Restraint Model Based On Cyclic-correlation For Doppler In The Multiplex System

The Multiplex System of Communication and Range Measurement is based on a carrier. It adopts the technology of Spread Spectrum, combining the Spread Spectrum Communication with range measurement. So it can achieve Spread Spectrum Communication and range measurement synchronously.Because the object relative to the terminal exist radial movement, it brings Doppler Effect. And the Doppler frequency shift makes the excursion of the signal carrier to the center frequency of receiver's filter. If the frequency alternation of two sending signals is not large enough, there will be mutual interference at the receiver, too. Meantime the Doppler frequency shift will make the signal exist phase error in a persistence time of one code. So there is important significance in Multiplex System to improve the capability of restraint of Doppler Effect.For the uncertainty of Doppler frequency shift, the capture of signal usually uses the PLL. Depending on the traction of PLL, the local carrier of VCO is close to the input carrier and tracks the changes of the input carrier. When the communication condition is disgusting, the usage of PLL has advantage over the capture of signal. But if the Doppler frequency offset exceed the capture range of PLL, the carrier synchronization will fail.In the communication of Multiplex System for the making principle of signal, the DS signal contains the periodicity of symbol and code. And it is a second order cyclostationary signal. In order to solve the carrier synchronization of dynamic environment, this paper applies cyclic spectrum theory to estimate the carrier value of the receiver signal and make this carrier value subtract from a intermediate frequency value. So we gain another carrier value and let the new carrier value act on Direct Digital Synthesizer to produce local carrier. Multiplying the receiving signal, we can get intermediate frequency signal of the receiver part and achieve the frequency locked function. In the end, the intermediate frequency acts on the Phase Locked Loop. With the help of PLL, the carrier synchronization and data demodulation can be fulfilled. The phase locked part is accomplished. By the frequency locked part of cyclic spectrum, we can gain fixed intermediateFrequency that is immune from Doppler Effect. So the illogicality of capture range and dynamic capability of PLL receiver will be solved in the dynamic environment. At the same time, the requirement of track precision and dynamic capability can be satisfied.