This paper addresses the problem of time synchronization in the IEEE 802.11a OFDM wireless communication system.In addition to the reference sequence usually used in conventional algorithms, recently the SIGNAL field of the physical packet has been exploited to improve the coarse time synchronization. To increase the performance of the fine time synchronization, we propose to use joint time synchronization and channel estimation based on the Maximum A Posteriori Probability criterion. Simulation results show that the probability of synchronization failure of the proposed synchronization algorithm is reduced as compared to existing methods.