JPH0580053U - Spread spectrum communication system receiver - Google Patents

Abstract

(57) [Abstract] [Purpose] A spread spectrum communication system receiver equipped with a device that prevents saturation of the AD converter in the receiver without reducing the SN ratio of the signal when external noise with a large amplitude is superimposed. It is to be realized. In a receiver that receives a spread spectrum signal, the AGC amplifier 34 that adjusts the level of the received signal to bring the signal with the maximum amplitude to an appropriate level and the frequency of the signal with the maximum amplitude of the output signal are analyzed. A frequency analyzer 53 that outputs a control signal and a variable frequency band limiting filter 52 that limits the passage of a signal in the frequency band by the control signal of the frequency are provided.

Description

[Detailed description of the device]

[0001]

[Industrial applications]

 The present invention relates to a direct spread spectrum communication system receiver, and more particularly to a spread spectrum communication system receiver in which deterioration of the SN ratio due to external noise in a narrow band is reduced.

[0002]

[Prior Art]

 FIG. 3 shows a principle configuration diagram of a direct spread spectrum spread method. The information from the information source 1 modulates the signal input from the local oscillator incorporated in the primary modulator 2. This modulation is digital modulation such as FSK (Frequency Shift Keying) and PSK (Phase Shift Keying). The output signal of the primary modulator 2 is modulated in the spread modulator 5 by the spread code generated in the spread code generator 4. A pseudo noise code (PN code) such as an M-sequence code is used as the spreading code generated by the spreading code generator 4. The PN code has a wide white spectrum and is characterized by a small power density per unit frequency.

The spread-modulated signal is frequency-converted in the frequency converter 6 by the local oscillation signal input from the local oscillator 7 into a high frequency signal, which is transmitted from the transmission antenna 8.

In the receiver, the signal received by the receiving antenna 11 is demodulated in the demodulation circuit 12 by the local oscillation signal from the local oscillator 13 and converted into an intermediate frequency. The output signal from the demodulation circuit 12 is demodulated in the spread demodulator 14 by the spread code from the spread code generator 15. This spread code is the same signal as the spread code generated by the spread code generator 4 in the transmitter, and the spread code generator 15 uses the synchronization signal generated by the code synchronization circuit 16 to generate the same timing as the spread code on the transmission side. The spread spectrum is reduced to the frequency spectrum of the primary modulation by performing the spread demodulation. This operation is called despreading.

The signal restored by this primary modulation signal is demodulated by the primary demodulator 17 to obtain an information signal. A conventional circuit example based on the above principle is shown in FIG. In this example, digital signal processing is performed based on the principle shown in the principle diagram of FIG. In the figure, the same parts as those in FIG. 3 are denoted by the same reference numerals. In the figure, (a) is a block diagram of the transmitter, and (b) is a block diagram of the receiver. The output noise of the PN code generator 21 is spread-modulated by the spread modulator 5 to the output signal of the primary modulator 2. This signal is converted into an analog signal by the DA converter 22 and unnecessary high frequency signals are removed by the LPF 23.

The output signal of the LPF 23 is amplified by the amplifier 24, and then converted into a high frequency signal by the local oscillation frequency from the local oscillator 7 in the frequency converter 5, and unnecessary frequency components such as harmonics of the high frequency signal are generated in the BPF 25. Is removed, amplified by the amplifier 26, and then transmitted from the transmitting antenna 8.

In the receiver shown in (b), the signal received by the receiving antenna 11 is filtered by the LPF 30 to remove unnecessary frequency components, amplified by the amplifier 31, and then transmitted from the local oscillator 13 by the mixer 32. It is converted to an intermediate frequency by the oscillating signal, and is input to the AGC amplifier 34 via BPF 33.

The AGC amplifier 34 rectifies the input signal and determines the gain of the amplifier in accordance with the magnitude of the input signal, thereby limiting the magnitude of the output signal and preventing the AD converter 35 from being saturated. ing.

The signal digitized by the AD converter 35 is inversed by the signal obtained by modulating the output signal of the carrier regeneration oscillator 37 at the multiplier 36 by the PN code at the output of the PN code generator 38 at the modulator 39. It is spread and returned to the primary modulation signal. The primary demodulator 40 primary demodulates the signal returned to the primary modulated signal and outputs an information signal. The digital signal processing circuit 41 is composed of the circuits after the AD converter 35.

[0010]

[Issues to be solved by the device]

 Here, although the AD converter is used on the receiving side, the gain of the AGC amplifier 34 provided in the preceding stage is lowered so that the AD converter 35 is not saturated when external noise is added to the received radio wave in space. .. However, in that case, the SN ratio is lowered due to the quantization noise of the AD converter 35 and the like.

As a countermeasure against this, there is a method of increasing the dynamic range of the AD converter 35, but this leads to an increase in cost. The present invention has been made in view of the above points, and its object is to improve the SN ratio of a signal when a large amplitude external noise is superposed in a receiver that receives and detects a spread spectrum signal. This is to realize a spread spectrum communication system receiver that can prevent the saturation of the detection device including the AD converter in the receiver without reducing the noise.

