JP2724951B2 - Spread spectrum communication system - Google Patents

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"), and more particularly to code shift keying (hereinafter referred to as "CSK").
The present invention relates to an improvement of an SS communication method using the communication method.

[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 susceptible to multipath and narrow-band colored noise, such as a LAN used in premises such as offices and factories.

On the other hand, in the recently used SS communication system, the DS system generally spreads a data spectrum by a spreading code and transmits information over a phase of an SS signal to transmit the data over a wide band. It has the advantage of eliminating disadvantages. However, when the phase characteristic changes in the transmission path, it may not be able to follow.

[0004] Therefore, the CSK method of transmitting data with or without an SS signal has attracted attention as one of the DS methods, basically corresponding to the case where it is difficult to transmit information in phase. For example, "High-performance power line SS modem"
The Institute of Electronics, Information and Communication Engineers, Spread Spectrum Technology and its Applications, March 22, 1989, SSTA, 89-8, 51
Pp. 57-57.

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

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

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

First, when the data is 1, the first correlator 3
(A) shows a high output because the correlation can be obtained 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 by the gate 6, and as a result, data 1 is output as the output (e). On the other hand, at the timing of B, since the data is 0 on the contrary, the second correlator 4
Is high, and the output (a) of the first correlator 3 is B
It is 0 at the timing of. As a result, the output (c) of the comparator 5 becomes negative and is gated by the gate signal (d) of the gate 6 to output data 0 of the output (e).

[0009]

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

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

[0011] Incidentally, there is a case where communication is performed by making cells. FIG. 6 is an explanatory diagram of a configuration example of networked cell communication. Cells B to G are arranged around a cell A.

In a general narrowband modulation system, different frequencies are 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 distinction for each cell is performed by changing the code to be used without dividing the frequency. The amount of interference between the codes is called a cross-correlation, and the smaller this value is, the smaller the other station interference is.

In the CSK system, for example, 4CSK
Since four types of codes are used, at least 12 types are required when there are six adjacent cells, and at least 28 types 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 in all cases. When many codes are formed with the same number of chips, it is inevitable that the cross-correlation deteriorates.
In particular, the shorter the code length, the smaller the number of codes with good cross-correlation and the greater the deterioration.

Further, in the CSK system, correlation outputs of several kinds of codes (for example, four kinds of codes for 4CSK) are compared.
Compared to the PSK method or the like, there is a drawback that it is less susceptible to interference with adjacent cells.

In particular, in a peripheral area of a cell, the electric field strength is weak and 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 using a code having a large spreading gain and a small cross-correlation can be considered. For this purpose, a demodulation circuit having several kinds of spreading code lengths is required, and the circuit scale is large. It was not realistic.

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

[0019]

According to the present invention, CS
In K communication, the correlator output level is detected and compared with a reference level. When the output level is lower than that level, the data signal for one bit of information is repeated,
Allotments for N code cycles are transmitted. As the level of the correlator output, the output level of the difference between the correlator levels of all the codes can be used. It is also possible to prepare several levels of reference values 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 bit of information according to the correlator output level, and a PN signal having one or more periods is assigned to them. The error rate can be improved by integrating the result or majority decision and decoding the information. In the CSK method, when interference from other stations is large, a correlation output is reduced and a correlator output of a code other than a transmission code is increased. Therefore, by using the correlator output level as a detection criterion,
When the interference is large, one bit of information can be repeated and transmitted in several PN code cycles.

[0021]

FIG. 1 is a block diagram of a transceiver for 2CSK.

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

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

In the present invention, one bit of information is one bit of data or two bits of data depending on the line condition of the transmission line.
Since the number of repetitions assigned to bits or more is changed, the information output unit 36 obtains an information output by performing integration or majority decision according to the number of data assigned by the data processing circuit 35.

That is, when a number of PN cycles are assigned to one bit of information, data obtained from an output for each PN cycle is obtained as an information output via a filter corresponding to the PN number cycle. Further, when a number of PN cycles are assigned to one bit of information, data obtained from an output for each PN cycle is stored for several cycles, and an information output is obtained by making a majority decision.

