intersymbolinterference

Intersymbol interference, often abbreviated as ISI, is a phenomenon that occurs in signal transmission when one symbol interferes with a subsequent symbol. This interference can degrade the quality of the received signal, making it difficult for the receiver to correctly interpret the transmitted information. ISI arises because communication channels are not perfect and exhibit characteristics that cause a transmitted pulse to spread out in time. This spreading means that the energy from one symbol can persist and overlap with the time interval allocated to the next symbol.

Several factors contribute to ISI. The most significant is the limited bandwidth of the communication channel. When a signal with a rapid change in amplitude, such as a digital pulse, is transmitted through a band-limited channel, its shape is distorted. The channel's frequency response, which is not flat across all frequencies, can attenuate or phase-shift different frequency components of the signal differently, leading to this distortion and pulse spreading. Reflections and multipath propagation, where the signal travels along multiple paths to the receiver, can also cause ISI. These different paths have varying lengths and delays, resulting in delayed copies of the original signal arriving at the receiver, which then overlap with other symbols.

The consequences of ISI can be severe, particularly in digital communication systems. If ISI is significant, the receiver might misinterpret a symbol, leading to bit errors. This can drastically reduce the data rate and reliability of the communication link. Techniques such as equalization are employed at the receiver to mitigate the effects of ISI by attempting to reverse the distortion introduced by the channel. Careful system design, including pulse shaping at the transmitter and selecting appropriate sampling times at the receiver, can also help minimize ISI.