JP3542986B2 - BbT product measuring device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for accurately measuring a BbT product of a waveform shaping filter used when generating a phase continuous multilevel FSK modulation signal.
[0002]
[Prior art]
In general, when performing communication regardless of wired or wireless, communication must be performed according to a preset communication standard. In addition, it must not interfere with communication performed on adjacent channels.
[0003]
However, if the spectrum of a signal used for communication spreads beyond a standard due to a failure of a communication device or the like, it interferes with communication of an adjacent channel.
[0004]
For this reason, it is necessary to check how wide the spectrum of the signal output from the communication device is.
[0005]
For example, as shown in FIG. 11, a GMSK modulation scheme, which is one of the phase continuous multi-level FSK modulation schemes, has a waveform shaping filter whose impulse response exhibits a Gaussian distribution characteristic with respect to a baseband signal Sa input in the NRZ format. In this method, the output signal Sc of the VCO (voltage controlled oscillator) 2 is frequency-modulated with a modulation index of 0.5 using the waveform-shaped signal Sb, and the signal Sc obtained by such a modulation method. Of the spectrum depends on the BbT product of the waveform shaping filter 1, that is, the product of the bandwidth of the waveform shaping filter 1 and the period of the symbol clock.
[0006]
FIG. 12 shows an example of the spectrum of the BbT product 0.3, and FIG. 13 shows an example of the spectrum of the BbT product 1.0.
[0007]
As can be seen from these figures, the smaller the BbT product of the waveform shaping filter, the higher the center concentration of the spectrum and the narrower the bandwidth. Therefore, the BbT product of the waveform shaping filter is a reference for evaluating the degree of spread of the spectrum of the modulated wave.
[0008]
In order to measure the BbT product of the waveform shaping filter used in such a GMSK modulation method, conventionally, the spread of the frequency component of the spectrum of the modulated wave is actually measured.
[0009]
That is, for the spectrum shown in FIG. 14, the maximum value Max of the power level is obtained, and the frequencies f1 and f2, which are lower by a predetermined level L (for example, 6 dB) from the maximum value Max around the frequency value f0 of the maximum value Max. Ask for.
[0010]
Then, the BbT product of the waveform shaping filter is obtained by calculating the ratio of the interval fw (frequency band) between the frequencies f1 and f2 and the symbol clock frequency fc of the modulation signal.
[0011]
[Problems to be solved by the invention]
However, as described above, in order to accurately calculate the BbT product of the waveform shaping filter from the ratio of the interval fw between the two frequencies f1 and f2 of the spectrum and the symbol clock frequency fc, the number of times of averaging the spectrum is increased. It is necessary to obtain the frequency interval fw with high accuracy, and it is necessary to process a large number of sample values of the spectrum data for the averaging process. Until the BbT product is obtained by the arithmetic processing on the large sample value, There was a problem that time became very long.
