JPS6124354A - Signal point discriminating system - Google Patents

Abstract

PURPOSE:To increase the margin to line distortion of a reception signal received from a line and to make the system suitable for numerical operation processing by providing the uniform margin to each discriminating area in a direction of phase angle and giving a constant error rate to the amplitude in the amplitude direction within a possible range. CONSTITUTION:Normal demodulation is applied to a transmitted signal by a demodulator and a reception signal point (x1, y1) is outputted. After a corresponding phase angle is obtained from the signal point (x1, y1) at a phase discrimination circuit, the amplitude is discriminated by an amplitude discrimination circuit and an area belonging to the signal point is decided. The margin to noise is made constant by dividing the area with boundary lines making the rate of the distance extending from a reference point to a signal point to the distance extending from the origin to a reference point, constant and the area is approximated by a circle having the center at the origin taking the circuit scale and processing speed into account. Then the distance extending from the origin to the signal point is calculated and the discrimination is attained with the radius of the circle, that is, the reference value.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a receiving circuit for a data transmission device using a quadrature amplitude modulation method, and particularly to a signal point determination method suitable for numerical calculation processing.

[Background of invention 0] When transmitting data at 9600 bits/second or the like using a voice band line, a quadrature amplitude modulation method is generally used.

For example, when transmitting a data code at a data transmission rate of 9600 bits/second, the data to be transmitted is divided into 4 bits, a certain calculation is performed on this data, and the result of this calculation is converted into the phase angle and amplitude as shown in Figure 1. The signal is modulated in accordance with one of the 16 reference points with , and sent to the line from the modem. Then, on the receiving side, a judgment is made by identifying which of these 16 reference points the received signal corresponds to,
Data is restored by performing certain calculations on the determination results.

For the following explanation, consider 16-level quadrature amplitude modulation used at 9600 bits/second. The reference signal point arrangement in 16-value orthogonal amplitude modulation is as shown in FIG. However, the signal actually transmitted over the line is affected by line distortion and the like and deviates from the reference signal point position in the phase angle direction and amplitude direction. Therefore, on the receiving side, it is necessary to estimate the transmitted reference signal point from the received signal containing the zV. FIG. 2 shows a conventional determination area for received signal points. According to the conventional method, as shown in FIG.
M is accessed, and the comparator repeatedly compares and determines the relevant area. For this reason, the conventional signal point determining device has to use a large-capacity ROM and repeat complicated processing, which has caused problems in terms of storage, economy, and processing speed.

Further, the conventional determination area shown in FIG. 2 has the following drawbacks: The phase margin is not constant within the same area, and the phase margin varies depending on the area.

A specific example is shown in FIG. 4. The phase margin is within a range of 90° until the amplitude value is l, but as the amplitude value increases beyond A, the phase margin range' becomes narrower. Furthermore, it can be easily understood from FIG. 2 that the amplitude value and the phase margin have a complicated relationship in other regions as well.

[Purpose of the invention]

The purpose of this development is to eliminate the drawbacks of the conventional method, to make each judgment region have equal margin in the phase angle direction, and to keep the error ratio to the amplitude value constant as much as possible in the amplitude direction. By setting the following, it is an object of the present invention to provide a signal point determination method that increases the margin against line distortion, etc. that a received signal receives from a line, and is suitable for numerical calculation processing.

[Summary of the invention]

Conventionally, the X component and the Focusing on the amplitude direction, the area to which the received signal point belongs is determined by determining the magnitude relationship between the amplitude value and a reference value determined based on the ratio of error to the amplitude value.

[Embodiments of the invention]

The basic operation of the present invention will be explained below with reference to FIG. The transmitted signal is subjected to normal demodulation operation by a demodulator,
The received signal point (-1+211) is output. Signal point (
After the phase determination circuit determines the corresponding phase angle from x+ + yl), the amplitude determination circuit determines the amplitude and determines the region to which the signal point belongs.

An embodiment of the present invention will be described below. Data transmission speed 9
For 600 bits/second, a 16-level quadrature amplitude modulation scheme is used. To identify this received signal point, 16 determination areas corresponding to 8 types of phases and 4 types of amplitudes are required. First, FIG. 6 shows a phase angle determination circuit that identifies eight different phases.

This will be explained with reference to FIG. As a border dividing the area,
Use straight lines passing through the four origins. The straight line is y = mx ', (1
), the leaning horse is m = ±α, ±β (2) However, α = t
5! le22.5°β=tamil6f5. Each determination area is equally divided by this boundary line in the phase angle direction centered on the origin, as shown in FIG. The X component and the X component of the received signal point are (”+y)=(”+
+2+), the signal point is determined according to the following procedure.

(α) Straight line 1 y=αX Determine whether it is positive or negative for busy -α:c, +2120 (5) < (A3 Straight line 2 7=-βX Ixl that determine whether it is positive or negative for k +2120 (41(c)
Straight line 5 yHkxs: Alternatively, the positive or negative of straight line 4 y=βX is determined to determine the phase region to which the reception point belongs.

