Eye pattern display method, eye pattern display apparatus, and communications apparatus

The position of an input signal in a two-dimensional plane is moved into the first quadrant, and based on the position of the signal point moved into the first quadrant, the origin of a signal point plane is shifted, and the signal for which the origin has been shifted is enlarged by a prescribed magnification factor for display on a display screen.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to an eye pattern display method and an eye 
pattern display apparatus for data transmission using a modem or the like. 
The invention also relates to a communications apparatus for use with the 
same. 
2. Description of the Related Art 
In data transmission using a modem, for example, data for transmission is 
encoded, before being transmitted, into signal points arranged in a 
two-dimensional or a complex plane (two-dimensional values or complex 
numbers). At the receiving end, the locations of the received signal 
points are determined, and based on the signal points thus determined, 
data demodulation is performed. 
The number of signal points and their locations in the two-dimensional or 
the complex plane are specified for each of various transmission schemes. 
Under ideal conditions, the received signal points would always appear in 
their specified locations, but in the presence of channel characteristic 
degradation, the received signal points tend to be displaced from the 
specified locations because of the superposition of noise, the occurrence 
of phase shifting, etc. This tendency becomes more pronounced as channel 
characteristic degradation increases. 
Since communication becomes impossible, for example, when the channel 
characteristics greatly degrade, it has been practiced to examine the 
reception condition of the modem and take necessary countermeasures. 
To examine the reception condition of a modem, the modem is connected to an 
oscilloscope on which an eye pattern is displayed to view a displacement 
of signal points, and based on the amount of displacement, the degree of 
eye pattern degradation (channel characteristic degradation) is 
determined. 
In recent years, there has been an increasing need for higher-rate 
transmission using modems. This can be attained by increasing the number 
of signal points to be transmitted. However, the number of signal points 
increases exponentially with increasing transmission rate; for example, 
128 signal points are required for a transmission rate of 14.4 Kbps 
specified in the ITU-T recommendation V.33, and a maximum of 896 signal 
points for a transmission rate of 28.8 Kbps specified in V.34. 
With low transmission rates, since the number of signal points required is 
small, the spacing of the signals displayed on an oscilloscope is 
relatively wide, so that the amount of displacement of the received signal 
points can be easily discerned by displaying the eye pattern on the 
oscilloscope. 
However, as the number of signal points increases, the signal point spacing 
falls compared to low-rate transmission. As a result, on the eye pattern 
displayed on the oscilloscope, the signal points are displayed closer to 
each other. This tendency becomes more pronounced as the transmission rate 
is increased. 
The closer spacing of the displayed signal points makes it difficult to 
discern whether each displayed signal point is located in its intended 
position or is displaced from that position, and if displaced, how much it 
is displaced. The result of this is the inability to accurately examine 
the degradation of the eye pattern. 
SUMMARY OF THE INVENTION 
In view of the above difficulty, it is an object of the present invention 
to provide a method and apparatus for eye pattern display by which eye 
pattern degradation can be examined accurately even if the number of 
signal points is increased. 
It is also an object of the invention to provide a communication apparatus 
for use with the same. 
According to the present invention, there is provided a method of 
outputting an eye pattern that indicates positions of reception signals on 
a two-dimensional plane, comprising the steps of: making a decision about 
which of plural regions contains a reception signal, said regions being 
defined by dividing the two-dimensional plane into a plurality of regions, 
each including at least one ideal signal; applying a moving operation, 
based on the decision made in step a), to the reception signal to move the 
reception signal on the two-dimensional plane, said moving operation being 
carried out such that ideal signals contained in the respective regions 
are superimposed on each other when the moving operation is applied 
thereto; and outputting the moved reception signal. 
According to the present invention there is also provided an apparatus for 
outputting an eye pattern that indicates positions of reception signals on 
a two-dimensional plane, comprising: means for making a decision about 
which of plural regions contains a reception signal, said regions being 
defined by dividing the two-dimensional plane into a plurality of regions, 
each including at least one ideal signal; means for applying a moving 
operation, based on the decision made by the decision making means, to the 
reception signal to move the reception signal on the two-dimensional 
plane, said moving operation being carried out such that ideal signals 
contained in the respective regions are superimposed on each other when 
the moving operation is applied thereto; and means for outputting the 
moved reception signal. 
