JP4685688B2 - Radio wave propagation analyzer - Google Patents

Description

  The present invention relates to a radio wave propagation analyzing apparatus, and more particularly to a radio wave propagation analyzing apparatus for analyzing propagation characteristics of a radio wave including a plurality of pilot carriers in a signal band.

  A propagation analysis apparatus that measures a delay profile of an OFDM (Orthogonal Frequency Division Multiplexing) signal performs IFFT (Inverse FFT) on a pilot carrier extracted from a received signal divided by a known reference pilot pattern. Therefore, various methods based on this method have been proposed (for example, see Patent Document 1).

  FIG. 1 shows a general configuration diagram of a propagation analyzer for obtaining a delay profile. In the figure, the received OFDM signal is mixed with the local signal from the local signal generator 2 by the mixer 1, and the obtained intermediate frequency signal is converted into a digital signal by the AD converter 3. Symbol synchronization is established by performing orthogonal demodulation and performing guard interval correlation in the guard interval correlation calculation unit 5. Thereafter, after the effective symbol is cut out by the window position control unit 6, an FFT (Fast Fourier Transform) calculation unit 7 performs an FFT calculation process to convert the signal into a frequency domain signal.

  The CP extraction unit 8 extracts a pilot carrier inserted for equalization from the signal converted into the frequency domain, and the division unit 9 performs complex division on the pilot carrier by the reference pilot signal output from the reference CP generation unit 10. The delay profile can be obtained by performing IFFT calculation on the propagation path characteristics (amplitude and phase fluctuations received in the propagation path) obtained by the delay profile measurement unit 11.

  Further, the linear interpolation unit 12 estimates the channel characteristics of the data carrier between the pilot carriers by linear interpolation from the channel characteristics of the pilot carriers on both sides of the data carrier, and supplies them to the demodulation unit 13. The demodulator 13 demodulates the data carrier supplied from the FFT calculator 7. The carrier signal-to-noise ratio measurement unit 14 measures the ratio between the power of the noise floor other than the carrier and the power of each carrier.

By the way, in order to obtain an accurate delay profile, generally, precise symbol synchronization and average processing over a plurality of symbols are required. Therefore, a delay profile measurement method combined with synchronization means as disclosed in Patent Document 2 is proposed. Has been.
JP 2002-335226 A JP 2000-134176 A

  In the device described in Patent Document 1, although propagation characteristics such as the S / N ratio and frequency characteristic for each carrier can be measured in addition to the delay profile, the arrival directions of the desired wave and the delayed wave observed with the delay profile are simultaneously obtained. There was a problem that we couldn't.

  Conventionally, a method for estimating the arrival direction of a desired wave having the maximum signal power using a pilot carrier included in an OFDM signal for equalization has been proposed. This method extracts pilot carriers from one OFDM signal symbol received by two antennas, suppresses the effects of multipath, etc., detects the inter-antenna phase difference of the desired wave, and estimates its arrival direction. . However, this method has a problem that the propagation characteristics of multipath, that is, the arrival direction of each delayed wave, the DU ratio that is the ratio of the desired wave signal power and each delayed wave signal power, and the delay time cannot be obtained simultaneously. .

  The present invention has been made in view of the above points, and provides a radio wave propagation analysis apparatus that can estimate the DU ratio and delay time of a delayed wave while estimating the direction of a radio wave from which a desired wave or a delayed wave arrives. For the purpose.

The invention according to claim 1 is a radio wave propagation analyzing apparatus that receives radio waves including a plurality of pilot carriers in a signal band with a plurality of antennas, and measures the arrival direction, DU ratio, and delay time of the radio waves,
Extracting means for extracting a pilot carrier from a signal in a frequency domain obtained by converting a signal received by an antenna of each system;
A direction-of-arrival calculation means for calculating a direction of arrival and a signal power of a desired wave by performing a correlation operation in a time domain between a pilot carrier of each system and a preset reference pilot carrier;
Synchronizing means for subtracting the desired wave component from the pilot carrier of each system and then synchronizing the delayed wave with phase rotation,
A delay time calculating means for calculating a delay time of the delay wave from the phase amount rotated by the synchronizing means;
Supply means for supplying the pilot direction of each system synchronized with the delay wave by the synchronization means to the arrival direction calculation means to calculate the arrival direction and signal power of the delay wave;
By having a DU ratio calculating means for calculating a DU ratio that is a ratio of the signal power of the desired wave and the signal power of the delayed wave,
At the same time as estimating the direction of the radio wave from which the desired wave or delayed wave arrives, the DU ratio and delay time of the delayed wave can be obtained.

