JP6272087B2 - Waveform equalizer and OFDM receiver - Google Patents

Description

  The present invention relates to a technique for waveform equalization of an OFDM modulated signal modulated by an orthogonal frequency division multiplexing (OFDM) system.

  In communication systems using orthogonal frequency division multiplexing (OFDM) such as terrestrial digital broadcasting in Japan, a redundant period called a guard interval is added to each symbol period. Even in a multipath environment where there is a main wave (the wave with the highest intensity among the received waves) and an incoming wave (hereinafter referred to as a delayed wave) with different timings such as reflection, the main wave When the time difference between each of the delayed waves is equal to or shorter than the guard interval, the received OFDM modulated signal can be correctly demodulated with almost no influence of the delayed waves. However, if there is a delayed wave exceeding the guard interval, the received signal modulated by the orthogonal frequency division multiplexing method (hereinafter referred to as OFDM modulated signal) may not be demodulated correctly, and the delay time of the delayed wave The larger the value is and the larger the amplitude of the delayed wave, the greater the effect.

  On the other hand, a technique for removing a delayed wave exceeding the guard interval using a waveform equalization filter is known (for example, see Patent Document 1).

JP 2003-46468 A

  However, the conventional waveform equalization filter operates to completely remove the delayed wave, but at the cost of increasing noise included in the output signal of the waveform equalization filter, the waveform equalization filter output signal is correctly corrected. There has been a problem that it may become impossible to demodulate.

  That is, when the delay wave is one wave, the input signal S of the waveform equalization filter is expressed by the equation (1). However, the input signal S is represented by a relative value of the amplitude of the delayed wave with respect to the amplitude of the main wave. Further, the characteristic Eq of the waveform equalizing filter that completely eliminates the delayed wave is expressed by the equation (2).

An example of the frequency characteristic Eq of the input signal S and an ideal waveform equalization filter is shown in FIG.

  In fact, a noise component (assuming Gaussian noise) is input to the waveform equalization filter in addition to the input signal S shown in the equation (1). This noise component is output as noise having the same frequency characteristic as the characteristic Eq of the waveform equalization filter. For this reason, the noise power included in the output signal of the waveform equalization filter increases as the delay wave to be suppressed by the waveform equalization filter increases.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a technique for suppressing a decrease in reception characteristics due to an increase in noise caused by waveform equalization.

The waveform equalizer of the present invention is used for an OFDM modulation signal, and includes delay information detection means, delay equalization means, mixing means, and mixing ratio setting means.
The delay information detecting means receives an OFDM modulated signal including a main wave and a delay wave with respect to the main wave as an input signal, and detects the amplitude of the delay wave and the delay time of the delay wave with respect to the main wave from the input signal. The detected delay time takes a positive or negative value according to the arrival timing of the delayed wave with respect to the main wave. The delay equalizing means outputs an equalized signal obtained by removing the delayed wave from the input signal according to the detection result of the delay information detecting means. The mixing means generates a waveform equalizer output signal obtained by mixing the input signal and the equalized signal in accordance with a preset mixing ratio. The mixing ratio setting unit suppresses the amplitude of the delayed wave so that the amplitude of the delayed wave in the waveform equalizer output signal is equal to or smaller than a preset guard interval mask according to the detection result of the delay information detecting unit. Set the mixing ratio to The guard interval mask is a well-known mask that defines the conditions for enabling demodulation of an OFDM modulated signal even when a delay wave is present, with respect to the delay time of the delay wave and the amplitude of the delay wave. (Refer to Technical Report “ARIBTR-B14 Volume 9” published by the Radio Industries Association, or “Report ITU-R BT.2209-1” of ITU (International Telecommunication Union))
According to such a configuration, the noise superimposed on the output of the waveform equalizer is removed in order to remove the delayed wave incompletely in a range where the demodulation of the OFDM modulation signal is possible, not completely removing the delayed wave. The reception characteristics can be effectively improved by waveform equalization without increasing the frequency more than necessary.

