Research On Algorithm For Space-time OFDM System Carrying Two-dimensional Space Information

With the development of digital communication technology, direction-finding has become an important part of communication system. The space-time modulation solves the problems of digital communication and direction-finding simultaneous on the basis of digital modulation theory. According with the problem of direction-finding precision, in this paper a new space-time OFDM modulation technology is proposed, which the azimuth and elevation message are modulated into signal space of sub-carriers directly. The signal was transmitted by multi-antennas and utilized the orthogonal property among sub-carriers. So the signal in single antenna receiver is OFDM modeled and sub-carrier modulation signal, which has a non-quadrature signal space which varies with the azimuth and elevant of receiver, contain the space message of transmitter to receiver and digital communication message. The receiver may demodulation the space-time OFDM signal to estimate the direction of receiver relative to transmitter. The main contents are as follows:1. To meet the challenge of tracking and multi-mode navigating to MAV in three-dimensional space, the eight-antenna array of space-time OFDM system is established, and proposed a new algorithm of resolving phase ambiguity. The performances of bit error rate and direction-finding through Gaussian channel are investigated.2. According with the problem of peak-to-average power ratio of space-time OFDM signals, which is different between with the OFDM signals. This paper presents a new algorithm to reduce the peak-to-average power ratio by utilization the freedom of transmitting by multi-antennas and sacrificing the transmitting slot. The performances of this algorithm are investigated.3. The orthogonal property among sub-carriers is destructed by carrier frequency offset which effecting the performance of system. This paper analysis the performance of direction-finding under the condition of carrier frequency offset. The frequency offset tracking algorithm based on cyclic prefix is used in space-time OFDM system. The performances were investigated by different length of cyclic prefix and different signal-to-noise ratio.