Telecom Techniques Guide


Inter-Symbol Interference in LTE

What is the multipath?

  • Due to the signal propagation phenomena, like reflection or diffraction, a receiver can receive several delayed versions of the same signal.
  • This creates Inter-Symbol Interference (ISI).
The multi-path impact is an overlapping of 2 symbols, called Inter-Symbol Interference (ISI).
The modulation is based on the amplitude and on the phase, so in case of overlapping there are 2 different
amplitudes and phases.
The receiver is not able to decode the state of the symbol.
  • The guard time is called the Cyclic Prefix (CP). It permits to facilitate demodulation.
  • The cyclic prefix transforms the classical channel convolution into a cyclic convolution which permits easy demodulation after FFT.
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