Question

1. What is inter-symbol interference? Describe the use of an eye diagram to measure different parameters of inter symbol interference.

Answer 1

In telecommunication, intersymbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable. The spreading of the pulse beyond its allotted time interval causes it to interfere with neighboring pulses. ISI is usually caused by multipath propagation or the inherent linear or non-linear frequency response of a communication channel causing successive symbols to "blur" together.

The presence of ISI in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible.

Ways to alleviate intersymbol interference include adaptive equalization and error correcting codes.

The eye diagram reveals imp ortant p erformance metrics for a communication link, including noise margin, ISI, timing sensitivity and zero-crossing jitter. In addition, the eye diagram shows the optimum sampling time for the receiver to regenerate a bitstream from the received signaling waveform.

Here, is how various parameters are measured using eye diagram!

More clearly!!

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