Overview on synchronization in OFDM systems

摘要

Orthogonal Frequency Division Multiplexing (OFDM) is a advance bandwidth efficient digital modulation technique highly adopted for the broadband wireless services because it gives high performance in the multipath fading environments. It is very robust against narrowband interference, but it is not totally free from drawbacks. There are timing and frequency synchronization error for which this technique is very sensitive. These errors are quite detrimental to the mutual orthogonality among the subcarriers which is main condition of the OFDM technique. If it is not resolved properly, it creates inter-symbol interference (ISI) and inter-channel interference (ICI). ISI and ICI increase the Bit Error Rate (BER) and creates packet loss in the transmission. Means, OFDM System has no proper use without precise synchronization technique to assure reasonable system performance. This paper provides an overview on the causes and the effects of these synchronization errors. It focuses on various symbol timing and carrier frequency acquisition schemes including coarse and fine synchronization techniques, using cyclic prefix or training symbols. It has also discussed the attention to implement different standards in the same wireless device using common frequency synchronization structure.