JP2003198257A - Band-limited waveform generation method and generation circuit thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a band-limited waveform generation method and a generation circuit which generate no inter-code interference, even when a symbol rate is not an integer fraction of a sampling frequency. <P>SOLUTION: A symbol sequence is mapped at a mapping portion 10, a band of the signal is limited at a roll-off filter 40, and a band-limited waveform is generated. A weighting portion 20 and a frequency spectrum correcting portions 30 are inserted into a subsequent stage of the mapping portion 10. From a waveform storing portion 22, which stores a waveform whose value assumes zero at both ends of a symbol section, the weighting portion 20 reads the waveform to be multiplied by a mapping output at a multiplier 23. The frequency spectrum correcting portion 30 corrects the attenuation of high-frequency components, generated by the weighting to be passed through the roll-off filter 40, thereby enabling a band-limited waveform, without intersymbol interference to be generated with respect to a symbol rate fB (communication rate) which is not an integer fraction of a sampling frequency fS. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method and apparatus for band limiting a signal. For example, the present invention relates to a band-limited waveform generating method and a generating circuit for a modulation signal that modulates a carrier wave. In particular, in a method and a circuit for generating a limited waveform of a modulation signal by sampling and filtering a symbol string (data string), a band in which intersymbol interference does not occur even when the symbol rate is not an integer fraction of the sampling frequency. The present invention relates to a method of generating a limited waveform and a circuit for generating the limited waveform. INDUSTRIAL APPLICABILITY The present invention can be applied to a software defined radio device capable of transmitting data to various receiving devices by arbitrarily setting the transmission rate by software.

[0002]

2. Description of the Related Art In recent years, there has been a demand for a software defined radio device capable of supporting various media (different modulation systems and transmission systems) by rewriting software. These devices require a function of generating a band-limited waveform corresponding to various transmission rates, particularly a band-limited waveform without intersymbol interference, especially in the transmitting unit. Conventionally, there are various band-limited waveform generation methods that meet this demand. For example, there is a method shown in FIG. 8 as a first conventional example. This is because after converting a symbol sequence transmitted at a symbol rate f _B (a signal frequency for transmitting a symbol) into an impulse sequence whose period T is equal to the reciprocal of the symbol rate f _{B in} the mapping unit 100, it is converted into a roll-off filter 110.
This is a method of forming a band-limited waveform by performing a filtering process with. Specifically, the sampling frequency f _S is set to an integral multiple of the symbol rate f _B, impulse train 2 value equal to the inverse of the original to the period T is the symbol rate f _B symbol sequence (a) of FIG. 9 To generate. Here, the impulse value is, for example, +125 for the symbol “1”,
A value such as -125 is given to the symbol "0". In this way, an impulse train (mapping output) corresponding to each symbol section is obtained as shown in FIG. Then, this is input to the roll-off filter. As shown in FIG. 10A, the roll-off filter has an impulse response such that it has a certain finite value at the center and becomes zero at a point distant from the center by an integral multiple of the symbol period T, The filter has a frequency characteristic as shown in (b). Specifically, for example, the impulse response of FIG. 10A is convolutively integrated with the mapping output. As a result, each symbol is converted into the waveform (filter output) shown in FIG. 9C and transmitted. In this way, at the center of the symbol, a constant value (for example, +
Therefore, it is possible to correctly determine the transmitted symbol (data) by examining the waveform value at the center of the symbol on the receiving side.

Further, as a second conventional example, an example in which a band-limited waveform is generated by converting a symbol string into a sample string whose envelope has an NRZ waveform with a period T (= 1 / f _B ) and then performing filtering. There is. For example, as shown in FIG. 11, the symbol string is sampled by the mapping unit 100 at a frequency f _S that is four times the symbol rate f _B.
Then, the roll-off filter 115 with NRZ correction is applied to it.
This is a method of filtering processing by. The signal change in this case is shown in FIG. The symbol string (a) is converted by the mapping unit 100 into a sample string consisting of four samples in the symbol interval as shown in (b). Specifically, for a symbol "0", a sample sequence consisting of four "-1" s is used, and for a symbol "1", four "+" s are used.
1 ”is generated. As a result, the mapping output comes to have the frequency characteristic of the NRZ signal shown in FIG. Therefore, band limitation is performed by the roll-off filter 115 having the characteristic shown in FIG. 13B, which takes into account the attenuation in this high frequency band. This characteristic is obtained by multiplying the frequency characteristic (d) of the conventional roll-off filter by the inverse characteristic (c) of the NRZ frequency characteristic. As a result, a band-limited waveform (filter output) without intersymbol interference as shown in FIG. 12C is obtained as in the first conventional example.

