JP2001177496A - Ofdm communication system and ofdm communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an OFDM communication system and an OFDM communication method by which deterioration in an error rate characteristic of a demodulation signal can be prevented. SOLUTION: A counter 507 counts signals denoting that an integration result exceeds a 1st threshold value. A magnitude correlation comparison section 508 controls a switch 501 to be closed when the count of the counter 507 reaches the unity or over. A discrimination section 503 controls a switch 504 so that the result of integration is outputted to a subtractor 505 when the result of integration is once a 2nd threshold value or below. A discrimination 506 outputs information to reset the 1st threshold value when the result of integration is in excess of a 3rd threshold value on the basis of the result of subtraction by the subtractor 505.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to OFDM (Ort).
hogonal frequency division
More particularly, the present invention relates to a communication device that performs synchronization pull-in by correlating a received signal with a known signal.

[0002]

2. Description of the Related Art In a conventional OFDM communication apparatus (hereinafter, referred to as an "OFDM communication apparatus"), generally, a synchronization acquisition signal is inserted into a transmission signal on a transmission side, and the synchronization acquisition signal is inserted on a reception side. To obtain symbol synchronization (that is, to detect the start timing of the FFT process). At present, as shown in FIG. 10, on the transmitting side, the transmission signal with the synchronization acquisition signal inserted therein is 4n (n = 1, 2, 2).
It has been studied to arrange on only the (3,...) -Th subcarrier and perform symbol synchronization acquisition on the receiving side by using a synchronization acquisition signal in a signal transmitted by this subcarrier.

When a transmission signal including a synchronization acquisition signal is arranged only in the 4n (n = 1, 2, 3,...) Th subcarrier, the OFDM signal, as shown in FIG. The period is １ ／ of that of a normal OFDM signal when arranged on subcarriers. As a result, the detection range of the frequency offset on the receiving side can be quadrupled.

Hereinafter, the conventional OFDM communication apparatus will be described with reference to FIGS. 12 and 13, taking a case where the period of an OFDM signal is set to 1/4 of the period of a normal OFDM signal. FIG. 12 is a schematic diagram showing a frame format used in a conventional OFDM communication device.

Referring to FIG. 12, the frame format mainly includes AGC symbols, synchronization symbols, and pilot symbols. Data is inserted after the pilot symbol. Here, AGC
Using five AGC signals 11 to 15 as symbols,
It is assumed that five synchronization signals 16 to 20 are used for synchronization pull-in, and the number of samples of each AGC signal and each synchronization signal is 16. The pilot symbols include GI (guard section) 21, C (pilot symbol) 22, and C (pilot symbol) 23.

FIG. 13 is a block diagram showing a configuration of a conventional OFDM communication apparatus. Referring to FIG.
The signal transmitted by the communication partner in accordance with the format shown in FIG. 13 is received by the OFDM communication apparatus shown in FIG. The received signal (received signal) is supplied to the A / D converter 3
1 and then converted to a digital signal by FFT (Fa
The signal is sent to a st Fourier Transform section 32 and a correlator 33.

[0007] The FFT unit 32 performs an FFT (Fourier transform) process on a received signal converted into a digital signal based on a timing signal from a timing generation unit 36 described later to thereby obtain a signal transmitted by each subcarrier. Take out.

On the other hand, the correlator 33 calculates a correlation value using the known signal and the received signal. This known signal is shown in FIG.
The synchronization signal (B16) shown in FIG.
erse Fast Fourier Transfo
rm) The processed signal.

The absolute value detector 34 calculates the absolute value of the correlation value calculated by the correlator 33. Maximum value detector 35
Detects the timing at which the absolute value of the correlation value calculated by the correlator 33 becomes maximum using the absolute value obtained by the absolute value detection unit 34. Timing generator 36
Sets the start timing of the FFT processing by the FFT unit 32 based on the timing detected by the maximum value detection unit 35, and outputs a timing signal to the FFT unit 32.

As described above, the maximum value detector 35 detects the timing at which the absolute value of the correlation value becomes the maximum, thereby detecting the timing for starting the FFT processing (that is, establishing the symbol synchronization). ) Is possible.

Next, the timing detection method by the maximum value detection unit 35 will be described with reference to FIG.
FIG. 14 is a flowchart showing a procedure for detecting the maximum value by the maximum value detection unit 35 in the conventional OFDM communication apparatus.

First, step (hereinafter referred to as "ST") 11
Then, a comparison is made between the integration result, that is, the absolute value of the correlation value calculated by the correlator 33 and a threshold value (threshold value for the correlation result). If the integration result is larger than the threshold value, the process proceeds to ST12, and if the integration result is equal to or smaller than the threshold value, the process proceeds to ST14.

