JPH09149003A - Method for generating frequency division multiplex signal and transmission/reception method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent rapid fluctuation of mean power, to reduce an incidence probability of peak power similarly to the case with that for other packets and to insert null data to a buffer. SOLUTION: In this method, transmission information stored tentatively in a buffer in a digital signal form is outputted to a frequency division multiplex signal transmitter, an orthogonal frequency division multiplex signal consisting of plural carriers subject to multi-value modulation by the transmission information is generated and sent, then the production of the transmission information is reduced than the transmission rate of the transmission information to generate the frequency division multiplex signal. When a prescribed amount of image data and voice data per unit time is not inputted and a data storage amount in the buffer is a prescribed amount or below, data having no regularity or random data are stored as a null packet to the buffer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency division multiplex signal generation method and a transmission / reception method, and more particularly to orthogonal frequency division multiplexing (OFDM) of a coded digital video signal or the like in a limited frequency band.
uency Division Multiplex)
The present invention relates to a frequency division multiplexed signal generation method and a transmission / reception method for converting into a signal and transmitting / receiving.

[0002]

2. Description of the Related Art One of the methods for transmitting coded digital video signals in a limited frequency band is 25
6 Quadrature Amplitude Modulation (QAM: Quadrature Am)
of multi-valued digital information such as the Plitute Modulation) using a large number of carriers
The OFDM method of transmitting as an M signal has been conventionally known because of its features such as resistance to multipath, resistance to interference, and relatively good frequency utilization efficiency. This OFDM system is a system in which a large number of carriers are arranged orthogonally and independent digital information is transmitted on each carrier. The phrase "carriers are orthogonal to each other" means that the spectrums of adjacent carriers become zero at the frequency position of the carrier.

According to this OFDM system, since a guard band period (guard interval) is set and information of the period is transmitted redundantly, transmission distortion caused by multipath of radio waves can be reduced. That is, in the reception of this OFDM signal, the amplitude and phase modulation components of the signal transmitted within the symbol period are detected, and the information value is decoded by these levels, so the signal of the first guard interval period is By removing and decoding
Since the frequency components of the multipath signal in the same symbol section and the signal to be received are the same, decoded digital data with less transmission distortion can be transmitted in a relatively narrow frequency band.

On the other hand, in other general transmission systems, the following is known for continuous transmission of information. A generation device for generating transmission information digitizes video information from a camera, VTR, etc., and further compresses the data by a standard technique such as MPEG to generate image data and audio data, respectively. Further, image data is grouped by a predetermined amount, an image header is added to it to form an image packet, voice data is grouped by a predetermined amount, and a voice header is added to form a voice packet. Send the voice packet to the transmitter.

At this time, it is technically difficult to completely match the amount of image data and audio data generated and the transmission rate of the transmitter. Therefore, when there is no packet to be transmitted, a predetermined amount of predetermined data is collected, a null header is added, and a null packet is formed and transmitted. In other words, conventionally, the generation amount of image data and audio data is set to be slightly smaller than the transmission rate of the transmission device, and null data is appropriately inserted to absorb this difference.

[0006]

In the general transmission system in which the null packet is generated and the transmission rates are matched, the null data has no particular meaning and may have any value. Normally, continuous values such as "00" or "FF" (hexadecimal notation) are often used. However, the OFDM
In a signal transmission system, using such values,
Rapid fluctuation of average power and generation of peak power 2
Two problems occur.

That is, it can be understood that the image data and the audio data are almost random data. Therefore, the OFDM wave also has a random waveform, and the average power between the symbols is almost constant. Therefore, depending on how to select the null data, the average power of the symbol including the null packet suddenly becomes larger or smaller than that of the symbol not including the null packet. Moreover, the value may continue for a certain period. This is a loose A at the receiver
It makes the design of GC (auto gain control) difficult.

The OFDM wave performs a calibration operation based on the reference data contained therein to correct the received data. The AGC of the receiver is the A / D of the received signal.
It is inserted to supplement the dynamic range of the converter, but it is designed to have a slow response in order to guarantee the calibration operation. The response to fluctuations in average power is not covered, but may be affected.

If the null data has a certain regularity, a peak value will be generated. If the symbol in which the peak value occurs is composed of only null packets, the error in the null data does not affect the device performance, but the reference data etc. included in that symbol may be captured as an incorrect value. There is. When the symbol in which the peak value occurs is composed of the null packet and the image packet or the audio packet, the possibility that a data error will occur further increases.

