step S6).

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. For example, although the present embodiment has been described as the apparatus of the OFDM wave delay profile measuring apparatus 1, the OFDM wave delay profile measuring method that considers the processing of each component of the apparatus 1 as one process of measuring the delay profile. It can also be considered. In this case, the same effect as that of the device 1 can be obtained.

1 is a block diagram of an OFDM wave delay profile measuring apparatus according to an embodiment of the present invention. It is based on embodiment of this invention. A frequency domain signal (demodulated carrier) in symbol units is obtained by this OFDM demodulation. This symbol-unit frequency domain signal (demodulation carrier) is a complex number, which is composed of a real part and an imaginary part. When the real part is displayed on a plane with the horizontal axis and the imaginary part on the vertical axis, As shown in 2.

FIG. 2A shows a demodulated carrier when the OFDM wave signal format is 64QAM, FIG. 2A shows a group having a spread (variation) of the demodulated carrier, and FIG. 2B shows a demodulated carrier. The phase reference point is shown.
It is a schematic diagram of multiple symbol signals. (A) is the figure which showed the example of the transfer function, (b) is the figure which showed the example of the delay profile. 2 is a flowchart for explaining the operation of the OFDM wave delay profile measuring apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 OFDM wave delay profile measuring apparatus 3 OFDM wave receiving means 5 Direct wave estimation means 5a Time domain signal conversion means 5b Unit symbol signal generation means 5c Multiple symbol signal generation means 7 Frequency domain conversion means 9 Transfer function derivation means 11 Delay profile conversion means 11 13 Delay profile measurement means 15 Measurement result judgment output means 15a Automatic logic judgment selection means

Claims (4)

In an OFDM wave delay profile measuring apparatus comprising delay profile measuring means for measuring a delay profile including a delay time of an OFDM wave delay wave and a DU ratio indicating an intensity ratio between the direct wave and the delay wave of the OFDM wave ,
OFDM wave receiving means for receiving the propagating OFDM wave;
By replacing the phase of the demodulated carrier obtained by demodulating the OFDM wave received by the OFDM wave receiving means with a phase reference point in the demodulated carrier, the direct wave having an excess time length exceeding the time length of the effective symbol length of the OFDM wave. Direct wave estimation means for estimating
A frequency domain transforming means for transforming the direct wave estimated by the direct wave estimating means and the OFDM wave, respectively, into a signal in the frequency domain;
The transfer function is obtained by complex-dividing the direct wave frequency domain signal, which is a signal in the frequency domain of the direct wave, converted by the frequency domain transforming unit, with the OFDM frequency domain signal, which is a signal in the frequency domain of the OFDM wave. A transfer function deriving means for deriving;
A delay profile conversion means for performing an inverse Fourier transform on the transfer function derived by the transfer function deriving means and converting the transfer function into a new delay profile;
A measurement result determination output means for determining and outputting a measurement result based on a comparison result of the new delay profile converted by the delay profile conversion means and the delay profile measured by the delay profile measurement means;
An OFDM wave delay profile measuring apparatus comprising: The direct wave estimating means converts a demodulated carrier obtained by demodulating the OFDM wave in units of symbols of the OFDM wave into a time domain signal that is a signal in the time domain of the effective symbol length; and
A unit symbol signal generating means for replicating a part of the guard interval period from the time domain signal converted by the time domain signal converting means and generating a unit symbol signal added to the time domain signal;
The OFDM wave delay profile measuring apparatus according to claim 1, comprising:   The direct wave estimation means includes a multiple symbol signal generation means for generating the unit symbol signal for a plurality of the symbols and generating a multiple symbol signal by connecting the generated symbol signals in the symbol order. The OFDM wave delay profile measuring apparatus according to claim 2.   The measurement result determination output means selects a measurement result included in the delay profile measured by the delay profile measurement means for the level of the delay wave that exists in common in both delay profiles, and the delay 4. The apparatus according to claim 1, further comprising automatic logic determination selection means for selecting a delay wave measured only by a new delay profile converted by the profile conversion means as a measurement result as it is. The OFDM wave delay profile measuring device described in 1.

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