JPS612441A - Code transmission system - Google Patents

Abstract

PURPOSE:To simplify the constitution of a receiving circuit and to improve an error ratio by appreciating and detecting the quality of a receiving signal, sending the appreciated result, comparing the appreicated value with a reference value, and selecting the information of the appreciated value exceeding the reference value out of the same information received plural times by a receiver. CONSTITUTION:When the repeated times of the same information is twice, the 1st information is temporally stored in a shift register 77. A comparator 80 decides an appreciated value twice, and if the value reaches a fixed reference level, sends its output each time. On the other hand, a clock signal fb is applied from a clock reproducing circuit 73 to a selecting circuit 78, and if the 2nd appreciated value out of the received information reaches the fixed reference level, a selecting circuit 78 selects the 2nd information inputted from an inversion circuit 79 and sends the selected information to an output OUT. If the 2nd appreciated value does not reach the fixed reference, the selecting circuit 78 selects the 1st information stored in the shift register 77 and sends the selected information to the output OUT. Consequently, the appreciated value of the received information which reaches the fixed reference is sent to the output OUT.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a digital code transmission system.

In particular, it relates to a system in which the same information is repeatedly transmitted in order to accurately transmit codes such as control signals in, for example, mobile radio systems where the condition of the transmission path is not always good.

[Conventional technology]

In order to reduce code errors on a transmission path, a method is known in which redundant transmission is performed by repeating the same information multiple times. In this method, increasing the number of repetitions increases redundancy and improves the accuracy of transmitted information, but generally the code mark rate of a series of information is not 50%, so a DC component is generated in the signal and DC Interrupted transmission lines and circuits have the disadvantage that good transmission cannot be achieved. Also, if there are consecutive marks or spaces in the code to be transmitted,
The drawback is that it is difficult to extract the clock signal.

On the other hand, a split phase code is known as a method of repeatedly transmitting the same code with positive and negative polarities. This is as shown in FIG. 2, where M represents a 1-bit information mark and S also represents a space. With this coding method, the polarity is always reversed within one bit of information, so there is no DC component in the signal, and the point where the signal level always crosses the zero level appears repeatedly, making it possible to extract the clock signal. It will never go away. However, when this split-phase code is transmitted over a transmission path with pulse noise or short-cycle fading, the information to be retransmitted is temporally adjacent, so
There is a drawback that the correlation with the same noise or fading is large, and the error rate is not necessarily improved.

Furthermore, since this sprint phase code inverts the polarity at the center of one information bit, its eye pattern has a wide open eye 21 and a small open eye 22, as shown in FIG. Assuming that the transmitted information code is random, the probability of passing through the two eyes 21 and 22 is 1/2, and the probability of passing through the small open eye 22 is 1/2.
In this case, there is a disadvantage that it is susceptible to code amount interference.

The present invention is based on an earlier application filed by the same inventor and applicant (Japanese Patent Application No. 116671/1983, filed on June 27, 1982).
The purpose of this invention is to provide improvements and specific embodiments of the device (unpublished at the time of filing of this application).

[Problem that the invention seeks to solve]

SUMMARY OF THE INVENTION An object of the present invention is to provide a code transmission system that has a small correlation with noise or fading even when the same information is repeatedly transmitted, and is less susceptible to code amount interference. Another object of the present invention is to provide a method for transmitting a signal without imbalance in the DC component of the signal. A further object of the present invention is to provide a method for transmitting a signal from which a clock signal can be easily extracted.

[Means for solving problems]

The present invention transmits the same transmission information a plurality of n times at intervals of two or more time slots with one polarity and the opposite polarity, and when the plurality of n is an even number, the number of transmissions of one polarity is opposite to the number of times of transmission of one polarity. In a code transmission system in which the number of transmissions of one polarity is equal and the difference between the number of transmissions of one polarity and the number of transmissions of the opposite polarity is 1 when the plurality n is an odd number, the reception device A means for evaluating and detecting signal quality and transmitting an evaluation value, a means for comparing this evaluation value with a reference value, and information whose evaluation value exceeds the reference value among multiple pieces of received identical information. and means for selecting.

