JP2787793B2 - Spread spectrum communication system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a spread spectrum communications
Equipped with a transmitter for transmission and a receiver for spread spectrum communication.
The present invention relates to a spread spectrum communication system .

[0002]

2. Description of the Related Art Conventionally, as a countermeasure against a data error during data transmission, data that could not be received is retransmitted,
When retransmission is difficult, a method of adding data for error detection of data or error correction data to the original data to have redundancy is used to improve data reliability.

[0003]

However, since retransmission requires a single transmission time, it is not suitable for a system requiring a high-speed response, and a function for requesting retransmission is incorporated in the system. And the system becomes complicated. In addition, even if error detection and error correction are performed, little effect can be expected for burst noise over a long period of time. Had issues.

[0004] The present invention has been made in view of such a situation, and not only has excellent noise resistance properties inherent to spread spectrum communication, but also takes advantage of multiplexing by code division. even without retransmission is so also to perform the same transmission as the retransmission.

[0005]

SUMMARY OF THE INVENTION In order to solve such a problem, the present invention provides a transmitter for spread spectrum communication.
Spectrum provided with a receiver for spread spectrum communication
In a spread communication system, transmission for spread spectrum communication is performed.
Transmit the data to the transmitter using the first pseudo-random code
A first spread-spectrum circuit for spread-spectrum, and a first pseudo-spread circuit.
Small second pseudo-random correlation for the random code
A second spectrum for spreading the data with a code
Supply to tram spreader and first spread spectrum circuit
The second spectrum with respect to the data supply timing
Slightly delays the data supply timing to the ram diffusion circuit.
Data delay circuit and first and second spectra
Combining to combine signals spread spectrum by spread circuit
Circuit and the signal synthesized by the synthesis circuit.
Transmission antenna for receiving signals for spread spectrum communication.
Signal from the transmitter for spread spectrum communication.
The receiving antenna to receive and the same as used on the transmitter side
A first pseudo code for generating first and second pseudo random codes
Pseudo random code generation circuit and second pseudo random code
A generating circuit and the first and second pseudo-random code generators;
Based on the pseudo-random code generated in the raw circuit,
First spread spectrum demodulating received signal at tenor
A demodulation circuit and a second spread spectrum demodulation circuit;
Output signals of the first and second spread spectrum demodulation circuits of FIG.
Data that was delayed by the sender and data that was not
A data reproduction circuit for reproducing the data signal based on the data
It is provided .

[0006]

According to the invention, data is stored in the first pseudo-lander.
Spread-spectrum modulation by
Slightly later than the first pseudo-random code
The second pseudo-random code with a small correlation to the
Spread-spectrum modulation, and this spread-spectrum modulation
The adjusted signals are combined and transmitted. And this
The transmitted signal is based on the first pseudo-Tendum code
And demodulated based on the second pseudo-random code.
The demodulated signal was delayed at the transmitter
Data is played back based on data and undelayed data.
It is.

[0007]

1 shows a spread spectrum communication according to the present invention.
FIG. 1 is a block diagram showing an embodiment of a transmitter for use in the present invention.
Measurement of temperature, humidity, wind speed, air pressure, etc. detected by a moving object
Fixed data is transmitted via the transmitter shown in FIG.
ing. The memory 1 stores these data in a sensor (not shown).
Sensor signal and measured by Sa, the transmitter-specific
Identification data is stored and read from there.
The data is delayed via the data delay circuit 2. data
The significance of the delay circuit will be described later.

When noise over the entire frequency band occurs
Or a bar over one or more periods of the pseudo-random code
When the noise occurs, the time delay of the transmission data
The communication with noise resistance can be performed by transmitting
And the data delay circuit 2 performs a delay for this
I have.

The data delay circuit 2 is, for example, as shown in FIG.
A plurality of D latches 2a to 2c are connected in cascade
When the signal shown in FIG. 3A is supplied,
(B), which in this example is a 2-bit delay
Let me. Both signals appear to be synchronized
Are separately synchronized on the receiving side, so that FIGS. 3 (a) and 3 (b)
No signal synchronization is required.

The output signal of the data delay circuit 2 is a spectrum signal.
To a modulation circuit (hereinafter referred to as an SS modulation circuit) 3.
The pseudo random code supplied from the pseudo random code generation circuit 4.
The spectrum is spread by the random code. And
With the carrier generated by the reference carrier generation circuit 5
Baseband modulated by the baseband modulation circuit 6
You.

On the other hand, the signal read from the memory 1 is
It is also supplied to the spectrum modulation circuit 7, where
The pseudo-random code generated by the random code generation circuit 8
Therefore, spread spectrum modulation is performed. And the reference carrier
Baseband modulation by carrier generated by generation circuit 5
The baseband modulation is performed by the circuit 9 and the baseband modulation is performed.
The signals subjected to baseband modulation by the adjustment circuits 6 and 9 are mixed.
Mixed by the mixer circuit 10 and transmitted from the antenna 11
Is done.