  In the present invention, the mixing ratio setting means sets the mixing ratio so that the magnitude of the delayed wave in the waveform equalizer output signal is suppressed to a value equal to or less than a value reduced by a certain margin in the guard interval mask. Also good. In this case, when an unexpected reception failure factor other than the delayed wave exists, the possibility that the demodulation of the OFDM modulation signal becomes impossible can be reduced.

  In the present invention, when the delay time of the delay wave is within a preset guard interval, the mixing ratio setting means determines that the magnitude of the delay wave in the waveform equalizer output signal is the magnitude of the delay wave in the input signal. The mixing ratio may be set so as to be suppressed to an optimal value set according to the above. That is, when the delay time of the delay wave is within the guard interval, it is not always necessary to perform waveform equalization, but the range in which the reception characteristic is further improved, i.e., the improvement effect of the reception characteristic by suppressing the delay wave, Waveform equalization may be performed in a range that exceeds the deterioration of reception characteristics due to an increase in noise accompanying suppression of delay waves.

  Specifically, for example, the mixing ratio setting means includes a noise increase determined by the amount of suppression of the delayed wave in the waveform equalizer output signal, and a required CN ratio increase determined by the size of the delayed wave in the waveform equalizer output signal. The optimum value may be set so that the sum of the values is minimized. The required CN ratio increase means that the CN ratio of the waveform equalizer output signal necessary for correctly demodulating the OFDM modulated signal is increased with respect to the required CN ratio when there is no delayed wave. Say.

  The waveform equalizer of the present invention includes modulation scheme specifying means for specifying the primary modulation scheme and coding rate of the OFDM modulation signal, and the mixing ratio setting means is a guard that is referred to according to the specified result in the modulation scheme specifying means. You may comprise so that an interval mask characteristic may be switched. In this case, the improvement of the reception characteristics by waveform equalization can be realized accurately according to each modulation method.

The waveform equalizer described above may be realized as an OFDM receiver together with a receiving unit that receives a signal and supplies the signal to the waveform equalizer and a demodulating unit that demodulates an output signal from the waveform equalizer.
In addition, the code | symbol in the parenthesis described in the claim shows the correspondence with the specific means as described in embodiment mentioned later as one aspect, Comprising: The technical scope of this invention is limited is not.

  In addition to the above-described waveform equalizer and OFDM receiver, the present invention includes a system including these waveform equalizer and OFDM receiver as components, a program for causing a computer to function as the waveform equalizer, and a waveform. It can be realized in various forms such as an equalization method.

It is a block diagram showing the structure of an OFDM receiver. It is a block diagram showing the structure of a waveform equalization part. It is the graph which illustrated the characteristic of the guard interval mask and the actual OFDM receiver. It is explanatory drawing which shows an OFDM demodulation operation principle. It is a graph showing the relationship between a delayed wave relative value and a required CN ratio increase. It is a graph showing the relationship between a delay wave relative value and the noise increase by a waveform equalization filter. It is the graph which showed the relationship between the amount of delay wave suppression, and the noise increase by a waveform equalization filter for every delay wave relative value of an input signal. It is the graph which showed the relationship between the delay time of a delay wave when the delay wave was suppressed to the value of the guard interval mask, and the noise increase by a waveform equalization filter for every delay wave relative value of an input signal. It is a graph showing the control characteristic in the case of 64QAM-3 / 4, (a) is the relationship between the delay time of a delay wave and the suppression amount of a delay wave (suppression control characteristic), (b) is according to the characteristic of (a). This is a relationship (effective noise increase characteristic) between the delay time of the delayed wave and the effective noise increase in the adaptive equalization signal obtained when the delayed wave is suppressed. It is a graph showing the control characteristic when suppression margin 3dB is added in 64QAM-3 / 4, (a) is a suppression control characteristic, (b) is an effective noise increase characteristic. It is a graph showing the control characteristic when suppression margin 3dB is added in 64QAM-2 / 3, (a) is a suppression control characteristic, (b) is an effective noise increase characteristic. It is a graph showing the control characteristic when suppression margin 3dB is added in 16QAM-3 / 4, (a) is a suppression control characteristic, (b) is an effective noise increase characteristic. It is a graph showing the control characteristic when suppression margin 3dB is added in 16QAM-3 / 4, (a) is a suppression control characteristic, (b) is an effective noise increase characteristic. It is the graph which showed the relationship between a delayed wave relative value and the optimal suppression amount for every modulation system. It is a graph which shows a mode that an effective noise increase changes when the suppression amount of a delay wave is shifted from the optimal suppression value. It is a graph which illustrates an ideal waveform equalization filter and the frequency characteristic of the input signal and output signal.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
[First Embodiment]
<Overall configuration>
As shown in FIG. 1, the OFDM receiver 1 of this embodiment includes a receiving unit 2, a waveform equalizing unit 3, and an OFDM demodulating unit 4.

