低信噪比罗兰-C接收机

摘 要 罗兰（远程导航的英文词组LOng RAnge Navigation的縮写字LORAN之音译）是全天候、全天时连续工作的远程无线电导航系统，我国也称为长河二号系统，主要由岸基发射设备、系统监测设备及用户设备组成。该系统是我国独立自主建立并控制的远程无线电导航系统，目前是仅次于GPS导航系统的第二大导航系统，也是我国海军舰船采用的无线电导航系统。几乎所有的舰船均配备了罗兰－C定位仪或罗兰－C接收机。但从使用效果看，定位性不佳。究其原因，由于在建设长河二号系统工程初期，考虑到力求用有限的财力资源构建能够覆盖在全中国沿海区域的远程导航系统，系统发射台的布设采用了远距离长基线的布台方式，虽然发射的功率很大，但在长基线情况下，接收点处的天地波时延差很小，降低了罗兰－C信号实际电平，而接收机几乎完全仿照国外的设备，可以讲没有一个接收机工作在信号的第三周期过零点。对于长基线工作情况，总有一个离接收点远的副台受到天波的干扰，因此，定位效果自然不佳。解决定位效果不佳直接的方法是能够自主化设计接收机，并且在接收机的信号处理方法上要有突破。现阶段要想在很短的时间内使国内的设计能力及水平有很大的提高是不现实的。因此，必须寻找其它有效途径。 课题依据海军装备部下达的《低信噪比罗兰－C接收机的研制》任务提出的。重点从信号接收和处理两方面就改善接收机性能做理论探讨和部分实验性研究。主要结果概括如下： 课题首先着重研究磁性天线对接收机抗干扰、抑制噪声等性能的改善，由于磁性天线具有方向性，从抗干扰和抑制噪声两方面出发，课题设计出一种既能抗干扰，又能抑制噪声的磁性天线。通过外场与电天线的比对实验，并对实验数据进行统计分析，表明磁性天线在信噪比以及时差稳定性两方面对接收机性能的改善优于电天线，磁性天线的信噪比高于电天线2－3db，且所测时差稳定性高于电天线。 其次，本文提出了一种用小波分析提取罗兰－C信号周期识别特征的新方法。常用的周期识别的方法有包络识别法和射频采用法，但是包络识别法容易造成包络的失真和延迟，射频采样法要求信噪比较高。如何在低信噪比的条件下提高周期识别的可靠性，已是罗兰－C系统接收设备中最困难的问题之一。为此，我们研究用小波分析来提取周期识别特征，课题选择了Bubble母小波，它和我们要处理的罗兰－C标准脉冲信号有很大的相似性，再计算出母小波经过整数平移、二进制展縮得到的函数系中有限项的系数，把这些系数作为周期识别信号的特征信息，利用这些特征信息实现周期识别。并通过小波分析法与通用方法再抗噪声以及连续波干扰下的性能比较，理论分析与计算机模拟结果表明新方法比传统的方法更能抗噪声、抗连续波干扰，采用该方法将有效地扩大 2

罗兰－C导航的作用距离。 最后，针对时差测量方法上研究用准正交分解法来测量时差。通用的时差测量方法是利用接收设备产生的基准脉冲去跟踪被测信号的某一特征点，然后通过测量接收机产生的跟踪主、副台信号的基准脉冲的间隔而间接地获得所测时差，但由于通用方法所测的时差误差偏大且时差稳定性低。为此，我们研究用准正交分解来测量时差，就是在原有类似正弦函数基础上构建一个余弦函数，首先计算出标准罗兰－C信号经过准正交分解后所得的时差，我们称这个时差为固定偏差（Δτ），然后再计算出在噪声干扰情况下的罗兰－C信号经过准正交分解后所得的时差（t’）,再用t’减去Δτ所得的时差（τ‘）就为我们所求的时差。经过理论分析与仿真，验证这种新方法比通用方法测量的时差值更准确且稳定性好。 关键词：罗兰－C信号；GPS；长河二号系统；监测接收机；磁性天线；电天线；周期识别；小波分析；准正交分解；时差测量；跟踪。 3

ABSTRACT LORAN is the system of long radio range navigation,which continues working everytime for any kind of weather .It is also called Changhe 2 navigation system and composed of transmission equipment on the station of bank,monitor equipment and user equipment.The system is built and controlled only by our country.At present,it is not only the second navigation system after GPS,but also is applied by our navy warships.All of warships almost have Loran-C apparatus of locating or Loran-C receiver.But the capability of location of this is not well from the efficient of applying.We take the reason into account that we spend limited finance to constitution and build LORAN,which can cover all coastal areas in china.The laying out of transmition stage of the system is adopted by the way of laying in the distance and long base line.Although the powe of transmition is very large,the time difference(TD) of received point is very little under the situation of the long base line,which can reduce the practical level of voltage of Loran-C signal.And yet,receivers almost follow equipment abroad,it is said that there is no receiver working at the third period of signal acrossing the zero.Towards working in long base line,there is always deputy stage far from the received point which was disturbed by celestial-wave.Therefore,the locating efficition is not well naturally.The direct idea of solving the bad locating efficition by which we should take initiate in designing receiver,and break through in the way of signal processing of receiver.At present,improving the capability and level of interior design in short time is not reality.Hence,we must look for other effective channel. The emphasis is expounded by rest on naval ministry of outfit sending down the mission of “The Research of Loran-C Receiver in Low SNR”.The focal point is making theory probing and part experimental study in the signal processing.The primary contributions and original ideas included in this dissertation are summarized below: First,we investigate the magnetic antenna improves the capability of fighting off interference and inhibiting noise to receiver.Because the magnetic antenna has orientation,considering fighting off the interference and inhibiting the moise,we have designed a kind of maganetic antenna which can fight off the interference and inhibit the noise. Through the experimentation of comparison with electrical antenna outside,and statistical snalyzation of data of experimentation,it is proved that magnetic antenna is better than electrical antenna in improving the capability of receiver in SNR and stability of TD.The maganetic antenna is higher at 2-3dB than electrical antenna,and the curved line of measured TD is more superior than electrical antenna.