JP4601212B2 - Data transmission equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a synchronization detection method for a data transmission apparatus using an orthogonal frequency division multiplexing modulation system and a data transmission apparatus to which this synchronization detection method is applied.
[0002]
[Prior art]
2. Description of the Related Art In recent years, an orthogonal frequency division multiplex modulation (OFDM) has been attracting attention as a multiplexing scheme for mobile radio and terrestrial digital radio communications, which has the characteristics of being resistant to multipath, fading, and ghosting. In this method, a signal obtained by digitally modulating a large number of tens to several hundreds of carriers arranged at the same frequency interval FS at each symbol frequency FSy (= 1 / TSy), that is, an OFDM signal (orthogonal) This is a method for transmitting an information code using a frequency division multiplexed modulation signal.
When a transmission signal modulated and transmitted by this method is received and demodulated on the receiving side, first, it is necessary to regenerate synchronization from the received OFDM signal.
Therefore, on the transmission side, synchronization of a null signal that is a no-signal period at the beginning of a frame that is a unit of data transmission processing in advance and a sweep signal that has a signal component that changes from the maximum frequency to the minimum frequency of the transmission band in a predetermined period A method of inserting symbols and detecting them on the receiving side to reproduce the synchronization has been proposed (TVJ Technical Report VOL.19, NO.18 issued in August 1995). Moreover, as an example of a specific method of detecting a null interval and clock synchronization using a sweep signal, there is an invention described in Japanese Patent Laid-Open No. 11-168446.
[0003]
Hereinafter, this example will be briefly described with reference to FIGS.
FIG. 5 shows the configuration of the receiver side of the digital data transmission apparatus that receives a transmission signal in which a null interval is inserted at regular intervals, detects the aforementioned null interval, and synchronizes with the received signal.
The transmission signal output from the transmitter Tx and having a null interval inserted at regular intervals is received by the receiver Rx, converted into a baseband signal by the RF / IF demodulator 31 of the receiver Rx, and A / D The digital reception signal S13 digitally converted by the converter 32 is supplied to the null section detector 10. The null interval detector 10 determines whether or not the received digital reception signal S13 is a null interval, and outputs a null interval detection pulse S14 with the configuration of FIG. 3 described later.
FIG. 3 is a block diagram showing a specific configuration of the null period detector 10 described above. The aforementioned digital reception signal S13 is input to the power calculator 2, and the power value S11 of the reception signal is obtained. The received signal power value S <b> 11 obtained by the power calculator 2 is input to the received signal amplitude determiner 6 and the average power calculator 3. The average power calculator 3 obtains the average power value for each symbol, for example, based on the received signal power value S11 for a predetermined period.
Further, in the delay unit 4, a predetermined delay (for example, one symbol period) is applied to the average power value obtained by the average power calculator 3, and output as a delayed average power value.
Then, the multiplier 5 multiplies the delay average power value by a predetermined coefficient value to obtain a threshold value corresponding to the average power value of the received signal, and outputs the threshold value to the received signal amplitude determiner 6.
Then, the received signal amplitude determination unit 6 compares the input received signal power value S11 with a level variable threshold value corresponding to the average power value of the received signal output from the multiplier 5, and the determination result. Output as S12. The determination result S12 is, for example, “H” level when the received signal power value S11 exceeds the threshold value, and “L” level when the received signal power value S11 falls below the threshold value.
Based on the determination result 12, the null section determiner 7 determines whether or not the L level period in which the received signal power value S11 falls below the threshold value continues for a predetermined length (time). If determined, a null section detection pulse S14 is output.
With the configuration as described above, a null interval is detected from the received signal, and synchronous reproduction is performed as the start point of the frame.
[0004]
[Problems to be solved by the invention]
When data is transmitted using a wireless transmission path such as a space, noise may be mixed in a signal received by a receiver and the C / N ratio may be deteriorated. In this case, the data transmission apparatus as described above not only causes a data error but also makes noise difficult to detect because noise is also superimposed on the above-described null period.
FIG. 4 shows the relationship between the power value in the null section of the received signal and the threshold value used in the received signal amplitude determiner.
FIG. 4C shows an example of the received signal power value S11 when there is little noise, and 21 indicates a null section. Reference numeral 22 denotes a threshold value used in the received signal amplitude determiner 6.
Here, since the received signal power value in the null section 21 is sufficiently low, a difference from the threshold value 22 calculated from the average power of the received signal power values in other periods is secured.
In this case, the received signal amplitude determiner 6 compares the received signal power value S11 with the threshold value 22, and the determination result S12 is as shown in FIG.