According to a second aspect of the present invention, a delay profile is obtained from a propagation path response obtained by dividing the pilot carrier extracted by the extracting means by the reference pilot carrier, and coarse delay times of the delayed wave are obtained in descending order of signal power. A delay profile means,
The synchronization means subtracts the desired wave component from the pilot carrier of each system, and then synchronizes with the delay wave by applying a phase rotation in which the coarse delay time of the delay wave is shifted back and forth at a minute time interval. Can be reduced.

In the invention according to claim 3, the synchronizing means subtracts the delayed wave component having the large signal power from the pilot carrier of each system synchronized with the delayed wave having the large signal power last time, and then delays the signal having the next largest signal power. By giving a phase rotation that shifts the coarse delay time back and forth at a minute time interval and synchronizing it with the delayed wave with the next largest signal power,
At the same time as estimating the direction of the radio wave from which the desired wave or delayed wave arrives, the DU ratio and delay time of each delayed wave can be obtained in descending order of signal power.

  According to the present invention, it is possible to estimate the direction of a radio wave from which a desired wave or a delayed wave arrives, and simultaneously obtain the DU ratio and delay time of the delayed wave.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. First, a method for estimating the direction of arrival of a desired wave will be described.

  In this embodiment, the transmission / reception number is assumed to be an OFDM signal in a format defined in “Portable OFDM digital radio transmission system for transmitting television broadcast program material” ARIB STD-B33. As shown in FIG. 2, this type of OFDM signal has a pilot carrier (CP: Continuous Pilot) at a frequency equal to every eight in the frequency direction and a known value for the purpose of channel equalization. (For example, “1” or “−1”) is BPSK modulated and inserted.

  FIG. 3 shows a block diagram of an embodiment of the radio wave propagation analyzing apparatus of the present invention. In the figure, the signals received by the antennas 20a and 20b installed at half-wavelength (λ / 2) intervals are down-converted to frequencies that allow digital signal processing by the frequency converters 21a and 21b, and the AD converter 22a. , 22b are converted into digital signals, and then demodulated by the orthogonal demodulation units 23a, 23b to be separated into IQ signals. Here, the quadrature demodulation is performed by digital signal processing after AD conversion, but it may be converted into a digital signal by AD conversion after being separated into IQ signals by quadrature demodulation.

  Next, symbol synchronization is established by performing the guard interval correlation calculation in the correlation calculation unit 24, one effective symbol of the desired wave is cut out by the window position control unit 25, and FFT calculation is performed by the FFT calculation units 26a and 26b. The CP extraction units 27a and 27b extract pilot carriers (CP).

  Here, if the local oscillation frequency and the sampling frequency in frequency conversion match in both systems, the symbol period may be established only in one system as shown in FIG. Also, it is assumed that symbol synchronization is complete and there is no phase rotation due to symbol cutout. Such complete symbol synchronization is hereinafter referred to as phase synchronization.

  The calibration units 28a and 28b complex-divide the pilot carrier by the calibration coefficient acquired by the previous calibration supplied from the calibration coefficient output unit 29 to obtain the first calibration CP. FIG. 4A shows a constellation of the first calibration CP.

  As for the method of obtaining the calibration coefficient, at the time of initial calibration, the antennas 20a and 20b are installed in the direction serving as a reference for arrival direction estimation, a transmission antenna is provided facing these antennas, and normal transmission is performed. An OFDM signal including the same pilot carrier is transmitted. The IQ signal value of the pilot carrier extracted by each of the CP extraction units 27a and 27b after receiving this OFDM signal is complex-divided by the IQ signal value of the reference pilot carrier, and held in the calibration coefficient output unit 29 as a calibration coefficient. .

  Thus, the pilot carrier extracted by the CP extraction units 27a and 27b at the time of transmission is complex-divided by the calibration coefficient, so that the frequency characteristic generated outside the wireless transmission path is canceled and calibrated.

