JP2000252949A - Digital ground wave propagation delay measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate a pseudo delay wave from propagation delay characteristics. SOLUTION: A digital ground wave propagation delay measuring instrument which receives a test transmission signal passing plural different propagation routes by an antenna to measure the propagation delay characteristics indicating delay times and reception levels of the test transmission signal in respective propagation routes is provided with an A/D conversion means 13 which performs A/D conversion of a signal extracted from the test transmission signal received by the antenna, a digital correlator 15 which calculates correlation characteristics between the signal outputted from the A/D conversion means and the same template signal as a signal included before transmission of the test transmission signal, a detector 17 which detects correlation characteristics calculated by the digital correlator 15 to obtain them as propagation delay characteristics, and a smoothing processing means 19 which uses a cepstrum processing means to eliminate a pseudo multipath signal which is included in propagation delay characteristics outputted from the detector 17 and is caused by using the digital correlator.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a case where a test transmission signal modulated by the same baseband signal transmitted from one or a plurality of radio wave transmission sources and passing through a plurality of different propagation paths is received. The present invention relates to a digital terrestrial propagation delay measuring device for measuring a propagation delay characteristic indicating a delay time and a reception level of each test transmission signal.

[0002]

2. Description of the Related Art In Japan, various preparations are underway to shift the terrestrial TV broadcasting system from a conventional analog broadcasting system to a digital broadcasting system. In the provisional digital terrestrial broadcasting system in Japan, Orthogonal Frequency Division Multiplex (hereinafter referred to as O)
(Abbreviated as FDM). This OFD
A signal transmitted by the M system (hereinafter referred to as an OFDM signal) is a signal obtained by orthogonal frequency multiplexing a digitally modulated signal (subcarrier) in a narrow band (about 1 to 4 kHz).

For this reason, when an OFDM signal is affected by frequency selective fading caused by multipath, which indicates that the same radio wave generated by spatial propagation is received via a plurality of propagation paths due to reflection or the like. When compared with a digitally modulated wave having the same band (hereinafter referred to as a conventional digitally modulated wave), the OFDM signal has an advantage in receiving performance.

That is, as shown in FIG. 10A, in a conventional digitally modulated wave, a received signal is distorted due to the influence of frequency selective fading over the entire band, and the receiving sensitivity is deteriorated. In contrast, OFD
In the M signal, fading can be equivalently regarded as amplitude and phase fluctuation for each subcarrier.
As shown in, amplitude gain occurs in a certain subcarrier,
Since the amplitude of a certain subcarrier is attenuated, the reception sensitivity increases in the same propagation path (under a multipath environment) as compared with a conventional digitally modulated wave, although it varies depending on the characteristics of the spatial propagation path. That is, it can be said that the method is more resistant to the multipath generation phenomenon.

In this OFDM signal, a multipath measure in a time domain called a guard interval is taken in order to sufficiently exhibit this characteristic. That is, FIG.
As shown in (1), by inserting a guard interval GI for providing redundancy in the symbol interval (modification data change cycle) of the OFDM signal, interference between symbols whose delay waves caused by multipath are temporally continuous can be caused. I try to prevent giving.

[0006] Due to these advantages, in the provisional digital terrestrial broadcasting system in Japan, a multi-frequency network (Multi-frequency network) shown in FIG.
Frequency Network (hereinafter abbreviated as MFN)
Single frequency network (Single Frequ
It is tentatively provided that the service is switched to an ency network (hereinafter abbreviated as SFN). However, FIG.
In the single frequency network (SFN) shown in (b),
In addition to the reflected waves from buildings, interference from neighboring stations also occurs, so during network design and installation, set the above guard interval and observe multipath,
Management becomes very important.

Next, a single frequency network (SFN) adopted in the digital terrestrial broadcasting provisional system will be verified. In analog terrestrial broadcasting, as shown in FIG. 12 (a), the channels of broadcast radio waves are different for each area in order to avoid radio wave interference within the same frequency CH (channel) (especially in China and the Kyushu region, etc.). Since there are many relay stations, very many CHs are used). In addition, in these areas and the weak electric field area, the influence of ghost becomes remarkable due to the influence of multipath, and it is very difficult to manage the network. Therefore, in analog terrestrial broadcasting, a multi-frequency network (MFN) is adopted.

On the other hand, in digital terrestrial broadcasting, the channel of the broadcast wave is not changed (SFN) for each area as in CDMA or the like, or only one channel is changed (DFN).
N) A network is configured.

[0009] Naturally, radio interference is caused by other radio waves in the same frequency channel. However, due to the characteristics of the OFDM system, multipath within an arbitrary time delay (guard interval GI) or same channel interference improves the reception sensitivity. That is, CD
Similar to the MA method (or more), gain can be obtained by using an interference wave.

However, this effect is most important as described above in the design of a network configuration (station, ERP: effective radiated power setting) for converging multipath and co-channel interference within an arbitrary time delay. It is very important to measure the multipath propagation delay profile, which is the propagation delay characteristic of each radio wave received through a different propagation path received at an arbitrary point, in order to verify the design and determine whether redesign is necessary. Become.

