JPS5854703B2 - Judgment circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a determination circuit that determines eight or more multivalue quadrature amplitude modulation signals.

When increasing the data transmission rate beyond the modulation rate, a method is generally adopted in which a plurality of signal points are arranged on a phase plane.

Such methods include phase modulation (PSK), which transmits signals based on how much the phase of the carrier wave differs from the phase of the reference wave, and multilevel quadrature amplitude, which transmits signals based on the difference in phase and amplitude. Modulation (hereinafter simply referred to as multilevel QAM) methods are known.

For example, in the 8-phase modulation method, as shown in Fig. 1, 8 ideal points 11 to 18 are set every 45 degrees with the ideal point 11 of absolute phase zero as a reference, and 8 types of data bits are assigned to these points. Allocate and communicate.

For example, CCITT Recommendation v1 Recommendation 129 16-value Q
In the AM method, as shown in Figure 2, 16 ideal points 19~
34 are provided, and 16 types of data bits are assigned to these for communication.

In this method, an ideal point 19 with a relative amplitude of 3 is located on the absolute phase zero.
and an ideal point 20 with a relative amplitude of 5 are arranged.

Similarly, two types of ideal points 21 to 26 are arranged at each point where the phase changes by 90 degrees.

Also, an ideal point 27 with a relative amplitude of 7 and a relative amplitude of 3 on the absolute phase of 45 degrees. Two ideal points 28 of /T are arranged.

Similarly, two types of ideal points 29 to 34 are arranged every time the phase changes by 90 degrees.

However, in the case of a received signal containing noise, the signal is not necessarily placed at each of the above-mentioned ideal points.

Therefore, these communication systems require a determination circuit that determines that when a received signal belongs to a certain area, it is a signal at an ideal point corresponding to that area.

When determining where a received signal exists in the phase plane, it is best to draw a perpendicular bisector of the line segment connecting all two adjacent ideal points and use it as the determination boundary. There are also fewer errors in superposition.

For example, in the 8-phase phase modulation method shown in FIG. 1 and the 16-value QAM method shown in FIG. 2, the boundaries shown by solid lines in the figures are the determination boundaries.

Comparing the determination boundaries of both systems, it is found that in the 8-phase phase modulation system, the ideal points exist on the same circumference, so all boundary lines are straight lines that intersect at the origin O.

Therefore, determining the received signal is relatively easy.

On the other hand, in the case of the QAM method, ideal points exist on four types of circumferences, and the boundary lines are complicated line segments as shown in the figure.

For this reason, determination of received signals in the QAM system has conventionally relied on the following method.

That is, the X component and Y component of the received signal in the orthogonal coordinate system
Read-only memory (ROM) using components as addresses
This is a method of referencing the value recorded in the .

Although this method is simple, in order to improve the accuracy of the determination, it is necessary to specify the address input corresponding to each ideal point in detail, which has the disadvantage that the required ROM size increases. .

For example, when the received signal has 8-bit precision, 28 x 28
= 216 memory capacity is required, and even if the judgment area is limited to the first quadrant by coordinate transformation, - that is, 1/4 of this
6 required word memory.

By the way, recent modems are usually equipped with automatic equalization using a microcomputer in order to correct distortion in communication lines.

If this existing microcomputer is used to perform calculation-based judgments, there is no need for a ROM for judgment, and at the same time there is no need to add a special arithmetic unit for judgment.However, in the QAM method, boundaries are complicated. Therefore, ROM was used for the determination.

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a determination circuit that does not require a ROM for determination.

In the present invention, first and second determining sections and a mapping section are provided, and among these, the first determining section determines which of the eight regions obtained by dividing the phase plane the received signal belongs to.

In addition, the mapping unit transfers the received signal to a specific one of these eight regions on the phase plane x=o, y=o, and x+y=o.
The second determination unit determines which ideal point the received signal corresponds to in the transformed area.

Then, the signal is decoded in the decoding section based on the determination outputs of the first and second determination sections.

Since all such signal processing can be performed by calculation, a ROM for determination is not required, and the above-mentioned purpose can be achieved in a distant manner.

The present invention will be described in detail below with reference to Examples.

FIG. 3 shows a determination circuit in one embodiment of the present invention.

The demodulated 16-value QAM signal (hereinafter referred to as input signal) is applied to the input terminal 41, and is sent to the first determination section 42 and the mapping section 43.
is supplied to

The first determination unit 42 determines which of the regions 0 to 7 shown in FIG. 4 the demodulated input signal belongs to according to the eight boundary lines shown in FIG.

Although this determination can be performed independently of the domain transformation of the input signal by the mapping section 43, in this embodiment, the mapping section 43
This is done at the same time as the area conversion.

Although the mapping unit 43 may ultimately convert the input signal into any region, a case where the input signal is converted into region 0 will be taken as an example.

First, in the first step, the determination unit 42 determines whether the Y coordinate of the input signal is positive or negative.

If it is negative, the mapping unit 43 converts the input signals existing in regions 4 to 7 to regions 0 to 3 with the X axis as the center of symmetry.

Next, in the second step, the determination unit 42 determines whether the X coordinate of the input signal is positive or negative.

If it is negative, the mapping unit 43 converts the input signals existing in areas 2 and 3 to areas 0 and 1 with the Y axis as the center of symmetry.