[0010] The present invention has been made in view of the above points,
To provide a frequency division multiplex signal generation method and a transmission / reception method for generating a frequency division multiplex signal in which null data is inserted while preventing a sudden change in average power and suppressing the occurrence probability of peak power to be as low as other packets. With the goal.

[0011]

In order to achieve the above object, the present invention outputs transmission information temporarily stored in a buffer in the form of digital signals to a frequency division multiplex signal transmitter, and multi-value modulates each with the transmission information. In generating and transmitting an orthogonal frequency division multiplex signal composed of a plurality of carriers, a method of generating a frequency division multiplex signal with a smaller amount of transmission information than the transmission rate of the transmission information is used. When a fixed amount of transmission information is not input and the amount of data stored in the buffer is less than a predetermined amount, non-regular data or random data is temporarily stored in the buffer as null data, or multi-level modulation is performed. 1/2 of the maximum absolute value in the constellation of
Data having no regularity or random data within a range of twice or less is temporarily stored in a buffer as null data, and then the null data is output as transmission information.

In the method of the present invention, when there is a type of transmission information in which a predetermined amount of data is not input per unit time among a plurality of types of transmission information, and the amount of data stored in the buffer is a predetermined amount. In the following cases, data having no regularity or random data is added as null data to the type of transmission information in which a predetermined amount of data is not input and is temporarily stored in a buffer, and then null data is output as transmission information. To do.

As described above, in the method of the present invention, since the data having no regularity or the random data is used as the null data, the rapid fluctuation of the average power can be suppressed,
Also, the probability of peak power generation is suppressed. Further, by setting the signal point arrangement of null data to a signal point arrangement that is 1/2 times or less of the absolute value, the probability of peak power generation can be further suppressed.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. First, an outline of an OFDM signal transmission / reception system that is a frequency division multiplexing signal transmission / reception method of the present invention will be described with reference to the block diagram of FIG.

In FIG. 4, video information (image, audio) obtained from a video source 1 such as a camera or a VTR is input to an information generating device 2 and coded, for example, MPEG system which is a color moving image coding system. Image data and audio data are compressed by the compression method. Further, the information generation device 2 collects the image data in units of 2 kbytes, and informs that the packet is a packet of image data (image header).
Is added to the head to form an image packet, the audio data is collected every 1 kbyte, and a packet header (audio header) notifying that it is a packet of audio data is added to the head to form an audio packet.

Here, since the amount of transmission information generated by the information generator 2 is set to be slightly smaller than the transmission rate, there are cases where image packets or audio packets to be transmitted are not waiting. In this case, a predetermined byte of data having no regularity or random data is prepared, and a packet header (null header) notifying that this is a null data packet is added to the beginning to form a null packet. Similarly to the image packet and the voice packet of No. 1, the packet is sent to the OFDM transmitter 3 at the request of the OFDM transmitter 3. The above null packet insertion method in the information generation device 2 relates to the frequency division multiplexed signal generation method of the present invention, and each embodiment will be described later.

The above-mentioned image packet, voice packet and null packet are subjected to an inverse discrete Fourier transform (IDFT) operation in an operation unit in the OFDM transmitter 3 to be converted into an in-phase signal (I signal) and a quadrature signal (Q signal). To be done. here,
Transmission information is transmitted as an OFDM signal using 256 carrier waves. Further, in order to facilitate the design of the analog signal system in the latter stage, double oversampling is used, and the above calculation unit uses the 512-point inverse discrete Fourier transform (IDF).
T) Perform an operation to generate an OFDM signal.

At this time, the number of input terminals of the arithmetic unit is 512 for the real part (R) signal and 512 for the imaginary part (I) signal.
There are a total of 127 from the 1st (n = 1) to the 127th (n = 127), and a total of 12 from the 385th (n = 385) to the 511th (n = 511).
An information signal is input to each of the seven input terminals, and a DC voltage (constant) is input to the 0th (n = 0) input terminal, which are transmitted at the center frequency of the transmitted carrier. For example, a fixed voltage for the pilot signal is input to the second input terminal, which is 1 / Nyquist frequency.
It is transmitted by a carrier having a frequency at both ends equivalent to twice the frequency.