In ST12, the threshold value used in ST11 is updated. That is, the integration result at the timing exceeding the threshold value is set as a new threshold value. Thereafter, after the count value of the counter is reset in ST13, the process proceeds to ST15.

On the other hand, in ST14, after the count value of the counter is incremented, the process proceeds to ST15. In ST15, it is determined whether or not the aperture information is L. Here, the aperture information is information for determining a range in which symbol synchronization is to be established, and is information determined from the level of a received signal. The fact that the aperture information is L corresponds to the end of the time for establishing the symbol synchronization.

In this case, it is assumed that the aperture information sets a range in which one synchronization signal is secured before and after correct synchronization timing as a period for establishing symbol synchronization. That is, the correct synchronization timing is the boundary point between the synchronization signal 20 and the guard section 21, and the period during which symbol synchronization is established is the synchronization signal 19 and the synchronization signal 2.
This is a point where the boundary point between the synchronization signal 20 and the guard section 21 is shifted rightward in the figure by 16 samples from the boundary point with 0.

In ST15, if the aperture information is not L, the process proceeds to ST17, and if the aperture information is L, the process proceeds to ST16. S
At T17, the count value of the counter is compared with the counter threshold value. If the count value is equal to or smaller than the counter threshold, the process proceeds to ST11 described above. If the count value is larger than the counter threshold, the process proceeds to ST16.

In ST16, the timing at which the integration result finally exceeds the threshold value is set as the symbol timing. As described above, when the count value of the counter (the number of times the integration result is equal to or less than the threshold value) exceeds the threshold value for the counter, or when the period for performing symbol synchronization set by the aperture information ends. Finally, the timing when the integration result exceeds the threshold value is set as the symbol timing, and the symbol synchronization is established.

[0018]

However, the above-mentioned conventional OFDM communication apparatus has the following problems. That is, in the above-mentioned conventional OFDM communication apparatus, a point in time during which symbol synchronization is established, where the absolute value of the correlation result is the largest is detected as the symbol timing. For this reason, when the period for performing the synchronization pull-in is set as described above according to the aperture information, as shown in FIG. 15, the correlation signal 10 and the synchronization signal 20 are set as a correlation peak having a certain magnitude. A correlation peak 42 occurs at a boundary point between the synchronization signal 20 and the guard section 21, and a correlation peak 43 occurs at a boundary point between the synchronization signal 20 and the guard section 21.

Since the correct synchronization timing is the boundary point between the synchronization signal 20 and the guard section 21 as described above, the correlation peak 41 must be detected as the maximum value. However, since the correlation peak 42 may have substantially the same size as the correlation peak 41, the correlation peak 42 may be detected as the maximum value. In this case, the symbol timing is erroneously set at the boundary point between the synchronization signal 19 and the synchronization signal 20, so that a timing error occurs. As a result, FF is applied to the received signal.
The error rate characteristic of the demodulated signal obtained by performing the T processing is degraded.

On the other hand, when the aperture information is set to secure a longer period for performing the synchronization pull-in,
That is, for example, when the time point at which the synchronization pull-in is started is set at the boundary point between the synchronization signal 16 and the synchronization signal 17 (when five synchronization signals are used in the synchronization pull-in process), a certain value is set. Therefore, the probability that the correlation peak 42 is detected as the maximum value is further reduced.
This further increases the probability that a timing error will occur, so that the error rate characteristic of the demodulated signal is more likely to deteriorate.

As described above, in the above-mentioned conventional OFDM apparatus, the probability of occurrence of a timing error is high, so that the error rate characteristic of the demodulated signal is deteriorated. The present invention has been made in view of the above, and an object of the present invention is to provide an OFDM communication device that reduces the probability of occurrence of a timing error, thereby preventing deterioration of the error rate characteristic of a demodulated signal.

[0022]

SUMMARY OF THE INVENTION An OFDM communication apparatus according to the present invention comprises: receiving means for receiving a signal transmitted by a communication partner as a received signal in accordance with a unit frame format including a plurality of sections for inserting a unit known signal; Calculating means for calculating a correlation value using the received signal and the unit known signal; and a reception value corresponding to a section located at an end in a unit frame format from among peak values in the correlation value calculated by the calculation means. Detecting means for detecting a peak value in a correlation value calculated using a signal as a maximum value; and setting means for setting a synchronization timing used for FFT processing on a received signal based on a timing at which the detected maximum value occurs. Is adopted.

