Symbol timing offset (STO) correction in orthogonal frequency division multiplexing (OFDM) based systems

摘要

OFDM is a Multicarrier modulation (MCM) technique, which in used in 4G standards. In OFDM systems, symbols are transmitted in parallel on several narrowband subcarriers, which are overlapping and orthogonal to each other. OFDM is superior to other systems because it incurs zero Inter Symbol Interference (ISI) or less amount of ISI which can be compensated by a single tap equalizer. OFDM is advantageous only when the orthogonality between the subcarriers is maintained. STO introduces phase shift, ISI and Inter Carrier Interference (ICI). Phase shift and ISI can be effectively compensated by using Cyclic Prefix (CP) but the effect of ICI introduces loss of orthogonality which causes severe loss in throughput. That is why STO should be effectively estimated and compensated to avoid throughput loss. In this paper the effect of STO on received OFDM symbols have been examined. Furthermore, frequency domain STO estimation and correction scheme have been studied and analyzed.