JP2003224540A - Spread spectrum receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a spread spectrum receive capable of synchronously catching a spread code even in various noise environments in which a fluctuation of a noise level and a fluctuation of a noise occurrence frequency take place frequently. <P>SOLUTION: A despreading part 12 obtains power intensity of an autocorrelation value by multiplying a spread spectrum signal subjected to spread modulation and transmission, by a spread code for demodulation whose chip phase is shifted by a chip phase varying part 11. A dispersion degree calculating part 13 calculates standard deviation as a dispersion degree of the calculated autocorrelation value. A threshold varying part 14 variably sets an optimum threshold on the basis of the calculated standard deviation value. A comparing part 15 then detects synchronization establishment or step-out of the spread code for demodulation by using a newly variably set threshold to compare the threshold with the autocorrelation value being an output of the despreading part 12. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spread spectrum receiver, and more particularly to synchronization acquisition of spread code in reception of spread spectrum signal.

[0002]

2. Description of the Related Art Conventionally, in a spread spectrum receiver of this type, for example, a noise power obtained prior to the timing of calculating a correlation value in each chip phase is used as a threshold,
An apparatus has been proposed that determines the synchronization of a correlation value (eg, Japanese Patent Laid-Open No. 122190/1993).

[0003]

However, in such a conventional spread spectrum receiver, the phase of the demodulation spread code is intermittently shifted, the power level of only the noise component immediately before that is obtained, and the level thereof is determined. Since the threshold value is increased / decreased in accordance with the above, there is a problem that it is difficult to detect the synchronization establishment or the out-of-synchronization of the demodulation spreading code when the noise level variation or the noise generation frequency variation frequently occurs. It was

The present invention has been made to solve such a problem, and enables spread code synchronization acquisition even in various noise environments in which fluctuations in noise level and fluctuations in frequency of noise frequently occur. A spread spectrum receiver is provided.

[0005]

A spread spectrum receiver according to the present invention comprises a phase changing means for shifting and outputting a chip phase of a demodulating spread code for demodulating a spread spectrum signal transmitted by spread modulation. Despreading means for despreading the spread spectrum signal by the demodulation spreading code output from the phase varying means to obtain its correlation value, and dispersion for calculating the degree of dispersion of the power intensity of the correlation value due to the chip phase shift The configuration includes a degree calculating means and a threshold varying means for variably setting a threshold serving as a reference when detecting the establishment of synchronization between the spread spectrum signal and the demodulation spread code.

With this configuration, even in various noise environments in which fluctuations in the noise level and fluctuations in the frequency of occurrence of noise frequently occur, it is possible to capture the spread code synchronously by setting a threshold value based on the degree of dispersion of the correlation value. You can

Further, the spread spectrum receiver of the present invention has a structure in which the degree of dispersion is either standard deviation or average deviation. With this configuration, the threshold can be appropriately variably set based on a calculation formula such as a standard deviation or an average deviation.

Further, the spread spectrum receiving apparatus of the present invention has a structure in which the calculation cycle of the correlation value calculated later is changed according to the value of the degree of dispersion calculated previously. With this configuration, it is possible to set an appropriate calculation cycle according to the fluctuation of the noise level and the frequency of occurrence of noise.

Further, the spread spectrum receiver of the present invention has a structure in which the comparison means detects the establishment of synchronization based on the detection conditions set hierarchically. With this configuration, it is possible to easily switch to an appropriate detection condition.

Further, the spread spectrum receiving apparatus of the present invention has a configuration in which the number of layers of the detection condition is changed according to the value of the degree of dispersion. With this configuration, it is possible to easily switch to an appropriate detection condition according to the fluctuation of the noise level and the frequency of occurrence of noise.

Further, the spread spectrum receiving apparatus of the present invention has a structure in which different thresholds are applied to each layer of the number of layers. With this configuration, it is possible to appropriately establish synchronization and detect out-of-synchronization in each layer according to the number of layers.

Further, in the spread spectrum receiving apparatus of the present invention, the threshold applied to each layer is 2 for each layer.
It has one threshold value and has a configuration for selecting a chip phase synchronization candidate from the two threshold values and the correlation value. With this configuration, it is possible to quickly select a chip phase synchronization candidate.

Further, in the spread spectrum receiver of the present invention, the two thresholds are composed of the first threshold and the second threshold having a value larger than the first threshold, and the correlation value is smaller than the first threshold. At this time, the phase changing means sequentially shifts the chip phase, and when the correlation value is larger than the first threshold value and smaller than the second threshold value, the hierarchy is switched and despreading is performed by the demodulation spreading code of the same chip phase. The obtained correlation value is compared with the first threshold value and the second threshold value in the layer after switching, and when it is larger than the second threshold in the layer after switching, synchronization of the spreading code is established. It has a configuration to judge. With this configuration, it is possible to quickly establish synchronization.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

(First Embodiment) FIG. 1 shows a first embodiment of the present invention.
FIG. 3 is a block diagram of a spread spectrum receiver in the exemplary embodiment. As shown in FIG. 1, the spread spectrum receiving apparatus of the present invention includes a chip phase varying unit 11 that shifts and outputs a chip phase of a demodulation spread code for demodulating a spread spectrum signal, and a spectrum transmitted by spread modulation. A despreading unit 12 that obtains an autocorrelation value by performing despreading processing on a spread signal by a demodulation spreading code with a chip phase shifted, and a degree of dispersion of power intensity of the autocorrelation value due to the chip phase shift are calculated. A dispersion degree calculation unit 13,
A threshold variable unit 14 that variably sets a threshold value that serves as a reference when detecting synchronization establishment between the spread spectrum signal and the demodulation spread code based on the degree of dispersion, and the autocorrelation value that is the output of the threshold value and the despreading unit 12. A comparison unit 15 that compares the power intensity and detects the synchronization establishment or out-of-synchronization of the demodulation spreading code according to the comparison result, and the despreading unit 1 according to the value of the dispersion degree.
2 includes a calculation period setting unit 16 that adaptively sets the calculation period of the autocorrelation value to be calculated, and a detection condition setting unit 17 that includes a threshold value changing unit 14 and a calculation period setting unit 16.

Next, the operation of the spread spectrum receiving apparatus according to the first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a dispersion degree diagram of the first autocorrelation value in the first embodiment of the present invention, FIG. 3 is the same flow chart, and FIG.
FIG. 6 is a second degree of dispersion diagram of the autocorrelation value. The threshold variable unit 14 and the calculation cycle setting unit 1 in the detection condition setting unit 17
6 sets a threshold value and a calculation cycle to initial values (step (hereinafter referred to as S) 1).

The chip phase changing unit 11 shifts the chip phase of the demodulation spread code (S2). The despreading unit 12 multiplies the spread spectrum signal obtained by removing the carrier frequency from the spread-modulated and transmitted signal by the demodulation spreading code whose chip phase is shifted by the chip phase varying unit 11 to obtain the autocorrelation value. The power intensity (relative value) is obtained (S3). The threshold variable unit 14 outputs the threshold value set to the initial value to the comparison unit 15.

The comparison section 15 compares the power intensity of the autocorrelation value output from the despreading section 12 with this threshold value (S
4) If the autocorrelation value is greater than or equal to the threshold value, it is determined that the spread code synchronization has been established, and the synchronization acquisition process ends (S5).
If the autocorrelation value <threshold value, it is confirmed whether the calculated autocorrelation value is a predetermined number (S6). If the number has not reached the predetermined number, the chip phase variable unit 11 is instructed to shift the phase of the demodulation spreading code (S2), and a series of processing is repeated based on the shifted demodulation spreading code. Be done.

When the autocorrelation value <threshold value continues for a plurality of times, a series of processes is repeated a plurality of times, and the autocorrelation value is calculated the same number of times. When the number reaches a predetermined number, the dispersion degree calculator 13 calculates the standard deviation or the average deviation as the dispersion degree of the calculated autocorrelation value (S7). In the following description, the standard deviation will be described, but the average deviation may be used.

The threshold variable unit 14 variably sets the optimum threshold based on the calculated standard deviation value (S8). After that, the comparison unit 15 detects the synchronization establishment or the out-of-synchronization of the demodulation spreading code by comparing with the autocorrelation value output from the despreading unit 12 using the newly variably set threshold value.

Further, according to the size of the standard deviation value calculated by the dispersion degree calculation unit 13 (S7), not only the threshold value variable unit 14 variably sets the threshold value, but also the calculation cycle setting unit 16 causes the despreading unit 12 to set the threshold value. The calculation processing time of the autocorrelation value is also from T1 to T
2 (T1 <T2) is variably set (S8). As shown in FIG. 2, when the calculation processing time T1 has a large standard deviation, there is a possibility that the S / N ratio of the received spread spectrum signal is lowered.

Therefore, as shown in FIG. 4, the S / N ratio is improved by increasing the autocorrelation value calculation processing time from T1 to T2. The difference widens, and the margin for the synchronization determination by the comparison unit 15 increases, so that it is possible to more reliably detect the establishment or the out-of-sync of the demodulation spreading code.

As described above, in the spread spectrum receiving apparatus according to the first embodiment of the present invention, the threshold value changing unit 14 variably sets the threshold value according to the magnitude of the standard deviation value calculated by the dispersion degree calculating unit 13. In addition, since the calculation period setting unit 16 is also configured to variably set the calculation processing time of the autocorrelation value in the despreading unit 12, there are various fluctuations in the noise level and the noise occurrence frequency. Even in a noisy environment, it is possible to acquire synchronization of spread codes.

(Second Embodiment) FIG. 5 shows a second embodiment of the present invention.
The figure showing the detection condition of the spread spectrum receiving apparatus in the embodiment of the present invention is shown, and the detection condition is hierarchically set, and the number of layers is set by the value of the standard deviation of the autocorrelation value. The difference from the first embodiment is that it has three threshold values, and the other configurations and effects are the same as those of the first embodiment.
The different points regarding the operation will be mainly described.

Next, the operation of the spread spectrum receiver according to the second embodiment of the present invention will be described with reference to FIGS. 1, 5 and 6. FIG. 6 is a dispersion degree diagram of the third autocorrelation value in the second embodiment of the present invention. The despreading unit 12 multiplies the spread spectrum signal that has been spread and modulated and transmitted, with the demodulation spreading code whose chip phase variable unit 11 has shifted all chip phases to obtain the power intensity of the autocorrelation value.

The dispersion degree calculation unit 13 calculates the standard deviation value D of the autocorrelation value, and the detection condition setting unit 17 calculates the standard deviation value D.
Depending on whether <= 4, 4 <D <= 9, or D> 9, the number N of detection conditions to be hierarchically set is set to 3, 4, or 5. Now, assuming that the obtained standard deviation value D is 5.5, since 4 <D <9, the number of layers N is set to 4 and the detection condition C
Is the first threshold value S1 = 20 with the layer name L of L4a, the second
The threshold value S2 = 38 and the calculation cycle T = 1 ms.

The autocorrelation value of the first chip phase is T = 1.
Since the first threshold value is 20 or less when judged by ms, the chip phase is shifted second and the autocorrelation value is judged by T = 1 ms. The autocorrelation value is the first threshold 20 and the second threshold 38.
Since the chip phase remains the same, the layer is moved to L = L4b, and when the autocorrelation value is again determined to be T = 3 ms, the chip phase is shifted to the third because the first threshold value is 60 or less. Reset to L4a.

The autocorrelation value of the third chip phase is T = 1.
Since the first threshold value is 20 or less when judged with ms, the chip phase is shifted to the fourth and the autocorrelation value is judged with T = 1 ms. Similarly, when the autocorrelation values of the fourth and fifth chip phases are determined and then the autocorrelation value of the sixth chip phase is determined at T = 1 ms, the value is between the first threshold value 20 and the second threshold value 38. , So the chip phase remains L = L
Move the hierarchy to 4b.

When the autocorrelation value is again determined to be T = 3 ms, it is between the first threshold value 60 and the second threshold value 114. Therefore, the chip phase is left as it is and the layer is shifted to L = L4c. This time, when T = 9 ms, the first threshold value is 180 or less, so the chip phase is shifted to the seventh position and reset to L = L4a. When the autocorrelation value of the seventh chip phase is judged at T = 1 ms, it is the second threshold value 38 or more, so it is judged that the synchronization of the spread code is established, and the synchronization acquisition operation is ended.

As described above, in the spread spectrum receiving apparatus according to the second embodiment of the present invention, the detection condition setting unit 17 has the detection conditions hierarchically, and further the autocorrelation calculated by the dispersion degree calculation unit 13 is used. The number of layers is set according to the value of the standard deviation of the values, and the detection conditions in each layer have two threshold values. Therefore, it is possible to change various noise levels and noises that frequently occur. Even in the environment, it is possible to quickly and accurately acquire the synchronization of the spread code.

In the above embodiment, the standard deviation values are 4> = D, 4 <D <= 9, D> 9, and the number of layers is 3, 4 and 5, respectively. The first threshold value, the second threshold value, and the calculation cycle in each layer have been described in the case of the values shown in FIG. 5, but the present invention is not limited to these values and similar effects can be obtained.

[0032]

As described above, according to the present invention, the degree of dispersion of the power intensity of the correlation value due to the shift of the chip phase is calculated, and the threshold is variably set based on the calculated degree of dispersion. It is possible to provide a spread spectrum receiving apparatus having an excellent effect that it is possible to acquire synchronization of spread codes even in various noise environments in which fluctuations and fluctuations in noise occurrence frequency occur frequently.

[Brief description of drawings]

FIG. 1 is a block diagram of a spread spectrum receiver according to a first embodiment of the present invention.

FIG. 2 is a dispersion degree diagram of a first autocorrelation value of the spread spectrum receiver according to the first embodiment of the present invention.

FIG. 3 is a flowchart showing the operation of the spread spectrum receiver according to the first embodiment of the present invention.

FIG. 4 is a dispersion degree diagram of a second autocorrelation value of the spread spectrum receiver according to the first embodiment of the present invention.

FIG. 5 is a diagram showing detection conditions of the spread spectrum receiver according to the second exemplary embodiment of the present invention.

FIG. 6 is a dispersion degree diagram of a third autocorrelation value of the spread spectrum receiver according to the second exemplary embodiment of the present invention.

[Explanation of symbols]

11 Chip phase variable unit 12 Despreading section 13 Dispersion degree calculator 14 Threshold variable part 15 Comparison section 16 Calculation cycle setting section 17 Detection condition setting section

Claims (8)

[Claims] 1. A phase varying means for shifting and outputting a chip phase of a demodulating spread code for demodulating a spread spectrum signal transmitted by spread modulation, and a demodulating spread code outputted from the phase varying means. Despreading means for performing despreading processing on the spread spectrum signal to obtain its correlation value, dispersion degree calculating means for calculating the dispersion degree of the power intensity of the correlation value due to the shift of the chip phase, and the spread spectrum signal And a threshold value varying means for variably setting a threshold value serving as a reference when detecting establishment of synchronization with the demodulation spread code. 2. The spread spectrum receiver according to claim 1, wherein the degree of dispersion is one of standard deviation and average deviation. 3. The spread spectrum receiving apparatus according to claim 1, wherein the calculation cycle of the correlation value calculated later is changed according to the value of the degree of dispersion calculated previously. 4. Based on detection conditions set hierarchically,
3. The spread spectrum receiving apparatus according to claim 1, wherein the comparison means detects the establishment of synchronization. 5. The spread spectrum receiving apparatus according to claim 4, wherein the number of layers of the detection condition is changed according to the value of the degree of dispersion. 6. The spread spectrum receiving apparatus according to claim 5, wherein different thresholds are applied to the respective layers of the number of layers. 7. The threshold applied to each layer has two thresholds for each layer, and the chip phase synchronization candidate is selected from the two thresholds and the correlation value. 7. The spread spectrum receiver according to claim 6. 8. The two thresholds are composed of a first threshold and a second threshold having a value larger than the first threshold, and when the correlation value is smaller than the first threshold, the phase The chip phase is sequentially shifted by the variable means, the correlation value is larger than the first threshold value, and the second
When the layer is smaller than the threshold of, the correlation value obtained by switching the layers and performing despreading with the demodulation spreading code of the same chip phase is used as the first threshold and the second threshold in the layer after the switching. 8. The spread spectrum receiving apparatus according to claim 7, further comprising: comparing and determining that the synchronization of the spreading code has been established when it is larger than the second threshold value in the layer after the switching.