The determination result S12 has a waveform in which the L level continues in the null period 21, and is in a state where the presence of the null section can be detected correctly.
On the other hand, FIG. 4E shows an example of the received signal power value S11 when the noise is large. The received power value S11 of the null section 21 of this waveform rises as noise is mixed in, and a difference from the threshold value 22 is not ensured. In this case, the determination result S12 is as shown in FIG. 4F, and the received power value S11 in the null section 21 does not continuously become the threshold value 22 or less. As a result, there arises a problem that the presence of the null interval cannot be detected correctly.
The present invention eliminates these drawbacks, and provides a data transmission device that can reliably detect a null interval even when large noise is mixed, and that can perform stable synchronization detection even in an unfavorable transmission path. It is the purpose.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a data transmission apparatus using a digital modulation method, and performing data reproduction on the receiving side based on a predetermined synchronization symbol group inserted in a transmission signal. A filter circuit for removing out-of-band noise of the received signal is provided on the receiving side, the power value of the received signal from which the out-of-band noise has been removed is obtained, and a threshold value is determined based on the average power value of the received signal power value for a predetermined period. , And using the received signal power value and the threshold value, detect and determine a no-signal period in the synchronization symbol group, and perform synchronous reproduction on the receiving side based on the determination result It is a transmission device.
The data transmission apparatus is a data transmission apparatus using an orthogonal frequency division multiplexing modulation system, and uses a digital filter as a filter circuit.
Furthermore, a means for obtaining the average power value obtained through the filter circuit and the average power value obtained without passing through the filter circuit and displaying the result of detecting the magnitude of the out-of-band noise by the difference between both values is added. This is a data transmission device.
In other words, by providing a filter means before the power calculation of the received signal, the received power calculation and average power calculation are performed for only the signal that should be received, and the result is used to detect the no-signal period (null section). Judgment is performed.
As a result, an increase in received power in the null section can be suppressed even when noise is mixed in the received signal. That is, a difference from the threshold value for determining the null section can be secured, and the null section can be normally detected.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the determination and detection of the null interval according to the present invention will be described with reference to FIG.
By providing the filter 1 in the preceding stage of the null interval detector 10, a digital reception signal S13 that has been subjected to a process for removing noise mixed in the digital reception signal is obtained and provided to the null interval detector 10. The filter 1 is suitable for each application such as the band of received signals, the nature of the noise, the circuit scale, etc., from a very general filter circuit such as an FIR type or an IIR type to a filter circuit having another special configuration. What is necessary is just to comprise with a circuit. Although not particularly illustrated, a 5-tap FIR filter (tap coefficients: −0.125, +0.75, +0.375, +0.75, and −0.125) was used in this example.
A signal obtained as a result of the filtering process is output to the power calculator 2 to obtain a received signal power value S11. The received signal power value S <b> 11 obtained by the power calculator 2 is input to the received signal amplitude determiner 6 and the average power calculator 3. The average power calculator 3 obtains the average power value for each symbol, for example, based on the received signal power value S11 for a predetermined period.
Further, in the delay unit 4, a predetermined delay (for example, one symbol period) is applied to the average power value obtained by the average power calculator 3, and output as a delayed average power value.
Then, the multiplier 5 multiplies the delay average power value by a predetermined coefficient value to obtain a threshold value corresponding to the average power value of the received signal, and outputs the threshold value to the received signal amplitude determiner 6.
Then, the received signal amplitude determination unit 6 compares the input received signal power value S11 with a level variable threshold value corresponding to the average power value of the received signal output from the multiplier 5, and the determination result. Output as S12. The determination result S12 is, for example, H level when the received signal power value S11 exceeds the threshold value, and L level when the reception signal power value S11 falls below the threshold value.
Based on the determination result 12, the null section determiner 7 determines whether or not the L level period in which the received signal power value S11 falls below the threshold value continues for a predetermined length (time), and determines that it is a null section. The null interval detection pulse 14 is output.
[0007]
Next, FIG. 2 shows the relationship between the power value in the null section of the received signal and the threshold value used in the received signal amplitude determiner.
FIG. 2A shows an example of the received signal power value S11 obtained based on the signal from which noise has been removed by the filter 1, and 21 indicates a null interval. Reference numeral 22 denotes a threshold value used in the received signal amplitude determiner 6.
Here, even if noise is mixed in the received signal, an increase in the received signal power value in the null section 21 as in the conventional waveform of FIG. 4E is suppressed, and the received signal power value in other periods is suppressed. A difference from the threshold value 22 calculated from the average power is secured. In this case, the received signal amplitude determination unit 6 compares the received signal power value S11 with the threshold value 22, and the determination result S12 is as shown in FIG. The determination result S12 has a waveform in which the L level continues in the null period 21, and the presence of the null section can be detected correctly.