[0012]

[Means for Solving the Problems]

 The present invention, which solves the above-mentioned problems, provides a spread spectrum communication type receiver that receives and demodulates a spread spectrum signal, and adjusts the level of the received signal so that the signal with the maximum amplitude becomes an appropriate level. An amplifier and a frequency analyzer that analyzes the frequency of the signal with the maximum amplitude of the output signal of the AGC amplifier and outputs a control signal of that frequency; and the frequency that is controlled by the control signal of the output of the frequency analyzer. And at least one variable frequency band limiting filter for limiting the passage of signals in the band.

[0013]

[Action]

 The received signal is output by the AGC amplifier by converting the signal having the maximum amplitude among the signals into a signal having an appropriate level. The frequency analyzer analyzes the frequency of the signal with the maximum amplitude in the input signal, sends the control signal of the frequency obtained by the analysis to the variable frequency band limiting filter, and the variable frequency band limiting filter Restrict passage.

[0014]

【Example】

 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The transmitter is the same as that shown in FIG.

FIG. 1 is a block diagram of a receiver according to an embodiment of the present invention. In the figure, the same parts as those in FIG. 4 are designated by the same reference numerals. In the figure, 51 is an amplifier for amplifying the intermediate frequency signal output from the BPF 33, and 52 is a variable frequency band limiting filter capable of changing the frequency band limited by a control signal from the outside.

Reference numeral 53 is a frequency analyzer that analyzes the frequency of noise from the output signal of the AD converter 35, detects the frequency of the maximum narrow band noise therein, and sends a control signal to the variable frequency band limiting filter 52.

Next, the operation of the embodiment configured as described above will be described with reference to the waveform diagram of FIG. As shown in the block diagram of the transmitter of FIG. 4 (a), the data signal sequence undergoes primary modulation by FSK or the like and outputs the signal of the waveform of the primary modulator 2 shown in FIG. This output is multiplied by the output signal of the PN code generator 21 and spread, and becomes a signal spread around the output frequency of the primary modulator 2 like the output after spreading. This has a waveform in which the frequency region is moved to the higher side like the frequency-converted antenna transmission output after frequency conversion in the frequency converter 6.

The signal received by the antenna 11 in the receiver shown in FIG. 1 is a signal in which noise is superimposed on the waveform as shown in. This received signal has the same waveform as that of the IF band output after frequency conversion after being converted to an intermediate frequency in the mixer 32, but has a different frequency.

An unnecessary frequency component such as a local oscillation frequency or a sum frequency is removed from the output of the mixer 32 by the BPF 33, is amplified by the amplifier 51, passes through the variable frequency band limiting filter 52, and is amplified by the AGC. It is input to the amplifier 34. As described above, the AGC amplifier 34 limits the magnitude of the output signal to a proper input level to the AD converter 35 and inputs it to the AD converter 35.

The amplitude of the signal digitally converted by the AD converter 35 is limited by the noise level of the AGC amplifier 34, so that its output is mainly a narrow band noise with maximum amplitude and is input to the digital signal processing circuit 41. The frequency is analyzed by the frequency analyzer 53.

The output of the frequency analyzer 53 tunes the variable frequency band limiting filter 52 to the frequency of the maximum amplitude noise. As a result, the output of the variable frequency band limiting filter 52 has a noise-free waveform shown in FIG. This signal reproduces the primary modulation signal in the digital signal processing circuit 41 to obtain the original data signal sequence as shown in.

As described above, according to the present embodiment, by having the variable frequency band limiting filter and the frequency analysis function, narrow band noise can be removed and communication with a good SN ratio can be performed. ..

The present invention is not limited to the above embodiment. The position of the variable frequency band limiting filter 52 may be arranged in front of the mixer 32.

The number of variable frequency band limiting filters 52 may be plural, and in that case, noise of plural frequency components can be removed. The functions of the PN code generator 38, the carrier reproducing oscillator 37, the primary demodulator 40, the frequency analyzer 53, and the like of the digital signal processing circuit 41 may be performed by an analog circuit.

It is also possible to use wired communication instead of wireless communication. The frequency conversion unit including the local oscillator 13 and the mixer 32 for converting to the intermediate frequency may not be used in the case of the low frequency carrier.

The frequency analyzer 53 may be placed before the variable frequency band limiting filter 52.

[0027]

[Effect of the device]

 As described above in detail, according to the present invention, even when an external noise having a narrow bandwidth and large amplitude is superimposed, it is possible to prevent the saturation of the AD converter without lowering the SN ratio of the received signal. The practical effect is great.

[Brief description of drawings]

FIG. 1 is a block diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a diagram showing changes in signal waveforms in a transmitter / receiver of a spread spectrum communication system using the receiver of this embodiment.

FIG. 3 is a principle block diagram of a direct spread spectrum spreader transceiver.

FIG. 4 is a block diagram of a conventional spread spectrum type transceiver.

[Explanation of symbols]

 34 AGC amplifier 52 Variable frequency band limiting filter 53 Frequency analyzer

Claims (1)

[Scope of utility model registration request] 1. A receiver of a spread spectrum communication system for receiving and demodulating a spread spectrum signal, and an AGC amplifier (34) for adjusting the level of the received signal to bring the signal with the maximum amplitude to an appropriate level, A frequency analyzer (53) that analyzes the frequency of the signal with the maximum amplitude among the output signals of the AGC amplifier (34) and outputs a control signal of that frequency, and a control signal of the output of the frequency analyzer (53). A spread spectrum communication system receiver, comprising: at least one variable frequency band limiting filter (52) for limiting the passage of a signal in the frequency band under control.