JP2002305492A - Orthogonal frequency division multiplex signal transmission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a transmission device by which an accurate synchronous signal can be easily obtained on a receiving side, in transmitting an OFDM signal. SOLUTION: A transmission side device of this system has an IFFT circuit which generates a multivalued QAM modulation signal, a guard interval setting circuit, and a clock signal generating circuit which drives both the circuits. Pilot signals, whose phases are set at prescribed values, at the starting points of a plurality of symbol sections and which have higher order frequencies with prescribed ratios to a frequency of a clock signal, are generated by the IFFT circuit. The pilot signals are sent out continuously across the plurality of symbol sections including guard interval sections and the pilot signals, are demodulated on the receiving device side, to generate a clock signal for driving an FFT.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to OFDM (Orthogonal Frequency Division Multiplexing).
cy Division Multiplexing)
The present invention relates to a signal transmitting apparatus, and particularly to an OFDM signal transmitting apparatus for receiving an OFDM signal suitable for digital mobile communication.

[0002]

2. Description of the Related Art A conventional OFDM signal transmitting apparatus will be described with reference to FIG. First, a digital information data signal is supplied to a serial / parallel conversion circuit 70 via an input terminal.
An error correction code is added as needed. The output signal of this circuit 70 is supplied to an IFFT circuit 71, and the output signal is supplied to a D / A converter 73 via a guard interval circuit 72 for reducing multipath distortion. Here, the signal is converted into an analog signal, and the next LPF 7
4 allows only the components of the required frequency band to pass. Output signals of the analog real and imaginary parts are supplied to a quadrature modulator 75, and an OFDM signal is output.

[0003] The OFDM signal is frequency-converted by a frequency converter 76 into a frequency band to be transmitted, and is supplied to the next transmitting unit 77, which transmits the signal through a linear amplifier and a transmitting antenna. Is done. The output signal of the intermediate frequency generation circuit 78 and the signal passed through the 90 ° shift circuit 78A are supplied to the quadrature modulator 75, respectively. The output signal of the circuit 78 is supplied to a clock signal generation circuit 79. The output clock signal of the circuit 79 is supplied to the serial-parallel conversion circuit 70, the IFFT circuit 71, the guard interval circuit 72, and the D / A converter 73, respectively.

Next, a conventional OFDM signal receiving apparatus for receiving a transmitted OFDM signal will be described with reference to FIG. The receiving section 80 amplifies the signal from the transmitting section 77 obtained by the receiving antenna constituting the same by a high frequency amplifier, and converts the carrier frequency to an intermediate frequency via a frequency converter 81 through an intermediate frequency amplifying circuit. 82, and further supplied to a quadrature demodulator 83. The output signal of the circuit 82 is supplied to an intermediate frequency generation circuit 89 via a carrier detection circuit 90. The output signal of the circuit 89 and the signal passed through the 90 ° shift circuit 89A are respectively supplied to the quadrature demodulator 83, and the output signals of the real and imaginary parts are decoded. The output signal of the quadrature demodulator 83 is the LPF 84
Is supplied to an A / D converter 85 via a digital converter, and is converted into a digital signal. The output signal of the quadrature demodulator 83 is also supplied to a synchronization signal generating circuit 91.

The output of the A / D converter 85 is sent to the FFT / QAM decoding circuit 8 through the next guard interval circuit 86.
7 is supplied. This FFT / QAM decoding circuit 87 is based on the supplied synchronization signal of the synchronization signal generation circuit 91,
Performs complex Fourier operation, real and imaginary part signals (real part, imaginary part) for each frequency of input signal
Is obtained, the level of the quantized digital signal transmitted by the digital information transmission carrier is obtained, and the digital information is decoded. The output signal of the FFT / QAM decoding circuit 87 is output via the parallel / serial conversion circuit 88. Here, if the intermediate frequency of the transmitting device and the intermediate frequency of the receiving device completely match, only the modulation component can be obtained, and there is no problem. However, the intermediate frequency generating circuit and the local oscillator of the frequency converter (not shown) ), If the frequency stability is not high, or if there is a phase error between the two output signals, the subsequent demodulation operation will be affected and the probability of occurrence of a symbol error will increase.

