| Data transmission rate in the communication networks for now can't satisfy the demand of users with the explosive development of wireless communication technique and communication service data rate, so people make a flurry of research and development activities dedicated to beyond 3G mobile communication systems. MC-CDMA is the combination of spread spectrum technique and multicarrier technique. MC-CDMA has many advantages: higher spectral efficiency, high speed data transmission, narrow band interference rejection capability and inter-signal interference rejection capability. This technology is considered as the core technology of the future 4G wireless communications, because it can be used for multimedia data transmission. MC-CDMA system is sensitive to the start position offset of frames that is brought by mismatching between transmitter's and receiver's oscillator. In order to assure the performance of MC-CDMA system, many researchers focus their research to the frame synchronization algorithms in MC-CDMA system.First, the history of mobile communication development is looked back. Then, the characteristics and the basic concept of wireless channel are discussed in detail. The fundamental principle and performance of OFDM and CDMA technologies are introduced and compared in the paper. The three solutions of OFDM-CDMA are set forth and analyzed. And so synchronization is the key problem for MC-CDMA system. There are three kinds of synchronal modes in MC-CDMA system: frame synchronization, carrier synchronization, sampling-bell synchronization. The frame synchronization is chiefly investigated in this paper. So the frame synchronization algorithm based on the correlation property of PN sequence and cyclic safeguard interval of ML are discussed in detail and simulated in computer.On the basis of algorithm of the basic correlation property of PN sequence, two improved algorithms are proposed in this paper. One increases BER controls the threshold which based on the correlation property of PN sequence with adaptive decision threshold control. The theoretical analysis and computer simulation show that the improved algorithm has more precise acquisition than the basic one. The other algorithm doesn't use adaptive decision threshold control. After using the correlation property of PN sequence to accomplish the approximate acquisition, different PN sequence as cyclic prefix of MC-CDMA frame accomplishes exact trace. This algorithm although brings down utilization of frequency band, but it can reach a lower complexity, a higher accuracy and a shorter consumption of time at the aspect of tracing frame. |
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