Carrier Frequency-Offset Compensation by Inter-Carrier Symbol Precoding at the Transmitter in OFDM Transmissions

摘要

The channel carrier frequency offset (CFO) is one of the major sources of Inter-Carrier Interference (ICI) in N-subcarriers OFDM transmissions. This paper analyzes the ICI reduction provided by an inter-carrier QAM symbol precoding at the transmitter, assuming that the CFO is known at least at the transmitting end and that it has low variability on links that involve quasi-static terminals. The performance metrics used are the bit-error probability (BER) vs. the signal over noise plus interference ratio (SINR) and the average power of ICI. The paper studies the impact of the frequency offset magnitude and number of neighboring subcarriers used in precoding upon the BER performance, for different values of the IFFT-FFT dimension N and for the 4, 16 and 64-QAM modulations. The results obtained show that BER decreases significantly, especially for high values of N and for 4 and 16-QAM, and that using a moderate number of adjacent subcarriers for precoding proves to be a reasonable tradeoff between BER performance and the amount of processing involved. The carrier frequency offset compensation at the transmitter also simplifies the synchronization and decreases the processing in the receiver.