[Effect]

The receiving device detects the evaluation value of the received signal, and if this evaluation value is greater than or equal to the reference value, the corresponding received signal is taken in as valid. , the configuration of the receiving circuit is simplified since it is only a matter of selecting.

〔Example〕

FIG. 1 is a diagram showing a transmission code string according to an embodiment of the present invention. The horizontal axis represents time and the vertical axis represents signal level. In this example, the same information is transmitted twice with an interval of 5 bits and with the polarity reversed. The broken line in the figure shows how the same information is transmitted again with the polarity reversed.

In this method, the interval between repeated identical information is 5
Since it is a bit, even if one pulse noise occurs, the possibility that it will simultaneously affect 5 bits apart is much smaller than the possibility that it will affect the neighboring bits, so redundancy is effective. used for. In addition, since the positive and negative polarities of this code are always reversed every 5 bits, even if the mark rate of information is not 50%, the mark rate of the code over a long period of time will be 50%, and no DC component will occur in the signal. .

In addition, since there is always a point where the signal level drops below the zero level due to this reversal of positive and negative, it does not become difficult to extract the clock signal even if the same code continues.

FIG. 4 is a block diagram of a transmitting device of an embodiment of the present invention for generating such a code. This example is a configuration diagram of a transmitting device that repeatedly transmits the same information several times. To generate the code string shown in FIG. 3, it is sufficient to set 2=2. The input information is input to the shift register 41 as serial information.

A clock signal Kfb synchronized with this input information is input to a frequency dividing circuit 42, and its frequency divided output fb is applied to a clock input of a shift register 41. In this shift register 41, M1 bit, M2 bit---1---
--1M, B1. The signal outputs each delayed by 1 and 2 are taken out and applied to the input of the selection circuit 43. At this time, an inversion circuit 44 is inserted so that the signal is inverted according to the polarity to be transmitted, and the signal is applied to the selection circuit 430. This selection circuit 43 is controlled by the output signal of the frequency divider circuit 42 to select and output necessary information. That is, in the selection circuit 43, the clock signal Kfb is 1.
Control is performed so that each time input signals are input, signals from inputs 1 to 11 are selected in order and sent to the output OUT. When up to three inputs have been selected, the shift register 41 shifts by one and the next decoder inputs, and the same operation is repeated.

In such a code transmission system, when the number of repetitions K of the same information is an even number, if the number of positive polarity transmissions is set equal to the number of negative polarity transmissions, the DC component of the signal over a long period of time will disappear. . Even when K is an odd number, if the difference between the number of transmissions of positive polarity and the number of transmissions of negative polarity is set to 1, the effect of deviation from 50% in the mark rate will be reduced to 1/1.
decreases to K.

FIG. 5 is a diagram showing a transmission code string according to another embodiment of the present invention. In this example, the same information is transmitted in consecutive blocks of 5 bits and this is repeated, and the same effect is obtained.

The eye pattern of the code string shown in FIG. 1 or the code string shown in FIG. 5 is as shown in FIG. There will be 4 types. Therefore, if the transmitted information is random, the probability that the signal passes through the eye pattern 61, which has a small opening, is 1/4, which is smaller than 1/2 in the case of a split-phase code, and the code amount will be affected accordingly. The possibility of

FIG. 7 is a configuration diagram of an embodiment of a receiving device according to an embodiment of the present invention. Compared to the invention of the prior application, this receiving device has the characteristics of the present invention.

The received signal modulated by the carrier wave is input to the demodulation circuit 71,
The demodulated signal (baseband signal) is input to the identification circuit 72 and the clock recovery circuit 73.

