JP3617741B2 - Receiver for spread spectrum communication - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a receiver for spread spectrum communication used for digital wireless communication such as a car phone and a cellular phone.
[0002]
[Prior art]
FIG. 3 shows a receiving section of a conventional spread spectrum mobile phone device, which includes a receiving antenna 1, a low noise amplifier circuit 2, a voltage controlled oscillator 3, an orthogonal detection circuit 4, an A / D conversion circuit 5, a data correlator 6, It comprises a digital synchronous detection circuit 7, an error correction code decoding circuit 8, a carrier phase rotation detection circuit 10, an averaging circuit 11, a D / A conversion circuit 12, and a data correlator timing control circuit 13.
[0003]
The reception signal captured by the reception antenna 1 is amplified by the low noise amplifier 2, is quasi-synchronously detected by the quadrature detection circuit 4 based on the reception local frequency from the voltage control oscillator 3, and is converted into a baseband signal. . The output of the quadrature detection circuit 4 is converted into a digital signal by the AD converter 5 separately for Ich and Qch, and a correlation with the spreading code used at the time of transmission is obtained by the correlator 6. The operation timing of the correlator 6 is controlled by the correlator timing control circuit 13. The output of the correlator 6 is input to the digital synchronous detection circuit 7 for synchronous detection, and the error correction code decoding circuit 8 decodes the error correction code, and the received data is demodulated. The output of the correlator 6 is also input to the carrier phase rotation detection circuit 10 to determine the speed of the carrier phase rotation due to the error of the reception local frequency generated by the voltage controlled oscillator 3, and then the time average is calculated by the averaging circuit 11. It is obtained, converted into an analog control voltage by the D / A conversion circuit 12, and input to the control voltage input terminal of the voltage controlled oscillator 3. The oscillation frequency of the voltage controlled oscillator 3 is controlled by this AFC (Automatic Frequency Control) control voltage so that the carrier phase rotation speed at the output of the correlator 6 becomes the lowest.
[0004]
[Problems to be solved by the invention]
However, in the conventional spread spectrum mobile phone apparatus, since the carrier phase rotation detection for AFC is performed using the output of the correlator 6 for data demodulation, the data symbol rate is low. In such a system, it is difficult to distinguish between carrier phase angle change due to data modulation and carrier phase rotation due to carrier frequency error, and AFC pull-in is not performed correctly. To avoid this problem, high accuracy is required. The crystal oscillator is required, and the parts cost is high.
[0005]
SUMMARY OF THE INVENTION The present invention solves the above-described conventional problems, and an object of the present invention is to provide a receiver for spread spectrum communication that reduces the required accuracy of a crystal oscillator and is excellent in low cost.
[0006]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention provides a data demodulation correlator and an AFC correlator operating in a separate system from the data demodulation correlator and fed back to a voltage controlled oscillator in a spread spectrum communication receiver. If the integration time of the AFC for the correlator is provided a control means for setting a length different from the integration time of the data demodulation correlator, for the data demodulation integration time of the correlator for the AFC at power The integration time of the correlator is set to be shorter than that of the correlator, and after the AFC pull-in is completed, the integration time of the AFC correlator is equal to the integration time of the data demodulation correlator or shorter than the integration time of the data demodulation correlator. It is supposed to be set longer.
As a result, the AFC pull-in range can be expanded regardless of the data symbol rate in the receiving device, and the required accuracy of the crystal oscillator used in the receiving device can be relaxed. At the same time, the AFC pull-in range can be expanded when the power is turned on. In addition, it is possible to suppress the AFC control residual by increasing the S / N after completion of the pull-in, so that the required accuracy of the crystal oscillator is not strict and the low-cost excellent receiver for spread spectrum communication Is obtained.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0009]
( Embodiment 1)
FIG. 1 shows the configuration of a spread spectrum communication transceiving apparatus according to the first embodiment of the present invention. Elements similar to those of the conventional example shown in FIG. In FIG. 1, 1 is a receiving antenna, 2 is a low noise amplifier circuit, 3 is a voltage controlled oscillator, 4 is a quadrature detection circuit, 5 is an A / D conversion circuit, 6 is a correlator for data, 7 is a digital synchronous detection circuit, 8 is an error correction code decoding circuit, 9 is an AFC correlator, 10 is a carrier phase rotation detection circuit, 11 is an averaging circuit, 12 is a D / A conversion circuit, 13 is a data correlator timing control circuit, and 14 is an AFC. Correlator timing control circuit.
