Research On MT-CDMA System Of Communication And Wireless Location With Multi-beam Space-time Modulation

With the rapid development of wireless communication, positioning has become the basic func-tion of communication systems, and high-speed communication also has become the people's urgent needs. Different from the existing wireless location technology, our study group proposed a new space-time modulation technique, which can be used to transmit microwave signal carrying 2-dimensional directional information. So the integrated system of communication and direc-tion-finding can be realized by using digital modulation theory. Based on the space-time modulation technology, a MT-CDMA system of communication and wireless location with multiple beams is stu-died, which is suitable for low SNR and high rate occasions. The main contents are as follows:Single-carrier system and spread-spectrum system with out-phase dual-beam modulation are analyzed and simulated. The principle of modulation and demodulation are illustrated. The paper also present how to choose the signal constellations of space-time modulation, how to design the time-domain modulation matrix, information matrix and spread-spectrum matrix, and how to develop the algorithm of information demodulation, beam parameter estimation and carrier phase estimation.A space-time OFDM system with dual-beam is studied, whose communication and direc-tion-finding performance are simulated. The maximum likelihood method based on cyclic prefix is used to realize symbol timing and carrier synchronization jointly. The performances were investigated by different length of cyclic prefix and different signal-to-noise ratio.The space-time MT-CDMA system with multiple beams is studied. An eight-element sparse an-tenna array is divided into four arrays to produce multi-beam. These arrays are stimulated one by one by the signal from different sub-carriers. The receiver use phase center offsets to remove multi-valued fuzzy from direction-finding using large spacing antenna. The direction-finding accuracy of the sys-tem was raised through developing the algorithm which combines coarse measurement with fine measurement. The performances of bit error rate and direction-finding through Gaussian channel are investigated.