JPH088513B2 - Automatic frequency control method - Google Patents

Description

TECHNICAL FIELD The present invention relates to an automatic frequency control system, and more particularly to an automatic frequency control system in a DS receiver.

[Conventional technology]

Figure 2 shows I-E-E-COM-34, Volume 303
Page March, 1986 "Noise Performance of Across Product AFC with Division Feedback for DPSK Signals" (IE ³ COM-34, No.3, MARC
H 1986 PP303, “Noise Performance of a Cross−Pro
duct AFC with Decision Feedback for DPSK Signal
FIG. 8 is a diagram showing a conventional automatic frequency control method shown in FIG.

In the figure, 1 is a directly spread received signal, 2 is a low-pass filter, 3 is an A / D converter, 4 is a correlator, 5 is a phase detector, and 6 is a VCXO (Voltage-Controlled Crystal Oscillator).
ator: voltage controlled crystal oscillator), 7 is a multiplier, and 8 is a π / 2 phase shifter.

 Next, the operation will be described.

First, the reception signal 1 directly spread in FIG. 2 is converted into a baseband signal by the multiplier 7 and the π / 2 phase shifter 8 multiplying two orthogonal local signals on the reception side, It passes through the low-pass filter 2 and is converted into a digital signal by the A / D converter 3. A PN (Pseude-Noise) code for the desired signal is prepared in the correlator 4, and the digitized signal is despread through the correlator 4 and then input to the phase detector 5.

The polarity of the output of the correlator 4 changes when the phase deviation exceeds ± 90 °. Therefore, the frequency deviation on the transmitting and receiving side is ± (90 ° / 360 °) x transmission speed, that is, the frequency range of 1/2 of the transmission speed, by detecting the component once in one data and feeding back negatively to VCXO6. If it is within the range, the phase deviation between one data becomes smaller than ± 90 °, so that it can be captured.

[Problems to be Solved by the Invention]

Since the conventional automatic frequency control method is configured as above, the frequency deviation on the transmitting and receiving side is ± (90 ° / 360 °) ×
If the transmission rate, that is, the frequency range of 1/2 of the transmission rate is exceeded, the phase deviation between 1 data exceeds ± 90 °, and there is a problem that it becomes impossible to capture.

The present invention has been made to solve the above problems, and the frequency deviation on the transmitting and receiving side is 1/2 of the transmission frequency.
It is an object to obtain an automatic frequency control method capable of capturing even if it becomes larger.

[Means for solving the problem]

The automatic frequency control method according to the present invention is, in the automatic frequency control method for a direct spread receiver, a local oscillator that generates a local signal and a first oscillator that detects the directly spread received signal based on the output of the local oscillator. Second
And the analog output signals from the first and second multipliers are sampled two times or more for one data and converted into digital signals.
A converter, first and second correlators that despread the outputs of the first and second A / D converters, respectively, and the first
And a phase detector for performing phase detection based on the outputs of the second and second correlators, and third and fourth correlators for despreading the outputs of the first and second multipliers, respectively. A first adder for adding the output of the first correlator and the output of the fourth correlator to output to the phase detector; the output of the second correlator; Third
And a second adder for adding the output of the correlator to the phase detector and outputting the result to the phase detector. It is designed to extend to the frequency range.

[Action]

In the automatic frequency control method according to the present invention, the range of the frequency deviation between the transmission and reception that can be captured is expanded to at least the frequency range of the transmission speed by detecting the phase at least twice in one data. If the deviation is at least within the frequency range of the transmission rate, the phase deviation between one data will be smaller than ± 90 ° and can be captured.

〔Example〕

 An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an automatic frequency control system according to an embodiment of the present invention. In the figure, 1 is a directly spread received signal, 2 is a low-pass filter, 3 is an A / D converter, 4 is a correlator, 5 is a phase detector, 6 is a VCXO, 7 is a multiplier, and 8 is π.
A / 2 phase shifter and 9 are adders.

 Next, the operation will be described.

In FIG. 1, the received signal 1 directly spread is converted into a baseband signal after being multiplied by two orthogonal local signals on the receiving side by a multiplier 7 and a π / 2 phase shifter 8 , Passes through the low-pass filter 2 and is converted into a digital signal by the A / D converter 3. The PN code for the desired signal is prepared in the correlator 4, and the digitized signal is despread after passing through the correlator 4 and the two adders 9 and input to the phase detector 5. The polarities of these two adder outputs change when the phase deviation exceeds ± 90 °. Therefore, the component is detected twice in one data
By negatively feeding back to the VCXO6, the frequency deviation on the transmitting and receiving side is ± 2 × (90 ° / 360 °) × transmission speed, that is, the phase deviation between 1 data is ± 90 ° if it is within the frequency range of the transmission speed. Since it is small, it can be captured.

Further, according to the present embodiment, the present device can be realized only by providing two more correlators 4 and increasing the number of samplings, so that the allowable range for capturing the frequency deviation between transmission and reception is higher than in the conventional case. Large and highly accurate ones can be obtained at a low cost with almost the same size as conventional ones.

Although the above embodiment has shown the case where the phase detection for one data is performed twice, the phase detection for one data may be performed four times.

Hereinafter, as another embodiment of the present invention, an automatic frequency control method when the phase detection for one data is set to four times will be described.

First, the directly spread received signal 1 is converted into a baseband signal after being multiplied by two local signals on the receiving side, which are orthogonal to each other, by a multiplier 7 and a π / 2 phase shifter 8 After passing through the low pass filter 2, it is converted into a digital signal by the A / D converter 3. In the correlator 4, a PN code for the desired signal is prepared, and the digitized signal passes through this correlator 4, passes through two adders 9, is despread, and is input to the phase detector 5. . The polarities of these two adder outputs change when the phase deviation exceeds ± 90 °. Therefore, by changing the clock signal for sampling in the above embodiment during one data and detecting the component four times and negatively feeding back to VCXO6, the frequency deviation on the transmitting and receiving side is ± 4 × (90 ° / 360 °). B. If the transmission speed is within the frequency range of twice the transmission speed, the phase deviation between one data will be smaller than ± 90 °, so that the data can be captured.

Further, in this embodiment, a device having the same size as that of the above embodiment and having a larger frequency deviation between transmission and reception which can be captured more easily than the above embodiment can be easily obtained.

In the above embodiment, the number of times of phase detection for one data is performed twice or four times. However, the number of times of phase detection is not limited to two or four times, and if it is two or more times. It's good.

〔The invention's effect〕

As described above, according to the automatic frequency control system according to the present invention, in the automatic frequency control system of the direct spread receiver, the local oscillator that generates the local signal and the received signal that is directly spread are output to the local oscillator. First and second multipliers that detect the respective signals based on the respective data, and first and second analog output signals from the first and second multipliers that are sampled twice or more for each data and converted into digital signals. A / D converter, and the above first and second
And a second correlator for despreading the outputs of the A / D converters, and a phase detector for performing phase detection based on the outputs of the first and second correlators and controlling the local oscillator. And adding the third and fourth correlators for despreading the outputs of the first and second multipliers, respectively, and the output of the first correlator and the output of the fourth correlator. A first adder that outputs to the phase detector, a second adder that outputs the output of the second correlator and an output of the third correlator, and outputs the sum to the phase detector. With an adder,
Since the range of frequency deviation between transmission and reception that can be captured by this automatic frequency control method is expanded to at least the frequency range of transmission speed, it can always be captured if the frequency deviation between transmission and reception is within the frequency range of transmission speed. There is an effect.

Further, according to the present invention, there is an effect that a highly accurate device having such a wide capture frequency range can be obtained at low cost and in a small size.

[Brief description of drawings]

1 is a block diagram of an automatic frequency control system according to an embodiment of the present invention, FIG. 2 is a block diagram of a conventional automatic frequency control system, and FIG. 3 is a block diagram of one data according to another embodiment of the present invention. It is a block diagram of an automatic frequency control system when phase detection is performed four times. In the figure, 1 is a received signal, 2 is a low-pass filter, and 3 is an A / D.
Converter, 4 correlator, 5 phase detector, 6 VCXO,
Reference numeral 7 is a multiplier, 8 is a π / 2 phase shifter, and 9 is an adder. In the drawings, the same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. An automatic frequency control system for a DS (Direct Sequence) receiver, which detects a local oscillator for generating a local signal and a directly spread received signal based on the output of the local oscillator. And a second multiplier, and first and second A / D converters for sampling the analog output signals from the first and second multipliers two or more times for one data and converting them into digital signals. And first and second correlators that despread the outputs of the first and second A / D converters, respectively, and phase detection is performed based on the outputs of the first and second correlators. A phase detector controlling the local oscillator, third and fourth correlators despreading the outputs of the first and second multipliers, respectively, and an output of the first correlator and the fourth correlation. And the output of the vessel A first adder that outputs to the phase detector, and a second addition that adds the output of the second correlator and the output of the third correlator and outputs to the phase detector. The automatic frequency control method is characterized by expanding the range of frequency deviation between transmission and reception that can be captured by this automatic frequency control method to at least the frequency range of transmission speed.