Further, there is a third conventional example as shown in FIG. This is a method of storing a band-limited waveform in the storage device 120 in advance, designating it with the shift register 121 and the counter 122, and transmitting it. The method of forming the stored waveform is as follows. When determining the band-limited waveform of an arbitrary section X of the symbol sequence (a) shown in FIG. 15, for example, if the time length of the impulse response is 5 symbols, first, within the section X of the impulse response (c) of two sections before and after that. All waveforms of are added and stored. For example, when determining the band-limited waveform of the center "1" of the symbol string "1""0""1""0""0" including the section X of FIG. 15, the preceding symbols "1""0". , And the subsequent waveforms within the interval X of the impulse response of the symbols “0” and “0” are added and stored in the memory device 10. If the two sections before and after are added, there are 2 ⁵ patterns. In addition, the waveform is stored, for example, in four time series. That is, each one-symbol section waveform is divided into four in time series and stored. In the case of generating the band-limited waveform, as shown in FIG. 14, the symbols (data) are sequentially input to the shift register 121 in synchronization with the symbol rate f _B to generate a 5-bit symbol pattern. Then, it is given to the addresses A ₆ A ₅ A ₄ A ₃ A ₂ of the storage device 120 to specify the stored pattern. Next, the values stored by being divided into four in time series according to the sample rate f _S are designated by addresses A ₀ and A ₁ , and the four values are sequentially read. As a result, waveform values at four sampling points corresponding to the section X are output. In practice, a band-limited waveform without intersymbol interference as shown in FIG. 15B is obtained by continuously performing it on all sections.

[0005]

However, in the methods based on the first and second conventional examples, the applicable symbol rate f _B is limited to an integer fraction of the sampling frequency f _S. Usually, a plurality of symbol rates (f _B1 , f _B2 , ..., F
_BN ), a band-limited waveform of a desired sampling frequency f _S is obtained by performing band limiting at a high sampling frequency f _S ′ that is a common multiple of these symbol rates and then thinning it out. FIG. 16 shows, as an example, a method of generating a band-limited waveform when the desired sampling frequency f _S is not an integral multiple of the symbol rate f _B (f _S / f _B = 11/3). In this example, the sampling frequency f _S ′ for band limitation is set to 3 times f _S , and a band limited waveform is generated in the same manner as in the first conventional example and then thinned to ⅓ to obtain a desired sampling. A waveform of frequency f _S is obtained. According to this method, when the individual symbol rate is high, the sampling frequency f _S 'when performing band limitation becomes very high, which makes it difficult to realize hardware. Further, when trying to support a new medium (modulation method or transmission speed) by rewriting software in the software defined radio device, the added symbol rate f _B is not necessarily an integral fraction of the sampling frequency f _S ′. Not necessarily. In such a case, the sampling frequency f _S '
However, there is a problem that the new media cannot be supported without changing the hardware, that is, without changing the hardware.

As a method based on the third conventional example,
Multiple symbol rates (f_B1，
f_B2,, f_BN) Virtual sampling that is a common multiple of
Frequency f _S'To create band-limited waveform data and store it in memory
By storing and reading the data at a specified interval
Desired sampling frequency f_STo get the output waveform of
There is. FIG. 17 shows a desired sampling frequency as an example.
Number f_SIs the symbol rate f_BIf it is not an integral multiple of (f_S
/ F_B= 11/3) method of generating band-limited waveform
It is a thing. Virtual sampling frequency f_S’F_S
Band-limited waveform in the same way as in the third conventional example.
Is calculated and stored in the memory. In this example, 1 symbol
11 pieces of waveform data are stored for each section. this
Desired sampling frequency f_S11-count coun
Change the address in increments of 3 using the
By outputting, the desired band-limited waveform is obtained. here
Then, the counter output looks like 0 → 3 → 6 → 9 → 1 → 4 ...
Change. This method has a high sampling frequency
f_SWaveform data similar to the one whose bandwidth is limited by '
Symbol rate f to remember_BIs sampling
Frequency f_SNeed not be an integer fraction of. But Naga
However, there is a problem that a large capacity memory is required. Well
Also, write software in software defined radio equipment.
Change to a new medium (modulation method or transmission speed)
If you try to add support, add a large amount of memory,
In other words, to new media without changing hardware
There is a problem that it becomes impossible to respond. The present invention is the above
It was made to solve the problem, and its purpose
Is the symbol rate f_BIs the sampling frequency f_SOrder of
Even if it is not a fraction,
Without adding a large amount of memory, i.e.
Band without intersymbol interference without changing hardware
To generate a limited waveform.

