JPH06177857A - Spread spectrum signal receiver - Google Patents

Abstract

PURPOSE:To obtain a high S/N even under the noise of a high level and high density. CONSTITUTION:A received spread spectrum signal is transmitted through a comb-shaped characteristic filter 31. In the filter 31, the main robe of the linear spectrum (until the 13th linear spectrum) of a pseudo random code for spread is used as a center, the frequency two times as high as the frequency of an information signal is used as a pass band. The inverse transformation of the bi-phase code of the output of the filter 31 is operated by a frequency converting part 33, and a spread spectrum demodulation is operated to the signal by a demodulating part 34. Thus, the noise can be diffused and turned to a nose 43 whose level is low, and the signal can be inverse-spread and turned to a signal 44 whose level is high.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to wired communication, wireless communication,
In particular, the present invention relates to a receiver for receiving a spread spectrum signal suitable for use in a noisy environment such as power line communication and space communication.

[0002]

2. Description of the Related Art In spread spectrum communication, for example, a signal 11 having a frequency characteristic as shown in FIG. 5A is spread by a pseudo random code signal and dispersed in a wide frequency band as shown by a curve 12 in FIG. 5B for transmission. However, even if noise 13 is mixed in during the transmission, the signal is narrowed and has a large level similar to the original signal 11 as shown in FIG. 5C by performing spectrum despreading with the pseudo random code signal on the receiving side. The noise 13 is demodulated into a signal 14 having a frequency characteristic and becomes noise 15 dispersed in a wide frequency band, and the level of each spectrum is small, so that a high S / N signal is obtained.

[0003]

However, the transmission line shown in FIG.
If a large level of noise 16 is densely present over a wide frequency band as shown in FIG. 5, even if the signal that has passed through this transmission path is despread, noise 15 as shown in FIG.
Is spread-spectrum, the same component of each spread spectrum of many noises is added, the level drop is slight, and a relatively large level of wide-band noise 17 is generated, which is the level of the spread-spectrum demodulated signal 14. Is small, and a sufficient S / N cannot be obtained.

It is conceivable to spread the spectrum sufficiently wide so that such a phenomenon does not occur. For that purpose, the code length of the pseudo-random code signal is lengthened or the spreading bandwidth is widened. However, there is a problem that the circuit scale becomes large, the cost becomes expensive, and the reliability is lowered. In addition, the spread band cannot be unlimitedly extended in relation to other communications.

[0005]

According to the first aspect of the present invention, a comb-shaped characteristic filter having a line spectrum of the pseudo random code signal as a pass band is provided before the spread spectrum demodulation section. Here, it is preferable that the comb-shaped characteristic filter having a line spectrum as a pass band allows only the line spectrum to pass when the information (signal) to be transmitted is an on / off signal. When the information to be transmitted is a signal having a frequency band, the double sideband or the single sideband of the information component appearing on both sides of the line spectrum is also passed. In any case, it is sufficient to pass only the main component having a large level, not all the line spectra.

According to the second aspect of the present invention, one sideband of the line spectrum is passed as the comb-shaped filter of the first aspect of the invention.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS To facilitate understanding of the present invention, the transmitting side will be described first. As shown in FIG. 3, in the spread spectrum communication transmitter, the information signal from the information source 21 modulates the carrier wave in the information modulator 22. This modulation is amplitude modulation, frequency modulation, phase modulation (PSK), or the like. This modulated output is spread-spectrum-modulated by the pseudo-random code signal from the PN code generator 24 in the spread-spectrum modulator 23, and the modulated output is frequency-converted into a signal in the transmission frequency band by the frequency converter 25, and then power amplified. The signal is amplified by the unit 26 and transmitted as a radio wave from the antenna, or is transmitted to the wired transmission path via the interface circuit.

The information modulating section 22 and the frequency converting section 25 are omitted, the spread spectrum modulation output is bi-phase coded, and a pseudo random code having an M sequence [3,1] 7-bit length is used to generate a PN code. The frequency of the clock from the clock oscillator 27 that operates the unit 24 is 175 kH
z, and the spectrum of each part when the speed of the information signal of the information source 21 is 1200 bps.