  The receiving unit 2 converts the OFDM modulated signal received by the antenna ANT into a pair of digital baseband signals BS having an orthogonal relationship by performing amplification, frequency conversion, A / D conversion, and the like. The receiving unit 2 also extracts a transmission parameter TP including at least a transmission mode, a guard interval ratio, a modulation scheme, and a coding rate from the baseband signal BS. Since the configuration of the receiving unit 2 is well known, detailed description thereof is omitted.

  The waveform equalization unit 3 uses the baseband signal BS as an input signal and outputs an output signal obtained by waveform equalization of the input signal. As shown in FIG. 2, the waveform equalization filter 31, the mixer 32, A delay / amplitude detector 33, a coefficient generator 34, and a mask storage unit 35 are provided.

  The delay / amplitude detector 33 detects the amplitude of the main wave and the delay wave included in the input signal, and the delay time of the delay wave with respect to the main wave. The waveform equalization filter 31 generates an equalization signal obtained by removing the delay wave from the input signal based on the detection result of the delay / amplitude detector 33. The delay / amplitude detector 33 and the waveform equalizing filter 31 are well known.

  The mixer 32 is an output of a coefficient equalizer 341 that multiplies the amplitude of the baseband signal BS by α in accordance with a coefficient α (0 ≦ α ≦ 1) obtained by a coefficient generator 34 described later, and the waveform equalizing filter 31. A coefficient unit 342 that multiplies the amplitude of the equalized signal by (1−α), and an adder 343 that generates an adaptive equalized signal ES obtained by adding the output of the coefficient unit 341 and the output of the coefficient unit 342 are provided. This adaptive equalization signal ES becomes the output signal of the waveform equalization unit 3.

  The mask storage unit 35 includes a non-volatile memory or the like, and stores guard interval masks (GI masks) set for each modulation scheme / coding rate that can be demodulated by the OFDM receiver 1. Examples of the modulation scheme / coding rate include “64QAM-3 / 4”, “16QAM-2 / 3”, “QPSK-1 / 2”, and the like. The first half 64QAM, 16QAM, and QPSK represent the primary modulation scheme, and the second half fraction represents the coding rate.

  The GI mask indicates a condition for correctly demodulating the OFDM modulated signal in the OFDM demodulator 4 and is required for an input signal (adapted equalization signal ES) to the OFDM demodulator 4 as shown in FIG. This is expressed by the relationship between the magnitude (allowable level) of the delayed wave and the delay time of the delayed wave. However, the magnitude of the delayed wave is a relative value of the amplitude of the delayed wave with respect to the amplitude of the main wave, expressed in decibels, and is hereinafter referred to as a delayed wave relative value. FIG. 3 shows a GI mask standardized by ARIB for a system (ISDB-T system, 64QAM-3 / 4, guard interval length 126 μs) used in Japanese terrestrial digital broadcasting, and commercially available OFDM. The result of having measured the characteristic of the receiver (receiver A, B, C) is illustrated. If the horizontal axis is the delay time of the delayed wave with respect to the main wave, and the vertical axis is the allowable level of the delayed wave relative value, the OFDM demodulator 4 can demodulate if the delayed wave in the adaptive equalization signal ES is below this allowable level. It represents that. For example, if the delay time is 150 μs and the delay wave relative value is −15 dB, demodulation is possible, but even if the delay time is the same, the delay wave relative value is −5 dB cannot be demodulated. As shown, commercially available OFDM receivers are designed to have characteristics that exceed the GI mask characteristics standardized by ARIB.

