JPH04199926A - Spread spectrum communication equipment - Google Patents

Abstract

PURPOSE:To suppress interference with another transmitter and influence owing to an interference signal by setting a level slightly lower than the maximum value of a correlation signal obtained in one cycle of a distribution code as a reference signal level. CONSTITUTION:Correlation detection means 1 and 2 correlate a first distribution code and a second distribution code, which are included in a wide band signal received by a receiver, and generate the correlation signal corresponding to a correlation degree. A comparison means 3 compares the signal level of the correlation signal with the signal level of a reference signal. A phase alteration means 4 refers to a compared result, alters the phase of the second diffusion code by a prescribed amount until the signal level of the correlation signal becomes more than the reference level. A reference signal setting means 5 sets the level slightly lower than the maximum level of the correlation signal obtained within one first period of the distribution code as the signal level of the reference signal. Thus, the alteration of the phase is continued even if a signal whose correlation level is low and which has the different distribution code is inputted. Thus, interference with another transmitter and influence owing to the interference signal are reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spread spectrum communication device, and particularly to a spread spectrum communication device that has a simple configuration and is resistant to interference and noise.

[Prior Art] Spread spectrum (SS) communication is increasingly being used as a method that has noise resistance and is suitable for long-distance communication.

In such SS communication, a data signal is modulated by a pseudo-noise spreading code such as an M-sequence code and transmitted as a wideband signal with a wide frequency band. A data signal is obtained by demodulating a wideband signal.

Among these, for example, Japanese Patent Laid-Open No. 2-72731 proposes a spread spectrum communication device that achieves initial synchronization and synchronization maintenance of spreading codes with a simple configuration and can be easily applied to portable communication devices. .

To briefly explain its configuration with reference to FIG. 4, the transmitter T modulates the FM modulated wave of the data signal with the M-sequence code as a spreading code output from the M-sequence code generation circuit 901 and transmits it as a wideband signal. . The code speed of the M-sequence code is determined by the clock pulse output from the clock generation circuit 902.

The receiver R receives and amplifies the broadband signal, mixes it with a local oscillation signal in a mixer 903, converts it into an intermediate frequency signal, and then performs FM demodulation to obtain a data signal. Here, the FM demodulated signal is input to a noise amplifier rectifier circuit 904, noise components are extracted, and the signal is rectified to become a noise level signal.

The noise level signal is input to the level determination circuit fi'J 905, and when the noise level is above a predetermined value, the phase change circuit 9
06 operates to change the phase of the clock pulse output from the clock generation circuit 907 by 1/4 bit.

M output from the M sequence code generation circuit 908 of the receiver R
The sequence code is the same as the code on the transmitting side, and the code output timing and speed are determined by the clock pulse that has passed through the phase change circuit 906. This M-sequence code is mixed into the wideband signal together with the local oscillation signal. Note that the clock pulses on the receiving side are slightly different in speed from the clock pulses on the transmitting side.

The noise level peaks and decreases near the point where the phases of the M-sequence codes on the transmitting side and the receiving side match, and become below the predetermined value. Therefore, if the phase of the M-sequence code on the receiving side is changed by a certain amount and the noise level becomes below a predetermined value,
The phases of both M-sequence codes are almost the same and are synchronized.

Since the code speeds of both M-sequence codes are slightly different, when the phase change is stopped, the noise level gradually increases and exceeds the above-mentioned predetermined value. When it crosses the line, it starts changing the phase again,
The phase change is repeated until the noise level becomes equal to or less than a predetermined value.

In this way, by repeatedly changing the phase of the M-sequence spreading code on the receiving side so that the noise level is below a predetermined value, the synchronization state of both spreading codes is maintained, and the data signal can be received satisfactorily.

[Problems to be Solved by the Invention] The spread spectrum communication device proposed above has an excellent feature of having a simple configuration, synchronizing signals, and enabling reliable communication, but there are still points to be improved. I'm leaving it behind. In other words, in order to ensure a wide communication range, it is necessary to be able to reliably determine the synchronization state even with a relatively weak received signal, and for this reason, the determination level of the level determination circuit must be set high. There is also a problem in that when a signal emitted from a transmitter or the like that uses an M-sequence code relatively similar to the above is received, the noise level decreases and interference occurs.

The present invention solves this problem, and aims to provide a spread spectrum communication device that is resistant to interference and interference signals.