According to this configuration, even when a plurality of correlation peaks occur in the correlation result, the correlation peak in the correlation value calculated using the reception signal corresponding to the section located at the end in the unit frame format is set to the maximum value. , It is possible to detect the exact synchronization timing. As a result, the probability of occurrence of a timing error can be reduced, so that it is possible to prevent the error rate characteristics of the demodulated signal from deteriorating.

In the OFDM communication apparatus according to the present invention, in the above-mentioned configuration, the detecting means sequentially compares a correlation value calculated by the correlating means with a first threshold value for a predetermined period, and the comparing means comprises: An updating means for updating the correlation value to a first threshold value when there is a correlation value larger than the first threshold value at the time of comparison; and an updating means for updating the first threshold value by the changing means. An initial setting means for setting the first threshold value to an initial value when the correlation value calculated by the correlation means falls below a second threshold value and then exceeds a third threshold value; And a maximum value detecting means for detecting the first threshold value at the end of the predetermined period as a maximum value.

According to this configuration, when the maximum value of the correlation result is detected, the third threshold value is set after the correlation result falls below the second threshold value in a state where the first threshold value is updated. When it exceeds, the first threshold value is returned to the initial value.
With this, even when a plurality of large correlation peaks occur, the correlation peak occurring at the correct synchronization timing can be detected as the maximum value, so that the probability of occurrence of a timing error can be reduced. Therefore, it is possible to suppress the deterioration of the error rate characteristic of the demodulated signal.

The communication terminal device of the present invention employs a configuration including any one of the above-mentioned OFDM communication devices.

According to this configuration, by providing the OFDM communication device that prevents the deterioration of the error rate characteristic of the demodulated signal, it is possible to provide a communication terminal device that realizes good communication.

According to the base station apparatus of the present invention,
The configuration including the FDM communication device is adopted.

According to this configuration, the provision of the OFDM communication apparatus for preventing the deterioration of the error rate characteristic of the demodulated signal provides a base station apparatus that realizes good communication.

An OFDM communication method according to the present invention includes a receiving step of receiving a signal transmitted by a communication partner as a received signal in accordance with a unit frame format including a plurality of sections for inserting a known unit signal, A calculating step of calculating a correlation value using a known signal; and a peak value in the correlation value calculated by the calculating means, which is calculated by using a reception signal corresponding to a section located at an end in a unit frame format. And a setting step of setting a synchronization timing based on a timing at which the detected maximum value occurs.

According to this method, even when a plurality of correlation peaks occur in the correlation result, the correlation peak in the correlation value calculated using the received signal corresponding to the end section in the unit frame format is set to the maximum value. , It is possible to detect the exact synchronization timing. As a result, the probability of occurrence of a timing error can be reduced, so that it is possible to prevent the error rate characteristics of the demodulated signal from deteriorating.

[0032]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventor has found that by the time the correlation value reaches the correlation peak,
Focusing on the tendency that once the value becomes smaller, it tends to be larger, and after the correlation value reaches the correlation peak,
In the case where the above trend is shifted, it is found that the correlation peak candidate at the time when the synchronization pull-in process is completed becomes the correct correlation peak by repeating the process of setting the correlation peak arriving thereafter as the correct correlation peak candidate. I came to.

That is, the gist of the present invention is that after the threshold value (first threshold value) for the correlation result is updated, the correlation result falls below the second threshold value, and then the third threshold value is set. If the value exceeds the threshold value, the process of returning the first threshold value to the initial value is repeated, and the first threshold value at the time when the synchronization pull-in process ends is detected as the maximum value.

Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. (Embodiment) FIG.
FIG. 3 is a schematic diagram illustrating an example of a unit frame format used by an FDM communication device. Referring to FIG. 1, the frame format mainly includes AGC symbols, synchronization symbols, and pilot symbols. Here, it is assumed that five AGC signals 101 to 105 are used as AGC symbols, and five synchronization signals 106 to 110 are used for synchronization pull-in.
It is assumed that the number of samples of the synchronization signal and each synchronization signal is 16. The pilot symbols are GI (guard section) 111, C (pilot symbol) 112 and C
(Pilot symbol) 113.

FIG. 2 shows an OF according to the embodiment of the present invention.
FIG. 2 is a block diagram illustrating a configuration of a DM communication device. In the present embodiment, the period of the OFDM signal is
Although the case where the period of the FDM signal is set to 1/4 will be described, the present invention is also applicable to a case where the period of the OFDM signal is appropriately changed.