An evaluation value detection circuit 74 is connected to the output of the demodulation circuit 71. The evaluation value detection circuit 74 will be explained in detail later, but here, as an example, when the input reception signal of the demodulation circuit 71 is an FM signal, it is a circuit that detects the amplitude of the input reception signal. The output of the evaluation value detection circuit 74 is connected to one input of the comparison circuit 75. This comparison circuit 7
The other input of 5 is supplied with a reference digital analog conversion Es.

On the other hand, the identification circuit 72 is supplied with the clock signal Kfb from the clock regeneration circuit 73, and the demodulated signal is identified and regenerated using a known method. The output signal of the identification circuit 72 is input to a shift register 77 and temporarily held. In this way, a plurality of outputs with different delay times are taken out, and these are input to the selection circuit 78.

The selection circuit 78 is switched and controlled by the output of the comparison circuit 75. The delay time interval of this shift register 77 is similarly equal to the time interval at which the same information is repeatedly received. Further, among the delayed outputs of the shift register 77, an inverting circuit 79 is inserted in a path where the polarity is inverted on the transmitting side and an output corresponding to the transmitted information appears.

In the device configured in this way, the same information transmitted multiple times on the transmitting side with the polarity reversed as described above is rectified into the same polarity and is simultaneously sent to the input of the selection circuit 78. appear. Also, at this time, the evaluation value of the received signal for the same information appears at the input of the comparison circuit 75. The comparison circuit 75 controls the selection circuit 78 to select the signal if this evaluation value exceeds the reference value, and sends it to the output.

In this example, the same information is repeated twice, and the first information is temporarily stored in the shift register 77.

The comparison circuit 80 judges the evaluation value twice, and if it reaches a certain standard, sends out an output each time. On the other hand, the clock signal fb is output from the clock regeneration circuit 73 to the selection circuit 7.
8, and this selection circuit 7 becomes valid synchronously when the second information is received. Therefore, if the second evaluation value of the repeatedly received information reaches a certain standard, the selection circuit 78 selects the second evaluation value inputted from the inversion circuit 79.
The information for the second time is selected and sent to the output OUT. When the second evaluation value does not reach a certain standard, the selection circuit 78 selects the first information stored in the shift register 77 and sends it to the output 011T. With this configuration, received information whose evaluation value has reached a certain standard is output. Since the circuit for making the selection is only a simple selection, there is an advantage that the circuit configuration is simpler than that disclosed in the above-mentioned prior application.

According to this receiving device, out of the same information received multiple times, information that is always higher than the reference value of the evaluation value of the received signal is selected and used, so a time diversity effect is obtained and the code Code transmission with good error susceptibility can be performed.

As the evaluation value detection circuit 74, for example, if the received signal is FM
Although it has been described that the amplitude of the received signal is detected when the received signal is a signal, in this embodiment, the magnitude of the envelope of the intermediate frequency signal of the demodulation circuit 71 is detected, and the detected output is passed through the logarithmic amplifier. It was configured as follows.

FIG. 8 shows a configuration example of yet another evaluation value detection circuit. In this example, the demodulated Haasband signal is branched, passed through a high-pass filter 81, noise outside the band is detected, passed through a squaring circuit 82, the power of the noise is calculated, and the output is The signal is passed through a low-pass filter 83 and averaged. According to this circuit, there is an advantage that the diversity effect can be effectively obtained even when the received signal is degraded due to deterioration other than a decrease in received power, such as interference.

〔Test results〕

FIG. 9 is a block diagram of a test apparatus according to an embodiment of the present invention. In FIG. 9, the transmitting device 101 is the embodiment device explained in FIG. 4, and the receiving device 102 is the embodiment device explained in FIG. The output signal of the transmitting device 101 is passed through a low-pass filter 103, inputted to a frequency modulation transmitter 104 for mobile radio communication, and transmitted to a pseudo channel 105. The receiving device 102 connects its input to this pseudo propagation path 105,
The signal output is given to the error rate measuring device 106 to measure the error rate. The pseudo propagation path 105 is a mobile radio communication system in urban areas, and eliminates standard fading and noise that occurs in the spatial propagation path between the mobile station and the base station! (This is a device that occurs in the contract, and is widely used when it is impossible to actually transmit radio waves into space due to radio regulations.

FIG. 10 shows the test results using this test device.

The clock signal of the transmission data code string is set to 2400 bps, and the repetition frequency of pseudo fading is set to 40 Hz.
The code error rate is measured with respect to the received voltage (median value) when A shows the measurement results using the apparatus according to the embodiment of the present invention, and B shows the same measurements as a comparative example using a split-phase code. 10
It can be seen that this is improved to 0.

[Response]

The present invention is extremely effective when implemented in a land mobile communication system in which the electric field strength of a transmission path changes drastically with movement, and in a system for transmitting and receiving control signals and other digital signals. In the land mobile communication system, in communication between a car traveling in an urban area and a fixed base station, the reception level varies deeply due to fading, on the order of several tens of dB, and the pinch of fading is on the order of several tens of Hz. In such a case, if the present invention is implemented and the repetition interval of the transmission code is set to several bits, the time interval will be several milliseconds when the transmission speed is about 1 kbps, so the reception state will change during that time. There is great potential for change and recovery. This makes it possible to significantly improve the code error rate. If the same code error rate is improved by increasing the power, it is considered to be equivalent to about 1° dB. Moreover, in mobile communication systems, devices are generally configured to cut off the DC level and transmit, so the present invention does not simply transmit the same information repeatedly, but inverts its polarity and repeatedly transmits the same information. This method is extremely effective.

〔Effect of the invention〕

According to the present invention, since the same information is repeatedly transmitted at time intervals, the probability that the same information will be affected by the same noise is reduced, and effective redundant transmission can be performed. Furthermore, since the polarity is reversed during repeated transmission, even if the mark rate of information is not 1/2, the mark rate over a long period of time becomes 1/2, and no DC component occurs in the signal. Furthermore, since the polarity change always causes a point where the signal crosses the zero level, extraction of the clock signal does not become difficult. Furthermore, in the encoding method of the present invention, the probability of passing through a narrow part of the eye pattern is smaller than in the case of a split phase signal, and the bit error rate is improved.

Furthermore, by introducing evaluation value detection into the receiving device,
The reliability and error rate of the received signal is further improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating a code sequence according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of the sprint phase of the conventional method. FIG. 3 is an explanatory diagram of the eye pattern of the split phase method. FIG. 4 is a diagram showing an example of the configuration of a transmitting device of an apparatus according to an embodiment of the present invention. FIG. 5 is a diagram illustrating another code sequence according to the embodiment of the present invention. FIG. 6 is an explanatory diagram of an eye pattern using codes according to an embodiment of the present invention. FIG. 7 is a configuration diagram of an embodiment of a receiving device according to an embodiment of the present invention. FIG. 8 is a side view of the configuration of the evaluation value detection circuit. FIG. 9 is a block diagram of a test apparatus according to an embodiment of the present invention. FIG. 10 is a diagram showing the measurement results by the test device.

Claims (1)

[Claims] (1) The transmitting device is equipped with means for temporarily storing transmitted information and means for inverting the polarity of the sign of the transmitted information, and transmits the same transmitted information multiple times at intervals of two or more time slots.
When the plurality n is an even number, the number of transmissions of one polarity is equal to the number of transmissions of the opposite polarity, and when the plurality n is an odd number. In some cases, in a code transmission system in which the difference between the number of transmissions of one polarity and the number of transmissions of the opposite polarity is set to 1, the receiving device includes a means for evaluating and detecting the quality of the received signal and transmitting an evaluation value. and means for comparing the evaluation value with a reference value, and means for selecting information whose evaluation value exceeds the reference value from among the plurality of received identical information. Code transmission method.