JP4955322B2 - Transmission line characteristic measuring instrument and wraparound canceller - Google Patents

Description

The present invention uses a received orthogonal frequency division multiplexing (OFDM) signal to generate a direct wave (desired wave) from a parent station to a relay station or a receiving station and between the parent station and the relay station or the receiving station. Delayed waves caused by reflections from buildings and mountains, etc., jumping waves of the same signal transmitted from other relay stations (hereinafter included in the delayed wave), single frequency network (SFN) In connection with measurement of transmission path characteristics indicating the relationship of sneak waves that are re-transmitted at the relay station directly or reflected on surrounding buildings or mountains, etc., especially for multiple channels or arbitrarily Transmission line characteristics that measure transmission line characteristics using the spectrum of the frequency bandwidth of It relates to the measuring device.

In addition, the present invention uses a transmission path characteristic measured from an OFDM signal to transmit a delayed wave caused by reflection of a building or a mountain between a master station and a relay station or a receiver station, or transmission from another relay station. Cancel the sneak wave that is received again by the reflected signal of the same signal (hereinafter included in the delayed wave) or the signal retransmitted by the SFN relay station directly or reflected by surrounding buildings or mountains In particular, the present invention relates to a sneak canceller that realizes batch erasure of sneak waves and delay waves of a plurality of channels or arbitrary frequency bandwidths.

In recent years, for example, in the terrestrial digital broadcasting, the OFDM transmission method is used. The OFDM transmission method is a method in which a large number of carriers orthogonal to each other are modulated by digital data to be transmitted, and these modulated waves are multiplexed and transmitted.

The OFDM transmission system has the characteristics that if the frequency bandwidth is constant and the number of carriers to be used is increased, the symbol time becomes longer and the addition of a guard interval signal makes it less susceptible to delay waves. . And because of this feature, there is a possibility that a single-frequency broadcast network, that is, SFN can be constructed. Therefore, as described above, the OFDM transmission system is the Japanese Integrated Services Digital-Terrestrial (ISDB- T) and European Digital Video Broadcasting-Terrestrial (DVB-T).

However, even in OFDM transmission, which is less susceptible to delay waves, signal quality degradation is inevitable when delay waves are present, so accurate transmission path characteristics can be analyzed as a means of analyzing propagation path conditions. A measurement method is desired. Further, in the relay stage, it is desired to eliminate the sneak wave and the delayed wave in order to suppress the degradation of the signal quality as much as possible.

  Here, the delayed wave and the sneak wave will be described with reference to FIG. Although the relay station 111 originally requires only the OFDM wave 101, the incoming wave 103 from another relay station or the delayed wave 107 that arrives after being reflected by an obstacle or the like arrives. In SFN, a sneak wave 105 of the transmission wave of the relay station 111 itself arrives at the reception antenna of the relay station 111 in addition to the delay wave. In order to normalize the retransmitted wave 109 to the user household, it is desirable to measure the characteristics of the incoming wave 103, the delayed wave 107 and the sneak wave 105 from the other relay stations with respect to the desired wave 101, and to delete other than 101 . The present invention is intended to accurately measure transmission path characteristics of a desired wave, an incoming wave from another relay station, a delayed wave and a sneak wave, and to efficiently eliminate unnecessary OFDM waves based on the measurement result. .

  For example, the following two methods are conceivable as methods for measuring the transmission path characteristics of incoming waves, delay waves, and sneak waves from other relay stations. By these methods, transmission path characteristics (transmission path transfer functions and delays) Profile (complex impulse response)). Further, the sneak canceller eliminates the sneak wave and the delayed wave by calculating the tap coefficient based on the delay profile measured by any one of these two methods.

(1) A transfer function is obtained from the pilot carrier inserted in the OFDM signal, and this transfer function is subjected to inverse discrete Fourier transform (IDFT) to obtain a delay profile, that is, a complex impulse response. Here, the pilot carrier is a reference signal whose phase and amplitude are known, which is used when demodulating a modulated signal. For details, see Non-Patent Document 1.

(2) The spectrum of the OFDM signal band is calculated, and the delay profile is obtained by IDFT of the spectrum. For details, see Non-Patent Document 2.