However, it is generated by the pseudo random code generation circuit 8.
The generated pseudo random code is generated by a pseudo random code generation circuit 4.
Correlation is low enough with the pseudo-random code generated in
Is set . In other words, there is a problem in code division.
The correlations used in the same transmitter
Select a code sequence with low correlation in advance
It is good to use it.

The pseudo-random code used here is simple
Is the M-sequence code obtained by feeding back the output of the shift register.
Signal or cross-correlation if there are multiple transmitters
Gold code etc. are used because of the low
There is no restriction on the type of the system code. Number of pseudo random code occurrences
As shown in FIG. 4, an example of the road 4 includes D latches 4a to 4e and
And an EOR circuit 4f. Pseudo-random code
The generation circuit 8 requires code sequences of different patterns
But at that time, it is realized by changing the position of the return
It can also be implemented by changing the number of shift register stages.
Can appear. What is important here is the pseudo
Both pseudo codes are used so that the random code can be distinguished at the time of reception.
Use a sufficiently low correlation of random codes
That is.

The spread spectrum modulation circuits 3 and 7 are two-phase
In the case of phase modulation, it can be configured with one EOR circuit. data
Fig. 5 shows the state where is modulated by a pseudo-random code.
You. However, FIG.
The interval and the pseudo-random code have the same period of one cycle.
But the real thing does not have to look like this
Absent. FIG. 5 shows a simple example, and FIG.
Modulated by a pseudo-random code generated by
No, not guaranteed randomness, just an example
It is shown. The transmitter configuration is Spectra
Baseband modulation before system modulation results in the same
FIG. 6 shows an example at that time.

FIG . 7 shows the structure of a receiver for spread spectrum communication.
FIG. 3 is a block diagram showing the configuration of
The resulting signal is generated by the pseudo random code generation circuits 22 and 23.
Demodulation circuit 2
Demodulated at 4 and 25.

Here, the pseudo random code generation circuit 22
The same pseudo-lander as the pseudo -random code generation circuit 4 on the transmission side
A pseudo random code generation circuit 23 generates
Pseudo-random code which is the same as the pseudo-random code generation circuit 8 on the side
Issue. And SS demodulation circuit 2
The demodulated outputs of the baseband demodulation circuits 4 and 25 are used as baseband demodulation circuits 26 and 27
Is demodulated into a baseband signal at
Played back to data.

In performing spread spectrum communication, a pseudo run is performed.
The reason for using dumb codes arises from their randomness
There is also spread spectrum, but sharp autocorrelation peaks
To show. The sharpness of this autocorrelation makes
During tuning, the sign of the peak can be used to determine the polarity of data 1 or 0.
Wear. The cross-correlation of the pseudo-random code used here is low
And the autocorrelation uses a large code,
In each SS demodulation circuit, the output shown in Fig. 8 is obtained.
You. (A) is restored by the pseudo random code generation circuit 23.
(B) is a pseudo-random code generation number.
This is a waveform demodulated by the path 22.

When this is compared with FIG. 3, the data is 1
A positive peak is output at the time, and a negative peak is output at 0
Have been. Further, in (a) and (b), the
A peak occurs with a time delay. Also, pseudo run
The correlation between dumb codes is low.
Then, the peak of (a) and the peak of (b) at the same time
Are irrelevant to each other, and
Even so, it happened to coincide.

Such a demodulator is well known in the art.
Type, especially digital matched filters
It can be easily realized with filters. The hatched part in FIG.
Strong burst noise. For this, (a)
However, even in (b), the peak of the correlation was erased.
You. However, due to the effect of the present invention, it is possible to receive
The reproduction of the data of the part that was not
This is made possible by referring to the

According to the present invention, data is actually retransmitted.
A short period of time in the retransmission the same degree of reliability of the data to Rimoharuka is
can get. Of course, the error detection and correction of the existing technology
It is possible to further improve reliability by combining
You. Also, depending on the nature of the noise, the first pseudo random
Significantly echoes the code, but the second pseudo-random code
It is conceivable that deterioration does not occur so much. Such a place
If the second pseudo random code is
Data can be reproduced based on demodulated data at
Become. In such cases, the transmission data itself is delayed
Can be sufficiently demodulated even when the symbol is not included.

Next, the data delay circuit 2 will be described in detail.
Spread spectrum communication uses a wide range of frequency bands
Noise immunity to noise that strongly affects specific frequencies.
Is very powerful.

In the spread spectrum communication, a frequency band to be transmitted is used.
Area with a pseudo-random code faster than the data rate
Spreads the transmitted data over a wide range of frequency components
In this way, noise resistance can be obtained. this is
Even if strong noise is added to a specific frequency, other spectrum
The information dispersed in the RAM is demodulated by
This is because a collecting process can be performed. This process
Usually called spectrum demodulation, specifically
Pseudo-random signal modulated by communication equipment by filter etc.
The autocorrelation is calculated by the number. That is, in FIG.
This is a process for creating an output waveform as shown.

In conventional narrow band communication,
If noise near the frequency of
Will be violated. Similarly, over a wide frequency range at the same time
Has almost the same frequency components as the pseudo-random code
Such noise is also received by spread spectrum communication
Becomes difficult. However, such noise happens by accident
The probability of doing so is very low.

It is assumed that the frequency is almost the same as that of the pseudo random code.
Even if disturbed by noise with several components,
Other pseudorandoms that have little correlation with pseudorandom codes
Use a code to modulate the data and send that signal as well.
Noise that affects one pseudorandom code
Is generated in the communication channel, the noise is
Probability of having a frequency band that matches the
Become.

For this reason, spread spectrum communication is not
One pseudo-random code for noise immunity
Even if communication by the
The reproduction of data by the system code becomes possible. This method is
Data transmission time
Become.

However, for example, due to fading, etc.
If the transmission path attenuation temporarily increases due to
Noise disturbance may occur for pseudo-random noise
There is a potential. In such a case, supply either modulation circuit.
If there is a delay in the data supplied, either
Are more likely to be rescued.

The amount of the delay is determined by
Although it is necessary to determine according to the line condition,
I'm doing it. The important thing here is to send one piece of data.
Don't send again after you've finished, ie resend
Instead of doing it, double the time axis (with little time
To send data).

Generally, when performing spread spectrum communication,
In addition, a pseudo random code is included in one bit of information data for one round.
Information data rate, pseudo random code
Decide the signal speed. In other words, the information data rate clock and
A clock different from the clock that generates the pseudo-random code
use. The clock of the pseudo-random code is
Faster than the data clock.

The pseudo-random code shown in FIG.
When configured in shift ^{register), (2} 5 -1) chip length
Are generated. Bits of information to send
1 bit of pseudo-random code to distinguish it from
Is defined as one chip. This pseudo-random code chip
The speed depends on the sign clock added in FIG.

Here, the pseudo random code is 31 chips long.
(= 2 ⁵ -1) The chip speed is 1 M chips / S. Sending
If the data rate to be transmitted is 10 Kbit / S, data 1
One cycle of pseudo random code in bit (100μS)
Since it is 31 μS, there are three periods.

At the time of transmission at the receiver of spread spectrum communication
The correlation is calculated using the same pseudo-random code used for
You. By using the orthogonality of the pseudo random code, one round
A sharp autocorrelation peak can be obtained for each period. this
The chip speed is 1M chip / S and the chip length is 31 chips.
Data at 10Kbit / S
1 bit of transmission data if 3 peaks can be detected for each bit
Can be demodulated. Also, two peaks due to majority vote
The data can be reproduced at the time of detection.

FIG . 8 shows one video per one cycle for simplicity.
To make sure they correspond. A peak appears on the positive side
If it shifts, data "1" will be "0" if it is a negative peak.
Will show the data. This peak is a pseudo-random mark
If the signal is 31 chips, it shows the value 31 at the peak and the correlation
In the state where it cannot be removed, it shows almost zero.

This is because the peak is 25 due to the noise environment.
Or 15 but other correlations are not
Set a threshold that is large enough to distinguish it from
The correlation value indicates a positive peak or a negative peak.
Or a peak is not determined.

The reason for modulating the delayed data is as follows.
Spread-spectrum modulation by another pseudo-random code.
Make a key. To create another pseudo-random code is a shift register
The number of stages can be changed, but feedback is provided by the EOR circuit.
It is also possible by changing the position where it is performed. Shift register
Changing the number of stages changes the period of the pseudo-random signal.
The peak generated during feedback of one bit of transmission data
The number changes between pseudo-random codes. this thing
Has essentially no effect on the invention. In FIG. 8 , another
How to change the position of feedback when making pseudo-random code
8 (a) and 8 (b) correspond to one data.
It has one peak.

The entire system is delayed by the transmitter.
I know the time in advance. For example, as shown in FIG.
The transmitter / receiver system that transmits data with a delay of 2 bits
When the system is constructed, the correlation value output on the receiving side is as shown in FIG.
Is obtained. Here, the symbol T is the time per bit.
Τ is the time required for radio wave propagation,
And the correlation output is derived from the pseudo-random code.
Of the delay time that occurs on the receiver side required for
Is shown.

FIGS. 3 and 8 show one bit of transmission data.
FIG.
Therefore, after the data of FIG. 3 is transmitted by one bit,
After T + τ, a correlation peak can be detected. This transmission and reception system
In the system, a delay of 2 bits in data, that is, 2T
Modulates the same data with another pseudo-random code after a delay of
doing.

In FIG . 8A, the peak observed at time T + τ
Is the data transmitted during the time 0 to T in FIG.
Tram spread modulation. Since there is a delay of 2T,
In FIG. 8B output to T + τ in FIG. 8A, 3T + τ
Observable in time.

A wide range of frequencies can be obtained by spread spectrum modulation.
Transmits in the waveband, so bursts at specific frequencies
Data error due to signal is unlikely, but still something
Or the correlation value itself
May be calculated small. This place
The correlation value cannot be obtained at the expected timing.
And data cannot be reproduced. 8T + τ in FIG.
Is just this time, and both pseudo-lanoda in FIGS. 8 (a) and 8 (b)
Data cannot be received.

The reproduction of the data is performed in both FIGS. 8 (a) and 8 (b).
Compare data. Only the data of Fig. 8 (a) and 2T
The data of FIG. 8B received with a delay is sequentially compared,
There is no problem when both match, but 8T + τ in FIG.
If neither (a) nor (b) can be received, (a)
From the data β of (8T + τ) -2T = 6T + τ
From (b), (8T + τ) + 2T = 10T +
The reproduction is performed using the data α of τ.

In the embodiment, two types of pseudo random codes are used.
However, this is not limited to the two types,
It doesn't matter what kind it is, even if it is small.
The noise resistance performance is improved. And a code with low cross-correlation
Use gold code generation circuit to prepare multiple
Can be easily realized.

[0041]

According to the present invention, as described above,
Data is spread by the first pseudo-random code.
Spread modulated and slightly later
Is the second pseudo-random code with a small correlation
Spread spectrum modulation by a pseudo-random code,
These spread spectrum modulated signals are combined and transmitted.
To be transmitted, and this transmitted signal
Are demodulated based on the first pseudo-random code, and
Demodulated based on the pseudo-random code of 2
Of the delayed signal and the delayed
Data is reproduced based on the new data.
If the other spread spectrum signal cannot be received,
The other signal that has a different correlation with
Noise-resistant communication can be performed without retransmission
Has an effect.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of a transmitter according to the present invention.

FIG. 2 is a circuit diagram illustrating an example of a data delay circuit.

FIG. 3 is a waveform diagram showing a signal delayed by a data delay circuit.

FIG. 4 is a circuit diagram showing an example of a pseudo random code generation circuit.

FIG. 5 is a diagram showing a relationship between data and a pseudo random code.

FIG. 6 is a block diagram showing another embodiment of the transmitter.

FIG. 7 is a block diagram illustrating a configuration of an embodiment of a receiver.

FIG. 8 is a waveform diagram showing a signal subjected to spread spectrum demodulation.

[Explanation of symbols]

1 ... memory, 2 ... data delay circuit, 3, 7 ... spectrum
System modulation circuit, 4, 8, 22, 23 ... pseudo-random code generation
Raw circuit, 5 ... Reference carrier wave generation circuit, 6, 9 ... Base van
Modulation circuit, 10: mixer circuit, 11: transmission antenna,
21: receiving antenna, 24, 25: spectrum demodulation times
, 26, 27 ... baseband demodulation circuit, 28 ... data reproduction circuit.

Claims (1)

(57) [Claims] A transmitter for spread spectrum communication and a spread spectrum communication system.
Spread spectrum communication with receiver for spread spectrum communication
In the communication system, the transmitter for spread spectrum communication includes a first spread spectrum circuit for spreading data with a first pseudo random code, and a second spread spectrum circuit having a small correlation with the first pseudo random code.
A second spread-spectrum circuit for spread-spectrum the data with a pseudo-random code of
The second spread spectrum circuit with respect to the supply timing;
Data that slightly delays the data supply timing to the road
A delay circuit, and a combining circuit for combining a signal spectrally spread by said first and second spectrum spreading circuit, transmission A for transmitting the signal synthesized by the synthesizing circuit
And the receiver for spread spectrum communication receives a transmission signal from the transmitter for spread spectrum communication.
Receiving antennas and the same first and second pseudo-runs used on the transmitter side.
A first pseudo-random code generation circuit for generating a dumb code;
And second pseudo-random code generation circuit, and the first and second pseudo-random code generation circuits
At the receiving antenna based on the pseudo-random code
First spread spectrum demodulation circuit for demodulating received signal
And second spread-spectrum demodulation circuit and outputs of the first and second spread-spectrum demodulation circuits
Of the signal, data delayed on the transmitting side and data not delayed
A data reproduction circuit that reproduces a data signal based on data
Spread spectrum communication system characterized by comprising:
M