Here, a total of 1 from the 1st to the 128th
The input information of the 28 input terminals is the center carrier frequency F0.
The input information of a total of 128 input terminals from the 384th to the 511th is transmitted by the information transmission carrier (+ 1st to + 128th carrier) on the upper side (high frequency side) of the (0th carrier). The lower (lower band side) carrier for information transmission (-128th to -1st carrier) is transmitted. In addition, 0 is input to the remaining 129th to 383rd input terminals (set to the ground potential), and the carrier wave in that portion (that is, ± 129th to ± 256th carriers) is input.
Is prevented (not used for data transmission).

Of the information transmission carrier waves, 216 are allocated for information data transmission and 32 are used for error correction (EC
C), the symbol period is about 2.65 ms, and the transmission rate is with ECC, about 748 kbps.
(≈248 × 8 bits / 2.65 ms), and without ECC about 652 kbps (≈216 × 8 bits /
2.65 ms).

The image bit rate is about 618 kbps,
The bit rate of voice is set to about 32 kbps, and data generated at about 650 kbps is transmitted. For these reasons, the adjustment data of about 2 kbps (= 652-650) is appropriately inserted.

As described above, the data obtained by performing the complex IDFT operation by assigning 4 bits to the real part and the imaginary part at each predetermined frequency by the operation unit in the OFDM transmitter 3 is the quadrature modulator. Then, an OFDM wave that is quadrature-modulated by using 256QAM modulation is generated and radio waves are emitted.

The OFDM receiver 4 receives the OFDM wave, performs a complex DFT operation, and then performs 256QAM demodulation to obtain 4 bits for each of the real part and the imaginary part at each predetermined frequency, and after aligning the transmission information. Playback device 5 for playback
Output to When the playback device 5 detects an image header from the input signal, the subsequent 2 kbytes are played back as image data, when the audio header is detected, the subsequent 1 kbyte is played back as audio data, and when a null header is detected, it is played back. It is discarded as null data until the image header or the audio header is detected from the subsequent input data. Needless to say, when the image data and the audio data are compressed, the reproduction device 5 expands them. The output of the reproduction device 5 is displayed by the video display device 6.

Note that the amount of null data does not have to be a fixed amount, until the next image header or audio header is detected. It may be determined that the data is null data, or the null data may be image data or audio data that has been transmitted or will be transmitted.

Next, each embodiment of the present invention will be described. FIG. 1 shows a flowchart for explaining the operation of the first embodiment of the present invention. In the figure, the information generating device 2 determines whether or not a predetermined amount of image data has been input (step 11), and if so, adds an image header to the beginning of the image data to form an image packet and Store in buffer (step 12). If a predetermined amount of image data has not been input, it is determined whether a predetermined amount of audio data has been input (step 13). If it has been input, an audio header is added to the beginning of the audio data to form an audio packet, and Store in buffer (step 12).

If the audio data has not been input by a predetermined amount, it is then monitored whether the storage amount in the buffer is less than or equal to the predetermined amount (step 15). It is determined whether or not a predetermined amount of data has been input, and if it is determined that the storage amount in the buffer is less than or equal to the predetermined amount, a null packet is stored in the buffer and the process returns to step 11. Here, the null packet has a configuration in which a predetermined byte of data having no regularity or random data described above is prepared and a null header is added to the head thereof.

Next, a second embodiment of the present invention will be described. In the second embodiment, as in the case of FIG. 1, neither image data nor audio data is input by a predetermined amount, and
The null packet is stored in the buffer when the storage amount of the buffer is less than or equal to a predetermined amount, but the configuration of this null packet is different from that of the first embodiment.

That is, the OFDM transmitter 3 shown in FIG. 5 wirelessly transmits OFDM in which each information carrier is 256QAM modulated, and the relationship between this 256QAM modulation and signal point arrangement is shown in FIG. 2 as is well known. The 4-bit data a, b assigned to a certain information carrier frequency has a signal point arrangement of P points, and has a magnitude (amplitude) A as a vector.
Then, the waveform has a phase θ and rotates by a predetermined amount.

