Inter-Symbol Interference in LTE

Inter-Symbol Interference in LTE

  • Definition: ISI is a phenomenon in LTE where symbols transmitted over a communication channel overlap, causing distortion in the received signal.
  • Causes:
    • Multipath Propagation: Signals take multiple paths with different delays, leading to overlapping symbols.
    • Time Dispersion: Variation in signal arrival times at the receiver contributes to ISI.
  • Impact on LTE:
    • Degrades Signal Quality: ISI results in difficulty in correctly interpreting symbols, leading to errors in data transmission.
    • Reduces Data Rate: Impairs the ability to transmit data at higher rates due to increased likelihood of errors.
  • Mitigation Techniques:
    • Equalization: Techniques such as linear equalization are employed to mitigate ISI by compensating for channel distortions.
    • Guard Intervals: Including guard intervals between symbols helps in reducing the impact of ISI.

In LTE, addressing ISI is crucial to ensure reliable and high-quality data transmission in wireless communication systems.

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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