JP2922707B2 - Automatic frequency control method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic frequency control system (hereinafter, referred to as an AFC system), and more particularly to an SS (Sprea) system.
d Spectrum) -GMSK (Gaussian Minimum Shift Keyi
ng), SS-2 phase PSK (Phase Shift Keying), SS-
AFC applicable to 4-phase PSK and SS-8-phase PSK systems
It is about the method.

[0002]

FIG. 9 shows an SS-GMS to which the present invention is applied.
It is a figure which shows the data before the modulation | alteration of a K modulation | demodulation system. In the figure, reference numeral 91 denotes a PN (Pseudo Noise) code, which is a random pattern of a predetermined length of data "1" and "0". 9
Reference numeral 2 denotes a data chip as data to be transmitted, which is added with one bit after the PN code 91. The PN code 91 and the data chip 92 form a new cycle of one cycle.

[0003] The SS-GMSK modulation / demodulation method to which the AFC method of the present invention is applied is such that GMSK modulation / demodulation is applied to a new data string created in this manner.

FIG. 2 is a diagram showing a conventional AFC system applied to such an SS-GMSK modulation / demodulation system. In the figure, 1 is a capture mode in which the frequency error between the transmission side and the reception side is converged to a certain range by utilizing the fact that the correlation level of the PN code between the transmission side and the reception side changes according to the frequency. A data reproduction / tracking mode that performs tracking to gradually match the frequency on the receiving side to the frequency on the transmitting side while reproducing the data using the phase change in each cycle of the new series after capturing the transmission wave. It is.

Next, this conventional AFC system is referred to as SS-GM
The operation when applied to SK modulation and demodulation will be described. In FIG. 2, in the acquisition mode 1, the frequency of the local oscillator on the receiving side is changed at a fixed step width, and the P and P on the transmitting side and the receiving side are changed.
The correlation between the N codes is obtained, and the frequency having the highest level of correlation is determined to be the frequency closest to the received carrier frequency. This is shown in FIG. In the example of FIG. 3, the frequency f ₀ is selected.

Next, in data reproduction / tracking mode 2 in FIG. 2, frequency tracking is performed while reproducing data. The operation in this mode is such that, as shown in FIG. 4, the phase change in one cycle of the new series is π (when the data is “1”) or 0 depending on whether the data chip of the new series is “1” or “0”. (When the data is “0”), and if the phase change for each new series cycle is π (point 12 in FIG. 4), it is determined that the data (data chip) is “1”. Then, if the phase change in each cycle of the new stream is 0 (point 11 in FIG. 4), it is determined that the data (data chip) is "0" and the data is reproduced. At this time, since the frequency on the receiving side has an error within a predetermined range with respect to the carrier frequency, tracking is performed to gradually match the error.

In the frequency control method for tracking, when the observed phase change corresponds to the first quadrant or the third quadrant, the frequency is lowered so that the phase on the receiving side is delayed (arrow A in FIG. 4). ). Conversely, when the frequencies correspond to the second and fourth quadrants, the frequency is increased so that the phase on the receiving side advances (see FIG. 4).
Arrow B).

[0008]

The conventional AFC system is configured as described above. Since the frequency tracking in the data reproduction / tracking mode is performed by the above-described control system, the AFC system is used during one cycle of the new sequence. There is a condition that the phase change due to the frequency error must be π / 2 or less. The reason is,
If a phase change of π / 2 or more occurs, the frequency control at the time of tracking works in a direction to further enlarge the phase change,
This is because the capture is further removed. As a result, there is a problem that the frequency switching width in the acquisition mode is restricted by this condition, and therefore, the frequency lock range is also restricted.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and has been developed in comparison with the conventional method.
Double with SK modulation and demodulation, double with SS-2 phase PSK modulation and demodulation, S
It is an object of the present invention to obtain an AFC system capable of obtaining a lock range four times as high with S-4 phase PSK modulation and demodulation and eight times with SS-8 phase PSK.

[0010]

According to an automatic frequency control system according to the first aspect of the present invention , transmission is performed at the end of a PN code.
Create a new series by adding the original data chip that should be
GMSK modulation and demodulation for the new sequence.
Of automatic frequency control method in modulation and demodulation method
Therefore, the correlation level between the PN code on the transmitting side and the receiving side
By taking advantage of the corresponding changes, the
Acquisition mode to converge frequency error to a certain range and transmission
After capturing the wave, take advantage of the phase change of
While reproducing the data using
Between the <br/> data reproduction / tracking mode for tracking for matching the frequency of the transmission side, a row of the tracking to the transmission wave generated by fixed data chips to a predetermined value
In addition to providing a tracking-only mode,
In this case, the data chip was generated by fixing the data chip to a predetermined value.
When a correlation level peak is detected for a modulated wave, it is captured.
The catching operation is stopped .