  Note that the GI mask is determined by the mathematical processing related to OFDM demodulation and the characteristics of the digital interpolation filter used for the reference carrier reproduction, and is all mathematically derived without any variation due to hardware performance. . For details, please refer to Equation (30) in the technical document “ARIBTR-B14 Volume 9” (hereinafter also referred to as “Technical Document 1”) published by the Radio Industries Association or the ITU (International Telecommunication Union) report “Report ITU-R”. Refer to Equation (30) of “BT.2209-1” (hereinafter also referred to as “Technical Document 2”).

  The coefficient generator 34 selects a GI mask corresponding to the modulation scheme / coding rate specified from the transmission parameter TP detected by the receiver 2, and the baseband signal according to the detection result of the delay / amplitude detector 33. When the delayed wave relative value in the BS is larger than the value of the selected GI mask, the coefficient α is set so that the delayed wave relative value in the adaptive equalization signal ES is suppressed to the value of the GI mask.

<Effect>
As described above, the waveform equalization unit 3 of the OFDM receiver 1 does not completely remove the delayed wave, but removes it within the minimum necessary range that allows demodulation of the OFDM modulated signal. The noise superimposed on the output signal of the unit 3 (adapted equalization signal ES) is not increased more than necessary, and the reception characteristics can be effectively improved by waveform equalization.

  When the waveform equalizing filter 31 that completely removes the delayed wave is used, if the delayed wave has the same amplitude (0 dB) as the main wave, the operation becomes unstable in principle (Equation (2) is Emanates). However, in the OFDM receiver 1, it is not necessary for the delayed wave to be completely removed from the output signal of the waveform equalizer 3, so that the waveform equalizing filter 31 can sufficiently output the delayed wave within a range where the operation is not unstable. What can be removed may be used.

[Second Embodiment]
Since the basic configuration of the second embodiment is the same as that of the first embodiment, the description of the common configuration will be omitted, and the description will focus on the differences.

  In the first embodiment, the coefficient generator 34 generates a coefficient so that the delayed wave relative value of the adaptive equalization signal ES is suppressed to the value of the GI mask when the delayed wave relative value of the baseband signal BS is larger than the GI mask. α is set. On the other hand, in the present embodiment, the coefficient generator 34 prepares in advance an optimal suppression value corresponding to the delayed wave relative value of the baseband signal BS, and the delay time of the delayed wave is within the guard interval. Even when the delayed wave relative value of the baseband signal BS is smaller than the GI mask, the coefficient α is set so that the delayed wave relative value of the adaptive equalization signal ES is suppressed to the optimal suppressed value if it is larger than the optimal suppressed value. This is different from the first embodiment.

<Calculation method of optimum suppression value>
Hereinafter, a method for calculating the optimum suppression value will be described. In the description, the required CN ratio increase and the noise increase by the waveform equalization filter 31 will be described as a premise.

<< Increase in required CN ratio >>
First, an outline of the required CN ratio increase and a derivation method will be described.
When there is a delayed wave that falls within the guard interval, the input signal (baseband signal BS) of the waveform equalizing filter 31 has a different signal level for each OFDM carrier (that is, for each frequency) as shown in FIG. The shape of the frequency characteristic exhibits a ripple on the frequency axis.

  Here, FIG. 4A shows a case where the average level of the input signal is the reference level, with the minimum signal level at which the OFDM-modulated signal can be demodulated for the input signal not including the delay wave as the reference level. In this case, the amplitude of many OFDM carriers is below the reference level, and the BER (bit error rate) of the entire input signal is at a level that cannot be recovered by error correction.

  FIG. 4B shows a case where the input signal shown in FIG. 4A is increased for both the main wave and the delayed wave. In this case, the number of OFDM carriers whose amplitude is below the reference level is reduced, and the BER of the entire input signal can be set to a level that can be recovered by error correction.

  This means that by increasing the input signal (main wave and delay wave), the required CN ratio, which is the minimum CN ratio necessary for enabling demodulation, increases. As shown in FIG. 5, the required CN ratio increases as the input signal (delayed wave relative value in the figure) increases. The required CN ratio increase is derived as follows.