  However, these conventional channel characteristic measuring instruments measure the channel characteristics of delay waves and sneak waves in the signal band of one channel from the carrier or spectrum in the signal band of one channel. The resolution was limited. In addition, in the conventional wraparound canceller based on these transmission path characteristic measurement methods, a delay wave or a wraparound transmission path characteristic in the signal band of one channel is measured from a carrier or spectrum in the signal band of one channel. Therefore, sneak waves and delay waves that can be eliminated are only for the signal band of one channel, and even within one channel band, frequencies outside the signal band, frequency bands corresponding to multiple channels, or arbitrary frequency bands The sneak wave and the delayed wave could not be eliminated.

In the conventional transmission line characteristic measuring device, when measuring a more detailed delay profile, it is conceivable to use a signal of a plurality of channels. However, since the pilot and signal spectrum do not exist at frequencies other than the signal band, the delay profile However, as shown in FIG. 11B, there is a problem that it is difficult to identify a delayed wave or a sneak wave. Further, in the conventional wraparound canceller, when sneak waves and delayed waves in frequency bands corresponding to a plurality of channels are to be deleted, a plurality of wraparound cancellers are prepared. As a result, the installation space for the cables connecting the cables and the relay device is increased, which increases the cost and requires additional installation costs.

  As described above, there is a strong demand for a transmission line characteristic measuring device that calculates a delay profile with higher time resolution. In addition to the signal band of one channel, a wrap canceller that cancels sneak waves and delay waves outside the signal band, a sneak canceller that cancels sneak waves and delay waves in the frequency band corresponding to multiple channels, or any frequency band There is a strong demand for a sneak canceller that eliminates sneak waves and delayed waves.

  In order to accurately cancel sneak waves and delayed waves of multiple channels with a single sneak canceller, the relative frequency arrangement of multiple channels is maintained, the transmission path characteristics are measured simultaneously, and the multiple channels in the relay station are measured. It is necessary to reflect the tap coefficient in a finite impulse response (FIR) filter.

  The following two methods are conceivable for simultaneously measuring the transmission path characteristics for a plurality of channels. One is a method of measuring transmission path characteristics for each channel, and the other is a method of measuring transmission path characteristics of a plurality of channels at once.

  However, in this first method, as shown in FIG. 2, since the symbol timing of the OFDM signal is generally not aligned for each channel, the timing for examining the transmission path characteristics, that is, the demodulation timing is different for each channel. become. Therefore, when the transmission line characteristics fluctuate with time, the operation of the canceller becomes unstable and the possibility of oscillation increases. Further, since a plurality of OFDM demodulators are required, there is a problem that costs are increased.

  In the second method, it is necessary to collectively demodulate the OFDM signals of a plurality of channels. However, as shown in FIG. 2, since the symbol timing of the OFDM signal is different for each channel, It is practically impossible to apply an optimal time window (FFT window) to a channel, and depending on the channel, OFDM demodulation may not be possible. In other words, transmission path characteristics may not be measured.

  As described above, it is difficult to measure the channel characteristics of a plurality of channels with the technique of performing OFDM demodulation based on the symbol timing. Similarly, it is difficult to design a wraparound canceller.

Furthermore, when using the spectrum of a plurality of channels by the second method, it is only necessary to obtain the shape of the spectrum, so the position of the FFT window may be arbitrary. However, in the presence of a plurality of channels, the spectrum shape is not flat even in the absence of a delayed wave or a sneak wave. Therefore, even if the transmission path characteristics are measured, that is, the delay profile is measured, the desired wave as shown in FIG. There remains a problem that the significant difference is small and it becomes difficult to identify delayed waves.
Michael Speth, Stefan Fechtel, Gunnar Fock, and Heinrich Meyr, “Optimum Receiver Design for OFDM. 49, no. 4, April 2001, pp. 571-578. S. Stein, J.A. J. et al. Jones (Author), Hideo Seki (Translation), “Modern Communication Line Theory”, Morikita Publishing, October 1970, pp. 121-130.

  In a transmission line in which a delayed wave or a sneak wave exists, the amplitude and phase of the frequency characteristic of the received OFDM signal change corresponding to the delay time, amplitude, and phase of the delayed wave or sneak wave. A conventional transmission path characteristic measuring instrument measures transmission path characteristics such as a transfer function and a delay profile from a spectrum within a signal band of one channel.

Further, in a conventional wraparound canceller, a tap coefficient of an FIR filter is calculated using transmission path characteristics measured from a spectrum within a signal band of one channel, and a signal for removing a delay wave and a wraparound wave by this FIR filter. Was generated.