[0007]

A band-limited waveform generating method according to claim 1 is a band-limited waveform generating method for limiting a bandwidth of a signal, wherein a signal based on an input symbol string is generated at a predetermined frequency. Sampling generates a mapping output consisting of a sample sequence, and in synchronization with the symbol transmission signal for transmitting the input symbol sequence, the mapping output has a predetermined value so that the envelope of the mapping output takes a zero value at both ends of each symbol section. It is characterized in that weighting is performed, and a band-limited waveform is generated by blocking a signal having a predetermined band or more by a filter having an action of correcting a change in frequency characteristic caused by the weighting.

A band limited waveform generating method according to a second aspect is the band limited waveform generating method according to the first aspect,
The predetermined weighting is characterized by being performed by multiplication of an arbitrary function that takes a zero value at both ends of each symbol section.

A band-limited waveform generating circuit according to a third aspect of the present invention is a band-limited waveform generating circuit for limiting the bandwidth of a signal, wherein an input symbol string is transmitted in synchronization with a symbol transmission signal, A mapping unit for sampling the transmitted signal at a predetermined frequency to generate a mapping output,
A weighting unit that weights the mapping output so that the envelope of the mapping output takes a zero value at both ends of each symbol section in synchronization with the symbol transmission signal, and weights the weighted output signal waveform-shaped by the weighting unit. While compensating for changes in frequency characteristics caused by
And a filter section for cutting off a predetermined band or more.

The band limited waveform generating circuit according to a fourth aspect is the band limited waveform generating circuit according to the third aspect.
4. The band-limited waveform generating circuit according to claim 3, wherein the weighting unit multiplies the sample sequence by an arbitrary function so that the envelope of sample values takes a zero value at both ends of each symbol section. The band limiting waveform generating circuit according to claim 5 is the band limiting waveform generating circuit according to claim 4, wherein the weighting unit stores an arbitrary function that takes a zero value at both ends of each symbol section in the waveform storage unit. It is characterized by doing.

[0011]

The band-limited waveform generating method according to the present invention is a band-limited waveform generating method for limiting the bandwidth of a signal, for example, a modulation signal for modulating a carrier wave. The based signal is sampled at a predetermined frequency to produce a mapping output. A signal based on an input symbol sequence is, for example, a symbol sequence (data sequence) transmitted by a symbol transmission signal (clock),
It is a signal string sampled at an arbitrary sampling frequency. The mapping output is, for example, the symbol "1".
Is +125, and the digital output value gives -125 to the symbol "0". Further, the arbitrary sampling frequency naturally has an arbitrary meaning in a range greater than twice the frequency of the symbol transmission signal. In the conventional example, the sampling frequency had to be an integral multiple of the frequency of the symbol transmission signal, but it is optional in the present invention. It may or may not be an integral multiple. It is applicable to both.

Then, the mapping output is subjected to predetermined weighting in synchronization with the symbol transmission signal so that the envelope of the mapping output value takes a zero value at both ends of each symbol section. That is, waveform shaping is performed so that the envelope of the mapping output always takes a zero value at both ends of each symbol section with respect to the mapping output. Then, the signal, that is, a predetermined band or more of the weighted output signal is cut off by a filter having an action of correcting the change in the frequency characteristic caused by the weighting to generate the band limited waveform. Here, the filter is, for example, a filter having a characteristic in which a filter having an inverse characteristic of the frequency spectrum of the weighted waveform and a roll-off filter are continuously connected. By performing the above processing, even when the symbol rate is not an integer fraction of the sampling frequency, the frequency characteristic of the filter output signal satisfies the first Nyquist criterion, so that the filter output causes intersymbol interference. There is no band-limited waveform.