  The first calibration CP obtained by the calibration units 28a and 28b varies from the original value as shown in FIG. 4A due to the influence of propagation path characteristics such as multipath. Therefore, in the unnecessary wave removal / phase rotation unit 30, the average IQ signal value of each group of the first calibration CP divided for each known IQ signal value (for example, “1” or “−1”) of the reference pilot carrier, Assuming an ideal signal value that is not affected by multipath or the like, each pilot carrier is replaced with the value to obtain the second calibration CP. The second calibration CP is indicated by a cross in FIG.

  When there is a delayed wave due to reflection or the like, the first calibration CP is distributed on a concentric circle substantially centered on the original position. Therefore, even if each of the first calibration CPs deviates from the original position, the plurality of first calibration CPs. The second calibration CP, which is the average IQ signal value of the calibration CP, can be regarded as indicating the original signal value without multipath effects.

  The second calibration CP output from the unnecessary wave removal / phase rotation unit 30 is supplied to IFFT calculation units 31a and 31b, and is converted from a frequency domain signal to a time domain signal by performing inverse Fourier transform on a symbol basis, thereby calculating a correlation. Supplied to the sections 32a and 32b.

  On the other hand, the reference pilot carrier generated by the reference CP generation unit 33 is subjected to inverse Fourier transform by the IFFT calculation unit 34 to convert from the frequency domain to the time domain. Correlation calculators 32a and 32b obtain cross-correlation values between the time domain signals of the received pilot carriers and the reference pilot carrier output from IFFT calculators 31a and 31b over the symbol period.

  The two-system cross-correlation values output from the correlation calculation units 32a and 32b are normalized by the normalization units 35a and 35b and supplied to the steering vector generation unit 36. Here, the elements having the two-system cross-correlation values as elements. The column vector of Formula 2 is generated as a steering vector indicating the direction of the desired wave.

  Here, as shown in FIG. 6, the phase difference φ depending on the direction of arrival of the desired wave is, for example, the second calibration CP in the time domain obtained by IFFT calculation of the second calibration CP obtained for each antenna system, and Since a column vector whose element is a normalized correlation calculation value with a reference pilot carrier in the time domain obtained by IFFT calculation of the reference pilot carrier represents a steering vector indicating the desired wave direction, it can be directly obtained from this steering vector. it can. The arrival angle θ of the desired wave can be obtained by substituting this phase difference φ into the following equation shown in FIG.

φ = (2πd · sin θ) / λ where d = λ / 2
Here, the above procedure will be described using mathematical expressions. The input complex vector Xm of the pilot carrier of the received OFDM signal is expressed by equation (1).

ただし、ｍは要素数、ｓは希望波、ｈ_ｄは希望波のステアリングベクトル、ｃ_ｉはｉ番目の相関性干渉波、ｈ_ｃ，ｉはｉ番目の相関性干渉波のステアリングベクトル、ｕ_ｊはｊ番目の非相関性干渉波、ｈ_ｕ，ｊはｊ番目の非相関性干渉波のステアリングベクトル、ｎは熱雑音である。

Here, m is the number of elements, s is the desired wave, _hd is the steering vector of the desired wave, c _i is the i-th correlated interference wave, h _{c, i} is the steering vector of the i-th correlated interference wave, u _j Is the jth uncorrelated interference wave, _{hu, j} is the steering vector of the jth uncorrelated interference wave, and n is the thermal noise.

Here, the correlation interference wave means multipath, and the non-correlation interference wave means interference wave other than multipath. On the other hand, the reference pilot carrier is r, and r = s. A correlation vector r _xr between the input complex vector Xm and the conjugate complex number r ^* (that is, s ^* ) of the reference pilot carrier r is expressed by equation (2). E [] represents the time average in [].

伝搬路に相関性干渉波が存在しない場合または無視できる場合、（２）式は次のように近似できる。

When there is no correlated interference wave in the propagation path or when it can be ignored, equation (2) can be approximated as follows.

r _xr ≈ E [| s | ² ] h _d
The correlation vector r _xr is normalized, and a steering vector having the number of elements m (m = 2) having the normalized value as an element is obtained. The phase difference detection unit 37 obtains the phase difference φ from the steering vector, and the arrival angle estimation unit 38 obtains an estimated value of the arrival angle θ from the phase difference φ.

