JPH01293012A - System for measuring level distribution of soft decision signal - Google Patents

Abstract

PURPOSE:To make the title system applicable even when a transmission section and reception section are separated from each other so that a signal level distribution can be measured while actual communication is performed by performing error correction coding on the transmission side and measuring signal level distribution characteristics by utilizing an error correction decoded output on the reception side. CONSTITUTION:The output of an error correction decoder 26 is the same as the input of an error correction coding circuit 25 on the transmission side as a result of error correction and, when the output is again coded by means of the same circuit as the error correction coding circuit 25 on the transmission side, the same signal as the input of a modulator 12 on the transmission side can be obtained. By using the signal as reference data, signal level measurement can be performed and a signal level distribution can be found.

Description

[Detailed Description of the Invention] [Table of Contents] Overview Industrial Field of Application Prior Art (Figures 4 to 7) Means for Solving the Problems to be Solved by the Invention (Figure 1) Function (Figure 1) Embodiments (Figures 2 and 3) Effects of the invention [Summary] Regarding a soft-decision signal level distribution measurement method for measuring signal level distribution characteristics when performing soft-decision decoding, transmission It can be applied even if the section and the receiving section are separated.
The purpose is to provide a method that has a simple circuit configuration and can measure signal level distribution characteristics while performing actual communication. In a communication system that transmits a signal and demodulates the received signal on the receiving side to reproduce the input signal, the transmitting side is provided with an error correction encoding means for error correction encoding the input signal, and also error correction decoding is performed on the demodulated signal. an error correction decoding means, a re-encoding means for encoding the output of the error correction decoding means in the same error correction code as that on the transmitting side, and comparing a signal obtained by delaying the demodulated signal with the output of the re-encoding means to determine its level. A signal level determining means for determining the signal level is provided on the receiving side.

[Industrial application field]

The present invention relates to a soft-decision signal level distribution measurement method for measuring signal level distribution characteristics when performing soft-decision decoding.

In communication systems, error correction technology that corrects errors occurring in transmission paths and improves line quality is important.
This is an indispensable technology, especially in satellite communication systems where signal propagation distance is long and signal attenuation is large.

Among these, soft-decision error correction decoding technology, which performs error correction on the receiving side by focusing on the distribution characteristics of the level of the demodulator output signal, can greatly improve error correction capability by combining with convolutional code/bicubi decoding methods, etc. It is an effective technique that can be improved.

In order to apply such soft-decision decoding technology to an actual communication system and fully demonstrate its effectiveness, it is necessary to understand the signal level distribution in the system in advance.

The signal distribution measurement method in soft-decision decoding can be applied even when the transmitter and receiver are separated, has a simple circuit configuration, and can monitor the signal level distribution while performing actual communication. It is desired that

[Conventional technology]

FIG. 4 shows an example of a conventional soft-decision signal level distribution measurement method.

On the transmitting side, a PN pattern generation circuit 11 generates a signal consisting of a PN pattern, and this signal is applied to a transmitter (Tx) 13 via a modulator 12, whereby it is modulated with a PN pattern using a predetermined modulation method. A transmission signal is generated, and this signal is transmitted to the receiving side via a transmission path.

On the receiving side, a receiving section (Rx) 14 receives this signal, and the received signal is demodulated through a demodulator 15 and converted to the original PN.
Play the pattern. The signal level determining circuit 16 determines the signal level by comparing the demodulated output and the PN pattern transmitted from the PN pattern generating circuit 11 via the delay circuit 17 bit by bit. Therefore, the delay time of delay circuit 17 is chosen to be equal to the delay time from the input of modulator 120 to the output of demodulator 15.

Now, the demodulator output level is divided into 8 levels from 0 to 7, and this is encoded into a 3-bit folded double code and output, and the signal level determination circuit 16 uses an exclusive OR (EX-OR) circuit. 161, the most significant bit (MSB) of the output of the demodulator 15 is inverted by the original signal that has passed through the delay circuit 17, and the rest is output as is, the result shown in FIG. 5 is obtained.

As is clear from FIG. 5, even when the input to the modulator 120 is at level 0, that is, the level corresponding to hard decision "0", the output of signal level determination circuit 16 is at level 0, that is, the level corresponding to hard decision "1". Also at the corresponding level, when the level change is the smallest in the output of the demodulator 15, it is "011".
Then, when the level changes in the opposite sign direction, the degree of change is equal to the output of the signal level determining circuit 16 and "0".
11”.

