JPH04196946A - Method and device for multilevel orthogonal amplitude modulation - Google Patents

Abstract

PURPOSE:To facilitate the acquisition of synchronism on the side of a demodulator while preventing the offset of a DC level at a base band signal by changing the arrangement of symbols on a phase plane and transmitting signals by using the combination of signal points rotationally symmetric for each 90 deg. on each phase plane. CONSTITUTION:In the case of P=7 and N=2, a transmitting data train 101 converted to seven data trains is inputted to a data train number and parallel/ serial conversion circuit 10, converted to the two pairs of four parallel transmitting data trains and converted to a pair of four serial transmitting data trains 102 later. A signal point combination change circuit 11 changes the symbol arrangement of inputted signal points and outputs four serial data trains 103 inputted to the modulation circuit. A multilevel modulation circuit 12 executes the multilevel orthogonal amplitude modulation of 12QAM to the four modulation circuit input serial data trains 3 and outputs a modulated signal 104.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a multilevel quadrature amplitude modulation method and apparatus used in a digital microwave communication system from the viewpoint of effective frequency utilization.

[Conventional technology]

In this type of conventional multilevel quadrature amplitude modulation method, P=7, N=
An example of a modulation device in case 2 is shown in FIG. The transmission data string 201 converted into 7 data strings is the number of data strings/
The signal is inputted to the l parallel-to-serial conversion circuit 20, where it is converted into two sets of four-column parallel transmission data strings, and then converted into 71 sets of four-column transmission serial data strings 202. The multilevel modulation circuit 21 outputs (27/2 cape) 12 to the input serial data string 202.
QAM multilevel orthogonal amplitude modulation is performed and a modulated signal 203 is output.

FIG. 4 is a diagram showing a combination of signal points on a phase plane according to this conventional example. ′ two consecutive independent times ta during multilevel quadrature amplitude modulation,
Let the phase planes at tb be A and B, respectively. The arrangement of signal points on the A and B polyphase planes is shown in FIG. 4(a). A 27-value multivalue signal is expressed as a combination of signal points on the A and B multiphase planes as shown in FIG. 4(b). Here, m is the order of the combination of signal points on the phase planes A and H.

[Problem to be solved by the invention]

In the conventional multilevel quadrature amplitude modulation method described above, when configuring a 2P multilevel signal on N phase planes, the arrangement of approximately 2p'8 symbols on one phase plane is rotationally symmetrical. Also, because the correspondence between the 2P value multivalue signal and the combination of signal points on each phase plane is not accurate, when the 2P value signal is viewed on one phase plane, it is divided into four phase quadrants. The problem is that because the signals are not distributed evenly to the signal points equidistant from the phase origin, a DC level offset occurs in the baseband signal input to the modulator, causing a problem when synchronization is pulled in during demodulation. There was a point.

[Means to solve the problem]

In the multilevel quadrature amplitude modulation method of the present invention, P is an integer equal to or greater than 3, and N is equal to or equal to 2.
In a multi-value quadrature amplitude modulation method in which a 2p-value multi-value signal is expressed by a combination of N phase planes each having approximately 2P/8 signal points, where P is an integer that is relatively prime and less than P. , the arrangement of the signal points is rotationally symmetrical every 90 degrees in any of the N phase planes.

The multi-value quadrature amplitude modulation device of the present invention has N (
In order to express it by a combination of phase planes (N is an integer equal to or greater than 2, relatively prime to P, and less than P), the P transmission data string is converted into a data string of approximately P/N columns. The column conversion circuit and the output data from the column conversion circuit are arranged so that the arrangement of signal points of the modulated signal subjected to multilevel orthogonal amplitude modulation by the output data string is rotationally symmetrical every 90 degrees in any of the N phase planes. It includes a signal point combination conversion circuit that converts a data string, and a modulation circuit that outputs a modulated signal subjected to multilevel orthogonal amplitude modulation using the data string from the signal point combination conversion circuit.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

□FIG. 1 is a block diagram of an embodiment of the multilevel quadrature amplitude modulation device of the present invention, where P=7. The case where N=2 is shown.

