Study On Blind Estimation Of TDDM-BOC Signal

Global navigation satellite system has been widely used in military communication and civilian mobile communication. However, with the development of national navigation system, navigation frequency bands become more and more crowded, and the signals in each frequency range interfere with each other, thus a new binary offset carrier(BOC) modulation signal was proposed by European Space Agency. In order to increase the security of information and improve the accuracy of acquisition and tracking, time division data modulation-binary offset carrier(TDDM-BOC) signal is generated by introducing TDDM based on the BOC modulation. At present, TDDM-BOC modulation signal has been used in the global positioning system(GPS) and Beidou satellite navigation system. Therefore, it has great significance to study blind estimation algorithms of TDDM-BOC signal.On the basis of detailed introducing the model and characteristics, blind estimation algorithms of TDDM-BOC signal are mostly studied. The main work of this thesis includes the following aspects:(1) For the blind estimation problem of parameters in TDDM-BOC signal, a algorithm based on cyclic autocorrelation is studied. Firstly, the cyclic autocorrelation function of TDDM-BOC signal is derived by using cyclic stationary characteristic. Then the carrier frequency, subcarrier rate and pseudo-code rate are estimated according to the cross-sectional view of cyclic autocorrelation characteristic for TDDM-BOC signal.(2) For the problem of TDDM-BOC signal, including the blind identification of the subcarrier type and blind parameters estimation, a method using cyclic spectrum envelope of the signal is studied. Firstly, the signal model is deduced when the subcarrier type of TDDM-BOC signal is sine and cosine respectively. Then the corresponding cyclic spectrum envelope is derived. Finally, subcarrier identification and parameters estimation can be completed by using single dimensional search of cyclic frequency domain. The simulation results show that the method is effective under the low signal-to-noise ratio(SNR).(3) For the problem of estimating pseudo-code period in multipath environment, a algorithm based on quadratic spectrum is studied for TDDM-BOC signal. Firstly, the TDDM-BOC signal model is derived in multipath environment. Then the power spectrum of the multipath TDDM-BOC signal is found, its secondary spectrum can be obtained by using Fourier transform of the power spectrum. Finally, the pseudo-code period of TDDM-BOC signal in multipath environment can be got by detecting spacing between peak pulses. The method of accumulative average is adopted to achieve the purpose of noise reduction and accurate estimation.(4) For the problem of blind parameters estimation in multi-user environment, a method using cyclic spectrum of TDDM-BOC signal is studied. Firstly, the spectral correlation function of the multi-user TDDM-BOC signal is deduced. Then the 4 maximum peaks and 4 adjacent peaks can be searched from the envelope of cyclic spectrum in zero frequency. Finally, the carrier frequency, subcarrier rate and pseudo-code rate are estimated according to the position of maximum peaks and adjacent peaks.(5) For the blind estimation problem of the combination code sequence and information sequence, a revised algorithm using singular value decomposition(SVD) is studied for TDDM-BOC signal. Firstly, the received signal is divided into double-symbol-period-length temporal vectors, with one-symbol-period overlapping, the observation matrix is formed by accumulating these vectors one by one. Then, an operation of SVD is applied to the matrix, and the estimation of the combination code sequence is obtained based on the left singular vector. At the same time, the information sequence can be estimated through the right singular vector.