  First, a relational expression between the BER (bit error rate) and the CN ratio under a white Gaussian noise environment is shown below. This relational expression varies depending on the modulation method, and the expression (3) is used for QPSK, the expression (4) is used for 16QAM, and the expression (5) is used for 64QAM. Also, Cp is the average power of the input signal, Ca is the rms (Root Mean Square) amplitude of the input signal, Np is the noise power, Na is the rms amplitude of the noise, and Erfc (x) is the equation (6). A complementary error function defined.

When Ua is the relative value (delay relative value) of the amplitude of the delayed wave with respect to the amplitude of the main wave, and τ is the delay time of the delayed wave with respect to the main wave, the frequency characteristic of the input signal is expressed by equation (7).

Substituting equation (7) into an equation (any one of equations (3) to (5)) corresponding to the modulation method, an error rate BER (ω) is obtained for each OFDM carrier identified by the angular frequency ω, The carrier amplitude Ca is calculated such that the average of BER (ω) for the carrier is the upper limit error rate BER0 at which error correction performed at the time of OFDM demodulation operates effectively, that is, satisfies the equation (8). Ncarrire represents the number of OFDM carriers.

The ratio of the carrier amplitude Ca thus obtained and the carrier amplitude obtained for the case where there is no delayed wave (Ua = 0 in the equation (7)) is the required CN ratio increase. Since the function representing the required CN ratio increase obtained by the equation (8) cannot be expressed by an analytical equation, it is practical to use an approximate equation. For details, see Technical Documents 1 and 2 above.

<< Noise increase by waveform equalization filter >>
Next, an outline of noise increase by the waveform equalizing filter 31 and a derivation method thereof will be described. Here, in order to facilitate understanding, the waveform equalizing filter 31 will be described as having a characteristic of completely removing the delayed wave.

  The increase in noise in the output of the waveform equalization filter 31, that is, the signal after delay wave suppression depends on the degree of suppression (that is, the amplitude of the delay wave), and as shown by the dotted line in FIG. Increases as the amplitude of A solid line in FIG. 6 indicates an effective increase in noise related to OFDM demodulation, and is calculated as follows.

  That is, the noise having the waveform equalizing filter characteristic expressed by the equation (2) is substituted into the equation (any one of the equations (3) to (5)) corresponding to the modulation method, and is identified by the angular frequency ω. BER (ω) is obtained for each carrier, and carrier amplitude Ca is obtained such that the average of BER (ω) for all carriers satisfies the equation (8). The ratio between the carrier amplitude Ca and the carrier amplitude when there is no delayed wave (Ua = 0 in the equation (2)) increases the effective noise. In other words, the noise increase due to the waveform equalization filter is only in that the noise represented by the equation (2) is used instead of the input signal represented by the equation (7) as compared with the case where the required CN ratio is increased. Differently, the calculation result is the same as the required CN ratio increase shown in FIG.

  This means that in the case of a delayed wave whose delay time is within the guard interval, an increase in noise when the waveform equalization is performed so as to completely eliminate the delayed wave is equal to an increase in the required CN ratio when the waveform is not equalized. Represents the size.

<< Optimum suppression value >>
Here, FIG. 7 shows a result of calculating an increase in noise when the delayed wave is not completely erased (completely equalized) but is left to some extent (incompletely equalized). In the figure, the horizontal axis represents the amount of delay wave suppression (equal to the coefficient α), and the vertical axis represents noise increase due to waveform equalization. Each curve in the figure is a delayed wave relative value of the input signal (baseband signal BS). As shown in the figure, the increase in noise increases rapidly as the amount of suppression of the delayed wave increases (moves the horizontal axis to the left), and becomes a substantially constant value when the amount of suppression increases to some extent.

  FIG. 8 shows the result of calculating the noise increase when the delayed wave exceeding the guard interval is equalized with the GI mask by changing the relative value of the delayed wave in the input signal. As shown in the figure, the increase in noise increases as the delay time increases and the value of the GI mask decreases, and increases as the delay wave relative value increases even at the same delay time.

  By the way, for a delayed wave exceeding the guard interval, the input signal cannot be correctly demodulated unless the delayed wave is suppressed to a value below the GI mask. In other words, in this case, suppression to the value of the GI mask is the minimum necessary waveform equalization.

  On the other hand, with respect to the delayed wave within the guard interval, the input signal can be correctly demodulated without suppressing the delayed wave. However, when the delayed wave is not suppressed, the required CN ratio is increased, and thus the noise is substantially increased. Considering that the increase in the required CN ratio when the delay wave is not suppressed (the waveform is not equalized) is equal to the noise increase due to the equalization filter when it is completely equalized, it is the minimum necessary for the delay wave within the guard interval. If incomplete equalization is performed, it can be expected that the total noise increase (the sum of the noise increase due to waveform equalization and the required CN ratio increase) decreases.

  FIG. 9 shows the result of calculating the optimum value (hereinafter referred to as “optimum suppression value”) of the delay wave suppression amount that minimizes the total noise increase. In FIG. 9A, the horizontal axis represents the delay time of the delay wave, and the vertical axis represents the delay wave suppression amount. The solid line in the figure indicates the GI mask, and each broken line indicates the optimum suppression value obtained for each delayed wave relative value of the input signal. For example, when the relative delay value of the input signal is 0 dB (U = 0 dB), the optimum suppression value is −4.6 dB, and when the relative delay value is −6 dB, the optimum suppression amount is −11.7 dB. .

  Based on this graph, the coefficient generator 34 uses the smaller of the GI mask and the optimal suppression value as the threshold value of the delayed signal relative value of the input signal, and the delayed signal relative value of the input signal exceeds the threshold value. If so, a coefficient α is generated so that the delayed wave relative value of the adaptive equalization signal ES is suppressed to the threshold value. FIG. 9B shows the total noise increase (hereinafter referred to as “effective noise increase”) when the delayed wave is suppressed according to the characteristics shown in FIG. 9A. When the waveform equalization is not performed on the delayed wave within the guard interval, the required CN ratio increases when the delay wave amplitude is 0 dB, which is a maximum value of 8.9 dB (64QAM-3 / 4) (see FIG. 7). When the above-mentioned waveform equalization is performed, it is increased by 6.5 dB (see FIG. 9B), and it can be seen that an improvement effect of about 2.4 dB can be obtained.

<Effect>
According to the second embodiment described in detail above, the following effects are obtained in addition to the effects of the first embodiment described above. In other words, in the present embodiment, the CN ratio is improved by performing the necessary minimum equalization for the delayed wave within the guard interval, so that the reception performance can be further improved.

[Other Embodiments]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form, without being limited to the said embodiment.

  (1) In the above embodiment, the delayed wave exceeding the guard interval is suppressed to the GI mask value, but this is a minimum waveform equalization, and other reception failure factors (other delayed waves and noise) If there is, there is a possibility that reception is impossible. Therefore, the delay wave suppression level may be set to a value that allows for a certain margin (suppression margin) than the GI mask value. FIG. 10 to FIG. 13 show characteristic examples when margins are set to 3 dB for several modulation schemes (64QAM-3 / 4, 64QAM-2 / 3, 16QAM-3 / 4, 16QAM-2 / 3). .

  (2) As shown in FIG. 14, the optimum suppression value takes various values depending on the modulation method and the delayed wave relative value of the input signal. For this reason, in the said 2nd Embodiment, it is necessary to prepare the optimal suppression value according to the variation as mapping beforehand. In contrast, the optimum suppression values calculated for typical modulation schemes (for example, 64QAM-3 / 4 and QPSK-2 / 3 used in Japanese terrestrial digital broadcasting) are used regardless of the modulation scheme. You may make it do. That is, as shown in FIG. 15, since the increase in noise is small even if the suppression amount deviates slightly from the optimal suppression value, it is possible to substitute a representative characteristic without finely controlling the suppression amount for each modulation method. I understand.

  Furthermore, instead of mapping the optimum suppression value, an approximate suppression value calculated using equation (9) may be used. However, Sup is an approximate suppression value, Und is a delayed wave relative value in the input signal, and Const is a fixed value. As the fixed value Const, a different value may be used for each modulation method, or a common value may be used regardless of the modulation method. In the former case, as the fixed value Const, the optimum suppression value when the delayed wave relative value is 0 dB may be used. In the latter case, as the fixed value Const, a value that is set so that the deviation from the optimum value suppression value falls within a predetermined value (for example, 5 dB) may be used for all usable modulation schemes.

