JP2002185364A - Method for detecting signal in spectrum spread communication - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method capable of identifying a signal from a noise even when a reception level is low in a spectrum spread communication. SOLUTION: An integrating circuit 11 integrates correlated value data representing a correlation between a reception signal and a spread symbol. A correction coefficient calculating circuit 12 calculates a correction coefficient based on the integrated value calculated by the preset reference value and the integrating circuit 11. A multiplier 13 multiplies the correlated value data by the coefficient. A maximum value detector 14 detects the maximum value of the correlated value data multiplied by the coefficient. A comparator 15 compares the detected maximum value with the preset threshold value to identify the signal to be the object with the noise.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for detecting a signal in spread spectrum communication, and more particularly to a method for distinguishing a signal from noise in spread spectrum communication.

[0002]

2. Description of the Related Art Spread spectrum communication is known as one of wireless communication systems. In spread spectrum communication, data is spread using a spreading code and transmitted. Then, the receiver reproduces data by despreading the received signal using the same code as the spreading code used in the transmitter. The spread spectrum communication method is as follows.
This is a fundamental technology for realizing CDMA (Code Division Multiple Access). Further, as a technique for realizing spread spectrum communication, a direct spread scheme and a frequency hopping scheme are known, but the direct spread scheme will be described below.

[0003] In the direct spreading method, a transmission device directly multiplies transmission data by a spreading code. The spreading code is a data string that is faster than the transmission data. And
The spread signal is carried on a carrier wave and transmitted to a wireless transmission path. On the other hand, the receiving device reproduces transmission data by multiplying the received signal by the same spreading code as the spreading code used in the transmitting device. Here, the multiplication process is substantially the same as the process of detecting the correlation between the received signal and the spread code. Then, the transmission data is reproduced based on the correlation value (a value in which the logical value of each chip of the received signal matches the logical value of each chip of the spread code).

The above example shows a case where a signal is transmitted between a pair of communication devices. In practice, however, a large number of communication devices (including base stations) usually exist in a communication area. .
For example, in the example illustrated in FIG. 8, a plurality of terminal devices 101 and 102 are provided for the base station 100. In this case, a wireless channel connecting the base station 100 and each terminal device is identified by a spreading code. That is, the base station 100
Is a spread code # when sending data to the terminal device 101.
When the data is spread using terminal number 01 and the data is sent to terminal device 102, the data is spread using spreading code # 02.

[0005] The terminal device 101 monitors the correlation between the received signal and the spreading code # 01 using a digital matched filter or the like. At this time, spreading code # 01 is included in the received signal.
If a signal spread by using is included, a peak of a correlation value is obtained at regular intervals, as shown in FIG. 9 (a). Therefore, terminal device 101 can detect whether or not a signal addressed to itself is being transmitted by monitoring the correlation between the received signal and spreading code # 01.
Specifically, for example, when the peak of the correlation value indicating the correlation exceeds a preset threshold value, it is determined that the signal addressed to itself is being transmitted. When detecting the signal addressed to itself, the terminal device 101 reproduces the transmission data from the correlation value using the timing at which the peak of the correlation value is obtained.

On the other hand, if the received signal does not include a signal spread using the spreading code # 01, the signal shown in FIG.
As shown in (1), the correlation between the received signal obtained in the terminal device 101 and the spreading code # 01 does not have a periodic peak. For example, during a period in which data is transmitted from the base station 100 to the terminal device 102, the terminal device 1
Assuming that no data was sent to 01,
The terminal device 101 receives a signal for transmitting data from the base station 100 to the terminal device 102. However, this signal is a signal obtained by spreading data using the spreading code # 02. Therefore, in this case, in terminal apparatus 101, the correlation between the received signal and spreading code # 01 does not increase, and no periodic peak appears.

[0007] Therefore, in this case, the correlation value does not exceed the threshold value, and terminal device 101 determines that a signal addressed to itself is not transmitted. Then, the terminal device 101 does not perform a process of reproducing data from the received signal. In addition, the signal that does not include the signal addressed to itself is
Recognized as noise.

As described above, the receiver of the spread spectrum communication can detect the signal addressed to itself by monitoring the correlation between the received signal and the spread code.

[0009]

In a wireless communication system, a receiving apparatus may not be able to obtain a sufficient reception level. The reception level varies depending on, for example, the distance between the transmission device and the reception device, the communication environment of the wireless transmission path, and the like.

When the reception level decreases, the correlation value indicating the correlation between the received signal and the spreading code also decreases. That is, in a receiver that monitors the correlation between a received signal and a spread code using a digital matched filter or the like, the obtained correlation value is generally proportional to the amplitude of the received signal. Decreases, the correlation value decreases even if the target signal is included in the received signal. As a result, if the reception level drops,
The peak of the correlation value between the received signal and the spreading code is lower than the threshold as shown in FIG. In this case, a situation may occur in which the target signal cannot be detected even though the target signal is being transmitted.

When the reception level is low, the reception signal is often amplified using an amplifier. However, when the amplification factor is increased, the S / N ratio is deteriorated. Therefore, when the reception level is significantly reduced, the received signal cannot be sufficiently amplified. Therefore, when the reception level is significantly reduced, a peak of the correlation value cannot be obtained sufficiently.

[0012] Further, if an attempt is made to set a threshold value that can detect a signal even when the reception level is reduced, a target signal is not included (for example, FIG. 9).
In the case (b), a signal is erroneously detected, which is not preferable. It is an object of the present invention to provide a method capable of distinguishing between a signal and noise even in a case where a reception level is low in spread spectrum communication.

[0013]

SUMMARY OF THE INVENTION A signal detection method according to the present invention is a method for detecting a signal in spread spectrum communication, which generates correlation value data indicating the correlation between a received signal and a spread code, and converts the data to a reception level. Based on the maximum value of the corrected correlation value data, it is determined whether a signal corresponding to the spreading code is included in the received signal.

In the above method, when the received signal includes a signal corresponding to the spread code, the correlation value data has a periodic peak. However, when the reception level is low, the correlation value data becomes smaller as a whole, and its maximum value also becomes smaller. Therefore, when the reception level of the signal corresponding to the spreading code is low and when the high power noise is received (when the reception level of the reception signal not including the signal corresponding to the spreading code is high), the correlation value is obtained. The maximum value of the data may not be identifiable. Therefore, in the present invention, by correcting the correlation value data based on the reception level, it is possible to distinguish between a case where the reception level of the signal corresponding to the spread code is low and a case where high power noise is being received. I have.

In the above method, the reception level may be determined based on an average value or an integration value of the correlation value data. In this case, the correlation value data is corrected by calculating a correction coefficient in accordance with a ratio between the average value or the integrated value of the correlation value data and a reference value corresponding thereto, and multiplying the correlation value data by the correction coefficient. It may be.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. In this embodiment, it is assumed that the direct spreading method is used as the spreading method. FIG. 1 is a block diagram of a receiving device used in a spread spectrum communication system. The receiving device reproduces transmission data from a signal received from the wireless network. The received signal is first multiplied by a periodic wave having the same frequency as the carrier. This periodic wave is generated by the oscillator 1 provided in the receiving device. Thereby, the frequency of the received signal is converted to that near the baseband.

After the high-frequency component is removed by the low-pass filter, the received signal on which the periodic wave is multiplied is subjected to A / D conversion.
It is provided to the converter 2. The A / D converter 2 outputs a plurality of bits of digital data corresponding to the amplitude of the received signal. That is, when the reception level is high, the A / D converter 2 outputs digital data having a large amplitude corresponding thereto, and when the reception level is low, the A / D converter 2 outputs digital data having a small amplitude corresponding thereto. I do. Correlation unit 3
Monitors the correlation between the data sequence generated by the A / D converter 2 and the same code as the spreading code used in the transmitting device, and notifies the detecting unit 4 of the correlation value data obtained by the monitoring.

The detecting section 4 determines whether or not a target signal (a signal addressed to the receiving apparatus) is being transmitted based on the correlation value data generated by the correlating section 3. Then, when a target signal is detected, the timing of code synchronization is detected from the correlation value data. The decoding unit 5 generates data corresponding to the correlation value data given at the code synchronization timing detected by the detection unit 4.

In the above-mentioned receiving apparatus, a technique according to the present invention particularly relates to a method of detecting a target signal in the detecting unit 4. FIG. 2 is a diagram showing the correlation between the received signal and the spread code, and shows the correlation value data generated by the correlation unit 3. Note that the received signal basically includes a plurality of wireless signals. That is, in a wireless communication system in which a plurality of terminal devices exist, each terminal can arbitrarily transmit a signal, and each terminal device can receive a wireless signal transmitted from the plurality of terminal devices.

FIG. 2A shows correlation value data when a target signal is included in the received signal. here,
The "target signal" is a signal for transmitting data addressed to the receiving device, and is a signal spread by the same spreading code as the spreading code used by the receiving device. Therefore, in this case, the correlation value data has a peak for each symbol time. The “symbol time” is assumed to be the same as the period of the spreading code.

A threshold value for detecting a target signal is set in the detection unit 4. This threshold is determined, for example, so as to satisfy the following condition. (1) When the received signal is sufficiently high and the target signal is included in the received signal, it becomes smaller than the peak of the correlation value data. (2) The target signal is included in the received signal. Otherwise, even if the reception level is sufficiently high, the peak value of the correlation value data becomes larger than the peak value of the correlation value data. ) Is compared with the above threshold value. At this time, if the peak value of the correlation value data is larger than the threshold value, it is assumed that the target signal has been received, and the synchronization detection process and the data reproduction process are started. On the other hand, if the peak value of the correlation value data is smaller than the threshold value, it is determined that the target signal has not been received, and the synchronization detection processing and the data reproduction processing are not started.

FIG. 2B shows the correlation value data when the target signal is not included in the received signal. In this case, the correlation value data does not have a periodic peak. Further, since the maximum value of the correlation value data does not exceed the threshold value, the detection unit 4 determines that the target signal has not been received.

By the way, in the receiving apparatus shown in FIG.
The average value of the correlation value data is determined depending on the reception level. For example, when the reception level is high, that is, when the amplitude of the received signal is large, the amplitude value of the digital data output from the A / D converter 2 is also large, so that the average value of the correlation value data is necessarily large. Become. On the other hand, when the reception level is low, that is, when the amplitude of the received signal is small, the amplitude value of the digital data output from the A / D converter 2 is also small, so that the average value of the correlation value data is necessarily small. Become.

Therefore, if the reception levels are the same (or if a sufficient reception level is maintained), regardless of whether the target signal is included in the reception signal or not. The average value of the correlation value data should be substantially constant. That is, if the reception level is constant, the integrated value obtained by integrating the correlation value data over one symbol time (or the total added value obtained by cumulatively adding the correlation value data) should be constant. For example, FIG.
If the cases shown in FIGS. 2A and 2B have the same reception level, the area of each shaded portion should be substantially the same. In other words, when the reception level decreases, the average value of the correlation value data decreases as the reception level decreases, regardless of whether the target signal is included in the reception signal.

FIG. 2C shows the correlation value data when the reception level is reduced. This example shows a case where a target signal is included in the received signal. In this case, the correlation value data is similar to the case shown in FIG.
It has a peak every symbol time. However, when the reception level is low, the correlation value data becomes smaller as a whole. Then, as a result, if the peak value for each symbol time becomes smaller than the threshold value, it cannot be detected even though the target signal is included in the received signal. Things happen.

By the way, in the receiving apparatus of this embodiment, A
The / D converter 2 outputs digital data corresponding to the amplitude of the received signal, and the correlator 3 outputs the correlation between the output data sequence of the A / D converter 2 and the spreading code. Therefore,
For example, if the amplitude of the received signal is reduced to １ ／, the average value of the correlation value data is also reduced to 、. As a result, the integrated value obtained by integrating the correlation value data over one symbol time (or the correlation value data) (Total addition value obtained by cumulatively adding) is also approximately １ ／.

The receiving apparatus of this embodiment focuses on this point and improves the accuracy of signal detection. That is, in the receiving apparatus of the present embodiment, the correlation value data generated by the correlation unit 3 is corrected based on the reception level, and the presence or absence of the target signal is detected using the corrected correlation value data. . As a method of detecting the reception level, an integrated value obtained by integrating the correlation value data over one symbol time (or a total added value obtained by cumulatively adding the correlation value data over one symbol time) is used. .

For example, when the integrated value obtained by integrating the correlation value data over one symbol time is の of a predetermined reference value set in advance, FIG. Thus, the correlation value data is corrected so that the value is doubled as a whole. As a result, the peak of the correlation value data for each symbol time becomes larger than the threshold value, and a target signal is detected. The “reference value” is, for example, an integrated value obtained by integrating the correlation value data when the reception level is sufficiently high over one symbol time.

As described above, in the receiving apparatus of the present embodiment,
Since the correlation value data is appropriately corrected according to the reception level, when the target signal is included in the reception signal, it can be detected even if the reception level is low. That is, the case where the reception level of the target signal is low and the case of high power noise (when the reception level is high and the target signal is not included in the received signal) can be correctly identified.

FIG. 4 is a block diagram of a circuit for detecting a target signal from a received signal. This circuit, for example,
The detection unit 4 is provided in the detection unit 4 shown in FIG. 1 and detects whether or not a target signal exists using the output of the correlation unit 3. The integration circuit 11 calculates an integration value of the correlation value data for each symbol time. This integrating circuit 11 is, for example, as shown in FIG.
As shown in (1), an adder 21, a register 22, and a gate circuit 23 are provided. Here, the adder 21 and the register 22 accumulatively add the correlation value data output from the correlation unit 3. Then, when a timing signal synchronized with the symbol time is given, the gate circuit 23
The information (addition value) held in the register 22 is output. As a result, an integrated value obtained by integrating the correlation value data over one symbol time is output. It is assumed that the register 22 is reset by the timing signal.

The correction coefficient calculating circuit 12 calculates a correction coefficient for correcting the correlation value data based on a preset reference value and the integrated value calculated by the integrating circuit 11. Specifically, the correction coefficient is calculated based on the ratio between the reference value and the integral value. For example, if the integrated value is の of the reference value, “2” is output as the correction coefficient.

The multiplier 13 multiplies the correlation value data by a correction coefficient. The maximum value detection circuit 14 detects the maximum value of the correlation value data multiplied by the correction coefficient for each symbol time. Then, the comparison circuit 15 compares the maximum value of the corrected correlation value data with a preset threshold value for each symbol time, and based on the result, the target signal is included in the received signal. It is determined whether or not it is included.

Next, the effects of the present invention will be described. Fig. 6 (a)
Is the maximum value of the correlation value data for each symbol time (or
FIG. In this figure, the detection frequency when the maximum value of the correlation value data is detected for each of a predetermined number of symbols is depicted. In FIG. 6A, the reception state A indicates a case where the target signal is included in the received signal and the reception level is high, and the reception state B indicates the target state in the received signal. A case where a signal is included but the reception level is low indicates that the reception state C indicates a large power noise (when the reception level is high and the target signal is not included in the reception signal).

As shown in FIG. 6 (a), when the target signal is included in the received signal (reception states A and B), the maximum value of the correlation value data is as follows: It becomes smaller accordingly. As a result, in this example,
The distributions of the maximum value of the correlation value data in the reception state B and the reception state C overlap each other.
In this case, the reception state B is determined based on the maximum value of the correlation value data.
And the reception state C are difficult to distinguish. That is, it is impossible to distinguish between a case where the reception level of the target signal is low and a case where high power noise is being received.

FIG. 7 is a diagram showing an integrated value of the correlation value data. In this figure, the occurrence frequency when the integral value of the correlation value data is calculated for each of a predetermined number of symbols is illustrated. The reception states A and B respectively correspond to the reception states A and B in FIG. Although the distribution of the high power noise at the time of reception is not particularly shown, since the reception level itself is high, the integrated value of the correlation value data is
The value is larger than that in the reception state B. Further, here, for simplicity of description, it is assumed that the central value of the integrated value in reception state A is a reference value used in correction coefficient calculation circuit 12.

In this case, in the reception state A, the correction coefficient obtained by the correction coefficient calculation circuit 12 is “1”. Therefore, the maximum value of the corrected correlation value data in the reception state A is basically the same as the maximum value of the correlation value data generated by the correlation unit 3.

On the other hand, in the reception state B, since the integrated value of the correlation value data is smaller than the reference value, the correction coefficient is
"Value greater than 1" is obtained. Therefore, reception state B
The maximum value of the corrected correlation value data in
Is larger than the maximum value of the correlation value data generated. As a result, the maximum value of the corrected correlation value data in the reception state B is close to the maximum value in the reception state A, as shown in FIG.

Further, in the receiving state C, the correction coefficient is smaller than the correction coefficient in the receiving state B because the integrated value of the correlation value data is larger than the integrated value in the receiving state B. Therefore, the reception state C
The maximum value of the corrected correlation value data in
Is not so large as compared with the maximum value of the correlation value data generated by. As a result, the maximum value of the corrected correlation value data in the reception state C becomes smaller than the maximum value in the reception state A or B as shown in FIG.

Therefore, the reception state B and the reception state C can be identified by using the maximum value of the corrected correlation value data. Specifically, setting a threshold value as shown in FIG. 6B makes it possible to distinguish between a case where the reception level of the target signal is low and a case where high power noise is being received.

When obtaining the maximum value and the integral value of the correlation value data, the values obtained by a plurality of samplings (for example, about 10 times or 16 times) may be averaged. If this method is introduced, the influence due to the variation in the correlation value data (particularly, the influence due to the variation in the maximum value of the correlation value data) can be suppressed.

In the above-described embodiment, the integration operation of the correlation value data is performed over one symbol time. However, the integration operation is performed for the timing when the peak of the correlation value data appears and for a certain period around the timing. You may. In this case, the time required for the integration process can be saved as compared with the case where integration is performed over one symbol time. However, the ability to discriminate between signal and noise is higher when the integration process is performed over one symbol time.

In the above embodiment, the correlation value data is corrected based on the integral value of the correlation value data.
The present invention is not limited to this. For example, detecting the reception level or the amplitude of the reception signal by another method,
The correlation value data may be corrected based on this. As an example, in a receiving apparatus in which the signal amplitude is adjusted using an amplifier that amplifies a received signal, the correlation value data may be corrected according to the amplification factor of the amplifier.

[0043]

According to the present invention, a signal and noise can be distinguished in a receiving apparatus for spread spectrum communication even when the reception level is low. Therefore, situations such as starting synchronous operation, data reproduction operation, antenna selection operation, etc. even when no signal is received, and situations in which those operations cannot be started despite signal reception, are avoided. Is done. Further, even when the reception level fluctuates, the signal and the noise can be accurately distinguished without changing the threshold value.

[Brief description of the drawings]

FIG. 1 is a block diagram of a receiving device used in a spread spectrum communication system.

FIG. 2 is a diagram illustrating a correlation between a received signal and a spreading code.

FIG. 3 is a diagram schematically showing an operation of correcting correlation value data.

FIG. 4 is a block diagram of a circuit for detecting a target signal from a received signal.

FIG. 5 is an example of an integration circuit.

6A is a diagram showing the maximum value of correlation value data, FIG.
FIG. 9 is a diagram showing the maximum value of the corrected correlation value data.

FIG. 7 is a diagram illustrating an integrated value of correlation value data.

FIG. 8 is a diagram illustrating an example of a spread spectrum communication system.

FIG. 9 is a diagram showing a correlation between a received signal and a spreading code.

[Explanation of symbols]

 2 A / D converter 3 Correlation unit 4 Detection unit 5 Decoding unit 11 Integrator circuit 12 Correction coefficient calculation circuit 13 Multiplier 14 Maximum value detection circuit 15 Comparison circuit

Claims (4)

[Claims] 1. A method for detecting a signal in spread spectrum communication, comprising: generating correlation value data representing a correlation between a received signal and a spread code; correcting the correlation value data based on a reception level; A signal detection method for determining whether or not a signal corresponding to the spread code is included in the received signal based on the maximum value of the correlation value data. 2. The method according to claim 1, wherein the reception level is obtained based on an average value or an integral value of the correlation value data. 3. The method according to claim 2, wherein a correction coefficient is calculated according to a ratio between an average value or an integrated value of the correlation value data and a reference value corresponding thereto, and the correction coefficient is added to the correlation value data. To correct the correlation value data. 4. A receiving apparatus in spread spectrum communication, comprising: generating means for generating correlation value data representing a correlation between a received signal and a spread code; and correcting means for correcting the correlation value data based on a reception level. Determining means for determining whether or not a signal corresponding to the spreading code is included in the received signal based on the maximum value of the corrected correlation value data; and And a reproducing unit for reproducing transmission data from a signal corresponding to the spread code when a signal corresponding to the spread code is included.