Next, a method of measuring a multipath propagation delay profile (propagation delay characteristic) will be described. The multipath propagation delay profile (propagation delay characteristic)
As shown in (a), for example, a direct wave 1
And a time difference and a level difference between each direct wave and each delayed wave 2 generated by reflecting the direct wave on an obstacle. In particular, in a domestic digital broadcasting system using a single frequency network (SFN), since the same signal is transmitted at the same frequency at different levels, a delayed wave that is not a reflected wave is received at an arbitrary receiving point. Could be done.

The multipath propagation delay profile shown in FIG. 13A is Fourier-transformed to obtain the multipath propagation delay profile shown in FIG.
As shown in (1), by changing the time domain to the frequency domain, a frequency characteristic of frequency selective fading is obtained.
Here, when the multipath propagation delay profile Ψe (t) is expressed as a linear system function, it is expressed by equation (1).

[0013]

(Equation 1)

M is the number of delayed waves 2, L _n is 1 for direct waves 1
And to level ratio between the n-th delayed wave 2 if the time difference between Delta] t _n is the direct wave 1 and n-th delayed wave 2, [delta] (t) is the Kronecker delta function. In particular, the _zeroth level ratio L ₀ = 1 and the time difference Δt ₀ = 0. Here, assuming that a transmission signal of the radio wave transmission source is x (t) and a signal received at an arbitrary reception point is y (t), this reception signal y
(T) can be expressed by equation (2).

[0015]

(Equation 2)

There are roughly two methods for measuring a multipath propagation delay profile (propagation delay characteristic).
The first measurement method uses an impulse for the transmission signal x (t) of the radio wave transmission source. This is the method used by radar and the like. If the transmitted signal x (t) is completely a Kronecker delta function, the received signal y (t)
Is completely equal to the multipath propagation delay profile Ψe (t).

However, the Kronecker delta function δ (t) is a theoretical function and cannot actually be generated. At least, if the transmission signal x (t) passes through some linear system (such as a filter) at the time of transmission, the transmission signal x (t) is distorted at that time, and as a result, the reception signal y (t) is multipath propagated. Delay profile Ψe
Not equal to (t). As a result, the transmission signal x (t)
Causes distortion to the multipath propagation delay profile Ψe (t), resulting in “blur”.

Further, since it is necessary to instantaneously generate a large power exceeding the peak value of a normal transmission signal,
It is necessary to change the power amplifier and the like exclusively for this measurement.
Therefore, this measurement method cannot be actually adopted.

The second measurement method is called a correlation method, and a multipath propagation delay profile (propagation delay) is calculated by calculating a correlation between a received signal and a test signal using a known test signal as a transmission signal. Characteristic). The measured multipath propagation delay profile Ψ (t) in this case is shown by equation (3).

[0020]

(Equation 3)

Here, t (t) is a template signal, which is the same as a part of the transmission signal x (t). "*" Means complex conjugate.

In this correlation method, it is not necessary to set a special condition for the transmission signal x (t). In this correlation method, since a known test signal must be used as a transmission signal x (t) in advance, it is necessary to determine a modulation pattern of a modulation signal output from a radio wave transmission source (transmission station). Usually, a pseudo-noise sequence (hereinafter abbreviated as PN) is used for this modulation pattern.

However, if an extremely long period PN is used, the measured multipath propagation delay profile Ψ
Although the measurement accuracy of (t) is improved, the hardware scale (or calculation scale) of the measurement system becomes enormous. Conversely, if a PN having an extremely short period is used, the measurement accuracy of the multipath propagation delay profile Ψ (t) is reduced, but the hardware scale (or the calculation scale) of the measurement system is reduced.

As described above, since the two are in a mutually contradictory relationship, it is necessary to optimize the setting of the PN period. Generally, as the period of the PN, the maximum value of the multipath propagation delay time that can be predicted by the equation (1), that is,
(4) As shown in equation 2 times the maximum ΔtM time difference Delta] t _n between the direct wave 1 and n-th delayed wave 2 (= 2DerutatM)
Is appropriately set as the period of the PN.

2ΔtM <PNperiod (4) FIG. 14 is a diagram showing a multipath propagation delay profile (propagation delay characteristic) measured using this correlation method.
The horizontal axis represents the delay time Δt of each delayed wave 2 from the direct wave 1, and the vertical axis represents the level ratio (dB) of the reception level of each delayed wave 2 to the reception level of the direct wave 1.

In the multipath propagation delay profile (propagation delay characteristic) of FIG. 14, the reception level is “1”.
, Four delayed waves 2 whose reception level is lower than the direct wave 1 are displayed. Therefore, the measurer can confirm the existence of each of the delayed waves 2, the delay time Δt of each of the delayed waves 2, and the reception level (level ratio) of each of the delayed waves 1, at a glance of the profile.

[0027]

However, the following problems still need to be solved in the method of measuring a multipath propagation delay profile (propagation delay characteristic) employing the above-described correlation method.

