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Orthogonal frequency division multiplexing (OFDM) is a viable technology for high-speed data transmission by virtue of its spectral efficiency and robustness to multi-path fading. These advantages can be achieved only with good synchronization both in time and frequency. This paper proposes new efficient synchronization methods for an OFDM-based system, IEEE 802.16d. For the coarse time synchronization and the fractional carrier frequency offset (CFO) estimation, a disjoint architecture is proposed that performs auto-correlations separately to achieve more reliable frequency synchronization and to reduce overall hardware complexity and power consumption. In addition, for the fine symbol timing offset (STO) and the integer CFO, a new joint estimation method employing parallel cross-correlations between the received samples and the pre-rotated training sequences is proposed. Experimental results show significantly superior performance to the previous synchronization methods. A prototype synchronizer based on the proposed methods is designed with a 0.25-mum CMOS process, which reduces power consumption by more than 60% compared to a conventional synchronizer.