JPH10336141A - Method for transmitting orthogonal frequency dividing multiplex signal, its device and idft arithmetic device used therefore - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable reproducing a pilot signal correctly in a receiving device so as to improve the decoding performance of transmitting information by transmitting invariant data where amplitude and a phase are invariant through the use of more than one class of a carrier wave pair which exists in a frequency position which forms a contact with a central carrier wave and also transmitting an information signal through the use of a part of remaining carrier waves. SOLUTION: The carrier waves in a DFDM signal for transmitting the pilot signal are converted into time base signals (an I signal and a Q single) as vectors to be mutually rotated in opposite directions. The combined I signal within the two carrier waves becomes twice as large as an original prescribed value in amplitude and the combined Q signal becomes zero. A I signal component is picked-up at a receiving device side so as to generate a sampling clock. An IDFT arithmetic circuit 4 calculates the reverse discrete Fourier transformation of digital data from an input circuit 2 and also calculates a pilot signal data from a pilot signal data inserting circuit 5 after it is supplied to a prescribed frequency assigning part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an orthogonal frequency division multiplexing signal transmission method, an orthogonal frequency division multiplexing signal transmitting apparatus and an IDFT arithmetic unit used therefor, and more particularly to orthogonal frequency division multiplexing (OFD) for multilevel modulated digital information.
The present invention relates to an orthogonal frequency division multiplexing signal transmission method for transmitting and receiving an M: Orthogonal Frequency Division Multiplex (M) signal, an orthogonal frequency division multiplexing signal transmission device for transmitting an OFDM signal, and an IDFT operation device used therefor.

[0002]

2. Description of the Related Art One method of transmitting coded digital video signals in a limited frequency band is as follows.
6 Quadrature Amplitude Modul (QAM)
2. Description of the Related Art An OFDM signal transmission method for transmitting digital information modulated by multi-level modulation such as an OFDM signal using a large number of carriers as an OFDM signal is conventionally known. This OFDM signal transmission method is a method in which a large number of carriers are arranged orthogonally and independent digital information is transmitted on each carrier. The OFDM signal transmission method is strong in multipath, is not easily disturbed, and has relatively good frequency use efficiency. There are features. Note that "carriers are orthogonal" means that the frequency spectrum of an adjacent carrier becomes zero at the frequency position of the carrier.

According to the OFDM signal transmission method, since a large number of carriers are modulated according to information to be transmitted and transmitted / received, an accurate phase synchronization signal is required for decoding a carrier in a receiving device. . In particular, when trying to transmit more information by multi-level modulation of each carrier, the phase stability of a clock signal required for signal decoding needs to be very high. Therefore, the transmitting device transmits a synchronization signal. The synchronization signal needs to be reproduced stably, and can be transmitted using a carrier wave. Is inserted into a dedicated symbol period and transmitted.

However, transmitting a synchronization signal in a dedicated symbol period allows the carrier to be reproduced without interference from the carrier, but at the same time lowers the transmission efficiency of the information signal. To be transmitted in bursts. However, to extend the transmission interval of the synchronization signal to some extent, in a reception environment where the reception state is constantly changing, such as mobile reception, even when the information signal must be decoded early when the reception channel is changed, Since the synchronization signal is transmitted in a burst manner, there is a certain time delay before decoding of the synchronization signal, which is not preferable.

Therefore, the pilot signal is always transmitted, and the receiving apparatus obtains the sample synchronization signal while switching the loop characteristics of the phase locked loop (PLL) circuit, thereby shortening the decoding time at the time of mobile reception, channel switching, and moving. Improved performance in reception.
An orthogonal frequency division multiplex signal transmitting / receiving device is conceivable. In this case, the pilot signal is decoded at a frequency set to a predetermined integer ratio with respect to the sample clock frequency in order to reduce the order of the multiplication operation for obtaining the clock frequency information of the fast Fourier transform (FFT) after decoding. In addition, the pilot signal is transmitted from a center carrier among a number of carriers constituting the OFDM signal on carriers at both ends of a frequency which is equivalent to a symmetric Nyquist frequency because it is desirable that the frequency be as high as possible. .

[0006]

In an OFDM signal transmitting and receiving system for transmitting and receiving such a pilot signal, it is important to accurately reproduce the pilot signal in a receiving apparatus for decoding transmission information. For this purpose, it is conceivable to make the amplitude of the pilot signal larger than that of other information data by making the amplitude of the carrier transmitting the pilot signal larger than that of the carrier transmitting other information. As means for achieving this, it is conceivable to make the information data relatively smaller than the amplitude of the pilot signal.

[0007] In order to generate an OFDM signal, an inverse discrete Fourier transform (IDFT) operation is performed on N complex numbers (real part data and imaginary part data) during a time interval T. Here, a general IDFT operation will be described. The IDFT operation is performed by repeating a product-sum operation called a butterfly operation. For example, in order to secure the calculation accuracy, information is allocated to upper bits within a range where the input of the first stage does not overflow, and as shown in FIG. 7, the input complex numbers AR + jAI, BR + jBI
Is performed while multiplying by 1/2. FIG.
Then, the angle notation of the rotor is omitted.

Here, considering that the value for the pilot signal and the value of the information to be transmitted are similarly input to the IDFT arithmetic unit, the numerical operation that does not cause overflow is performed in a range that does not overflow the numerical value for the pilot signal. As a result, information is assigned to bits, and as a result, a small numerical value for information must be assigned. that time,
If an inexpensive signal processor for fixed-point arithmetic or a short arithmetic data length (hereinafter referred to as DSP) is used, or if a general IDFT arithmetic unit is used, there is a problem in the accuracy of the arithmetic result obtained. It is possible to do.

[0009] The present invention has been made in view of the above points,
Orthogonal frequency division multiplex signal transmission method that can easily and inexpensively transmit a pilot signal with a larger amplitude than that of a carrier of information data and thereby improve decoding performance of transmission information by accurate reproduction of the pilot signal in a receiver. Also, an orthogonal frequency division multiplexing signal transmitting apparatus and an ID having high calculation accuracy even when using an inexpensive DSP or IDFT arithmetic unit used therefor
An object of the present invention is to provide an FT operation device.

[0010]

In order to achieve the above object, an orthogonal frequency division multiplexing signal transmission method according to the present invention provides a method of transmitting an orthogonal frequency division multiplexing signal to a center carrier among a plurality of carriers having different frequencies from each other. With one or more pairs of carriers present at symmetric frequency positions, amplitude and phase are transmitted between symbols using constant data.
The signal points of the invariant data are arranged symmetrically with respect to the in-phase axis or the orthogonal axis, and an information signal is transmitted using at least a part of the remaining carrier.

Here, the invariable data is a plurality of pilot signals for generating a decoding reference clock on the receiving side. In the present invention, the signal point arrangement of the invariant data is
Since they are arranged at positions symmetrical to each other with respect to the in-phase axis or the orthogonal axis, among the calculation results obtained by the IDFT calculation, the calculation result of the invariable data is made larger than the calculation result based on another information signal. be able to.

In order to achieve the above object, the transmitting apparatus according to the present invention is configured so that at least an information signal is input to a predetermined input unit and an n-times (n is an even number of 2 or more) inverse discrete Fourier transform. An arithmetic circuit that performs an arithmetic operation to output an arithmetic result obtained by performing frequency-time conversion, and as a predetermined arithmetic result of the arithmetic result of the arithmetic circuit, the signal point arrangement is at a position symmetrical with respect to the in-phase axis or the orthogonal axis. Symmetry with respect to the center carrier by modulating the output operation result of the arranged insertion circuit for inserting a value for a plurality of invariant data whose amplitude and phase are invariable, and an arithmetic circuit including the value inserted by the insertion circuit. Generating means for generating an orthogonal frequency division multiplexed signal in which a pair of carriers present at different frequency positions are modulated with one or more sets of invariable data, and a part of the remaining carriers are modulated with an information signal. It is obtained by a configuration in which a transmission means for transmitting the exchange frequency division multiplexed signal.

Alternatively, the orthogonal frequency division multiplexing signal transmitting apparatus of the present invention performs at least an information signal input to a predetermined input unit and performs an inverse sampling Fourier transform operation of n times (n is an even number of 2 or more) oversampling. The calculation result obtained by adding a plurality of values for invariant data whose amplitude and phase are invariant and whose signal point constellations are arranged symmetrically with respect to the in-phase axis or the orthogonal axis is added to the calculation result obtained by performing the calculation. By modulating the operation result of the arithmetic circuit and the arithmetic circuit, one or more pairs of carriers present at frequency positions symmetric with respect to the center carrier are modulated with one or more sets of invariable data, and a part of the remaining carrier is converted into an information signal. And a transmitting means for transmitting the orthogonal frequency division multiplexed signal, which is modulated by the above.

In the apparatus of the present invention, a pair of carriers present at symmetrical frequency positions with respect to the center carrier are modulated by one or more sets of invariable data, and a part of the remaining carriers is modulated by an information signal. When generating a multiplex signal,
In order to insert or add a value for a plurality of invariant data in which the signal point arrangement is arranged at a position symmetrical with respect to the in-phase axis or the orthogonal axis with respect to the IDFT operation result of the information signal, the amplitude and the phase are invariable. The operation result of the invariant data can be made larger than the operation result based on another information signal.

[0015]

Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing first and second embodiments of an orthogonal frequency division multiplex signal transmission method and an orthogonal frequency division multiplex signal transmission apparatus according to the present invention. This embodiment is characterized by an IDFT arithmetic unit 4 and a pilot signal data insertion circuit 5, and the other blocks have the same configuration as the conventional one.

In FIG. 1, input terminal 1 receives digital data to be transmitted. The digital data is, for example, a color moving image coded display system M
There are digital video signals and audio signals compressed by an encoding method such as the PEG method. The input digital data is supplied to an input circuit 2 and an error correction code is added as necessary based on a clock from a clock frequency divider 3. The clock divider 3 divides an intermediate frequency of 10.7 MHz from the intermediate frequency oscillator 10 and generates a clock synchronized with the intermediate frequency.

The digital data to which the error correction code has been added is supplied from the input circuit 2 to the IDFT operation device 4.
The IDFT operation device 4 is composed of an inexpensive DSP for fixed-point operation or having a short operation data length. ) And a quadrature signal (Q signal), and the pilot signal data from the pilot signal data insertion circuit 5 is supplied to a predetermined frequency allocating unit as described later to perform an IDFT operation.

As an example, when the data sequence N is transmitted by 256 carriers, the IDFT arithmetic unit 4 uses double oversampling and uses the number of points M (= 2N) generates an OFDM signal by performing a 512-point IDFT operation.
Each carrier of the OFDM signal is modulated by 256 QAM, and each carrier transmits 8-bit information. At this time, the input assignment to the IDFT operation device 4 is as follows when the numbers are sequentially assigned in the input frequency alignment type.

N = 0 to 128 An information signal for modulating the carrier is provided.

N = 129-383 Carrier level is set to 0
And no signal is generated.

N = 384-511 An information signal for modulating the carrier is provided.

That is, the number of input sections of the IDFT arithmetic unit 4 is 512 for the real part signal and 512 for the imaginary part signal, respectively, and the first (n = 1) to 127th of them are provided. 12 up to (n = 127)
An information signal is input to a total of 127 input units of seven each and 385th (n = 385) to 511th (n = 511), and a direct current is input to the 0th (n = 0) input unit. Voltage (constant) is input, and the 128th (n = M / 4) and 3
Conventionally, pilot signal data is input to the 84th (n = 3M / 4) input section. In this embodiment, as described later, the pilot signal data is calculated during the calculation of the input section data. Insertion circuit 5 inserts pilot signal data.

Here, a total of 1 from the 1st to the 128th
The input information of the 28 input units is a carrier for information transmission on the upper side (higher frequency side) with respect to the center carrier frequency F0 for transmitting the input information of the 0th input unit (this is a positive carrier or a positive carrier in this specification). 384
The input information of a total of 128 input units from the 1st to the 511th is a carrier for information transmission lower (lower side) with respect to the center carrier frequency F0 (this is referred to as a negative carrier or a carrier in this specification). , Carrier waves at frequency positions symmetrical with respect to the center carrier frequency F0 have the same absolute value).

In particular, the input pilot signals at the 128th and 384th inputs of the IDFT arithmetic unit 4 are IDFT
As a result of the operation, the positive 128th carrier at both ends and the frequency which is equivalent to half the Nyquist frequency and 38
The signal is transmitted by the fourth (ie, negative 128th) carrier wave, and 0 is input to the remaining 129th to 383th input portions (the ground potential), so that the carrier wave of that portion is not generated. (Not used for data transmission).

The IDFT operation device 4 thus operates as follows.
A double oversampling IDFT operation is performed, and as a result OFDM of 257 carriers including the 0th center carrier is performed.
Signals, of which nine carriers including the 0th, 128th positive and 128th negative carriers are used for pilot signals, reference data and other auxiliary signals, and the remaining 248 carriers carry information. Used for transmission. Therefore, the input circuit 2 outputs 248 signals during one symbol period.
The digital data of bytes, that is, 248 pairs of parallel data of 4 bits each in one symbol period
It is inputted to a pair of input parts of the real part and the imaginary part of the FT arithmetic unit 4.

The IDFT arithmetic unit 4 thus operates as follows.
A double oversampling IDFT operation is performed, and as a result, an in-phase signal (I signal) and a quadrature signal (Q signal) transmitted by 257 waves are obtained, and then multipath distortion is reduced to the I signal and the Q signal, respectively. , And then output to the output buffer 7.

The output buffer 7 has a time axis signal (I signal and Q signal) in which 256 pieces of input information are 512 points in one IDFT operation as a result of the output operation of the IDFT operation device 4.
In contrast, the circuit is generated in a burst manner, whereas the circuits subsequent to the output buffer 7 are continuously operated at a constant reading speed of the contents of the output buffer 7, and are provided for adjusting the time difference between the two. ing.

Based on the clock from the clock divider 3 in FIG. 1, I
The I and Q signals resulting from the DFT operation are supplied to a D / A converter / low-pass filter (LPF) 8, where they are converted into analog signals using the clock from the clock divider 3 as a sampling clock. , LPF, the I signal and the Q signal of the components in the required frequency band are passed and supplied to the quadrature modulator 9, respectively.

The quadrature modulator 9 uses the intermediate frequency of 10.7 MHz from the intermediate frequency oscillator 10 as a first carrier, and sets the phase of this intermediate frequency to 90 ° by the 90 ° shifter 11.
A 10.7 MHz intermediate frequency shifted by 0 ° is used as a second carrier, and 257 waves (positive / negative 128 bits) are subjected to quadrature amplitude modulation (QAM) with the I and Q signals of the digital data input from the D / A converter and LPF 8, respectively. An OFDM signal comprising a set of carriers and one center carrier is generated, and the center carrier frequency is 10.7 MHz. The OFDM signal output from the quadrature modulator 9 is frequency-converted by the frequency converter 12 into an RF signal in a predetermined transmission frequency band, and then subjected to transmission processing such as power amplification in the transmission unit 13 and radiated from an antenna (not shown). You.

Next, the main part of the embodiment of the present invention, I
The DFT operation device will be described in more detail. First,
To explain the signal point arrangement of the pilot signal, FIG.
(A) shows one of the 128th and 384th carriers in the OFDM signal transmitting the pilot signal.
A vector f in which the in-phase component (I-axis component) of the 28th carrier is set to zero and the quadrature component (Q-axis component) is set to a predetermined value a
_128, the in-phase component 384 th carrier is set to zero, indicating the the vector f ₃₈₄ is set to a predetermined value -a and quadrature component, and arranged symmetrically with respect to the I axis Fig.

These carriers are converted into time axis signals (I signal and Q signal) as vectors f ₁₂₈ and f ₃₈₄ rotating in opposite directions, and transmitted. That is, the _128th carrier represented by the vector f128 is converted into an I signal shown in FIG. 2B and a Q signal shown in FIG. 2C. On the other hand, the _384th carrier represented by the vector f384 is
As shown in FIG. 2D, the I signal in phase with the I signal in FIG.
The signal is converted into a Q signal having a phase opposite to that of the Q signal shown in FIG.

Therefore, when set in this way, the composite I signal of these two carriers shows 2a whose amplitude is twice the original predetermined value a, as shown in FIG. Further, the combined Q signal of the two carrier waves becomes zero as shown in FIG. Therefore, if you set this way,
The receiving apparatus can extract the I signal component and generate a sampling clock based on the extracted I signal component.

Next, the IDFT operation device 4 will be described. First, the flow of the conventional IDFT calculation will be described. The input frequency assignment of the conventional output time axis data integer type IDFT operation and the operation results of the first and second stages are treated as complex numbers in consideration of double oversampling.
Table 1 shows the bit reverse order. At the time of calculation, no signal is given to the 0th input unit transmitted on the 0th carrier (hereinafter also referred to as the 0th carrier: the same applies to other carriers).

As described above, pilot signal data is input to the 128th and 384th input sections (the first and second input sections).
The pilot signals are allocated to the 28th carrier and the 384th carrier), respectively, as described with reference to FIG.
A signal point arrangement of 0 + ja and 0-ja is set. The 128th and 384th carriers are carriers located at both ends symmetric with respect to the center carrier in the occupied band of the OFDM signal. Further, in Table 1, R0 and I0 mean information to be transmitted, each of which includes 4-bit information.

[0035]

[Table 1] When looking at the numerical values of the input assignments in Table 1, the calculation accuracy is better when these numerical values are assigned as the maximum numerical values that can be represented by a data length subject to restrictions such as a DSP. Therefore, information is assigned to the upper bits. Of course,
The value for the pilot signal is also better to be the maximum value, and when the amplitude level of the pilot signal is larger than the information signal,
As a result, a small numerical value for information must be assigned.

Therefore, the ID of the first embodiment of the present invention is
The FT arithmetic unit is characterized in that a predetermined numerical value is inserted in the middle of the calculation for the predetermined frequency allocating unit, and more specifically, the first and second stages of the pilot signal of the previous example are omitted, and Table 2 As shown, a predetermined numerical value is inserted in the place of the second stage calculation result.

[0037]

[Table 2] As the numerical value of b in Table 2, for example, when calculating with a data length of 16 bits, b = 7FFFF in hexadecimal notation
h, -b = 8001h is inserted. Table 1 shows that when the maximum value is set in the first stage, it becomes 1/2 in the second stage. Therefore, when the maximum value b is set in the second stage as shown in Table 2, this becomes This means that the maximum value that can be expressed is set to twice. Since the maximum value that can be expressed for other carriers for the information signal is the upper limit, a pilot signal having twice the amplitude level can be generated as a result without deteriorating the calculation accuracy of the information signal.

Next, a second embodiment will be described. In the second embodiment, the IDFT operation device 4
Performs quadrature oversampling, performs a 512-point IDFT operation, and generates an OFDM signal.

In this case, as in the first embodiment, the conventional calculation results of the portion related to the input time allocation and the pilot signal for the first, second and third stages of the output time axis data alignment type IDFT calculation are shown. , And Table 3. However, Table 3
Where s = √2. At the time of calculation, no signal is given to the 0th input unit transmitted on the 0th carrier. Also,
Pilot signal data is input to the 64th and 448th input units (pilot signals are allocated to the 64th and 448th carriers), and signal points of 0 + ja and 0-ja are respectively described as described with reference to FIG. Arrange them. These 64th carrier and 448th carrier are
These carriers are symmetrical with respect to the center carrier of the occupied band of the OFDM signal and are located at both ends. In Table 1, R0, I0
Means information to be transmitted, each of which includes 4-bit information.

[0040]

[Table 3] Here, the IDFT arithmetic device according to the second embodiment is characterized in that a predetermined numerical value is inserted into a predetermined frequency allocating unit from the middle of the calculation, and more specifically, the first and second pilot signals of the previous example are inserted. The operation of the stage is omitted, and a predetermined numerical value shown in Table 4 is inserted into the result of the operation of the second stage.

[0041]

[Table 4] When the maximum value that can be expressed is given as the numerical value of b in Table 4, a pilot signal having an amplitude level twice that of the information signal can be generated. That is, when the maximum value is set in the first stage, it is halved in the second stage.
As can be seen, the maximum value b in the second stage as shown in Table 4
Is set to twice the maximum value that can be expressed in the first stage. Since the maximum value that can be expressed for other carriers for the information signal is the upper limit, a pilot signal having twice the amplitude level can be generated as a result without deteriorating the calculation accuracy of the information signal.

In this case, as another method, the first, second, and third stage calculations may be omitted, and a predetermined numerical value as shown in Table 5 may be inserted in the third stage calculation result. .

[0043]

[Table 5] When the maximum value that can be expressed is given as the numerical value of sb in Table 5, a pilot signal having an amplitude level of 2√2 times the information signal can be generated.

It should be noted that the present invention is not limited to the above-described first and second embodiments, and the IDFT arithmetic unit 4 can perform the same processing even for 8 times oversampling or more. Also, 5
Although the 12-point IDFT calculation is taken as an example, the same effect can be obtained by using an IDFT calculation of less or more than 12 points.

Also, with respect to the signal point arrangement of the pilot signal, a diagram symmetrically arranged with respect to the in-phase axis of 0 + ja and 0-ja has been described, however, with respect to the in-phase axis of a + ja and a-ja. They may be arranged symmetrically.

Further, when the antennas are arranged symmetrically with respect to the orthogonal axis, the time axis waveform of the in-phase component shows zero, and the time axis waveform of the orthogonal component is generated. What is necessary is just to extract and generate a sampling clock based on this. When the signal point arrangement of the pilot signal is changed, it goes without saying that a numerical value corresponding to the change is inserted at the corresponding stage calculation result.

Next, a third embodiment of the present invention will be described. In this embodiment, as in the first embodiment, an ID of 512 points is obtained by double oversampling.
This is an example of performing FT operation. When the signal points of the pilot signal are arranged as shown in FIG. 2A, the I signal component of the pilot signal obtained on the receiving side is shown in FIG. 2F, and the Q signal component of the pilot signal is shown in FIG. become. Although this is shown as an analog signal waveform obtained by D / A conversion of data, when the same is digitally displayed, FIG.
(A) to (C).

That is, since the pilot signal is transmitted on a carrier having a frequency half the Nyquist frequency,
The time axis data of the in-phase component of the pilot signal obtained on the receiving side is 0, -2a, 0, 2 as shown in FIG.
a, 0, -2a,. . . , And the time axis data of the orthogonal component is always 0 as shown in FIG. Therefore,
In the third embodiment, the receiving apparatus extracts and transmits / receives an OFDM signal into which a pilot signal is inserted so as to extract a time-axis waveform of an in-phase component and generate a sampling clock based on the extracted time-axis waveform.

FIG. 4 is a block diagram showing a third embodiment of the orthogonal frequency division multiplex signal transmission method and the orthogonal frequency division multiplex signal transmission apparatus according to the present invention. In the figure, the same components as those of FIG. 1 are denoted by the same reference numerals, and description thereof will be omitted.
This embodiment is characterized by the IDFT arithmetic unit 14,
The other blocks have the same configuration as in FIG.

In FIG. 4, the number of input sections of the IDFT arithmetic unit 14 is 512 for the real part signal and 512 for the imaginary part signal, respectively. A total of 127 units up to the 127th (n = 127) and 51 units from the 385th (n = 385)
An information signal is input to the first (n = 511) total of 127 input sections, and a DC voltage (constant) is input to the 0th (n = 0) input section, and the 128th (n = 511) M /
Conventionally, pilot signal data is input to the 4th and 384th (n = 3M / 4) input sections. However, in this embodiment, as described later, the data of the input section is fixed during the calculation. Data is inserted.

FIG. 5 is a block diagram showing an example of the IDFT arithmetic unit 14. As shown in FIG.
4 is an IDFT calculator 141, adders 142 and 143,
It comprises fixed data string generators 144 and 145. The IDFT calculator 141 performs an IDFT calculation of 512 points by the above twice oversampling,
The 256 pieces of input information are output in bursts as 512 time axis signals, that is, I signals and Q signals.

The I signal is supplied to an adder 142, which outputs 0, 0 for each sampling period from a fixed data sequence generator 144.
-2a, 0, 2a, 0, -2a,. . . Are added to the fixed data string of the fixed pattern output in the order of. On the other hand, the Q signal is supplied to the adder 143, and is added to the constantly zero data input from the fixed data string generator 145 and output. It should be noted that always adding to 0 data is equivalent to not adding anything, so that the adder 143 and the fixed data string generator 145 need not be provided.

Thus, the 128th carrier and the third
By allocating pilot signals to 84 carriers as shown in FIG. 3 (A), a simple numerical sequence as described above can be obtained.
By adding the result to the IDFT operation result, a result equivalent to the operation is obtained.

Further, the value of a can be arbitrarily selected, the amplitude level of the pilot signal can be arbitrarily increased from the information signal, and the calculation accuracy for other information is not affected at all. That is, when the fixed data sequence is not added, since the data length is finite, the IDFT calculation is performed within a range that can be represented by a numerical value. Although the calculation accuracy decreases, the carrier can be calculated using the maximum numerical value that can be expressed by adding the fixed data sequence, and the pilot signal can be increased by adding the fixed data sequence to the IDFT calculation result.

Obviously, the data for the pilot signal input to the IDFT calculator 141 may be calculated by allocating zero or the like. This can be achieved by configuring the fixed data generators 144 and 145 in advance with a storage circuit such as a ROM and adding the results to the output of the IDFT calculator as the calculation result. Alternatively, even when the operation is realized by software, a similar result can be obtained by adding to the operation result.

It should be noted that the present invention is not limited to the above-described embodiment, and the same processing can be performed for 4 times oversampling or 8 times oversampling or more. For example, the numerical sequence at the time of quadruple oversampling is 0, -sa, -2a, -sa, 0, sa, 2a, s
a, 0, −sa,... (where s = √2).
Also, the IDFT calculation of 512 points is taken as an example,
The same applies to IDFT operations below and above.

As shown in FIG. 2A and FIG. 3A, 0+
Although the figure in which ja and 0-ja are arranged symmetrically with respect to the in-phase axis has been described, signal point arrangements a + ja and a-ja which are arranged symmetrically with respect to the in-phase axis may be adopted.

Further, when the signal points of the pilot signal are arranged symmetrically with respect to the orthogonal axis, the time axis waveform of the in-phase component shows zero and the time axis waveform of the orthogonal component is generated. In the above, a time axis waveform of the orthogonal component is extracted, and a sampling clock may be generated based on the extracted waveform. When the signal point arrangement of the pilot signal is changed, the corresponding numerical sequence is naturally added. However, since these numerical sequences can be easily calculated, the ROM
The data string to be stored in the storage device can be easily obtained.

In the third embodiment, a numerical sequence consisting of only pilot signals is added as invariant data. However, when there is a carrier that transmits invariant data (such as reference data) between symbols, for example, for reception decoding. When the reference data or the like is sent, these numerical data may be stored together with the numerical data in a storage circuit and added to the IDFT operation result.

The OFDM signal transmitted as described above is received by, for example, a frequency division multiplexed signal receiving device having a known configuration as shown in FIG. In this frequency division multiplexed signal receiving apparatus, OFD input via a spatial transmission path is
The M signal is received by a receiving unit 21 via a receiving antenna, is then subjected to high-frequency amplification, is further frequency-converted to an intermediate frequency by a frequency converter 22, is amplified by an intermediate-frequency amplifier 23, and is then subjected to carrier extraction and quadrature demodulation. 44.

The carrier extraction circuit portion of the carrier extraction and quadrature demodulator 24 is a circuit for extracting the center carrier (carrier) of the input OFDM signal as accurately as possible with a small phase error. Here, each carrier for transmitting information is placed adjacent to every 387 Hz that is a symbol frequency and OFD
Since the M signal is formed, the carrier for information transmission adjacent to the center carrier is also separated by 387 Hz from the center frequency, and in order to extract the center carrier, the carrier for information transmission adjacent to the carrier only 387 Hz is separated. A circuit with high selectivity is required so as not to be affected.

The center carrier F0 extracted by the carrier extraction and quadrature demodulator 24 is supplied to the intermediate frequency oscillator 25, where it is 10.7 phase-locked to the center carrier F0.
Generate an intermediate frequency of MHz. Intermediate frequency oscillator 2
5 is directly supplied to the quadrature demodulator 24 as the first demodulation carrier, while the phase is shifted by 90 ° by the 90 ° shifter 26, and then the carrier extraction and quadrature demodulation are performed as the second demodulation carrier. Is supplied to the vessel 24.

As a result, an analog signal (frequency division multiplexed signal) equivalent to the analog signal input to the quadrature modulator 9 of the transmitter is demodulated and extracted from the quadrature demodulator section of the carrier extraction and quadrature demodulator 24. , A low-pass filter (LPF) 28
, A signal of a required frequency band transmitted as OFDM signal information is passed, supplied to an A / D converter 29, and converted into a digital signal.

What is important here is the sampling timing for the input signal of the A / D converter 29, which is based on a sample synchronization signal having a frequency twice the Nyquist frequency, which is generated from the pilot signal by the synchronization signal generation circuit 27. Generated. That is, the pilot signal is set at a predetermined integer ratio with respect to the sample clock frequency, and the frequency of the pilot signal is multiplied according to the frequency ratio to obtain the timing of the sample clock. Since the amplitude of the pilot signal is larger than that of the information signal, the pilot signal is reproduced reliably and stably.

The synchronization signal generation circuit 27 receives the demodulated analog signal and generates a sample synchronization signal by a PLL circuit which performs phase synchronization with a pilot signal transmitted as a continuous signal in each symbol period including a guard interval period. A generating circuit section, a symbol synchronization signal generating circuit section for examining a phase state of a pilot signal based on a signal extracted from a part of the sample synchronization signal generation circuit section, detecting a symbol period, and generating a symbol synchronization signal; A system clock generating circuit for generating a system clock such as a section signal for removing a guard interval period from the signal and the symbol synchronization signal.

The digital signal extracted from the A / D converter 29 is supplied to a guard interval period processing circuit 30, where the digital signal is less affected by multipath distortion based on the system clock from the synchronization signal generation circuit 27. Is obtained and supplied to the FFT / QAM decoding circuit 31.

The FFT (Fast Fourier Transform) circuit section of the FFT / QAM decoding circuit 31 performs a complex Fourier operation based on the system clock from the synchronizing signal generation circuit 27, and outputs the output signal of the guard interval period processing circuit 30 for each frequency. The signal levels of the real part and the imaginary part are calculated.

The real part of each frequency obtained by the above,
Each signal level of the imaginary part is compared with the demodulated output of the reference carrier by the QAM decoding circuit section, whereby the level of the quantized digital signal transmitted by the carrier for digital information transmission is obtained. Decrypted. The decoded digital information signal is subjected to output processing such as parallel-serial conversion by the output circuit 32 and is output to the output terminal 33.

In the above embodiment, the number of pilot signals has been described as two transmitted on carriers located at both ends of a plurality of carriers of the OFDM signal. Therefore, the pilot signal may be transmitted using two or more sets of carriers among the one-to-one set of carriers at symmetric frequency positions with respect to the center carrier.

[0070]

As described above, according to the present invention,
Using an inexpensive DSP or IDFT arithmetic unit (or a simple hardware configuration), the operation result of the invariant data such as the pilot signal can be easily made larger than the operation result based on other information signals. The amplitude level of invariant data such as a pilot signal for an information signal to be obtained can be increased easily and with high calculation accuracy. Thus, according to the present invention, the decoding performance of transmission information can be improved by accurate reproduction of a pilot signal in a receiving device.

Further, according to the present invention, it is not necessary to perform frequency-to-time conversion of invariant data such as a pilot signal for each symbol for each symbol, so that the operation time can be reduced. Furthermore, according to the present invention, since a plurality of pilot signals are transmitted and received, even when one of the pilot signals has a reduced amplitude level due to fading, accurate reproduction can be performed by the other pilot signal.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an orthogonal frequency division multiplex signal transmission method and an orthogonal frequency division multiplex signal transmission apparatus according to the present invention.
FIG. 3 is a block diagram of the embodiment.

FIG. 2 is an analog diagram showing a signal point arrangement of pilot signals transmitted according to the present invention and an IDFT operation output.

FIG. 3 is a digital diagram showing a signal point arrangement of a pilot signal transmitted according to the present invention and an IDFT operation output.

FIG. 4 is a block diagram of a third embodiment of an orthogonal frequency division multiplex signal transmission method and an orthogonal frequency division multiplex signal transmission device according to the present invention.

FIG. 5 is a block diagram of an example of an IDFT operation device of a main part in FIG. 4;

FIG. 6 is a block diagram illustrating an example of a receiving side of the orthogonal frequency division multiplexing signal transmission method according to the present invention.

FIG. 7 is a diagram illustrating a butterfly operation.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Digital signal input terminal 2 Input circuit 3 Clock divider 4, 14 IDFT arithmetic unit 5 Pilot signal data insertion circuit 7 Output buffer 9 Quadrature modulator 10 Intermediate frequency oscillator 31 FFT, QAM decoding circuit 141 IDFT arithmetic units 142, 143 Adder 144, 145 Fixed data string generator

Claims (7)

[Claims] An amplitude and a phase between symbols using one or more pairs of a pair of carriers present at symmetric frequency positions with respect to a center carrier among a plurality of carriers having different frequencies constituting an orthogonal frequency division multiplexed signal. While transmitting the invariant data, the signal point arrangement of the invariant data is arranged at a position symmetrical with respect to the in-phase axis or the orthogonal axis, and the information signal is transmitted using at least a part of the remaining carrier. An orthogonal frequency division multiplexing signal transmission method, characterized in that: 2. The orthogonal frequency division multiplexed signal transmission method according to claim 1, wherein the invariable data is a plurality of pilot signals for generating a decoding reference clock on a receiving side. 3. An at least information signal is input to a predetermined input unit, and an n-times (n is an even number greater than or equal to 2) oversampling inverse discrete Fourier transform operation is performed to output a frequency-time converted operation result. A plurality of invariable data whose signal points are arranged at symmetric positions with respect to an in-phase axis or a quadrature axis and whose amplitude and phase are invariable, as a predetermined operation result of the operation results of the operation circuit. And a modulation circuit that modulates the output operation result of the operation circuit including the value inserted by the insertion circuit, so that a pair of carrier waves present at symmetric frequency positions with respect to the center carrier wave is one. Generating means for generating an orthogonal frequency division multiplexed signal which is modulated by the set or more of the invariable data and a part of the remaining carrier is modulated by the information signal; and An orthogonal frequency division multiplexing signal transmitting apparatus, comprising: a transmitting unit for transmitting. 4. An IDFT arithmetic unit used in an arithmetic circuit in an orthogonal frequency division multiplex signal transmitting apparatus according to claim 3, wherein a predetermined numerical value is inserted into the predetermined frequency allocating unit during the operation. 5. An operation result obtained by inputting at least an information signal to a predetermined input unit and performing an n-times (n is an even number equal to or greater than 2) oversampling inverse discrete Fourier transform operation includes a signal point arrangement An arithmetic circuit that outputs an arithmetic result obtained by adding a plurality of values for invariant data whose amplitude and phase are invariable and that are arranged at positions symmetric with respect to the in-phase axis or the orthogonal axis, and an output arithmetic result of the arithmetic circuit. By performing modulation, orthogonal frequency division multiplexing in which a pair of carriers present at symmetric frequency positions with respect to a center carrier is modulated by one or more sets of the invariable data, and a part of the remaining carriers is modulated by the information signal. An orthogonal frequency division multiplex signal transmission apparatus, comprising: a generation unit that generates a signal; and a transmission unit that transmits the orthogonal frequency division multiplex signal. 6. The orthogonal frequency division multiplex signal transmission apparatus according to claim 3, wherein the invariable data is a plurality of pilot signals for generating a decoding reference clock on a receiving side. 7. A storage circuit in which a plurality of values for a plurality of invariant data whose amplitude and phase are invariant are stored in advance at signal point arrangements symmetrically arranged with respect to an in-phase axis or an orthogonal axis, and an information signal. Is input to a predetermined input unit, and performs an n-times (n is an even number equal to or greater than 2) oversampling inverse discrete Fourier transform operation, and a value from the storage circuit as an output operation result of the operation unit 6. An IDFT operation device used in an operation circuit in an orthogonal frequency division multiplex signal transmission device according to claim 5, further comprising an adder for adding and outputting.