That is, even if the pseudo-noise sequence (PN) satisfies the above-mentioned equation (4), the modulation pattern of the transmission signal has the measured multipath propagation delay profile Ψ (t) as shown in FIG. In addition to the direct wave 1 and each delayed wave 2, many pseudo waves (pseudo multi-pulse components) 3 are generated.

The reason why a large number of pseudo waves (pseudo multi-pulse components) 3 are generated is that, in theory, the calculation formula (3) showing the multipath propagation delay profile Ψ (t) is an infinite integral, This is because the calculation of the actual multipath propagation delay profile is performed by integration in a finite interval as shown in Expression (5) so as to satisfy Expression (4).

[0030]

(Equation 4)

Since the integration process in this finite section is an unavoidable compromise in realizing the system, the observer (observer) uses the multipath propagation delay profile shown in FIG. ), It is necessary to carry out a manual operation to visually detect and detect.

Therefore, since the pseudo delayed wave (pseudo multi-pulse component) 3 and each of the regular delayed waves (multipath) 2 cannot be clearly distinguished, the measurer (observation) is required in the process of detecting the delayed wave (multipath) 2. There is a problem that the individual difference of the person) becomes a measurement error. In addition, the work load of the operator (observer) increases, and the multipath propagation delay profile (propagation delay characteristics)
Measurement efficiency decreases.

The present invention has been made in view of such circumstances, and by utilizing the properties of a direct wave, a delayed wave, and a pseudo-delayed wave included in the once measured propagation delay characteristics, the propagation delay characteristics can be reduced. It is an object of the present invention to provide a digital terrestrial wave propagation delay measuring device capable of almost eliminating a pseudo delayed wave, accurately measuring a delay time and a reception level of a regular delayed wave with respect to a direct wave, and measuring accurately.

[0034]

According to the present invention, a test transmission signal modulated by the same baseband signal, which has passed through a plurality of different propagation paths, is received by an antenna, and a signal including the baseband signal is extracted. On the basis thereof, any one of the test transmission signals transmitted through a plurality of propagation paths is used as a reference test signal, and each delay time and each reception level of the test transmission signal in each propagation path are used as a reference test signal. This is applied to a digital terrestrial propagation delay measuring device that measures the propagation delay characteristic shown in FIG.

In order to solve the above-mentioned problem, in the digital terrestrial propagation delay measuring apparatus of the present invention, A / D conversion of a signal including a baseband signal extracted from a test transmission signal received by an antenna is performed. / D conversion means;
A digital correlator for calculating a correlation characteristic between a signal output from the A / D conversion means and a digital template signal identical to a baseband signal included before a test transmission signal is transmitted; A detector for detecting the correlation characteristic calculated by the modulator to obtain a propagation delay characteristic, and a cepstrum processing of a pseudo multipath signal caused by using the digital correlator included in the propagation delay characteristic output from the detector. And a smoothing processing means for removing using a means.

In the digital terrestrial propagation delay measuring apparatus thus configured, the correlation characteristic calculated by the digital correlator is detected by the detector and becomes the propagation delay characteristic. Within this propagation delay characteristic, among the test transmission signals that have passed through a plurality of propagation paths, for example, if a direct wave or the like is used as a reference, the reference test signal and a plurality of signals that are delayed with respect to this reference test signal are received. In addition to the test transmission signal (delay wave), a pseudo multipath signal (pseudo delay wave) caused by using a digital correlator is included.

This pseudo multipath signal has a higher frequency component than each received test transmission signal to be measured, and the reception level is significantly reduced as compared with each test transmission signal. By utilizing such characteristics of the pseudo multipath signal, the pseudo multipath signal is removed from the propagation delay characteristics using the cepstrum processing means.

Specifically, LOG conversion is performed, and Fourier transform is performed in a state where the level difference between the signal level of each received test transmission signal and the signal level of the pseudo multipath signal is enlarged, and the characteristic of the frequency axis is obtained. In this state, high frequency components are removed. Then, a high-frequency pseudo multipath signal is removed by performing an inverse Fourier transform on the propagation delay characteristic from which the high-frequency component has been removed.

The present invention also provides a method for receiving a test transmission signal, which has been modulated with the same baseband signal and has a guard interval at a predetermined time, via an antenna, through a plurality of different propagation paths, and Extract
Based on this, any one of the test transmission signals transmitted through a plurality of propagation paths is used as a reference test signal, and each delay time and each reception level of the test transmission signal in each propagation path are determined. The present invention is applied to a digital terrestrial propagation delay measuring device for measuring the propagation delay characteristics shown.

In order to solve the above problem, A / D conversion means for A / D converting a signal including the baseband signal extracted from the test transmission signal received by the antenna, and this A / D conversion means A digital correlator for calculating a correlation characteristic between the signal output by the means and the same digital template signal as the baseband signal included before the test transmission signal is transmitted; and a digital correlator calculating the correlation characteristic. A detector for detecting a correlation characteristic to obtain a propagation delay characteristic, a primary smoothing processing means for removing a pseudo multipath signal caused by a guard interval included in the propagation delay characteristic output from the detector, and The pseudo-multipath signal caused by using the digital correlator included in the propagation delay characteristic smoothed by the next smoothing processing means using the cepstrum processing means A secondary smoothing processing means for to, 1
And a display for displaying a propagation delay characteristic from which each pseudo multipath signal has been removed by the secondary and secondary smoothing processing means.