The decoder 18 decodes the output of the signal level determination circuit 16 to generate pulses, and the appearance frequency counter 19 counts and displays the pulses for a certain period of time. For example, when "Oll" is designated as the measurement pattern, the frequency with which the demodulator 15 obtains the output with the smallest level change can be determined by measuring over a certain period of time in the circuit shown in FIG. Similarly, the measurement patterns “OIO”, “001”,
- When specified, the level change will be level change, respectively.
You can know the appearance frequency at level 2 and -.

Note that the configuration of the signal level determination circuit 16 shown in FIG. 4 is an example in which folded binary representation is performed for the judgment output, and a different configuration may be required if the code format is different. Needless to say.

FIG. 6 shows an example of the signal level distribution characteristics obtained in this manner. The signal level distribution characteristics obtained in this case are the same when "O" (hard decision) is input and "1" (hard decision) is input on the transmitting side. In the same figure, the appearance frequency of each level measured by the receiving side demodulator output when "0" is transmitted on the transmitting side is illustrated, and 0 among the 8 levels appears the most frequently.
It has been shown that the appearance frequency does not become O even at other levels due to the presence of noise and the like. Level 3 in Figure 6
The following are determined to be "0" at the demodulator output, but 4 or more are determined to be "1" at the demodulator output, resulting in a bit error.

FIG. 7 shows another example of the conventional soft-decision signal distribution measurement method.

In FIG. 7, the PN pattern synchronization circuit 20 generates a PN pattern, and the signal level determination circuit 16 uses this to determine the signal level, but the PN pattern in this case must be synchronized at the output of the demodulator 15. There is.

Therefore, the timing synchronization circuit 23 detects the timing of the PN pattern at the demodulator 15 output by receiving the PN pattern output and the MSB of the il tN unit 15 output. The delay circuit 22 has a delay time that changes according to the timing signal of the timing synchronization circuit.
The PN pattern generated by the pattern generation circuit 21 is delayed. The PN pattern generation circuit 21 generates a PN pattern on the transmitting side.
It generates the same PN batts as the pattern generating circuit 11, and therefore, the circuit of FIG. 7 can measure the signal level distribution characteristics in the same way as the circuit of FIG. 4.

[Problem to be solved by the invention]

In the soft decision signal level distribution measurement method shown in Fig. 4,
Although it is possible to obtain the signal level distribution characteristic curve most accurately, it is difficult to apply it to communications between remote locations or mobile communications because the transmitter and receiver must be directly connected. Furthermore, it is not possible to measure signal level distribution characteristics while performing actual communication.

In the soft-decision signal distribution measurement method shown in FIG. 7, measurement is possible even when the transmitting side and the receiving side are far apart, but it is necessary to synchronize the PN pattern on the receiving side. Such a synchronous circuit is difficult to implement due to the large circuit scale, and when the error rate in the demodulator output is large, it becomes difficult to achieve synchronization, resulting in a decrease in measurement accuracy.
Measurement may become impossible. Also, in this method, it is not possible to measure the signal level distribution characteristics while performing actual communication.

The present invention is intended to solve the problems of the prior art, and can be applied even when the transmitting section and receiving section are separated, has a simple circuit configuration, and can perform actual communication. The purpose of the present invention is to provide a method that can measure signal level distribution characteristics.

[Means to solve the problem]

As the basic configuration of the present invention is shown in FIG. 1, the transmitting side transmits a signal modulated with a predetermined modulation method according to the input signal, and the receiving side demodulates the received signal to convert the input signal. In the communication system for reproduction, an error correction encoding circuit 5 is provided on the transmitting side, and an error correction decoder 26, a re-encoding circuit 27, and a signal level determining circuit 16 are provided on the receiving side. .

The error correction encoding circuit 5 performs error correction encoding on the input signal.

The error correction decoder section performs error correction decoding on the demodulated signal.

The re-encoding circuit 27 encodes the output of the error correction decoder 26 into the same error correction code as that on the transmitting side.

The signal level determining circuit 16 compares the delayed demodulated signal with the output of the re-encoding means 27 to determine its level.

[For production]

The soft-decision signal level distribution measurement method of the present invention has the basic configuration shown in FIG. 1, and operates as follows.

On the transmitting side, actual transmission data or PN pattern input is subjected to error correction encoding in the error correction encoding circuit section, and the output signal is sent to the transmitting section (Tx) via the transformer 12.
13, thereby generating a transmission signal modulated by a predetermined modulation method using an error correction coded signal, and this signal is transmitted to the receiving side via a transmission path.