Referring to FIG. 2, a signal transmitted by a communication partner in accordance with the format shown in FIG. 1 is received by the OFDM communication apparatus shown in FIG. The received signal (received signal) is converted into a digital signal by the A / D converter 201, and then the FFT unit 202 and the correlator 2
03 is sent.

The FFT unit 202 performs an FFT process on a received signal converted into a digital signal based on a timing signal from a timing generation unit 206 described later to extract a signal transmitted by each subcarrier.

On the other hand, correlator 203 calculates a correlation value using the known signal and the received signal, and outputs the calculated correlation value to absolute value detection section 204. This known signal is a signal obtained by subjecting one synchronization signal (B16) shown in FIG. 1 to IFFT processing. Further, the correlator 203 detects the reception level of the reception signal using the reception signal from the A / D converter 201, and outputs the detected reception level to the maximum value detection unit 205 described later. The specific configuration of the correlator 203 will be described later. The absolute value detection unit 205 calculates the absolute value of the correlation value calculated by the correlator 203.

The maximum value detecting section 205 firstly outputs
Aperture information is generated using the reception level from No.3. This aperture information sets a period during which symbol synchronization is established (synchronization pull-in processing). In addition,
In the present embodiment, a case will be described in which a range in which one synchronization signal is secured before and after correct synchronization timing is set as a period for performing synchronization pull-in based on aperture information. That is, the correct synchronization timing is
This is a boundary point between the synchronization signal 110 and the guard section 111, and the period during which symbol synchronization is established is the synchronization signal 109.
From the boundary point between the synchronization signal 110 and the synchronization signal 110
This is a point where the boundary point between the data and the guard section 111 is shifted to the right in the figure by the number of samples of 16. Note that the present invention is also applicable to a case where the period for performing the synchronization pull-in is appropriately changed according to the aperture information.

Further, the maximum value detecting section 205 uses the absolute value obtained by the absolute value detecting section 204 to calculate the correlation value calculated by the correlator 203 during the period set by the aperture information as described above. The timing at which the absolute value becomes maximum is detected. The specific configuration of the maximum value detection unit 205 will be described later.

The timing generation unit 206 performs an FFT based on the timing detected by the maximum value detection unit 205.
Setting the start timing of the FFT processing by the unit 202;
A timing signal is output to FFT section 202. As described above, the maximum value detection unit 205 detects the timing at which the absolute value of the correlation value becomes the maximum, so that symbol synchronization can be established.

Next, a specific configuration of the correlator 203 will be described with reference to FIG. FIG. 3 is a block diagram illustrating a configuration of a correlator in the OFDM communication apparatus according to the embodiment of the present invention.

[0043] In FIG. 3, the received signal converted into a digital signal by the A / D converter 201 (hereinafter referred to as "A / D output signal.") Is output to the delay unit 301a ₁₅ and a multiplier 302a _16.

The delay unit 301a ₁₅ delays the A / D output signal by a unit symbol. The multiplier 302a ₁₆ includes a first 16 symbol in the known signal described above, multiplies the A / D output signal, and outputs the multiplication result to the adder 303a _15. The multiplier 302a ₁₅ includes a first 15 symbol in the known signal described above, which is delayed by the delay unit 301a ₁₅ A
/ D output signal, and the multiplication result is added to the adder 303a ₁₅
Output to The adder 303a ₁₅ adds the multiplication result from the multiplication result and the multiplier 302a ₁₅ from multiplier 302a _16.

Similarly, the delay unit 301a ₁
The A / D output signal delayed by 1a ₂ by a unit symbol delay. The multiplier 302a ₁ includes a first symbol in the known signal described above, multiplies the A / D output signal delayed by the delay unit 301a _1, and outputs the multiplication result to the adder 303a _1. The adder 303a ₁ includes an adder 30
3a ₂ and the multiplication result from the multiplier 302a ₁ are added, and the addition result is used as a correlation output to obtain the absolute value detection unit 2 shown in FIG.
04. The above is the specific configuration of the correlator 203.

Next, a specific configuration of the maximum value detecting section 205 will be described with reference to FIGS. 4 and 5. FIG. FIG. 4 is a block diagram illustrating a configuration of the maximum value detection unit 205 in the OFDM communication apparatus according to the embodiment of the present invention.

In FIG. 4, the absolute value of the correlation result, that is, the integration result, sent from the absolute value detection unit 204 is
01, the switch 404, and the reprocessing unit 406. The subtractor 401 subtracts the result of the integration from the first threshold value stored in the memory 402, and determines the result of the subtraction by the determination unit 4.
03 is output. The specific configuration of the reprocessing unit 406 will be described later.

