JPH06216876A - Demodulator for spread spectrum communication - Google Patents

Abstract

PURPOSE:To obtain the small sized and inexpensive demodulator for spread spectrum communication by eliminating the need for a circuit used to eliminate a frequency deviation between transmission and reception. CONSTITUTION:A square sum of biphase matched filter outputs in pattern matching in a matched filter 6 has a peak when no frequency deviation is in existence between transmission and reception, the deteriorated square sum corresponds to the frequency deviation between transmission and reception and it is extracted by a frequency deviation extract section 12 and an output frequency of a voltage controlled oscillator 14 is controlled to decrease the frequency deviation thereby controlling an orthogonal demodulator 2 and eliminating the frequency deviation between transmission and reception and then automatic frequency control is implemented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a demodulator for spread spectrum communication.

[0002]

2. Description of the Related Art FIG. 2 is a block diagram showing a conventional demodulator for spread spectrum communication. In FIG. 2, 21 is an input signal, 22 is a quadrature demodulator, and a 90 ° phase shifter 23
And a pair of multipliers 24. Reference numeral 25 is an LPF (low pass filter), and 26 is a matched filter, which comprises a pair of correlators 27. 28 is a pair of squarers, 29 is an adder, 30 is a synchronization acquisition unit, 31 is a phase detection unit, 32 is a data demodulation unit, and 33 is demodulation data. 34 is a loop filter, 35 is a voltage controlled oscillator, 36 is a 1/2 frequency divider, 37 is a frequency deviation detection circuit, BPF (band pass filter) 38, squarer 39, BPF (band pass filter) 40, It is composed of a multiplier 41 and a frequency offset discriminator 42.

The operation of the conventional demodulator for spread spectrum communication configured as described above will be described below. First, the input signal 21 input to the frequency deviation detection circuit 37 is band-limited by the band-pass filter 38, squared by the squarer 39, and the second-harmonic component is extracted by another band-pass filter 40. The output at this time becomes CW because the phase component of the spread code is removed. This output is multiplied by the signal from the voltage-controlled oscillator 35 by the multiplier 41 to convert the frequency, and then the frequency offset delimiter 42
At, the deviation of the carrier frequency from the default value is detected, and an error voltage corresponding to the frequency deviation is generated. Then, the output signal from the loop filter 34 drives the voltage controlled oscillator 35, and the loop circuit traces in the direction of reducing the frequency deviation. In addition, the output frequency of the voltage controlled oscillator 35 is 1 /
When the frequency is divided into 1/2 by the frequency divider 36, the signal has a predetermined IF frequency. When this is input to the quadrature demodulator 22 including the 90 ° phase shifter 23 and the pair of multipliers 24 and multiplied by the input signal 21, a two-phase baseband signal from which the frequency deviation is removed is obtained.

Then, these two-phase baseband signals are input to the matched filter 26 after removing unnecessary harmonics by the low-pass filter 25. In the matched filter 26, the pair of correlators 27 and the incoming pseudo-noise signal sequence of the two-phase baseband signals are used in the correlator 27.
Pattern matching is performed with the reference pseudo noise signal sequence held inside. Next, with a pair of squarer 28 and adder 9,
The sum of squares of the output of the matched filter 26 is detected, and the output is sent to the synchronization acquisition unit 30. The synchronization acquisition unit 30 detects a timing signal at which the pattern matching output has a peak, that is, a matched pulse that is a signal synchronized with the information signal included in the input signal 21.

On the other hand, the two-phase output of the matched filter 26 is also sent to the phase detecting section 31, and the matched pulse detected by the synchronization capturing section 30 causes the two phases of the matched filter 26 to be matched. Latch the output. These two-phase signals are orthogonal, and the input signal 21
Since the phase component of the information signal is included in the data demodulation unit 32, the phase component of the information signal is extracted from these signals.
Then, the data is judged from the extracted phase and the demodulated data 33 is output.

[0006]

However, in the above-described conventional spread spectrum communication demodulator, a frequency deviation detecting circuit for directly detecting the frequency deviation from the input signal of the intermediate frequency in order to eliminate the frequency deviation between the transmission and the reception. However, there is a problem in that the circuit configuration becomes complicated.

The present invention solves the above problems and eliminates the need for a circuit for directly detecting a frequency deviation from an input signal of an intermediate frequency in order to eliminate a frequency deviation between transmission and reception. , A more compact demodulator for spread spectrum communication is provided.

[0008]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides a sum of squares of two-phase matched filter outputs when pattern matching is achieved in the matched filter without any frequency deviation between transmission and reception. Taking advantage of the fact that the amount of deterioration corresponds to the frequency deviation between transmission and reception, with time as a peak, and controlling the voltage-controlled local oscillator to reduce the value, the frequency deviation between transmission and reception is removed. It was made possible.