According to the present invention, there is also provided a communication 
apparatus for demodulating a modulated signal and obtaining a reception 
signal having a two-dimensional value, comprising: means for making a 
decision about which of plural regions contains a reception signal, said 
regions being defined by dividing the two-dimensional plane into a 
plurality of regions each including at least one ideal signal; means for 
applying a moving operation, based on the decision made by the decision 
making means, to the reception signal to move the reception signal on the 
two-dimensional plane, said moving operation being carried out such that 
ideal signals contained in the respective regions are superimposed on each 
other when the moving operation is applied thereto; and means for 
outputting the moved reception signal.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Before describing the preferred embodiments according to the present 
invention, examples of the related art are given with reference to the 
accompanying drawings. 
FIG. 1 is a block diagram showing a portion of a prior art modem apparatus 
which is related to an eye pattern display. In FIG. 1, reference numeral 1 
is an equalizer for removing noise from the received signal; 2 is a 
decision-making device for making a decision about each received signal 
point and for outputting the result of the decision; and 6 is a 
digital-analog converter (hereinafter called the D/A converter) for 
converting the digital signal output from the equalizer 1 into an analog 
signal for output. The output of the D/A converter 6 is coupled via an 
output terminal to an oscilloscope for displaying an eye pattern. The 
double lines shown in FIG. 1 and subsequent figures indicate that the 
value carried thereon is a two-dimensional value or a complex number. 
Signal points output from the modem are displayed on the screen of the 
oscilloscope. 
FIGS. 2 and 3 each show an example of the eye pattern displayed on the 
oscilloscope. FIG. 2 shows an eye pattern in normal condition, and FIG. 3 
shows an eye pattern in degraded condition. FIGS. 2 and 3 each show an eye 
pattern for a 4-state signal set. 
In the case of the normal eye pattern, the signal points are located in 
respective ideal positions as shown in FIG. 2. On the other hand, in the 
case of a degraded eye pattern, the signal points are spread out around 
the point where each point should be located, as shown in FIG. 3, for 
example. 
Such an eye pattern is displayed on the screen of the oscilloscope and the 
amount of displacement of the signal points from the ideal positions is 
examined to determine the reception condition of the modem, the degree of 
channel degradation, etc. 
With low transmission rates, since the number of signal points required is 
small, the spacing of the signals displayed on the oscilloscope is 
relatively wide, so that the amount of displacement of the received signal 
points can be easily discerned by displaying the eye pattern on the 
oscilloscope. 
However, as the number of signal points increases, the signal point spacing 
falls compared to low-rate transmission. As a result, in the eye pattern 
displayed on the oscilloscope, the signal points are displayed closer to 
each other. This tendency becomes more pronounced as the transmission rate 
is increased. 
The closer spacing of the displayed signal points makes it difficult to 
discern whether each displayed signal point is located in its intended 
position or is displaced from that position and, if displaced, by how much 
it is displaced. The result of this is the inability to accurately examine 
the degradation of the eye pattern. 
The preferred embodiments of the present invention will now be described 
with reference to the accompanying drawings. 
FIG. 4 is a diagram showing a modem apparatus according to one embodiment 
of the present invention. FIG. 4 specifically shows a portion of the modem 
apparatus related to eye pattern display. 
In the figure, reference numeral 1 is an equalizer, and 2 is a 
decision-making device. The equalizer 1 and the decision-making device 2 
are identical to those described with reference to FIG. 1. 
Reference numeral 3 is a quadrant rotator which makes a decision about 
which quadrant of the coordinate plane contains the received signal point 
and which carries out a quadrant rotation on the basis of the result of 
the decision; 4 is an origin shifter for shifting the origin of the signal 
point coordinates rotated by the quadrant rotator 3 and correspondingly 
shifting, or translating (i.e., applying a shift, or translation, 
operation to) the signal; 5 is an enlarger for enlarging the signal point 
coordinate plane whose origin has been shifted by the origin shifter 4; 
and 6 is a D/A converter for converting a digital signal to an analog 
signal for output on an oscilloscope. This embodiment of the invention 
will be described in further detail below with reference to the drawing. A 
detailed description of each constituent element is given in conjunction 
with a description of its operation. 