The transmission data string 1゜1 converted into 7 data strings is input to the data string number/digital serial conversion circuit 10, and each of 2M 4
After being converted into parallel transmission data strings of 4 columns, it is converted into a set of 4 columns of transmission serial data strings 102. The signal point combination conversion circuit 11 performs conversion on the symbol arrangement of the input signal points, and converts it into a four-column modulation circuit input serial data string 10.
Outputs 3. The multilevel modulation circuit 12 performs 12QAM multilevel orthogonal amplitude modulation on the four columns of modulation circuit input serial data strings 103 and outputs a modulated signal 104.

FIG. 2 is a diagram showing the phase plane of the modulated signal and the combination of signal points after conversion by the signal point combination conversion circuit 11. Let the phase planes at two consecutive and independent times ta and tb be A and B, respectively. On the A and B polyphase planes, as shown in FIG. 2(a), three sets (1-4, 5-8, 9-12) of four signal points arranged rotationally symmetrically are provided.

When transmitting a 27-value multi-value signal (27/2≠)12
On the phase plane using QAM, (12×12=) 144 combinations of signal points are possible.

Therefore, as shown in Fig. 2(b), the signal points on the multiples of 4 side from the phase plane A (8 from 1 to 8 or 4 from 9 to 12) and the signal points on the multiples of 4 from the phase plane B. (12 pieces from 1 to 12 or 1
~8) signal points are combined, totaling 27
A combination of signal points. Note that m is the phase plane A, B
This is the order of the combinations of signal points.

Above P=7. Although the embodiment has been described for the case where N=2, P is an integer of 3 or more, N is an integer of 2 or more, and N is any P that is smaller than P and prime with P.

The same effect can be obtained by applying the present invention to N combinations.

〔Effect of the invention〕

As explained above, the present invention converts the symbol arrangement on the phase plane in a multilevel orthogonal amplitude modulation method that transmits one signal as a combination of signal points on a plurality of phase planes, and converts the symbol arrangement on each phase plane into 90 By transmitting signals using a combination of signal points that are rotationally symmetrical for each degree, the DC level in the baseband signal of the modulator input, which is caused by uneven signal point density in each quadrant in each phase plane, can be reduced. This has the effect of preventing offset and facilitating synchronization pull-in on the demodulator side.

[Brief explanation of the drawing]

Fig. 1 is a professional diagram showing one embodiment of the present invention, and Figs. 2 (a) and (b) are diagrams showing the phase plane of the modulated signal and the combination of signal points in the embodiment shown in Fig. 1. , FIG. 3 is a block diagram showing an example of a conventional multilevel quadrature amplitude modulation device, and FIGS. 4(a) and (b) are diagrams showing combinations of phase planes and signal points according to the conventional example shown in FIG. It is. 10... Number of data strings/parallel-serial conversion circuit, 11... Signal point combination conversion circuit, 12... Multi-level modulation circuit, 1
01... Transmission data string, 102... Transmission serial data string, 103... Modulation circuit input serial data string, 104...
...Modulation signal.

Claims (1)

[Claims] 1, P is an integer equal to or greater than 3, and N
Let be an integer equal to or greater than 2, relatively prime to P, and less than P, and the combination of N phase planes each having approximately 2^P^/^N signal points has a value of 2^P. In a multilevel quadrature amplitude modulation method for expressing a multilevel signal,
A multilevel orthogonal amplitude modulation method, characterized in that the arrangement of the signal points is rotationally symmetrical every 90 degrees in any of the N phase planes. 2, 2^ P-value (P is an integer equal to or greater than 3) multi-valued signals of N (N is an integer equal to or greater than 2 and relatively prime to P and less than P) A column conversion circuit that converts P transmission data sequences into approximately P/N data sequences to be expressed by a combination of phase planes, and arrangement of signal points of a modulated signal that is multi-level orthogonal amplitude modulated by the output data sequence. is 90 in any of the N phase planes.
a signal point combination conversion circuit that converts the data string from the column conversion circuit so that it becomes rotationally symmetrical for each degree, and a modulation that outputs a modulation signal that is multi-level orthogonal amplitude modulated with the data string from the signal point combination conversion circuit. A multilevel quadrature amplitude modulation device characterized by comprising a circuit.