[0008]
Next, a second embodiment of the present invention will be described with reference to FIG.
Here, in addition to the null interval detector 10, the power calculator 11, the average power calculator 12, and the noise detector 13 are provided to obtain the magnitude of the out-of-band noise, and the detection result is externally displayed by the display device 14. To display.
First, the digital reception signal S <b> 13 is given to the power calculator 11, a reception signal power value in a state where noise is mixed is obtained, and is output to the average power calculator 12. The average power value obtained without passing through the filter 1 by the average power calculator 12 is given to the noise detector 13 together with the average power value obtained through the filter 1 by the average power calculator 3. The noise detector 13 detects the magnitude of out-of-band noise based on the difference between the two values, and outputs the result to the display device 14. In this display device 14, by displaying the magnitude of out-of-band noise on the outside of the receiver using an LED, a meter, etc., the situation of noise can be grasped at the site where the receiver is used, and a more stable reception point It can be used as an effective judgment material when finding.
Further, when the AGC circuit 15 for controlling the reception signal level is provided in the previous stage of the A / D converter 32 in FIG. By using the value as a control signal for the AGC circuit 15, AGC processing can be performed in accordance with the power of the received signal including noise, and saturation of the A / D converter 32 in the subsequent stage can be avoided. It becomes.
Although the above embodiment shows an example applied to the detection of a null symbol that is one of the synchronization symbol groups, it may be applied to the detection of a sweep signal that is the same synchronization symbol, for example. Needless to say, the noise mixed in the signal is effective not only for Gaussian noise propagating in space but also for interference waves from adjacent channels.
[0009]
【The invention's effect】
As described above, according to the present invention, since the noise of the received signal is removed by the filter circuit to suppress the increase in the average power value in the null section, the null section is reliably detected even when large noise is mixed. Therefore, it is possible to provide a data transmission apparatus that can perform stable synchronization detection even in a transmission path under adverse conditions.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a null interval detector according to the present invention.
FIG. 2 is a waveform diagram of each part for explaining the operation of the present invention.
FIG. 3 is a block diagram illustrating a prior art null interval detector.
FIG. 4 is a waveform diagram of each part for explaining the operation of the prior art.
FIG. 5 is a block diagram showing a configuration of a receiver.
[Explanation of symbols]
1: filter, 2: power calculator, 3: average power calculator, 4: delay unit, 5: multiplier, 6: received signal amplitude determiner, 7: null interval determiner, 10: null interval detector, 11 : Power calculator, 12: average power calculator, 13: noise detector, 14: display device 15: AGC, 21: null section, 22: threshold value, 31: RF / IF demodulator, 32: A / D converter.

Claims (4)

A data transmission apparatus using a digital modulation method, which performs synchronous reproduction on the reception side based on a predetermined synchronization symbol group inserted in the transmission signal, and removes out-of-band noise of the reception signal on the reception side. A filter circuit is provided to obtain a power value of the received signal from which the out-of-band noise has been removed, and a threshold value is calculated based on an average power value of the received signal power value for a predetermined period. Detecting and determining a no-signal period in the synchronization symbol group using a threshold value, and adding means for performing synchronous reproduction on the receiving side based on the determination result ;
Means for obtaining the average power value obtained through the filter circuit and the average power value obtained without passing through the filter circuit and displaying the result of detecting the magnitude of the out-of-band noise by the difference between the two values are added. ,
A data transmission device characterized by the above.   A data transmission apparatus according to claim 1, wherein the data transmission apparatus is a transmission apparatus using an orthogonal frequency division multiplexing modulation system.   3. The data transmission apparatus according to claim 1, wherein a digital filter is used as the filter circuit. A data transmission apparatus using an orthogonal frequency division multiplexing modulation system that performs synchronous reproduction on the reception side based on a predetermined synchronization symbol group inserted in the transmission signal. Provide a digital filter to remove noise,
A power value of the received signal from which the out-of-band noise is removed is obtained, a threshold value is calculated based on an average power value of the received signal power value for a predetermined period, and the received signal power value and the threshold value are used to calculate the threshold value. Detecting and determining a no-signal period in the synchronization symbol group, and adding means for performing synchronous reproduction on the receiving side based on the determination result ;
Means for obtaining the average power value obtained through the filter circuit and the average power value obtained without passing through the filter circuit and displaying the result of detecting the magnitude of the out-of-band noise by the difference between the two values are added. ,
A data transmission device characterized by the above.

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