Ofdm signal transmitting method and ofdm signal receiving device

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to an OFDM signal transmission method suitable for digital television broadcasting, digital audio broadcasting, or digital television material transmission equipment, and in particular, an OFDM signal transmission method for accurately and stably reproducing a reference carrier frequency signal on the receiving side. And the OFDM signal receiver.

【0002】

[Overview of the Invention] The present invention relates to a method of transmitting an OFDM (Orthogonal Frequency Division Multiplexing) signal, and inserts one or more types of unmodulated carrier signals at predetermined positions in a synchronous signal section of an OFDM signal. Then, the signal is transmitted intermittently, and on the receiving device side, those signals are taken out and a frequency lock loop is configured to lock the frequency of the voltage control oscillator that generates the signal of the reference transport frequency, so that accurate and stable reference transport is performed. It reproduces the carrier of the frequency.

【0003】

[Conventional technology]

The OFDM signal transmission method has many features such as strong multipath, relatively high frequency utilization efficiency, a spectrum close to white Gaussian noise, and less likely to interfere with other services, especially for mobile objects. It is an excellent transmission method for digital audio broadcasting, digital television broadcasting, and digital television material transmission.

【0004】

Conventionally, regarding the reproduction of the reference carrier frequency signal for demodulating the OFDM modulated signal, the frequency shift is caused by the method of reproducing by frequency locking based on the reproduced frame synchronization signal or by detecting the phase error of the received data. A method of making corrections is used.

【0005】

[Problems to be Solved by the Invention]

However, an accurate and stable reference can be used in either of the method of reproducing by frequency locking based on the frame synchronization signal and the method of correcting the frequency deviation by detecting the phase error of the received data. There is a problem that the carrier frequency signal cannot be reproduced.

【0006】

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an OFDM signal transmission method and an OFDM signal receiving device capable of reproducing an accurate and stable reference carrier frequency signal.

【0007】

[Means for solving problems]

In order to achieve the above object, the invention of claim 1 inserts one or more types of unmodulated carrier signals of different frequencies in the same repeating pattern at predetermined positions in the synchronous signal section of the OFDM signal on the transmitting side. It is characterized in that it transmits intermittently, and on the receiving side, it locks to the frequency of the highest level unmodulated carrier signal among the unmodulated carrier signals and reproduces the reference carrier frequency signal for demodulating the OFDM signal. It is a thing.

【0008】

According to the above configuration, the level of the OFDM signal is lowered due to the frequency characteristics on the transmission line, etc., but it is locked to the frequency of the unmodulated carrier signal with the smallest level drop among the plurality of unmodulated carrier signals. Since the reference carrier frequency signal is reproduced, accurate and stable reference carrier frequency signal can be reproduced.

【0009】

The invention of claim 2 is characterized in that, in the OFDM signal transmission method according to claim 1, the insertion level of the unmodulated carrier signal is made higher than that of other information transmission signals on the transmitting side.

【0010】

According to the above configuration, since the insertion level of the unmodulated carrier signal is set to be higher than that of other OFDM signals (information transmission signals), more stable reproduction is possible.

【0011】

The invention of claim 3 is an intermittently transmitted OFDM signal in which one or more types of unmodulated carrier signals having different frequencies are inserted at predetermined positions in a synchronous signal section of the OFDM signal in the same repeating pattern on the transmitting side. A means for receiving and extracting one or more kinds of unmodulated carrier signals having different frequencies from the received signals, a means for extracting the highest level unmodulated carrier signal among these signals, and the extracted none. It is characterized by including a voltage-controlled oscillator loop means that locks to the frequency of the modulated carrier signal, and a means that reproduces a reference carrier frequency signal for demodulating the OFDM signal from the loop means.

【0012】

According to the above configuration, it is possible to reproduce an accurate and stable reference carrier frequency signal as in the invention of claim 1.

【0013】

According to the invention of claim 4, in the OFDM signal receiving device according to claim 3, the means for extracting the unmodulated carrier signal from the received signal is an unmodulated carrier signal inserted at a predetermined position in the synchronous signal section of the OFDM signal. It is provided with a band blocking filter for the frequency of the unmodulated carrier for detecting the insertion period of the filter, and a means for gate the insertion period of the unmodulated carrier signal in the received signal by the gate signal generated from the output of this filter. It is a feature.