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

On the other hand, the outputs of the first and second correlators 29 and 30 are supplied to a correlation output selector 33 separately from the comparator 31.
Is input to Here, the correlation output having the larger output is selected. This is obtained by adding the number of cycles of the PN code cycle on the transmitter side depending on the line condition. After this,
The reference value comparator 34 compares the reference value with a preset reference value to determine whether the current line is a line with a good C / N or how much interference is caused by other stations. If the value is smaller than the reference value, the number of data corresponding to one 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. Is maintained by the reference value comparator 34 so as to maintain the current number of PN code periods corresponding to
Control.

Other examples of the reference value include the following. Several levels are prepared as reference values, and one bit of information can be assigned 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 output level of the maximum correlator is detected, and the correlator output level of the PN code having the maximum output (including the integrated output of the PN number cycle) is obtained. Detecting the minimum correlator output level (including the integrated output of several PN cycles), and when the ratio exceeds a reference value according to the ratio of the maximum output level to the difference between the maximum and minimum output levels. Can transmit one bit of information in one PN cycle, and if less than one bit, transmit one bit of information in several PN cycles.

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

On the transmitting side, the information is converted into transmission data by the data generation section 20. Whether the information of one bit is converted to transmission data of one bit or the transmission of a plurality of bits repeatedly is determined by the above-described reference value comparison. Based on the judgment of the container 34. Thereafter, the PN code generator 23 generates PN code sequences PN1 and PN0 according to the data 1,0. This PN code is supplied to a local oscillation signal generator 21 by a modulator 22.
Is modulated from the signal 21 and transmitted from the transmitting antenna 25 after passing through the up-converter 34. In addition,
A signal (flag) indicating how many times one bit of information has been repeatedly transmitted is incorporated 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 other station interference.

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

As described above, 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 a second embodiment of the present invention. The basic configuration is the same as that of FIG. 1, but the output of the correlation output comparator 31 is used as a correlation output serving as a reference for determining how many times transmission data is repeated for one bit of information. The output of the comparator 31 is sent to the correlation output shaping section 37, and the output is sent to the reference value comparator 34-1 and compared with the reference value. When the interference of another station is large, generally, the correlation output for the desired code decreases and the correlation output for the non-desired code increases. Therefore, by comparing the level difference between the two signals, it is possible to determine the state 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 data generator 20 may be controlled by the reference value comparator 34-1 to increase the number of repetitions of the PN code.

As described above, by using the present invention, a signal can be transmitted with a low error rate even when other-station interference is strong. As a result, the CSK method can be applied to the case of cellular communication, and the conventional problems can be solved.

Although 2CSK is used as an example here, the present invention does not lose its generality even if it is multi-CSK such as 4CSK or 8CSK.

The data processing circuit 35 and the information output unit 3
6 and the like can be handled by software.

[0039]

As described above, according to the present invention, the 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 scheme for cell communication.

[Brief description of the drawings]

FIG. 1 is a block diagram of one 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.

5 (a) to 5 (e) are waveform diagrams at a to e in FIG. 4, respectively.

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

[Explanation of symbols]

 Reference Signs List 20 data generation unit 21 local oscillation signal generator 22 modulator 23 PN code generator 24 up-converter 25 transmission antenna 26 reception antenna 27 down-converter 28 2-divider 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)

(57) [Claims] 1. A data generator for generating a data signal by repeating one bit of information, and a PN code generator for encoding data from the data generator into one cycle or more of a PN code 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 for comparing the demodulated level with a reference value;
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 by a data generation unit according to the magnitude of the correlation output compared with the reference value. A spread spectrum communication system characterized by controlling the number of repetitions of a data signal corresponding to one 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 an output of a correlator having a maximum output. 3. The value to be compared with the reference value in the reference value comparator is a ratio of a level of the correlator having the maximum output to a difference between the level of the correlator having the minimum output and the level of the correlator having the minimum output. The spread spectrum communication system according to claim 1, wherein: 4. The reference value is prepared in several steps, and the number of data signal repetitions corresponding to one bit of information is changed according to each reference value.
Spread spectrum communication system as described. 5. When an arbitrary number of PN code periods are assigned to an arbitrary number of data signals repeated for one bit of information, data obtained from an output for each PN period is determined according to the number of PN code periods. 5. An information output is obtained through a filtered filter.
Spread spectrum communication system as described. 6. When a number of PN code cycles corresponding to an arbitrary number of data signals repeated for one bit of information are assigned, a data signal obtained from an output for each PN cycle is converted to a corresponding PN code cycle. 5. The spread spectrum communication system according to claim 1, wherein the information is output by storing for several minutes and making a majority decision.