JPS59163933A - Modulating method of spread spectrum communication - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a modulation method for spread spectrum communication in which a carrier wave is modulated by both a pseudo-noise code and an information signal.

[Prior art]

Spread spectrum communication transmits the information signal to be transmitted using a carrier wave modulated using a pseudo-noise code to have a band sufficiently wider than the unique spectrum width of the information signal. Its development is urgently needed because it has many advantages, such as being superior in its elimination effect, enabling selective addressing, and increasing the number of stations that can simultaneously use the same frequency band.

For details on spread spectrum communication, see Journal of the Institute of Electronics and Communication Engineers 1982
September issue (VOL65.IVh9), Electronic Science 1978
It is described in the November issue, etc., and its summary is as follows.

In this communication, a carrier wave is firstly modulated with a signal having a wide frequency band to widen the spectrum band of the carrier wave, and a radio wave is transmitted by secondarily modulating the carrier wave with an information signal. The station that receives this radio wave performs correlation detection using a signal that is completely in phase with the primary modulated signal, demodulates the detected signal, and extracts an information signal. In this case, it is desirable that the signal used for primary modulation has a uniform spectrum, such as white noise, but when white noise is used, the receiving side obtains a signal that is exactly in phase with the signal used for modulation. Therefore, correlation detection cannot be performed on the receiving side. For this reason, a pseudo-noise code is used that has a spectrum similar to white noise but is composed of regular pulses.

The outline of spread spectrum communication is as above, but for easier understanding, Figure 1 is shown.

The principle will be explained with reference to FIG. The waveforms of each signal on the transmitting side and the receiving side are as shown in FIGS. 1(a) to 1(f). (a) shows a pseudo-noise code, which has two values, and is composed of a plurality of pulses with different signal durations. Here, the order of modulation is that even if the carrier wave is modulated with a pseudo-noise code and the resulting signal is modulated with an information signal, the pseudo-noise code is modulated with an information signal, and then the carrier wave is modulated with this signal. Since the results obtained are the same in both cases, in order to make the explanation easier to understand, it is assumed that the modulation is performed in the latter order. The shortest signal duration TS of the pseudo-noise code is 1/1°0~''/100 of the minimum duration TD of the information signal shown in (b).
0 (in the figure, 1/4 is selected for convenience of drawing). Then, when the pseudo noise code shown in (a) is modulated by the information signal shown in (b), the signal shown in (c) is obtained, and when the carrier wave is modulated with this signal shown in (e), (
The transmission signal shown in b) is obtained, and this signal is transmitted as radio waves. On the receiving side, when the signal shown in (d) is received, correlation detection is performed using a pseudo-noise code having exactly the same phase as the pseudo-noise code shown in (,), and the signal shown in (,) is obtained. This means that the carrier wave is the information signal shown in (b) and is 2
The waveform is exactly the same as that obtained by phase modulation. and,
When the signal shown in (,) is demodulated, a signal equivalent to the information signal (b) is obtained as shown in (f).

The spectra of these signals are shown in FIGS. 2(a) to 2(f). The pseudo noise code is 1 as shown in (1)
．． It is represented by an emission line spectrum with a bandwidth of 4s, and
The information signal is represented by a spectrum with a bandwidth of "/TD" as shown in (b). When the pseudo-noise code is modulated with the information signal, a signal with a bandwidth of 1/T8 is obtained as shown in (C). When this signal (C) is used to modulate a carrier wave of frequency fc, a signal having a bandwidth of 2/T8 is obtained as shown by the symbol "A" in (d). When the receiving side receives the signal shown in (d) and performs correlation detection, the symbol "
A signal with a bandwidth of 2/TD is obtained as shown by "2/TD", and when this is demodulated, the same signal as the information signal shown in (b) with a bandwidth of "/TD" is obtained as shown in (f). The bandwidth of the modulated radio waves is widened to 2/T8 as shown by the symbol "A" in Figure 2 (d), but even if there is noise or interference in this, these Since the bandwidth is very narrow compared to the bandwidth of radio waves spread by pseudo-noise codes, the spectrum of noise and interference is shown in (d) with the symbol "
It can be expressed as the shaded area as shown in ``.''. If we calculate the correlation output of radio waves mixed with noise and interference in this way, we can obtain a signal with a narrow band that has the bandwidth of VTD because the radio waves modulated with pseudo-noise codes are correlated. Interference has no correlation with pseudo-noise codes generated on the receiving side, so the symbol "," is used in parentheses.
The signal is output as a signal with a spread band, as shown in the shaded area indicated by "2". On the receiving side, if the signal shown in (,) is demodulated and the demodulated signal is output through a low-pass filter,
The influence of noise and interference on the desired signal of the demodulated output signal is (
As shown in the shaded area in f), the noise and interference components, which may be small, are part of the signal spread by the pseudo-noise code and are therefore unintelligible like white noise.

For this reason, even if there is interference such as noise or interference, these will only be mixed in as unintelligible noise, resulting in very good confidentiality. Further, since different types of pseudo-noise codes can be easily obtained, selective addressing can be easily performed by assigning different pseudo-noise codes to each receiving station.

The outline of spread spectrum communication is as described above, but in order to carry out this communication, it is a necessary condition for the receiving side to generate a pseudo-noise code whose phase is completely synchronized with that of the transmitting side.

To solve this problem, conventional methods have been proposed in which synchronization information is detected from received radio waves using a narrow band filter using a Costas loop or the like, and the phase of the pseudo-noise code on the receiving side is matched with that on the transmitting side.

However, with such conventional methods, even if the pseudo-noise codes are synchronized, the narrow bandwidth of the filter means that more information signal components are removed than necessary, resulting in code errors in the information signal. Therefore, the information signals that can be used are limited to those having redundancy.

[Object and structure of the invention]

Therefore, the purpose of this invention is to be able to completely synchronize the phase of the pseudo-noise code on the receiving side with that on the transmitting side, and to also make it possible to completely synchronize the phase of the pseudo-noise code on the transmitting side as in the conventional case. An object of the present invention is to provide a modulation method for spread spectrum communication that can prevent code errors that occur due to the above.

In order to achieve such an object, the present invention prepares a plurality of pseudo-noise codes, and selects and uses the pseudo-noise codes according to the state of the information signal. Hereinafter, the present invention will be described in detail using drawings showing embodiments.

〔Example〕

FIG. 3 is a block diagram of a transmitting device configured to apply the present invention. In the figure, 1 is a pseudo-noise code generator that generates a pseudo-noise code s1 that repeats the same pattern with a period T, and a pseudo-noise code S2 that has the same pattern but a phase difference of -. It has become. 2
is an AND circuit that performs an AND operation between the pseudo-noise code S2 and the information signal supplied via the terminal 4; 5 is an oscillator that generates a carrier wave; 6a, (ib is a modulator; 1 is a synthesis circuit;
8 is a transmitter.

FIG. 4 is a block diagram of the receiving device. In the same figure,
10 is a wide band pass filter, 11 is a local oscillator, 12 is a frequency converter, 13 is a pseudo noise code generator, 1
4a t 14b is a correlator. The pseudo-noise code generator 13 generates pseudo-noise codes 83 and 84 having exactly the same pattern as the pseudo-noise codes s1 and s2 generated by the pseudo-noise code generator 1 on the transmitting side, and generates pseudo-noise codes 83 and 84 according to the frequency supplied to the terminal 13m. The pattern repetition period of the generated pseudo-noise code is changed. The correlators 14 and 14b correlate the pseudo-noise code of the received signal with the pseudo-noise code generated by the pseudo-noise code generator 13, and only correlate K of the received radio waves that have a correlation with the pseudo-noise code. Output is now available. isa, 15b is a band pass filter, 16a, 16b is a detector, 1γ
a.

17b is an integrator, 18a and 18b are comparators that generate an output voltage when the input voltage exceeds a predetermined value, 19 is a voltage controlled oscillator, 20 is a synchronous circuit, 21 is an AND circuit,
22 is an output terminal. The synchronous circuit 20 has a terminal 20a,
When no voltage is supplied to either terminal 20b, it is in search mode and generates a voltage that changes significantly over time, and when voltage is supplied to either terminal 2oa or 20b, it is in tracking mode. Thus, a voltage is generated that maximizes the voltage supplied to the terminals 20c and 20d.

The operation of the device configured as described above is as follows. In the transmitter of FIG. 3, the pseudo-noise code generator 1 generates different types of pseudo-noise codes, namely, one pseudo-noise code S1 that repeats the same pattern every period T, and the other pseudo-noise code that repeats the same pattern. However, a pseudo noise code S2 whose phase differs by T/2 is generated. The pseudo-noise code S1 constantly modulates the carrier wave generated by the oscillator 5 in the modulator 6a, but the pseudo-noise code S2 uses an AND circuit only when the information signal supplied via the terminal 4 is at the "1" level. 2 is turned on, the signal is supplied to the modulator 6b only at this time and modulates the carrier wave. The nine signals modulated by the modulators 6B and 6b are combined in the combining circuit T, so that when the information signal is at the "1" level, the radio waves transmitted via the transmitter 8 are both pseudo-noise codes s1 and 82. It's a modulated thing,
When the information signal is at the "o" level, it is modulated only with the pseudo-noise code S1. This means that a plurality of pseudo-noise codes are selected depending on the state of the information signal.

The radio waves modulated and sent out in this manner are received by the receiving device shown in FIG.
After passing through, the signal is converted to an intermediate frequency by a frequency converter 12 and supplied to correlators 14a and 14b. At this time,
The pseudo-noise codes 83, 84 on the receiving side are completely synchronized with the pseudo-noise codes 81, 82 on the transmitting side, and the pseudo-noise codes 83 and 83 have the same phase as Sl, and the phases of 84 and 84 have the same phase. If it is assumed that the output of the correlator 14a is always a carrier wave, and the output of the correlator 14b is that the correlation between the signal input to the correlator 14b and the pseudo noise code S4 is obtained only when the information signal is at the "1" level. Therefore, the carrier wave is output only at this time, but when the information signal is at the "0" level, there is no correlation between the received signal and the pseudo noise code S4, so the output of the correlator 14b is a signal with a spread spectrum. Output. The output signals of the correlators 14a and 14b are passed through the bandpass filter 1.
If the output signal is supplied to the detectors 16a and 16b via sa and 15b and integrated, an output signal is always obtained from the integrator 17B.
An output signal is obtained only when the level is .

If the voltage of the output signal at this time is set to be larger than the predetermined value judged by the comparators 18a and 18b, the comparator 181 always generates an output voltage, and the comparator 18b generates an output voltage when the input voltage is supplied. only generates an output voltage. Since these output voltages are outputted via the AND circuit 21, an output corresponding to the information signal is given to the output terminal 22. On the other hand, the output voltage of the comparator 19a, 1 (lb) is the terminal 20a of the synchronous circuit 20.

20b, but since the output voltage of the comparator 18a is always generated, the synchronization circuit 20 operates in a tracking mode and outputs such that the voltage supplied to the terminals 20c and 20d is maximum. Generates voltage. As a result, the voltage controlled oscillator 19 generates a signal with a frequency corresponding to the supplied voltage, so the pseudo noise code generator 13
generates a pseudo-noise code corresponding to the frequency of this signal. When the voltage supplied to the terminal 20C220d becomes maximum, it means that the phases of the pseudo noise codes on the transmitting side and the receiving side completely match, so that accurate tracking is always performed.

The above explanation is for the case where the pseudo noise codes on the transmitting side and the receiving side are synchronized, but there is no guarantee that this synchronization is achieved when the power is turned on. In such a case, the correlator 14a,
Since both of 14b output signals with spread spectrum, the bandpass filters 15 & , 15b
The output of comparator 18 & , is very small.
18b does not generate any output voltage. Therefore, since voltage is not supplied to both terminals 20a and 20b, the synchronous circuit 20 is in a search mode and generates a signal whose voltage changes significantly over time.

Therefore, the frequency of the signal generated by the voltage controlled oscillator 19 and the phase of the pseudo-noise code generated by the pseudo-noise code generator 13 change significantly over time. As a result, the phase of the pseudo-noise code generated from the pseudo-noise code generator 13 eventually matches the phase of the pseudo-noise code on the transmitting side. Thereafter, the synchronous circuit 20 is operated in the same manner as described above.
When in tracking mode, accurate synchronization is achieved.

Note that in the above embodiment, the two types of pseudo-noise codes have exactly the same pattern, and the repetition period of the pattern is shifted by half a period, but this is because no matter which phase synchronization is tracked, the shortest time is achieved. This is to enable synchronization. Therefore, if the time required to achieve synchronization is not an issue, the 2' types of pseudo-noise codes need only be different, and any pattern and phase relationship may be used. . Furthermore, although the information signal has been described as having a binary value, analog transmission can also be performed by using more types of information signals and selecting pseudo-noise codes according to each value.

〔effect〕

As explained above, the modulation method for spectrum communication according to the present invention selects the type of pseudo-noise code depending on the state of the information signal, so that the narrow band that was previously required on the receiving side is Since a filter is no longer necessary, it is possible to prevent code errors in information signals that would otherwise occur due to synchronization of pseudo-noise codes.

[Brief explanation of drawings]

1 and 2 are graphs showing the waveform and spectrum of each signal to explain the outline of spread spectrum communication, and FIGS. 3 and 4 are examples of a transmitting device and a receiving device to which the present invention is applied. FIG. 1.13...pseudo-noise code generator, 5...oscillator, 13a, 5b...modulator, 7...combining circuit, 8...transmitter, 14a, 14b... ...-correlator,
15a, 15b...Band pass filter, 19
... Voltage controlled oscillator, 20... Synchronous circuit. Patent applicant Hitachi Electronics Co., Ltd. Hitachi, Ltd. Agent Masaki Yamakawa (and one other person)

Claims (1)

[Claims] A modulation method for spread spectrum communication, characterized in that in spread spectrum communication in which a carrier wave is modulated by a pseudo noise code and an information signal, the type of pseudo noise code is selected depending on the state of the information signal.