【作者】 张平华；

【导师】 王玲；

【作者基本信息】 湖南师范大学 ， 电路与系统， 2006， 硕士

【摘要】 扩频技术因其本身固有的干扰抑制特性得到了迅速的发展,其中直接序列扩频通信(Direct Sequence Spread Spectrum,DSSS)系统是典型的扩频通信系统之一。DSSS系统的抗干扰能力由扩频处理增益决定,可以通过增加带宽来增加扩频增益,但是实际中由于带宽和技术方面的限制扩频增益总是有限的。窄带干扰(Narrow-Band Interference,NBI)由于其功率谱密度比宽带干扰高得多,所以它对DSSS系统的破坏性更强,当有强窄带干扰存在时仅靠系统自身的抗干扰能力很难保证系统高质量的通信,甚至可能造成系统通信中断。因此,研究有效的窄带干扰抑制技术具有重大的实际意义。 论文首先分析了时域线性滤波技术、时域非线性滤波技术和频域变换滤波技术,这些传统的滤波方法在抑制窄带干扰方面都存在一定的限制和缺陷。小波包变换(Wavelet-packet Transform,WPT)具有多分辨分析能力和良好的时频局部化特性,能有效地跟踪输入信号的频谱变化,迅速把干扰定位在一定的频域范围,因此将小波包变换应用于干扰抑制的研究引发了人们的兴趣。 论文在对传统的干扰抑制方法进行比较和总结后,给出了一种改进的基于ATF(Adaptive Time-frequency)的自适应时频干扰抑制方法。研究了用ATF实现直扩通信系统中输入信号的分解,分析了该算法抵消窄带干扰的机理,对原有算法进行了优化并给出了相应的自适应去干扰算法。采用自适应滤波技术取代子带剔除法,自适应地跟踪窄带干扰,改善了有用信号的丢弃情况,有效地抑制了窄带干扰。分析和仿真结果表明,基于ATF算法的自适应小波包时频干扰抑制方法比传统的子带剔除法在性能上更为优越,干扰定位速度也较快,干扰抑制能力强。更多还原

【Abstract】 The technique of spreading spectrum has got rapid progress because of its inherent anti-jamming character. Direct sequence spread spectrum (DSSS) is a typical spreading spectrum techinque. The anti-jamming ability of DSSS system is decided by its processing gain, which can be increased by augmenting the bandwidth. However, processing gain is always finite because there are some restrictions in bandwidth and techniques in a practical system. A narrowband interference (NBI) has a greater power spectral density. Thus it will bring more strong devastation to the DSSS system than a broadband one does.So it is difficult for DSSS system to ensure a high quality of communication by itself when strong interference exists, even communication may be intermitted. Therefore researching more efficient techniques to suppress the narrowband interference has great practical significance.Firstly,Many kinds of filter techniques are presented in this paper, e.g. linear and nonlinear filters in the time domain and filters in the frequency domain.These traditional filters have some limitations and defects for suppressing narrowband interference.Due to its multiresolution and good time-frequency properties ,wavelet-packet transform can track the spectrum varieties of the input signals. And then the interference is localized in a definite frequency domain. So the application of wavelet-packet transform to interference-excision has hold people’s interest.Through comparing and summarizing the traditional filters, anovel adaptive interference suppression scheme based on Adaptive Time-frequency (ATF) is put forward. In this scheme, the decomposition of the received signal realized by adaptive time-frequency in DSSS systems is studied.The performance evaluation of the excision techniques via ATF is presented. The optimal adaptive NBI rejection arithmetic is also proposed using the adaptive filter instead of sub-band excision, which suppresses NBI efficiently and impoves loss of the avail signal. Analyzed and simulation results show that the interference suppression method of adaptive wavelet packet decomposition based on the ATF algorithm will obtain better performance than that of conventional sub-band elimination. Additionally the orientation speed of the adaptive algorithm can be increased. NBI can be suppressed effectively.更多还原