[0010]
The operation of the spread spectrum communication receiving apparatus configured as described above will be described below. The reception signal captured by the reception antenna 1 is amplified by the low noise amplifier 2, quasi-synchronously detected by the quadrature detection circuit 4, and frequency-converted to a baseband signal. The output of the quadrature detection circuit 4 is converted into a digital signal by the AD converter 5 separately for Ich and Qch, and a correlation with the spreading code used at the time of transmission is obtained by the data correlator 6. Synchronous detection is performed, the error correction code decoding circuit 8 decodes the error correction code, and the received data is demodulated. The operation timing of the data correlator 6 is controlled by the correlator timing control circuit 13. On the other hand, the AFC correlator 9 also obtains the correlation with the spreading code used at the time of transmission, and obtains the carrier phase rotation speed due to the error of the reception local frequency generated by the voltage controlled oscillator 3 in the carrier phase rotation detection circuit 10. The time average is obtained by the averaging circuit 11, converted to an analog control voltage by the D / A conversion circuit 12, and input to the control voltage input terminal of the voltage controlled oscillator 3. With this AFC control voltage, the oscillation frequency of the voltage controlled oscillator 3 is controlled so that the carrier phase rotation speed at the output of the data correlator 6 is minimized. The operation timing of the AFC correlator 9 is controlled by the correlator timing control circuit 14.
[0011]
Here, the operation of the carrier phase rotation detection circuit 10 will be described. When the data modulation is QPSK modulation, the received signal subjected to quasi-synchronous detection appears at four points separated by 90 degrees on the I and Q planes. These points are rotated by an integer multiple of 90 degrees for each data symbol, and operation is performed so that the points always gather in the same quadrant. When this operation is performed, when the frequency of the received local signal is equal to the carrier frequency of the transmitter, it completely overlaps with one point, but when there is an error in the received local frequency, the carrier phase is rotated every symbol time. Will overlap at an angle shifted by. If this shift angle is smaller than the phase change due to data modulation, the phase rotation angle per symbol can be obtained from this shift angle, and the frequency error of the received local signal can be calculated. From this, it can be seen that, at the same carrier frequency, the range in which the correct error frequency can be detected becomes narrower as the data symbol rate decreases. However, the integration time of the data correlator 6 must be equal to the data modulation symbol time, but the integration time of the AFC correlator 9 is not necessarily the same as the data modulation symbol time. It is also possible to set the integration time shorter than the symbol time. Thereby, the phase rotation speed detection range in the carrier phase rotation detection circuit 10 can be expanded. However, in this case, since the partial correlation of the spreading code is used, a code having excellent partial correlation characteristics is used as the spreading code. When the data modulation is BPSK, the synchronously detected received signal appears at two points separated by 180 degrees on the I and Q planes. These points are rotated by an integer multiple of 180 degrees for each data symbol, and operation is performed so that the points always gather in the same quadrant. The subsequent processing is the same as in the case of QPSK modulation.
[0012]
As described above, according to the first embodiment of the present invention, the AFC correlator 9 is provided separately from the data demodulation, and the integration time of the AFC correlator 9 is set as the integration time of the data demodulation correlator 6. By providing the correlator timing control circuit 14 set to different lengths , the required accuracy of the crystal oscillator can be relaxed, and a low-cost and excellent spread spectrum communication receiver can be realized.
[0013]
(Embodiment 2)
FIG. 2 shows the configuration of a spread spectrum communication receiving apparatus according to the second embodiment of the present invention. Elements similar to those in FIG. In FIG. 2, 1 is a receiving antenna, 2 is a low noise amplifier circuit, 3 is a voltage controlled oscillator, 4 is a quadrature detection circuit, 5 is an A / D conversion circuit, 6 is a data correlator, 7 is a digital synchronous detection circuit, 8 is an error correction code decoding circuit, 9 is an AFC correlator, 10A is a carrier phase rotation detection circuit, 11 is an averaging circuit, 12 is a D / A conversion circuit, 13 is a data correlator timing control circuit, and 14A is an AFC. Correlator timing control circuit.
