JPH05276211A - Hierarchized modulation system for digital signal - Google Patents

Abstract

PURPOSE:To lover the error rate of significant data and to effectively use a transmission line by performing hierarchized modulation fitting in the significance of a signal. CONSTITUTION:Plural digital signals 4 are inputted to a modulation factor control circuit 2. Such signals 4 are discriminated by the significance. The circuit 2 controls the significance corresponding to the signal 4. The output of an oscillator 3 is modulated by a modulation circuit 1 based on the output of the circuit 2, and desired modulated output 5 can be obtained. In such a case, it is possible to perform transmission with high efficiency by allocating information with high significance to a first bit and information with low significance to a third bit.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a modulation system used when transmitting digital signals.

[0002]

2. Description of the Related Art Conventionally, a modulator used for transmitting a digital signal uses phase modulation or quadrature amplitude modulation, but the distance between codes (in the case of phase modulation, the phase difference between codes and quadrature amplitude modulation). In the case of modulation, the difference in amplitude between the codes) was evenly spaced. A signal space diagram of the conventional 8-phase phase modulation system is shown in FIG. As shown in this figure, the intervals between the respective codes are 45 degrees. Since the error occurrence rate with respect to noise is inversely proportional to the distance between codes, the error rate of any code is the same and the strength with respect to noise is also the same in the conventional modulation scheme in which the distances between codes are all the same. Therefore, when the noise intensity exceeds a certain value, the error occurrence rate of any signal rapidly increases. In a communication path in which the noise level fluctuates greatly, such as rain attenuation in satellite communication, it becomes impossible to receive a signal at all during heavy rain. Also, if a large margin for rain is taken, useless power will be sent when it is sunny.
Although some of the information to be transmitted is very important and some is not so important, the non-important information may be slightly erroneous, but it is desirable to convey the important information without error. However, the conventional modulation method cannot make the distinction. Therefore, a method of distinguishing information according to its importance, that is, a method of layering information, depends on the encoding method.

[0003]

The problems to be solved by the present invention are that the error rate characteristic cannot be changed at the stage of modulation due to the importance of information in the conventional system, and that the value of noise strength is If this is exceeded, the error occurrence rate for all signals will rapidly increase, making communication or broadcasting impossible at all.

[0004]

According to the present invention, the rate of error with respect to noise is changed, that is, hierarchized, by modulating the code distance in the signal space at unequal intervals. By increasing the distance for important data and making it stronger against noise and shortening it for less important data, hierarchical modulation of digital signals can be performed, and efficient signal transmission can be performed.

[0005]

The operation of the modulation system of the present invention will be described below with reference to a circuit configuration diagram (FIG. 1) and a signal space diagram (FIG. 2) showing an embodiment of the phase modulation system. The plurality of digital signals 4 are input to the modulation degree control circuit 2. At this time, it is assumed that the digital signals are distinguished by importance. Here, since the 8-phase modulation is used, the digital signal input is 3 bits. The modulation degree control circuit 2 controls the modulation degree as shown in Table 1 according to the signal.

[0006]

[Table 1]

In the example shown in Table 1, the distance of the first bit is long and the distance of the third bit is short, and the arrangement is as shown in FIG. 2 in the signal space diagram. In the conventional modulation method, the distance of each code is constant at 45 degrees, and the arrangement is as shown in FIG. Based on the modulation degree control circuit 2, the output of the oscillator 3 is modulated by the modulation circuit 1 to obtain a desired modulated wave output 5. FIG. 4 shows the code error rate characteristics with respect to the signal level (C / N). As shown in FIG. 4, in 8-phase phase modulation,
When it becomes smaller than 18 dB, the error rate deteriorates sharply for all codes, but in the layered modulation system of the present invention, the signal can be transmitted even if the first bit is weakened to 12 dB. Assign important information to the first bit,
By assigning less important information to the third bit,
It is possible to perform efficient transmission. Further, the modulation system of the present invention operates in a wide range of signal levels because all bits do not deteriorate at the same time as shown in FIG. FIG. 5 shows an embodiment in which the quadrature amplitude modulation is hierarchized. In the conventional 16QAM (16-phase quadrature amplitude modulation),
Although the distances a and b between the codes are the same, in the present invention, the distance is changed to weight the signals. The ratio of a to b may be arbitrary. In the case of the conventional 16QAM, the code error rate is 10 ⁻³
The C / N ratio for realizing the above is about 19 dB, but a and b
In the layered modulation with the ratio of 1: 2, the C / N is improved to about 15.5 dB for 2 out of 4 bits.

[0008]

Since the present invention is constructed as described above, it has the following effects. By performing hierarchical modulation according to the importance of the signal, the error rate of important data can be reduced, and the limited transmission line can be effectively used. The attenuation due to rainfall on the satellite line may be interrupted because the time is short or there is a large attenuation. According to the present invention, since a wide range of signal levels can be dealt with, the time during which communication is interrupted is shortened.

[Brief description of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention.

FIG. 2 is a signal space diagram showing an embodiment of the present invention.

FIG. 3 is a signal space diagram of a conventional 8-phase phase modulation method.

FIG. 4 is a diagram showing a code error rate characteristic with respect to a signal level.

FIG. 5 is a signal space diagram showing an embodiment of the present invention.

[Explanation of symbols]

 1 Modulation Circuit 2 Modulation Degree Control Circuit 3 Oscillator 4 Digital Signal Input 5 Modulation Wave Output 11, 12, 13 Code on Signal Space Diagram 21 1st Bit Error Rate Curve 22 2nd Bit Error Rate Curve 23 3rd Bit Error rate curve 24 Error rate curve of 8-phase modulation

Claims (4)

[Claims] 1. A hierarchical modulation system for digital signals, characterized in that the distances between codes in a signal space diagram are made unequal by changing the modulation degree for some signals of a plurality of digital signal inputs. . 2. The modulation system is a phase modulation system.
Hierarchical modulation method of the described digital signal. 3. The modulation method is an amplitude modulation method.
Hierarchical modulation method of the described digital signal. 4. The hierarchical modulation system for digital signals according to claim 1, wherein the modulation system is a quadrature amplitude modulation system.