Further, according to a second aspect of the present invention, there is provided an automatic
The wave number control method is S instead of the GMSK modulation / demodulation method.
S-2 phase PSK, SS-4 phase PSK, SS-8 phase PSK
This is applied to any one of the modulation and demodulation methods .

[0012]

The invention according to claim 1 of the present application is constructed as described above.
As a result, the phase uncertainty can be reduced by one, the phase change in one cycle of the new sequence during tracking can be reduced to π or less, and the step width of frequency switching in the acquisition mode can be reduced by 2 (In the case of SS-GMSK modulation / demodulation). As a result, the lock range has also doubled (SS
-GMSK modulation / demodulation).
In addition, tracking only mode with the remaining capture mode time
You can perform the same operation as
It can be shortened to that Do not.

[0013] The invention of claim 2 of the present application is as described above.
With this configuration, SS-2 phase PSK, SS-4
Phase PSK or SS-8 phase PSK modulation / demodulation method
Frequency switching step in acquisition mode
Can be significantly larger than the width and lock range in the conventional method and that Do.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an AFC system according to an embodiment of the present invention. In the figure, reference numerals 1 and 2 denote an acquisition mode and a data reproduction / tracking mode similar to those of the conventional apparatus shown in FIG. 3
Is a tracking-only mode, in which the transmitting side fixes all data (data chips) to "0" in this mode, and the receiving side tracks a modulated wave in which this data is fixed to "0". Note that the period may be set to a time required until the frequencies on the transmitting side and the receiving side gradually approach to each other and become practically identical by executing this mode.

Hereinafter, the operation of the present invention will be described (S
S-GMSK modulation / demodulation). In FIG. 1, in acquisition mode 1, the frequency of the local oscillator on the receiving side is switched with a certain fixed step width, and the frequency at which the correlation level of the PN code on the transmitting and receiving sides is the highest is the frequency closest to the carrier frequency of the received wave. Is determined.

Next, in FIG. 1, in tracking-only mode 3, the transmitting side always sets the new series of data chips to “0”,
Therefore, on the receiving side, since the phase change in one cycle of the new sequence is always “0” (point 11 in FIG. 5), as shown in FIG. In the case of １８０180 °, the frequency is lowered to delay the phase on the receiving side (arrow A in FIG. 5).
In the case of 0 ° to 360 °, the frequency is increased to advance the phase on the receiving side (arrow B in FIG. 5). Therefore, in the case of this control method, the phase change due to the frequency error need only be π or less during one cycle of the new sequence, and this condition has twice as much margin as the conventional method. Therefore, the frequency switching step width and the lock range in the capture mode can be doubled as compared with the conventional case, and the synchronization can be stably and quickly realized.

In the data reproduction / tracking mode 2 in FIG. 1, the data chip of the new series is "1" or "0".
The phase change in one cycle of the new sequence is π (when the data chip is “1”) and 0 (when the data chip is “0”)
), Data reproduction and frequency tracking are performed. As shown in FIG. 4, the frequency tracking control method lowers the frequency when the observed phase change is in the first and third quadrants, and increases the frequency when the observed phase change is in the second and fourth quadrants.

In the above embodiment, all the data chips in the tracking-only mode are fixed to "0", but all the data chips in this mode are set to "1".
May be fixed. In this case, the phase change in one cycle of the new sequence is always π, but the frequency switching step width in the acquisition mode and the effect of expanding the lock range are the same as when the value is fixed to “0”.

In the above embodiment, no condition is given for the data chip in the capture mode. However, the data chip in the capture mode is always fixed to "0", the frequency is switched, and the correlation level is observed. If the capturing operation is stopped when the correlation peak is detected, the same operation as in the tracking-only mode can be performed with the remaining capturing mode time, and the tracking-only mode time can be reduced.

In the above embodiment, the case of the SS-GMSK modulation / demodulation is shown. In the AFC system, the data of FIG. 9 is subjected to two-phase PSK, four-phase PSK, and eight-phase PSK modulation / demodulation. , SS-4 phase PSK, SS-8 phase PSK modulation and demodulation. In both cases, the frequency switching step width and the lock range in the acquisition mode are 2 compared to the conventional AFC system.
It can be magnified twice, four times and eight times.

FIGS. 6, 7 and 8 show SS-2 · P, respectively.
Regarding control of frequency tracking in SK, SS-4.PSK, SS-8.PSK modulation and demodulation, a conventional AFC system and a current AFC system will be compared.

As shown in FIGS. 6 (a), 7 (a), and 8 (a), in the conventional method, the frequency lowering area (hatched area in the figure) and the frequency increasing area are shown. Appear alternately, so that the lock range is narrow, so that the frequency switching step width in the correlation calculation for acquiring the frequency cannot be made large. However, FIGS. 6 (b), 7 (b), and 8 (b) According to the present method shown in FIG. 5, the region for lowering the frequency is limited to the first and second quadrants, and the region for increasing the frequency is limited to the third and fourth quadrants. Can be changed, the lock range is expanded, and it is possible to capture even if the frequency switching step width is increased.

