Two symbol timing estimation methods using Barker and Kasami sequence as preamble for OFDM-based WLAN systems

Abstract

The estimation of the exact point for the start of the symbol is significant as the orthogonal frequency division multiplexing (OFDM) systems are very sensitive to timing errors. In the IEEE 802.11a wireless local area network (WLAN), each data packet starts with a preamble consisting of ten short training symbols followed by two long training symbols. The timing metric is computed through autocorrelation of the received samples and their delayed copies. When the preambles are known to the receiver, the timing metric is obtained by crosscorrelation of the received samples with the locally generated samples. The correlation peak of the timing metric indicates the correct symbol time. The symbol timing synchronization schemes in IEEE 802.11a WLAN systems use short training symbols to estimate a coarse symbol time via autocorrelation and then use long symbols to find a fine symbol time via crosscorrelation. In this paper, Barker and Kasami codes are proposed to be used as preambles for timing estimation in OFDM WLAN systems. Timing estimation makes use of correlation of preamble. So preamble with good autocorrelation property has to be chosen. The proposed scheme develops a simple preamble structure and gives more accurate estimate of symbol timing.