[0012]
An object of the present invention is to provide a BbT product measuring apparatus which can solve this problem and can obtain an accurate BbT product with a small number of sample values in a short time.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, a BbT product measuring device of the present invention comprises:
A BbT product for receiving a phase continuous multi-level FSK signal obtained by frequency-modulating a baseband signal in the NRZ format with a predetermined modulation index by a modulation signal obtained by shaping the waveform with a waveform shaping filter, and measuring a BbT product of the waveform shaping filter In the measuring device,
Phase detection means (22) for detecting an instantaneous phase with respect to the input continuous phase multi-level FSK signal;
Symbol clock synchronization processing means (23) for performing symbol clock synchronization processing on the input phase continuous multi-level FSK signal;
Phase sampling means (24) for sampling the phase detected by the phase detection means at the timing obtained by the symbol clock synchronization processing means;
Phase transition value detection means (25) for detecting a phase transition value of the phase obtained by the phase sampling means with respect to the immediately preceding phase obtained by the phase sampling means;
Symbol data detecting means (26) for detecting symbol data from the sign of the phase shift value detected by the phase shift value detecting means;
Storage means (27) for storing the symbol data detected by the symbol data detection means and the phase transition value used for detecting the symbol data in association with each other;
A pattern setting unit (28) for setting an arbitrary reference pattern;
The pattern of the symbol data stored in the storage means is compared with a reference pattern set by the pattern setting unit, and whether or not the pattern of the symbol data stored in the storage means matches the reference pattern is determined. Pattern determination means (29) for determination;
A phase transition value extraction unit (30) for extracting a phase transition value corresponding to an intermediate symbol of the pattern from the storage unit when the pattern determination unit determines that the pattern matches;
Average calculating means (31) for calculating an average value of the phase shift values extracted by the phase shift value extracting means;
A database unit (31) storing in advance information indicating a relationship between a phase transition value for a symbol in the middle of the reference pattern and a BbT product of the waveform shaping filter;
BbT product detection means (32) for obtaining a BbT product of the waveform shaping filter based on the average value of the phase transition value calculated by the averaging means and the information stored in the database unit. I have.
[0014]
Further, the BbT product measuring device according to claim 2 of the present invention is the BbT product measuring device according to claim 1,
In the database unit, information indicating a relationship between a BbT product and a value obtained by normalizing the phase shift value extracted by the phase shift value extracting unit using the value of the modulation index is stored in advance,
The BbT product detection unit is configured to perform the waveform shaping filter based on a value obtained by normalizing the average value of the phase transition value calculated by the average calculation unit with the modulation index and information stored in the database unit. The BbT product is obtained.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings, but before that, the principle of the present invention will be described.
[0016]
As described above, the GMSK modulation scheme, which is one of the phase continuous multi-level FSK schemes, is a scheme in which a baseband signal is frequency-modulated by a signal obtained by shaping the waveform with a waveform shaping filter (Gaussian filter). As is well known, the Gaussian function attenuates rapidly as it moves away from the origin. Specifically, it attenuates exponentially in proportion to the square of the distance from the origin.
[0017]
Therefore, the influence of the nearest code is dominant in the inter-symbol interference, and the influence of the further distant symbols is negligible to a negligible degree. It has been confirmed that the influence of only the intersymbol interference and the influence of the symbols farther apart are negligibly small.
[0018]
The present invention focuses on this point, and obtains the BbT product from the degree of the influence of the intersymbol interference.
[0019]
That is, as described above, assuming that the inter-symbol interference is affected only by the nearest symbol and not affected by other symbols, “000” and “001” including three consecutive symbols as a symbol sequence. , "010",..., "110", "111".
[0020]
Here, considering the symmetry of the positive and negative signs, if the symbols are continuous around the origin such as “000”, the opposite symbols around the origin such as “001” and “100” When it occurs, it can be grouped into three cases where the symbol opposite to the origin, such as “101”, occurs before and after. Among these, the effect of intersymbol interference is greatest among the symbols at the origin. This is the case where the opposite symbol occurs before and after.
[0021]
In addition, since the influence of intersymbol interference appears as a phase shift value of a symbol, the relationship between the phase shift value of a symbol and the BbT product when a signal having a pattern in which the influence of intersymbol interference is greatest as described above is input. Is obtained in advance, and when a pattern in which the influence of intersymbol interference is greatest appears in an input signal whose BbT product is unknown, the BbT product can be obtained from the phase transition value of the symbol.
[0022]
FIG. 1 shows a configuration of a BbT product measuring device 20 based on the above principle.
In FIG. 1, the demodulation processing unit 21 includes a phase detection unit 22, a symbol clock synchronization processing unit 23, a phase sampling unit 24, a phase transition value detection unit 25, and a symbol data detection unit 26.
[0023]
The phase detector 22 detects the instantaneous phase of the input phase continuous FSK signal Sd to be measured.