  Therefore, the transmission line characteristic measuring device can measure the delay profile only with the time resolution determined by the reciprocal of the channel bandwidth.

In the wraparound canceller, the delay wave and sneak wave within the measured channel band could be removed by the FIR filter, but the delay wave and sneak wave outside the channel band could not be removed. There wasn't.

  Furthermore, in the wraparound canceller, pay attention to the number of channels to be relayed for each relay station and the frequency relationship between channels, and the increase or decrease of the number of channels. I had to change the configuration of the wraparound wave canceller as appropriate.

Therefore, the present invention proposes a transmission line characteristic measuring device and a wraparound canceller having a time resolution determined by the reciprocal of the bandwidth over a plurality of channels.

In addition, in a relay station that performs relaying at the same frequency (SFN), it is possible to delete a delayed wave and a sneak wave of a plurality of channels that must be relayed by a single canceller, thereby further increasing the number of relay stations in each region. We propose a wraparound canceller system that makes it possible to design delay wave and wraparound cancellers in the same way.

According to the first aspect of the present invention, a Fourier transform unit that calculates a frequency spectrum by Fourier-transforming a signal of a plurality of channels obtained by multiplexing subcarrier signals of a predetermined frequency channel, and a frequency using a plurality of the frequency spectra. An average value calculating unit that calculates an average value for each, a reference spectrum is calculated using the frequency spectrum, a frequency band outside the signal band of the frequency spectrum, and a frequency outside the signal band using the reference spectrum A spectrum correction unit for correcting the spectrum level of the boundary frequency band between the band and the signal band to the same level as the spectrum level of the signal band; and inverse delay transforming the frequency spectrum obtained by the correction to obtain a delay profile And an inverse Fourier transform unit for calculating .

The invention according to claim 2 is a sneak canceller for retransmitting a signal of a plurality of channels formed by multiplexing subcarrier signals of a predetermined frequency channel, and a delayed wave that eliminates a sneak wave and a delayed wave. An erasure unit, a Fourier transform unit that Fourier-transforms the signals of the plurality of channels and calculates a frequency spectrum, an average value calculation unit that calculates an average value for each frequency using a plurality of the frequency spectra, and the frequency spectrum The reference spectrum is calculated using the reference spectrum, and the level of the frequency band outside the signal band of the frequency spectrum and the spectrum level of the frequency band outside the signal band and the boundary frequency band between the signal band and The spectrum correction unit that corrects the level to the same level as the level, and the spectrum obtained by the correction A reciprocal calculation unit for reciprocalizing, an inverse Fourier transform for calculating a delay profile by performing inverse Fourier transform on the frequency spectrum obtained by the correction, and the delay profile obtained as a calculation result of the inverse Fourier transform unit Tap coefficient calculation unit that calculates the amplitude, delay time, and phase characteristics of an erasure signal generated by the delay wave cancellation unit based on the complex value of each or the amplitude, delay time, and phase characteristics of each sneak wave and delay wave With .
According to a third aspect of the present invention, there is provided a sneak canceller for retransmitting a signal of a plurality of channels obtained by multiplexing subcarrier signals of a predetermined frequency channel, and a delayed wave that eliminates a sneak wave and a delayed wave. An erasing unit; a discrete Fourier transform unit that Fourier-transforms the signals of the plurality of channels to calculate a frequency spectrum; an average value calculation unit that calculates an average value for each frequency using a plurality of the frequency reception spectra; and the frequency spectrum A reference spectrum is calculated using the reference spectrum, and a frequency band outside the signal band of the frequency spectrum and a spectrum level of a frequency band outside the signal band and a boundary frequency band between the signal band and the reference spectrum are used to calculate the spectrum level of the signal band. The spectrum is corrected to the same level as that of the spectrum and to obtain the reciprocal of the frequency spectrum. Torr inverse correction unit, inverse Fourier transform unit that calculates a delay profile by performing inverse Fourier transform on the inverse of the frequency spectrum obtained by the correction, and complex number of the delay profile obtained as a result of calculation by the inverse Fourier transform unit A tap coefficient calculation unit that calculates the amplitude, delay time, and phase characteristics of the cancellation signal generated by the delay wave cancellation unit based on the value, or the amplitude, delay time, and phase characteristics of each sneak wave and delay wave Prepare .