The determination unit 403 determines whether the switch 404 and the counter 405 are based on the result of the subtraction from the subtractor 401.
Control. That is, the determination unit 403 stores the integration result in the memory 40 when the integration result is larger than the first threshold value.
In addition, the switch 404 is controlled so as to output the count value to 2, and the counter 405 is controlled so as to reset the count value. Conversely, when the integration result is equal to or less than the first threshold value, the determination unit 403 controls the switch 404 not to output the integration result to the memory 402 and sets the switch 405 so that the count value is incremented. Control.

When the integration result is larger than the first threshold value, the determination unit 403 sends a signal indicating that the integration result has exceeded the first threshold value to a reprocessing unit 406 described later. Output.

The switch 404 executes or interrupts the output of the integration result to the memory 402 under the control of the determination unit 403 as described above. The switch 404 outputs the reset information to the memory 402 when the reset information is sent from a reprocessing unit 406 described later.

The memory 402 stores an initial value as a first threshold value. When an integration result is sent via the switch 404, the integration result is stored as a new first threshold value. When the reset information is sent via the switch 404, the initial value is stored as a new first threshold value. The memory 402 outputs the stored first threshold value to the subtractor 401.

The counter 405 resets or increments the count value under the control of the determination unit 403 as described above, and outputs the count value to the subtractor 407. The counter 405 is provided with a reprocessing unit 406 described later.
When the reset information is sent from, the count value is reset.

The subtracter 407 subtracts the count value from the counter 405 from the threshold value for the counter, and outputs the result of the subtraction to the determination unit 408. The determination unit 408 determines the result of the subtraction performed by the subtractor 407, and outputs the result of the determination to the logical sum operation unit 410. That is, the determination unit 408
Outputs "1" to the OR operation unit 410 when the count value of the counter 405 exceeds the threshold value for the counter, and when the count value of the counter 405 is equal to or less than the threshold value for the counter. Has a logical sum operation unit 410
Is output as "0".

On the other hand, aperture generation section 409 generates the above-described aperture information using the reception level from correlator 203, and outputs the generated aperture information to logical sum operation section 410. That is, the aperture generation unit 409 outputs “0” to the logical sum operation unit 410 during the synchronization pull-in period, and outputs “1” when the synchronization pull-in period ends.

The logical sum operation unit 410 calculates the logical sum of the judgment result from the judgment unit 408 and the aperture information from the aperture generation unit 409, and outputs the synchronization establishment signal only when the operation result is "1". Timing generation unit 20 described above
6 is output. That is, the logical sum operation unit 410 determines that the synchronization pull-in period has ended or that the integration result is the first
Only when the number of times equal to or less than the threshold value exceeds the counter threshold value, in the synchronization pull-in process, the timing at which the integration result becomes maximum is determined by the timing generation unit
Output to

Next, a specific configuration of the reprocessing unit 406 will be described with reference to FIG. FIG. 5 is a block diagram illustrating a configuration of the reprocessing unit 406 in the maximum value detection unit 205 in the OFDM communication apparatus according to the embodiment of the present invention.

In FIG. 5, the counter 507 increments the count value when a signal indicating that the integration result has exceeded the first threshold value is sent from the determination unit 403 described above, and will be described later. When reset information is sent from the determination unit 506, the count value is reset. The counter 507 outputs the count value to the magnitude comparing unit 508.

The magnitude comparing unit 508 compares the count value of the counter 507 with the magnitude, and controls the switch 501 based on the comparison result. That is, the size comparison unit 50
8 is a switch 5 when the count value of the counter 507 is 1 or more (when the integration result exceeds the first threshold value (that is, when the first threshold value is updated)).
01 is closed, and conversely, when the count value of the counter 507 is less than 1 (when the integration result is equal to or less than the first threshold value (that is, when the first threshold value is not updated)). , The switch 501 is opened.

The switch 501 is in the initial state.
It is open. The switch 501 outputs the absolute value (integration result) of the correlation result to the subtractor 502 and the switch 504 under the control of the magnitude comparison unit 508. The subtractor 502 performs a subtraction between the integration result and the second threshold value, and outputs the subtraction result to the determination unit 503. In addition,
The second threshold value will be described later.

The determination section 503 controls the switch 504 based on the result of the subtraction by the subtractor 502. That is, the determination unit 503 controls to close the switch 504 once the integration result becomes smaller than the second threshold value.

The integration result is input to the switch 504 via the switch 501. This switch 504 is open in an initial state. This switch 5
04 executes the output of the integration result to the subtractor 505 under the control of the determination unit 503.

