JPH06311136A - Spread spectrum communication system - Google Patents

Abstract

PURPOSE:To provide spectrum diffusion communication using a CSK(code shift keying) system even when the interference of other stations is strong. CONSTITUTION:A correlation output selector 33 selects larger correlation output in either a first correlator 29 or a second correlator 30. A reference value comparator 34 compares the output level of the correlator with a reference value. A data generation part 20 is controlled by the size and an information 1 bit is decided to be one period of a PN code or the repetitive signal of the several periods of the PN code so as to transmit it.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to spread spectrum (hereinafter referred to as SS) communication using direct spread (hereinafter referred to as DS), particularly code shift keying (hereinafter referred to as CSK).
The present invention relates to the improvement of the SS communication method using.

[0002]

2. Description of the Related Art In conventional data communication, communication using a narrow band modulation method is generally used. These can realize demodulation in a receiver with a relatively small circuit, but have a drawback that they are weak against multipath and narrow band colored noise like a LAN used in a premises such as an office or a factory.

On the other hand, in the SS communication system which has been used recently, in the DS system, the spectrum of the data is generally spread by a spread code, and the phase of the SS signal is added to the information to be transmitted in a wide band. It has the advantage of eliminating drawbacks. However, it may not be able to follow when the phase characteristic changes in the transmission path.

Therefore, the CSK method of transmitting data depending on the presence or absence of the SS signal has been attracting attention as one of the DS methods, which corresponds to the case where it is basically difficult to transmit information in phase. For example, "High performance power line SS modem"
Institute of Electronics, Information and Communication Engineers, Spread Spectrum Technology and its Application Study Group, March 22, 1989, SSTA, 89-8, 51
~ Page 57.

FIG. 4 is a block diagram showing an example of the structure of the receiver. In the CSK method, 1 and 0 of data are distinguished by changing the code to be transmitted. On the transmitter side, PN code 1 is transmitted when the data is 1, and PN code 0 is transmitted when the data is 0. To send.

In FIG. 4, on the receiver side, the received input signal 1 is divided into two by a two-way divider 2, and a first correlator 3 for PN code 1 and a second correlator for PN code 0 are provided. Input the same signal to 4. First and second correlators 3 and 4
Is output to the comparator 5, data is formed in the gate 6, and the output signal 7 is output.

FIGS. 5A to 5E are explanatory views showing the states of the respective signals at the points a to e in FIG. 4 at this time.

First, when the data is 1, the first correlator 3
The output (a) of is high because the correlation can be taken at the timing of A, while the output (b) of the second correlator 4 is
At the timing of A, 0 is output. Therefore, the comparator 5
Output (c) becomes positive and is gated by the gate signal (d) generated in the gate 6, and as a result, data 1 is output as the output (e). On the other hand, at the timing of B, on the contrary, since the data is 0, the second correlator 4
Output (b) is high, and the output (a) of the first correlator 3 is B
Is 0 at the timing. As a result, the output (c) of the comparator 5 becomes negative, and the data 0 of the output (e) is output by being gated by the gate signal (d) of the gate 6.

[0009]

As described above, the CSK system can be realized with a simple structure, and the amount of transmission can be increased easily by increasing the types of codes to be transmitted.

For example, in order to double the transmission capacity, four kinds of codes are used, and the code (1) is used for data (1,1).
(1,0) has a code 2, (0,1) has a code 3, (0,1)
0) may be assigned as indicated by reference numeral 4. In addition, eight types of codes may be used to triple the number.

By the way, there are cases where communication is performed in cells. FIG. 6 is an explanatory diagram of a configuration example of networked cell communication, in which cells B to G are arranged around the cell A in the periphery.

In a general narrow band modulation system, a different frequency is used for each cell in order to avoid interference between the cell A and the cells B to G. On the other hand, since the DS system of SS communication occupies a wide band, the cells are distinguished from each other by dividing the code to be used without dividing the frequency. The amount of interference between the codes is called cross-correlation, and the smaller this value, the smaller the interference of other stations.

In the CSK system, for example, 4CSK
Since four types of codes are used, at least 12 types of codes are required when there are six adjacent cells, and 28 types or more of codes are required when the same code is separated by two or more cells.

In general, it is difficult to generate a large number of codes having good cross-correlation for all, and when many codes are made with the same number of chips, it is unavoidable that the cross-correlation deteriorates.
In particular, the shorter the code length, the less the number of codes with good cross-correlation and the greater the deterioration.

Further, in the CSK system, since the correlation outputs of several kinds of codes (for example, 4 kinds of 4CSK) are compared,
As compared with the PSK system and the like, it has a drawback that it is weak against interference with adjacent cells.