On the receiving side, a receiving section (Rx) 14 receives this signal, and the received signal is demodulated through a demodulator 15 to reproduce an error correction encoded signal. The error correction decoder 26 performs error correction decoding on this signal to generate a signal consisting of the same data as the input to the error correction encoding circuit section on the transmitting side. This signal is used as the received data output. The re-encoding circuit 27 performs error correction encoding on the output signal of the error correction decoder 26 again using the re-encoding circuit 27, which includes the same circuit as the error correction encoding circuit 25 on the transmitting side.

The signal level determining circuit 16 determines the signal level by comparing bit by bit the output of the demodulator 15 and the output signal of the re-encoding circuit 27, which are input via the delay circuit 28. Therefore, the delay time of delay circuit 28 in this case is selected to be equal to the delay times of error correction decoder 26 and re-encoding circuit 27. Note that designation of the measurement pattern in the decoder 18 and measurement of the signal level distribution characteristic by counting the frequency of appearance of the corresponding signal level are the same as in the conventional case shown in FIG. 4 or FIG. 7.

In FIG. 1, as a result of error correction, the output of the error correction decoder 26 is the same as the input of the error correction encoding circuit 5 on the transmitting side; By re-encoding in the circuit, it is possible to obtain the same signal as the input of the modulator 12 on the transmitting side, so by using this as reference data,
Measurements of the signal level can be made, thereby determining the signal level distribution.

The error correction method in the basic configuration shown in Figure 1 is as follows:
Any method can be used, and there are no particular restrictions on the configuration of the encoding circuit, but differences in error correction ability will cause differences in the measurement accuracy of soft-decision signal distribution characteristics.

〔Example〕

FIG. 2 shows an embodiment of the present invention, in which the error correction encoding and error correction decoding systems are used at a coding rate R=1/2.
The configuration is shown when a convolutional code/Viterbi decoding method with constraint &=1 is used.

On the transmitting side, the error correction encoding circuit 5 has a coding rate R=
1/2. It performs convolutional encoding with the constraint length = 7, and uses a 7-bit shift register 251 and an exclusive OR (E
X-OR) circuits 252, 253, parallel/series (S/
P) Consisting of a conversion circuit 254 and a shift register 25. The output of the first to fourth bits and the seventh bit of the shift register 25t are input in parallel to the EX-OR circuit 252, and the signal obtained by inputting the transmission data or PN pattern in series to the shift register 251 is 1st bit, 3rd bit. 4th bit and 6th bit. 7th bit output in parallel EX-
The signal obtained by inputting it to the OR circuit 253 is
By inputting to the S conversion circuit 254, the P/S conversion circuit 5. produces a convolutionally encoded output consisting of a serial signal. The modulator 12 consists of a two-phase modulator, and the output from the error correction coding circuit section is used to control the transmission section (Tx
) 13 to generate a transmission signal, and this signal is transmitted to the receiving side via a transmission path.

On the receiving side, a receiving section (RX) 14 receives this signal. The demodulator 15 consists of a two-phase demodulator, and converts the received signal into two
A 3-bit demodulated output consisting of a binary folded code is generated by phase repeating. The error correction decoder 26 is a serial/parallel (S/
P) Conversion circuit 26! and coding rate R=1/2. To restraint length =
The Viterbi decoder 262 converts the 3-bit demodulated signal from the demodulator 15 into a parallel signal.
to generate an error corrected received data output.

The re-encoding circuit 27 consists of the same circuit as the error correction encoding circuit, including a 7-bit shift register 27I, an exclusive OR (EX-OR) circuit 2721273, and a parallel/serial (P
/S) conversion circuit unit, and generates an output obtained by convolutionally encoding the output of the error correction decoder 26.

The signal level determining circuit 16 determines the signal level by comparing bit by bit the output of the demodulator 15 and the output signal of the re-encoding circuit 27, which are input via the delay circuit 28. Therefore, the delay time of delay circuit 28 in this case is selected to be equal to the delay times of error correction decoder 26 and re-encoding circuit 27. Note that designation of the measurement pattern in the decoder 18 and measurement of the signal level distribution characteristic by counting the frequency of appearance of the corresponding signal level are the same as in the conventional case shown in FIG. 4 or FIG. 7.

In the embodiment shown in FIG. 2, signal level distribution characteristics can be measured in the same way even when other error correction methods are used.

