| Direct Sequence Spread Spectrum(DSSS)communication has the advantages of strong confidentiality,anti-multipath fading,anti-interference,low interception rate and good code division multiple access capability.It is widely used in military communications and civil communications.Direct Sequence Code Division Multiple Access(DS-CDMA)communication uses multi-channel pseudo-random code modulation corresponding information code to broaden its spectrum,and it is widely used in the fields of GPS global satellite positioning systems,third-generation wireless mobile communication systems,communication measurement and control,many military communications and so on,so it has received much attention.For the fields of civil communication control,military communication reconnaissance,information security,the receiver needs to estimate the spread spectrum sequence in advance to implement blind dispreading of the intercepted signal to obtain the transmitted data information.Therefore,it is of great significance to estimate the parameters of DSSS signal and DS-CDMA signal.In this thesis,the signal model of pulse shaping DSSS and DS-CDMA is firstly presented.Then,the blind estimation algorithm of the characteristic parameters of two signals is studied and analyzed.The main research contents are as follows:1.Aiming at the problem of blind estimation of DSSS signal parameters and code sequence,that the transmission waveform is limited to rectangular pulse shaping,the blind estimation of pseudo-code period and pseudo-code sequence of pulse shaping DSSS signal is studied.In the actual communication system,the transmission waveform of DSSS signal is not carried by rectangular pulse.Therefore,it is not known whether the existing blind estimation algorithm is suitable for other pulse shaping DSSS signals.In this thesis,the DSSS signal is passed through shaper such as raised cosine pulse,square root raised cosine pulse,Gaussian pulse,and triangular pulse,and the blind estimation of its main parameters and pseudo-code sequence is analyzed.The research shows that the quadratic spectrum and singular value decomposition method can realize the blind estimation of the pseudo-code period and pseudo-code sequence of the above four pulse shaping DSSS signals.2.Aiming at the problem of the blind estimation of asynchronous long code Direct Sequence Code Division Multiple Access signal(DS-CDMA)pseudo sequence in low SNR,a blind estimation method based on nested iterative least squares projection and library search algorithm is proposed.Firstly,the method uses short code DS-CDMA signal with missing data to reconstruct the long code DS-CDMA signal,and based on this,the signal is segmented to construct the observation data matrix with overlapping time windows.Secondly,the maximum likelihood theory is used to mathematically model for the data matrix,and the pseudo-code sequence was estimated by the nested iterative least squares projection.Finally,the estimated pseudo-code sequence is searched in a limited generator polynomial to obtain the generator polynomial of each user.3.For the problem of blind estimation of synchronous and asynchronous long code DS-CDMA signal pseudo sequence in multi-channel a blind dispreading method for synchronous and asynchronous long code DS-CDMA signals based on parallel factors is proposed.Firstly,the received signal is modeled into tensor model based on multi-channel technology,and on this basis,the long code DS-CDMA signal is equivalent to short code DS-CDMA signal with missing data.Then,the synchronous/asynchronous long code DS-CDMA signal is segmented according to the time window of single the pseudo code period and twice the pseudo code period,respectively,constructing the observation data matrix of the signal,and the observation data matrix is equivalent to miss parallel factor.Finally,the regular alternating least squares algorithm is used to decompose the parallel factor,and the pseudo code sequence of each users of the synchronous and asynchronous long code DS-CDMA signal is further estimated. |
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