α3:1+7H≧0(5) Or - β3:+ + y170(6) The above processing is performed by the arithmetic circuit and judgment circuit shown in FIG.
Output the corresponding phase angle. FIG. 8 shows the processing procedure 70- of the phase determination circuit.

Next, in the region of the corresponding phase angle, the received signal point is determined based on the amplitude. Here, by dividing the area with boundary lines that keep the ratio of the distance from the reference point to the signal point to the distance from the origin to the reference point constant, the margin against noise can be kept constant, but the circuit Considering scale and processing speed, it can be approximated by a circle centered at the origin.

° This allows determination to be made by calculating the distance from the origin to the signal point and comparing it with the radius of the circle, that is, the reference value. Phase angles of 0° and 90° are used as actual reference values.

In the region of 180° and 270°, the amplitude of the reference point is 5 and 5
Therefore, if each error is E, , E2, then E
1/5=E2/s -'-E+ /E2 = s/s The distance between the two reference points in the same phase region is divided into 5=5, that is, a circle with a radius of 3.75.

Similarly, in the regions of phase angles of 45.155, 225°, and 515°, the circle has a radius of 2.12. FIG. 9 shows the determination area. The amplitude determination circuit will be explained with reference to FIG.

The phase angle determined by the phase determination circuit is oo.

If it is 90', 180°, or 270', select the standard value of 6 and set it to 45°.

If the angle is 155°, 225°, or 515°, the reference value α2 is selected.

The received signal point is (” + 1) = (”+ r 2f
+), the distance t from the origin to the signal point can be found using the following equation.

t2=$1'+y, 2 (7) The arithmetic circuit calculates the square of the distance t, and the determination circuit compares it with a reference value.

(d) Phase angle is 0°, 90", 180',
270'(7) Area α12 is t2(s) (g) Phase angle force 4s°, 155°1225°, s
ls'' area 2>2 α' 2 t(9) The area to which the reception point belongs is determined by the above determination.

The processing procedure will be explained using an example. Now, as shown in Figure 11, the X component of the received vector, y5! Each minute is (”, >
)=C2,6,-3,2).

However, ex = tan 22.5' medium 0.41β =
The tan is 2.41 in 67.5°.

(α) From equation (5), −(on x2.6 )−3,2= −4,266<
0(At From formula (4), (2,41X 2.6 ) -3,2=3.066 >
0(C) (From formula 51 (0 tearsX2.6) -5,2': -2,154(Q
From the above, it is determined that the signal point ('', y)=(2, 6, -5, 2) belongs to the phase angle region of 515 degrees.

Next, a comparison is made with the reference value cL2 for 315°.

α22== (2,12)2=: 4.5 distance t is (7
) From the formula, z=(2,6)2+(-3,2)2.17(g), °
, α2'< t2 The reference point of the area to which the signal point (2, 6, -3, 2) belongs is (
515).

〔Effect of the invention〕

According to the present invention, a large-capacity ROM is not required as in the past, and determination can be performed with fewer calculations. In addition, the judgment region has an equal margin in the phase angle direction, and the error rate for the amplitude value in the amplitude direction is set to be equal within the possible range, so there is margin against the influence of noise on the received signal from the line, etc. The signal points can be determined with high accuracy.

[Brief explanation of drawings]

Fig. 1 is a reference signal point constellation diagram, Fig. 2 is an explanatory diagram of the conventional judgment area, Fig. 5 is an explanatory diagram of the conventional judgment method, Fig. 4 is an explanatory diagram of allowable phase variation due to amplitude variation, FIG. 5 is an explanatory diagram of the operating principle of an embodiment of the present invention, FIG. 6 is an explanatory diagram of a phase determination area, FIG. 7 is an explanatory diagram of a phase determination circuit, and FIG. 8 is a diagram of a phase determination processing procedure. 9 is an explanatory diagram of the determination area, FIG. 10 is an explanatory diagram of the amplitude determination circuit, and FIG. 11 is an explanatory diagram of the same embodiment. A: Signal point with small amplitude, A: Signal point with large amplitude. ,・−′無＼″ 一一

Claims (1)

[Claims] 1. When a received signal is expressed as a signal on a plane formed by an x component and a y component, a signal that determines which region of a plurality of regions on the plane the signal point belongs to In the point determination method, a boundary line defined as a linear function passing through the origin on the plane that equalizes the margin of phase shift of signal points with respect to the reference point of each region,
A first calculation circuit that calculates by substituting the component and y component into the relational expression of the boundary line, and a first judgment circuit that determines the magnitude relationship between the boundary line and the received signal based on the calculation result. a determination circuit, a reference value determined from the ratio of the distance from the reference point to the signal point to the distance from the coordinate origin to the reference point, and a second calculation circuit that calculates the distance from the coordinate origin to the signal point; A signal point determination method characterized in that it is possible to determine to which region a signal point belongs by an amplitude determination circuit including a second determination circuit that determines the magnitude relationship between the calculation result and the reference value.