Further, although the embodiment shown in FIG. 2 uses a two-phase modulator and a two-phase demodulator, it is also possible to use a four-phase or polyphase modulator or demodulator.

FIG. 3 shows another embodiment of the present invention, illustrating a configuration using a four-phase modulator and a four-phase dredge.

On the transmitting side, the error correction encoding circuit 5 generates an error correction encoded output consisting of orthogonal ■ channel and Q channel signals in response to transmission data or PN pattern input. The modulator 12 consists of a four-phase modulator, and receives orthogonal code signals 1. The transmitter (Tx
) 13 is subjected to four-phase modulation to generate a transmission signal, and this signal is transmitted to the receiving side via a transmission path.

On the receiving side, a receiving section (RX) 14 receives this signal. The demodulator 15 consists of a 4-phase demodulator and converts the received signal into 4 phases.
Phase demodulation is performed to generate 3-bit demodulated outputs each consisting of a binary folded code corresponding to the orthogonal code signals I and Q.

The error correction decoder 26 performs error correction decoding on this input,
Generates error corrected received data output.

The re-encoding circuit 27 consists of the same circuit as the error correction encoding circuit section, and uses the output of the error correction decoder 26 to generate orthogonal code signals 1. An error correction encoded output consisting of Q is generated.

The signal level determination circuit 16 receives the output of the I channel of the demodulator 15 which is input via the delay circuit 28 and the re-encoding circuit 27.
The signal level is determined by comparing the output signal of (1) with the output of the channel for each focus. Therefore, the delay time of the delay circuit 28 in this case is selected to be equal to the delay time of the error correction decoder 2G and the re-encoding circuit 27. Note that designation of the measurement pattern in the decoder 18 and measurement of the signal level distribution characteristic by counting the frequency of appearance of the corresponding signal level are the same as in the conventional case shown in FIG. 4 or FIG. 7.

In the embodiment shown in FIG. 3, the configuration is shown in which the signal level distribution characteristics are measured only for the signal of the channel (1). It is also possible to measure the signal level distribution characteristics of a Q-channel signal using this method. Furthermore, by providing circuits for signals of both channels, it is also possible to measure the signal level distribution characteristics of signals of both channels.

In this way, in the soft-decision signal level distribution characteristics measurement method of the present invention, the input signal is subjected to slander correction coding on the transmitting side, and the signal level distribution characteristics are measured on the receiving side using the error correction decoded output as a reference signal. I try to do it. In this case, the decoded output of the error correction decoder is not completely error-free, but the error rate is much smaller than the error rate that occurs in the transmission path or the soft-decision distribution probability that you are trying to measure.
Measurement accuracy is virtually undegraded.

Furthermore, in an actual communication system, an error correction encoding circuit and an error correction decoder are usually already in use, so there is almost no increase in circuit scale by applying the method of the present invention.

〔Effect of the invention〕

As explained above, according to the present invention, the transmitting side performs error correction encoding on the input signal, and the receiving side uses the error correction decoded output to measure the signal level distribution characteristics. It can be used even if the receiver is separated from the receiver, the circuit configuration is simple, and the signal level distribution can be measured while performing actual communication.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the basic configuration of the present invention, Fig. 2 is a diagram showing an embodiment of the invention, Fig. 3 is a diagram showing another embodiment of the invention, and Fig. 4 is a diagram showing a conventional soft FIG. 5 is a diagram showing an example of the determination signal level distribution measurement method. FIG. 5 is a diagram showing the demodulator output level and the output of the signal level determination circuit. FIG. 6 is a diagram showing an example of signal level distribution characteristics. Conventional soft-decision signal level distribution measurement method % formula % 16...Signal level determination circuit 18--Dehder 19-Appearance frequency counter 5--Error correction encoding circuit -Error correction decoder 27 −・−Recoding circuit

Claims (1)

[Claims] In a communication system in which a transmitting side transmits a signal modulated using a predetermined modulation method according to an input signal, and a receiving side demodulates the received signal and reproduces the input signal, the input signal is error-corrected. An error correction encoding means (25) for encoding the demodulated signal is provided on the transmitting side, and an error correction decoding means (26) for error correction decoding the demodulated signal.
), a re-encoding means (27) for encoding the output of the error correction decoding means (26) in the same error correction code as that on the transmitting side, and a signal obtained by delaying the demodulated signal as the output of the re-encoding means (27). A soft-decision signal level distribution measuring method characterized in that a signal level determining means (16) for comparing and determining the level is provided on the receiving side.