What is Carrier Frequency Offset in OFDM?

Carrier Frequency Offset:

Carrier frequency offset (CFO) occurs when the local oscillator signal for down conversion in the receiver does not synchronize with the carrier signal contained in the received signal. This phenomenon can be attributed to two factors: frequency mismatch in the transmitter and the receiver oscillators, and the Doppler effect as the transmitter and/or the receiver is moving. When this occurs, the received signal will be shifted in frequency,

                                             Fig: Carrier Frequency Offset

For an OFDM system, the orthogonality among subcarriers is maintained only if the receiver uses a local oscillation signal that is synchronous with the carrier signal contained in the received signal. Otherwise, mismatch in carrier frequency can result in inter-carrier interference (ICI). Practically, the oscillators in the transmitter and the receiver can never be oscillating at identical frequency. Hence, carrier frequency offset always exists, even if there is no Doppler effect

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