In this paper, a frame synchronization system for bi-orthogonal modulation systems is treated. The bi-orthogonal modulation systems use several orthogonal sequences and their inverses for data transmission. Because of these several sequences, the bit error rate performance improves. However, the bi-orthogonal modulation system is more difficult to acquire frame timing than the systems such as the conventional Direct Sequence Spread Spectrum systems which use only one sequence for data transmission. A frame timing acquisition system analyzed in this paper is based on the method which uses a differential detector. By use of the differential detector the receiver obtains the frame timing information regardless of the transmitted sequence. In this paper the authors analyze the initial acquisition time which takes the probability of the false alarm into account. It is found that the rapid increase of the initial acquisition time can be reduced by increasing the number of verification and by raising the threshold level.
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