In particular, in the peripheral area of the cell, the electric field strength is weak and the interference from other cells is strong, so that it is impossible to communicate with a code having a small spreading gain.

Therefore, in the peripheral area of the cell, a method of using a code having a large spreading gain and a small cross-correlation can be considered, but for that purpose, a demodulating circuit having several kinds of spreading code lengths is required and the circuit scale is large. It wasn't realistic.

In view of the above points, the present invention provides a system capable of performing stable communication within a cell in CSK communication by adding a simple circuit.

[0019]

In the present invention, the CS
In K communication, the correlator output level is detected and compared with a reference level. When the level is lower than that level, the data signal for 1 bit of information is repeated to obtain P
Allocate N code number cycles and transmit. As the level of the correlator output, the output level of the difference compared with the correlator levels of all codes can be used. It is also possible to prepare the reference value in several steps and change the number of repetitions of the data signal corresponding to one bit of information.

[0020]

According to the present invention, one or more data signals are generated for one information bit according to the correlator output level, and PN signals having one or more cycles are allocated to them, and the receiver side The error rate can be improved by integrating it or making a majority decision and decoding the information. In the CSK method, when the interference from other stations is large, the correlation output decreases and the correlator output of a code other than the transmission code increases. Therefore, by using the correlator output level as the detection reference,
When the interference is large, one bit of information can be repeatedly transmitted in the PN code number cycle.

[0021]

1 is a block diagram of a transmitter / receiver in the case of 2CSK.

Transmission and reception are assumed to be time division multiplexed.
First, the receiving system will be described.

A signal composed of a PN code 1 corresponding to the data 1 and a PN code 0 corresponding to the data 0 transmitted from the partner station is received by the receiving antenna 26, and thereafter, via the down converter 27, a two-way divider 28. And is input to the first correlator 29 and the second correlator 30. The outputs of these correlators are input to the comparator 31,
Data is formed at the gate 32. This is shown in FIG.
It is the same as that explained above.

In the present invention, 1 bit of information is 1 bit of data or 2 bits of data depending on the line condition of the transmission line.
Since the number of bits or more allocated and repeated is changed, information output is obtained from the information output unit 36 by performing integration or majority decision according to the number of data allocated in the data processing circuit 35.

That is, when the PN number cycle is assigned to one bit of information, the data obtained from the output for each PN cycle is output through the filter corresponding to the PN number cycle. Further, when the PN number cycle is assigned to one bit of information, the data obtained from the output for each PN cycle is stored for several cycles and the majority output is determined to obtain the information output.

At this time, the number of allocated data is determined by a flag indicating the number of allocations included in the information, as described in the description of the transmitter described later.

On the other hand, the outputs of the first and second correlators 29 and 30 are separated from the comparator 31 by the correlation output selector 33.
Entered in. Here, the correlation output having the larger output is selected. Depending on the line conditions, the transmitter side outputs the sum of the PN code period number of cycles. After this,
The reference value comparator 34 compares it with a preset reference value to determine whether the current channel has a good C / N or the degree of interference with other stations. When it is smaller than the reference value, the number of data corresponding to 1 bit of information generated by the data generator 20 described later is changed, and the number of repetitions of the PN code cycle is changed. When it is larger than the reference value, at least 1 bit of information is generated. So that the current number of PN code periods corresponding to
To control.

Other examples of the reference value include the following. It is possible to prepare several stages as reference values, and each reference value can allocate 1 bit of information to an arbitrary number of repetitions of the PN cycle according to the reference value.

Further, the output levels of all the correlators are detected, the maximum correlator output level is detected, and the correlator output level of the PN code having the maximum output (including the integral output of the PN number period) is obtained. , The minimum correlator output level (including the integral output of PN number period) is detected, and the ratio exceeds the reference value, depending on the ratio between the maximum output level and the difference between the maximum and minimum output levels. Can transmit 1 bit of information in a PN1 cycle, and if less than 1 bit of information, can be transmitted in a PN number cycle.

Generally, at the same frequency, both transmission and reception show the same line condition, so that the information generation speed and the number of information repetitions of the data generation section 20 on the transmission side are controlled according to the criterion of the reference value comparator 34.

On the transmitting side, the data generating section 20 converts information into transmission data. Whether the information 1 bit is converted into 1 transmission data or repeatedly transmitted with a plurality of bits is compared with the above reference value. Based on the judgment of the container 34. After that, the PN code generator 23 generates a series of PN codes PN1 and PN0 from the data 1 and 0. This PN code is transmitted by the modulator 22 to the local oscillation signal generator 21.
The signal Lo from 21 is modulated, passed through the up-converter 34, and then transmitted from the transmitting antenna 25. In addition,
A signal (flag) indicating how many times 1 bit of information is repeatedly transmitted is included in the information signal.

As described above, according to the present invention, it is possible to allocate one bit of information to several bits of transmission data depending on the situation such as C / N or interference with other stations.

FIG. 2 is a graph of the error rate improvement degree when one bit of information is repeatedly transmitted three times. The vertical axis represents the bit error rate (BER). In this example, 1-2
It can be seen that the dB is improved.

Thus, by using the present invention,
The transmission rate can be changed according to the line condition, and as a result, the error rate can be improved.

FIG. 3 is a block diagram of the second embodiment of the present invention. Although the basic configuration is the same as that of FIG. 1, the output of the comparator 31 of the correlation output is used as the correlation output that serves as a reference for determining how many times transmission data is repeated for 1 bit of information. The output of the comparator 31 is sent to the correlation output shaping unit 37, and the output is sent to the reference value comparator 34-1 and compared with the reference value. When the interference of other stations is large, generally, the correlation output for the desired code decreases and the correlation output for the undesired code increases. Therefore, by comparing the level difference between these two signals, it is possible to judge the condition of the C / N or the interference wave as in the first embodiment. When the level of the desired code is lower than the reference value, the reference value comparator 34-1 controls the data generator 20 to increase the number of repetitions of the PN code.

As described above, by using the present invention, it is possible to transmit a signal with a low error rate even when the interference with other stations is strong. As a result, the CSK method can be applied even in the case of cell communication, and the conventional problems can be solved.

Although 2CSK is used here as an example, the present invention does not lose its generality even if it uses multiple CSKs such as 4CSK and 8CSK.

Further, the data processing circuit 35 and the information output section 3
6 and the like can be handled by software.

[0039]

As described above, according to the present invention, SS communication by the CSK method can be used even under the interference of other stations. As a result, it becomes possible to use the CSK method for communication in a cell.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention.

FIG. 2 is a graph showing an error rate improvement according to the present invention.

FIG. 3 is a block diagram of another embodiment of the present invention.

FIG. 4 is a block diagram of a conventional CSK receiver.

5A to 5E are waveform diagrams in a to e of FIG. 4, respectively.

FIG. 6 is an explanatory diagram of a configuration example of networked cell communication.

[Explanation of symbols]

 20 data generator 21 local oscillation signal generator 22 modulator 23 PN code generator 24 up-converter 25 transmitting antenna 26 receiving antenna 27 down-converter 28 2 distributor 29 first correlator 30 second correlator 31 comparator 32 Gate 33 Correlation output selector 34 Reference value comparator 35 Data processing circuit 36 Information output unit 37 Correlation output shaping unit

Claims (6)

[Claims] 1. A data generator capable of repeatedly generating 1 bit of information as a data signal, and a PN code generator for encoding data from the data generator into a cycle of 1 or more PN codes per information bit. Code shift keying signal transmitting means having, a plurality of correlators for demodulating the received code shift keying signal, means for detecting the level of the demodulated signal,
A reference value comparator that compares the demodulated level with a reference value,
And a code shift keying signal receiving means for processing data from the output of the correlator and outputting information, wherein the reference value comparator is generated in the data generator by the magnitude of the correlation output compared with the reference value. Spread spectrum communication system characterized by controlling the number of repetitions of a data signal corresponding to 1 bit of information. 2. The spread spectrum communication system according to claim 1, wherein the level of the received signal compared with the reference value by the reference value comparator is the output of the correlator having the maximum output. 3. The value compared with the reference value by the reference value comparator is a ratio of the level of the correlator having the maximum output and the difference between the level of the correlator having the maximum output and the level of the correlator having the minimum output. The spread spectrum communication system according to claim 1. 4. The reference value is prepared in several steps, and the number of data signal repetitions corresponding to 1 bit of information is changed according to each reference value.
The spread spectrum communication system described. 5. When an PN code period of a corresponding number is assigned to an arbitrary number of data signals repeated for 1 bit of information, the data obtained from the output for each PN period depends on the PN code period number. 5. An information output is obtained via a filtered filter.
The spread spectrum communication system described. 6. When the number of PN code periods corresponding to an arbitrary number of data signals repeated for 1 bit of information is assigned, the data signal obtained from the output for each PN period is the period of the corresponding PN code. The spread spectrum communication system according to claim 1, wherein the information output is obtained by storing for several minutes and making a majority decision.