  According to the present invention, it is possible to measure transmission path characteristics such as frequency characteristics and delay profiles with higher accuracy than conventional transmission path characteristic measuring devices using signals of a plurality of channels.

Furthermore, according to the present invention, a delayed wave and a sneak wave generated in a relay broadcast station that relays signals of a plurality of channels can be eliminated by one sneak canceller. Therefore, it is possible to reduce the cost of a relay device for a plurality of channels.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 4 shows a transmission line characteristic measuring instrument according to the first embodiment of the present invention. The transmission path characteristic measuring apparatus according to the present embodiment uses a discrete Fourier transform unit that calculates a reception spectrum by performing a discrete Fourier transform process on a digitized reception signal (OFDM signal), and a frequency using a plurality of the calculated reception spectra. An average value calculating unit for calculating an average value for each, a spectrum correcting unit for calculating a reference spectrum from the calculated received spectrum, correcting the received spectrum using the calculated reference spectrum, and a complex for the corrected received spectrum. An inverse discrete Fourier transform unit for performing an inverse discrete Fourier transform process for calculating an impulse response value (delay profile).

Among these, the discrete Fourier transform unit does not care about the symbol timing with respect to the received signal, starts sampling at an arbitrary start timing, and performs signal strength for each discrete frequency of the received signal which is a time signal by the discrete Fourier transform | R _i (k) | (or | R _i (k) | ² ) is acquired. This R _i (k) corresponds to a spectrum. Here, i is the total number of N-point discrete Fourier transforms after the start of measurement by the discrete Fourier transform unit, and 0 ≦ k <N (N: the number of points of the discrete Fourier transform). Note that the acquisition point (ie, k) of R _i (k) does not necessarily match the frequency of the subcarrier signal of the OFDM signal, and the acquisition point number N of k does not need to match the frequency band of the OFDM signal, What is necessary is just to select suitably to such an extent that required precision can be ensured.

The average value calculation unit calculates an average value of a plurality of spectra | R _i (k) | (or | R _i (k) | ² ) for each frequency, and | R (k) | = E [| R _i ( k) |] (or | R (k) | ² = E [| R _i (k) | ² ]).
(Equation 1)
| R (k) |
= E [| R _i (k) |]
= (| R _{jM + 1} (k) | + | R _{jM + 2} (k) | +
... + | R _{jM + M} (k) |) / M (0 ≦ k <N)
(Or
(Equation 2)
| R (k) | ²
= E [| R _i (k) | ² ]
= (| R _{jM + 1} (k) | ² + | R _{jM + 2} (k) | ² +
... + | R _{jM + M} (k) | ² ) / M (0 ≦ k <N)
)
However, j is the number of times the average value is calculated by the average value calculation unit since the start of measurement and satisfies j ≧ 0, M is the number of spectra used for calculating the average value, and M ≧ 1 Meet.

Next, in the spectrum correction unit, the average value R (k) of the received spectrum is expressed by (Expression 3) based on the average value X (k) of the transmission spectrum and the transfer function S (k) of the transmission path.
| R (k) | = | S (k) |. | X (k) | (0 ≦ k <N)
(Or
(Equation 4)
| R (k) | ² = | S (k) | ² · | X (k) | ² (0 ≦ k <N)
)
(For details, see Fumio Takahata, "Digital Wireless Communication", Bafukan, June 2002, pp.127-129, Yoichi Saito, "Modulation and Demodulation of Digital Wireless Communication," IEICE, 1996. February, pp.164-166, and Moji Kuwahara, “Digital Microwave Communication”, Planning Center, 1984, p.196.) The spectrum | R (k) | (or | R (k) | ² ) inputted from the average value calculation unit is divided by | (or | X (k) | ² ), and | S (k) | (or | S (K) | ² ) is obtained.
(Equation 3)
| S (k) | = | R (k) | / | X (k) | (0 ≦ k <N)
(Or
(Equation 4)
| S (k) | ² = | R (k) | ² / | X (k) | ² (0 ≦ k <N)
)

Here, the reference spectrum | X (k) | (or | X (k) | ² ) is the signal band in the average value | R (k) | (or | R (k) | ² ) of the received spectrum. (Hereinafter referred to as a signal region), a boundary region between a signal region and a frequency band outside the signal band (hereinafter referred to as a boundary region), and a frequency region outside the signal band (hereinafter referred to as an outside signal region). The reference spectrum is calculated separately. First, the average values T and U in the frequency direction of the signal region and the non-signal region are calculated, and the spectrum of the boundary region is a function F _k (with the average value T of the signal region and the average value U of the non-signal region as variables. T, U). The function F _k (T, U) has one of the following three forms according to the relationship between the sampling frequency and the frequency at which the signal exists, and the number of points of the discrete Fourier transform: 1. Different functions at each normalized frequency (hereinafter referred to as frequency) k 2. a function that differs at some k on the lower frequency side (hereinafter referred to as the lower boundary region) than the signal region and that differs at some k on the higher frequency side (hereinafter referred to as the upper boundary region) than the signal region; The same function can be determined in advance at all frequencies k.

Here, an example of a reference spectrum calculation procedure will be described with reference to FIGS. 5 and 6. FIG. 5 shows a reception spectrum when a delayed wave exists in addition to the desired wave. In the figure, the reception spectrum is the signal outer region 1, the lower boundary region 1, the signal region 1, the upper boundary region 1, the signal outer region 2, the lower boundary region 2, the signal region 2, the upper boundary region 2, the signal outer region 3, the lower It can be divided into a boundary region 3, a signal region 3, an upper boundary region 3,..., A signal region 5, an upper boundary region 5, and an outside signal region 6. First, the average value T in the frequency direction of the reception spectrum of all frequencies k in the signal region 1 to 5 of | R (k) | (or | R (k) | ² ), and all of the out-of-signal regions 1 to 6 An average value U in the frequency direction is calculated, and each is set as a spectrum of all frequencies in the signal region and a spectrum of all frequencies in the non-signal region. Next, the calculated average values T and U are substituted into a predetermined function F _k (T, U) to calculate a spectrum of each frequency k in the boundary region. FIG. 6 shows an example of the reference spectrum | X (k) | (or | X (k) | ² ) obtained from the reception spectrum of FIG. 5 by the above procedure. FIG. 7 summarizes FIG. 5 and FIG. In FIG. 7, FIG. 7 (a) shows a spectrum of a normal OFDM signal when neither a delayed wave nor a sneak wave exists. FIG. 7A shows an example of a spectrum in the case where five channels do not exist at continuous frequencies but are scattered. 7B is the same spectrum as FIG. 5, FIG. 7C is the same reference spectrum as FIG. 6, and FIG. 7D is a diagram after the spectrum correction unit corrects the reception spectrum of FIG. Received spectrum | S (k) | (or | S (k) | ² ). This | S (k) | (or | S (k) | ² ) is not strictly called a spectrum but is called a transfer path transfer function (or power transfer function), but in this specification ( This will be referred to as “reception” spectrum.

  8 and 9 show normal spectra when the channel arrangement is different from that shown in FIG. 7 (FIGS. 8A and 9A), and received spectra when there is a delayed wave (FIG. 8B and FIG. 9). 9 (b)), the reference spectrum (FIG. 8 (c), FIG. 9 (c)), and the received spectrum after correction (FIG. 8 (d), FIG. 9 (d)). FIG. 10 shows a normal spectrum when only one channel is received (FIG. 10A), a received spectrum when a delayed wave exists (FIG. 10B), a reference spectrum (FIG. 10C), And FIG. 10D shows a reception spectrum after correction.

Next, the inverse Fourier transform unit performs inverse Fourier transform on the spectrum | S (k) | (or | S (k) | ² ) input from the spectrum correction unit to calculate a delay profile, that is, a complex impulse response. FIG. 11A is a delay profile calculated from the spectrum (corrected received spectrum) of FIG. 7D. For comparison, FIG. 11B shows a delay profile calculated from the reception spectrum (reception spectrum before correction) in FIG. In FIG. 11A, it is easy to distinguish between the desired wave and the delayed wave, whereas in FIG. 11B, it is difficult to distinguish between the desired wave and the delayed wave. Therefore, in the first embodiment of the present invention, it can be seen that the transmission line characteristics can be measured with higher accuracy than the conventional transmission line characteristic measuring instrument.

Next, a wraparound canceller according to a second embodiment of the present invention will be described with reference to FIG.

A relay apparatus including a wraparound canceller includes a reception antenna that receives a signal for a plurality of channels having a predetermined carrier frequency from an upper apparatus, and a transmission antenna that transmits a signal for a plurality of channels having the same carrier frequency to a lower apparatus. A relay processing unit that performs relay processing for amplifying signals for a plurality of channels. The wraparound canceller is provided between the reception antenna and the transmission antenna (in this embodiment, between the reception antenna and the relay processing unit). This sneak canceller has a delay wave canceling unit (comprising an adder and a filter) that cancels the sneak wave and delay wave, and a control parameter that detects the characteristics of the sneak wave and delay wave and calculates the control parameter of the delay wave canceling unit A calculation unit.

Among these, the control parameter calculation unit (FIG. 13) inserts an inverse calculation unit between the spectrum correction unit and the inverse discrete Fourier transform unit of the transmission path characteristic measuring device according to the first embodiment, and the inverse discrete Fourier transform. A tap coefficient value calculation unit is provided after the conversion unit, and control parameters are determined based on complex values acquired from the inverse discrete Fourier transform calculation results or characteristic values (amplitude ratio, delay time, and phase) of each sneak wave and delay wave. calculate.

  Here, the operation of the spectrum correction unit of the wraparound canceller in the relay device for a single frequency network will be described with reference to FIG. It is assumed that the reception spectrum when the relay device starts the relay operation and a sneak wave exists is shown in FIG. At this time, the spectrum correction unit calculates FIG. 14B as a reference spectrum based on FIG. Further, the spectrum correction unit calculates the spectrum shown in FIG. 14C by dividing the reference spectrum shown in FIG. 14B from the received spectrum shown in FIG.

  Next, the operation of the reciprocal calculation unit will be described. The reciprocal number calculation unit calculates the reciprocal number (FIG. 14D) of the spectrum output from the spectrum correction unit (FIG. 14C).

Further, the functions of the spectrum correction unit and the reciprocal calculation unit in the control parameter calculation unit of FIG. 13 can be combined into one as the spectrum reverse correction unit of FIG. That is, the correction of the spectrum obtained by dividing the reference spectrum from the received spectrum by the spectrum correcting unit and the calculation of the reciprocal of the spectrum output from the spectrum correcting unit by the reciprocal calculating unit can be realized by dividing the received spectrum from the reference spectrum. Therefore, the functions of the spectrum correction unit and the reciprocal calculation unit in the control parameter calculation unit of FIG. 13 can be reduced to one by combining them as the spectrum reverse correction unit of FIG.

  Examples of operations of the spectrum correction unit and the reciprocal calculation unit in a channel arrangement different from FIG. 14 are shown in FIGS. In particular, FIG. 18 shows a case where only one channel is relayed. FIGS. 16 (a), 17 (a), and 18 (a) show a reception spectrum when a relay operation is started and a sneak wave exists, FIGS. 16 (b), 17 (b), and FIG. 18 (b) is a reference spectrum, FIG. 16 (c), FIG. 17 (c) and FIG. 18 (c) are corrected received spectra, and FIG. 16 (d), FIG. 17 (d), and FIG. d) shows a spectrum obtained by reversing the corrected spectrum.

  Next, the inverse discrete Fourier transform unit will be described. The inverse discrete Fourier transform unit performs inverse discrete Fourier transform on the spectrum output from the reciprocal calculation unit to obtain a delay profile (complex impulse response value). For example, when FIG. 14D is input to the inverse discrete Fourier transform unit, the delay profile of FIG. 19A is obtained.

Here, when there is no reciprocal calculation unit, FIG. 14C is input to the inverse discrete Fourier transform unit, and the delay profile of FIG. 19B is obtained. In FIG. 19B, in addition to the primary component necessary as the tap coefficient value of the FIR filter when eliminating the sneak wave, an impulse response value of an unnecessary secondary component or more is calculated. This unnecessary second-order or higher impulse response value becomes a factor that degrades the ability to cancel the sneak wave by the sneak canceller.

  The delayed wave canceling unit includes an adder and a filter (for example, a complex FIR filter). The adder adds the received signal received by the receiving antenna and the signal output from the filter (having an opposite phase to the sneak wave or delay wave), thereby eliminating the sneak wave or delay wave included in the received signal. Further, the filter changes the characteristics of the signal output from the adder based on the control parameter, and uses this as the output signal of the filter. In such a configuration, the control parameter calculation unit calculates a coefficient (for example, a tap coefficient of the FIR filter) so as to output a sneak wave or a delayed wave from the filter without including a direct wave (desired wave). It should be noted that a well-known update coefficient can be introduced when updating the coefficient.

As described above, according to the present invention, sneak waves for a plurality of channels can be accurately measured and can be erased.

It is the figure which showed transmission and reception of terrestrial digital broadcasting as an example of OFDM transmission. There are direct waves (desired waves), delayed waves due to reflections, and sneak waves. It is a figure which shows the frequency arrangement | positioning in case there exist multiple channels, and the demodulation timing of the OFDM wave containing multiple channels. It is a figure which shows the relationship between a signal zone | band and a channel zone | band. It is a figure which shows the structure of a transmission-line characteristic measuring device. It is a figure which shows the reception spectrum at the time of multi-channel reception when a delay wave exists besides a desired wave. It is a figure which shows the reference spectrum calculated from FIG. FIG. 7 is a diagram showing a reception spectrum when a plurality of channels are sparsely arranged, and FIGS. 7A to 7D are reception spectra at normal time (when there is no delay wave or sneak wave). The received spectrum when the delayed wave is present, the reference spectrum calculated from the received spectrum when the delayed wave is present, and the received spectrum after correcting by dividing the received spectrum of (b) by the reference spectrum of (c) FIG. FIG. 8 is a diagram showing a reception spectrum when a plurality of channels are continuously arranged. FIGS. 8A to 8D are receptions at normal time (when there is no delay wave or sneak wave). Spectrum, reception spectrum when delay wave exists, reference spectrum calculated from reception spectrum when delay wave exists, reception spectrum after correcting by dividing reference spectrum of (c) from reception spectrum of (b) FIG. FIG. 9 is a diagram showing a reception spectrum when there are a plurality of channels and the signal band is narrower than the measurement band. FIGS. 9A to 9D are each normal (when there is no delay wave or sneak wave). Received spectrum, received spectrum when delay wave exists, reference spectrum calculated from received spectrum when delayed wave exists, received signal after correcting by dividing reference spectrum of (c) from received spectrum of (b) It is a figure which shows a spectrum. FIG. 10 is a diagram showing a reception spectrum when there is only one channel and the signal band is narrower than the measurement band. FIGS. 10A to 10D are normal times (when there is no delay wave or sneak wave). Received spectrum, received spectrum when delay wave exists, reference spectrum calculated from received spectrum when delayed wave exists, received signal after correcting by dividing reference spectrum of (c) from received spectrum of (b) It is a figure which shows a spectrum. 11 is a diagram showing a delay profile (impulse response value), FIG. 11 (a) is a delay profile obtained by inverse discrete Fourier transform of FIG. 7 (d), and FIG. 11 (b) is FIG. It is a figure which shows the delay profile calculated | required by carrying out the inverse discrete Fourier transform of b). It is a figure which shows the structure of a wraparound canceller. FIG. 13 is a diagram illustrating a configuration in a case where the principle of the transmission path characteristic measuring device of FIG. FIG. 14 is a diagram showing a reception spectrum when a plurality of channels are sparsely arranged, and FIGS. 14A to 14D respectively show a reception spectrum when a sneak wave exists and a sneak wave. The figure which shows the received spectrum which calculated | required the reference spectrum calculated from the receiving spectrum of the time, the receiving spectrum after dividing the (b) reference spectrum from the receiving spectrum of (a), and the inverse of the receiving spectrum of (c) It is. It is a figure which shows an example of the structure which deform | transformed the structure of the control parameter calculation part of the wraparound canceller of FIG. 13, and reduced the amount of calculations. FIG. 16 is a diagram illustrating a reception spectrum when a plurality of channels are continuously arranged. FIGS. 16A to 16D are a reception spectrum when a sneak wave exists and a sneak wave, respectively. The reference spectrum calculated from the reception spectrum at the time of performing, the reception spectrum obtained by dividing the reception spectrum of (a) by dividing the reference spectrum of (b) and the reception spectrum obtained by reversing the reception spectrum of (c) are shown. FIG. FIG. 17 is a diagram showing a reception spectrum when there are a plurality of channels and the signal band is narrower than the measurement band. FIGS. 17A to 17D are a reception spectrum and a sneak wave when a sneak wave exists, respectively. The reference spectrum calculated from the received spectrum when the signal exists, the received spectrum obtained by correcting the (b) reference spectrum by dividing the (b) received spectrum, and the received spectrum obtained by reversing the received spectrum (c) FIG. FIG. 18 is a diagram showing a reception spectrum when there is only one channel and the signal band is narrower than the measurement band. FIGS. 18A to 18D are a reception spectrum and a sneak wave when a sneak wave exists, respectively. The reference spectrum calculated from the received spectrum when the signal exists, the received spectrum obtained by correcting the (b) reference spectrum by dividing the (b) received spectrum, and the received spectrum obtained by reversing the received spectrum (c) FIG. 19 is a diagram showing a delay profile (impulse response value), FIG. 19A is a delay profile obtained by inverse discrete Fourier transform of FIG. 14D, and FIG. 19B is FIG. It is a figure which shows the delay profile calculated | required by carrying out the inverse discrete Fourier transform of c).

Explanation of symbols

101 ... Direct wave from transmitter to repeater 103 ... Incoming wave from other transmitter 105 ... Sneak wave 107 of output of relay itself ... Reflected wave 109 from obstacle ... Transmitted wave from repeater to receiving antenna 111 ... Repeater 601 ... Average value in the frequency direction of the signal domain 603 ... Average value in the frequency direction of the non-signal domain 1201 ... Reception antenna 1203 ... Transmitting antenna 1205 ... Round-off canceller 1207 ... Relay processing unit

Claims (3)

A Fourier transform unit that Fourier-transforms a signal of a plurality of channels obtained by multiplexing subcarrier signals of a predetermined frequency channel, and calculates a frequency spectrum;
An average value calculating unit for calculating an average value for each frequency using a plurality of the frequency spectra;
A reference spectrum is calculated using the frequency spectrum, and a frequency band outside the signal band of the frequency spectrum and a spectrum level of a frequency band outside the signal band and a boundary frequency band between the signal band and the reference spectrum are used. Spectrum correction unit for correcting the signal band to the same level as the spectrum level of the signal band,
An inverse Fourier transform unit that performs inverse Fourier transform on the frequency spectrum obtained by the correction and calculates a delay profile;
Channel characteristic measuring device, characterized in that it comprises a. A sneak canceller used for retransmission of signals of a plurality of channels obtained by multiplexing subcarrier signals of a predetermined frequency channel,
A delay wave canceling unit for canceling a sneak wave or delay wave;
A Fourier transform unit that Fourier-transforms the signals of the plurality of channels and calculates a frequency spectrum;
An average value calculating unit for calculating an average value for each frequency using a plurality of the frequency spectra;
A reference spectrum is calculated using the frequency spectrum, and using the reference spectrum, a frequency band outside the signal band of the frequency spectrum, and a spectrum level of a frequency band outside the signal band and a boundary frequency band of the signal band are A spectrum correction unit for correcting the signal band to the same level as the spectrum level;
A reciprocal calculation unit for reversing the spectrum obtained by the correction;
An inverse Fourier transform unit for inverse Fourier transforming the frequency spectrum obtained by the correction and calculating a delay profile;
Based on the complex value of the delay profile obtained as a calculation result of the inverse Fourier transform unit, or the amplitude, delay time, and phase characteristics of each sneak wave and delay wave, the cancellation signal generated by the delay wave canceling unit A tap coefficient calculator for calculating amplitude, delay time, and phase characteristics;
Wraparound canceller characterized in that it comprises a. A sneak canceller used for retransmission of signals of a plurality of channels obtained by multiplexing subcarrier signals of a predetermined frequency channel,
A delay wave canceling unit for canceling a sneak wave or delay wave;
A discrete Fourier transform unit that Fourier-transforms the signals of the plurality of channels and calculates a frequency spectrum;
An average value calculating unit for calculating an average value for each frequency using a plurality of the frequency reception spectra;
A reference spectrum is calculated using the frequency spectrum, and using the reference spectrum, a frequency band outside the signal band of the frequency spectrum, and a spectrum level of a frequency band outside the signal band and a boundary frequency band of the signal band are A spectrum inverse correction unit that raises the signal band to the same level as the spectrum level and corrects the reciprocal of the frequency spectrum;
An inverse Fourier transform unit for inverse Fourier transforming the inverse of the frequency spectrum obtained by the correction and calculating a delay profile;
Based on the complex value of the delay profile obtained as a calculation result of the inverse Fourier transform unit, or the amplitude, delay time, and phase characteristics of each sneak wave and delay wave, the cancellation signal generated by the delay wave canceling unit A tap coefficient calculator for calculating amplitude, delay time, and phase characteristics;
A wraparound canceller characterized by comprising: