JP4374328B2 - Delay measuring device - Google Patents

Description

  The present invention relates to a technique for correctly and easily performing delay measurement of an OFDM (Orthogonal Frequency Division Multiplexing) signal used for terrestrial digital broadcasting.

The terrestrial analog broadcasting of the VHF band and UHF band currently used has been shifted to terrestrial digital broadcasting started in some areas since 2003. In 2010, the terrestrial analog broadcasting replaced the terrestrial analog broadcasting. Wave digital broadcasting services will be implemented in all regions.
In this terrestrial digital broadcasting, UHF band OFDM signals are used, but when switching to terrestrial digital broadcasting in an area where VHF band terrestrial analog broadcasting is received, propagation from the broadcasting station to the receiving area is performed. I need to investigate the situation.

Delay measurement is known as a main measurement item regarding such a propagation state.
As shown in FIG. 9, in the delay measurement, the level and arrival of the direct wave A1 that is output from the broadcasting station 1 and arrives directly in the area 2, for example, and the delayed wave A2 that is reflected by the reflector 3 etc. and arrives in the area 2 This is a measurement for detecting a timing difference, and the characteristic of the difference between the levels of the signals A1 and A2 and the arrival timing is generally called a delay profile.

  In terrestrial digital broadcasting, in order to prevent the degradation of the received image with respect to the multipath as described above, as shown in FIG. 10, a portion having a predetermined time width Tg from the head of each symbol S (i) constituting the OFDM signal. A signal component called a guard interval GI is inserted in.

  The guard interval GI is the same signal component as the signal of the last time width Tg of each symbol S (i), and by providing this redundant signal component, for example, within the range of the time width Tg from the direct wave. Even if there is a delayed wave that arrives after being delayed, the data can be demodulated correctly.

  For example, when a delayed wave A2 having a low level arrives after being delayed by a time Tx as shown in FIG. 11B with respect to a direct wave A1 having a high level as shown in FIG. 11 (c), a symbol non-interference unit Ba in which signals of the same symbol of the direct wave A1 and the delayed wave A2 are combined, and a symbol interference unit Bb in which signals of different symbols are combined. Alternately appear, and a delay profile can be obtained with high accuracy by performing predetermined processing on the signal sequence of the symbol non-interference portion Ba in which signals having strong correlations are combined.

FIG. 12 shows the configuration of the delay measuring apparatus 10 based on the above principle.
The delay measuring apparatus 10 receives an OFDM signal of a measurement target channel from a signal B0 input via an antenna (not shown) by the frequency converting unit 11, converts the OFDM signal into a predetermined intermediate frequency band, and converts this intermediate frequency band. The signal B1 is converted into a digital signal B2 by the A / D converter 12.

  The quadrature demodulator 13 performs a quadrature demodulation process on the digital signal B2 and outputs baseband signals I and Q.

  The symbol timing detection means 14 receives the baseband signals I and Q and detects the input timing of a specific position (here, the head position) of the symbols constituting the OFDM signal.

  The window position designating unit 15 designates the value set by the operation of the operation unit 16 to the window position signal generating unit 17 as the start timing Ta of a signal sequence cut-out process for a symbol described later.

  The window position signal generating means 17 uses the input timing at the head position of the symbol detected by the symbol timing detecting means 14 as a reference timing, and after the Ta time has elapsed from the reference timing, the window position signal W having a predetermined time width Tw is signal-sequence cut. Output to the output means 18.

  The signal train cut-out means 18 receives the signal trains I ′ and Q ′ input while receiving the window position signal W from the window position signal generating means 18 among the input baseband signals I and Q. Output.

  The delay profile generation means 19 extracts a transmission line characteristic from a pilot signal or the like included in the symbol by a Fourier transform process on the signal series I ′ and Q ′ cut out by the signal line cutting means 18, and reverses the transmission line characteristic. By the Fourier transform process, a delay profile is generated that represents the level of each signal component and the arrival timing difference that are included in the input signal B0 to be measured, transmitted from the same transmission source, and arrived at different timings through different paths.

  The display data generation unit 20 generates display data of the waveform of the delay profile generated by the delay profile generation unit 19 on the orthogonal coordinate with the horizontal axis representing time and the vertical axis representing level. Is displayed on the display 21 so that the display position becomes the specified position.

Next, the operation of the delay measuring apparatus 10 having the above configuration will be described.
A combined wave B of FIG. 13C, which is a combination of the direct wave A1 shown in FIG. 13A and the delayed wave A2 shown in FIG. 13B, is used as the input signal B0, and the level of the direct wave A1 is It is assumed that it is larger than the level of the delay wave A2.

  This synthesized wave B is converted to an intermediate frequency band by the frequency converter 11, converted to a digital signal B 2 by the A / D converter 12, converted to baseband signals I and Q by the orthogonal demodulator 13, and symbol timing detection The means 14 detects the reference timing t (i) corresponding to the symbol head position, as shown in FIG. The reference timing detected here corresponds to the symbol head position of the direct wave A1 having a high signal level.

  If the signal position extraction start timing Ta is specified by the window position specifying means 15 with respect to the reference timing t (i), the window position signal generating means 17 to the signal string extracting means 18 is shown in FIG. The window position signal W having a predetermined width Tw is output after the elapse of time Ta from the reference timing t (i) as shown in (d) of FIG. 13, and the window position signal W is output as shown in (e) of FIG. The signal trains I ′ and Q ′ during the period are cut out and output to the delay profile generation means 19.

  The above processing is performed on, for example, four consecutive symbols S (i) to S (i + 3), thereby obtaining a signal sequence necessary for accurately extracting transmission path characteristics, and receiving the signal sequence. The generation unit 19 generates a delay profile representing the levels of the direct wave A1 and the delayed wave A2 and the arrival time difference Tx, as shown in FIG.

  Then, the data of the delay profile is averaged, for example, by the display data generating means 20, and as shown in FIG. 14, the display 21 is arranged so that the display position of the direct wave A1 having the maximum level becomes the specified position on the time axis. Is displayed.

  Since the window position in the above example is before the delay time Tx, a symbol interference unit Bb in which signal components of different symbols are combined is included in the head portion of the extracted signal sequence. Due to the influence of the symbol interference unit Bb, the delay profile generation accuracy is lowered and the noise floor of the displayed delay profile is increased. However, the window position designation means 15 changes the signal sequence extraction start timing Ta to delay time Tx. As the value approaches, the number of symbol interference parts included in the extracted signal sequence decreases, the delay profile generation accuracy increases, and the noise floor of the displayed delay profile decreases.

  Therefore, in order to obtain a highly accurate measurement result, the measurer operates the operation unit 16 to vary the signal sequence extraction start timing Ta so that the noise floor of the displayed delay profile waveform is minimized. .

  A technique for generating and displaying a delay profile of an OFDM signal used for terrestrial digital broadcasting as described above is disclosed in, for example, the following Patent Document 1.

Japanese Patent Laid-Open No. 2004-236076

  In the delay measuring apparatus 10 described above, when the waveform of the delay profile is displayed, the maximum level waveform is displayed at a specified position within a certain time width Tg. That is, as shown in FIG. 14, since the waveform of the delay profile is displayed in the measurement range of Tb in the + direction and Tc in the − direction from the specified position t0 within the measurement time width Tg, the delay wave A2 is represented by Tb. When arriving at a larger delay time Tx, as indicated by the dotted line in FIG. 14, it may be displayed at the image position before the direct wave A1, and there is a possibility that the evaluation of the measurement result is erroneous. Note that the measurement range is not limited to Tg, and, for example, 1/3 of the normal symbol length is used. However, the above problem also occurs even if the measurement range changes.

  Further, since the designation of the window position is set regardless of the measurement range, there is an inconvenience that a highly accurate measurement result cannot be obtained unless the window position variable operation as described above is performed.

  The present invention improves these points and makes it possible to arbitrarily change the measurement range, that is, the display position of the maximum level waveform of the delay profile, so that the time-position relationship of each incoming wave included in the OFDM signal is correct in the order of arrival. It is an object of the present invention to provide a delay measuring device that can display and automatically set an appropriate window position for the measurement range.

In order to achieve the above object, a delay measuring apparatus according to claim 1 of the present invention comprises:
Symbol timing detection means (14) for detecting a specific position of a symbol of an OFDM signal to be measured, to which a guard interval having a predetermined time width (Tg) is added at the beginning ;
Window position designating means (32, 32 ') for designating a window position for extracting a signal sequence of a predetermined length from the symbol with reference to the specific position detected by the symbol timing detection means;
Window signal generating means (17) for generating a window signal for cutting out a signal sequence at a window at a position specified by the window position specifying means on the basis of the specific position detected by the symbol timing detecting means;
A signal sequence cutting means (18) for cutting out the signal sequence of the predetermined length at the position specified by the window position signal from the symbol of the OFDM signal to be measured;
A transmission path characteristic is extracted by a Fourier transform process for the signal string cut out by the signal string cutout means, and a level of each incoming wave included in the OFDM signal to be measured is obtained by an inverse Fourier transform process for the transmission line characteristic. Delay profile generation means (19) for generating a delay profile representing a difference in arrival timing;
A display (21) for displaying the waveform of the delay profile generated by the delay profile generating means on the time axis;
An operation unit (16);
Measurement range designating means (31, 31 ') for designating a measurement range having a time width of the guard interval, and within which the position designated by an operation on the operation unit is a time reference position ,
The waveform of the delay profile is set so that the waveform display position of the arrival wave with the maximum level of the delay profile generated by the delay profile generation means is the time reference position within the measurement range specified by the measurement range specification means. Display data generating means (33) for generating display data and displaying the display data on the display ,
According to the operation of the operation unit, the waveform display position for the incoming wave with the maximum level of the delay profile can be moved from the left end to the right end on the time axis of the display .

A delay measuring device according to claim 2 of the present invention is the delay measuring device according to claim 1,
The window positions specified by the window position specifying means change in conjunction with each other in a state in which the front ends of the window positions coincide with a position obtained by subtracting the time reference position from the width of the measurement range .

As described above, in the present invention, the display range for the arriving wave with the maximum level of the delay profile is set within the measurement time width by the measurement range designating unit for designating the measurement range using the position designated by the operation of the operation unit as the time reference position . Therefore, the waveform of each incoming wave included in the OFDM signal can be correctly displayed in the order of arrival, and there is little risk of erroneous evaluation on the measurement result.

  In addition, since the window position specified by the window position specifying means and the time reference position specified by the measurement range specifying means are linked, highly accurate delay measurement can be performed without troublesome operations.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows the configuration of a delay measuring apparatus 30 to which the present invention is applied. It should be noted that the frequency measuring unit 11, the A / D converter 12, the quadrature demodulator 13, the symbol timing detecting unit 14, the operation unit 16, the window position signal generating unit 17, the signal sequence extracting unit 18, the delay of the delay measuring device 30. Since the profile generation means 19 and the display device 21 are the same as those of the delay measuring apparatus 10, the same reference numerals are given and the description thereof is omitted.

  The delay measuring device 30 is provided with a measurement range specifying means 31, a window position specifying means 32, and a display data generating means 33 in addition to the above configuration requirements.

Measuring range specifying means 31, a time reference position t0 where waveform is displayed on the level maximum of the incoming wave of a delay profile obtained by the delay profile generating unit 19, according to the operation of the operation unit 16, a predetermined measurement time span This is for specifying arbitrarily in Tg. As described above, the measurement time width is generally 1/3 of the symbol length, but here, the measurement time width is assumed to be equal to the time width of the guard interval GI.

  Further, the window position designation means 32 uses the signal extraction start timing Ta at which Ta = Tg−t0 is established, for example, as information indicating the window position with respect to the time reference position t0 designated by the measurement range designation means 31. It designates to the position signal generating means 17.

