OFDM. Cyclic Prefix and ISI

1. How does OFDM reduce ISI?
2. How does cyclic prefix remove ISI?
3. Why is OFDM robust against ISI?
4. What is OFDM cyclic prefix?

How does OFDM reduce ISI?

The basic principal of OFDM is to split the channel in to N number of sub channels and transmission of signal using orthogonal carriers, through these sub channels. OFDM converts frequency selective channel in to flat frequency channel so it can completely eliminate the Inter symbol interference (ISI) [5] .

How does cyclic prefix remove ISI?

The cyclic prefix acts as a buffer region or guard interval to protect the OFDM signals from inter symbol interference. We have learned that we minimize the ISI a lot when we make the size of the symbol larger (the size of the delay spread becomes relatively minor compared to the larger size).

Why is OFDM robust against ISI?

Due to the relatively long OFDM symbol time in combination with a cyclic prefix, OFDM provides a high degree of robustness against channel-frequency selectivity.

What is OFDM cyclic prefix?

3.2 Cyclic prefix for OFDM. A cyclic prefix is created to prevent intersymbol interference (ISI) when an OFDM signal is transmitted in a dispersive channel. As shown in Figure 13.5, the cyclic prefix (CP) is essentially an identical copy of the last portion of the OFDM symbol appended before the OFDM symbol.