JPS62133842A - Multi-value orthogonal amplitude modulation system - Google Patents

Abstract

PURPOSE:To prevent the deterioration of a bit error rate by inserting a signal point arrangement converter between a differential/rotation object coder and a D/A converter to widen the interval between signal points closest to the boundary of each quadrant. CONSTITUTION:Input data of 4-bit 2-series input data is converted by a binary signal of signal point arrangement to eliminate the phase uncertainty of a recovered carrier in the differential/rotating object coder 1 and the result is fed to a signal point arrangement converter 4. Then the conversion is applied so as to widen the interval between closest signal points to the boundary of each quadrant and the result is inputted to a modulator 3 via a D/A converter 2. The modulator 3 outputs the carrier wave while applying orthogonal amplitude modulation based on the D/A conversion output.

Description

[Detailed Description of the Invention] [Summary] In a multilevel orthogonal amplitude modulation system, a signal point arrangement converter is provided between a differential/rotating symmetric encoder and a digital/analog converter that removes phase uncertainty of a reproduced carrier wave. is inserted, and the interval between the signal points closest to the boundary of each quadrant is widened to improve the deterioration of the bit error rate.

[Industrial application field]

The present invention relates to an improvement in a multilevel quadrature amplitude modulation method used in digital microwave communications.

In recent years, various digital microwave systems, such as 64 (
I! Although the L-quadrature amplitude modulation method (hereinafter abbreviated as 640AM method) has been put into practical use, there is a trend towards 256QAM method and more multilevel modulation in order to improve frequency utilization efficiency.

However, as multileveling progresses, the required performance of the device becomes stricter, so it is necessary for the device to minimize deterioration in, for example, bit error rate.

[Conventional technology]

FIG. 3 is a block diagram of a conventional example, and FIG. 4 is a signal point arrangement diagram of FIG. 3, but shows the case of the 2560 static system.

In addition, the numbers written below each signal point are from the second bit to
The corresponding data is obtained by adding the first focus number written in parentheses at the upper right of each quadrant to the front of the second bit of the fourth bit data. For example, the data for point A is written as 100100, but 1 in the upper right corner of the first quadrant
Adding 1 actually indicates 11001100.

Now, the operation of FIG. 3 will be explained with reference to FIG. First, in FIG. 3, two input 4-bit series (Ich
, Qch) is applied to the differential encoder 11 in the differential/rotating symmetric encoder l.

Here, "Digital Microwave Communication" supervised by Moriji Kuwahara, published by Planning Center on March 1, 1985, p. 106-107.
As shown in , information is not placed at the position of point 18, but information is placed at the transition of the position so that correct data can be demodulated without knowing the absolute phase of the transmitted signal.

That is, the differential encoder 11 performs a summation operation of 4 on yL = xL'', and the receiving side differential decoder (not shown) performs the summation operation on
By performing the difference calculation of iJ lE (xL +41))'f-1=''b and converting it to the original signal, demodulation can be performed without knowing the absolute phase of the transmitted signal.

Note that yL indicates the encoder output, and yL indicates the encoder input. The summation operation and the difference operation are paired operations, and the two are collectively called differential conversion.

Next, the output of the differential encoder 11 is further transmitted to a rotationally symmetric encoder 12.
As shown in FIG. 4, the signs of the second to fourth bits are arranged so that the same signs in each quadrant are spaced 90 degrees apart.

For example, signal point B in the fourth quadrant of FIG. (excluding 1-bit and 7-bit codes). Therefore, during demodulation, the phase of the reference carrier wave is 0.
Even if there is a phase uncertainty of 90, 180, 270 degrees and 90 × n degrees, there will be no change in the second to fourth bits, so the above differential conversion can be performed only on the first bit signal. Usually, the second to fourth bit signals are passed through without being converted.

Here, n indicates an integer.

Therefore, when 11001100 is input to the rotational encoder 12, 11111111 is outputted, which is converted to the maximum analog amount by the digital/analog converter 21.22,
The modulator 3 performs orthogonal amplitude modulation on the carrier wave, and the carrier wave is placed at the position of point A.

Thereafter, the input data is converted into an analog quantity corresponding to each position in the point layout diagram No. 41 in FIG. 4, and arranged at the positions shown in FIG. 4, respectively.

[Problem that the invention seeks to solve]

Here, as shown in the signal point arrangement diagram of FIG. 4, within the same quadrant, for example, the lower 3 bit signal point D (000010)
Even if it is mistaken for the adjacent bit 00111 or 001010, only one bit will be lost.

However, when an error occurs beyond the quadrant, a multi-bit error occurs. For example, as shown in the column "Number of errors when crossing quadrants" in FIG. 4, a maximum of 6 bits may be erroneous. Therefore, there is a problem that the error rate deteriorates.

[Means for solving problems]

The above problem can be solved by providing a signal point constellation converter 4 in the multilevel quadrature amplitude modulation section, as shown in FIG. This problem is solved by the multiplant quadrature amplitude modulation method of the present invention, which improves the error rate.

[Effect]

The present invention reduces the possibility of errors occurring across quadrants by widening the spacing between the signal points closest to the boundaries of each quadrant.

That is, a signal point arrangement converter 4 in which the signal point arrangement shown in FIG. I converted it to a signal point arrangement and added it to the digital/analog converter. Therefore, the number of erroneous signal points beyond the quadrant is reduced, so the bit error rate is improved.

〔Example〕

FIG. 1 is a block diagram of an embodiment of the present invention, and FIG. 2 is a signal point constellation diagram of FIG. 1. The added part in the embodiment of the present invention is a signal constellation converter 4.

In addition, the same symbols indicate the same objects throughout the figures, and 256
The case of 0 meter method is shown.

Therefore, the operation shown in FIG. 1 will be explained with reference to FIGS. 2 and 4.

As shown in FIG. 1, two input 4-bit series (I c
h, Qch) is converted by a differential/rotation symmetric encoder 1 into a binary signal having a signal point arrangement as shown in FIG. 4, and is applied to a signal point arrangement converter 4. This signal point constellation converter is composed of, for example, a read-only memory,
Since the data for converting the signal point arrangement in Figure 4 to the signal point arrangement in Figure 2 is written, the output from the rotational encoder is attenuated to create the signal point arrangement as shown in Figure 2. 256Q
AM waves can be obtained. This improves the bit error rate.

〔Effect of the invention〕

As explained in detail above, since the interval between the signal points closest to the boundary of each quadrant is widened, there is an effect that the deterioration of the bit error rate is improved.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a signal point arrangement diagram of Fig. 1, Fig. 3 is a block diagram of a conventional example, and Fig. 4 is a signal point arrangement diagram of Fig. 3. . In the figure, 1 is a differential/rotation symmetric encoder, 2 is a digital/analog converter, 3 is a modulator, and 4 is a signal point constellation converter.塘2 Diagram I Reverse" Kida 1's Pro-Novshi 4 Graduation 3 Tosho

Claims (1)

[Claims] A differential/rotating symmetrical code unit (1) that encodes a plurality of input digital signals so that phase uncertainty of a reproduced carrier is removed; and the differential/rotating symmetrical code unit (1). In the multilevel quadrature amplitude modulation section, which includes a digital/analog converter (2) that converts the output of A multilevel orthogonal amplitude modulation system characterized in that a signal point arrangement converter (4) is provided to widen the interval between signal points closest to the boundary of a quadrant, thereby improving the bit error rate.