A band limited waveform generating method according to a second aspect is the band limited waveform generating method according to the first aspect,
The predetermined weighting is performed by multiplication of an arbitrary function that takes a zero value at both ends of each symbol section. Here, the arbitrary function is, for example, a periodic function such as a triangular wave or a sine wave having a zero value.

The band-limited waveform generating circuit according to a third aspect of the present invention is a band-limited waveform generating circuit that limits the bandwidth of a signal, for example, a modulated signal that modulates a carrier wave, and the mapping unit is an input symbol sequence. Based on the signal, that is, the symbol sequence transmitted from the symbol transmission signal is sampled at a predetermined frequency and a mapping output is generated based on the sample sequence. The mapping output is, for example, a digital output value that gives +125 to the symbol “1” and −125 to the symbol “0”. Then, the weighting section performs weighting in synchronization with the symbol transmission signal so that the envelope of the mapping output becomes zero at both ends of each symbol section. Then, the signal having a predetermined band or more is cut off by the filter section having the function of correcting the change in the frequency characteristic caused by the weighting, and the signal is transmitted. Here, the filter unit is, for example, a high-frequency signal cutoff filter having a characteristic having an inverse characteristic of the frequency spectrum of the weighted waveform and a characteristic in which a roll-off filter is continuously connected. With such a configuration, even when the symbol rate is not an integer fraction of the sampling frequency, the frequency characteristic of the filter output satisfies the first Nyquist criterion, and therefore the filter output has a band without intersymbol interference. It becomes a limited waveform.
Further, in the present invention, the sampling frequency can be arbitrarily set higher than twice the frequency of the symbol transmission signal. That is, the sampling frequency need not be an integral multiple that is higher than the symbol transmission signal as in the conventional case.
It can be arbitrary.

The band limited waveform generating circuit according to a fourth aspect is the band limited waveform generating circuit according to the third aspect,
The weighting unit multiplies the sample sequence by an arbitrary function that takes a zero value at both ends of each symbol section. The arbitrary function is, for example, a triangular wave or a sine wave whose sample values are zero at both ends of each symbol section.

A band limited waveform generating circuit according to a fifth aspect is the band limited waveform generating circuit according to the fourth aspect.
The weighting unit stores in the waveform storage unit an arbitrary function that takes a zero value at both ends of each symbol section. The storage device is, for example, a ROM or a RAM whose value can be easily designated and output at high speed. Using such a storage device, for example, an arbitrary function is time-sequentially divided into, for example, 16 and stored as data values. Since the arbitrary waveform is stored in advance in the storage device, the multiplication value can be output easily and at high speed. That is, the band-limited waveform generating circuit according to claim 4 can be easily realized. The storage device can of course thin out the waveform value by setting the address and output it. That is, it is not necessary to output all the waveform values divided into 16 and stored. It may be divided into four and outputted. The amount of calculation is reduced and a faster response is possible.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment) A band-limited waveform generating method of the present invention will be described below with reference to the drawings. Figure 1
1 shows an embodiment of a generator circuit to which the band-limited waveform generating method of the present invention is applied. The figure is a configuration block diagram. The band-limited waveform generating circuit of the present invention includes a mapping unit 10 that maps a signal based on an input symbol sequence, a weighting unit 20 that weights the output of the signal, and a frequency spectrum correction unit 3 that corrects a frequency spectrum distorted by the weighting unit.
0, a filter unit 4 that cuts off a predetermined band of the corrected signal
It consists of zero. In addition, as shown in the figure, the weighting unit 20
Is composed of a counter device 21, a waveform storage unit (ROM) 22, and a multiplier 23.

The mapping unit 10 is a device for sampling a symbol string transmitted at a symbol transmission signal (symbol rate f _B ) at a predetermined frequency to generate a digital value (mapping output). The mapping output is, for example, an output in which +125 is associated with the symbol “1” and −125 is associated with the symbol “0”. The symbol sequence means a data sequence transmitted in time series. The weighting unit 20 is a device for multiplying the mapping output by the multiplication unit 23 by the waveform of the waveform storage unit 22. The frequency spectrum correction unit 30 is a device that corrects the frequency spectrum changed by weighting. The filter unit 40 is a device that cuts off a predetermined band, that is, a high band of the corrected signal.