  Further, the display data generating unit 33 is configured so that the display position of the waveform for the incoming wave with the maximum level of the delay profile generated by the delay profile generating unit 19 becomes the time reference position specified by the measurement range specifying unit 31. Display data of the delay profile waveform is generated and displayed on the display 21.

  With the delay measuring apparatus 30 configured as described above, for example, as shown in FIGS. 2A and 2B, the width of the guide interval GI with respect to the incoming wave A1 having the maximum level and the incoming wave A1. When obtaining the delay profile for the incoming wave A2 delayed by Tg, if the time reference position t0 = 0 is designated by the measurement range designating means 31, the waveform for the incoming wave A1 having the maximum level of the delay profile as shown in FIG. Is displayed at the left end where t0 = 0 within the measurement time width Tg, and the measurement range is a range from 0 to Tg, whereby the waveforms for the incoming waves A1 and A2 are correctly displayed in the order of arrival. The

  Further, the window position designating means 32 sets the signal extraction start timing Ta for the synthesized wave B in FIG. 2C to be equal to Tg (= Tg-0) in response to the designation of the measurement range. Only the symbol non-interference part Ba of the incoming wave A1 and the incoming wave A2 is cut out by the window position signal W in FIG.

  The delay profile obtained by this cut-out process is highly accurate, and the floor noise of the waveform of the delay profile displayed in the measurement range is sufficiently low.

  Further, for example, as shown in FIGS. 4A to 4C, delay profiles when different incoming waves A2 and A3 exist at positions of Tg / 2 before and after the maximum level incoming wave A1 are shown. In such a case, when the time reference position t0 = Tg / 2 is designated by the measurement range designating unit 31, the waveform display position for the incoming wave with the maximum level of the delay profile is the center of the measurement time width Tg as shown in FIG. Thus, the measurement range becomes −Tg / 2 to Tg / 2, and the waveforms for each of the incoming waves A1, A2, and A3 are correctly displayed in the order of arrival.

  Further, the window position designating means 32 for the designation of the measurement range is set so that the signal extraction start timing Ta for the composite wave B shown in FIG. 4D is equal to Tg / 2 (= Tg−Tg / 2). 4 so that only the symbol non-interference portion Ba for the incoming waves A1 to A3 is cut out by the window position signal W in FIG.

  The delay profile obtained by this cutting is highly accurate, and the floor noise of the waveform of the delay profile displayed in the measurement range is sufficiently low.

  Further, as shown in FIGS. 6A and 6B, the delay for the incoming wave A1 having the maximum level and the incoming wave A2 that arrived earlier than the incoming wave A1 by the width Tg of the guide interval GI. When obtaining the profile, if the time reference position t0 = Tg is designated by the measurement range designation means 31, the display position of the waveform of the arriving wave with the maximum level of the delay profile becomes the right end of the measurement time width Tg as shown in FIG. The range is -Tg to 0, and the waveforms of the incoming waves A1 and A2 can be correctly displayed in the order of arrival.

  Further, the window position specifying means 32 for setting the measurement range sets the signal extraction start timing Ta for the composite wave B in FIG. 6C to be equal to 0 (= Tg−Tg), Only the symbol non-interference part Ba of the incoming waves A1 and A2 is cut out by the window position signal W in FIG.

  The delay profile obtained by this cutting is highly accurate, and the floor noise of the waveform of the delay profile displayed in the measurement range is sufficiently low.

  As described above, the delay measuring apparatus 30 according to the embodiment can arbitrarily set the time reference position where the waveform of the arrival wave with the maximum level of the delay profile is displayed within the predetermined time width Tg by the measurement range specifying means 31. Therefore, the waveform for each incoming wave can be displayed correctly in the order of arrival, and there is little risk of erroneous evaluation on the measurement result.

  Further, the window position designated by the window position designating means 32 to the window signal generating means 17 changes following the position corresponding to the time reference position designated by the measurement range designating means 31, so that a troublesome operation is performed. Without delay, highly accurate delay measurement can be performed.