In the digital terrestrial propagation delay measuring apparatus thus configured, the propagation delay characteristic detected by the detector includes a direct wave or the like as a reference test signal, which is delayed with respect to this reference test signal. A plurality of received test transmission signals (delayed waves), a pseudo multipath signal (pseudo delayed wave) caused by using a digital correlator, and a pseudo multipath signal (pseudo delayed wave) caused by a guard interval are included. .

Since the pseudo multipath signal caused by the guard interval appears after the elapse of a delay time determined based on the guard interval time width from the reception time of the reference test signal, the primary smoothing processing means causes the pseudo multipath signal to be caused by the guard interval. The pseudo multipath signal is removed. The pseudo multipath signal caused by using the digital correlator is removed by the secondary smoothing processing means using the cepstrum processing means.

Therefore, in the measured propagation delay characteristics,
Only a reference test signal such as a direct wave and a plurality of normal test transmission signals (delayed waves) received with a delay with respect to the reference test signal are included.

Further, the cepstrum processing means in the digital terrestrial propagation delay measuring apparatus according to each of the above-mentioned inventions comprises: LOG conversion means for performing LOG conversion of the input propagation delay characteristic;
Fourier transform means for Fourier-transforming the propagation delay characteristic LOG-transformed by the LOG transform means, high-frequency component removing means for removing high-frequency components in the propagation delay characteristic Fourier-transformed by the Fourier transform means, Fourier inverse transform means for performing Fourier inverse transform on the propagation delay characteristic after the high frequency component has been removed by the component remover and outputting the result.

[0045]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a schematic configuration of a digital terrestrial propagation delay measuring device according to an embodiment. The test signal 5a modulated by the OFDM method output from the test signal generator 5 in the radio wave transmission source 22 is a baseband signal, and a guard interval GI7 is inserted as shown in FIG. As 6a,
Radio waves are radiated via the antenna 8.

As shown in Table 1, the length of the guard interval GI7 is, depending on the purpose of use, the internal division ratio of the symbol time length of the test signal 5a, 1/4, 1/8, 1/16, 1 /.
32. Therefore, multipath propagation delay profiles (propagation delay characteristics) are measured at various reception points, and the length of the guard interval GI7 is optimally set based on the measured results.

[0047]

[Table 1]

A part of the test transmission signal transmitted from the antenna 8 of the radio wave transmission source 22 is received as a direct wave (reference test signal) 9a by the antenna 10 of the embodiment. Further, part of the test transmission signal transmitted from the antenna 8 is reflected by the building 11 and received by the antenna 10 as a delayed wave (multipath) 9b. The received signal 10a including the direct wave 9a signal and the delayed wave (multipath) 9b signal received by the antenna 10 is demodulated by the channel converter 12 into a pair of baseband signals I (t) and Q (t). After that, the signal is converted into digital baseband signals I (n) and Q (n) by the A / D converter 13.

The digital baseband signals I (n) and Q (n) output from the A / D converter 13 are
Are input to a complex correlator 15 as a digital correlator. The template signal generator 16 is a template signal 16a that is the same baseband signal as the test signal 5a output from the test signal generator 5 on the side of the radio wave transmission source 22 and is converted into a pair of digital baseband signals. To the complex correlator 15.

The complex correlator 15 receives the digital baseband signals I (n) and Q (n) and the pair of digital baseband signal template signals t (n).
Is calculated and transmitted to the next detector 17.
The detector 17 detects the input correlation characteristic and outputs it as a multipath propagation delay profile (propagation delay characteristic) Q (i).

The multipath propagation delay profile (propagation delay characteristic) Q (i) output from the detector 17 is as follows:
It is input to the next smoothing processing unit 18. Primary smoothing processing unit 1
8 removes the pseudo delay wave (pseudo multipath) 4 shown in FIG. 14 as a pseudo multipath signal resulting from the guard interval GI7 included in the input multipath propagation delay profile (propagation delay characteristic). To the secondary smoothing processing unit 19.

The secondary smoothing section 19 performs multipath propagation delay profile (propagation delay) after removing the pseudo delay wave (pseudo multipath) 4 caused by the guard interval GI7 in the primary smoothing section 18. The pseudo delay wave (pseudo multipath) 3 shown in FIG. 14 as a high-frequency pseudo multipath signal resulting from the use of the complex correlator 15 included in the characteristic is removed, and the final multipath propagation delay profile ( As the propagation delay characteristic) D (i), the display unit 20
Display output.