【0014】

According to the above configuration, the unmodulated carrier signal inserted at a predetermined position in the synchronous signal section of the OFDM signal is detected by using the band blocking filter. Therefore, in order to extract the unmodulated carrier signal, It is not necessary to transmit another signal for generating a gate signal, and the gate signal can be created only from the unmodulated carrier signal transmitted intermittently, so that an efficient transmission method can be configured. Further, even if the frequency of the OFDM signal deviates, the transmission period of the unmodulated carrier signal can be stably detected by making the attenuation frequency width of the band blocking filter wider than the deviation. ..

【0015】

BEST MODE FOR CARRYING OUT THE INVENTION

<First Embodiment> FIG. 1 shows an example of an unmodulated carrier signal of a reference carrier frequency transmitted from the transmitting side in the first embodiment of the OFDM signal transmission method according to the present invention, and FIG. Shows the circuit configuration of the first embodiment of the OFDM signal receiving device according to the present invention.

【0016】

As shown in FIG. 1, on the transmitting side, a reference carrier frequency signal (frequency f), which is the center frequency of the OFDM transmission frequency band, is located at a predetermined position in the synchronization signal section of the OFDM signal._cUnmodulated carrier signal, hereinafter, as appropriate, "f"_cA signal ") is inserted and transmitted intermittently. On the receiving side, it is transmitted intermittently f_cThe signal is used for frequency locking, and the reference carrier frequency signal is reproduced. This enables accurate and stable reproduction of the reference carrier frequency signal. Also, f for reference frequency lock_cIf the signal level is made higher than other OFDM signals (information transmission signals), more stable reproduction becomes possible.

【0017】

As shown in FIG. 2, the apparatus for reproducing an OFDM signal includes a bandpass filter (BPF) 101, multiplexers 103 and 104, a voltage controlled oscillator (VCO) 105, and a π / 2 phase shifter 108. In addition, the reference carrier frequency signal detection circuit (hereinafter, "f")_cIt is called "detection circuit". ) 111, a bandpass filter (BPF) 113, a 1 / N frequency divider 114,116, a phase comparator 117, a loop filter 118, and a control circuit 119.

【0018】

The bandpass filter 101 inputs the received IF signal 100, generates an OFDM modulated signal 102, and outputs it.

【0019】

In the multiplexer 103, the baseband I signal 109 of the OFDM signal is generated from the OFDM modulated signal 102 based on the output signal 106 of the voltage controlled oscillator 105. Further, in the multiplexer 104, the baseband Q signal 110 of the OFDM signal is generated from the OFDM modulation signal 102 based on the output signal 107 of the phase shifter 108 in which the output signal of the voltage controlled oscillator 105 is shifted by π / 2. .. The generated baseband I signal and Q signal are supplied to an FFT circuit (not shown), where they are subjected to a discrete Fourier transform to become received data.

【0020】

On the other hand, f_cIn the detection circuit 111, the OFDM modulation signal 102 output from the bandpass filter 101 is input to generate the reference carrier frequency signal 112 and supplied to the bandpass filter 113, and the reference carrier frequency signal controls the frequency lock. It is supplied to the control circuit 119 as a signal 120 indicating the period to be performed. This f_cAs shown in FIG. 3, the detection circuit 111 is composed of a band blocking filter (BEF) 201, a gate signal creation circuit 203, and a reference frequency signal extraction circuit 205.

【0021】

The band blocking filter 201 attenuates the reference carrier frequency signal, and its frequency characteristics are shown in FIG. In the figure, the OFDM spectrum is shown by the dashed line, and the band-blocking filter (BEF) 201 is the reference carrier f, which is the central carrier._cHas the property that the relative level drops sharply. Therefore, in this band blocking filter 201, f is shown in FIG. 5 (A) from the OFDM signal 200 shown in FIG. 5 (A)._cA signal (BEF passing signal) 202 is generated so that the period in which the signal is transmitted is almost no signal. The BEF pass signal 202 is input to the gate signal creation circuit 203, where the gate signal 204 shown in FIG. 6C is generated. Then, in the reference carrier frequency signal extraction circuit 205, the generated gate signal is f for the active time._cPass the signal. As a result, f from the OFDM signal 200_cOnly the signal is extracted.

【0022】

Therefore, this f_cAccording to the detection circuit 111, in order to extract the reference carrier frequency signal, it is not necessary to transmit another signal for generating the gate signal, and the gate signal is created only from the reference carrier frequency signal transmitted intermittently. Is possible, and an efficient transmission method can be configured.

【0023】

Further, as shown in the BEF characteristics in FIG. 4, even if there is a frequency shift due to the Doppler effect during propagation or a frequency shift of the local signal oscillator of the receiver, the attenuation frequency width of the BEF is made wider than the shift. , It becomes possible to detect the transmission period of the reference carrier frequency signal, and it becomes possible to reproduce the reference carrier frequency signal stably.

【0024】

In the bandpass filter 113, f_cOnly the signal passes and is output to the frequency divider 114. In the 1 / N divider 114, the supplied f_cThe frequency of the signal is divided by I / N and supplied to the phase comparator 117.

【0025】

A phase-locked loop (PLL) is composed of a phase comparator 117 and a loop filter 118, and the 1 / N divider 114 f._cThe phase of the signal whose frequency is divided by I / N and the signal whose output signal from the voltage controlled oscillator 105 is divided by 1 / N by the 1 / N divider 114 is compared and the phase difference is calculated. A proportional signal is supplied to the control circuit 119 via the loop filter 118.

【0026】

In the control circuit 119, the signal proportional to the phase difference and f_cA signal 120 indicating a period for performing frequency lock control output from the detection circuit 111 is input, and the period for performing frequency lock control, that is, f._cThe output signal 106 of the voltage controlled oscillator 105 has a frequency f only when the signal is received._cIt is controlled to converge to.

【0027】

As described above, according to the first embodiment, on the transmitting side, the center frequency f of the OFDM transmission frequency band is set at a predetermined position in the synchronization signal section of the OFDM signal._cThe reference carrier frequency signal of the above is inserted and transmitted intermittently, and in the OFDM signal receiver, the reference carrier frequency f is transmitted from the received signal._cTake out the signal and this f_cSince the reference carrier frequency signal is reproduced by the voltage controlled oscillator loop that locks to the frequency of the signal, the reference carrier frequency signal can be reproduced accurately and stably.

【0028】

<Second Embodiment> FIG. 6 shows an example of an unmodulated carrier signal transmitted from the transmitting side in the second embodiment of the OFDM signal transmission method according to the present invention, and FIG. 2 shows the present invention. The circuit configuration of the second embodiment of the OFDM signal receiving device is shown.

【0029】

As shown in FIG. 6, on the transmitting side, the center frequency f of the OFDM transmission frequency band_cAgainst f_c× A / N = f₁× B / N f_c× C / N = f₂× D / N (A, B, C, D, N are arbitrary integers) Two frequencies in a relationship f₁, f₂Is inserted into a predetermined position in the synchronous signal section of the OFDM signal and is transmitted intermittently. Intermittently transmitted on the receiving side f₁Signal or f₂The higher level of the signals is used for frequency locking, and the reference carrier frequency signal is reproduced. As a result, even when the level of any of the unmodulated carrier signals is lowered due to fluctuations in frequency characteristics on the transmission path, it is possible to reproduce a reference carrier frequency signal that is more accurate and stable. Also, f for reference frequency lock₁Signal or f₂If the level of the signal f is made higher than that of other OFDM signals (information transmission signals), more stable reproduction becomes possible.

【0030】

The apparatus for reproducing the OFDM signal in the second embodiment is a bandpass filter (BPF) 301, a multiplexer 303, 304, a voltage controlled oscillator (VCO) 305, and a π / 2 phase shifter 308, as shown in FIG. And have. Also, the unmodulated carrier frequency f₁Signal detection circuit (hereinafter, "f"₁It is called "detection circuit". ) 311 and bandpass filter (BPF) 313, level detector 314, B / N divider 315, A / N divider 317, phase comparator 318, and loop filter 319. There is. In addition, the unmodulated carrier frequency f₂Signal detection circuit (hereinafter, "f"₂It is called "detection circuit". ) 321 and bandpass filter (BPF) 323, level detector 324, D / N divider 325, C / N divider 326, phase comparator 327, loop filter 328, and control circuit. It is configured with 332.

【0031】

In this receiving device as well, similarly to the receiving device in the first embodiment shown in FIG. 2, the OFDM modulated signal 302 generated from the received IF signal 300 by the band passing filter 301 is supplied to the multiplexers 303 and 304, and the multiplexer 303 has a voltage. The baseband I signal 309 of the OFDM signal is generated based on the output signal 306 of the control oscillator 305, and the multiplexer 304 is based on the output signal 307 of the phase shifter 308 which is the phase shift of the output signal of the voltage control oscillator 305 by π / 2. The base band Q signal 310 of the OFDM signal is generated from the OFDM modulated signal 302. These baseband I signal Oyo generated beauty Q signals are supplied to the FFT circuit (not shown), the reception data where it is a discrete Fourier transform.

【0032】

Also, f₁In the detection circuit 311 as in the circuit configuration shown in FIG. 3, the blocking frequency is f.₁The unmodulated carrier frequency f from the OFDM modulated signal 302 output from the bandpass filter 301 using the band blocking filter.₁The signal 312 is extracted and supplied to the bandpass filter 313. In the bandpass filter 313, f₁Only the signal is passed and supplied to the level detector 314. In level detector 314, the supplied f₁If the signal level of the signal is above the specified value, f₁A level signal 330 is generated and supplied to the control circuit 332, and f₁The signal is supplied to the B / N divider 315. In the B / N divider 315, the supplied f₁The frequency of the signal is divided by B / N and supplied to the phase comparator 318.

【0033】

In the phase comparator 318, f divided by B / N₁The phase difference between the signal and the output signal of the voltage controlled oscillator 305 divided by the A / N divider 317 is calculated, and the phase difference proportional signal 320 is input to the control circuit 332 via the loop filter 319. Be supplied.

【0034】

On the other hand, f₂In the detection circuit 321, the blocking frequency is f.₂The unmodulated carrier frequency f from the OFDM modulated signal 302 output from the bandpass filter 301 using the band blocking filter.₂The signal 322 is extracted and supplied to the bandpass filter 323. For bandpass filter 323, f₂Only the signal is passed and fed to the level detector 324. In the level detector 324, the supplied f₂If the signal level of the signal is above the specified value, f₂A level signal 331 is generated and supplied to the control circuit 332, and f₂The signal is supplied to the D / N divider 325. In the D / N divider 325, the supplied f₂The frequency of the signal is divided by D / N and supplied to the phase comparator 327.

【0035】

In the phase comparator 327, f divided by D / N₂The phase difference between the signal and the output signal of the voltage controlled oscillator 305 divided by the C / N divider 326 by the C / N divider 326 is calculated, and the phase difference proportional signal 329 is input to the control circuit 332 via the loop filter 328. Be supplied.

【0036】

Each phase difference proportional signal 320,329 is input to the control circuit 332 via each loop filter 319,328, and is output from the level detector 314 f.₁Level signal 330 and f output from level detector 324₂A level signal 331 is input, and based on these signals, f₁Signal or f₂Only when a signal is detected, the output signal 306 of the voltage controlled oscillator 305 has a frequency f by the control signal 333 obtained by selecting the phase difference proportional signal 320 or 329 related to the signal having the higher level of either of these two signals._cIt is controlled to converge to.

【0037】

Thus, according to the second embodiment, two intermittently transmitted unmodulated carrier signals (f).₁Signal, f₂Using the signal), one of the unmodulated carrier signals (f)₁Signal, f₂Even when the level of the signal) drops due to fluctuations in the frequency characteristics on the transmission path, the reference carrier frequency signal can be accurately and stably reproduced on the receiving device side.

【0038】

In the second embodiment, the unmodulated carrier signal is f.₁Signal and f₂Although it is two signals, it may be one or three or more signals.

【0039】

[Effect of the invention]

As described above, according to the invention of claim 1, on the transmitting side, one or more types of unmodulated carrier signals having different frequencies are inserted at predetermined positions in the synchronous signal section of the OFDM signal in the same repeating pattern. It was transmitted intermittently, and on the receiving side, it was locked to the frequency of the highest level unmodulated carrier signal among the unmodulated carrier signals, and the reference carrier frequency signal for OFDM signal demodulation was reproduced. It is possible to accurately and stably reproduce the reference carrier frequency signal.

【0040】

According to the invention of claim 2, since the insertion level of the unmodulated carrier signal is set to be higher than that of other information transmission signals on the transmitting side, more stable reproduction is possible.

【0041】

According to the invention of claim 3, the OFDM transmitted intermittently by inserting one or more types of unmodulated carrier signals of different frequencies in the same repeating pattern at a predetermined position in the synchronous signal section of the OFDM signal on the transmitting side. A means for receiving a signal and extracting one or more kinds of unmodulated carrier signals having different frequencies from the received signals, and a means for extracting the highest level unmodulated carrier signal among these signals, and this extraction. The invention of claim 1 comprises a voltage-controlled oscillator loop means that locks to the frequency of the unmodulated carrier signal and a means that reproduces a reference carrier frequency signal for decoding the OFDM signal from the loop means. Similarly, the reference carrier frequency signal can be reproduced accurately and stably.

【0042】

According to the invention of claim 4, the means for extracting the unmodulated carrier signal from the received signal is unmodulated for detecting the insertion period of the unmodulated carrier signal inserted at a predetermined position in the synchronous signal section of the OFDM signal. Since it was composed of a band blocking filter for the carrier frequency and a means for gate the insertion period of the unmodulated carrier signal in the received signal by the gate signal generated from the output of this filter, in order to extract the unmodulated carrier signal, It is not necessary to transmit another signal for generating a gate signal, and it is possible to create a gate signal only from the unmodulated carrier signal transmitted intermittently, which enables efficient reception. Further, even if the frequency of the OFDM signal deviates, the transmission period of the unmodulated carrier signal can be stably detected by making the attenuation frequency width of the band blocking filter wider than the deviation. ..

[Simple explanation of drawings]

[Figure 1]

It is explanatory drawing which shows an example of the unmodulated carrier signal of the reference carrier frequency transmitted from the transmission side in 1st Embodiment of the OFDM signal transmission method which concerns on this invention.

[Figure 2]

It is a block diagram which shows the circuit structure in 1st Embodiment of the OFDM signal receiving apparatus which concerns on this invention.

[Fig. 3]

It is explanatory drawing which shows the structural example of the reference carrier frequency signal detection circuit using a band blocking filter (BEF).

[Fig. 4]

It is explanatory drawing which shows the frequency characteristic of a band blocking filter.

[Fig. 5]

It is explanatory drawing which shows the signal of each part of the reference transport frequency signal detection circuit shown in FIG.

[Fig. 6]

It is explanatory drawing which shows an example of the unmodulated carrier signal transmitted from the transmission side in the 2nd Embodiment of the OFDM signal transmission method which concerns on this invention.

[Fig. 7]

It is a block diagram which shows the circuit structure in the 2nd Embodiment of the OFDM signal receiving apparatus which concerns on this invention.

[Explanation of symbols]

100 Received IF signal 101,301 OFDM signal bandpass filter 102,302 OFDM modulated signal 103,104,303,304 Multiplexer 105,305 Voltage Control Oscillator (VCO) 106,306 VCO output signal 108,308 (π / 2) phase shifter 109,309 Baseband I signal of OFDM signal Baseband Q signal of 110,310 OFDM signal 111 Reference carrier frequency signal detection circuit (f)_cDetection circuit) 112 Reference carrier frequency signal 113 Bandpass filter 114,116 (1 / N) divider 117,318,327 Phase comparator 118,319,328 Loop filter 119,332 Control circuit 201 Bandwidth Block Filter 203 Gate signal creation circuit 205 Reference carrier frequency signal extraction circuit 311 Unmodulated carrier signal detection circuit (f)₁Detection circuit) 313 (f₁Signal) Bandpass filter 314,324 level detector 315 (B / N) divider 317 (A / N) divider 321 Unmodulated carrier signal detection circuit (f)₂Detection circuit) 323 (f₂Signal) Bandpass filter 325 (D / N) divider 326 (C / N) divider