  In the above embodiment, the window position is changed following the time reference position specified by the measurement range specifying means 31. However, like the delay measuring device 30 'shown in FIG. Based on the above operation, the window position designating means 32 'designates the window position (signal string cutout start timing Ta) to the window position signal generating means 17, and the measurement range designating means 31' is configured according to the window position. A configuration in which the time reference position t0 is changed following up may be used. Even in this case, the same operation as that of the above-described embodiment can be obtained by maintaining the relationship of Ta = Tg-to.

  In the delay measurement devices 30 and 30 'of the above-described embodiment, the time reference position and the window position are interlocked. However, each may be set independently.

  In addition, the delay measuring devices 30 and 30 ′ of the above embodiment have the frequency converting unit 11 for converting the OFDM signal in the UHF band into the intermediate frequency band, but this does not limit the present invention. The intermediate frequency band signal output from a digital broadcast wave receiver, or a signal obtained by digitally converting the signal, or a baseband signal after quadrature demodulation is received as an OFDM signal to be measured. Also good.

The figure which shows the structure of embodiment of this invention Operation explanatory diagram of the embodiment The figure which shows the measurement result with respect to the state of FIG. Operation explanatory diagram of the embodiment The figure which shows the measurement result with respect to the state of FIG. Operation explanatory diagram of the embodiment The figure which shows the measurement result with respect to the state of FIG. The figure which shows the structure of other embodiment. Illustration of multipath Diagram showing OFDM signal format Diagram showing the relationship between multiple incoming waves and synthesized waves Configuration diagram of conventional equipment Operation explanatory diagram of conventional equipment The figure which shows the example of a display of the measurement result of the conventional device

Explanation of symbols

  DESCRIPTION OF SYMBOLS 11 ... Frequency conversion part, 12 ... A / D converter, 13 ... Quadrature demodulator, 14 ... Symbol timing detection means, 15 ... Window position designation means, 16 ... Operation part, 17 ... Window position Signal generating means, 18... Signal train cutting means, 19... Delay profile generating means, 20... Display data generating means, 21... Display, 30, 30 '.... Delay measuring device, 31, 31'. ... Measurement range designation means, 32, 32 '... Window position designation means, 33 ... Display data generation means

Claims (2)

Symbol timing detection means (14) for detecting a specific position of a symbol of an OFDM signal to be measured, to which a guard interval having a predetermined time width (Tg) is added at the beginning ;
Window position designating means (32, 32 ') for designating a window position for extracting a signal sequence of a predetermined length from the symbol with reference to the specific position detected by the symbol timing detection means;
Window signal generating means (17) for generating a window signal for cutting out a signal sequence at a window at a position specified by the window position specifying means on the basis of the specific position detected by the symbol timing detecting means;
A signal sequence cutting means (18) for cutting out the signal sequence of the predetermined length at the position specified by the window position signal from the symbol of the OFDM signal to be measured;
A transmission path characteristic is extracted by a Fourier transform process for the signal string cut out by the signal string cutout means, and a level of each incoming wave included in the OFDM signal to be measured is obtained by an inverse Fourier transform process for the transmission line characteristic. Delay profile generation means (19) for generating a delay profile representing a difference in arrival timing;
A display (21) for displaying the waveform of the delay profile generated by the delay profile generating means on the time axis;
An operation unit (16);
Measurement range designating means (31, 31 ') for designating a measurement range having a time width of the guard interval, and within which the position designated by an operation on the operation unit is a time reference position ,
The waveform of the delay profile is set so that the waveform display position of the arrival wave with the maximum level of the delay profile generated by the delay profile generation means is the time reference position within the measurement range specified by the measurement range specification means. Display data generating means (33) for generating display data and displaying the display data on the display ,
The delay measuring device characterized in that the waveform display position of the arrival wave with the maximum level of the delay profile can be moved between the left end and the right end on the time axis of the display according to the operation of the operation unit. . 2. The delay measuring apparatus according to claim 1, wherein the window position specifying means changes in conjunction with each other in a state in which a tip of the window position specified by the window position specifying means coincides with a position obtained by subtracting the time reference position from the width of the measurement range. .

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