[0024]
The symbol clock synchronization processing means 23 performs a symbol clock synchronization process on the continuous phase FSK signal Sd at a known symbol clock frequency fc.
[0025]
The phase sampling means 24 samples the phase detected by the phase detection means 22 at the timing obtained by the symbol clock synchronization processing means 23.
[0026]
The phase shift value detecting means 25 sequentially obtains, as a phase shift value Δφ, an amount by which the phase obtained by the phase sampling means 24 has shifted from the phase obtained immediately before by the phase sampling means 24. .
[0027]
The symbol data detection means 26 obtains either “1” or “0” symbol data d from the sign of the phase transition value Δφ obtained by the phase transition value detection means 25.
[0028]
The symbol data d obtained by the demodulation processing unit 21 is stored in the memory 27 as storage means in the detection order in association with the phase transition value Δφ used when obtaining the symbol data.
[0029]
The pattern setting unit 28 is for setting an arbitrary reference pattern, and here, two patterns of “101” and “010” are set among patterns composed of three consecutive symbols. .
[0030]
The pattern determination means 29 determines a pattern Pi = (d _i , d _{i + 1} , d _{i + 2} ) composed of three symbol data successively stored in the memory 27 and a reference pattern “101” set in the pattern setting unit 28. , And “010” to determine whether the pattern Pi matches one of the reference patterns “101” and “010”.
[0031]
The phase shift value extracting unit 30 determines a phase shift corresponding to an intermediate symbol di _{+ 1} of the pattern Pi when the pattern determining unit 29 determines that the pattern Pi matches one of the reference patterns “101” and “010”. The value Δφ _{i + 1} is read from the memory 27.
[0032]
The average calculating means 31 obtains an average value (referred to as an absolute average value) H of the absolute values of the phase transition values Δφ _{i + 1} extracted by the phase transition value extracting means 30.
[0033]
Note that this absolute average value H is the absolute average value H (0) of a plurality of phase transition values Δφ (0) corresponding to the intermediate symbol “0” extracted when the pattern Pi matches the reference pattern “101”. ) And the absolute average value H (1) of a plurality of phase transition values Δφ (1) corresponding to the intermediate symbol “1” extracted when the pattern Pi matches the reference pattern “010”. is there.
[0034]
FIG. 2 shows the relationship between the change in symbol data and the change in phase.
In FIG. 2, when symbol data of “1” is continuous as in pattern A, the phase transition value between the symbols is π / 2, and when symbol data of “0” is continuous as in pattern B, , The phase shift value between the symbols is -π / 2. When the same symbols continue in this way, the pattern determination unit 29 outputs a determination result of mismatch.
[0035]
When the symbols “1” and “0” occur alternately as in the patterns C and D, the pattern determining unit 29 outputs a matching determination result, and the phase shift value extracting unit 30 outputs “101”. The phase transition value Δφ (0) corresponding to the intermediate symbol “0” of the pattern “” and the phase transition value Δφ (1) corresponding to the intermediate symbol “1” of the pattern “010” are extracted from the memory 27.
[0036]
The average calculating means 31 having received these phase shift values sets an absolute average value H (0) of a predetermined number N of phase shift values Δφ (0) corresponding to the symbol “0” and a predetermined number N corresponding to the symbol “1”. An absolute average value H (1) of the number N of phase transition values Δφ (1) is obtained, and the average value H is calculated.
[0037]
The BbT product detecting means 32 is information indicating the relationship between the absolute average value H of the phase shift value calculated by the averaging means 31 and the BbT product of the waveform shaping filter and the phase shift value stored in the database 33 in advance. , The BbT product of the waveform shaping filter is obtained.
[0038]
That is, the database unit 33 measures the BbT product of the waveform shaping filter obtained in advance by experiment and the average value of the phase transition values of the intermediate symbols when three consecutive symbol data are “101” and “010”. The BbT product detection means 32 stores the information of the approximate expression representing the relationship between the BbT product and the phase shift value obtained by the calculation. By substituting the value H into the approximation formula, the BbT product of the waveform shaping filter is obtained.
[0039]
FIG. 3 is a characteristic F showing the relationship between the BbT product and the phase shift value obtained experimentally. This characteristic F is the absolute average value because the phase shift value monotonically increases with respect to the BbT product. The BbT product is uniquely determined for H.
[0040]
As described above, in the BbT product measuring apparatus 20 according to the embodiment, the relationship between the phase transition value and the BbT product for a symbol that changes in a specific pattern is obtained in advance, and the BbT product is used for an unknown phase-continuous multivalued FSK signal. A phase transition value when the obtained symbol changes in a specific pattern is obtained. From the obtained phase transition value and information indicating a relationship between the phase transition value and the BbT product obtained in advance, a phase continuous multi-value is obtained. Since the BbT product of the waveform shaping filter used for generating the FSK signal is determined, the BbT product can be measured accurately with a small number of sample data.
[0041]
Also, in the BbT product measuring device 20 of this embodiment, as described above, the average value calculating means 31 calculates the absolute average value H () of the predetermined number N of phase transition values Δφ (0) corresponding to the intermediate symbol “0”. 0) and an absolute average value H (1) of a predetermined number N of phase transition values Δφ (1) corresponding to the intermediate symbol “1”, and further averaging the final average value H of the phase transition values. Is calculated, the BbT product can be accurately measured even when there is a frequency synchronization error.
[0042]
That is, if there is a frequency synchronization error, the spectrum of the modulated signal shifts as shown in FIG. 4, and the relationship between the symbol and the phase transition value becomes asymmetric with respect to the reference phase as shown in FIG. The difference between the absolute value of the phase shift value Δφ (0) corresponding to the intermediate symbol “1” and the absolute value of the phase shift value Δφ (1) corresponding to the intermediate symbol “1” increases. ”And the absolute average value H (1) of the phase transition value Δφ (1) corresponding to the intermediate symbol“ 1 ”are finally calculated by averaging the absolute average value H (0) of the phase transition value Δφ (0) corresponding to the intermediate symbol“ 1 ”. Since the average value H of the typical phase shift value is calculated, the BbT product can be accurately measured without being affected by the frequency synchronization error as described above.
[0043]
The database 33 stores an approximate expression that directly represents the relationship between the BbT product of the waveform shaping filter and the phase transition value. However, as shown in FIG. The information indicating the relationship between the value k obtained by normalizing the phase shift value Δφ using the value of the modulation index M and the BbT product of the waveform shaping filter is stored in the database unit 33, and the BbT product detection unit 32 The absolute average value H of the phase shift value calculated by the calculating means 31 is normalized by a known modulation index M, and the value k obtained by the normalization is multiplied by the value k and the BbT product stored in the database unit 33. May be determined based on the information indicating the relationship (1), and in this case, one common information can correspond to different modulation indices.
[0044]
In addition, a table in which the range of the value k and the BbT product are associated with each other is stored in the database unit 33, for example, as shown in FIG. The absolute average value H of the values may be normalized using the value of the modulation index, and the range k in the table of FIG. 7 obtained by the normalization may be checked to determine the BbT product. .
[0045]
In addition, by using the value obtained by normalizing the phase transition value Δφ with the modulation index M, the BbT product can be obtained even when the modulation index is unknown.
[0046]
FIG. 8 shows the configuration of the BbT product measuring device 20 'corresponding to the case where the modulation index is unknown as described above.
[0047]
The BbT product measuring device 20 'has a modulation index detecting means 40 for measuring a modulation index M from an input phase continuous FSK signal, and the BbT product detecting means 32 is obtained by the modulation index detecting means 40. The absolute value H of the phase transition value calculated by the averaging means 31 is normalized by the modulation index M, and the value k obtained by the normalization, the value k stored in the database unit 33 ', and BbT The BbT product of the waveform shaping filter is obtained based on the information indicating the relationship with the product.
[0048]
In the above description, the reference pattern is composed of three symbols, focusing only on the influence of the nearest intersymbol interference, but more accurate measurement can be performed by taking into account the influence of symbols that are further apart. .
[0049]
For example, there are 32 patterns composed of five symbols, “00000”, “00001”,..., “11111”. Among them, the effect of intersymbol interference is greatest among the symbols that are alternately inverted. The patterns are “10101” and “01010”.
[0050]
Therefore, for this pattern, the relationship between the phase transition value corresponding to the intermediate symbol and the BbT product (or the relationship between the value k normalized by the modulation index and the BbT product) is determined in advance in the same manner as described above, and stored in advance in the database unit 31. If these “10101” and “01010” are set as reference patterns by the pattern setting means 28, the symbols of “10101” and “01010” are used as in the patterns C ′ and D ′ in FIG. The BbT product can be obtained in the same manner as described above from the phase shift value corresponding to the intermediate symbol at the time of detection. In this case, not only the two symbols before and after the intermediate symbol but also the two symbols before and after the intermediate symbol are taken into account, so that more accurate measurement is possible.
[0051]
Further, in the above description, the alternate inversion pattern in which the influence of the intersymbol interference is the largest is used as the reference pattern. However, any other pattern may be used as long as the pattern includes a different code. It does not need to be the symbol at the center.
[0052]
In the above description, the binary FSK signal in which one symbol of the phase continuous FSK signal is either “0” or “1” has been described, but the present invention is similarly applied to signals other than binary. it can.
[0053]
For example, one symbol is a continuous phase quaternary FSK signal (modulation index 0.75) that takes one of "00", "01", "10", and "11", and the inter-symbol is three symbols in the same manner as described above. When examining the influence of interference, the symbol and the phase transition value change as shown in FIG. 10, and among these change patterns, the symbol changes from “00” → “11” → “00” as in pattern E. The case and the case where the symbol changes from “11” → “00” → “11” like the pattern G are most affected by the intersymbol interference.
[0054]
Accordingly, for the patterns E and G, the relationship between the phase transition value corresponding to the intermediate symbol and the BbT product is obtained in advance and stored in the database unit 33, and the patterns E and G are set as reference patterns by the pattern setting unit 28. By doing so, the BbT product can be obtained in the same manner as described above.
[0055]
Also, the BbT product can be obtained for a pattern that changes from “10” → “01” → “10”. When such a pattern is used, the accuracy of the pattern is slightly lower than that of the patterns E and G described above, but the appearance rate of the pattern is increased, so that the time required to collect the number of samples necessary for detecting the BbT product is short.
[0056]
【The invention's effect】
As described above, the BbT product measuring apparatus of the present invention previously obtains the relationship between the BbT product and the phase transition value of the intermediate symbol of the symbol sequence that changes in the same pattern as the reference pattern, and determines the phase of the unknown BbT product. A phase transition value when the symbol obtained for the continuous multi-level FSK signal changes in the same pattern as the reference pattern is obtained, and the obtained phase transition value and the relationship between the previously obtained phase transition value and the BbT product are calculated. Since the BbT product of the waveform shaping filter used for generating the phase-continuous multi-level FSK signal is obtained based on the BbT product, the BbT product can be measured accurately with a small number of samples in a short time.
[0057]
Further, information indicating the relationship between the value obtained by normalizing the phase shift value by the modulation index and the BbT product is stored in the database in advance, and the BbT product detection means modulates the phase shift value calculated by the average calculation means. If the configuration is such that the BbT product is detected from the normalized value and the information in the database unit by the exponent, the BbT product can be detected with common information that does not depend on the modulation index.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of an embodiment of the present invention; FIG. 2 is a diagram showing a relationship between a symbol and a phase shift value; FIG. 3 is a diagram showing a relationship between a phase shift value and a BbT product; FIG. FIG. 5 is a diagram showing a spectrum of a modulated signal when there is an error. FIG. 5 is a diagram showing a relationship between a symbol and a phase shift value when there is a frequency error. FIG. 6 is a diagram showing a value obtained by normalizing the phase shift value by a modulation index and BbT. FIG. 7 is a table showing the relationship with the product. FIG. 8 is a table showing the configuration corresponding to the case where the modulation index is unknown. FIG. FIG. 10 is a diagram showing a relationship between a symbol and a phase shift value in the case of being composed of FIG. 10 is a diagram showing a relationship between a symbol and a phase shift value in the case of a phase continuous quaternary FSK signal. FIG. 12 is a diagram showing a configuration for implementing the method. Figure [EXPLANATION OF SYMBOLS] for explaining a detection method of FIG. 14 is a conventional BbT product showing a spectrum of a GMSK modulation signal of FIG. 13 BbT product 1.0 showing the spectrum of a GMSK modulation signal
1 ... waveform shaping filter, 2 ... VCO, 20, 20 '... BbT product measuring device, 21 ... demodulation processing unit, 22 ... phase detection means, 23 ... symbol clock synchronization processing means, 24 ... phase Sampling means 25, phase transition value detection means 26, symbol clock detection means 27, memory 28, pattern setting means 29, pattern determination means 30, phase transition value extraction means 31, ... Average calculation means, 32 ... BbT product detection means, 33, 33 '... Database section, 40 ... Modulation index detection means

Claims (2)

A BbT product for receiving a phase continuous multi-level FSK signal obtained by frequency-modulating a baseband signal in the NRZ format with a predetermined modulation index by a modulation signal obtained by shaping the waveform with a waveform shaping filter, and measuring a BbT product of the waveform shaping filter In the measuring device,
Phase detection means (22) for detecting an instantaneous phase with respect to the input continuous phase multi-level FSK signal;
Symbol clock synchronization processing means (23) for performing symbol clock synchronization processing on the input phase continuous multi-level FSK signal;
Phase sampling means (24) for sampling the phase detected by the phase detection means at the timing obtained by the symbol clock synchronization processing means;
Phase transition value detection means (25) for detecting a phase transition value of the phase obtained by the phase sampling means with respect to the immediately preceding phase obtained by the phase sampling means;
Symbol data detecting means (26) for detecting symbol data from the sign of the phase shift value detected by the phase shift value detecting means;
Storage means (27) for storing the symbol data detected by the symbol data detection means and the phase transition value used for detecting the symbol data in association with each other;
A pattern setting unit (28) for setting an arbitrary reference pattern;
The pattern of the symbol data stored in the storage means is compared with a reference pattern set by the pattern setting unit, and whether or not the pattern of the symbol data stored in the storage means matches the reference pattern is determined. Pattern determination means (29) for determination;
A phase transition value extraction unit (30) for extracting a phase transition value corresponding to an intermediate symbol of the pattern from the storage unit when the pattern determination unit determines that the pattern matches;
Average calculating means (31) for calculating an average value of the phase shift values extracted by the phase shift value extracting means;
A database unit (31) storing in advance information indicating a relationship between a phase transition value for a symbol in the middle of the reference pattern and a BbT product of the waveform shaping filter;
BbT product detection means (32) for obtaining a BbT product of the waveform shaping filter based on the average value of the phase transition value calculated by the averaging means and the information stored in the database unit. A BbT product measuring device, characterized in that: In the database unit, information indicating a relationship between a BbT product and a value obtained by normalizing the phase shift value extracted by the phase shift value extracting unit using the value of the modulation index is stored in advance,
The BbT product detection unit is configured to perform the waveform shaping filter based on a value obtained by normalizing the average value of the phase transition value calculated by the average calculation unit with the modulation index and information stored in the database unit. The BbT product measuring apparatus according to claim 1, wherein the BbT product measuring apparatus is configured to obtain a BbT product of:

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