[0014]
The operation of the spread spectrum communication receiving apparatus configured as described above will be described below. The reception signal captured by the reception antenna 1 is amplified by the low noise amplifier 2, is quasi-synchronously detected by the quadrature detection circuit 4, and is frequency-converted into a baseband signal. The output of the quadrature detection circuit 4 is converted into a digital signal by the A / D converter 5 separately for Ich and Qch, and the correlation with the spreading code used at the time of transmission is obtained by the data correlator 6. 7 is synchronously detected, and the error correction code decoding circuit 8 decodes the error correction code, and the received data is demodulated. The operation timing of the data correlator 6 is controlled by the correlator timing control circuit 13. On the other hand, the AFC correlator 9 also obtains the correlation with the spread code used at the time of transmission, the carrier phase rotation detection circuit 10A obtains the speed of the carrier phase rotation due to the error of the reception local frequency, and the averaging circuit 11 A time average is obtained, converted to an analog control voltage by the D / A conversion circuit 12, and input to the control voltage input terminal of the voltage controlled oscillator 3. With this AFC control voltage, the oscillation frequency of the voltage controlled oscillator 3 is controlled so that the carrier phase rotation speed at the output of the data correlator 6 is minimized. The operation timing of the AFC correlator 9 is controlled by the correlator timing control circuit 14A. In the initial state, the integration time of the AFC correlator 9 is set to be shorter than the integration time of the data correlator 6, and AFC pull-in is performed. Try to increase the range. Then, an AFC pull-in completion flag indicating that the error frequency has become smaller than the set value is output from the carrier phase rotation detection circuit 10A, and is input to the AFC correlator timing control circuit 14A. When the AFC correlator timing control circuit 14A receives the AFC pull-in completion flag, it sets the integration time of the AFC correlator 9 to be long, thereby integrating for a long time instead of narrowing the detection range of the error frequency. Increase noise suppression effect.
[0015]
As described above, according to the second embodiment of the present invention, the integration time of the AFC correlator 9 is set to be shorter than the integration time of the data demodulation correlator 6 when the power is turned on. By providing a correlator timing control circuit 14A that sets the integration time of the correlator 9 for use longer than the integration time of the correlator 6 for data demodulation, the AFC pull-in range is expanded when the power is turned on. By increasing N, the AFC control residual can be kept small.
[0016]
【The invention's effect】
As described above, the present invention includes a data demodulation correlator, and AFC correlator that operates by feedback to another system a and the voltage controlled oscillator and the data demodulation correlator integration time of the AFC correlators the and control means for setting a length that is different from the data integration time of the demodulation correlator, the integration time of the correlator for the AFC is set shorter than the integration time of the data demodulation correlator when the power is turned on After the AFC pull-in is completed, the spread time of the AFC correlator is set to be equal to or longer than the integration time of the data demodulation correlator. Since it is a communication receiver, the AFC pull-in range is expanded regardless of the data symbol rate in the receiver, and the required accuracy of the crystal oscillator used in the receiver is reduced. It is possible, work to expand AFC pull-in range at the time of power-on, after retraction completion to increase the S / N, it is possible to reduce the AFC control error, therefore, the cost required accuracy of the crystal oscillator is not severe An effect is achieved that an excellent spread spectrum communication receiver can be realized.
[Brief description of the drawings]
FIG. 1 is a schematic block diagram of a spread spectrum communication receiver in Embodiment 1 of the present invention. FIG. 2 is a schematic block diagram of a spread spectrum communication receiver in Embodiment 2 of the present invention. Schematic block diagram of receiver for spread spectrum communication [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Reception antenna 2 Low noise amplifier circuit 3 Voltage control oscillator 4 Quadrature detection circuit 5 A / D conversion circuit 6 Data correlator 7 Digital synchronous detection circuit 8 Error correction code decoding circuit 9 AFC correlator 10, 10A Carrier phase rotation detection Circuit 11 Averaging circuit 12 D / A conversion circuit 13 Correlator timing control circuit 14 for data, 14A Correlator timing control circuit for AFC

Claims (1)

A data demodulation correlator, and AFC correlator operating is fed back to another system a and the voltage controlled oscillator and the data demodulation correlators integrates the integral time of the AFC correlators of the data demodulation correlator time and control means for setting a different length to,
When the power is turned on, the integration time of the AFC correlator is set shorter than the integration time of the data demodulation correlator, and after the AFC pull-in is completed, the integration time of the AFC correlator is set to the integration time of the data demodulation correlator. It is set equal to or longer than the integration time of the data demodulating correlator .

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