JPH0396137A - Spread spectrum receiver - Google Patents

Abstract

PURPOSE:To improve anti-disturbing wave characteristic and anti-fading characteristic by separating a reception signal to two systems with different bands and outputting selectively one of the two systems based on the result of comparison of the level of each separated signal. CONSTITUTION:A reception signal is separated into two systems (a), (b) by a filter 11 passing information A and a filter 12 passing information B and respective outputs are given to detection circuits 13, 14 and multipliers 16, 17. The detection circuits 13, 14 detect each filter output, the levels of the detection outputs are compared and a selector switch 20 selects a system of a lower level in response to the comparison output. Then the filter output of the selected system is multiplied with a PN clock by the multipliers 16, 17 to apply the frequency shift thereby obtaining easily the same center frequency by each system. Thus, anti-disturbing wave characteristic and anti-fading characteristic are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spread spectrum receiver, and particularly relates to an improvement using a Manchesterized PN code. [Summary of the Invention] In a spread spectrum receiving device, the structure is simplified by using the property that the same information is divided into two parts and transmitted in the frequency domain by Manchesterizing the PN code. [Prior Art] Spread spectrum communication (hereinafter abbreviated as SS communication) performs primary modulation on the transmitting side using a code called a PN code that is much faster than the information signal to be transmitted, and then performs secondary modulation ( The order of primary modulation and secondary modulation is interchangeable), and the receiving side performs despreading by correlation detection between the PN code and the received signal, and then demodulates the information signal by synchronous detection etc. be. ．． This method is generally said to be resistant to interference waves and selective fading, and the reasons for this are explained below. First, regarding the anti-jamming characteristics, when the received signal is mixed with narrow-band interference waves as shown in Figure 12 (a), the signal spectrum obtained as a result of correlation detection between the received signal and the PN code. is the signal or B as shown in Figure 12(b).
d, and conversely, the interference wave is spread over the bandwidth Bc. When this output signal is passed through a bandpass filter with a bandwidth of Bd, the interference wave power is reduced to Bd/Be as shown in FIG. 12(c) (this is called processing gain). In other words, it can be said that there is resistance to interference waves by the amount of this processing gain. Note that the interference wave becomes white noise due to correlation detection and becomes unintelligible noise.

Next, regarding the selective fading resistance characteristic, when selective fading occurs due to multipath interference, ripples occur in the received signal within the bandwidth Be as shown in Figure 13, and a part of the signal Information will be lost. However, since the information signal is spread to create multiple information signals, the information remains overall, and the information signal can be restored by despreading. In other words, unlike narrowband communication, it can be said to have resistance to selective fading by spreading the spectrum. However, if interference waves enter at a level higher than the processing gain, as shown in Fig. 14(a),
As shown in (b) and (Q), even after correlation detection, the information signal is buried in noise and cannot be recovered. Note that this assumes that synchronization is achieved; in reality, interference waves above a certain level below the processing gain will cause synchronization to become impossible and information to be restored. Also, depending on the interval (frequency) and depth (attenuation) of ripples caused by selective fading, and the level of the received signal (depending on the ratio to thermal noise), even if despreading is performed using correlation detection, the information signal may be affected by thermal noise. It gets buried and cannot be restored. In other words, in an environment without selective fading as shown in Fig. 15, the information signal can be restored by despreading even if the spread information signal is less than thermal noise, but as shown in Fig. 16, it causes deep fluctuations. Due to selective fading, much of the information is lost, and even after despreading, the information signal is buried in thermal noise and may not be able to be recovered.

Therefore, in conventional methods, in order to improve these problems, the same information is divided into multiple bands and transmitted in the same way as narrowband communication, and the band that is least affected by interference waves and selective fading is selected. It was thought. For example, as shown in FIG. 4(a), the PN code generation circuit l
There is a method of multiple transmission using multipliers 2, 3, 4, local oscillators 5, 6, adder 7, etc.

Figure 4(b) shows the frequency spectrum of the output. [Problems to be Solved by the Invention] However, this conventional method requires a plurality of carrier waves, multipliers, etc. at the time of transmission, and has the drawback that an inexpensive receiving device cannot be constructed. Furthermore, the number of parts increases, and there are also problems in miniaturization.