  Next, an operation for obtaining the arrival direction, DU ratio, and delay time of each delayed wave forming a multipath in descending order of signal power will be described with reference to the flowchart of FIG.

  In FIG. 7, the signal received in step S2 is quadrature demodulated to be separated into IQ signals. In step S4, symbol interval is established by performing guard interval correlation calculation, and one effective symbol of the desired wave is cut out. In step S6, the extracted effective symbol is subjected to an FFT operation, and in step S8, a pilot carrier is extracted.

  In step S10, the first calibration CP is obtained by complex division of the pilot carrier by the calibration coefficient. In step S12, the second calibration CP is obtained, the steering vector indicating the desired wave direction is obtained, and the desired wave arrival angle θd and the desired wave signal power D shown in FIG.

  In step S14, the unnecessary wave removing / phase rotating unit 30 obtains the second direction obtained in the process of obtaining the arrival direction of the desired wave from the first calibration CP after dividing by the calibration coefficient shown in FIG. The calibration CP is subtracted, and the resulting signal is defined as a third calibration CP. FIG. 4B shows the third calibration CP.

  The third calibration CP corresponds to the one in which the desired wave component is removed, and the phase rotation of each carrier with respect to the same time shift is given to each third calibration CP, and the shifted time has the largest signal power among the delayed waves. When the delay time of the object (first delay wave) coincides, the result is as shown in FIG. 5A, and this is defined as a fourth calibration CP. This shows a state in which phase synchronization is established with the first delayed wave. That is, it shows a state where there is no phase rotation of adjacent pilot carriers and ideal symbol synchronization is achieved, and this corresponds to cutting out effective symbols of delayed waves at the window positions shown in FIG. The delayed waves are named first, second, and third delayed waves in descending order of signal power.

Thereafter, similarly to the desired wave, a fifth calibration CP, which is an average value for each signal value shown in FIG. 5A, is obtained for each antenna system, and the arrival direction of the first delayed wave is obtained. On the other hand, in order to obtain the DU ratio of the first delayed wave, the mean squares of the absolute values of the amplitudes of the second calibration CP and the fifth calibration CP are respectively obtained as the signal power D of the desired wave and the signal power U of the first delayed wave. Find it as ₁ .

  The processing such as phase rotation and desired wave removal described here is performed mainly in the unnecessary wave removal / phase rotation unit 30 in FIG. 3, and the obtained phase rotation amount and signal power are respectively calculated as delay time calculation units. 41 and the DU ratio calculation unit 42, and a delay time and a DU ratio are obtained. Further, in order to reduce the calculation load, the delay profile measuring unit 40 roughly obtains the delay time of the delayed wave, and based on the value, obtains an accurate phase rotation amount that can achieve phase synchronization.

  Hereinafter, a method for phase-synchronizing with the delayed wave will be described in detail. The delay profile measuring unit 40 obtains a propagation path response by dividing a pilot carrier obtained after performing FFT operation on the received signal by the reference pilot carrier, and performing IFFT operation on this propagation path response to obtain a rough waveform as shown in FIG. A delay profile is obtained (steps S16 and S18 in FIG. 7).

  The accuracy of this delay profile deteriorates due to frequency deviation and symbol synchronization deviation. Conventionally, in order to increase accuracy, after synchronizing with high accuracy by various frequency synchronization means and symbol synchronization means, the accuracy of the delay profile is improved by performing averaging over a plurality of symbols through a symbol filter.

  In the present invention, such a means is not used, and each delayed wave is obtained from a rough delay profile as shown in FIG. 9 obtained from the same pilot carrier for one symbol as used for obtaining the direction of arrival of the desired wave. Only coarse delay times are obtained in descending order of signal power.

In the coarse delay profile shown in FIG. 9, first, a point where the signal power has a maximum value is obtained, and a point where the absolute value of the signal power is the second largest after the desired wave is detected as the first delayed wave. The time difference is obtained as an approximate delay time τ ′ _u1 of the first delay wave. Similarly, an approximate delay time τ ′ _u2 of the second delayed wave is obtained.