Information supplied to the spread spectrum modulator 23
The report signal has a spectral power density as shown in Figure 4a.
And its bandwidth is 1200 Hz. Pseudo-random code
The line spectrum of the signal is the spectrum shown in Fig. 4b.
The interval is 25 kHz = R_C/ (2 ⁿ-1) (n = 3, R_C
= 175 kHz), the envelope of the line spectrum is (sinx
/ X)²Becomes The spread spectrum modulated output is shown in Figure 4c.
As shown in Fig. 2b, the information signal is
It appears as a band and this bandwidth is 2.4kH
z. This spread spectrum modulation output is the frequency converter
By biphasic coding at 25, as shown in FIG.
The whole vector shifts to the higher side by 175 kHz.

Next, an embodiment of the present invention is shown in FIG. The spread spectrum signal received via the antenna or the interface circuit is, in this embodiment, a comb characteristic filter 31.
Passed through. The filter 31 uses each spectrum of the spread pseudo random code signal of the spread signal as a pass band in the received spectrum. The output of the filter 31 is amplified by the high frequency amplifier 32, frequency-converted by the frequency converter 33 so as to restore the frequency conversion performed by the frequency converter 25 on the transmission side, and supplied to the spread spectrum demodulator 34. The spread spectrum demodulation unit 34 despreads the input signal by the pseudo random code signal from the PN code generation unit 35 and demodulates it. A phase shift of the pseudo random code of the PN code generation unit 35 with respect to the spread pseudo random code of the spread spectrum signal received by the time discrimination control circuit 37 of the synchronization unit 36 is detected, and P is set so as to eliminate this shift.
The N code generator 35 is synchronized. The demodulation output of the spread spectrum demodulation unit 34 is demodulated by the information demodulation unit 38, the information signal is taken out and supplied to the output terminal 39.

The frequency characteristic of the comb-shaped characteristic filter 31 is
In the case of the numerical example, the line spectrum in the main lobe of the frequency characteristic of the pseudo-random code signal of the PN code generator 35 (FIG. 2b) is centered and the frequency band of 2.5 kHz is the pass band. Let's pass up to the 13th line spectrum. Therefore, even if a high level and high density noise 41 is generated in the received signal as shown in FIG. 2A, the frequency component of the output of the filter 31 is as shown in FIG.
1b to 1 of the pseudo random code signal as shown in FIG.
Both sidebands up to the third line spectrum and noise 42 in that frequency band are formed. The output of this filter 31 is subjected to the inverse conversion of the biphase code in the frequency conversion unit 33, and
The spectrum is as shown in. This spread spectrum demodulation output, as shown in FIG. 2d, the noise 42 is dispersed over a wide frequency band to form a low level noise 43, and the signal is collected by despreading to become a large level signal 44.
High S / N is obtained.

As the frequency characteristic of the comb-shaped characteristic filter 31, it is preferable that only the line spectrum is passed when the modulation signal is an on / off signal. For other modulated signals, only one sideband of the line spectrum may be passed. Therefore, in this case, in the above numerical example, one pass band may be half of 2.5 kHz, and the S / N can be further increased.

[0013]

As described above, even if the noise is present in a dense and high level over a wide band, a filter having a comb-shaped characteristic whose pass frequency is the main line spectrum of the pseudo-random code signal is used. By providing the signal before the spread demodulation unit, a spread spectrum demodulation output with high S / N can be obtained. Moreover, it is not necessary to increase the code length of the pseudo-random code so much, the circuit scale of the PN code generator may be small, and the reliability is high. Further, the frequency can be effectively used.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a spectral power density distribution in a main part in FIG.

FIG. 3 is a block diagram illustrating a spread spectrum communication transmitter.

FIG. 4 is a diagram showing a spectral power density distribution in the main part in FIG.

FIG. 5 is a diagram showing a spectrum power density distribution for explaining a spread spectrum signal.

Claims (2)

[Claims] 1. A spread spectrum receiver for spread spectrum demodulating a received signal in a spread spectrum demodulation section using a pseudo random code signal, wherein a line spectrum of the pseudo random code signal is used as a pass band before the spread spectrum demodulation section. A spread spectrum signal receiver, characterized in that a comb-shaped characteristic filter is provided. 2. A spread spectrum receiver for spread spectrum demodulating a received signal in a spread spectrum demodulation section with a pseudo random code signal, wherein one side of a line spectrum of the pseudo random code signal is provided before the spread spectrum demodulation section. A spread spectrum signal receiver characterized in that a comb-shaped characteristic filter having a wave band as a pass band is provided.