Abstract: ‍ ‍The preamble sequences in OFDM systems are usually designed for timing synchronization and frequency offset estimation， and do not contain any bits of information. Modulating the preamble sequence with extra information improves the spectral efficiency and expands its original functions. By cyclic shift and phase rotation of CAZAC sequence， a new scheme of embedding information bits in preamble sequence design is proposed. The modulated CAZAC sequence still has constant envelope and good periodic autocorrelation， and the corresponding time-frequency synchronization algorithm and information demodulation method are presented. Compared with the existing works， the proposed preamble design greatly improves the capability of bits carrying without deterioration of performances of timing synchronization and frequency offset estimation. The analysis and simulation results demonstrate that for the same length of preamble sequence， the proposed scheme is superior to the existing methods in terms of information carrying capacity and reliability， and achieves good timing synchronization and frequency offset estimation performance.