Finally, in the third step, the determination unit 42 determines on which side of the straight line Y=X the input signal is present.

If the input signal exists in area 1, the mapping unit 43 transforms the input signal into area 0 with Y=X as the center of symmetry.

In the three-stage discrimination by the first determination unit 42, the stage in which the input signal is not converted is represented by a symbol "x", and the stage in which the input signal is transformed is represented by a symbol "○". The relationship between and the discrimination results of each stage is as shown in the table below.

In other words, it is uniquely determined in which region the input signal exists through three stages of discrimination.

At the stage when the determination of the region of the input signal has been completed by the determining section 42, the input signal has been converted to region 0.

This converted input signal is then supplied to the second determination section 44.

The determination unit 44 determines the signal according to the boundary line in area 0 as shown in FIG.

The boundary line is defined by four ideal points 19, 20, 27, 28, and if they are given coordinates in terms of relative amplitude, then X-0,5Y-1,75=0, Y=1.5,
X=4, X+Y-4=0, 1.5Y-X+1.75
It can be expressed as =O.

Therefore, the determination unit 44 determines whether the input signal is a converted input signal or an input signal which is originally present in region 0, as shown in the flowchart of FIG. 6, for example.

In other words, the determination unit 44 determines the boundary line y=1.5 as a first step.
Determine which side of the input signal is present.

For input signals that exist below the boundary line y-1, 5, there are three corresponding ideal points (19, 20° 27
) exists, so it is further determined whether it exists on the left or right side of the boundary line X=4.

As a result, it can be seen that if the value of the X coordinate of the input signal is thicker than 4 (relative amplitude 4), the input signal corresponds to the ideal point 20 located at the coordinate (5tO).

In addition, if the value of the X coordinate is smaller than 4, that is, if the input signal exists on the left side of the coordinate, then the boundary line
, 5Y-1, 75=0 on which side the input signal is present is determined.

As a result, the ideal point 27 located at the coordinates (1°1)
Either the ideal point 19 located at the coordinates (3,0) or the ideal point 19 is determined.

On the other hand, when the input signal exists above the boundary line y-1, 5, there are similarly three corresponding ideal points (20, 27, 2
8) Exists.

In this case, first, it is determined which side of the boundary line X+Y-4=O it is on, and thereby it is determined whether the input signal corresponds to the ideal point 27 located at the coordinates (Ll).

For input signals that do not correspond to the ideal point 27, next it is determined which side of the boundary line 1.5Y-X+1.75=O the input signal is located at the coordinates (S, O). It is determined whether the point corresponds to point 20 or the ideal point 28 located at coordinates (3, 3).

In this way, the determination result regarding the region by the first determination section 42 and the information on the ideal point in region 0 by the second determination section 44 are supplied to the decoding section 45, and the output terminal 46 outputs the final determination output. , a data bit corresponding to one of the 16 ideal points is output.

For example, if the first determination section outputs region 3 and the second determination section outputs ideal point 20, decoding section 45 will output data bits corresponding to ideal point 24 to output terminal 46.

In this way, according to the present invention, in realizing the optimal boundary line,
By combining the mapping circuit part and two types of judgment circuit parts, each judgment algorithm is simplified, so judgment can be made only by calculation, and the large capacity R required in the past is reduced.
OM becomes unnecessary.

Note that the signal processing of the first and second determining sections and the mapping section of the determining circuit of the present invention can be performed quickly if a microcomputer controlled by a program performs the signal processing.

[Brief explanation of the drawing]

Figure 1 is a signal determination diagram showing the arrangement of ideal points in the 8-phase phase modulation system and the optimal boundary line for determination, and Figures 2 to 6
The figures are for explaining one embodiment of the present invention, of which Figure 2 is a signal determination diagram showing the arrangement of ideal points and boundary lines for determination in the 16-value QAM system, and Figure 3 is a signal determination diagram showing the boundary line for determination. A block diagram of the circuit, FIG. 4 is a judgment area diagram showing the area judged by the first judging section, FIG. 5 is a judgment boundary diagram showing the boundary judged by the second judging section, and FIG. It is a flowchart of the determination performed by the determination unit. 0 to 7... area, 19 to 34... ideal point, 42... first determination section, 43...
Mapping unit, 44... second determination unit.

Claims (1)

[Claims] For 18 or more multilevel orthogonal amplitude modulation signals, 1
In a determination circuit that determines an input signal using an optimal boundary line that divides a phase plane so that ideal points and regions correspond one-to-one, the position of the input signal is determined by orthogonal coordinates (x , y) when x=o, y=o and X
A first determination unit that determines by calculation which of the eight regions divided by ±Y=0 the input signal belongs to; a mapping unit that converts the area into any one of the eight divided areas by moving symmetrically with respect to the line segment; and a calculation unit that performs a calculation on the area converted by the mapping unit according to the optimal boundary line. A determination circuit comprising: a second determination section that determines an ideal point to be determined; and a decoding circuit that decodes a signal corresponding to each ideal point based on the determination outputs of the first and second determination sections. . 2 The area to be transformed by the calculation of the mapping unit is X≧O2￥≧0
2. The determination circuit according to claim 1, wherein the determination circuit is a region satisfying X-Y2O. 3. The determination circuit according to claim 1, wherein the calculations of the first and second determination sections and the mapping section are performed by a microcomputer controlled by a program.