FIG. 5 is a diagram showing the configuration of the quadrant rotator 3, 
origin shifter 4, and enlarger 5 in equivalent circuit form. In this 
embodiment, the received signal point is moved into the first quadrant, 
based on which result the origin shifting, enlargement, and other 
operations are performed. From a real component and an imaginary component 
of a signal input as a complex number, the quadrant rotator 3 makes a 
decision about which quadrant contains the input signal, and based on the 
result of the decision, applies a rotation to the signal so that the 
signal point is moved into the first quadrant. 
In FIG. 5, reference numeral 31 is a decision-making device for making a 
decision about which quadrant contains the input signal, and 32 is a 
multiplier for applying a rotation to the input signal on the basis of the 
decision made by the decision-making device 31. When neither the real 
component Re nor the imaginary component Im of the signal input to the 
quadrant rotator 3 is less than 0, the decision-making device 31 decides 
that the signal is located in the first quadrant. In this case, since the 
signal point is already in the first quadrant, the rotation operation is 
not performed. When the real component Re of the input signal is less than 
0 and the imaginary component Im is not less than 0, the decision-making 
device 31 in the quadrant rotator 3 decides that the signal is in the 
second quadrant. In this case, the multiplier 32 rotates the input signal 
through -90 degrees to move the signal point into the first quadrant. When 
the real component and imaginary component of the signal point are both 
less than 0, the decision-making device 31 decides that the signal point 
is in the third quadrant. In this case, the multiplier 32 rotates the 
signal point through -180 degrees to move the signal point into the first 
quadrant. When the real component of the signal point is not less than 0 
and the imaginary component is less than 0, the decision-making device 31 
decides that the signal point is in the fourth quadrant, so that the 
multiplier 32 rotates the signal point through -270 degrees to move the 
signal point into the first quadrant. In this manner, the quadrant rotator 
3 makes a decision about the location of the input signal and, based on 
the result of the decision, performs the rotation operation to move the 
signal into the first quadrant. 
FIG. 6 is a diagram showing the signal point arrangement for an input 
signal in 256 QAM. In FIG. 6, white dot A indicates a signal point 
received at a certain instant in time. Black dots each indicate an ideal 
signal point location, and X1 to X16 and Y1 to Y16 indicate the coordinate 
values of the real components and imaginary components, respectively, of 
the respective signal points. In the figures and description hereinafter 
given, numeric values in square brackets are in hexadecimal. In the 
example shown in FIG. 6, the signal points are arranged spaced [001000] 
apart. Note, however, that the signal points indicated by black dots are 
not necessarily displayed on the screen of the oscilloscope. The eye 
pattern shown in FIG. 6 represents 256 signal point values. 
In FIG. 6, when the point A is received, the equalizer 1 outputs a signal 
containing a real component [003260] and an imaginary component [FFE5A3] 
indicating the coordinate values of the point A. Based on this signal, the 
quadrant rotator 3 makes a decision about in which quadrant the point A is 
located in the coordinate vector plane. In the illustrated example, the 
real component is greater than 0 and the imaginary component is smaller 
than 0, so that the quadrant rotator 3 decides that the point A is located 
in the fourth quadrant. Based on the result of the decision, the quadrant 
rotator 3 rotates the signal [003260], [FFE5A3] of the point A through 
-270 degrees, and outputs a signal containing a real component [001A5D] 
and an imaginary component [003260]. 
FIG. 7 shows an eye pattern after the signal has been moved into the first 
quadrant. White dot B indicates the signal point after the point A has 
been rotated through -270 degrees, and is represented by coordinate values 
[001A5D] and [003260]. In this manner, the quadrant rotator 3 convolves 
the eye pattern into the first quadrant. Since all signal points are moved 
into the first quadrant by the quadrant rotator 3, the number of signal 
points can in effect be reduced by a factor of 4. 
The signal from the quadrant rotator 3 is input to the origin shifter 4. 
The quadrant rotator 3 is coupled to the origin shifter 4, as shown in 
FIG. 5. The origin shifter 4 shifts the origin for the signal point 
rotated by the quadrant rotator 3 and correspondingly shifts, or 
translates (i.e., applies a shift or translation to) the associated signal 
points. 
In FIG. 5, reference numeral 41 is an AND circuit for ANDing the input 
signal with [01E000]; 42 is a first adder for adding [001000] to the 
output of the AND circuit 41; and 43 is a second adder for subtracting the 
output of the first adder 42 from the signal input to the origin shifter 
4. The operation of each element will be described in detail later. 
The AND circuit 41 in the origin shifter 4 ANDs the coordinate values of 
the input signal point with [01E000]. In the example of FIG. 7, the 
coordinate values [001A5D] and [003260] of the point B are each ANDed with 
[01E000]. 
The output of the quadrant rotator 3 is ANDed with [01E000] for reasons to 
be explained hereinafter. First, [01E000] is ANDed with each of the 
coordinate values of X9, X10, X11, X12, X13, X14, X15, and X16 on the X 
axis. 
The coordinate of X9 is [000800]. This can be expressed in binary as 
EQU 0000 0000 0000 1000 0000 0000 
On the other hand, [01E000] can be expressed in binary as 
EQU 0000 0001 1110 0000 0000 0000 
These are ANDed as shown below. 
______________________________________ 
0000 0000 0000 10000 0000 0000 
AND) 0000 0001 1110 0000 0000 0000 
0000 0000 0000 0000 0000 0000 
______________________________________ 
This is converted to hexadecimal as [000000]. Likewise, 
______________________________________ 
X10 [001800] 
0000 0000 0001 1000 0000 0000 
AND) 0000 0001 1110 0000 0000 0000 
0000 0000 0000 0000 0000 0000 
. . . [000000] 
X11 [002800] 
0000 0000 0010 1000 0000 0000 
AND) 0000 0001 1110 0000 0000 0000 
0000 0000 0010 0000 0000 0000 
. . . [002000] 
X12 [003800] 
0000 0000 0011 1000 0000 0000 
AND) 0000 0001 1110 0000 0000 0000 
0000 0000 0010 0000 0000 0000 
. . . [002000] 
X13 [004800] 
0000 0000 0100 1000 0000 0000 
AND) 0000 0001 1110 0000 0000 0000 
0000 0000 0100 0000 0000 0000 
. . . [004000] 
X14 [005800] 
0000 0000 0101 1000 0000 0000 
AND) 0000 0001 1110 0000 0000 0000 
0000 0000 0100 0000 0000 0000 
. . . [004000] 
X15 [006800] 
0000 0000 0110 1000 0000 0000 
AND) 0000 0001 1110 0000 0000 0000 
0000 0000 0110 0000 0000 0000 
. . . [006000] 
X6 [007800] 
0000 0000 0111 10000 0000 0000 
AND) 0000 0001 1110 0000 0000 0000 
0000 0000 0110 0000 0000 0000 
. . . [006000] 
______________________________________ 
As can be seen, the ANDing of the respective coordinate values with 
[01E000] yields the same value between X9 and X10, between X11 and X12, 
between X13 and X14, and between X15 and X16. Extending this, we have the 
following relations. 
______________________________________ 
Input AND result 
______________________________________ 
[000000] - [001FFF] . . . 
[000000] 
[002000] - [003FFFF] . . . 
[002000] 
[004000] - [005FFF] . . . 
[004000] 
[006000] - [007FFF] . . . 
[006000] 
______________________________________ 
The same applies for the Y axis 
The above will be explained with reference to FIG. 7. In FIG. 7, the signal 
point plane is divided into a plurality of square regions each enclosed by 
dashed lines. Four ideal signal points are arranged in each square region. 
In FIG. 7, square region A in which the point B is located lies from 
[000000] to [001FFF] on the X axis and from [002000] to [003FFF] on the Y 
axis. When a signal point within this region is ANDed with [01E000], an 
X-axis value [000000] and a Y-axis value [002000] are obtained. These 
coincide with the coordinates of point a in the square region A. 
That is, by ANDing with [01E000] and calculating the coordinate values of 
the lower left corner of each square region in FIG. 7, it is possible to 
determine in which square region the signal point in question is located. 
Next, in the origin shifter 4, [001000] is added to the X-axis component 
and Y-axis component of the signal ANDed with [01E000]. The results are 
shown below. 
______________________________________ 
Input Sum 
______________________________________ 
[000000] - [001FFF] . . . 
[001000] 
[002000] - [003FFF] . . . 
[003000] 
[004000] - [005FFF] . . . 
[005000] 
[006000] - [007FFF] . . . 
[007000] 
______________________________________ 
As shown in FIG. 7, each square region enclosed by dashed lines measures 
[002000] in both the X and Y directions. Therefore, by adding [001000], 
which is half the length along each axis of the square region, to the 
signal obtained by ANDing the coordinates of the received signal with 
[01E000], the center point of the square region in which the received 
signal point is located can be calculated. 
In the square region A shown in FIG. 7, the coordinates of the point a are 
[000000] on the X axis and [002000] on the Y axis. By adding [001000] to 
these coordinate values, we have 
EQU [000000]+[001000]=[001000] 
EQU [002000]+[001000]=[003000] 
These coincide with the coordinate values of point C in FIG. 7. In this 
manner, the center point of the square region A can be obtained. 
Next, the position of the point B, rotated into the first quadrant, is 
calculated relative to the point C as the shifted origin. Since the 
coordinates of the point B are [001A5D] and [003260], 
EQU real component [001A5D]-[001000]=[000A5D] 
EQU imaginary component [003260]-[003000]=[000260] 
Thus coordinates [000A5D] and [000260] are obtained which are the new 
coordinate values of the point B in the coordinate system with the shifted 
origin. 
FIG. 8 shows an eye pattern obtained after the origin has been shifted. 
Point D indicates the position of the point B after its coordinates have 
been obtained relative to the shifted origin. 
As shown in FIG. 8, the center point C of the square region A is shifted to 
the origin of FIG. 8, and correspondingly, the point B is shifted to the 
position of the point D. In FIG. 8, the black dots indicate ideal signal 
point locations, but these are not necessarily displayed on the screen. 
With the above processing, all the outputs from the origin shifter are 
convolved into the square region where four ideal signal points are 
arranged. Therefore, by performing the origin shifting, the number of 
signal points rotated into the first quadrant, in effect, can be further 
reduced by a factor of 16, and thus by a factor of 64 compared to the 
number of signal points shown in FIG. 6. 
The value [01E000] can be determined appropriately according to the common 
size of each of the square regions into which the first quadrant is split 
or divided as seen in FIG. 7 or to the total number of signal points. For 
example, when displaying a 16-value eye pattern on an oscilloscope, a 
value into which four of the signal points moved into the first quadrant 
can be quantized, should be taken instead of [01E000]; in the illustrated 
example, [01C000] is such a value. In this case, each square region 
enclosed by solid lines in FIG. 7 is treated as a unit, and the following 
values are obtained. 
______________________________________ 
Input AND result 
______________________________________ 
[000000] - [003FFF] . . . 
[000000] 
[004000] - [007FFF] . . . 
[004000] 
______________________________________ 
In this case, the length of each side of the square region is [004000]; 
therefore, to obtain the center point, [002000] should be added to 
[000000] or [004000]. Thus, point C' in FIG. 7 can be made as the origin 
of the square region A'. 
The value with which to AND the output signal of the quadrant rotator 3 and 
the value added to obtain the center point can be appropriately determined 
according to how the coordinates of signal points are taken, how large is 
the square region used as a unit of display, etc. 
By supplying the output of the origin shifter 4 to the oscilloscope, the 
eye pattern of FIG. 8 can be displayed on the screen of the oscilloscope. 
However, since the size of the eye pattern of FIG. 8 is the same as the 
size of one square region in FIG. 7, if the number of signal points is 
very large, it may not be possible to accurately discern the amount of 
displacement of signal points since the signal points are displayed very 
close to each other. Therefore, the enlarger 5 in FIG. 5 performs 
processing to enlarge the eye pattern for display on the oscilloscope. 
In the enlarger 5, the real component and imaginary component of the input 
signal are each multiplied by a magnification factor 4.0. For point D in 
FIG. 8 
EQU real component [000A5D].times.4.0=[002974] 
EQU imaginary component [000260.times.4.0=[000980] 
The eye pattern produced by multiplying by the magnification factor 4.0 is 
shown in FIG. 9. In FIG. 9, point E corresponds to the position of the 
point D in FIG. 8 after multiplying its coordinate values by the 
magnification factor 4.0, and is represented by coordinates [002974] and 
[000980]. By magnifying the signal values output from the origin shifter 4 
in this manner, the eye pattern shown in FIG. 8 is magnified four times 
for display on the oscilloscope. Therefore, the spacing of the signal 
points is correspondingly enlarged so that even if the amount of 
displacement of the received signal point (point E) is small, the 
displacement from its specified location can be discerned, thus 
facilitating the examination of eye pattern degradation. 
FIG. 10 is a flowchart illustrating the operating procedure in accordance 
with the present embodiment. The procedure for eye pattern display 
according to this embodiment will be described below with reference to 
FIG. 10. In step 1, a decision is made as to whether the real component of 
the signal supplied from the equalizer 1 is not less than 0. If it is 
decided that the real component is not less than 0, then in step 2, or if 
it is decided that the real component is less than 0, then in step 3, a 
decision is made as to whether the imaginary component of the input signal 
is not less than 0. 
If it is decided in step 2 that the imaginary component is not less than 0, 
it follows that the signal is located in the first quadrant. There is no 
need to rotate the signal; thus in step 4, both the real component and 
imaginary component of the received signal are directly output. 
On the other hand, if it is decided in step 2 that the imaginary component 
is less than 0, it follows that the signal is located in the fourth 
quadrant. Then, in step 5, processing is performed to move the signal from 
the fourth quadrant to the first quadrant. More specifically, the value of 
the real component of the received signal is taken as the imaginary 
component of the moved signal, and the value obtained by multiplying the 
imaginary component of the received signal by -1 is taken as the real 
component of the moved signal. The resulting signals are then output. 
If it is decided in step 3 that the imaginary component is not less than 0, 
it follows that the signal is located in the second quadrant. Then, in 
step 6, processing is performed to move the signal from the second 
quadrant to the first quadrant. More specifically, the value obtained by 
multiplying the real component of the received signal by -1 is taken as 
the imaginary component of the moved signal, and the value of the 
imaginary component of the received signal is taken as the real component 
of the moved signal. The resulting signals are then output. 
On the other hand, if it is decided in step 3 that the imaginary component 
is less than 0, it follows that the signal is located in the third 
quadrant. Then, in step 7, processing is performed to move the signal from 
the third quadrant to the first quadrant. More specifically, the value 
obtained by multiplying the real component of the received signal by -1 is 
taken as the real component of the moved signal, and the value obtained by 
multiplying the imaginary component of the received signal by -1 is taken 
as the imaginary component of the moved signal. The resulting signals are 
then output. 
After signal rotation in any of the steps 4 to 7, the process proceeds to 
step 8 where the signal rotated into the first quadrant is ANDed with a 
first prescribed value which is predetermined based on the number of 
signal points. The first prescribed value corresponds, for example, to the 
previously mentioned [01E000]. 
Thereafter, in step 9, a second prescribed value, which is predetermined 
based on the number of signal points, is added. With this operation, 
origin shifting based on the received signal point is accomplished. 
After shifting the origin, in step 10 the result of the addition from step 
9 is multiplied by a prescribed magnification factor; the eye pattern can 
thus be enlarged for display. 
After the enlarging operation, the resulting signal is converted by the D/A 
converter into an analog signal which is output to the oscilloscope 
connected thereto via a terminal. The oscilloscope displays the input 
signal on its screen. 
As described, according to the above embodiment, the number of signal 
points displayed on an oscilloscope can be reduced, thus widening the 
spacing of the signal points and thereby facilitating the examination of 
the eye pattern compared to the prior art method. 
While the above embodiment has been described by taking a modem as an 
example, it will be appreciated that the invention may be applied to other 
apparatus. Further, the above embodiment has dealt with a configuration in 
which all the constituent elements from the quadrant rotator 3 onward are 
internal to the modems; however, it will be recognized that the object of 
the invention can be accomplished if all or some of these elements are 
provided in the display device such as an oscilloscope. 
Furthermore, in the above embodiment, the output of the enlarger is 
supplied to the oscilloscope for displays; alternatively, the output of 
the quadrant rotator or the output of the origin shifter may be supplied 
to the oscilloscope for display. That is, from which element the signal 
should be output to the oscilloscope can be determined appropriately, 
according to the transmission rate of the apparatus concerned, that is, 
the number of signal points.