Research On Acquisition And Tracking Algorithm For High Dynamic Spread Spectrum Receiver

As the spread spectrum technology has a strong anti-noise ability and good concealment,spread spectrum techniques such as direct signal spread spectrum?DSSS?techniques are often used in the field of military communications,such as ballistic missiles,high-speed fighters and aeronautical vehicles,where the spread spectrum receiver mainly to achieve the correct spread of the received signal spread,and its design determines the performance of the spread spectrum system.Synchronous despreading technology is the key to the spread spectrum receiver.It mainly includes acquisition and tracking.Acquisition refers to the process for local signal and the received signal generated by the receiver,to achieve the pseudo-code phase and carrier frequency of two signals roughly the same.After the acquisition,tracking refers to the process of realization the pseudo-code phase completely aligned and carrier frequency exactly the same.With high dynamic conditions,due to the large relative movement speed and acceleration of the sending and receiving side,the Doppler frequency offset and frequency deviation rate for spread spectrum signal will be large.Ordinary acquisition and tracking algorithms are difficult to implement synchronous despreading in a timely manner,resulting in an increase of system error rate.In order to solve the problem,the paper analyzes the influence of high dynamic on the acquisition and tracking algorithms,the dynamic index of the spread spectrum system is proposed:relative motion maximum speed 10km/s,maximum acceleration1g?g?28?9.8 m/s²?,minimum bit signal to noise ratio-22dB.and the PMF-FFT-based acquisition algorithm and algorithm of carrier tracking aided pseudo-code tracking are designed.For PMF-FFT acquisition algorithm,the paper analyzes the influence of some correlation length and FFT operation points on the performance of the algorithm,and determines their value by simulation.the paper compares the advantages and disadvantages of the two strategies of threshold judgment and selection judgment.The CFAR?Constant False Alarm Rate?threshold decision strategy based on Tong detector is used as the decision strategy of the acquisition algorithm.Finally,the test results based on the system dynamic indicators,the probability of acquisition is found as 86%,and the average number of pseudo-code cycles experienced is 327.For carrier tracking algorithm,the paper designs an improved PLL tracking structure based on Kalman filter,including linear Kalman filter and extended Kalman filter structure,and the equations on the carrier phase,frequency offset and frequency deviation rate of three parameters such as the state equation and observation equation.By analyzing the frequency discrimination of the phase detector,The tracking structure based on extended Kalman filter is determined.For pseudo-code tracking algorithm,the tracking structure based on the delay locked loop is designed,the discriminant algorithm based on the normalized pre-subtraction delay correlation and its correlation interval are determined.The loop bandwidth is determined by simulation.Finally,the test results based on the system dynamic indicators,it is found to be effectively track the normalized frequency offset of the linear change,and the maximum tracking error is2?10^-3.