In the drawing, 13 is a point of phase change = π / 2, 14 is a point of phase change = 3π / 2, and 15 is a point of phase change = 3π / 2.
A point of π / 4, 16 indicates a point of phase change = 3π / 4, 17 indicates a point of phase change = 5π / 4, and 18 indicates a point of phase change = 7π / 4.

As a result, the constraints on the phase change due to the frequency error are as shown in Table 1.

[0025]

[Table 1]

As a result, the frequency switching step width and the lock range in the capture mode are twice as large as those of the conventional AFC system in SS-2 · PSK and four times in SS-4 · PSK.
Twice as large as SS-8.PSK, and 8 times larger with the current AFC method.

[0027]

As described above, according to the first aspect of the present invention,
According to such an automatic frequency control method, at the end of the PN code,
In an automatic frequency control method in a modulation / demodulation method in which a new sequence is created by adding an original data chip and GMSK modulation and demodulation are performed on the new sequence, the correlation level between the PN code on the transmission side and the reception side is the frequency. Using a change corresponding to the capture mode that converges the frequency error between the transmitting side and the receiving side within a certain range, and using a phase change for each cycle of a new sequence after capturing the transmission wave While reproducing the data, the data reproduction / tracking is performed to match the frequency on the receiving side to the frequency on the transmitting side.
Between the tracking mode, with Keru set tracking only mode data chip is all fixed to a predetermined value, said capture mode
In data mode, data chips are generated with a fixed value.
When the correlation level peak is detected for the modulated wave
Since the so that to cancel the capture operation at point, the frequency switching step width and the lock range in the acquisition mode, as compared with the conventional system, can be greatly expanded, when the remaining acquisition mode
The same operation as in the tracking-only mode can be performed between
There is an effect that can shorten the time required for the tail-only mode.

According to the automatic frequency control system according to the second aspect of the present invention, the automatic frequency control according to the first aspect is provided.
In the system, instead of the GMSK modulation / demodulation system, SS
For 2-phase PSK, SS-4 phase PSK, SS-8 phase PSK
Since it is applied to any of the modulation and demodulation methods,
, SS-2 phase PSK, SS-4 phase PSK, SS-
In any of the modulation and demodulation methods of 8-phase PSK, the acquisition mode
Frequency switching step width and lock range
Has the effect that it can be greatly expanded compared to the conventional method .

[Brief description of the drawings]

FIG. 1 is a diagram showing an AFC system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional AFC system.

FIG. 3 is an operation diagram in a capture mode according to the related art and the present invention.

FIG. 4 is a diagram illustrating control in a data reproduction / tracking mode according to the related art and the present invention.

FIG. 5 is a diagram showing control in a tracking-only mode according to the present invention.

FIG. 6 is a diagram illustrating control in SS-2 · PSK modulation / demodulation.

FIG. 7 is a diagram showing control in SS-4 PSK modulation / demodulation.

FIG. 8 is a diagram illustrating control in SS-8 / PSK modulation / demodulation.

FIG. 9 is a diagram showing a data string on which SS-GMSK modulation / demodulation is performed.

[Explanation of symbols]

 1 Acquisition Mode 2 Data Reproduction / Tracking Mode 3 Tracking Only Mode 11 Phase Change = 0 Point 12 Phase Change = π 13 Phase Change = π / 2 14 Phase Change = 3π / 2 15 Phase Change = π / 4 point 16 Phase change = 3π / 4 point 17 Phase change = 5π / 4 point 18 Phase change = 7π / 4 point 91 PN code 92 Data chip

Claims (2)

(57) [Claims] At the end of claim 1 PN code, by adding the original data chips to be transmitted to create a new sequence, the modulation and demodulation method for performing GMSK modulation and demodulation on the <br/> series of new In the automatic frequency control method in the above, an acquisition mode that converges the frequency error between the transmission side and the reception side to a certain range by utilizing the fact that the correlation level of the PN code on the transmission side and the reception side changes according to the frequency. A data reproduction / tracking mode for performing tracking to match the frequency on the receiving side to the frequency on the transmitting side while reproducing the data using the phase change in each cycle of the new sequence after capturing the transmission wave. Rutotomo provided tracking only mode for performing the tracking, the relative transmission wave generated by fixed data chips to a predetermined value between the
In the capture mode, the data chip is fixed to a predetermined value.
Peak of the correlation level for the modulated wave
An automatic frequency control method in which the capturing operation is stopped at the time of detection . 2. The automatic frequency control system according to claim 1,
There are, instead of the GMSK modulation and demodulation scheme, SS-2 phase PSK,
Reversion of either SS-4 phase PSK or SS-8 phase PSK
Automatic frequency control method characterized in that applied to the regulating system.