JPH09261114A - Spread spectrum communication method and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To construct a simple receiving circuit by securing the difference between the basic clock frequency of a PN code of the receiving side and that of the transmitting side and obtaining a synchronous state between both PN codes. SOLUTION: A clock generator 17 which generates the clocks of constant frequency different from the clock of the transmitting side is connected to an PN code generator 14 of the receiving side via a clock operation part 16. The clock pulse signal (k) that is oscillated by the generator 17 undergoes elimination of a prescribed number of its pulses at the part 16. Thus the signal (k) whose pulses are partly eliminated is inputted to the generator 14. As a result, a correlative state is maintained. The diffusion signal that is received in a correlative state secured for the phases of PN codes between the transmitting and receiving sides is extracted after undergoing the FM modulation in a waveform equal to that of the carrier signal of the transmitting side. Then the received data signals that undergone the FM modulation are converted into the digital signals according to their frequency, and these digital signals are demodulated into the transmission data.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system, and more particularly to a spread spectrum communication method and apparatus.

[0002]

2. Description of the Related Art Spread spectrum communication was proposed in the 1940's and is expected to be put into practical use because it is superior in noise resistance and interference resistance to conventional narrow band communication. In this spread spectrum communication, transmission data is spread-modulated using a pseudo noise code (PN code) on the transmission side and transmitted, and the reception side demodulates it again using the PN code to obtain transmission data information. is there. In this spread spectrum communication, the frequency range used is spread about 10 to 1000 times as compared with normal wireless communication, so that the peak value of the radio wave intensity can be lowered and there is interference in some frequencies. Can communicate, is resistant to noise, and is not easily eavesdropped. As the spreading method, there are a direct spreading method, a frequency hopping method, a chirp method, and the like, but as a general practical communication, the direct spreading method is mainly used.

In this direct spread spectrum system,
At the transmitting side, first, a PN code in which signals of "1" and "0" levels randomly arranged using a clock of a constant frequency are repeated at a constant cycle is created. This PN code is multiplied by the transmission data signal (carrier signal), that is, multiplied by +1, -1 in accordance with the PN code "0", "1" to perform BPSK modulation. As a result, a spread modulation signal whose frequency is spread is generated.

On the receiving side, the received spread signal is again PN
The code is multiplied and demodulated to the original carrier signal to obtain a transmission data waveform. In this case, the PN code on the receiving side has the same frequency and phase as the PN code on the transmitting side and cannot be completely demodulated unless they are synchronized. This PN code is formed by a circuit that combines a plurality of flip-flops in series, and
The number of clocks in a cycle is represented by 2 ⁿ −1, ^where n is the number of flip-flops. For example, in a circuit using five flip-flops, one clock cycle is 31 clocks. Such a repetition cycle has PN codes of various cycles from 15 clocks to several thousand clocks, and random spread modulation is performed according to each PN code. It is not easy to synchronize this PN code between the transmitting side and the receiving side.

Conventionally, in order to synchronize this PN code,
A circuit incorporating a SAW convolver was used, or a variable frequency clock generator was used.

[0006]

SUMMARY OF THE INVENTION However, SAW
The convolver is expensive and has a problem that the degree of freedom in design is small because the circuit configuration that can be incorporated is limited. Further, if the variable frequency clock generator is used, the circuit has to be configured as an analog circuit, the configuration becomes complicated, the assembly of hardware becomes complicated, and the reliability of accuracy is not sufficient. .

The present invention has been made in view of the above-mentioned drawbacks of the prior art. It is possible to construct a simple receiving circuit without using a special element such as a SAW convolver which is expensive and has a large use constraint, and to transmit a fixed frequency signal. By using a digital circuit with a clock generator consisting of
An object is to provide an inexpensive spread spectrum communication system with a simple configuration.

[0008]

In order to achieve the above-mentioned object, the present invention transmits a basic clock frequency of a PN code on the receiving side in a spread spectrum communication data transmission system for performing data transmission by a spread spectrum system by direct spread. Synchronize with the PN code of the transmitting side by making it different from the basic clock frequency of the PN code of the receiving side and shifting the phase of the PN code of the receiving side in correspondence with a predetermined number of clocks so that the correlation of both PN codes can be obtained. , And provides a spread spectrum communication method characterized by demodulating data in this synchronized state.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment,
It is characterized in that the phase of the basic clock of the PN code on the receiving side is removed to delay the phase and keep the synchronization state with the PN code on the transmitting side.

Another preferred embodiment is characterized in that the phase is advanced by adding a pulse of the basic clock of the PN code on the receiving side to maintain the synchronization state with the PN code on the transmitting side.