[Object of the invention] Therefore, the object of the present invention is to solve the problem in spread spectrum communication.
The object of the present invention is to provide an inexpensive and simple receiving device with excellent anti-interference characteristics and anti-fading characteristics. [Means for Solving the Problems] In order to achieve the above object, a first invention provides a spread spectrum receiver that demodulates an information signal spread spectrum by a Manchesterized PN code. The gist of the present invention is to have a filter that separates the signals into two signals, a means for comparing the levels of each signal separated by the filter, and a switching means for selectively outputting one of the two systems based on the comparison result. ．． A second invention is a spread spectrum receiver similar to the above, which includes weighting means for setting the level of the received signal to a predetermined level, frequency conversion means for shifting the frequency of the received signal to a predetermined frequency, and the receiving device. a switch for selecting the signal and the frequency-shifted signal; a filter for extracting a predetermined band of the signal selected by the switch;
The gist of the present invention is to include comparison means for comparing the level of the weighted signal and the level of the signal passed through the filter and switching the switch.

Furthermore, a third invention is a spectrogram spread receiver similar to the above, which is shifted by a filter that separates the received signal into two systems with different bands, and a frequency conversion means that shifts the separated signals to predetermined frequencies. The gist thereof is to include means for synthesizing each signal.

[Operation] Generally, as a multi-wave resistant modulation method, a method is known in which an information signal is Manchesterized. This demodulates the information signal by performing a redundant phase shift at the center of one bit of the information signal as shown in FIG. 1, and by performing one-bit delay detection as shown in FIG. In FIG. 2, LPF is a low-pass filter, M is a multiplier, and T is a delay device.

With this method, as long as the delay time difference is within an appropriate range, the eye of the information signal pattern will not close, even if, for example, two waves interfere with each other at the same level and in opposite phases. In other words, an effect equivalent to performing a type of multipath diversity reception can be obtained.

The spread spectrum receiver according to the present invention applies the characteristics of the above-mentioned system in the frequency domain. That is, as shown in FIG. 3(a), by Manchester-izing the PN code in the Manchester-ized PN code generation circuit 8, in the frequency domain, the same information is divided into A and 82 pieces and transmitted (see FIG. (b)) has the property that it is equal to In FIG. 3, 9 is a multiplier and 10 is a local oscillator. By utilizing this property, Fig. 4(a),
The same effect as the two-wave transmission example shown in (b) can be obtained. An example of the structure of the Manchesterized PN code generation circuit is shown in the fifth section.
It is shown in the figure. this is. The PN code is Manchester-ized by performing an exclusive OR with the logic circuit EX-OR of the PN code and the PN clock, and inverting the output.
[Embodiment] A first embodiment of the spread spectrum receiver according to the present invention is shown in FIG. In the same figure, 11.12 and l9 are band-limiting filters, 13 and l4 are detection circuits, 15 is a comparison circuit, 16 and 17 are multipliers, l8 is a PN clock oscillator,
20 is a selection switch.

In the first embodiment, the received signal is separated into two systems (a) and (b) by a filter 1l that passes A and a filter 12 that passes B in FIG. 3(b),
The respective outputs are the detection circuits 13 and 14 and the multipliers 16 and 17.
given to. Each of the detection circuits 13 and 14 detects the respective filter output, and the level of the detection output is compared in the comparison circuit 15. In response to the comparison output, the selection switch 2
0 selects a low level system. Filter 1 like this
In 1.12, by limiting the band of the received signal and separating it into two systems, when interference waves are mixed in, the fact that the received signal energy is higher in the band where the interference waves exist is used. .

The filter output of the selected system is frequency-shifted by multiplying it by the PN clock in a multiplier 16 or 17, so that both systems can easily obtain the same center frequency.

Figure 7 shows an example of the actual operation of the first embodiment. The numbers in the figure correspond to the numbers in Figure 6. If there is an interference wave as shown in the figure in the received signal in ■, after passing through filter 11, ■
, after passing through the filter l2, it becomes as shown in ■6. This is detected and the levels are compared, and the selection switch 20 is selected based on the information.
selects the system (b). As a result, a signal without interference waves as shown in (■) can be obtained at the output.

Next, a second embodiment of the spread spectrum receiver according to the present invention is shown in FIG.

In the figure, 20 is a weighting circuit, 21 and 22 are detection circuits, 23 is a comparison circuit, 24 is a selection switch, 25 is a multiplier, 26 is a PN clock oscillator, and 27 is a band limiting filter.

In the above embodiment, (c). (
The weighting circuit 20 is installed in advance so that the signal levels of the outputs of the detection circuits 21 and 22 in the system d) are equal.
Weighting (here, for example, 1/2 of the total level) is performed (Fig. 9 (1)). In addition, filter 2
7 is a band limit that allows the received signal to pass through B in FIG. 3(b). Here, when interference waves are mixed in, a level difference occurs between the outputs of each detection circuit 21 and 22, and the output state of the comparison circuit 23 changes. Based on the comparison circuit output, the selection switch 24 selects a1 or a2.If aal is selected, no frequency shift is performed, and if a2 is selected. A shift of 2fPN, which is twice the frequency of the PN clock, is performed. FIG. 9 shows an example of the actual operation of the above embodiment. Figure 3 (b
), when interference waves are mixed into B in Figure 9 (2)
As shown in Figure 8, in ■, the level of both the interference wave and the information signal becomes 1/2 due to weighting, but in ■, the signal and interference wave remain at the same level, and when these are detected and the levels are compared, (c ) < (d). The @ selection switch 24 selects a2 based on this comparison information. As a result, a frequency shift is performed as shown in FIG. 9 (3), and the filter 2
7, a signal free of interference waves is obtained. Both the secondary harm wave and the information signal are at 1/2 the level, but in case (3), there is no interfering wave and the signal remains at the same level, and when these are detected and the levels are compared, (c)>(d). At this time, the comparison circuit 23 does not generate comparison information, and the selection switch 24 is also kept in the same state ((a) selected).

With such a configuration, a signal free of interference waves can be obtained at the output.

Next, a third embodiment of the spread spectrum receiver according to the present invention is shown in FIG. In the same figure. 31 and 32 are band limiting filters. 33
34 is a multiplier, 35 is a PN clock oscillator, 36 is an adder, and 37 is a band limiting filter.

According to this structure, the received signal is
It is divided into two systems (e) and (f) by a band-limiting filter 31 that passes B and a band-limiting filter 32 that passes B. A frequency shift is performed by multiplying by , and the signals of both systems are synthesized so that they have the same center frequency.

An example of the actual operation of the above embodiment is shown in FIG.

The numbers in the figure correspond to the numbers in FIG. If selective fading like ■ occurs in the received signal,
This received signal is separated by filters 31 and 32 like ■, aill, frequency shifted by the PN clock, and O, O.
Make sure that the signals of both systems have the same frequency, as in By combining these two systems in the adder 36, the result becomes 0, and an output with reduced selective fading can be obtained. In addition, in the first to third embodiments, the transmitter is shown in FIG. 3(a).
Although the configuration is as follows, it goes without saying that the configuration is not limited to this.

[Effects of the Invention] As explained above, according to the present invention. In spread spectrum communication, the configuration of a receiving device can be simplified by converting the PN code into Manchester code.

[Brief explanation of drawings]

Figure 1 is an explanatory diagram of the method of Manchesterizing an information signal, Figure 2 is a diagram showing the demodulation method of the Manchesterized signal, and Figure 3 (a) is the basic method of using Manchesterization in a spread spectrum transmitter. Explanatory diagram, Figure 3(b)
is its frequency spectrum diagram, FIGS. 4(a) and 4(b) are explanatory diagrams of an example of two-wave transmission, FIG. 5 is an explanatory diagram of a configuration example and operation of a Manchester-ized PN code generation circuit, and FIG.
7 is a block diagram showing the first embodiment of the present invention, FIG. 7 is a diagram explaining its operation, FIG. 8 is a block diagram showing the second embodiment of the invention, FIG. 9 is a diagram explaining its operation, FIG. 10 is a block diagram showing a third embodiment of the present invention, FIG. 11 is an explanatory diagram of its operation, and FIGS. 12 to 16 are explanatory diagrams of spread spectrum communication. 11, 12, 19...band limit filter, 13.14...detection circuit, 15...
...Comparison circuit, 16.17...
Multiplier, 18...PN clock oscillator, 20...Selection switch.

Claims (3)

[Claims] (1) In a spread spectrum receiver that demodulates an information signal that has been spread spectrum using a Manchesterized PN code, a filter that separates the received signal into two systems with different bands, and a comparison of the levels of each signal separated by the filter. and switching means for selectively outputting one of the two systems based on the comparison result. (2) A spread spectrum receiver that demodulates an information signal that has been spread spectrum using a Manchesterized PN code, which includes weighting means that sets the level of the received signal to a predetermined level, and a frequency that shifts the frequency of the received signal to a predetermined frequency. a conversion means; a switch for selecting the received signal and the frequency-shifted signal; a filter for extracting a predetermined band of the signal selected by the switch; a level of the weighted signal; A spread spectrum receiving device comprising: comparing means for comparing the signal level with a signal level obtained by switching the switch and switching the switch. (3) A spread spectrum receiver that demodulates an information signal that has been spread spectrum using a Manchesterized PN code, which includes a filter that separates the received signal into two systems with different bands, and a filter that shifts each separated signal to a predetermined frequency. A spread spectrum receiving device comprising: a frequency conversion means; a means for synthesizing each shifted signal;