Research On Multipath Reception Technology Of Variable Rate Spread Spectrum Communication Systems

With the convenience brought by wireless communication gradually becoming more and more popular,people spend more and more time on the “net”,and the issue of security and confidentiality of the communication process is getting more and more attention.However,the open nature of wireless communication transmission not only makes it susceptible to channel fading but also opens the door for third-party interception.In addition to the traditional use of coded encryption to protect user data,researchers have also considered physical layer information security in recent years.Based on this background,a method for designing a waveform of a wireless communication signal using a variable-rate spread spectrum method with non-stationary signal characteristics is proposed.Since the essence of variable rate spread spectrum wireless communication technology is still direct sequence spread spectrum(DSSS),multipath interference cannot be ignored when it is applied to an actual system.The traditional fixed-rate spreadspectrum communication system utilizes the auto-correlation property of the pseudo noise sequence,extracts,separates,delays,and adds the multipath signals to obtain a large gain to counter multi-path interference.In the variable-rate spread spectrum communication system,due to the time-varying of the spreading rate,the correlation characteristics between sequences of adjacent transmission symbols are different from those of the fixedrate spread spectrum communication system,which is equivalent to the introduction of multiple access interference in multipath channels.Therefore,the difficulty of multi-path reception is improved.This paper mainly studies the impact of intersymbol interference on the symbol of the transmitting end in variable rate spread spectrum communication systems and the RAKE receiving technology under multipath interference.First,the hidden characteristics of the instantaneous spectrum of conventional fixed-rate spread spectrum communication signals are briefly introduced.Since the ergodicity and cyclostationary characteristics of the signal are not eliminated,the third party can effectively intercept the communication signal through cyclic spectrum estimation and higher-order spectrum estimation.Starting from the physical layer waveform design,variable-rate spread spectrum communication technology using a time-varying chip period is introduced.This technology can effectively suppress the ergodicity and the cyclostationary characteristics of the communication signal,thus undermining the basic assumptions on which the traditional signal detection methods are based,making the larger the observable measurement,the more ambiguous the feature description of the communication signal,thus greatly improving the communication system.Security.Then,the principle of the traditional spread spectrum communication system and the capture and tracking process are introduced.For the problem of multipath interference,the principle of diversity combining and receiving technologies and the key technologies of common RAKE receivers are introduced.Then,the communication parameters construction scheme for variable-rate spread-spectrum communication systems is given and the difficulties encountered in practical applications are analyzed.Based on this,a simplified scheme for constructing communication parameters of variable-rate spread-spectrum communication systems is proposed,and the randomization pair is analyzed.Spread-spectrum chip selfcorrelation performance.Then the characteristics of the inter-symbol interference at the transmit end introduced by the time-varying characteristics of the spreading chip period in the variable-rate spread-spectrum communication system are analyzed.It is found that the maximum inter-symbol interference introduced is relatively minor,which can be ignored in practical applications.Finally,the multipath interference of variable rate spread spectrum communication system is analyzed,and a combined interference cancellation RAKE receiver scheme based on FFT is proposed.Simulation analysis shows that in the single-user scenario,the proposed method can obtain 0.5~1dB reception gain.