[0006]

In transmission and reception of an OFDM signal, it is very difficult to completely reproduce the phases of all the carrier waves on the receiving side without having a time-axis fluctuation component. However, since a guard interval circuit is set on the transmission side to reduce multipath distortion, when a transmission signal under such conditions is received, the transmission signal is divided into an effective symbol period portion and a guard interval portion. There is a problem that it is more difficult to reproduce the phase completely in the same state as the transmitting side. The present invention has been made by paying attention to the above points, and an OFDM signal transmitting apparatus in which a specific carrier of OFDM is set as a carrier for a pilot signal so that a synchronization relationship on a receiving side can be kept constant. The purpose is to provide.

[0007]

The present invention comprises the following means. That is, an IFFT and pilot signal generation circuit for supplying a digital information signal to generate a multi-level QAM modulation signal, a guard interval setting circuit configured to transmit a part of the modulation signal repeatedly for a predetermined time, and A clock signal generating circuit for generating a clock signal for driving the circuit, wherein the IFFT and pilot signal generating circuits maintain the same phase at the starting points of the plurality of effective symbol sections in adjacent effective symbol sections, In addition, the pilot signal of a higher frequency having an integer frequency ratio relationship with the clock signal is caused to be an odd multiple of half a wavelength in a guard interval section set by the guard interval setting circuit, so that the pilot signal is continued. Orthogonal frequency division multiplexing characterized by being configured to be transmitted. Signal transmission apparatus.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an OFDM signal transmitting / receiving apparatus according to the present invention will be described below with reference to FIGS. FIG. 1 shows an embodiment of an OFDM signal transmitting apparatus. Digital data transmitted here is a compressed audio or video signal. An OFDM signal transmitting apparatus arranges a large number of carriers orthogonally, and transmits independent digital information on each carrier. Since the carriers are orthogonal, the spectrum of the adjacent carrier is determined by the frequency position of the carrier. Becomes zero. IFFT circuit technology is used to create this orthogonal carrier. During a time interval T which is a window section in the IFFT, N
By performing an inverse DFT (Discrete Fourier Transform) using a plurality of complex numbers, an OFDM signal can be generated, and each point of the inverse DFT corresponds to a modulation signal output. The N is also referred to as an IFFT or FFT cycle, and is described in detail by Corona (issue date: 19
(May 20, 1993), "Television Society, edited by Seiki Imai, Signal Processing Engineering", pp. 74-75.

The basic specifications of the apparatus according to this embodiment shown in FIGS. 1 and 2 are as follows. (a) Center carrier frequency: 100 MHz (b) Number of carriers for transmission: 248 waves (c) Modulation method: 256 QAM OFDM (d) Number of carriers used: 257 waves (e) Transmission bandwidth: 100 kHz, used bandwidth: 99 kHz ( f) Transfer rate: 750 kbps (g) Guard interval: 60.6 μsec As shown in FIG. 1, for example, a digital information signal that is an audio or video signal in which an information signal is compressed by an encoding method such as MPEG is input to an input terminal. The signal is supplied to the serial / parallel conversion circuit 2 via an interface 1, and an error correction code is added as necessary. In this circuit 2, input signals are arranged as 256QAM modulation signals and output. This 256QA
M-modulation defines 16 levels in the amplitude direction and 16 levels in the angle direction for each carrier to transmit information.
In this method, 256 values of 6 × 16 are specified and transmitted.
In this embodiment, information is transmitted using 248 waves out of 257 carriers, and the remaining 9 waves are used for calibration and for transmitting other auxiliary signals.

The serial-to-parallel conversion circuit 2 is configured to output 248 bytes of digital data during one symbol period, that is, 248 sets of 4-bit parallel data during one symbol period. The output signal of the serial-parallel conversion circuit 2 is IF
FT and pilot signal generation circuit 3. The circuit 3 operates by the clock signal output from the clock signal generation circuit 10 and operates by 2
56QAM modulation is performed, and each output signal is output as a real and imaginary component. The IFFT / pilot signal generation circuit 3 uses an IFFT circuit having a period of N. Discrete frequency point information corresponding to N discrete frequency points (sample points) in each effective symbol period set by the IFFT circuit Are output from the IFFT and pilot signal generation circuit 3. The Nyquist frequency is 1 of the sample clock frequency in the IFFT of the period N.
/ 2, and the pilot signal is transmitted as information of the Nyquist frequency, that is, Nyquist frequency information. Since the Nyquist frequency is の of the sample clock frequency, the receiving apparatus can decode and multiply the Nyquist frequency information to generate a sampling position signal (sample clock signal) for operating the FFT circuit. . The Nyquist frequency information is input to the real part input terminal R of the IFFT and the IFFT of the pilot signal generation circuit 3.
It is obtained by applying a signal of a constant level to the terminal of the N / 2th frequency in the (imaginary part input terminal I).

The output signals of the IFFT / pilot signal generation circuit 3 are supplied to a guard interval setting circuit 4 having a next RAM (random access memory) 4A, and the guard interval setting circuit 4 causes a multipath signal on a transmission path to be transmitted. A guard interval gi of a predetermined section for reducing distortion is set as shown in FIG. The guard interval setting circuit 4 is operated by the clock signal output from the clock signal generation circuit 10 and changes the last part in the window section (effective symbol period ts) obtained from the IFFT and pilot signal generation circuit 3 to the window section. Place it just before. In order to set the guard interval, the guard interval setting circuit 4 reads out the signal from the IFFT / pilot signal generation circuit 3 which has been taken into the RAM (4A) of the guard interval setting circuit 4 and reads the last period of the effective symbol period ( This period is set equal to gi.), and returns to the beginning of the effective symbol period, reads out the data of the effective symbol period ts, and sends out the signal of the symbol period ta. The Nyquist frequency information (pilot signal)
It is transmitted even within the guard interval, but before and after IFF
In order to maintain continuity with the T window section signal, the transmitted pilot signal is made to have an integer wavelength within the guard interval.

Although the case where the Nyquist frequency is used as the pilot signal has been described, the Nyquist frequency is not necessarily required as long as it has a simple integer ratio relationship with the sample clock signal. A thing may be used. When considering an IFFT having a period M, a pilot signal is arranged at a position １ ／ of the Nyquist frequency, that is, at the M / 4th frequency, and the carrier to be transmitted by OFDM is M / Mth from the first in the IFFT.
The signals output up to the fourth and from the 3M / 4th to the Mth are used. Thus, the period M = 2N
, An IFFT output signal equivalent to the case of using an IFFT with a period of N can be obtained. Therefore, a continuous pilot signal including the guard interval can be transmitted, and the pilot signal is decoded.
By multiplying by 4, a sample clock signal can be obtained. If the window section signal information of the FFT can be separately decoded, the FFT operation of the OFDM signal can be performed in combination with the sample clock signal obtained in this embodiment, and the OFD signal can be obtained.
The decoding of the M signal can be performed.

Next, the symbol period set by the guard interval setting circuit 4 will be described with reference to FIG. First, the used bandwidth is 99 kHz, and the cycle of the IFFT is N = 25.
When the number is 6, the effective symbol frequency fs and the effective symbol period ts are respectively as follows. fs = 99,000 / 256 = 387 Hz ts = 1 / fs = 2586 μsec In addition, when the guard interval period gi, which is a multipath distortion removal section, is determined for three pilot signal wavelengths,
gi is set as follows. gi = (1 / 49,500) × 3 = 60.6 μsec At this time, the symbol period ta and the symbol frequency fa are respectively as follows. ta = ts + gi = 2586 + 60.6 = 2646.6
μsec fa = 1 / ta = 378 Hz

The output signal of the guard interval setting circuit 4 is supplied to a D / A converter 5 where it is converted into an analog signal, and only components in a required frequency band are passed by the next LPF 6. Real analog value,
The imaginary output signal is supplied to the next quadrature modulator 7,
The modulator 7 is supplied with the output signal of the 10.7 MHz intermediate frequency generation circuit 9 and the signal passed through the 90 ° shift circuit 8, respectively, and outputs an OFDM signal. This OF
The DM signal is frequency-converted by a frequency converter 11 into a frequency band to be transmitted, supplied to the next transmission unit 12, and transmitted via a linear amplifier and a transmission antenna constituting the same. The output signal of the 10.7 MHz intermediate frequency generation circuit 9 is also supplied to the clock signal generation circuit 10. In the clock signal generation circuit 10, a clock signal for driving the IFFT and pilot signal generation circuit 3 and a clock signal for driving the guard interval setting circuit 4 are a common clock signal supplied from the intermediate frequency generation circuit 9. Generated based on 248
Since the set of 4 + 4 bits of parallel data is transmitted by 248 carriers, the transmission rate of the present apparatus is 248 bytes per symbol period. Therefore, the transmission rate per second is approximately 750 Kbits.

Next, the phase relationship between the guard interval, the symbol period, and the synchronization signal (pilot signal) will be described with reference to the drawings. Here, FIGS. 7, 8 and 1
The description related to 0 is described as a reference example of the present embodiment. In FIG. 7 shown as a reference example, a synchronization signal (pilot signal) having the same phase is generated in each symbol period.
A case where a synchronization signal of an integer wavelength exists in the guard interval will be described. (This is a first example of generating a continuous synchronization signal without reversing the polarity.) IFFT shown in FIG. 7 is synonymous with the effective symbol period and the IFFT period, and is the end portion (right portion) of the IFFT period
1 cycle is just before the IFFT period (left part)
Of the guard interval G. In this example,
Synchronous signal (pilot signal) in phase for every IFFT period
Are generated, and the synchronization signal (pilot signal) has an integer wave in the guard interval, so that the pilot signal is continuously generated over a plurality of symbol periods. The case of FIG. 3 described above is the same as the case of FIG. 7, and since the synchronization signal (pilot signal) has an integer wave also in the guard interval section, the pilot signal is continuously generated over a plurality of symbol periods. I have.

In FIG. 8 shown as a reference example, a case will be described in which a synchronization signal (pilot signal) having the same phase is generated in every other symbol period and a synchronization signal having an odd multiple of half a wavelength is present in the guard interval. . (This is a second example of generating a continuous synchronization signal without inverting the polarity.) IFFT is synonymous with the effective symbol period and the IFFT period, and is a half cycle of the end portion (right portion) of the IFFT period. Is used as it is as a signal of the guard interval before (left) of the IFFT period. In this example, the IFFT
A synchronization signal (pilot signal) of opposite polarity is generated for each period, and a synchronization signal having an odd multiple of half a wavelength also exists in the guard interval, so that the pilot signal is continuous over a plurality of symbol periods (symbol periods). Has been generated.

Referring to FIG. 9, a case where a synchronization signal exists in the guard interval G at an odd multiple of a half wavelength will be described. (This is a first example of generating a synchronization signal with inverted polarity.) In this case, the polarity of the pilot signal is inverted at the start point of the guard interval, and the phase of the pilot signal for each symbol period is the same. . That is, the terminal voltage corresponding to the frequency at which the IFFT synchronization signal for generating the frequency division multiplex signal is generated is fixed for each symbol, and the synchronization signal having the same phase is always generated. Therefore, when the guard interval is an odd multiple of half a wavelength, the synchronization signal becomes a continuous signal if the polarity of the synchronization signal is inverted every other symbol period on the receiving device side. In this case, it is possible to detect a synchronization signal using a PLL circuit in a phase synchronization circuit as shown in FIG.

Referring to FIG. 10 shown as a reference example, a case where a synchronization signal (pilot signal) exists at an even multiple of a half wavelength in a guard interval will be described. (This is a second example of generating a synchronization signal with inverted polarity.) As shown in FIG. 10, when a synchronization signal (pilot signal) existing in a guard interval is an integer wave (an even multiple of half a wavelength). Even if there is a synchronization signal, if the synchronization signal is inverted and output every other symbol period as in the case of FIG. 9, a synchronization output in which the polarity is inverted for each symbol is obtained. Also in this case, the synchronization signal can be detected using a PLL circuit as shown in FIG.

FIG. 11 shows a phase synchronization circuit for detecting a synchronization signal inverted every other symbol period. This phase synchronization circuit includes a phase comparator PD2 (112), an Amp
(Amplifier 113), LPF (114), and VCO circuit (115) are provided with a signal switch 116 composed of an exclusive OR at the VCO output of a PLL circuit. Phase comparator PD1 (111)
Constitutes a synchronous detection circuit having the VCO output of the phase locked loop as an input. The frequency division multiplexed signal including the synchronization signal applied to the input terminal 110 is input to both the phase synchronization circuit and the synchronization detection circuit PD1 (111). This phase locked loop circuit includes a phase comparator PD2 (112) and an amplifier (1
13), a PLL composed of an LPF (114), a VCO (115), and a signal switch (116). The signal switch (1) is switched according to the output of the PD1 (111) that has been synchronously detected.
Although the configuration is such that the output of the VCO circuit 115 of the PLL is inverted in 16), the synchronization signal whose polarity is inverted for each symbol is detected by the synchronization detection circuit and the phase comparator PD2 (112) constituting the PLL Has the polarity inverted V
Since the CO output is supplied, the lock operation is continuously performed even for the synchronization signal whose polarity is inverted.

FIG. 12 shows output waveforms at terminals B and A in FIG. Output A is a synchronization signal output waveform, and output B is a symbol synchronization signal transmitted with its polarity inverted for each symbol period (symbol period). FIG. 13 shows another embodiment of FIG. 11, in which the signal switch 136 includes a phase comparator PD2.
(132) and the amplifier 133. The synchronous signal is detected at the same time as the synchronous signal is inverted, and the polarity of the error signal is inverted. The operation is performed in the same manner as in FIG. In any case, even if the synchronization signal is inverted every other symbol period (symbol period), it is detected and the PL is detected.
To invert the characteristics of the L loop, the VCO continues to operate continuously without being inverted. Therefore, decoding of the synchronization signal can be performed normally.

Next, an embodiment of an OFDM signal receiving apparatus applied to the present invention will be described with reference to FIGS. Each component of the receiving device is configured by a circuit that operates in the opposite direction to the transmitting device. The receiving unit 20 amplifies the signal from the transmitting unit 12 obtained by the receiving antenna constituting the receiving unit 20 with a high-frequency amplifier and supplies the amplified signal to the frequency converter 21. This output signal is supplied to the intermediate frequency amplifier circuit 22,
The signal is output from the intermediate frequency amplifier circuit 22 as a reception signal of a predetermined level. The output signal of the intermediate frequency amplifier circuit 22 is
Quadrature demodulator 23 and carrier detection (carrier extraction) circuit 2
9 respectively. FIG.
Phase comparator (multiplier) 41, LPF 42, V
PLL composed of a CO circuit 43 and a 1/4 frequency dividing circuit 45
An intermediate frequency oscillation circuit 31 having a circuit and supplied with the output signal is a circuit for extracting a center carrier with a small phase error.

In this embodiment, carriers for transmitting information are arranged adjacent to each other at every 378 Hz which is a symbol frequency, and constitute an OFDM signal. The information carrier adjacent to the center carrier is also separated by only 378 Hz. The center carrier needs to transmit information without being affected by the adjacent information carrier, and a circuit with high selectivity is used. In this embodiment, the center carrier is extracted using a PLL circuit.
/ 2, a crystal oscillator that oscillates at about ± 200 Hz (V
CXO) as a voltage controlled oscillator (VCO) 43,
Activate the circuit. The LPF used in the PLL circuit also has a cutoff frequency sufficiently lower than 378 Hz. The output signal of the intermediate frequency generation circuit 31 and the signal passed through the 90 ° shift circuit 30 are used as a multiplier 40,
The output signals of the real and imaginary parts (real part, imaginary part) are supplied to the quadrature demodulator 23 having 41, respectively. The real part and imaginary part output signals are LPF2
4 for passing a signal of a required frequency band transmitted as OFDM signal information, sampling an input analog signal, and supplying an output signal to an A / D converter (sampling circuit) 25; Convert to digital signal.

In the sample synchronizing signal generating circuit 32, a sample clock signal before frequency multiplication is generated by a PLL circuit which is phase-synchronized with a pilot signal, and an analog output signal of the quadrature demodulator 23 is supplied to this circuit.
The PLL is phase-synchronized with the pilot signal transmitted as a continuous signal in each symbol section including the guard interval period, and a demodulated pilot signal is obtained. In the transmitting device, the pilot signal is set to a predetermined integer ratio with respect to the sample clock frequency, and performs frequency multiplication according to the frequency ratio to obtain a sample clock signal. The guard interval processing circuit 26 can obtain an effective symbol period signal of the period ts at an arbitrary timing within the symbol period ta from the transmitted signal, and from the effective symbol period signal of which the influence of the multipath distortion is smaller, Then, an output signal is supplied to the FFT / QAM decoding circuit 27.

The symbol synchronization signal generating circuit 33 for detecting the symbol period detects the symbol period. The next FFT and QAM decoding circuit 27 is supplied with the obtained clock synchronization signal and symbol synchronization signal,
Performs complex Fourier operation, real and imaginary part signals (real part, imaginary part) for each frequency of input signal
Find the level of The real part, imaginary part signal level of each frequency obtained in this way is compared with the real part of each carrier to be transmitted, and the demodulated output of the reference carrier for transmitting the reference value of the imaginary part, The level of the quantized digital signal transmitted by the digital information transmission carrier is determined, and the digital information is decoded. This circuit 2
7 is output via the parallel / serial conversion circuit 28.

Next, referring to FIG.
The sample synchronization (sample clock) signal generation circuit 32 will be described below. The purpose of this circuit is to extract a pilot signal transmitted at a constant level and generate an accurate sample synchronization (sample clock) signal based on the extracted pilot signal. First, the VCO circuit 43 constituting the carrier detection circuit 29 is oscillated at a frequency of 42.8 MHz, which is four times the intermediate frequency 10.7 MHz. VCO circuit 4
The output signal of No. 3 is supplied to multipliers 40 and 41 via 1/4 frequency dividing circuits 44 and 45, respectively. One multiplier 41
The output signal is supplied to the LPF 42, and a component equal to or lower than the symbol frequency is extracted. The output signal controls the VCO circuit 43. A loop including the multiplier 41, the LPF 42, the VCO circuit 43, and the frequency divider 45 forms a PLL circuit.

The intermediate frequency-amplified signal is applied to the input terminals of the multipliers 40 and 41, and orthogonal decoding is performed by this circuit, and output signals of a real part and an imaginary part are obtained. The sample synchronization signal generation circuit 32 is supplied with the real part output signal from the quadrature demodulator 23 and detects a Nyquist frequency component transmitted as a pilot signal. Dividing ratio variable circuit (V
The output signal of the VCO circuit 43 is supplied to the (CO circuit) 50, and the frequency division ratio is set to 1/426 to 1/438. The multiplier 52 in the sample synchronization signal generating circuit 32 is supplied with the output signal from the quadrature demodulator 23 and the signal of the VCO circuit through the 1/2 frequency dividing circuit 51, and operates as a phase comparator. Do.

The output signal of the multiplier 52 is passed by the LPF circuit 53 so that only the error signal relating to the frequency control passes. The delay circuit 54 and the addition circuit 55 are circuits for attenuating adjacent carrier components, and have a symbol frequency of 387.
The characteristic has a dip in Hz. VCO circuit
(Division ratio variable circuit) In the PLL circuit composed of 50, a multiplier 52, and an LPF 53, a VCO output signal synchronized with a continuous pilot signal included in a real part output signal of the quadrature demodulator 23 of the carrier extraction unit is output. Oscillated, 99kHz
As a sample clock output signal. In the above embodiment, the case where an IFFT having a period of 256 is used to generate carriers of 257 waves has been described. However, as another embodiment, an example in which an IFFT having a period of 512 is used will be described below. In the embodiment using the IFFT having a period of 512, the Nyquist frequency is not used as the pilot frequency, but a high-order frequency having a simple integer ratio relationship with the sample clock signal is used.

That is, when considering an IFFT with a period M, a pilot signal is arranged at a position of 1/2 of the Nyquist frequency, that is, at the M / 4th frequency, and the carrier transmitted by OFDM is more than the first in the IFFT. Signals output as the M / 4th and the 3M / 4th to the Mth are used. Thus, the IF of the period M = 2N
Even if the FT is used, an output signal of the IFFT equivalent to the case of using the IFFT having the period N can be obtained. Therefore, a continuous pilot signal including the guard interval can be transmitted, and a sample clock signal can be obtained by decoding this pilot signal and quadrupling it.

In the sample synchronizing signal generating circuit used at this time, the frequency of the pilot signal is the same as that of the embodiment in which the period N is 256, but the FF shown in FIG.
The sample clock frequency for driving the T, QAM decoding circuit 27 is twice as long as the period N is 256. Accordingly, a double 198 kHz sample clock signal is output. Therefore, this sample synchronization signal generation circuit
The frequency division ratio of the frequency division ratio variable circuit 50 is １ ／
13 to 1/219, and the fact that the dividing ratio of the 1/2 divider circuit 51 is 1/4, and the other configuration is the same as that of FIG. 4 and the description thereof is omitted. .

[0030]

In the OFDM signal transmitting apparatus according to the present invention, the guard interval period is determined by the same sample clock as that used to drive the IFFT and pilot signal generation circuit, and the pilot signal used for transmitting the sample clock information has the guard interval. The period is also set to be continuous, and the frequency spectrum of the actually transmitted pilot signal is single. Therefore, a pilot signal having no jitter can be decoded in the receiving apparatus, and it becomes easy to set the same time relationship between the IFFT circuit operating in the transmitting apparatus and the FFT circuit operating in the receiving apparatus.
The FFT operation can be performed in a form close to the signal that has been subjected to the FT operation, and more accurate information transmission becomes possible. Further, the phase synchronization method according to the present invention can be performed continuously or
Synchronization information can be normally decoded with respect to synchronization signal information inverted and transmitted for each symbol period (symbol period). This means that even when the time-division synchronization signal is decoded with phase noise in mobile reception or the like, it can be received while correcting it, so that the clock synchronization signal and the symbol position signal can be decoded well. Furthermore, since symbol synchronization information is inserted into a pilot signal transmitted as an information signal, the synchronization signal can be decoded before a time-division synchronization signal arrives. This has the effect of decoding a frequency division multiplexed signal.

[Brief description of the drawings]

FIG. 1 is a block diagram of an embodiment of an OFDM signal transmitting apparatus according to the present invention.

FIG. 2 is a block diagram of an embodiment of an OFDM signal receiving apparatus applied to the present invention.

FIG. 3 is a diagram illustrating a relationship between a symbol period of an OFDM signal and a guard interval according to the present invention.

FIG. 4 is a block diagram of a carrier extraction unit and a sample synchronization signal generation unit of the OFDM signal receiving apparatus according to the embodiment applied to the present invention.

FIG. 5 is a block diagram of a conventional OFDM signal transmission device.

FIG. 6 is a block diagram of a conventional OFDM signal receiving device.

FIG. 7 is a diagram illustrating a relationship between a synchronization signal and a symbol period.

FIG. 8 is a diagram illustrating a relationship between a synchronization signal and a symbol period.

FIG. 9 is a diagram illustrating a relationship between a synchronization signal and a symbol period according to the present invention.

FIG. 10 is a diagram showing a relationship between a synchronization signal and a symbol period.

FIG. 11 is a diagram illustrating an example of a phase synchronization circuit.

FIG. 12 is a diagram illustrating an output waveform of a phase locked loop.

FIG. 13 is a diagram showing another example of the phase synchronization circuit.

[Explanation of symbols]

 Reference Signs List 2 serial-parallel conversion circuit 3 IFFT, pilot signal generation circuit 4 guard interval setting circuit 4A RAM (random access memory) 5 D / A demodulator 6, 24, 42, 53, 114, 134 LPF 7 quadrature modulator 8, 30 90 ° shift circuit 9, 31 Intermediate frequency generation circuit 10 Clock signal generation circuit 11, 21 Frequency converter 12 Transmitter 20 Receiver 23 Quadrature demodulator 25 A / D converter (sampling circuit) 26 Guard interval processing circuit 27 FFT, QAM decoding circuit 28 Parallel-serial conversion circuit 29 Carrier detection circuit 32 Sample synchronization signal generation circuit 33 Symbol synchronization signal generation circuit 40, 41, 52 Multipliers (phase comparators) 43, 50, 115, 135 VCO circuits 44, 45 1 / 4 frequency dividing circuit 51 1/2 frequency dividing circuit 111, 112, 131 , 132 Phase comparator (PD) 116, 136 Signal switch

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenji Sugiyama 3-12 Moriyacho, Kanagawa-ku, Yokohama-shi, Kanagawa Japan F-term (reference) 5K022 DD01 DD13 DD18 DD23 DD33 DD42

Claims (1)

[Claims] A digital information signal is supplied to a multi-valued QAM.
IFFT and pilot signal generation circuit for generating a modulation signal, a guard interval setting circuit configured to repeatedly transmit a part of the modulation signal for a predetermined time, and a clock signal for generating a clock signal for driving both circuits A generator circuit, wherein the IFFT and pilot signal generation circuits maintain the phases at the start points of the plurality of effective symbol sections in the same phase in adjacent effective symbol sections, and have a frequency ratio relationship between the clock signal and the integer. A pilot signal of a certain higher-order frequency is made to exist in an odd multiple of a half wavelength in a guard interval section set by the guard interval setting circuit, so that the pilot signal is continuously transmitted. Orthogonal frequency division multiplex signal transmission device.