[Means for Solving the Problems] The present invention will be described in detail: a transmitter that modulates a data signal with a periodically repeated first spreading code and transmits it as a wideband signal; , the above first
In a spread spectrum communication device, a receiver obtains the data signal by demodulating it with a second spreading code that is the same as the above spreading code but has a slightly different code speed and is repeated at the above period. Correlation detecting means 1.2 correlates the first spreading code and the second spreading code included in the wideband signal and generates a correlation signal according to the degree of correlation, and converts the signal level of the correlation signal into a reference signal. means 3 for comparing the phase with the signal level of the second spreading code; and phase changing means 4 for changing the phase of the second spreading code by a fixed amount, referring to the comparison result, until the signal level of the correlation signal becomes equal to or higher than the reference level. A reference signal setting means 5 is provided for setting the signal level of the reference signal to a level slightly lower than the highest level of the correlation signal obtained within the first period of the spreading code.

[Operation] In the spread spectrum communication device having the above configuration, the phase-open signal reaches the highest level of autocorrelation when the transmitting and receiving spreading codes completely match within one period of the spreading code,
The correlated signal level due to cross-correlation with signals with different spreading codes will be lower. Therefore, since the reference signal level is set to a level slightly lower than the above maximum level,
Only when the correlation signal reaches the highest level, the phase change of the second spreading code is stopped and a synchronized state is achieved.Even if a signal with a different spreading code with a low correlation level is input, the phase change continues and the synchronized state is achieved. It won't happen.

[Embodiment] FIG. 1 shows an embodiment of the present invention, and the figure shows the main circuit of a receiver. The configurations of the other parts of the transmitter and receiver are the same as those of the conventional communication device described above.

A correlator 1 is provided on the line leading from the high frequency amplifier circuit to the intermediate frequency amplifier circuit (both shown in Figure 4), and a part of the output correlation signal is passed through an active bandpass filter centered on the op amplifier 21. The signal is inputted to an envelope detection circuit 2 having a correlation signal, and outputted to a comparison circuit 3 at the next stage as a DC detection signal having a magnitude corresponding to the amplitude of the correlation signal.

The detected signal is output from the comparator 31 of the comparator circuit 3.
A reference signal is input to the "+" terminal of the comparator 31, and a reference signal is input to the "-" terminal of the comparator 31 from a reference level setting circuit, which will be described later.

The reference level setting circuit 5 includes a computer 51.4 circuit switch group 52.4, the operation of which will be described later.A reference signal generation circuit 53 outputs reference signals of four different levels. The signal level of the reference signal is higher toward level 4 than level 1, and the switch group 52 is selectively activated by the output signal of the computer 51, so that one of the reference signals of levels 1 to 4 is output to the comparator. It is input to the "-" terminal of 31.

Reference numeral 4 denotes a phase change circuit, which includes a clock generation circuit 41 having a crystal oscillator, a binary counter 42, a flip processor 143, a multiplexer 44, and the like. The clock pulse output from the clock generation circuit 41 is
'C of binary counter 42 and flip-flop tube 43
It is input to the “L” terminal, is frequency-divided, and is input to the “L” terminal of the multiplexer 44.
It is input to each input terminal of "0", "1", "2", and "3". The pulses input to these input terminals "0" to "3" are out of phase with each other by 1./4 period (pit).The frequency of the above clock pulse is several tens of Hz higher than that of the transmitting side. .

A command signal from the computer 51 is input to the A terminal and B terminal of the multiplexer 44, and input pulses from each of the terminals "0" to "3" are selected according to the binary code of the command signal and output to the "Y" terminal. be done.

Reference numeral 6 denotes an M-sequence code generation circuit consisting of a shift register 61 and an exclusive OR gate 62. A pulse from the "Y" terminal of the multiplexer 62 is input to the rCLJ terminal of the shift register 61, and the code speed is determined. has been done.

The M-sequence code output from the code generation circuit 6 is mixed with the output signal of the local oscillation circuit 7 by a mixer 8, and the mixing output is input to the correlator 1.

The operation of the communication device having such a configuration will be explained with reference to FIG. 2, focusing on the processing of the computer.

In the main routine '100 of the figure, step.

In step 101, the registers, timers, memory, etc. of the computer 51 are initialized. In this initial setting, one of the switch groups 52 is selectively activated, and the comparator 31
A reference signal of level 1 is inputted to the terminal.

In step 102, the multiplexer 44
' Commands to output a clock pulse delayed by 4 bits. As a result, the phase of the M-sequence code is delayed (slided) by 1/4 bit. In step 103, it is determined whether the output of the comparator circuit 3 has reached the "1" level. If it is "0", the process returns to step 102, and if it is "1", the process returns to step 1.
Proceed to 04.

In step 104, the switch group 52 is selectively activated to input the level 2 reference signal to the comparator 31, and in step 105, the M-sequence code is slid in the same manner as in step 102 above. In step 106, if the output of the comparison circuit 3 is "0", the process advances to step 107, where it is determined whether the M-sequence code has been slid by one period (31 bits), and if it has not been slid, the process returns to step 105.

- If there is a periodic slide, the process proceeds to step 108, where the switch group 52 is activated to return the reference signal to level 1 and fix it. Then, the process moves to step 120, a synchronization holding operation.

If the output of the comparator circuit 3 reaches the "1" level in step 106, the process proceeds to step 109.

Steps 109 to 113 are steps 104 to 10 described above.
The same operation as in 8 is performed. However, level 3 is set in step 109, level 2 is fixed in step 113, and when the output of the comparator circuit reaches the "1" level in step 111, the process proceeds to step 114.

Similar operations are performed in steps 114-118. If the output of the comparator circuit 3 reaches the "1" level in step 116, the process proceeds to step 119. In step 11, the reference signal is fixed at level 4, and the process proceeds to step 120, where a synchronization holding operation is started.

An example of such operation will be explained with reference to FIG. In FIG. 1, when the envelope detection signal serving as the correlation signal exceeds the level 1 reference signal a, it switches to the level 2 reference signal a, and when it further exceeds this, it switches to the level 2 reference signal a.

In the figure, the maximum level of the signal due to autocorrelation exceeds level 3, but does not exceed level 4. Thus, at the end of the 31-bit code period, a level 3 reference signal is set, and synchronization is thereafter maintained using this reference signal.

In a synchronized state, the code speeds on the transmitting and receiving sides are slightly different, so the synchronization gradually deviates and the level of the correlation signal gradually decreases, but when it drops below level 3, the code starts sliding again and synchronizes immediately. is recovered.

Note that if the level of the correlation signal S exceeds the level 4 reference signal a (Fig. 3 (2)), it is assumed that no higher level will appear within one cycle of the code, and the level 4 is fixed and immediately Move to sync state.

If there is another transmitter near the transmitter that outputs an approximate M-sequence code, the correlation signal due to cross-correlation may exceed the level 2 reference signal a, as shown in (3) in the figure. be. However, within one cycle of the code, a correlation signal due to autocorrelation exceeding level 3 appears, and level 3 is eventually fixed after transition to the synchronization state. therefore,
Synchronization is not effected by transmission signals of other transmitters that do not reach level 3, thus effectively preventing interference.

In the above embodiment, a five-stage M-sequence code is used as the spreading code, but there is no limit to the number of stages, and it is of course possible to use other codes other than the M-sequence.

It is not necessary to change the phase of the spreading code every 1/4 bit, and the level of the reference signal is not limited to four levels.

In addition, instead of setting multiple fixed level reference signals, a slide for one period of the spreading code is performed before transitioning to the synchronization hold state, and the value obtained by subtracting a constant value from the maximum value of the correlation signal during that time. It is also possible to set the level of the reference signal as the level of the reference signal.

[Effects of the Invention] As described above, in the spread spectrum communication device of the present invention, a level slightly lower than the maximum value of the correlation signal obtained during one period of the spreading code is set as the reference signal level. It is possible to minimize the effects of interference with other transmitters and interference signals.

[Brief explanation of the drawing]

1 to 3 show an embodiment of the present invention, FIG. 1 is a circuit diagram of the main part of the communication device, FIG. 2 is a flowchart showing the operation of the computer, and FIG. 3 explains the operation of the communication device. FIG. 4 is a block diagram of the overall configuration of a conventional communication device. 1... Correlator 2... Envelope detection circuit 3... Comparison circuit 4... Phase change circuit 5... Reference signal setting circuit

Claims (1)

[Claims] a transmitter that modulates a data signal with a first spreading code that is periodically repeated and transmits the signal as a wideband signal; A spread spectrum communication device comprising a receiver that demodulates the data signal by demodulating the data signal using a second spreading code that is repeated periodically, the first spreading code included in the wideband signal received by the receiver and the first spreading code included in the wideband signal received by the receiver. correlation detecting means for calculating the correlation with the spreading code of No. 2 and emitting a correlation signal according to the degree of correlation; means for comparing the signal level of the correlation signal with the signal level of the reference signal; a phase changing means for changing the phase of the second spreading code by a fixed amount until the signal level of the correlation signal becomes equal to or higher than a reference level; and a reference level setting means for setting a somewhat low level as the reference level.