The Design Of The Synchronization Algorithms For IEEE 802.16m

IEEE 802.16m is one of the candidate standards for the IMT-Advanced, i.e., the next generation mobile wireless communication system. Both IEEE 802.16m downlink and uplink use OFDMA. Due to the orthogonality of the subcarriers, OFDMA has lower inter-cell and intra-cell interferences, and is easier to achieve higher data rate compared with CDMA. To maintain the orthogonality, accurate time and frequency synchronizations are very important. This thesis investigates the synchronization algorithms for the IEEE 802.16m system.In this thesis, the downlink synchronizations based on the PA-Preamble is firstly discussed, which include coarse and fine time synchronization, integer subcarrier and fractional subcarrier frequency synchronization. Then the design principals of the Ranging channels are analyzed, which include the ranging preamble characteristics and allocations, the supporting cell diameters of different Ranging channel formats, and the effect of high Doppler frequency on the Ranging channels, etc. Based on these analyses, the uplink accessing and synchronization algorithms are proposed.Both downlink synchronization based on the PA-Preamble and uplink synchronization based on the Ranging channels rely on the preambles located in the subcarriers which are continuous in time and frequency. In IEEE 802.16m, these preambles are sent only once per superframe. In high mobility environment, the coherent time of the wireless channel may be less than the interval of the preambles. Thus, the synchronization based on the preambles may not be able to achieve good performance in high mobility environment. In this thesis, a channel estimation assisted time and frequency synchronization based on the interspersed pilots is proposed. Comparing with the existing synchronization algorithms based on the interspersed pilots, this algorithm utilizes the channel estimation results, and is able to eliminate the time and frequency synchronization bias caused by the dispersive wireless channel. Thus, it can achieve better performance.Because synchronization usually has high real-time requirements, when the synchronization algorithms are designed, all possible resources are used to lower the complexity without sacrificing the performance.