FIG. 9 is a diagram showing a multipath propagation delay profile (propagation delay characteristic) D (i) after the pseudo multipath signal output and displayed on the display unit 20 has been removed.
From the smoothed multipath propagation delay profile (propagation delay characteristic) D (i) shown in FIG. 9, the experimenter can determine the delay time Δt _n from the direct wave 1 where the characteristic delayed wave (multipath) 2 is generated. That is, the position and existence) are measured, and the level ratio L _n at the delay time Δt _n in the multipath propagation delay profile Q (i) before smoothing shown in FIG. 14 is extracted. Thereby, a dominant regular delayed wave (multipath) 2 can be effectively extracted.

Next, details of each part will be described in order.

The specification of the test transmission signal 6a output from the antenna 8 of the radio wave transmission source 22 is determined as shown in FIG. Basic parameters are selected from the parameters of mode 3 in Table 1 described above so as to conform as much as possible to the actual transmission signal. Therefore, the length of the guard interval GI = 1/32 of the symbol time length is selected.

As a result, since this guard interval GI exists, the multipath propagation delay profile (propagation delay characteristic) measured by the correlation method of the OFDM signal has the time of the direct waves 1 to GI7 as shown in FIG. A level ratio proportional to the internal division ratio of the guard interval GI (in this case, 20
A pseudo delayed wave (pseudo multipath) 4 of log (1/32) = about -30 dB is generated.

In FIG. 1, a received signal 10a input from an antenna 10 is demodulated by a channel converter 12 into a pair of baseband signals I (t) and Q (t).

FIG. 3 is a block diagram showing a detailed configuration of the channel converter 12. The frequency of the received signal r (t) received by the antenna 10 is selected by a tunable filter (a band-pass filter whose center frequency can be selected) 12a. Then, after being amplified by the amplifier 12b, the local signal of the primary local oscillator 12c and the mixer 12d are down-converted to the center frequency f _if of a reception filter (a filter for selecting a desired one channel), and the frequency is selected by the reception filter 12e. Is done.

The intermediate frequency signal output from the receiving filter 12e is divided into a local signal of a secondary local oscillator 12h, a 90 ° phase shifter 12i, a pair of mixers 12f,
12g and a pair of filters 12j and 12k,
The signal is demodulated into a pair of baseband signals I (t) and Q (t). The received signal demodulated into a baseband signal is represented by y (t).
And This is a representation of the received signal y (t) of equation (2) in a different format.

Y (t) = I (t) + jQ (t) (6) where I (t) is the in-phase component of the received signal y (t), and Q (t) is the received signal. This is a quadrature component of the signal y (t).

A pair of baseband signals I (t), Q
The received signal y (t) composed of (t) is A / D shown in FIG.
Each of the ADCs 13a and 13b in the converter 13 performs sample quantization at a sampling period Ts, and
c, 13d. The sampled sequence of the sampled received signal is shown in equation (7). y (n) = I (n) + jQ (n) (7) n is a sequence index of the sampled sequence. Here, the memory length D of each of the waveform memories 13c and 13d needs to be at least a quotient obtained by dividing (2 OFDM symbols + 2 guard intervals GI section) by the sampling period Ts as shown in FIG.

D> int (1.25 ms * 2 / Ts) (8) Accordingly, data in the space of each of the waveform memories 13 c and 13 d is mapped at addresses 0 to D−1. That is, Expression (9) is satisfied. 0 ≦ n <D (9) In the A / D converter 13, the memory management unit 13 e requests the memory writing unit 13 f to perform sampling / memory writing, thereby obtaining an amount corresponding to the time of the expression (8). Only, the received signal y (t) expressed by the equation (6) is sampled as y (n), and written and stored in each of the waveform memories 13a and 13b at an address according to the equation (9). After the completion of the accumulation, the reception signal y (n) of the desired sampling sequence can be read from the desired address.

When the sampling / memory writing request is made and the sampling is completed, the arithmetic unit 1
4 performs signal processing. The sampling / memory write request is made by the complex correlator 15 incorporated in the operation unit 14. The complex correlator 15 performs the correlation operation represented by the equation (10), and calculates the received signal y (n) and the template signal t
The complex correlation characteristic Ψ ₁ (m) with (n) is obtained.

[0064]

(Equation 5)

Here, t * (nm) is obtained by sampling the template signal t * (t-τ) of the equation (3) at a sampling period Ts. K is a representation of the OFDM symbol length in the digital domain, and has a relationship of OFDM symbol length (real time) = KTs.

The complex correlator 15 sends the calculated complex correlation characteristic Ψ ₁ (m) to the next detector 17.

The detector 17 receives the input complex correlation characteristic Ψ ₁
The absolute value detection processing shown in equation (11) is performed on (m), and a temporary multipath transmission delay profile is obtained.

Q (m) = | Ψ ₁ (m) | (11) The detector 17 temporarily stores and holds the calculated tentative multipath transmission delay profile Q (m) and uses the equation (12). And the calculated tentative multipath transmission delay profile Q
Search for the maximum value of (m). max (Q (m)) = Q (m ₀ ) (12) Here, m ₀ is a time index of a sequence address at which Q (m) has the maximum value.

Next, the temporary multipath transmission delay profile Q (m) is calculated by using equation (13) and defining the maximum value (generally a direct wave) in equation (10) as time 0. Do it again.

[0070]

(Equation 6)

Similarly, the equation (11) is recalculated using the equation (14), and the reception time of the direct wave 1 showing the maximum value is used as a reference (time =
0), the elapsed time from this reference time, ie,
A multipath transmission delay profile Q (i) using the delay period from the reference time as a variable is calculated.

Q (i) = | Ψ ₀ (i) | (14) When this multipath transmission delay profile Q (i) is graphed in decibel display, it becomes as shown in FIG. As shown, the calculated multipath transmission delay profile Q (i) includes a direct wave 1 and a plurality of regular delayed waves 2.
In addition, one pseudo delay wave (pseudo multipath) 4 caused by the guard interval GI7 and a number of high frequency pseudo delay waves (pseudo multipath) 3 caused by employing the complex correlator 15 are included. It is. The detector 17 stores and holds the calculated multipath transmission delay profile Q (i) and sends it to the primary smoothing processing unit 18.

The primary smoothing processing section 18 generates a pseudo delay wave (pseudo multipath) generated by the guard interval GI7 included in the multipath transmission delay profile Q (i).
Suppress 4.

Here, the procedure for converting the multipath transmission delay profile Q (i) into a multipath transmission delay profile Ψ ₀ (i) in decibels will be described.

First, the digitally converted received signal y
Test signal x (n) for (n), template signal t
Since (n) is an OFDM signal, the portion where n = 0 to K can be expressed by equation (15).

[0076]

(Equation 7)

Here, k is a subcarrier index,
c_kIs the amplitude coefficient of the subcarrier, M ₁, M_TwoIs the lowest / most
Upper subcarrier number, b_kI, B_kQIs the subcarrier change
It is a key symbol. Here, the test signal x (n) of equation (15)
Is processed by K-point FFT (Fast Fourier Transform) (1
6)

FFT [x (n)] = X (k) = c _k (b _kI + jb _kQ ) (16) Similarly, if the received signal y (n) is subjected to K-point FFT processing, the following equation (17) is obtained.

FFT [y (n)] = Y (k) = (Φ _0I (k) + Φ _0Q (k)) c _k (b _kI + jb _kQ ) (17) FFT [Ψ ₀ (i)] = ( Φ _0I (k) + Φ _0Q (k)) (18) Then, by performing IFFT (Inverse Fast Fourier Transform) on these, a multipath transmission delay profile Ψ ₀ (i) in decibels is obtained.

IFFT (FFT [y (n)] / FFT [x (n)]) = IFFT (Φ _0I (k) + Φ _0Q (k)) = Ψ ₀ (i) (19) The point is that equation (19) and equation (13) are different. In the multipath propagation delay profile Ψ ₀ (i) obtained by the calculation of the equation (13), a pseudo delay wave (pseudo multipath) 4 due to the guard interval GI is generated for the correlation calculation, while In equation (20), it does not occur because it is a block operation.

The actual operation is performed as follows. That is, the signal sequence is extracted from the time index of the sequence address m ₀ only for the section of K, and the FFT operation is performed according to the equation (17). Next, the template signal t
The FFT operation is also performed on (n) in accordance with equation (16). After that, the former FFT result is quotient with the latter FFT result, and the IFFT is performed again. This calculation is performed based on equation (20).

FFT [y (n)] = Y (k) = Y (k) _i + jY (k) _q FFT [t (n)] = T (k) = X (k) = X (k) _i + jX (K) _q IFFT (FFT [y (n)] / FFT [t (n)]) = IFFT [{Y (k) _i + jY (k) _q ｝ ｛X (k) _i -jX (k) _q ｝ / {X (k) _i ² -jX (k) _q ² }] = { ₀ (i) (20) Therefore, the multipath propagation delay profile Ψ ₀ (i) calculated using the equation (20) Includes a pseudo delay wave (pseudo multipath) 4 caused by the guard interval GI7.
Does not occur.

The first-order smoothing processing section 18 calculates the multipath propagation delay profile Ψ ₀ (i) calculated using the equation (20).
And sends it to the next secondary smoothing processing unit 19.

The second-order smoothing processing section 19 uses a digital complex correlator 15 included in the input multipath transmission delay profile Ψ ₀ (i) to generate a high-frequency pseudo delay wave (pseudo multipath). 3 is suppressed using a cepstrum processing technique. This cepstrum processing method is mainly used for image restoration, seismic wave analysis, and audio signal analysis. The operation principle will be described with reference to FIGS.

First, as shown in FIG. 6, the multipath transmission delay profile Ψ ₀ output from the primary smoothing processing unit 18 has the original delay wave (multipath) 2 as shown in equation (21). It is assumed that it can be expressed as a product of the component D (i) and the component N (i) of the pseudo delayed wave (pseudo multipath) 3. | Ψ ₀ (i) | = D (i) N (i) (21) Further, the logarithmic value (LOG conversion) of the equation (21) is calculated. _{log | Ψ 0 (i) |} = logD (i) + logN (i) ... (22) the pseudo-delayed wave (pseudo multipath) 3 components N (i), lo
gN (i) contains many high frequency components, and the component D (i) of the original delayed wave (multipath) 2 contains many low frequency components. Therefore, as shown in FIG.
The multipath transmission delay profile し て₀ is subjected to IFFT processing by removing the high-frequency component by processing, and the component N (i) of the pseudo delay wave (pseudo multipath) 3 is obtained from the multipath transmission delay profile Ψ _0. Can be removed.
This processing is represented by equations (23) and (24).