[0009]

According to the present invention, the demodulation for spread spectrum communication, which has the above-described structure, enables automatic frequency control without a circuit for directly detecting the frequency deviation from the input signal of the intermediate frequency and has a simpler structure and a smaller size. The device can be realized.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a demodulator for spread spectrum communication according to this embodiment. In FIG. 1, 1 is an input signal and 2 is a quadrature demodulator, which is composed of a 90 ° phase shifter 3 and a pair of multipliers 4. Reference numeral 5 is an LPF (low-pass filter), 6 is a matched filter, which is composed of a pair of correlators 7. 8 is a pair of squarers, 9 is an adder,
Reference numeral 10 is a synchronization acquisition unit, 11 is a synchronization holding unit, 12 is a frequency deviation extraction unit, 13 is a data demodulation unit, 14 is a voltage control local oscillator, and 15 is demodulation data.

The operation of the demodulator for spread spectrum communication configured as above will be described below. First, the input signal 1 is multiplied by the output signal of the voltage-controlled local oscillator 14 by the quadrature demodulator 2 including the 90 ° phase shifter 3 and the pair of multipliers 4, and the two-phase orthogonal baseband signals are reproduced. To be done. Then, these two-phase baseband signals are input to the matched filter 6 after removing unnecessary harmonics by the low-pass filter 5. In the matched filter 6, two correlators 7 perform pattern matching between an incoming pseudo noise signal sequence of two-phase baseband signals and a reference pseudo noise signal sequence held inside the correlator 7, and then a pair of 2 The multiplier 8 and the adder 9 detect the sum of squares of the outputs of the in-phase output and the quadrature output of the matched filter 6, and send the output to the synchronization acquisition unit 10. The synchronization acquisition unit 10 detects an output when pattern matching is achieved, that is, a matched pulse which is a signal synchronized with the information signal included in the input signal 1.

The two-phase output of the matched filter 6 is also sent to the data demodulation section 13. These two-phase signals are orthogonal to each other and include the phase component of the information signal of the input signal 1. Therefore, the phase component of the information signal is extracted from these signals, the data is determined from the extracted phase, and the demodulated data 15 is output.

On the other hand, the sum of squares of the output of the matched filter 6 is also sent to the synchronization holding unit 11, and based on the matched pulse detected by the synchronization acquisition unit 10, the matched filter when the subsequent pattern matching is achieved. Sum of squares of the output of 6,
That is, by holding the timing of the matched pulse, synchronization is maintained between transmission and reception.

At this time, the matched pulse has a peak when there is no frequency deviation between transmission and reception, and its deterioration corresponds to the frequency deviation between transmission and reception. Therefore, in the frequency deviation extraction unit 12, the synchronization acquisition unit 10 is used. The deterioration amount is detected from the matched pulse detected in step S1, and the quadrature demodulator 2 is controlled by controlling the output frequency of the voltage-controlled local oscillator 14 so that the deterioration amount becomes small. It can be removed and automatic frequency control is performed.

[0015]

As described above, according to the present invention, in order to remove the frequency deviation between transmission and reception, automatic frequency control can be performed without providing a circuit for directly detecting the frequency deviation from the input signal of the intermediate frequency. A demodulator for spread spectrum communication having a simpler structure and a smaller size and lower cost can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of a demodulator for spread spectrum communication according to an embodiment of the present invention.

FIG. 2 is a block diagram showing the configuration of a conventional demodulator for spread spectrum communication.

[Explanation of symbols]

 1 Input Signal 2 Quadrature Demodulator 3 90 ° Phase Shifter 4 Multiplier 5 Low Pass Filter (LPF) 6 Matched Filter 7 Correlator 8 Squarer 9 Adder 10 Sync Capture Section 11 Sync Hold Section 12 Frequency Deviation Extraction Section 13 data demodulation unit 14 voltage control local oscillator 15 demodulation data

Claims (1)

[Claims] 1. A quadrature demodulator comprising a 90 ° phase shifter for reproducing a two-phase orthogonal signal from an input signal and a pair of multipliers, and a low-pass filter for removing unnecessary harmonics from the two-phase signal. A matched filter comprising a filter and a pair of correlators for despreading by performing pattern matching between the incoming pseudo-noise signal sequence of the two-phase signals and a reference pseudo-noise signal sequence held inside the correlator; A pair of a squarer and an adder for detecting the sum of squares of the output of the matched filter, a synchronization acquisition unit for performing synchronization acquisition from the sum of squares, and a synchronization holding unit for maintaining synchronization after the synchronization acquisition.
A data demodulation unit that determines received data from the output of the matched filter and demodulates it, and a frequency deviation that extracts a frequency deviation between transmission and reception from the matched pulse detected by the synchronization acquisition unit when pattern matching is achieved in the matched filter. A demodulator for spread spectrum communication, comprising: an extraction unit; and a voltage-controlled local oscillator that controls the quadrature demodulator so as to reduce the value of the extracted frequency deviation.