The operation of each component will be described with reference to the signal change diagram of FIG. First, a symbol train is transmitted to the mapping unit 10 at a symbol rate f _B in synchronization with a symbol transmission signal from a memory device (not shown) in which data is stored. The symbol sequence is 11101101 shown in FIG.
Etc., and here is the NRZ signal. The mapping unit 10 samples at a sampling frequency f _S having an arbitrary frequency higher than twice the symbol rate f _B. For example, sampling is performed at a sampling frequency f _S of f _B : f _S = 3: 11. FIG. 3 shows a detailed mapping output when the NRZ symbol '1' is sampled under this condition. As shown,
Four values (for example, +125) are mapped in the period 1 / f _B = 11. When the symbol is 0, the polarity of the mapping output is inverted. If this is done for all symbol columns, a mapping output as shown in FIG. 2 (b) is obtained.

The mapping output is then weighted by the weighting unit 20 to the predetermined waveform stored in the waveform storage unit 22. The details of weighting are shown in FIG. The predetermined waveform stored in the waveform storage unit 22 is, for example, a sine waveform that has a zero value at both ends of each symbol section. This sine waveform is, for example, one in which a sine wave is stored at a frequency of f ′ (= 3f _S ) or one in which the result of calculation is stored. Here, it is clear that the waveform storage unit 20 needs to hold only the weighted waveform for one symbol, and thus the required memory capacity is significantly smaller than that of the second conventional example. An arbitrary waveform value is selected from the waveform storage unit 22 and multiplied by the mapping output. The selection is made by the output of the counter device 21 of FIG. For example,
In 3 jumps, that is, count values 0, 3, 6, 9, 1, 4,
When 7, ..., Corresponding waveform values are output and multiplied by the multiplier 23. As a result, the weighted output shown in FIG. 2C is obtained. That is, a weighted output signal having a zero value is generated in synchronization with both ends of each symbol section. This method allows the sampling frequency f _S to be arbitrary under the condition that the sampling frequency f _S is higher than twice the symbol rate f _B. That is, the sampling frequency f _S need not be an integral multiple of the symbol rate f _B as in the conventional case. It can be arbitrary.

Next, this signal is corrected by the frequency spectrum correction unit 30. This is because the weighting in the preceding stage changes the frequency spectrum. For example,
When weighted by the sine waveform as described above, it is affected by the frequency characteristic shown by the broken line A in FIG. That is, the frequency spectrum changes according to the characteristic of the following expression (3).

[Formula 1] P _sin (f) = 4 (1 + COS (2πfT)) / {π ² · (1-4f ² T ² ) ² } (1) In order to correct this, the frequency spectrum correction unit 30 The frequency characteristic shown in FIG. 6, that is, the function of the inverse characteristic of Expression (1) is multiplied. As a result, the frequency characteristic is corrected.

Finally, the high frequency band of the signal whose frequency spectrum has been corrected by the filter section 40 is cut off. The filter unit 40 is, for example, a roll-off filter. As a result, the frequency characteristics of the filter output satisfy the Nyquist first criterion, and the filter output without intersymbol interference shown in FIG. 2D is obtained.

FIG. 7 shows an eye pattern showing the quality of the output signal (transmission signal). FIG. 7A is an eye pattern when a band-limited waveform according to the present invention is output, and FIG. 7B is an eye pattern when weighting based on the second conventional example is not performed. As can be seen from the figure, when weighting is applied, the waveform converges at two positive and negative points at the symbol determination point (arrow in the figure), and no intersymbol interference occurs. On the contrary, when weighting is not performed as in the conventional case, intersymbol interference occurs at the symbol determination point. If this signal without intersymbol interference is taken in at the proper timing (symbol decision point) synchronized with the symbol rate on the demodulation side, it can be demodulated accurately without code error. The vertical axis of the eye pattern is the signal level, and the horizontal axis is the time. As described above, in the present embodiment, the sample frequency f _S (> 2 times the symbol rate f _B ) can be set arbitrarily, so that it is possible to support a system in which the sampling frequency f _S is fixed in advance.

(Modification) The above embodiment is only one example, and various modifications can be considered. For example, although the frequency spectrum correction unit 30 is provided after the weighting unit 20 in the above embodiment, the frequency spectrum correction function may be included in the filter unit 40. Further, in the above embodiment, the weighting is performed with a sine wave, but it may be performed with a waveform having another shape such as a triangular wave. It is sufficient if it is a periodic function in which both ends of the symbol section always take a zero value. Although the storage method of the waveform storage device 22 is not particularly limited, the value may be a storage of the periodic function value obtained by calculation, or a value obtained by sampling an actual periodic function and A / D converting it. . Either may be used.

[Brief description of drawings]

FIG. 1 is a configuration block diagram of a band-limited waveform generating circuit according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a signal change according to the embodiment of the present invention.

FIG. 3 is an explanatory diagram of a mapping output method according to an embodiment of the present invention.

FIG. 4 is an explanatory diagram of a weighted output generation method according to the embodiment of the present invention.

FIG. 5 is a frequency characteristic diagram when a symbol string is converted into a rectangular waveform (solid line) and a sine waveform (broken line).

FIG. 6 is a frequency characteristic diagram of an inverse characteristic with respect to weighting according to the embodiment of the present invention.

FIG. 7 shows a signal waveform with weighting and its eye pattern (a) according to an embodiment of the present invention, and a signal waveform with no weighting and its eye pattern (b).

FIG. 8 is a configuration block diagram of a band-limited waveform generating circuit according to a first conventional example.

FIG. 9 is an explanatory diagram of a signal waveform change by the band limiting waveform generating circuit of the first conventional example.

FIG. 10 is a characteristic explanatory diagram of a roll-off filter.

FIG. 11 is a configuration block diagram of a band-limited waveform generating circuit according to a second conventional example.

FIG. 12 is an explanatory diagram of a signal waveform change by the band limiting waveform generating circuit of the second conventional example.

FIG. 13 is an explanatory diagram of frequency characteristic correction by the band-limited waveform generating circuit of the second conventional example.

FIG. 14 is a configuration block diagram of a band-limited waveform generating circuit according to a third conventional example.

FIG. 15 is an explanatory diagram of a signal waveform change by the band limiting waveform generating circuit of the third conventional example.

FIG. 16 is a signal change diagram illustrating phase shift generation in the band-limited waveform generating circuit of the first conventional example.

FIG. 17 is an explanatory diagram of a phase shift occurrence due to thinning according to a band limiting waveform generating circuit of a third conventional example.

[Explanation of symbols]

10 ... Mapping section 20 ... Weighting unit 21 ... Counter device 22 ... Waveform storage unit 23 ... Multiplier 30 ... Frequency spectrum correction unit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shiro Ito             Aichi Prefecture Nagachite Town Aichi District             Ground 1 Toyota Central Research Institute Co., Ltd.

Claims (5)

[Claims] 1. A band-limited waveform generating method for limiting the bandwidth of a signal, wherein a signal based on an input symbol string is sampled at a predetermined frequency to generate a mapping output consisting of a sample string, and the input symbol string is generated. In synchronism with a symbol transmission signal for transmitting the symbol output signal, the mapping output is given a predetermined weighting so that the envelope of the mapping output has a zero value at both ends of each symbol section, and the change in the frequency characteristic caused by the weighting is corrected. A band-limited waveform generating method, wherein a band-limited waveform is generated by blocking a predetermined band or more of the signal by a filter including the action. 2. The band-limited waveform generating method according to claim 1, wherein the predetermined weighting is performed by multiplication of an arbitrary function having a zero value at both ends of each symbol section. 3. A band-limited waveform generating circuit for limiting the bandwidth of a signal, wherein an input symbol sequence is transmitted in synchronization with a symbol transmission signal,
A mapping unit that samples the transmitted signal at a predetermined frequency to generate a mapping output, and the envelope of the mapping output has a zero value at both ends of each symbol section in the mapping output in synchronization with the symbol transmission signal. A weighting section for weighting so as to obtain, and a filter section for compensating for a change in frequency characteristics caused by weighting for the weighted output signal waveform-shaped by the weighting section and for blocking a predetermined band or more. Characteristic band-limited waveform generation circuit. 4. The band limiting waveform generating circuit according to claim 3, wherein the weighting unit multiplies the sample sequence by an arbitrary function that takes a zero value at both ends of each symbol section. 5. The band limited waveform generating circuit according to claim 4, wherein the weighting unit stores the arbitrary function having a zero value at both ends of each symbol section in a waveform storage unit.