[0086] G (l) = FFT [Log | Ψ 0 (i) |] = FFT [logD (i) + logN (i)] ... (23) to cut the high frequency part of the G (l). −> T (k) IFFT [T (k)] ≡D (i) (24) Therefore, in the secondary smoothing processing unit 19, as shown in FIG. The input multipath transmission delay profile Ψ ₀ (i) is LOG-converted by the LOG conversion unit 19a, and furthermore, the FFT processing unit 1
9b performs fast Fourier transform. The component N (i) of the pseudo-delay wave (pseudo-multipath) 3 is obtained by multiplying the fast Fourier-transformed multipath transmission delay profile G (i) by a frequency window signal from which low-frequency components are removed by the mixer 19c. Remove. Pseudo delayed wave (pseudo multipath) 3
Of the multipath transmission delay profile G (i) from which the component N (i) has been removed is subjected to inverse Fourier transform by the inverse FFT processing unit 19d to obtain the final multipath transmission delay profile D (i).
Get.

The final multipath transmission delay profile D (i) output from secondary smoothing processing section 19 is shown in FIG.
Are displayed on the display unit 20 shown in FIG.

FIG. 9 is a diagram showing the final multipath transmission delay profile D (i). As shown in the figure, the pseudo delay wave (pseudo multipath) 4 caused by the guard interval GI and the pseudo delay waves (pseudo multipath) 3 caused by the complex correlator 15 are removed, and the direct wave 1 and the original delay are removed. Wave 2 only.

However, in this method, the position information (the presence or absence of the delay wave, the delay time Δtn) of each delay wave 2 can be detected accurately, but an error occurs in the detection of the level ratio Ln. For this reason, the experimenter has shown in FIG.
The final multipath transmission delay profile D (i) shown in
Then, the time position of each delay wave 2 is visually measured, and the level ratio Ln at that time (delay time) Δtn is calculated by multipath propagation delay profile Q shown in FIG.
Extract from (i).

More specifically, as shown in FIG. 8, a dial 21a for designating the time axis position of the multipath propagation delay profile displayed on the display unit 20 is provided on the operation panel 21 of the measuring apparatus. The time (delay time) 21b specified by 21a and the level value 21c of the profile at the specified time (delay time) 21b are displayed.

In the digital terrestrial delay measuring apparatus thus configured, the direct wave 1 and the direct wave 1 are included in the multipath propagation delay profile Q (i) detected by the detector 17 in the arithmetic unit 14. A plurality of delayed waves 2 received with a delay with respect to 1; a plurality of pseudo delayed waves (pseudo multipath) caused by using a digital complex correlator 15
3 and a pseudo delayed wave (pseudo multipath) 4 caused by the guard interval GI7.

Therefore, the pseudo delay wave (pseudo multipath) 4 caused by the guard interval Gi7 is removed by the primary smoothing processing section 18, and the pseudo delay wave (pseudo multipath) caused by using the complex correlator 15 is obtained. (Pass) 3 is removed by the secondary smoothing processing unit 19.

Therefore, in the final multipath propagation delay profile D (i), as shown in FIG. 9, only the direct wave 1 and a plurality of delayed waves 2 delayed with respect to the direct wave 1 are received. Or included. Therefore, the direct wave 1 and the plurality of delayed waves 2 can be reliably grasped.

The inventor has confirmed by simulation the operation of the digital terrestrial propagation delay measuring apparatus of this embodiment. Table 2 shows the specifications of the multipath propagation delay profile used for the simulation. Specifically, it is assumed that received signal 10a of antenna 10 includes each delayed wave having delay time Δt and level ratio Ln shown in Table 2. Then, the final multipath propagation delay profile D (i) is calculated under the conditions of the respective delay waves, the respective delay times Δt are obtained, and each level is calculated from the multipath propagation delay profile Q (i) from the detector 17. Table 3 shows the results of the determination of the ratio Ln.

[0095]

[Table 2]

[0096]

[Table 3]

As shown in Table 3, it can be understood that the measurement is performed with high accuracy while suppressing the effects of the pseudo delayed waves (pseudo multipaths) 3 and 4.

[0098]

As described above, in the digital terrestrial propagation delay measuring apparatus of the present invention, the direct wave, the delayed wave, the guard interval, and the like included in the once measured propagation delay characteristic (multipath propagation delay profile) are obtained. By utilizing the properties such as the frequency of the pseudo delay wave (pseudo multipath) component caused by using the digital correlator, the pseudo delay can be calculated from the once measured propagation delay characteristic (multipath propagation delay profile) propagation delay characteristic. Wave (pseudo multipath) components are almost eliminated. Therefore, it is possible to accurately measure the delay time and the reception level of the original delayed wave with respect to the direct wave without overlooking it.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a digital terrestrial propagation delay measuring apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing a frame configuration of a test transmission signal in the digital terrestrial propagation delay measuring apparatus.

FIG. 3 is a detailed block diagram of a channel converter incorporated in the digital terrestrial propagation delay measuring device.

FIG. 4 is a detailed block diagram of an A / D converter incorporated in the digital terrestrial propagation delay measuring device.

FIG. 5 is a detailed block diagram of a secondary smoothing processing unit incorporated in the digital terrestrial propagation delay measuring apparatus.

FIG. 6 is a waveform chart for explaining the operation principle of the secondary smoothing processing unit.

FIG. 7 is a frequency characteristic diagram for explaining the operation principle of the secondary smoothing processing unit.

FIG. 8 is a diagram showing an operation panel of the digital terrestrial propagation delay measuring device.

FIG. 9 is a view showing a final multipath propagation delay profile measured by the digital terrestrial propagation delay measuring apparatus.

FIG. 10 is a diagram for explaining characteristics of an OFDM modulation method;

FIG. 11 is a diagram showing a guard interval incorporated in a transmission signal of the OFDM modulation method.

FIG. 12 is a diagram showing a comparison between MFN and SFN in the terrestrial broadcasting system;

FIG. 13 is a view for explaining basic characteristics of a multipath propagation delay profile.

FIG. 14 is a diagram showing a multipath propagation delay profile before each pseudo delay wave is removed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Direct wave 2 ... Delayed wave 3, 4 ... Pseudo delay wave 5 ... Test signal generator 6 ... Test transmission signal generator 7 ... Guard interval 8, 10 ... Antenna 12 ... Channel converter 13 ... A / D converter 14 ... Arithmetic unit 15 Complex correlator 16 Template signal generator 17 Detector 18 Primary smoothing processing unit 19 Secondary smoothing processing unit 20 Display unit 22 Radio wave source

Claims (3)

[Claims] Claims: 1. A plurality of different propagation paths,
An antenna (10) receives a test transmission signal modulated with the same baseband signal, extracts a signal including the baseband signal, and, based on the extracted signal, transmits a test transmission signal that has passed through the plurality of propagation paths. A digital terrestrial propagation delay measuring device for measuring propagation delay characteristics indicating each delay time and each reception level of a test transmission signal in each propagation path, using any one of the test transmission signals as a reference test signal; A / D converting a signal including the baseband signal extracted from the test transmission signal received by the antenna to A / D
Calculating a correlation characteristic between a signal output from the A / D conversion means and a digital template signal identical to a baseband signal included before the test transmission signal is transmitted; A digital correlator (15), a detector (17) for detecting a correlation characteristic calculated by the digital correlator and setting it as a propagation delay characteristic, and the digital signal included in the propagation delay characteristic output from the detector. A digital terrestrial propagation delay measuring device comprising: a smoothing processing means (19) for removing a pseudo multipath signal caused by using a correlator by using a cepstrum processing means. 2. It has been via a plurality of different propagation paths,
A test transmission signal modulated with the same baseband signal and provided with a guard interval at a predetermined time is received by an antenna, the baseband signal is extracted, and the baseband signal is extracted through the plurality of propagation paths. Digital terrestrial propagation delay measurement for measuring propagation delay characteristics indicating each delay time and each reception level of a test transmission signal in each propagation path, using any one of the test transmission signals as a reference test signal. An apparatus for A / D converting a signal including the baseband signal extracted from a test transmission signal received by the antenna,
Calculating a correlation characteristic between a signal output from the A / D conversion means and a digital template signal identical to a baseband signal included before the test transmission signal is transmitted; A digital correlator (15), a detector (17) for detecting a correlation characteristic calculated by the digital correlator to obtain a propagation delay characteristic, and a guard included in the propagation delay characteristic output from the detector. Primary smoothing processing means (18) for removing pseudo multipath signals caused by intervals, and the use of the digital correlator included in the propagation delay characteristics smoothed by the primary smoothing processing means Secondary smoothing processing means (19) for removing pseudo multipath signals to be processed using cepstrum processing means; and removing the pseudo multipath signals by the primary and secondary smoothing processing means. The indicator for indicating a propagation delay property (20)
A digital terrestrial propagation delay measurement device comprising: 3. The cepstrum processing means includes: a LOG conversion means (19a) for performing LOG conversion of the input propagation delay characteristic; and a Fourier transform means (19b) for performing a Fourier transform on the propagation delay characteristic LOG-transformed by the LOG conversion means. ), A high-frequency component removing means (19c) for removing high-frequency components in the propagation delay characteristic subjected to Fourier transform by the Fourier transform means, and a propagation delay after the high-frequency components have been removed by the high-frequency component removing means. 3. The digital terrestrial propagation delay measuring device according to claim 1, further comprising an inverse Fourier transform means (19d) for performing an inverse Fourier transform of the characteristic and outputting the result.