(3) In the above embodiment, it is assumed that there is one delay wave, the input signal S is expressed by equation (1), and the waveform equalization filter characteristic Eq is expressed by equation (2). When there are a plurality of waves, the input signal S is expressed by the equation (10), and the waveform equalization filter characteristic Eq is expressed by the equation (11). What is necessary is just to make a setting. However, Uk is a relative amplitude (delayed wave relative value) with respect to the main wave of the delayed wave specified by k, and τk is a relative delay time with respect to the main wave of the delayed wave specified by k.

In particular, when the waveform equalizing filter 31 is configured to control the suppression value for each delay wave, the optimum suppression value obtained from Uk and τk may be applied for each delay wave. On the other hand, when the waveform equalizing filter 31 is configured to control the suppression value for all the delayed waves at once, the control may be performed on the most critical delayed wave.

  (4) Each component of the present invention is conceptual and is not limited to the above embodiment. For example, the functions of one component may be distributed to a plurality of components, or the functions of a plurality of components may be integrated into one component. Further, at least a part of the configuration of the above embodiment may be replaced with a known configuration having the same function. In addition, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment.

  DESCRIPTION OF SYMBOLS 1 ... OFDM (Orthogonal Frequency Division Multiplexing) receiver 2 ... Reception part 3 ... Waveform equalization part 4 ... OFDM demodulation part 31 ... Waveform equalization filter 32 ... Mixer 33 ... Delay / amplitude detector 34 ... Coefficient generator 35 ... Mask storage unit 341, 342 ... Coefficient unit 343 ... Adder ANT ... Antenna

Claims (6)

A waveform equalizer (3) used for an OFDM modulated signal,
The OFDM modulation signal including a main wave and a delay wave with respect to the main wave is used as an input signal (BS), and a delay for detecting the magnitude of the delay wave and the delay time of the delay wave with respect to the main wave from the input signal Information detection means (33);
Delay equalization means (31) for outputting an equalized signal obtained by removing the delayed wave from the input signal according to the detection result of the delay information detection means;
Mixing means (32) for generating a waveform equalizer output signal (ES) obtained by mixing the input signal and the equalized signal in accordance with a preset mixing ratio;
The mixing ratio is set so that the magnitude of the delayed wave in the waveform equalizer output signal is suppressed to a value equal to or smaller than a preset guard interval mask according to the detection result of the delay information detecting means. Mixing ratio setting means (34);
A waveform equalizer comprising:   The mixing ratio setting means sets the mixing ratio so that the magnitude of the delayed wave in the waveform equalizer output signal is suppressed to a value equal to or lower than a value obtained by reducing the guard interval mask by a certain margin. The waveform equalizer according to claim 1.   When the delay time of the delay wave is within a preset guard interval, the mixing ratio setting means sets the delay wave magnitude in the waveform equalizer output signal to the delay wave magnitude in the input signal. The waveform equalizer according to claim 1 or 2, wherein the mixing ratio is set so as to be suppressed to an optimum value set accordingly.   The mixing ratio setting means includes an increase in noise in the waveform equalizer output signal determined by an amount of suppression of the delayed wave in the waveform equalizer output signal with respect to a delayed wave in the input signal, and an increase in the waveform equalizer output signal. 4. The waveform equalizer according to claim 3, wherein the optimum value is set so that the sum of the required CN ratio increase determined by the magnitude of the delayed wave is minimized. Modulation scheme specifying means (2) for specifying a primary modulation scheme and a coding rate of the OFDM modulation signal;
5. The waveform equalization according to claim 1, wherein the mixing ratio setting unit switches a guard interval mask characteristic to be referred to according to a specification result obtained by the modulation method specifying unit. vessel. Receiving means (2) for receiving a signal;
The waveform equalizer (3) according to any one of claims 1 to 5, which performs waveform equalization on an input signal of a signal received by the receiving means.
Demodulation means (4) for demodulating the output signal from the waveform equalizer;
An OFDM receiver (1) comprising: