[LabVIEW]Eye Pattern(眼图的应用)

Introduction

In this lab, I learnt the knowledge about eye pattern, inter-symbol interference and raised-cosine function. I also tried to derive the formula of raised-cosine function to explore the effect of the value of α in functions htand Hω. Then I try to write the formula nodes in the case of different values of  α by using knowledge of theory. As the result, I get three different types eye pattern.

The theoretical knowledge：

In telecommunication, an eye pattern, also known as an eye diagram, is an oscilloscope display in which a digital signal from a receiver is repetitively sampled and applied to the vertical input, while the data rate is used to trigger the horizontal sweep.

Several system performance measures can be derived by analyzing the display. If the signals are too long, too short, poorly synchronized with the system clock, too high, too low, too noisy, or too slow to change, or have too much undershoot or overshoot, this can be observed from the eye diagram. An open eye pattern corresponds to minimal signal distortion. Distortion of the signal waveform due to intersymbol and interference and noise appears as closure of the eye pattern (John G Proakis, 2001)

Figure 1 eye pattern

We can also get many information by obverting the eye pattern:

Figure 2 eye pattern information

Lab results & Analysis：

1. The program diagram in LabVIEW

Figure 3The program diagram in LabVIEW

Then we can take a look at the formula node with three different values of α：

Figure 4 α=0.5

Figure 5α=0.75

1. Lab results & Analysis

Figure 6 case 1

Figure 7 case 2

Figure 8  case 3

Then we can use the theoretical knowledge about eye pattern to analysis the result of our experiment.

1. We can find that the amount of distortion at sampling instant of the triangle waveform is minimum, and the sinc function is maximum.
2. We can take a look at amount of noise that can be tolerated by the signal we can find that for this tern, the raised-cosine function is approximate to the triangle waveform, and they are better than the sinc function.
3. We can look at the slope of these three eye parttern. The slope equals to the sensitivity to timing error. For the quality of the signal, the lower the slope, the better quality we get. So, we can find the triangle waveform have highest quality.

1. Answer of question

Question1

The signal in reality is the sum of many different waveforms.

Question2

The first method is increasing the spacing between the signals.

The second method is copying or duplicating an initial part of the symbol, and inserting the end of it. And it acts as Cyclic Prefix.

Question3

Sample near each peak so we need to make the pulse signal with nTs+t0.

Question4

For h(t): As the value of α goes down, waveform of h(t) is mare like the raised-cosine function.

For H(w): As the value of α goes down, the function H(w)gets smoother and smoother

Question5

With the value of α increasing, the ISI decreasing, so that the waveform become more and more like the impulse signal, so that the bandwidth become wilder.

1. Feedback

The time is so short, and I cannot find the answer to this problem.

Experience

In this lab, I learnt the knowledge about eye pattern, inter-symbol interference and raised-cosine function. I also tried to derive the formula of raised-cosine function to explore the effect of the value of α in functions ht and Hω. Then I try to write the formula nodes in the case of different values of  α by using knowledge of theory. As the result, I get three different types eye pattern. And know the mainly information that contain by eye pattern for instance, the amount of distortion at sampling instant and amount of noise that can be tolerated by the signal.

Score