In FIG. 2, the null data is randomly selected from the signal point arrangement in the dotted line frame. If random, phase matching of each frequency is avoided, and as a result, many carriers are frequency division multiplexed.
The occurrence of peak values above a predetermined value of the wave is suppressed, and the amplitude of null data is set to be slightly smaller than that of 4-bit data, so the probability of occurrence of peak values above the above specified value is further reduced, A small change in average power is enough. Selecting the signal point constellation in FIG. 2 indicates that normally 3 bits are selected when 4 bits are selected.

As another example, it is not necessary to limit the number to 3 bits in particular, and it is possible to select within a range in which the dotted line frame in FIG. 2 is further widened.

Next, a third embodiment of the present invention will be described with reference to the flowchart of FIG. Image data and audio data may be understood to be almost random data, but each compression method, or in particular, a state in which no audio is compressed may be considered, and each randomness may have a characteristic.

In the above-mentioned first and second embodiments, it is assumed that the image packet, the voice packet, and the null packet are transmitted from the information generating device 2 to the OFDM transmitting device 3 in series, although not particularly stated. . Here, consider a case where image packets and audio packets are transmitted in parallel. O
In the FDM transmitter 3, if the frequencies for the image and the voice are determined in advance and the respective data are assigned to these respective frequencies, the average power between the symbols becomes more stable. Then, the null data is appropriately inserted into the image data and the audio data.

That is, in FIG. 3, the information generating apparatus 2 determines whether a predetermined amount of image data has been input (step 21), and if so, determines whether a predetermined amount of audio data has been input. If a predetermined amount of voice data is also input (step 22), it is packetized and stored in the buffer in the information generating device 2 (step 23). Therefore, at this time, null data is not stored in the buffer.

On the other hand, when the predetermined amount of image data is input but the voice data is not input,
It is determined whether or not the amount of data in the buffer is less than or equal to a predetermined amount (step 24). When the amount of data is less than or equal to the predetermined amount, null data is added to the voice data to be packetized and stored in the buffer (step 25).
It returns to 1 and determines whether or not a predetermined amount of image data has been input.

If it is determined in step 21 that a predetermined amount of image data has not been input, it is determined whether or not a predetermined amount of audio data has been input (step 26). Is stored in the buffer by adding null data to the image data and storing it in the buffer (step 28). If it is not less than the predetermined amount, the process returns to step 21. It is determined whether a predetermined amount of image data has been input.

If it is determined that both the image data and the audio data have not been input by the predetermined amount (steps 21 and 26), it is determined whether the data amount in the buffer is less than or equal to the predetermined amount (step 29). When the amount is less than the predetermined amount, null data is added to each of the image data and the audio data to packetize and store in the buffer (step 2
5) If the amount is not less than the predetermined amount, the process returns to step 21 and it is determined whether the predetermined amount of image data has been input.

Next, a fourth embodiment of the present invention will be described. In the fourth embodiment, similar to FIG. 1, neither a predetermined amount of image data nor audio data is input, and
The null packet is stored in the buffer when the storage amount of the buffer is less than or equal to a predetermined amount, but the content of the null packet is different from that of the first and second embodiments.

The null data is data whose transmission timing is not guaranteed. But someday it will be transmitted. Therefore, it is possible to transmit data of a type that has no time restriction. Null data is not guaranteed in the short term transmission rate, but is guaranteed to some extent in the long term. Therefore, although uncertain, it is possible to transmit the type of data that needs to ensure a certain transmission rate.
Therefore, such kind of data is transmitted instead of null data. Of course, the data to be transmitted instead of the null data may be understood to be almost random data, like the image data and the audio data. As this data, for example, it is conceivable to repeatedly transmit information such as the transmission date and time, the transmission place, and the sender code.

[0039]

As described above, according to the present invention,
By using non-regular data or random data as null data, abrupt fluctuations in average power can be suppressed, and the probability of peak power generation can be suppressed. Therefore, a gradual AGC design in the receiver can be facilitated,
Further, even if the null data includes the reference data or the like in the same symbol, it is possible to prevent the reference data or the like from being taken as an erroneous value. Further, according to the present invention, by setting the signal point constellation of null data to a signal point constellation that is 1/2 times or less of the absolute value, the average power is somewhat reduced, but the probability of peak power generation can be further suppressed. , Receiver A
This makes it easier to design the GC and further improves the reliability of transmission and reception of the orthogonal frequency division multiplexed signal.

[Brief description of the drawings]

FIG. 1 is a flowchart for explaining the operation of the first, second and fourth embodiments of the method of the present invention.

FIG. 2 is a signal point arrangement diagram for explaining a second embodiment of the method of the present invention.

FIG. 3 is a flow chart for explaining the operation of the third embodiment of the method of the present invention.

FIG. 4 is a configuration diagram showing an embodiment of a transmission / reception method of the present invention.

[Explanation of symbols]

 2 information generating device 3 OFDM transmitting device 4 OFDM receiving device 5 reproducing device 11-16, 21-30 processing steps

Claims (5)

[Claims] 1. A transmission information temporarily stored in a buffer in the form of a digital signal is output to a frequency division multiplex signal transmission device to generate an orthogonal frequency division multiplex signal composed of a plurality of carrier waves, each of which is multi-value modulated by the transmission information. In the method of generating the frequency division multiplexed signal by reducing the generation amount of the transmission information from the transmission rate of the transmission information when transmitting the transmission, when a predetermined amount of the transmission information is not input per unit time, and When the amount of data stored in the buffer is less than or equal to a predetermined amount, non-regular data or random data is temporarily stored as null data in the buffer, and then the null data is output as the transmission information. And a method for generating frequency division multiplexed signals. 2. Transmission information temporarily stored in a buffer in the form of a digital signal is output to a frequency division multiplex signal transmission device as data of a real part and an imaginary part of a complex inverse discrete Fourier transform operation, and the frequency division multiplex signal transmission device outputs the information. In generating and transmitting an orthogonal frequency division multiplex signal composed of a plurality of multi-value modulated carriers, in the method for generating the frequency division multiplex signal by reducing the amount of transmission information generated from the transmission rate of the transmission information, When a predetermined amount of the transmission information is not input per unit time and when the amount of data stored in the buffer is equal to or less than the predetermined amount, 1 / maximum of the maximum absolute value in the multipoint modulation signal point arrangement After temporarily storing non-regular data or random data within the range of twice as null data in the buffer, Frequency division multiplex signal generating method and outputs the data as the transmission information. 3. A quadrature composed of a plurality of carrier waves, which are output from a plurality of types of transmission information temporarily stored in a buffer in the form of digital signals to a frequency division multiplex signal transmitter and are multi-value modulated by the plurality of types of transmission information. When generating and transmitting a frequency division multiplexed signal, in the method of generating the frequency division multiplexed signal by reducing the generation amount of the transmission information from the transmission rate of the plurality of types of transmission information, among the plurality of types of transmission information When there is transmission information of a type in which a predetermined amount of data is not input per unit time and when the amount of data stored in the buffer is less than or equal to a predetermined amount, the type of transmission in which the predetermined amount of data is not input After adding non-regular data or random data to the information as null data and temporarily storing it in the buffer, the null data Frequency division multiplex signal generating method and outputs as the transmission information. 4. The frequency division multiplex signal generation method according to claim 1, wherein as the null data, data of a type that is uncertain but has only to be transmitted within a predetermined time is used. . 5. An image packet in which an image header is added to image data collected for each first predetermined amount by an information generating device, and an audio packet in which an audio header is added to voice data collected for each second predetermined amount. And transmitting the image packet and the audio packet to the frequency division multiplex signal transmission device at the request of the frequency division multiplex signal transmission device, and if there is no packet to be transmitted, data having no regularity or random data A null packet in which a null header is added to a third predetermined amount is sent to the frequency division multiplex signal transmission device, and the frequency division multiplex signal transmission device outputs the input packet to a real part and an imaginary part of a carrier wave of each predetermined frequency. Of the complex inverse discrete Fourier transform and then orthogonal modulation is performed to generate and transmit an orthogonal frequency division multiplexed signal. Then, the orthogonal frequency division multiplex signal is received by the frequency division multiplex signal receiving device, orthogonal demodulation is performed after the complex discrete Fourier transform operation, and data of the real part and the imaginary part of the carrier wave of each predetermined frequency is obtained and aligned. Then, the reproduction device receives the signal from the frequency division multiplex signal reception device, and when the image header is detected, the subsequent first predetermined amount of input data is reproduced as the image data, When the header is detected, the subsequent second predetermined amount is reproduced as the audio data, and when the null header is detected, the input data is discarded until the image header or the audio header is detected. Frequency division multiplexing signal transmission / reception method.