The phase rotation amount of the k-th pilot carrier corresponding to the obtained delay time τ ′ _u1 is exp (j2πf _k τ ′ _u1 ), and using the obtained phase rotation amount as a guide, a preset minute time interval Δτ Thus, the phase rotation amount corresponding to the accurate delay time of the first delayed wave is obtained as a determination condition that phase synchronization can be achieved. Here, f _k represents the frequency of the k-th pilot carrier.

  The smaller the value of the minute time interval Δτ, the better the accuracy. However, if the coarse delay time obtained by the delay profile is greatly deviated, the time required for the determination process to be performed below becomes longer, and is required. Set appropriately considering the accuracy of delay time and processing time.

The unnecessary wave removal / phase rotation unit 30 centered around the phase rotation amount exp (j2πf _k τ ′ _u1 ) in the third calibration CP, and shifted the phase rotation amount discretely back and forth in units of Δτ. And combinations that can achieve phase synchronization are determined based on pilot carrier variations (steps S20 and S22 in FIG. 7).

  When the amount of phase rotation is not exactly phase-synchronized with the first delayed wave, each pilot carrier varies around the origin as shown in FIG. On the other hand, when the amount of phase rotation is synchronized with the first delayed wave, there are other delayed waves, and even if the dispersion of each pilot carrier increases, the phase difference between adjacent pilot carriers is minimized. As shown in FIG. 5A, it can be roughly divided into two signal values of BPSK modulation.

  As a method for determining that the variation of the pilot carrier is minimum, there is a method for determining that the dispersion of the IQ signal value of the pilot carrier is minimum. Moreover, you may determine by the average value of the phase difference between adjacent pilot carriers becoming the minimum. In these determinations, not all pilot carriers may be used, but only some pilot carriers may be used.

The means for phase synchronization described here does not need to be implemented by both antenna systems, but is performed by either system, and the other performs phase rotation based on this result. If the phase rotation amount when phase synchronization is achieved is exp (j2πf _k τ _u1 ), and τ _u1 = τ ′ _u1 + Δτ × i (i is an integer), the delay time τ of the first delay wave _u1 can be obtained with high accuracy with the resolution of the set time interval Δτ.

Further, the arrival direction of the desired wave was obtained from the fourth calibration CP with phase synchronization obtained by multiplying the third calibration CP obtained for each antenna system by the phase rotation amount exp (j2πf _k τ _u1 ). Similarly to the above, the arrival angle estimation unit 38 obtains the arrival direction θ _u1 of the first delayed wave. Furthermore, from the ratio of the signal power D of the desired wave obtained previously and the signal power U ₁ of the first delayed wave obtained in the same manner as the signal power D from the fifth calibration CP shown in FIG. The DU ratio calculation unit 42 obtains the DU ratio of the first delayed wave (step S24 in FIG. 7).

Further, for the second delayed wave, the unnecessary wave elimination / phase rotation unit 30 obtains the sixth calibration CP shown in FIG. 5B in step S26 of FIG. 7 according to the above procedure, and in steps S28 and S30. In the unnecessary wave elimination / phase rotation unit 30, a variable related to time is discretely expressed in units of Δτ with the sixth calibration CP centered on the phase rotation amount exp [j2πf _k (τ ′ _u2 −τ ′ _u1 )]. By multiplying the phase rotation amount shifted forward and backward, the delay time τ _u2 of the second delayed wave is obtained from the phase rotation amount of the seventh calibration CP (shown in FIG. 5C) in which the phase is synchronized. In step S32, the arrival angle estimation unit 38 obtains the arrival direction _θu2 of the second delayed wave. Furthermore, from the ratio of the signal power D of the desired wave obtained previously and the signal power U ₂ of the second delayed wave obtained in the same manner as the signal power D, the DU ratio calculation unit 42 To obtain the DU ratio of the second delayed wave.

  Thereafter, even when the third and fourth delayed waves exist, the arrival direction, DU ratio, and delay time can be obtained sequentially according to the above procedure.

  In this way, the arrival direction of the desired wave can be obtained, and the arrival direction, DU ratio, and delay time of each delayed wave that greatly affects the reception characteristics can be obtained in descending order of signal power.

  In the above embodiment, the OFDM signal in the format defined by ARIB STD-B33 has been described. However, the “terrestrial digital television broadcast transmission method” terrestrial digital television broadcast wave defined by ARIB STD-B31 is used. The included pilot carrier (SP: Scattered Pilot) is also a BPSK-modulated signal like the pilot carrier, although the position of the inserted carrier is different. Therefore, the present invention can be easily applied. Note that the present invention can be applied to any signal format that includes a plurality of pilot carriers in the signal band, such as an OFDM signal, even if it is not an OFDM signal.

  The CP extraction units 27a and 27b correspond to the extraction unit described in the claims, the arrival angle estimation unit 38 corresponds to the arrival direction calculation unit, the unnecessary wave removal / phase rotation unit 30 corresponds to the synchronization unit, and the delay time. The calculating unit 41 corresponds to a delay time calculating unit, the unnecessary wave removing / phase rotating unit 30 corresponds to a supplying unit, the DU ratio calculating unit 42 corresponds to a DU ratio calculating unit, and the delay profile measuring unit 40 is a delay profile unit. It corresponds to.

It is a general block diagram of the propagation analyzer which calculates | requires a delay profile. It is a figure for demonstrating an OFDM signal. It is a block diagram of one embodiment of a radio wave propagation analysis device of the present invention. It is a figure which shows the constellation of the calibrated pilot carrier. It is a figure which shows the constellation of the calibrated pilot carrier. It is a figure which shows the relationship between a phase difference and the arrival direction of a desired wave. It is a flowchart of the operation | movement which calculates | requires the arrival direction, DU ratio, and delay time of each delay wave. It is a figure for demonstrating the phase synchronization of a delay wave. It is a figure which shows a rough delay profile.

Explanation of symbols

20a, 20b Antenna 21a, 21b Frequency converter 22a, 22b AD converter 23a, 23b Orthogonal demodulator 24 Correlation calculator 25 Window position controller 26a, 26b FFT calculator 27a, 27b CP extractor 28a, 28b Calibration unit 29 Calibration Coefficient output unit 30 Unwanted wave removal / phase rotation unit 31a, 31b IFFT operation unit 32a, 32b Correlation operation unit 33 Reference CP generation unit 34 IFFT operation unit 35a, 35b Normalization unit 36 Steering vector generation unit 37 Phase difference detection unit 38 Arrival Angle estimation unit 40 Delay profile measurement unit 41 Delay time calculation unit 42 DU ratio calculation unit

Claims (3)

A radio wave propagation analyzer that receives radio waves including a plurality of pilot carriers in a signal band with a plurality of antennas and measures the arrival direction, DU ratio, and delay time of radio waves,
Extracting means for extracting a pilot carrier from a signal in a frequency domain obtained by converting a signal received by an antenna of each system;
A direction-of-arrival calculation means for calculating a direction of arrival and a signal power of a desired wave by performing a correlation operation in a time domain between a pilot carrier of each system and a preset reference pilot carrier;
Synchronizing means for subtracting the desired wave component from the pilot carrier of each system and then synchronizing the delayed wave with phase rotation,
A delay time calculating means for calculating a delay time of the delay wave from the phase amount rotated by the synchronizing means;
Supply means for supplying the pilot direction of each system synchronized with the delay wave by the synchronization means to the arrival direction calculation means to calculate the arrival direction and signal power of the delay wave;
A radio wave propagation analyzing apparatus, comprising: a DU ratio calculating means for calculating a DU ratio that is a ratio of the signal power of the desired wave and the signal power of the delayed wave. In the radio wave propagation analyzer according to claim 1,
A delay profile unit that obtains a delay profile from a channel response obtained by dividing the pilot carrier extracted by the extraction unit by the reference pilot carrier, and obtains coarse delay times of the delayed wave in descending order of signal power;
The synchronization means subtracts a desired wave component from the pilot carrier of each system, and then synchronizes the delayed wave with a phase rotation by shifting a rough delay time of the delayed wave back and forth at a minute time interval. Radio wave propagation analyzer. In the radio wave propagation analyzer according to claim 2,
The synchronization means subtracts a delay wave component with a large signal power from a pilot carrier of each system synchronized with a delay wave with a large signal power last time, and then subtracts a coarse delay time of the delay wave with the next large signal power at a minute time interval. A radio wave propagation analyzer characterized by applying a phase rotation shifted back and forth to synchronize with a delayed wave having the next largest signal power.

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