On preamble design for timing and frequency synchronization of OFDM systems over Rayleigh Fading Channels

Abstract

Synchronization in Orthogonal Frequency Division Multiplexing (OFDM) based systems, is a primordial task due to the sensitivity to symbol timing and carrier frequency offset of OFDM. There are two ways to synchronize the air access in wireless systems: unframed (packet based) and framed transmission. Both of them are based on well designed sequences, with a low Peak Average to Power Ratio (PAPR), good low cross-correlation and impulse-like auto-correlation characteristics (e.g., Pseudo Noise (PN) sequence and Constant Amplitude Zero Auto Correlation (CAZAC)). In the present paper we make a comparative study of short and long preambles existing in the literature. Additionally we propose a long preamble, based on a CAZAC sequence weighted by a Golay Rudin Shapiro sequence. The reviewed preambles were evaluated in the Schmidl and Cox timing metric. By simulation in MATLAB we get the Mean Square Error (MSE) of the estimation, and the Bit Error Rate (BER) of transmitted data, in an environment defined by a Rayleigh Fading Channel with Additive White Gaussian Noise (AWGN), Coarse Timing and Frequency Offset.