The subtracter 505 subtracts the integration result sent via the switch 504 from the third threshold value, and outputs the subtraction result to the determination unit 506. The third threshold value will be described later.

The determination unit 506 outputs reset information based on the result of the subtraction by the subtractor 505. That is,
When the integration result exceeds the third threshold value, the determination unit 506 outputs the reset information to the counter 405 and the switch 40.
4. Output to the counter 507. Also, the judgment unit 5
06, the reset information is output.
1 and the switch 504 are returned to the initial state.

Here, the state in which the integration result exceeds the third threshold value (that is, the state in which reset information is output) means that the integration result exceeds the first threshold value and then the second threshold value. This corresponds to a state where the value falls below the value and exceeds the third threshold value.

Next, a timing detection method by the maximum value detection unit 205 will be described with reference to FIG. FIG.
FIG. 5 is a flowchart showing a maximum value detection procedure by the maximum value detection unit 205 in the OFDM communication apparatus according to the embodiment of the present invention.

Referring to FIG. 7, first, in ST701, the integration result, that is, the absolute value of the correlation value calculated by correlator 203, is compared with the first threshold value. If the integration result is greater than the first threshold value, the process proceeds to S
The process shifts to T702, and conversely, if the integration result is equal to or less than the first threshold, the process shifts to ST704.

In ST702, the first threshold value used in ST701 is updated. That is, the integration result at the timing exceeding the first threshold value is set as a new first threshold value. Thereafter, in ST703, the counter 4
After the count value of 05 has been reset, the process proceeds to ST70.
Go to 5.

On the other hand, in ST704, after the count value of counter 405 has been incremented, the process proceeds to ST704.
Go to 5.

In ST705, it is determined whether or not the aperture information is L. The fact that the aperture information is L corresponds to the end of the time for establishing the symbol synchronization.

In ST705, when the aperture information is L
If not, the process shifts to ST707. If the aperture information is L, the process shifts to ST706. In ST707, it is determined whether or not the first threshold has been updated. When the first threshold is updated, that is, when the integration result exceeds the first threshold,
The process proceeds to ST708, and if the first threshold has not been updated, that is, if the integration result is equal to or smaller than the first threshold, the process returns to ST701 described above.

In ST708, reprocessing is performed by reprocessing section 406 in maximum value detecting section 205. The reprocessing procedure by the reprocessing unit 406 will be described later. After the reprocessing by the reprocessing unit 406, the process proceeds to ST709.

In ST709, the count value of counter 405 is compared with the counter threshold value. If the count value is equal to or less than the threshold value, the process proceeds to S
Returning to T701, if the count value is larger than the threshold, the process moves to ST706.

In ST706, the timing at which the integration result finally exceeds the first threshold value is set as the symbol timing. As described above, when the count value of the counter 405 (the number of times the integration result is equal to or less than the first threshold value) exceeds the counter threshold value, or the period for performing symbol synchronization set by the aperture information has ended. In this case, the timing at which the integration result finally exceeds the first threshold is set as the symbol timing, and the symbol synchronization is established.

Next, the procedure of the re-processing by the re-processing unit 406 will be described with reference to FIG. 6 and FIG. FIG.
FIG. 5 is a schematic diagram showing an example of a transition of an integration result in the OFDM communication apparatus according to the embodiment of the present invention. FIG.
FIG. 9 is a flowchart showing a reprocessing procedure by a reprocessing unit 406 in the maximum value detection unit 205 in the OFDM communication apparatus according to the embodiment of the present invention.

Referring to FIG. 6, it is clear that the correlation characteristic has the following tendency. That is, the integration result once becomes a small value after the correlation peak 602 occurs at the boundary point between the synchronization signal 109 and the synchronization signal 110, and then becomes a large value again. After that, the synchronization signal 110 and the guard interval 11 which are correct synchronization timings
At the boundary point with 1, a correlation peak 601 occurs. Conventionally, a correlation peak 60
There is a possibility that the timing when 2 occurs may be detected.

Therefore, in the present embodiment, the integration result is
It is noted that a correct correlation peak appears after exceeding the first threshold, below the second threshold, and further above the third threshold. That is, when the integration result changes as described above, the first threshold value updated so far is reset to the initial value. As a result, the size of the correct correlation peak 601 is set as the first threshold value, so that the time when the correlation peak 601 occurs can be detected as the correct synchronization timing.

The second threshold value and the third threshold value can be appropriately changed in accordance with various conditions. As is apparent from FIG. 6, the third threshold value> the second threshold value. Needless to say, the threshold value is set.

The procedure for realizing the above processing can be represented by a flowchart shown in FIG. First, ST
At 801, the result of integration is compared with a second threshold value. If the integration result is smaller than the second threshold, the process moves to ST802. Conversely, if the integration result is equal to or larger than the second threshold, the process proceeds to ST803.

In ST802, after flag 1 is set to "H", the process proceeds to ST804. In ST803, after flag 1 is set to "L", the process proceeds to ST80.
Move to 4.

In ST804, it is determined whether flag 1 is "H" or "L". Flag 1 is "H"
In other words, if the integration result has become smaller than the second threshold value, the process proceeds to ST805. Conversely, when the flag 1 is “L”, that is, when the integration result has not become smaller than the second threshold value, the reprocessing ends.

In ST805, the result of integration is compared with the third threshold value. That is, if the integration result is greater than the third threshold value, the process proceeds to ST806, and if the integration result is less than or equal to the third threshold value, the process ends.

In ST806, a counter (counter 40
5 (FIG. 4) and the counter 507 (FIG. 5)), the first threshold value is returned to the initial value, and the switch 501 and the switch 504 are set as described above.
(FIG. 5) is returned to the initial state. Thereafter, the reprocessing ends.

After the reprocessing is completed, the subsequent processing shifts to ST709 (see FIG. 7). According to the maximum value detection procedure of the maximum value detection unit 205 as described above, the first threshold value changes as described below. Referring to FIG. 6, when the integration result reaches correlation peak 602, the first threshold value is set to the magnitude of correlation peak 602. In this state, since the first threshold value has been updated, reprocessing is performed.

While the reprocessing continues to be performed, the integration result falls below the second threshold and then exceeds the third threshold. When the integration result exceeds the third threshold value, the first threshold value is returned to the initial value by reprocessing. This allows
The timing at which the correlation peak 602 occurs is not erroneously detected as the correct timing.

Thereafter, the first threshold value is updated each time the integration result increases, so that the magnitude of the correlation peak 601 becomes the final first threshold value. As a result, the timing at which the correlation peak 601 occurs is detected as a correct symbol timing. Therefore, the probability that a timing error occurs is reduced, and the possibility that the error rate characteristic of the demodulated signal is deteriorated is reduced.

Next, the error rate characteristic of the demodulated signal in the present embodiment will be described with reference to FIG. FIG.
FIG. 6 is a diagram showing an example of a computer simulation result of an error rate characteristic in the OFDM communication apparatus according to the embodiment of the present invention. In FIG. 9, the PER (packet error rate) of the demodulated signal with respect to the ratio between the noise power density of the demodulated signal ("NO" in the figure) and the average code energy per bit of the demodulated signal ("Eb" in the figure) is shown. OFDM communication apparatus according to the present embodiment (proposed scheme) and OFD communication apparatus of conventional scheme
Each of the M communication devices is shown.

The conditions of the computer simulation are as follows:
It is as follows. Packet size: 54 bytes, modulation method: 16QA
M, demodulation method: synchronous detection, maximum Doppler frequency: 50
Hz, propagation model: 18-wave Rayleigh fading model, delay dispersion: 150 ns, error correction: Viterbi decoding (coding rate: 9/16, constraint length: 7) As is clear from FIG. 9, the OFD according to the present embodiment
The packet error rate in the M communication device is improved by one digit or more as compared with the conventional system.

As described above, OFD according to the present embodiment
According to the M communication device, when the maximum value of the correlation result is detected, the correlation result falls below the second threshold and then exceeds the third threshold in a state where the first threshold is updated. At times, the first threshold value is returned to the initial value. Thereby, even when a plurality of large correlation peaks occur,
Since the correlation peak occurring at the correct synchronization timing can be detected as the maximum value, the probability of occurrence of a timing error can be reduced. Therefore, it is possible to suppress the deterioration of the error rate characteristic of the demodulated signal.

Although the present embodiment has been described with respect to a case where a range in which one synchronization signal is secured before and after the correct synchronization timing is set as the period for performing the synchronization pull-in, the present invention relates to a case where the synchronization pull-in is performed. Is also applicable to a case in which the period for performing is set wider. For example, referring to FIG. 6, when the synchronization pull-in is started at a boundary point between the synchronization signal 105 and the synchronization signal 106 (when five synchronization signals are used in the synchronization pull-in process). In, five correlation peaks having a certain magnitude including the correlation peak 601 occur, but the final first threshold is set to the magnitude of the correlation peak 601.

Further, in this embodiment, the case where the number of synchronization signals in the synchronization symbol is set to 5 has been described. However, the present invention reduces the number of synchronization signals in the synchronization symbol to two or more. As long as the condition for setting is satisfied, the present invention can be applied to a case where the number of synchronization signals is appropriately increased or decreased.

OFDM explained in the above embodiment
The communication device can be mounted on a communication terminal device or a base station device in a digital mobile communication system.

[0092]

As described above, according to the present invention,
After the threshold (first threshold) for the correlation result is updated, if the correlation result falls below the second threshold and exceeds the third threshold, the first threshold Is repeated as an initial value, and the first threshold value at the time when the synchronization pull-in process is completed is detected as the maximum value. Therefore, the probability of occurrence of a timing error is reduced, so that the error rate of the demodulated signal is reduced. OFDM that prevents deterioration of characteristics
A communication device can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an example of a unit frame format used by an OFDM communication apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of an OFDM communication apparatus according to an embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a correlator in the OFDM communication apparatus according to the embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a maximum value detection unit in the OFDM communication apparatus according to the embodiment of the present invention.

FIG. 5 is a block diagram showing a configuration of a reprocessing unit in a maximum value detection unit in the OFDM communication apparatus according to the embodiment of the present invention.

FIG. 6 is a schematic diagram showing an example of a transition of the integration result in the OFDM communication apparatus according to the embodiment of the present invention.

FIG. 7 is a flowchart showing a maximum value detection procedure by a maximum value detection unit in the OFDM communication apparatus according to the embodiment of the present invention.

FIG. 8 is a flowchart showing a reprocessing procedure by a reprocessing unit in a maximum value detection unit in the OFDM communication apparatus according to the embodiment of the present invention.

FIG. 9 is a diagram showing an example of a computer simulation result of an error rate characteristic in the OFDM communication apparatus according to the embodiment of the present invention.

FIG. 10 is a schematic diagram showing an arrangement of subcarriers in a conventional OFDM communication apparatus.

FIG. 11 is a schematic diagram showing a period of an OFDM symbol in a conventional OFDM communication device.

FIG. 12 is a schematic diagram showing a frame format in a conventional OFDM communication device.

FIG. 13 is a block diagram showing a configuration of a conventional OFDM communication device.

FIG. 14 is a flowchart showing a maximum value detection procedure by a maximum value detection unit in a conventional OFDM communication apparatus.

FIG. 15 is a schematic diagram showing a transition of an integration result in a conventional OFDM communication device.

[Explanation of symbols]

 106 to 110 Synchronization signal 203 Correlator 204 Absolute value detection unit 205 Maximum value detection unit 206 Timing generation unit 202 FFT unit 401, 407, 502, 505 Subtractor 402 Memory 403, 408, 503, 506 Judgment unit 404, 501 504 switch 405, 507 counter 406 reprocessing unit 409 aperture generation unit 410 OR operation unit 508 size comparison unit

Claims (5)

[Claims] 1. A receiving means for receiving, as a received signal, a signal transmitted by a communication partner in accordance with a unit frame format including a plurality of sections for inserting a unit known signal, using the received signal and the unit known signal. Calculating means for calculating a correlation value, and a peak in a correlation value calculated using a received signal corresponding to a section located at an end in a unit frame format from among peak values in the correlation value calculated by the calculating means. OFDM communication comprising: detecting means for detecting a value as a maximum value; and setting means for setting a synchronization timing used for FFT processing on a received signal based on a timing at which the detected maximum value occurs. apparatus. 2. The comparison device according to claim 1, wherein the detection device compares the correlation value calculated by the correlation device with a first threshold value for a predetermined period of time.
Updating means for updating the correlation value to a first threshold value when there is a correlation value larger than the threshold value; and updating the first threshold value by the changing means, If the calculated correlation value falls below the second threshold value and then exceeds the third threshold value, an initial setting means for setting the first threshold value to an initial value; An OFDM communication apparatus, comprising: a maximum value detecting means for detecting the first threshold value at the time of termination as a maximum value. 3. The OFD according to claim 1 or claim 2.
A communication terminal device comprising an M communication device. 4. The OFD according to claim 1 or 2,
A base station device comprising an M communication device. 5. A receiving step of receiving, as a received signal, a signal transmitted by a communication partner in accordance with a unit frame format including a plurality of sections for inserting a unit known signal, and correlating the received signal with the unit known signal. A calculating step of calculating a value, and a peak value in a correlation value calculated using a reception signal corresponding to a section located at an end in a unit frame format from among peak values in a correlation value calculated by the calculating unit. A detection step of detecting as a maximum value, a setting step of setting a synchronization timing based on the timing at which the detected maximum value occurs,
An OFDM communication method, comprising: