Frequency synchronization algorithms for 802.11n based MIMO-OFDM systems: A performance analysis

Orthogonal Frequency Division Multiplexing (OFDM) is a bandwidth efficient signaling scheme for digital communications that was first proposed by Chang. In OFDM, the spectrum of individual orthogonal subcarriers mutually overlaps, giving therefore an optimum spectrum efficiency. A data communications system based on OFDM is particularly sensitive to frequency offset in the channel. Frequency offset is a phenomena, which causes phase shift and hence, reduction in signal strength at the output of the filters matched to each of the carriers and introduces ICI from other carriers which are now no longer orthogonal to the filter. In OFDM the carriers are inherently closely spaced in frequency compared to the channel bandwidth, the tolerable frequency offset becomes a very small fraction of the channel bandwidth. This paper is based on the study and comparison of algorithms that estimate the carrier and sampling frequency offsets from the demodulated data signals in the receiver. An implementation of these techniques to correct the respective offsets along with the performance of these algorithms, via simulation, is also presented.