In order to carry out the method of the present invention, a transmitter for frequency-modulating the data to be transmitted, a clock oscillator for generating a constant basic clock pulse, and a basic clock from this clock oscillator are provided on the transmitter side. A PN code generator for creating a PN code based on the above, and a spread modulator for spreading-modulating the frequency-modulated data with the PN code, and a receiver side clock oscillator on the transmitter side. A clock oscillator for generating basic clock pulses of different frequencies, a clock operating unit for removing a part of the basic clock pulse of the clock oscillator of the transmitter or adding a pulse, and a clock signal from the clock operating unit. Create a PN code based on the PN code generator and the receiving side PN code generator. A mixer for mixing the spread signal and the spread signal sent from the transmitting side, and a level detector for detecting the level of the output signal from the mixer and inputting the detected signal to the clock operating unit are provided. Provided is a spread spectrum communication device characterized by being provided.

[0012]

1 is a block diagram showing the configuration of a transmitting side of a spread spectrum communication system according to an embodiment of the present invention. 2 to 4 show examples of signal waveforms on each line of the block diagram of FIG. The information to be transmitted is formed by the modulated data generator 1 as digital data of "1" and "0", as shown in FIG. This modulated data generator 1 has a PLL synthesizer 2
, The transmission data is FM-modulated as shown in FIG. 2B, and "1" and "0" of the transmission data signal a are connected.
A carrier signal b whose frequency has changed according to is formed. This PLL synthesizer 2 includes a PN code generator 3
Together with the spread modulator 4.

The PN code generator 3 is connected to a clock generator (not shown) that generates a reference clock pulse signal having a constant frequency. The PN code generator 3 creates a PN code in which randomly-arranged "1" and "0" level signals are repeated at a constant cycle by using a constant frequency clock from the clock generator. This PN code signal is shown by d in FIG. 3, for example.

The spread modulator 4 spread-modulates the transmission data in accordance with the PN code signal d. That is, the PN code "
Corresponding to 0 "and" 1 ", the carrier signal a has" +1 ","
The carrier signal of the "1" part is inverted by -1 "(multiplied by -1) to form a spread signal as shown in Fig. 3c. E
As shown in, the power is amplified and the amplitude becomes large. The spread signal e amplified by the amplifier 5 is filtered by the filter 6.
As shown in FIG. 4, the frequency band B portion other than the transmission band A including the center frequency to be transmitted is cut and transmitted from the antenna.

FIG. 5 is a block diagram of the receiving side of the spread spectrum communication system according to the embodiment of the present invention. Further, g to q in FIGS. 6 to 10 show signal waveforms on each line in the block diagram in FIG.

The spread signal received via the antenna is amplified by the high frequency amplifier 7 to obtain a spread signal g as shown in FIG. This spread signal g is input to the frequency mixer 8. A spread modulator 13 connected to the local oscillator PLL circuit 12 is connected to the frequency mixer 8. A PN code generator 14 is connected to the spread modulator 13.
As will be described later, the PN code generator 14 creates a PN code j (FIG. 7) that approximates the PN code on the transmission side by using a clock having a frequency different from the reference clock on the transmission side. Note that the PN code waveform in FIG. 7 is drawn in part for the sake of explanation, and the one-cycle waveform is formed so as to almost match the one-cycle waveform of the transmission-side PN code d in FIG. To be done. That is, the receiving side PN code generator 14
Uses a circuit composed of flip-flops having the same configuration as the transmitting side to create a PN code by changing only the clock frequency.

The local oscillator PLL circuit 12 has a fixed frequency difference according to the frequency of the signal data to be demodulated.
Generate signal h (FIG. 7). The PLL signal h is spread-modulated by the spreading modulator 13 by multiplying by +1, -1 in accordance with "0" and "1" of the PN code signal j in the same manner as the receiving side described above. The spread signal is as shown by i in 7. The spread state of this spread signal i is the PN that formed it.
Since the code j is almost the same as the PN code d on the transmission side, the shape of one period is almost the same as the shape of the spread signal c or e (FIG. 3) on the transmission side. Therefore, if the spread signal i on the receiving side is synchronized with the spread signal on the transmitting side (that is, the spread signal g received), the PN code on the receiving side and the transmitting side can be synchronized and the transmission data can be demodulated.

In the frequency mixer 8, the received spread signal g and the spread signal i from the local oscillator PLL are superposed by multiplication by the multiplication circuit so that the synchronization state can be detected. This superposed signal is further passed through a filter 9 to cut frequencies other than necessary to prevent interference. The signal thus obtained becomes a signal whose amplitude increases in a certain fixed period, as indicated by m in FIG. This is because the clock frequencies of the PN code on the transmitting side and the PN code on the receiving side are different, so that the phases of the two PN codes gradually shift with time, and the signal level increases when the phases match. It is repeated at regular time intervals. Such a mixed signal m is formed as a correlation waveform signal n by the intermediate frequency amplifier 10. The correlation waveform signal n has a triangular shape in which the phases of the two PN codes substantially coincide with each other and rises when the correlation begins to take place, increases as the correlation increases, reaches a peak at the time of complete coincidence, and then slopes and falls. It becomes a pulse signal.
This triangular correlation pulse signal n is shaped into a digital pulse signal of "1" and "0" by a level detector 15 composed of a comparator, as shown by o in FIG. To be done.

On the other hand, the receiving side PN code generator 14
Includes a clock generator 17 for generating a clock having a constant frequency different from the clock on the transmission side.
Connected via The clock pulse signal k (FIG. 8) oscillated from the clock generator 17 is the clock operation unit 1
6, a predetermined number of pulses are removed, and the clock signal in which a part of the pulses has been removed is P as shown in l of FIG.
It is input to the N code generator 14. As a result, the correlated state is maintained, as will be described later.

The received spread signal in the state where the phases of the PN codes on the transmitting side and the receiving side are correlated with each other has the same waveform F as that of the carrier signal b on the transmitting side (FIG. 2), as shown by p in FIG.
It is M-modulated and taken out. The FM-modulated received data signal p is converted into digital signals of "1" and "0" as indicated by q in FIG. 10 according to its frequency, and the transmission data a (FIG. 2) is demodulated. It

The method of synchronizing the PN codes on the transmitting side and the receiving side will be further described below with reference to FIGS. 11 and 12. FIG. 11A is a graph of a signal waveform showing the correlation strength based on the correlation function when there are two identical PN codes, and similar to n in FIG. It is a signal waveform which shows correlation between codes. Correlation starts to take place at time t1, almost completely matches at t2, gradually shifts in phase again, and loses correlation at time t3. After a further time, the correlation starts again at time t4,
The peak occurs at t5, and the correlation disappears at t6.

The correlation function y is represented by y = PN (t) × PN (t + τ) t: time τ: phase difference. When τ = 0, y = PN (t) × PN
When (t) = 1, synchronization is achieved (t2 and t5 of signal waveform A),
When τ = ± 1 (clock), the correlation is 0 (t of signal waveform A
1, t3, t4, t6). Since PN is a periodic correlation function, assuming that one period is N clocks, correlation is obtained every N and a synchronous state is established.

In this example, the basic clock frequency of the PN code on the transmitting side is ft, and the basic clock frequency of the receiving side is f.
When r is set, fr> ft, and Δf = fr−ft
= 1 KHz, and one cycle of the PN code is 31 clocks. In this case, both PN codes are out of phase for one clock every 31 clocks, and when converted into time, one clock corresponds to 1 ms, and synchronization is achieved every 31 ms. At this time, since fr ≠ ft, the phases do not exactly match, but since Δf / fr (or ft) ≈0, it can be regarded as almost perfect synchronization.

In the correlation state shown in FIG. 11A, reception cannot be performed in the non-correlated portion from t3 to t4, so it is necessary to continue the synchronization state. To this end, B of FIG.
As shown by C and D, the phases are sequentially shifted by one clock each time, and by adding them, it is possible to synchronize almost continuously and to demodulate the received signal continuously. Become. In order to shift the phase in this way, for example, in A of FIG. 11, the PN code on the receiving side is forcibly delayed by n clocks at the time (t3) when the correlation ends. If n = 1, as shown in FIG. 12 (A), the phase is shifted by one clock at the end of one triangular pulse, and synchronization is achieved in a substantially continuous state. If n = 2, as shown in FIG. 12 (B), the phase is shifted by 2 clocks at the end of one triangle pulse, and synchronization is achieved in a continuous triangle pulse state. If n = 3, FIG.
As shown in (C), a continuous waveform shifted by 3 clocks is obtained.

The clock operation for such phase synchronization will be described more specifically with reference to FIG. In the level detector 15 (FIG. 5) described above, the triangular correlation signal is converted into the digital signal o (FIG. 9).
At the falling edge of this digital pulse, the required number of clocks are removed. That is, in the circuit composed of the three flip-flops (FF) 18, 19, 20 in FIG.
The input signal (r) is input to one input terminal of the first FF 18.
, The digital pulse signal o (FIG. 9) from the level detector 15 (FIG. 5) is input, and the other input side terminal receives the basic signal from the clock generator 17 (FIG. 5) as an input signal (v). Input the clock k (FIG. 8). Each FF18, 1
The output signals of 9 and 20 are represented by (s) (t) (u). Output (t) of this FF19 and output (u) of FF20
Is input to the terminal of the clock deletion circuit 21 together with the basic clock (v) as shown. This allows
The basic clock pulse in the portion corresponding to the end positions of (t) and (u) is deleted, and a pulse drop signal as shown in (w) is obtained.

FIG. 14 shows an example of the clock addition circuit.
That is, in the above-mentioned embodiment, the basic clock is removed at the time of the fall of the correlation pulse to delay the phase for synchronization, but the present invention is not limited to this method, and the fall of the correlation pulse It is also possible to advance the phase and synchronize by adding a necessary number of clocks to the basic clock at this point. In order to create such an additional clock, a delay is added to the basic clock (v), and by inputting the above-mentioned (t) (u) together with this basic clock signal, the clock signal added with the pulse is added to the clock adding circuit. It is output from the terminal (x) 22.

[0027]

As described above, in the present invention, the basic clock frequency of the PN code on the receiving side is made different from the basic clock frequency of the PN code on the transmitting side, and each P
The spread signals modulated using the N code are superposed, the level is detected, and the clock is deleted or added in a correlated state so that the phase of the PN code on the receiving side is shifted to continue the synchronization. Therefore, a simple receiver circuit is configured without using a special element such as a SAW convolver that is expensive and has a large use constraint as in the past, and a digital signal is generated by using a clock generator composed of a fixed frequency oscillator. By using the circuit, an inexpensive spread spectrum communication system with a simple structure can be obtained.

[Brief description of drawings]

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

2 is a wiring line a in the block diagram of FIG.
It is a signal waveform diagram on b.

FIG. 3 shows the wiring line c in the block diagram of FIG.
It is a signal waveform diagram on d and e.

FIG. 4 is an explanatory diagram of signal waveforms on a wiring line f in the block diagram of FIG.

FIG. 5 is a block diagram showing a configuration of a receiving side of the spread spectrum communication system according to the exemplary embodiment of the present invention.

6 is a signal waveform diagram on the wiring line g in the block diagram of FIG.

FIG. 7 is a wiring line h in the block diagram of FIG.
It is a signal waveform diagram on i, j.

FIG. 8 is a wiring line k, in the block diagram of FIG.
It is a signal waveform diagram on l.

9 is a wiring line m, in the block diagram of FIG.
It is a signal waveform diagram on n and o.

10 is a signal waveform diagram on the wiring lines p and q in the block diagram of FIG.

FIG. 11 is an explanatory diagram of a PN code synchronization continuation method according to the present invention.

FIG. 12 is an explanatory diagram of a synchronization state when the number of clock delays is changed.

FIG. 13 is an explanatory diagram of a clock removal method.

FIG. 14 is a circuit diagram of a clock addition method.

[Explanation of symbols]

1: Modulation data generator, 2: PLL synthesizer, 3:
PN code generator, 4: spread modulator, 5: amplifier, 6:
Filter, 7: high frequency amplifier, 8: frequency mixer, 9:
Filter, 10: Intermediate frequency amplifier, 11: Data demodulator, 12: PLL for local oscillation, 13: Spread modulator, 14: P
N code generator, 15: level detector, 16: clock operating unit, 17: clock generator.

Claims (4)

[Claims] 1. In a spread spectrum communication data transmission system for performing data transmission by a spread spectrum system by direct spread, a basic clock frequency of a PN code on a receiving side is different from a basic clock frequency of a PN code on a transmitting side,
PN of the receiving side so that the correlation of both PN codes can be obtained
A spread spectrum communication method characterized by synchronizing the PN code on the transmitting side by shifting the phase of the code in correspondence with a predetermined number of clocks, and demodulating the data in this synchronized state. 2. A PN on the transmitting side by delaying the phase by removing the pulse of the basic clock of the PN code on the receiving side.
The spread spectrum communication method according to claim 1, wherein the synchronization state with the code is continued. 3. The spread spectrum communication according to claim 1, wherein the phase is advanced by adding a pulse of the basic clock of the PN code on the receiving side to maintain the synchronization state with the PN code on the transmitting side. Method. 4. A modulator for frequency-modulating data to be transmitted, a clock oscillator for generating a constant basic clock pulse, and a PN based on the basic clock from the clock oscillator on the transmitter side.
A PN code generator for generating a code, and a spread modulator for spread-modulating the frequency-modulated data by the PN code are provided, and a receiver having a basic frequency different from that of the clock oscillator on the transmitter side. A clock oscillator for generating a clock pulse, a clock operating unit for removing a part of a basic clock pulse of the clock oscillator of the transmitting device or adding a pulse, and a PN based on a clock signal from the clock operating unit.
A PN code generator that creates a code, a mixer that mixes the spread signal created using the PN code generator on the receiving side with the spread signal sent from the transmitting side, and the level of the output signal from this mixer And a level detector for inputting the detection signal to the clock operation unit, and a spread spectrum communication device.